Acid base balance

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Dietary Reference Intakes (DRI) The Dietary Reference Intakes (DRI) include two sets of values that serve as goals for nutrient intake—Recommended Dietary Allowances (RDA) and Adequate Intakes (AI). The RDA reflect the average daily amount of a nutrient considered adequate to meet the needs of most healthy people. If there is insufficient evidence to determine an RDA, an AI is set. AI are more tentative than RDA, but both may be used as goals for nutrient intakes. (Chapter 2 provides more details.)

In addition to the values that serve as goals for nutrient intakes (presented in the tables on these two pages), the DRI include a set of values called Tolerable Upper Intake Levels (UL). The UL represent the maximum amount of a nutrient that appears safe for most healthy people to con- sume on a regular basis. Turn the page for a listing of the UL for selected vitamins and minerals.

Estimated Energy Requirements (EER), Recommended Dietary Allowances

(RDA), and Adequate Intakes (AI) for Water, Energy, and the Energy Nutrients

Age (yr)

Males 0–0.5 — 62 (24) 6 (13) 0.7e 570 60 — 31 4.4 0.5 9.1 1.52 0.5–1 — 71 (28) 9 (20) 0.8f 743 95 — 30 4.6 0.5 11 1.20 1–3g — 86 (34) 12 (27) 1.3 1046 130 19 — 7 0.7 13 1.05 4–8g 15.3 115 (45) 20 (44) 1.7 1742 130 25 — 10 0.9 19 0.95 9–13 17.2 144 (57) 36 (79) 2.4 2279 130 31 — 12 1.2 34 0.95 14–18 20.5 174 (68) 61 (134) 3.3 3152 130 38 — 16 1.6 52 0.85 19–30 22.5 177 (70) 70 (154) 3.7 3067h 130 38 — 17 1.6 56 0.80 31–50 22.5i 177 (70)i 70 (154)i 3.7 3067h 130 38 — 17 1.6 56 0.80 �50 22.5i 177 (70)i 70 (154)i 3.7 3067h 130 30 — 14 1.6 56 0.80

Females 0–0.5 — 62 (24) 6 (13) 0.7e 520 60 — 31 4.4 0.5 9.1 1.52 0.5–1 — 71 (28) 9 (20) 0.8f 676 95 — 30 4.6 0.5 11 1.20 1–3g — 86 (34) 12 (27) 1.3 992 130 19 — 7 0.7 13 1.05 4–8g 15.3 115 (45) 20 (44) 1.7 1642 130 25 — 10 0.9 19 0.95 9–13 17.4 144 (57) 37 (81) 2.1 2071 130 26 — 10 1.0 34 0.95 14–18 20.4 163 (64) 54 (119) 2.3 2368 130 26 — 11 1.1 46 0.85 19–30 21.5 163 (64) 57 (126) 2.7 2403j 130 25 — 12 1.1 46 0.80 31–50 21.5i 163 (64)i 57 (126)i 2.7 2403j 130 25 — 12 1.1 46 0.80 �50 21.5i 163 (64)i 57 (126)i 2.7 2403j 130 21 — 11 1.1 46 0.80

Pregnancy 1st trimester 3.0 �0 175 28 — 13 1.4 46 0.80 2nd trimester 3.0 �340 175 28 — 13 1.4 71 1.10 3rd trimester 3.0 �452 175 28 — 13 1.4 71 1.10

Lactation 1st 6 months 3.8 �330 210 29 — 13 1.3 71 1.30 2nd 6 months 3.8 �400 210 29 — 13 1.3 71 1.30

NOTE: For all nutrients, values for infants are AI. Dashes indicate that values have not been determined. aThe water AI includes drinking water, water in beverages, and water in foods; in general, drinking water and other beverages contribute about 70 to 80 percent, and foods, the remainder. Conversion factors: 1 L � 33.8 fl uid oz; 1 L � 1.06 qt; 1 cup � 8 fl uid oz.

bThe Estimated Energy Requirement (EER) represents the average dietary energy intake that will maintain energy balance in a healthy person of a given gender, age, weight, height, and physical activity level. The values listed are based on an “active” person at the reference height and weight and at the midpoint ages for each group until age 19. Chapter 9 and Appendix H provide equations and tables to determine estimated energy requirements.

cThe linolenic acid referred to in this table and text is the omega-3 fatty acid known as alpha-linolenic acid.

dThe values listed are based on reference body weights.

eAssumed to be from human milk.

fAssumed to be from human milk and complementary foods and beverages. This includes approximately 0.6 L (∼2½ cups) as total fl uid including formula, juices, and drinking water.

gFor energy, the age groups for young children are 1–2 years and 3–8 years.

hFor males, subtract 10 calories per day for each year of age above 19.

iBecause weight need not change as adults age if activity is maintained, reference weights for adults 19 through 30 years are applied to all adult age groups.

jFor females, subtract 7 calories per day for each year of age above 19.

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Recommended Dietary Allowances (RDA) and Adequate Intakes (AI) for Vitamins

Age (yr) Infants 0–0.5 0.2 0.3 2 5 1.7 0.1 65 0.4 125 40 400 5 4 2.0 0.5–1 0.3 0.4 4 6 1.8 0.3 80 0.5 150 50 500 5 5 2.5 Children 1–3 0.5 0.5 6 8 2 0.5 150 0.9 200 15 300 5 6 30 4–8 0.6 0.6 8 12 3 0.6 200 1.2 250 25 400 5 7 55 Males 9–13 0.9 0.9 12 20 4 1.0 300 1.8 375 45 600 5 11 60 14–18 1.2 1.3 16 25 5 1.3 400 2.4 550 75 900 5 15 75 19–30 1.2 1.3 16 30 5 1.3 400 2.4 550 90 900 5 15 120 31–50 1.2 1.3 16 30 5 1.3 400 2.4 550 90 900 5 15 120 51–70 1.2 1.3 16 30 5 1.7 400 2.4 550 90 900 10 15 120 �70 1.2 1.3 16 30 5 1.7 400 2.4 550 90 900 15 15 120 Females 9–13 0.9 0.9 12 20 4 1.0 300 1.8 375 45 600 5 11 60 14–18 1.0 1.0 14 25 5 1.2 400 2.4 400 65 700 5 15 75 19–30 1.1 1.1 14 30 5 1.3 400 2.4 425 75 700 5 15 90 31–50 1.1 1.1 14 30 5 1.3 400 2.4 425 75 700 5 15 90 51–70 1.1 1.1 14 30 5 1.5 400 2.4 425 75 700 10 15 90 �70 1.1 1.1 14 30 5 1.5 400 2.4 425 75 700 15 15 90 Pregnancy �18 1.4 1.4 18 30 6 1.9 600 2.6 450 80 750 5 15 75 19–30 1.4 1.4 18 30 6 1.9 600 2.6 450 85 770 5 15 90 31–50 1.4 1.4 18 30 6 1.9 600 2.6 450 85 770 5 15 90 Lactation �18 1.4 1.6 17 35 7 2.0 500 2.8 550 115 1200 5 19 75 19–30 1.4 1.6 17 35 7 2.0 500 2.8 550 120 1300 5 19 90 31–50 1.4 1.6 17 35 7 2.0 500 2.8 550 120 1300 5 19 90

NOTE: For all nutrients, values for infants are AI. The table on page Y defi nes units of nutrient measure. aNiacin recommendations are expressed as niacin equivalents (NE), except for recommendations for infants younger than 6 months, which are expressed as preformed niacin. bFolate recommendations are expressed as dietary folate equivalents (DFE).

cVitamin A recommendations are expressed as retinol activity equivalents (RAE). dVitamin D recommendations are expressed as cholecalciferol and assume an absence of adequate exposure to sunlight. eVitamin E recommendations are expressed as �-tocopherol.

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Recommended Dietary Allowances (RDA) and Adequate Intakes (AI) for Minerals

Age (yr) Infants 0–0.5 120 180 400 210 100 30 0.27 2 110 15 200 0.003 0.01 0.2 2 0.5–1 370 570 700 270 275 75 11 3 130 20 220 0.6 0.5 5.5 3 Children 1–3 1000 1500 3000 500 460 80 7 3 90 20 340 1.2 0.7 11 17 4–8 1200 1900 3800 800 500 130 10 5 90 30 440 1.5 1.0 15 22 Males 9–13 1500 2300 4500 1300 1250 240 8 8 120 40 700 1.9 2 25 34 14–18 1500 2300 4700 1300 1250 410 11 11 150 55 890 2.2 3 35 43 19–30 1500 2300 4700 1000 700 400 8 11 150 55 900 2.3 4 35 45 31–50 1500 2300 4700 1000 700 420 8 11 150 55 900 2.3 4 35 45 51–70 1300 2000 4700 1200 700 420 8 11 150 55 900 2.3 4 30 45 �70 1200 1800 4700 1200 700 420 8 11 150 55 900 2.3 4 30 45 Females 9–13 1500 2300 4500 1300 1250 240 8 8 120 40 700 1.6 2 21 34 14–18 1500 2300 4700 1300 1250 360 15 9 150 55 890 1.6 3 24 43 19–30 1500 2300 4700 1000 700 310 18 8 150 55 900 1.8 3 25 45 31–50 1500 2300 4700 1000 700 320 18 8 150 55 900 1.8 3 25 45 51–70 1300 2000 4700 1200 700 320 8 8 150 55 900 1.8 3 20 45 �70 1200 1800 4700 1200 700 320 8 8 150 55 900 1.8 3 20 45 Pregnancy �18 1500 2300 4700 1300 1250 400 27 12 220 60 1000 2.0 3 29 50 19–30 1500 2300 4700 1000 700 350 27 11 220 60 1000 2.0 3 30 50 31–50 1500 2300 4700 1000 700 360 27 11 220 60 1000 2.0 3 30 50 Lactation �18 1500 2300 5100 1300 1250 360 10 13 290 70 1300 2.6 3 44 50 19–30 1500 2300 5100 1000 700 310 9 12 290 70 1300 2.6 3 45 50 31–50 1500 2300 5100 1000 700 320 9 12 290 70 1300 2.6 3 45 50

NOTE: For all nutrients, values for infants are AI. The table on page Y defi nes units of nutrient measure.

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Tolerable Upper Intake Levels (UL) for Vitamins

Age (yr)

Infants 0–0.5 — — — — — 600 25 — 0.5–1 — — — — — 600 25 —

Children 1–3 10 30 300 1000 400 600 50 200 4–8 15 40 400 1000 650 900 50 300 9–13 20 60 600 2000 1200 1700 50 600

Adolescents 14–18 30 80 800 3000 1800 2800 50 800

Adults 19–70 35 100 1000 3500 2000 3000 50 1000 �70 35 100 1000 3500 2000 3000 50 1000

Pregnancy �18 30 80 800 3000 1800 2800 50 800 19–50 35 100 1000 3500 2000 3000 50 1000

Lactation �18 30 80 800 3000 1800 2800 50 800 19–50 35 100 1000 3500 2000 3000 50 1000

aThe UL for niacin and folate apply to synthetic forms obtained from supplements, fortifi ed foods, or a combination of the two. bThe UL for vitamin A applies to the preformed vitamin only.

cThe UL for vitamin E applies to any form of supplemental �-tocopherol, fortifi ed foods, or a combination of the two.

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c Tolerable Upper Intake Levels (UL) for Minerals

Age (yr)

Infants 0–0.5 — — — — — 40 4 — 45 — — 0.7 — — — — 0.5–1 — — — — — 40 5 — 60 — — 0.9 — — — —

Children 1–3 1500 2300 2500 3000 65 40 7 200 90 1000 2 1.3 300 3 0.2 — 4–8 1900 2900 2500 3000 110 40 12 300 150 3000 3 2.2 600 6 0.3 — 9–13 2200 3400 2500 4000 350 40 23 600 280 5000 6 10 1100 11 0.6 —

Adolescents 14–18 2300 3600 2500 4000 350 45 34 900 400 8000 9 10 1700 17 1.0 —

Adults 19–70 2300 3600 2500 4000 350 45 40 1100 400 10,000 11 10 2000 20 1.0 1.8 �70 2300 3600 2500 3000 350 45 40 1100 400 10,000 11 10 2000 20 1.0 1.8

Pregnancy �18 2300 3600 2500 3500 350 45 34 900 400 8000 9 10 1700 17 1.0 — 19–50 2300 3600 2500 3500 350 45 40 1100 400 10,000 11 10 2000 20 1.0 —

Lactation �18 2300 3600 2500 4000 350 45 34 900 400 8000 9 10 1700 17 1.0 — 19–50 2300 3600 2500 4000 350 45 40 1100 400 10,000 11 10 2000 20 1.0 —

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dThe UL for magnesium applies to synthetic forms obtained from supplements or drugs only.

NOTE: An Upper Limit was not established for vitamins and minerals not listed and for those age groups listed with a dash (—) because of a lack of data, not because these nutrients are safe to consume at any level of intake. All nutrients can have adverse effects when intakes are excessive.

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Frances Sienkiewicz Sizer Ellie Whitney

NutritionNutrition TWELFTH EDITION

Concepts and Controversies

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Nutrition: Concepts and Controversies, 12th edition

Frances Sienkiewicz Sizer and Ellie Whitney

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about the authors

Frances Sienkiewicz Sizer

M.S., R.D., F.A.D.A., attended Florida State University where, in

1980, she received her B.S. and, in 1982, her M.S. in nutrition. She

is certifi ed as a charter Fellow of the American Dietetic Associa-

tion. She is a founding member and vice president of Nutrition and

Health Associates, an information and resource center in Talla-

hassee, Florida, that maintains an ongoing bibliographic database

tracking research in more than 1,000 topic areas of nutrition. Her

textbooks include Life Choices: Health Concepts and Strategies; Mak-

ing Life Choices; Th e Fitness Triad: Motivation, Training, and Nutri-

tion; and others. She was a primary author of Nutrition Interactive,

an instructional college-level nutrition CD-ROM that pioneered

the animation of nutrition concepts for use in college classrooms.

She has lectured at universities and at national and regional confer-

ences, and actively supports ECHO, a local hunger and homeless-

ness relief organization in her community.

Eleanor Noss Whitney

Ph.D., received her B.A. in Biology from Radcliff e College in 1960

and her Ph.D. in Biology from Washington University, St. Louis,

in 1970. Formerly on the faculty at Florida State University, and a

dietitian registered with the American Dietetic Association, she now

devotes full time to research, writing, and consulting in nutrition,

health, and environmental issues. Her earlier publications include

articles in Science, Genetics, and other journals. Her textbooks include

Understanding Nutrition, Understanding Normal and Clinical Nutri-

tion, Nutrition and Diet Th erapy, and Essential Life Choices for college

students and Making Life Choices for high-school students. Her most

intense interests presently include energy conservation, solar energy

uses, alternatively fueled vehicles, and ecosystem restoration.

To all who seek nutrition knowledge and to all who teach and nourish others.

–Fran

To Max, Zoey, Emily, Rebecca, Kalijah, and Duchess with love.

–Ellie

brief contents

Food Choices and Human Health 11

Nutrition Tools—Standards 2 and Guidelines 29

The Remarkable Body 683

Carbohydrates: Sugar, Starch, Glycogen, 4 and Fiber 106

The Lipids: Fats, Oils, Phospholipids, 5 and Sterols 149

The Proteins and Amino Acids 1896

The Vitamins 2267

Water and Minerals 2768

Energy Balance and Healthy Body 9 Weight 324

Nutrients, Physical Activity, 10 and the Body’s Responses 370

Diet and Health 40711

Food Safety and Food Technology 44512

Life Cycle Nutrition: 13 Mother and Infant 490

Child, Teen, and Older Adult 53114

Hunger and the Global 15 Environment 573

Appendixes A-1

Glossary GL-1

Index IN-1

Assessments and Goals 18

Obstacles to Change 18

Start Now 19

Food Feature: How Can I Get Enough Nutrients Without Consuming Too Many Calories? 20

Media Menu 21

Self Check 21

Controversy 1: Sorting the Imposters from the Real Nutrition Experts 23

Chapter 2 Nutrition Tools— Standards and Guidelines 29

Nutrient Recommendations 30

Dietary Reference Intakes 30

Goals of the DRI Committee 30

Understanding the DRI Intake Recommendations 32

How the Committee Establishes DRI Values—An RDA Example 33

Setting Energy Requirements 34

Why Are Daily Values Used on Labels? 34

Dietary Guidelines for Americans 35

Diet Planning with the USDA Food Guide 37

Think Fitness: Recommendations for Daily Physical

Activity 37

The Food Groups and Subgroups 40

The Discretionary Calorie Concept 40

Chapter 1 Food Choices and Human Health 1

A Lifetime of Nourishment 2 The Diet and Health Connection 3

Genetics and Individuality 3

Think Fitness: Why Be Physically Active? 4

Other Lifestyle Choices 4

Healthy People 2010: Nutrition Objectives for the Nation 4

The Human Body and Its Food 5 Meet the Nutrients 6

Can I Live on Just Supplements? 7

The Challenge of Choosing Foods 8 The Abundance of Foods to Choose From 8

How, Exactly, Can I Recognize a Nutritious Diet? 10

Why People Choose Foods 11

The Science of Nutrition 13 The Scientifi c Approach 13

Scientifi c Challenge 13

Can I Trust the Media to Deliver Nutrition News? 15

My Turn: Lose Weight While You Sleep! 16

National Nutrition Research 16

Consumer Corner: Reading Nutrition News with an Educated Eye 17

A Guide to Behavior Change 18

The Process of Change 18

contents

vi C o n t e n t s

The Mechanical Aspect of Digestion 79

The Chemical Aspect of Digestion 82

Are Some Food Combinations More Easily Digested Than Others? 84

If “I Am What I Eat,” Then How Does a Peanut Butter Sandwich Become “Me”? 84

Absorption and Transportation of Nutrients 86

A Letter from Your Digestive Tract 88

The Excretory System 92 My Turn: I Am What I Drink 92

Storage Systems 93 When I Eat More Than My Body Needs, What Happens to the Extra Nutrients? 93

Variations in Nutrient Stores 93

Conclusion 93

Media Menu 94

Self Check 94

Controversy 3: Alcohol and Nutrition: Do the Benefi ts Outweigh the Risks? 95

Chapter 4 Carbohydrates: Sugar, Starch, Glycogen, and Fiber 106

A Close Look at Carbohydrates 107

Sugars 107

Starch 109

Glycogen 110

Fiber 110

The Need for Carbohydrates 111

If I Want to Lose Weight and Stay Healthy, Should I Avoid Carbohydrates? 112

Why Do Nutrition Experts Recommend Fiber-Rich Foods? 113

Recommendations and Intakes 118

Diet Planning Application 44 MyPyramid: Steps to a Healthier You 45

Flexibility of the USDA Food Guide 46

My Turn: Right Size—Supersize? 47

Portion Control 48

A Note About Exchange Systems 49

Consumer Corner: Checking Out Food Labels 50

Food Feature: Getting a Feel for the Nutrients in Foods 56

Media Menu 59

Self Check 59

Controversy 2: Are Some Foods “Superfoods” for Health? 61

Chapter 3 The Remarkable Body 68

The Body’s Cells 69 Genes Control Functions 70

Cells, Tissues, Organs, Systems 71

The Body Fluids and the Cardiovascular System 71

The Hormonal and Nervous Systems 74

What Do Hormones Have to Do with Nutrition? 74

How Does the Nervous System Interact with Nutrition? 75

The Immune System 76 Immune Defenses 76

Infl ammation 77

The Digestive System 78

Why Do People Like Sugar, Salt,

and Fat? 78

The Digestive Tract 79

vi iC o n t e n t s

Usefulness of Fats in the Body 150

Usefulness of Fats in Food 152

A Close Look at Lipids 152

Triglycerides: Fatty Acids and Glycerol 152

Saturated Versus Unsaturated Fatty Acids 153

Phospholipids and Sterols 155

Lipids in the Body 156

Digestion and Absorption of Fats 156

Transport of Fats 158

Storing and Using the Body’s Fat 159

Dietary Fat, Cholesterol, and Health 160

Recommendations for Lipid Intakes 160

Lipoproteins and Heart Disease Risk 161

What Does Food Cholesterol Have to Do with Blood Cholesterol? 163

Recommendations Applied 164

Think Fitness: Why Exercise the Body for the Health of the Heart? 166

Essential Polyunsaturated Fatty Acids 166

The Need for Essential Fatty Acids 166

Omega-6 and Omega-3 Fatty Acid Families 167

Recommendations for Omega-3 Fatty Acid Intake 168

Consumer Corner: Seafood Safety— Balancing Risks and Benefi ts 170

The Eff ects of Processing on Unsaturated Fats 171

What Is “Hydrogenated Vegetable Oil,” and What’s It Doing in My Chocolate Chip Cookies? 171

What Are Trans-Fatty Acids, and Are They Harmful? 172

My Turn: Heart to Heart 173

From Carbohydrates to Glucose 119 Digestion and Absorption of Carbohydrate 119

Consumer Corner: Refi ned, Enriched, and Whole-Grain Foods 120

Why Do Some People Have Trouble Digesting Milk? 123

The Body’s Use of Glucose 125 Splitting Glucose for Energy 125

How Is Glucose Regulated in the Body? 126

Handling Excess Glucose 127

Think Fitness: What Can I Eat to Make Workouts Easier? 128

The Glycemic Index of Food 129

Diabetes 130 The Perils of Diabetes 130

Prediabetes and the Importance of Testing 131

Type 1 Diabetes 131

Type 2 Diabetes 132

My Turn: 21st Century Epidemic? 132

Management of Diabetes 133 Nutrition 133

Physical Activity 135

If I Feel Dizzy Between Meals, Do I Have Hypoglycemia? 135

Food Feature: Finding the Carbohydrates in Foods 136

Media Menu 141

Self Check 141

Controversy 4: Are Carbohydrates “Bad” for Health? 143

Chapter 5 The Lipids: Fats, Oils, Phospholipids, and Sterols 149

Introducing the Lipids 150

vi i i C o n t e n t s

Which Foods Provide High-Quality Protein? 208

Protein Defi ciency and Excess 210

What Happens When People Consume Too Little Protein? 210

Marasmus 210

Kwashiorkor 211

PEM at Home 212

Is It Possible to Consume Too Much Protein? 213

Food Feature: Getting Enough but Not Too Much Protein 214

Media Menu 217

Self Check 218

Controversy 6: Vegetarian and Meat- Containing Diets: What Are the Benefi ts and Pitfalls? 219

Chapter 7 The Vitamins 226

Defi nition and Classifi cation of Vitamins 227

The Fat-Soluble Vitamins 228

Vitamin A 229 Roles of Vitamin A and Consequences of Defi ciency 229

Vitamin A Defi ciency Around the World 231

Vitamin A Toxicity 231

Vitamin A Recommendations 232

Food Sources of Vitamin A 232

My Turn: Take Your Vitamins? 234

Beta-Carotene 234

Vitamin D 235 Roles of Vitamin D 235

Fat in the Diet 174 Added Fats 174

Meat, Poultry, Fish, Dried Peas and Beans, Eggs, and Nuts 174

Milk, Yogurt, and Cheese 176

Grains 177

Food Feature: Defensive Dining 178

Media Menu 183

Self Check 183

Controversy 5: Good Fats and Bad Fats— Which Are Which? 184

Chapter 6 The Proteins and Amino Acids 189

The Structure of Proteins 190 Amino Acids 190

How Do Amino Acids Build Proteins? 191

The Variety of Proteins 192

Think Fitness: Can Eating Extra Protein Make Muscles Grow Stronger? 196

Denaturation of Proteins 196

Digestion and Absorption of Dietary Protein 197

Protein Digestion 197

What Happens to Amino Acids After Protein Is Digested? 198

The Importance of Protein 199

The Roles of Body Proteins 199

Amino Acids to Glucose 203

Food Protein: Need and Quality 204 How Much Protein Do People Really Need? 204

Consumer Corner: Protein and Amino Acid Supplements 205

My Turn: Veggin’ Out 206

Nitrogen Balance 207

ixC o n t e n t s

Ribofl avin Roles and Sources 251

Niacin Functions 252

Folate Roles 253

Vitamin B12 Roles 256

Vitamin B6 Roles 257

Biotin and Pantothenic Acid 259

Non-B Vitamins 259

Food Feature: Choosing Foods Rich in Vitamins 264

Media Menu 267

Self Check 268

Controversy 7: Vitamin Supplements: Do the Benefi ts Outweigh the Risks? 269

Chapter 8 Water and Minerals 276

Water 278 Why Is Water the Most Indispensable Nutrient? 278

The Body’s Water Balance 279

Quenching Thirst and Balancing Losses 280

How Much Water Do I Need to Drink in a Day? 280

Are Some Kinds of Water Better for My Health Than Others? 282

Safety and Sources of Drinking Water 283

Safety of Public Water 283

Water Sources 283

Too Little Vitamin D—A Danger to Bones 236

Too Much Vitamin D—A Danger to Soft Tissues 236

Vitamin D from Sunlight 236

Is Sunlight Exposure a Safe Source of Vitamin D? 236

Intake Recommendations 237

Food Sources 237

Vitamin E 238 Roles of Vitamin E 239

Vitamin E Defi ciency 239

Toxicity of Vitamin E 240

Vitamin E Recommendations and U.S. Intakes 240

Food Sources of Vitamin E 240

Vitamin K 241 Roles of Vitamin K 241

Defi ciency of Vitamin K 241

Vitamin K Toxicity 242

Requirements and Sources of Vitamin K 242

The Water-Soluble Vitamins 242 Think Fitness: Vitamins for Athletes 243

Vitamin C 243 The Roles of Vitamin C 244

Defi ciency Symptoms 244

Vitamin C Toxicity 245

Vitamin C Recommendations 245

Consumer Corner: Vitamin C and the Common Cold 246

Food Sources of Vitamin C 246

The B Vitamins in Unison 248 B Vitamin Roles in Metabolism 248

B Vitamin Defi ciencies 248

The B Vitamins as Individuals 250 Thiamin Roles 250

x C o n t e n t s

What Are the Risks from Underweight? 325

What Are the Risks from Too Much Body Fat? 326

What Are the Risks from Central Obesity? 326

How Fat Is Too Fat? 327

The Body’s Energy Balance 328

Energy In and Energy Out 329

How Many Calories Do I Need Each Day? 329

Estimated Energy Requirements (EER) 330

The DRI Method of Estimating Energy Requirements 331

Body Weight Versus Body Fatness 331 Body Mass Index (BMI) 332

Measures of Body Composition and Fat Distribution 332

How Much Body Fat Is Ideal? 333

The Mystery of Obesity 334 Hunger and Appetite—“Go” Signals 334

Satiation and Satiety—“Stop” Signals 336

Inside-the-Body Causes of Obesity 337

My Turn: How Many Calories? 339

Outside-the-Body Causes of Obesity 339

Think Fitness: Activity for a Healthy Body Weight 340

How the Body Loses and Gains Weight 341

Moderate Weight Loss Versus Rapid Weight Loss 342

Weight Gain 344

Consumer Corner: Popular Fad Diets 345

Achieving and Maintaining a Healthy Body Weight 346

What Diet Strategies Are Best for Weight Loss? 347

Body Fluids and Minerals 284 Water Follows Salt 284

Consumer Corner: Bottled Water 285

Fluid and Electrolyte Balance 286

Acid-Base Balance 287

The Major Minerals 288 Calcium 288

My Turn: Drink Your Milk! 290

Phosphorus 291

Magnesium 292

Sodium 294

Potassium 296

Chloride 298

Sulfate 299

The Trace Minerals 299 Iodine 299

Iron 301

Think Fitness: Exercise-Defi ciency Fatigue 303

Zinc 305

Selenium 307

Fluoride 308

Chromium 308

Copper 309

Other Trace Minerals and Some Candidates 309

Food Feature: Meeting the Need for Calcium 312

Media Menu 315

Self Check 316

Controversy 8: Osteoporosis: Can Lifestyle Choices Reduce the Risks? 317

Chapter 9 Energy Balance and Healthy Body Weight 324

The Problems of Too Little or Too Much Body Fat 325

xiC o n t e n t s

Fat and Physical Activity 385

Protein for Building Muscles and for Fuel 386

How Much Protein Should an Athlete Consume? 387

Vitamins and Minerals—Keys to Performance 388

Do Nutrient Supplements Benefi t Athletic Performance? 388

Nutrients of Concern 389

Fluids and Temperature Regulation in Physical Activity 390

Water Losses During Physical Activity 390

Fluid and Electrolyte Needs During Physical Activity 391

Sodium Depletion and Water Intoxication 392

Consumer Corner: What Do Sports Drinks Have to Offer? 393

Other Beverages 394

Food Feature: Choosing a Performance Diet 394

Media Menu 399

Self Check 399

Controversy 10: Ergogenic Aids: Break- throughs, Gimmicks, or Dangers? 400

Chapter 11 Diet and Health 407

Nutrition and Immunity 409

The Concept of Risk Factors 410

Cardiovascular Diseases 412 Atherosclerosis 413

Risk Factors for CVD 415

Think Fitness: Ways to Include Physical Activity in a Day 419

Recommendations for Reducing CVD Risk 420

Physical Activity in Weight Loss and Maintenance 352

What Strategies Are Best for Weight Gain? 354

Medical Treatment of Obesity 355

Herbal Products and Gimmicks 357

Once I’ve Changed My Weight, How Can I Stay Changed? 358

Food Feature: Behavior Modifi cation for Weight Control 359

Media Menu 362

Self Check 362

Controversy 9: The Perils of Eating Disorders 363

Chapter 10 Nutrients, Physical Activity, and the Body’s Responses 370

Fitness 371

Benefi ts of Fitness 371

Physical Activity Guidelines 372

The Essentials of Fitness 374 How Do Muscles Gain in Size and Strength? 375

What Are the Benefi ts of Resistance Training? 376

How Does Cardiorespiratory Training Benefi t the Heart? 377

Think Fitness: Exercise Safety 377

The Active Body’s Use of Fuels 379 Glucose Use and Storage 380

Activity Intensity, Glucose Use, and Glycogen Stores 380

Activity Duration, Glucose Use, and Glycogen Stores 382

My Turn: How Much Is Enough? 384 Degree of Training Affects Glycogen Use 385

xi i C o n t e n t s

Toxins, Residues, and Contaminants in Foods 463

Natural Toxins in Foods 463

Pesticides 464

My Turn: Organic: Does It Matter? 467

Consumer Corner: Organic Foods 468

Animal Drugs 469

Environmental Contaminants 470

Are Food Additives Safe? 473

Regulations Governing Additives 473

Additives to Improve Safety and Quality 474

Flavoring Agents 475

Fat Replacers and Artifi cial Fats 477

Incidental Food Additives 478

Conclusion 479 Food Feature: Processing and the Nutrients in Foods 480

Media Menu 482

Self Check 482

Controversy 12: Genetically Modifi ed Foods: What Are the Pros and Cons? 483

Chapter 13 Life Cycle Nutrition: Mother and Infant 490

Pregnancy: The Impact of Nutrition on the Future 491

Preparing for Pregnancy 491

The Events of Pregnancy 493

Increased Need for Nutrients 494

Food Assistance Programs 499

How Much Weight Should a Woman Gain During Pregnancy? 499

Nutrition and Hypertension 422 How Does Blood Pressure Work in the Body? 422

Risk Factors for Hypertension 423

How Does Nutrition Affect Hypertension? 424

My Turn: Fast-Food Generation? 425

Consumer Corner: Complementary and Alternative Medicine 427

Nutrition and Cancer 429 How Does Cancer Develop? 430

Which Diet Factors Affect Cancer Risk? 432

Conclusion 434 Food Feature: The Dash Diet: Preventive Medicine 435

Media Menu 439

Self Check 439

Controversy 11: Nutritional Genomics: Can It Deliver on Its Promises? 440

Chapter 12 Food Safety and Food Technology 445

Microbes and Food Safety 447 How Do Microbes in Food Cause Illness in the Body? 447

Food Safety from Farm to Table 450

Safe Food Practices for Individuals 452

Problem Foods 456 Meats and Poultry 457

Raw Produce and Other Foods 458

How Can I Avoid Illness When Traveling? 460

Advances in Microbial Food Safety 461

Irradiation 461

Other Technologies 462

xi i iC o n t e n t s

Chapter 14 Child, Teen, and Older Adult 531

Early and Middle Childhood 532

Feeding a Healthy Young Child 532

Mealtimes and Snacking 535

How Do Nutrient Defi ciencies Impair a Child’s Brain? 538

The Problem of Lead 538

Food Allergy, Intolerance, and Aversion 540

Can Diet Make a Child Hyperactive? 542

Physical Activity, Television, and Children’s Nutrition Problems 543

Dental Caries 543

Is Breakfast Really the Most Important Meal of the Day for Children? 545

How Nourishing Are the Meals Served at School? 545

Nutrition in Adolescence 547

Nutrient Needs 548

Common Concerns 549

Consumer Corner: Nutrition and PMS 550

Eating Patterns and Nutrient Intakes 550

The Later Years 551

Nutrition in the Later Years 552 Energy and Activity 552

Think Fitness: Benefi ts of Physical Activity for the Older Adult 554

Protein Needs 554

Carbohydrates and Fiber 554

Fats and Arthritis 555

Vitamin Needs 555

Water and the Minerals 556

Can Nutrition Help People to Live Longer? 557

Weight Loss After Pregnancy 500

Should Pregnant Women Be Physically Active? 501

Think Fitness: Physical Activities for the Pregnant Woman 502

Teen Pregnancy 502

Why Do Some Women Crave Pickles and Ice Cream While Others Can’t Keep Anything Down? 502

Some Cautions for the Pregnant Woman 503

Drinking During Pregnancy 505 Alcohol’s Effects 505

Fetal Alcohol Syndrome 506

Experts’ Advice 507

Troubleshooting 507 Diabetes 508

Hypertension 508

Preeclampsia 508

My Turn: Bringing Up Baby 508

Lactation 509 Nutrition During Lactation 509

When Should a Woman Not Breastfeed? 510

Feeding the Infant 511 Nutrient Needs 511

Why Is Breast Milk So Good for Babies? 512

Formula Feeding 516

Consumer Corner: Formula’s Advertising Advantage 517

An Infant’s First Foods 518

Looking Ahead 520

Food Feature: Mealtimes with Infants 521

Media Menu 523

Self Check 523

Controversy 13: Childhood Obesity and Early Chronic Diseases 524

xiv C o n t e n t s

How Can People Engage in Activism and Simpler Lifestyles at Home? 586

Consumer Corner: Saving Money and Protecting the Environment 587

Government Action 589

Private and Community Enterprises 589

Educators and Students 589

Food and Nutrition Professionals 589

Individuals 589

Media Menu 589

Self Check 590

Controversy 15: Toward Sustainable Food Production: How to Go Forward? 591

Appendixes A-1 Table of Food Composition

B-0 WHO Nutrition Recommendations; Canadian Guidelines and Meal Planning

C-0 Aids to Calculations

D-1 Choose Your Foods: Exchange Lists for Diabetes

E-1 Food Patterns to Meet the Dietary Guidelines for Americans 2005

F-0 Notes

G-0 Answers to Self Check Questions

H-1 Physical Activity and Energy Requirements

Glossary GL-1

Index IN-1

Immunity and Infl ammation 559

Can Foods or Supplements Affect the Course of Alzheimer’s Disease? 559

Food Choices of Older Adults 560

My Turn: Eating Solo 562

Food Feature: Single Survival and Nutrition on the Run 562

Media Menu 564

Self Check 565

Controversy 14: Nutrient-Drug Interac- tions: Who Should Be Concerned? 566

Chapter 15 Hunger and the Global Environment 573

Hunger 574

Hunger in the United States 575

What U.S. Food Programs Are Directed at Stopping Domestic Hunger? 576

What Is the State of World Hunger? 578

The World Food Supply and the Environment 581

Threats to the Future Food Supply 581

Environmental Degradation and Hunger 582

A World Moving Toward Solutions 585 My Turn: How Responsible Am I? 586

whole-grain foods, mercury in seafood, amino acid supplements, vitamin C and the common cold, bottled water, organic foods, and other nutrition-related marketplace issues.

By popular demand, we have retained our Snapshots of vita- mins and minerals. Th ese concentrated capsules of information depict food sources of vitamins and minerals, present the DRI recommended intakes and Tolerable Upper Intake Levels, and off er the chief functions of each nutrient along with defi ciency and toxicity symptoms.

New or major terms are defi ned in the margins of chapter pages where they are introduced and also in the Glossary at the end of the book. Defi nitions in Controversy sections are grouped together in tables and also appear in the Glossary. Th e reader who wishes to locate any term can quickly do so by consulting the index, which lists the page numbers of defi ni- tions in boldface type.

Two useful features close each chapter. First, the Media Menu

off ers important and useful Internet web sites, Th e second is the popular Self Check that provides study questions, with answers in Appendix G to provide immediate feedback to the learner.

Controversies Th e Controversies of this book’s title invite you to explore beyond the safe boundaries of established nutrition knowledge. Th ese optional readings, which appear at the end of each chapter, delve into current scientifi c topics and emerging controversies. All are up to date; those that are new to this edition are listed next.

Chapter Contents Chapter 1 begins the text with a personal challenge to students. It asks the question so many people ask of nutrition educators— “Why should people care about nutrition?” We answer with a lesson in the ways in which nutritious foods aff ect diseases, and present a continuum of diseases from purely genetic in origin to those almost totally preventable by nutrition. After present- ing some beginning facts about the genes, nutrients, bioactive food components, and nature of foods, the chapter goes on to present the Healthy People goals for the nation. It concludes

with a discussion of scientifi c research in nutrition to lend a perspective on the context in which study results may

be rightly viewed. Chapter 2 brings together the con-

cepts of nutrient allowances, such as the Dietary Reference Intakes, and diet planning using the Dietary

Guidelines for Americans and the USDA MyPyramid Food Guide. Chapter 3 presents a thorough, but brief, introduction to the work-

ings of the human body from the genes to the organs, with major em-

phasis on the digestive system. New in

preface

A billboard in Louisiana reads, “Come as you are. Leave dif- ferent,” meaning that once you’ve seen, smelled, tasted, and

listened to Louisiana, you’ll never be the same. Th is book extends the same invitation to its readers: Come to nutrition science as you are, with all of the knowledge and enthusiasm you possess, with all of your unanswered questions and misconceptions, and with the habits and preferences that now dictate what you eat.

But leave diff erent. Take with you from this study a more com- plete understanding of nutrition science. Take a greater ability to discern between nutrition truth and fi ction, to ask sophisticated questions, and to fi nd the answers. Finally, take with you a bet- ter sense of how to feed yourself in ways that not only please you and soothe your spirit, but that nourish your body as well.

For over a quarter of a century, Nutrition: Concepts and Con-

troversies has been a cornerstone in nutrition classes across North America, serving the needs of students and professors in building a healthier future. In keeping with our tradition, in this, our 12th edition, we continue exploring the ever-changing frontier of nutrition science, confronting its mysteries through its scientifi c roots. We maintain our sense of personal connec- tion with instructors and learners alike, writing for them in the clear, informal style that has become our trademark.

Pedagogical Features Th roughout these chapters, features tickle the reader’s interest and inform. For both verbal and visual learners, our logical presentation and our lively fi gures keep interest high and un- derstanding at a peak. Our many fi gures throughout the chap- ters reinforce important basic concepts. Th e photos that adorn many of our pages add pleasure to reading.

New in this edition, Concept Links in margins direct stu- dents to earlier foundation discussions relating to topics at hand. Page numbers ease the fi nding of critical subject matter in earlier chapters.

Many tried-and-true features return in this edition: Each chapter begins with “Do You Ever . . .” questions to pique interest and set a personal tone for the information that follows. My Turn

features follow, inviting the reader to hear stories from students in nutrition classes around the nation and to off er evidence-based solutions to real-life situations. Th ink Fitness reminders ap- pear from time to time to alert read- ers to ways in which physical activ- ity links with nutrition to support health. Th e Food Feature sections that appear in most chapters act as bridges between theory and prac- tice; they are practical applications of the chapter concepts that help readers to choose foods according to sound nutrition principles. New in this edition are Concepts in Action activi- ties that integrate chapter concepts with the Diet Analysis Plus program. Consumer Corners present information on

xvi P r e f a c e

New table of discretionary calories. New photos illustrating food components that provide discre- tionary calories. Changed vegetable and fruit reference sizes to 1 cup for consis- tency with MyPyramid. Revamped ethnic food fi gure. New Healthy Eating Index defi ned. New fi gure, “How Does the U.S. Diet Stack Up?”

Controversy 2 Updated with new phytochemical information and reorga- nized table of phytochemicals, sources, and actions.

Chapter 3 New section explains and defi nes infl ammation as part of the immune response. New table introduces digestive enzyme terms and names gen- eral categories. Expanded coverage of ulcer, GERD.

Controversy 3 Improved organization. New fi gure (simple) and expanded text conveys new emphasis on free-radical generation and damage from oxidative stress from alcohol metabolism. New statistics from CDC on binge drinking. New fi gure correlating likelihood of traffi c accidents with BAC. Much new information on alcohol intake and increased cancer risks.

Chapter 4 New organization. New material on infl ammation, particularly with colon health and diabetes. New paragraphs on sugar alcohols, with reference to artifi - cial sweetener coverage in Chapter 12 and to dental caries in Chapter 14. Updated diabetes maps.

Controversy 4 New Controversy on health eff ects of carbohydrates.

Chapter 5 Reorganized several topics. Expanded coverage of omega-3 fatty acids, with new Con- sumer Corner on choosing safe varieties of seafood, including risks from mercury in both saltwater and freshwater fi sh. New emphasis that saturated fat guidelines apply to women (dispelling myth that heart disease is a man’s disease).

Controversy 5 Introduces importance of dietary pattern.

Chapter 6 Updated. Moved most epigenetic information to new Contro- versy 11. Included gene regulation among major functions.

Controversy 6 New emphasis on vegetarian meal planning, with new tables and fi gures to assist.

this edition is an introduction to the topic of infl ammation as part of the immune response. Chapters 4–6 are devoted to the energy-yielding nutrients—carbohydrates, lipids, and protein. Th e infl ammation concept introduced in Chapter 3 is expanded in discussions of diabetes, colon health, and heart disease. Gene regulation takes its place among major functions of body pro- teins. Controversy 4 is entirely new, addressing the theories and fables surrounding the health eff ects of dietary carbohydrates. In Controversy 6 a new emphasis on diet planning for vegetar- ians will assist in sound vegetarian meal planning.

Chapters 7 and 8 present the vitamins, minerals, and water. Chapter 9 relates energy balance to body composition, obesity, and underweight and provides guidance to life-long weight maintenance. Chapter 10 presents the relationships between physical activity, athletic performance, and nutrition, with some guidance about products marketed to athletes. Chapter 11 ap- plies the essence of the fi rst ten chapters to two broad and rap- idly changing areas within nutrition: immunity and disease prevention. Readers will revisit the relationships among oxida- tion, infl ammation, and diseases that were introduced in earlier chapters. Th e new Controversy 11 provides a general overview of the emerging science of nutritional genomics.

Chapter 12 delivers urgently important concepts of food safety. It also addresses the usefulness and safety of food addi- tives, including artifi cial sweeteners and artifi cial fats, formerly topics found in Chapters 4 and 5. Chapters 13 and 14 emphasize the importance of nutrition through the life span and issues sur- rounding childhood obesity in Controversy 13. Chapter 14 in- cludes nutrition advice for feeding preschoolers, schoolchildren, teens, and the elderly, where readers will fi nd the concluding discussion of infl ammation, immunity, and chronic diseases.

Chapter 15 touches on the vast problems of the global food supply and world and U.S. hunger, and links each reader to the meaningful whole through sustainable daily choices available to them. Th e Controversy introduces some challenges in pro- viding the world’s food.

New to This Edition Every section of each chapter of this text refl ects the changes in nutrition science occurring since the last edition. Th e changes range from subtle shifts of emphasis to entirely new sections that demand our attention. Here, we mention just a few of the most salient changes from the last edition. Readers will discover many, many others.

Chapter 1 As of this edition, the term nonnutrient has been replaced with “phytochemical,” “nutrient,” or “bioactive food component,” as appropriate. Condensed several sections and fi gures. Defi ned double-blind controlled human study. Clarifi ed cost of nutritious food: price per calorie versus cost per serving.

Controversy 1 Added defi nition of certifi ed diabetes educator.

Chapter 2 New greater emphasis on discretionary calories.

xvi iP r e f a c e

New table: lifestyle modifi cations to reduce blood pressure. Revised the AHA table of strategies to reduce heart disease risk; moved it into heart disease section. Updated, reorganized table: selected herbs, claims, risks, and evidence. Moved into cancer discussion and updated the table: recom- mendations to reduce cancer risk. Revised the table of cancer at specifi c sites and factors that increase or decrease risk.

Controversy 11 Th is new Controversy presents a simple introduction to nutri- tional genomics. It places the emerging science in the context of today’s applications and marketplace.

Chapter 12 Updated information throughout. Added artifi cial sweeteners and artifi cial fats. New explanation of the process of extrusion and its eff ects on nutrients.

Controversy 12 Updated information throughout; introduces the Svalbard

Global Crop Diversity Trust seed vault.

Chapter 13 New discussion of vitamin D during pregnancy. Enhanced discussion of weight gain during pregnancy. Updated table of weight gain guidelines during pregnancy. New section on weight loss after pregnancy. Added a list of the harms of smoking during pregnancy. Enhanced discussion of diabetes during pregnancy. New discussion of hypertension during pregnancy. Revised spina bifi da fi gure. New fi gure comparing breast milk, formula, and cow’s milk. New table of supplements for full-term infants.

Controversy 13 New obesity diet recommendations and activity guidelines.

Chapter 14 New information on lead’s lingering eff ects through life. New MyPyramid for preschoolers and kids fi gure. Expanded discussion of dental caries and added caries fi gure formerly in Controversy 4. New food skills table adapted from MyPyramid website. New table: 2008 Physical Activity for Americans—Key Guide- lines for Older Adults. New discussion of infl ammation and aging eff ects on immu- nity and chronic disease.

Controversy 14 New table on high-tyramine foods.

Chapter 15 All hunger data updated. New emphasis on the obesity-poverty paradox, with new fi gure. New name: Feed America, formerly America’s Second Harvest New name: Supplemental Nutrition Assistance Program (SNAP), formerly the Food Stamp Program.

New health correlations for red and processed vs white meats. Information correlated to 2009 ADA position paper.

Chapter 7 New organization, with more subheadings. Updated information throughout the chapter. New content on vitamin D; new fi gure of declining U.S. se- rum vitamin D values. New fi gure depicting B vitamin defi ciency symptoms of the tongue and mouth. New photo depiction of niacin defi ciency dermatitis. All graphs updated.

Controversy 7 Updated; new research on contamination of today’s supple- ments.

Chapter 8 New organization with more subheadings. Updated information throughout the chapter. New fi gure on U.S. beverage consumption. New CDC guidelines for sodium. New theory: lifetime sodium exposure and irreversible hyper- tension. New fi gure: calcium economy example, which demonstrates the arithmetic behind calcium recommendations.

Controversy 8 Addresses infl ammatory processes and osteoporosis.

Chapter 9 Updated information throughout the chapter. Reorganized much of the information with new subheadings. New fi gure of obesity rates vs Healthy People target. New section explaining the adipokine/infl ammation/central obesity links. Defi ned adipokine. New information on brown adipose tissue. New 2008 Physical Activity Guidelines for Americans information. New Consumer Corner on Fad Diets with new fi gure compar- ing popular diets. New fi gure for gastric surgeries. New emphasis on society’s role in eating disorders.

Chapter 10 New, contemporary approach updates this chapter with many new fi gures and tables, new terminology, and ACSM guidelines. Included 2008 Physical Activity Guidelines for Americans and ACSM guidelines for conditioning. Greater emphasis on resistance training for physical activity and sports. Added new tables and fi gures.

Chapter 11 Revised fi gure showing interrelationships among chronic diseases. Expanded information on oxidized LDL cholesterol, infl am- mation, and plaque. New Food Feature: the DASH diet. New table: risk factors for chronic diseases.

xvi i i P r e f a c e

information you fi nd inside this book home with you. Use it in your life: nourish yourself, educate your loved ones, and nurture others to be healthy. Stay up with the news, too. For despite all the confl icting messages, infl ated claims, and even quack- ery that abound in the marketplace, true nutrition knowledge progresses with a genuine scientifi c spirit, and important new truths are constantly unfolding.

Acknowledgments To Philip, most heartfelt thanks. Our sincere thanks also to Linda Kelly DeBruyne for her work with Chapter 11, Chapter 13, and beyond. Th anks also to Spencer Webb for his valuable assistance and contemporary perspectives in Chapter 10, and thanks to Wende Webb for taking the lead in development of our new Concepts in Action feature. Rebbecca Skinner, thank you for your early mornings and creative input into Chapter and Controversy 15. Th anks also to Alex Rodriguez and Kathy Guilday for their cheerful and competent attention to details.

Our special thanks to our publishing team: Yolanda Cossio, Peggy Williams, Nedah Rose, Miriam Myers, Elesha Feld- man, Alexis Glubka, Carol Samet, and Melanie Field for their dedication to excellence. Th ank you, Laura McGinn, for your creative and energetic marketing ideas and approach.

We would also like to thank the authors of the student and in- structor ancillaries for the 12th edition: Alana Cline, who revised and expanded the test bank; Mary Ellen Clark, who contributed materials to the instructor’s manual; Jana R. Kicklighter, who authored the study guide; and Michelle Grodner and Daniel Santibanez, who provided content for the student website.

Reviewers of the 12th Edition As always, we are grateful for the instructors who took the time to comment on this revision. Your suggestions were in- valuable in strengthening the book and suggesting new lines of thought. We hope you will continue to provide your comments and suggestions. Alex Kojo Anderson, University of Georgia, Athens

Sharon Antonelli, San Jose City College

L. Rao Ayyagari, Lindenwood University

James W. Bailey, University of Tennessee

Karen Basinger, Montgomery College

Leah Carter, Bakersfi eld College

Melissa Chabot, SUNY @ Buff alo

Priscilla Connors, University of North Texas

Monica L. Easterling, Wayne County Community College District

Jena Nelson Hall, Butte Community College

Eimear M. Mullen, Northern Kentucky University

Steven Nizielski, Grand Valley State University

David J. Pavlat, Central College

Begoña Cirera Perez, Chabot College

Liz Quintana, West Virginia University

Janice M. Rueda, Wayne State University

Donal Scheidel, University of South Dakota

Carole A. Sloan, Henry Ford Community College

Leslie S. Spencer, Rowan University

Ilene Sutter, California State University, Northridge

Barbara P. Zabitz, Wayne County Community College District

New table: tips for thrifty food shopping. New discussion of aquaculture.

Controversy 15 Extensively revised to emphasize sustainability.

Ancillary Materials Students and instructors alike will appreciate the innovative teaching and learning materials that accompany this text. Th e popular “Do It!” exercises appear in CengageNow, an online resource center of study tools for students that includes out- comes assessment through student self-testing and automatic grading features; “Do It!” exercises that provide an opportu- nity for students to practice chapter concepts interactively; a behavior-change planner for healthy eating, weight control, and physical activity; new Pop-up Tutors that reinforce key concepts and provide students with further instruction and practice on particularly diffi cult topics, such as metabolism, digestion, and absorption; and MyTurn case study videos that give students the opportunity to problem-solve with relevant, contemporary nutrition stories of their peers. Students also can access these videos via WebTutor for Blackboard and WebCT, and through links embedded in the Cengage Learning eBook.

Th e Instructor’s Manual features ready-to-use assignment materials including food label and diet planning worksheets, ideas for in-class activities, and class preparation tools such as learning objectives, chapter summaries, lecture presentation outlines, and text-specifi c handouts. Th e Test Bank off ers a rich assortment of multiple-choice and essay questions to test for both fact recall and deeper comprehension. Both of these publications, along with PowerPoint lectures and images, vid- eos, JoinIn quizzes, and ExamView testing software preloaded with the test bank questions will be available on the Power- Lecture DVD-ROM.

Transparency acetates from the 10th edition are also avail- able; instructors can request the handy correlation guide to as- sist in reorganizing their transparencies for the 12th edition.

Diet Analysis Plus 9.0 Diet Analysis Plus allows students to track their diet and phys- ical activity and to analyze the nutritional value of the food they eat so that they can adjust their diets to reach personal health goals—all while gaining a better understanding of how nutrition relates to, and impacts, their lives.

It includes a 20,000+ food database; 11 customizable reports for analysis; 10 new assignable labs; custom food and recipe features; the latest Dietary Reference Intakes; and goals and actual percentages of essential nutrients, vitamins, and miner- als. Use the Concepts in Action activities in Nutrition: Con-

cepts and Controversies to show students how the concepts they learn in the text relate to their personal nutrition goals.

Message to You Our purpose in writing this text, as always, is to enhance our readers’ understanding of nutrition science and motivation to apply it. We hope the information on this book’s pages will reach beyond the classroom into our readers’ lives. Take the

11Food Choices and Human Health

do you ever . . . Question whether your diet can • make a real difference between getting sick or staying healthy?

Purchase supplements, believing • them more powerful than food for ensuring good nutrition?

Wonder why you prefer the foods • you do?

Become alarmed or confused by • news and media reports about nutrition science?

Try to change your diet, but fail?•

Keep reading . . .

LO 1.1 Discuss how particular lifestyle choice can either positively impact or harm overall health.

LO 1.2 Defi ne the term nutrient and be able to list the six major nutrients.

LO 1.3 Recognize the fi ve characteristics of a healthy diet and give suggestions for using them.

LO 1.4 Summarize how a particular culture or circumstance can impact a person’s food choices.

LO 1.5 Describe and give an example of the major types of research studies.

LO 1.6 Discuss why national nutrition survey data are important for the health of the population.

LO 1.7 List the major steps in behavior change and devise a plan for making successful long-term changes in the diet.

LO 1.8 Recognize misleading nutrition claims in advertisements for dietary supplements and in the popular media.

Learning Objectives To find learning objective topics in this chapter, look for text headings with a corresponding “LO” number above the heading. After reading this chapter, you should be able to accomplish the following:

2 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

I f you care about your body, and if you have strong feelings about food, then you have much to gain from learning about nutrition—the science of how food

nourishes the body. Nutrition is a fascinating, much talked about subject. Each day, newspapers, radio, and television present stories of new fi ndings on nutrition and heart health or nutrition and cancer prevention, and at the same time advertisements and commercials bombard us with multicolored pictures of tempting foods—pizza, burgers, cakes, and chips. If you are like most people, when you eat you sometimes wonder, “Is this food good for me?” or you berate yourself, “I probably shouldn’t be eating this.”

When you study nutrition, you learn which foods serve you best, and you can work out ways of choosing foods, planning meals, and designing your diet wisely. Knowing the facts can enhance your health and your enjoyment of eating while relieving your feelings of guilt or worry that you aren’t eating well.

Th is chapter addresses these “why, what, and how” questions about nutrition:

Why• care about nutrition? Th e nutrients interact with body tissues, adding a

little or subtracting a little, day by day, and thus change the very foundations

upon which the health of the body is built.

What• are the nutrients in foods, and what roles do they play in the body? Meet

the nutrients and discover their general roles in building body tissues and main-

taining health.

What• constitutes a nutritious diet? Can you choose foods wisely, for nutrition’s

sake? And what motivates your choices?

How• do we know what we know about nutrition? Scientifi c research reports

provide an important foundation for understanding nutrition science.

And• how do people go about making changes to their diets?

Controversy 1 concludes the chapter by off ering ways to distinguish between trustworthy sources of nutrition information and those that are less reliable.

LO 1.1

A Lifetime of Nourishment If you live for 65 years or longer, you will have consumed more than 70,000 meals and your remarkable body will have disposed of 50 tons of food. Th e foods you choose have cumulative eff ects on your body. As you age, you will see and feel those eff ects—if you know what to look for.

Your body renews its structures continuously, and each day it builds a little mus- cle, bone, skin, and blood, replacing old tissues with new. It may also add a little fat if you consume excess food energy (calories) or subtract a little if you consume less than you require. Some of the food you eat today becomes part of “you” tomorrow.

Th e best food for you, then, is the kind that supports the growth and mainte- nance of strong muscles, sound bones, healthy skin, and suffi cient blood to cleanse and nourish all parts of your body. Th is means you need food that provides not only the right amount of energy but also suffi cient nutrients, that is, enough water, carbohydrates, fats, protein, vitamins, and minerals. If the foods you eat provide too little or too much of any nutrient today, your health may suff er just a little today. If the foods you eat provide too little or too much of one or more nutrients every day for years, then in later life you may suff er severe disease eff ects.

A well-chosen array of foods supplies enough energy and enough of each nutri- ent to prevent malnutrition. Malnutrition includes defi ciencies, imbalances, and excesses of nutrients, alone or in combination, any of which can take a toll on health over time.

KE Y POINT The nutrients in food support growth, maintenance, and repair of the body. Defi ciencies, excesses, and imbalances of energy and nutrients bring on the diseases of malnutrition.

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When you choose foods with nutrition in mind, you can enhance your own well-being.

food medically, any substance that the body can take in and assimilate that will enable it to stay alive and to grow; the carrier of nourish- ment; socially, a more limited number of such substances defi ned as acceptable by each culture.

nutrition the study of the nutrients in foods and in the body; sometimes also the study of human behaviors related to food.

diet the foods (including beverages) a person usually eats and drinks.

nutrients components of food that are indispensable to the body’s functioning. They provide energy, serve as building material, help maintain or repair body parts, and support growth. The nutrients include water, carbohy- drate, fat, protein, vitamins, and minerals.

malnutrition any condition caused by excess or defi cient food energy or nutrient intake or by an imbalance of nutrients. Nutrient or energy defi ciencies are forms of undernutri- tion; nutrient or energy excesses are forms of overnutrition.

chronic diseases long-duration degen- erative diseases characterized by deterioration of the body organs. Examples include heart disease, cancer, and diabetes.

genome (GEE-nome) the full complement of genetic information in the chromosomes of a cell. In human beings, the genome consists of about 35,000 genes and supporting materi- als. The study of genomes is genomics. Also defi ned in Controversy 11.

genes units of a cell’s inheritance; sections of the larger genetic molecule DNA (deoxyribo- nucleic acid). Each gene directs the making of one or more of the body’s proteins.

DNA an abbreviation for deoxyribonucleic (dee-OX-ee-RYE-bow-nu-CLAY-ick) acid, the threadlike molecule that encodes genetic information in its structure; DNA strands coil up densely to form the chromosomes (Chapter 3 provides more details).

3A L i f e t i m e o f N o u r i s h m e n t

The Diet and Health Connection Your choice of diet profoundly aff ects your health, both today and in the future. Only two common lifestyle habits are more infl uential: smoking and other tobacco use, and excessive drinking of alcohol. Of the leading causes of death listed in Table 1-1, four are directly related to nutrition, and another—motor vehicle and other accidents—is related to drinking alcohol.

Many older people suff er from debilitating conditions that could have been largely prevented had they known and applied the nutrition principles known today. Th e chronic diseases—heart disease, diabetes, some kinds of cancer, dental disease, and adult bone loss—all have a connection to poor diet.1* Th ese diseases cannot be prevented by a good diet alone; they are to some extent determined by a person’s genetic constitution, activities, and lifestyle. Within the range set by your genetic inheritance, however, the likelihood of developing these diseases is strongly infl u- enced by your food choices.

KE Y POINT Nutrition profoundly aff ects health.

Genetics and Individuality Consider the role of genetics. Genetics and nutrition aff ect diff erent diseases to varying degrees (see Figure 1-1). Th e anemia caused by sickle-cell disease, for ex- ample, is purely hereditary and thus appears at the left of Figure 1-1 as a genetic condition largely unrelated to nutrition. Nothing a person eats aff ects the person’s chances of contracting this anemia, although nutrition therapy may help ease its course. At the other end of the spectrum, iron-defi ciency anemia most often results from undernutrition. Diseases and conditions of poor health appear all along this continuum, from almost entirely genetically based to purely nutritional in origin; the more nutrition-related a disease or health condition is, the more successfully sound nutrition can prevent it.

Furthermore, some diseases, such as heart disease and cancer, are not one dis- ease but many. Two people may both have heart disease, but not the same form; one person’s cancer may be nutrition-related but another’s may not be. Individual people diff er genetically from each other in thousands of subtle ways, so no simple statement can be made about the extent to which diet can help any one person avoid such diseases or slow their progress.

Th e recent identifi cation of the human genome establishes the entire sequence of the genes in human DNA. Th is work has, in essence, revealed the body’s instruc- tions for making all of the working parts of a human being. A new wealth of infor- mation has emerged to explain the workings of the body, and nutrition scientists are working quickly to apply this knowledge to benefi t human health.2 Later chapters expand on the emerging story of nutrition and the genes.

Adult bone loss (osteoporosis)

Cancer

Infectious diseases

Diabetes

Hypertension

Heart disease

Iron deficiency (anemia)

Vitamin deficiencies

Mineral deficiencies

Toxicities

Poor resistance to disease

Down syndrome

Hemophilia

Sickle-cell anemia More nutrition- related

Less nutrition- related (genetic)

Blue shading indicates that a cause of death is related to nutrition; the light yel- low indicates that it is related to alcohol.a

Percentage of Total Deaths

Heart disease1. 26.5%

Cancers2. 22.8%

Strokes3. 5.9%

Chronic lung 4. disease

5.3%

Accidents5. 4.7%

Alzheimer’s 6. disease

3.1%

Diabetes mellitus7. 2.9%

Pneumonia and 8. infl uenza

2.6%

Kidney disease9. 1.8%

Blood infections10. 1.4%

aHypertension (high blood pressure), a nutrition-related cause of death, ranks at number 13.

Source: National Center for Health Statistics.

Leading Causes

of Death, U.S.

table 1-1

Did You Know? Anemia is a blood condition in which red blood cells, the body’s oxygen carriers, are inadequate or impaired and so cannot meet the oxygen demands of the body. (More about the anemia of sickle-cell disease in Chap- ter 6; iron-defi ciency anemia is described in Chapter 8.)

Not all diseases are equally infl uenced by diet. Some are almost purely genetic, like the anemia of sickle-cell disease. Some may be inherited (or the tendency to develop them may be inherited in the genes) but may be infl uenced by diet, like some forms of diabetes. Some are purely dietary, like the vitamin and mineral defi ciency diseases.

Nutrition and Disease figure 1-1

*Reference notes are found in Appendix F.

4 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

KE Y POINT Choice of diet infl uences long-term health within the range set by genetic inheritance. Nutrition has little infl uence on some diseases but strongly aff ects others.

Other Lifestyle Choices Besides food choices, other lifestyle choices also aff ect people’s health. Tobacco use and alcohol and other substance abuse can destroy health. Physical activity, sleep, stress, and other environmental factors can also help prevent or reduce the severity of some diseases. Physical activity is so closely linked with nutrition in supporting health that most chapters of this book off er features called Th ink Fitness, such as the one above.

KE Y POINT Personal life choices, such as staying physically active or using tobacco or alcohol, also aff ect health for the better or worse.

Healthy People 2010: Nutrition Objectives for the Nation Th e U.S. Department of Health and Human Services sets 10-year health objec- tives to reduce disease risks for the nation in its publication Healthy People.3 Th e nutrition-related objectives for the year 2010, listed in Table 1-2, provide a quick scan of the nutrition-related objectives set for this decade. Th e inclusion of nutrition and food-safety objectives shows that public health offi cials consider these areas to be top national priorities.

By mid-decade, the U.S. population was making progress toward meeting many of the targets of Healthy People 2010. Positive strides have been made toward reduc- ing rates of certain foodborne infections and several cancers.4 Deaths from heart disease and stroke are also declining, but on the negative side, heart disease remains the leading cause of death among adults. In addition, the numbers of overweight people and those diagnosed with diabetes are soaring. To fully meet the current Healthy People 2010 goals, our nation must take steps to reverse current increasing trends toward overweight and diabetes.5

Did You Know? The human genome is 99.9% the same in all people; all of the normal variations such as dif- ferences in hair color, as well as variations that result in diseases such as sickle-cell anemia, lie in the 0.1% of the genome that varies.

Only about 2% of the human genome contains genes. Scientists are asking, “What does the rest do?”

think fitness Why Be Physically Active?

Why should people bother to be physically active? While a person’s daily food choices can powerfully affect health, the combination of nutrition and physical activity is more powerful still. People who are

physically active can expect to re- ceive at least some of the benefits listed in the margin. If even half of these benefits were yours for the asking, wouldn’t you step up to claim them? In truth, they are yours

to claim, at the price of including physical activity in your day. Chap- ter 10 explores the topics of fitness and physical activity.

START NOW

Ready to make a change? Consult the online behavior-change planner to explore a method for changing your current behaviors at www.cengage.com/sso.

Potential benefits of physical activity include:•

Reduced risk of cardiovascular diseases.•

Increased cardiovascular endurance.•

Increased muscle strength and endurance.•

Increased flexibility.•

Reduced risk of some types of cancer •

(especially colon and breast).

Improved mental outlook and lessened •

likelihood of depression.

Improved mental functioning.•

Feeling of vigor.•

Feeling of belonging—the companionship •

of sports.

Strong self-image and belief in one’s •

abilities.

Reduced body fat, increased lean tissue.•

A more youthful appearance, healthy skin, •

and improved muscle tone.

Greater bone density and lessened risk of •

adult bone loss in later life.

Increased independence in the elderly.•

Sound, beneficial sleep.•

Faster wound healing.•

Lessening or elimination of menstrual pain.•

Improved resistance to infection.•

http://www.cengage.com/sso

5T h e H u m a n B o d y a n d I t s F o o d

Th e next section shifts our focus to the nutrients at the core of nutrition science. As your course of study progresses, the individual nutrients may become like old friends, revealing more and more about themselves as you move through the chapters.

KE Y POINT The U.S. Department of Health and Human Services sets nutrition objectives for the nation each decade.

LO 1.2

The Human Body and Its Food As your body moves and works each day, it must use energy. Th e energy that fuels the body’s work comes indirectly from the sun by way of plants. Plants capture and store the sun’s energy in their tissues as they grow. When you eat plant-derived foods such as fruits, grains, or vegetables, you obtain and use the solar energy they have stored. Plant-eating animals obtain their energy in the same way, so when you eat animal tissues, you are eating compounds containing energy that came origi- nally from the sun.

Th e body requires six kinds of nutrients—families of molecules indispensable to its functioning—and foods deliver these. Table 1-3 lists the six classes of nutrients.

Increase • nutrition education among consumers and in educational settings at all levels.

Increase the proportion of children, adolescents, and adults who are at a • healthy weight.

Reduce • growth retardation among low-income children under age 5 years.

Increase the proportion of persons aged 2 years and older who consume at least two daily servings of • fruit.

Increase the proportion of persons aged 2 years and older who consume at least three daily servings of • vegetables, with at least one- third being dark green or orange vegetables.

Increase the proportion of persons aged 2 years and older who consume at least six daily servings of • grain products, with at least three being whole grains.

Increase the proportion of persons aged 2 years and older who consume less than 10% of calories from • saturated fat.

Increase the proportion of persons aged 2 years and older who consume no more than 30% of calories from • total fat.

Increase the proportion of persons aged 2 years and older who consume 2,400 milligrams or less of • sodium.

Increase the proportion of adults with • high blood pressure who are taking action to control their blood pressure.

Increase the proportion of persons aged 2 years and older who meet dietary recommendations for • calcium.

Reduce • iron defi ciency among young children, females of childbearing age, and pregnant females.

Reduce • anemia among low-income pregnant females in their third trimester.

Reduce • key vitamin and mineral defi ciencies in pregnant women.

Increase the proportion of children and adolescents aged 6 to 19 years whose intake of • meals and snacks at school contributes to good overall dietary quality.

Increase the proportion of worksites that offer • nutrition or weight management classes or counseling.

Increase the proportion of physician offi ce visits made by patients with a diagnosis of cardiovascular disease, diabetes, or hyper-• lipidemia that include counseling or education related to diet and nutrition.

Reduce deaths from anaphylaxis caused by • food allergies.

Increase the number of consumers and retail establishments who follow key • food-safety practices and reduce key foodborne illnesses.

Increase • food security among U.S. households and in so doing reduce hunger.

Source: Details about these and hundreds of other objectives are available from the U.S. Department of Health and Human Services, Healthy People 2010: Cornerstone to Prevention (Washington, D.C.: Government Printing Offi ce, 2000), online at www.health.gov/healthypeople or call (800) 367-4725.

Healthy People 2010 Nutrition-Related Objectives table 1-2

energy the capacity to do work. The energy in food is chemical energy; it can be converted to mechanical, electrical, thermal, or other forms of energy in the body. Food energy is measured in calories, defi ned on page 7.

http://www.health.gov/healthypeople

6 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

Four of these six are organic; that is, the nutrients contain the element carbon de- rived from living things.

Meet the Nutrients Th e human body and foods are made of the same materials, arranged in diff erent ways (see Figure 1-2). When considering quantities of foods and nutrients, scien- tists often measure them in grams, units of weight.

The Energy-Yielding Nutrients Foremost among the six classes of nutrients in foods is water, which is constantly lost from the body and must constantly be re- placed. Of the four organic nutrients, three are energy-yielding nutrients, mean- ing that the body can use the energy they contain. Th e carbohydrates and fats (fats are also called lipids) are especially important energy-yielding nutrients. As for pro-

The nutrients that contain carbon are organic.

Carbon Oxygen Hydrogen Nitrogen Minerals

Water ✓ ✓

Carbohydrate ✓ ✓ ✓

Fat ✓ ✓ ✓

Protein ✓ ✓ ✓ ✓ b

Vitamins ✓ ✓ ✓ ✓a b

Minerals ✓

aAll of the B vitamins contain nitrogen; amine means nitrogen. bProtein and some vitamins contain the mineral sulfur; vitamin B12 contains the mineral cobalt.

Elements in the Six Classes of Nutrients table 1-3

Vitamins Minerals Fat Protein Carbohydrate Water

Foods and the human body are made of the same materials.

Components of Food and the Human Body figure 1-2

Energy-yielding nutrients are also called • macronutrients because they are needed in relatively large amounts in the diet.

Vitamins and minerals are known as • micro-

nutrients because they are needed in only tiny amounts.

organic carbon containing. Four of the six classes of nutrients are organic: carbohydrate, fat, protein, and vitamins. Strictly speaking, organic compounds include only those made by living things and do not include compounds such as carbon dioxide, diamonds, and a few carbon salts.

grams units of weight. A gram (g) is the weight of a cubic centimeter (cc) or milliliter (ml) of water under defi ned conditions of tem- perature and pressure. About 28 grams equal an ounce.

energy-yielding nutrients the nutri- ents the body can use for energy—carbohy- drate, fat, and protein. These also may supply building blocks for body structures.

7T h e H u m a n B o d y a n d I t s F o o d

tein, it does double duty: it can yield energy, but it also provides materials that form structures and working parts of body tissues. (Alcohol yields energy, too, but it is a toxin, not a nutrient—see the note to Table 1-4.)

Vitamins and Minerals Th e fi fth and sixth classes of nutrients are the vitamins and the minerals. Th ese provide no energy to the body. A few minerals serve as parts of body structures (calcium and phosphorus, for example, are major constitu- ents of bone), but all vitamins and minerals act as regulators. As regulators, the vitamins and minerals assist in all body processes: digesting food; moving muscles; disposing of wastes; growing new tissues; healing wounds; obtaining energy from carbohydrate, fat, and protein; and participating in every other process necessary to maintain life. Later chapters are devoted to these six classes of nutrients.

The Concept of Essential Nutrients When you eat food, then, you are pro- viding your body with energy and nutrients. Furthermore, some of the nutrients are essential nutrients, meaning that if you do not ingest them, you will develop defi ciencies; the body cannot make these nutrients for itself. Essential nutrients are found in all six classes of nutrients. Water is an essential nutrient; so is a form of carbohydrate; so are some lipids, some parts of protein, all of the vitamins, and the minerals important in human nutrition.

Calorie Values Food scientists measure food energy in kilocalories, units of heat. Th is book uses the common word calories to mean the same thing. It behooves the person who wishes to control food energy intake and body fatness to learn the calo- rie values of the energy nutrients, listed in Table 1-4. Th e most energy-rich of the nutrients is fat, which contains 9 calories in each gram. Carbohydrate and protein each contain only 4 calories in a gram (see Table 1-4).

Scientists have worked out ways to measure the energy and nutrient contents of foods. Th ey have also calculated the amounts of energy and nutrients various types of people need—by gender, age, life stage, and activity. Th us, after studying human nu- trient requirements (in Chapter 2), you will be able to state with some accuracy just what your own body needs—this much water, that much carbohydrate, so much vi- tamin C, and so forth. So why not simply take pills or dietary supplements in place of food? Because, as it turns out, food off ers more than just the six basic nutrients.6

KE Y POINT Food supplies energy and nutrients. Foremost among the nutrients is water. The energy-yielding nutrients are carbohydrates, fats (lipids), and protein. The regulator nutrients are vitamins and minerals. Food energy is measured in calories; food and nutrient quantities are often measured in grams.

Can I Live on Just Supplements? Nutrition science can state what nutrients human beings need to survive—at least for a time. Scientists are becoming skilled at making elemental diets—liquid diets with a precise chemical composition that are lifesaving for people in the hospital who cannot eat ordinary food. Th ese formulas, administered to severely ill people for days or weeks, support not only continued life but also recovery from nutrient defi ciencies, infections, and wounds.

Lately, marketers have taken these liquid supplement formulas out of the medi- cal setting and have advertised them heavily to healthy people of all ages as “meal replacers” or “insurance” against malnutrition. Th e truth is that a diet of real food is superior to supplements.7 Nutrients and other food components interact with each other in the body and operate best in harmony with one another.8 Formula diets are essential to help sick people to survive, but they do not enable people to thrive over long periods. Even in hospitals, elemental diet formulas do not support optimal growth and health, and they often lead to medical complications.9 Although serious problems are rare and can be detected and corrected, they show that the composi- tion of these diets is not yet perfect for all people in all settings. Healthy people

The energy a person consumes in a day’s meals comes from these three energy- yielding nutrients; alcohol, if consumed, also contributes energy.

Energy Nutrient Energy

Carbohydrate 4 cal/g

Fat (lipid) 9 cal/g

Protein 4 cal/g

Note: Alcohol contributes 7 calories/gram that the human body can use for energy. Alcohol is not classed as a nutrient, however, because it interferes with growth, maintenance, and repair of body tissues.

Calorie Values of

Energy Nutrients

table 1-4

CONCEPT LINK 1-1 Throughout this text, Concept Links like this one point the reader to previous concepts that underlie current discussions.

Weight, measure, and other conversion • factors needed for the study of nutrition are found in Appendix C.

essential nutrients the nutrients the body cannot make for itself (or cannot make fast enough) from other raw materials; nutrients that must be obtained from food to prevent defi ciencies.

calories units of energy. In nutrition sci- ence, the unit used to measure the energy in foods is a kilocalorie (kcalorie or Calorie): it is the amount of heat energy necessary to raise the temperature of a kilogram (a liter) of water 1 degree Celsius. This book follows the common practice of using the lowercase term calorie (abbreviated cal ) to mean the same thing.

dietary supplements pills, liquids, or powders that contain purifi ed nutrients or other ingredients (see Controversy in Chapter 7).

elemental diets diets composed of puri- fi ed ingredients of known chemical composi- tion; intended to supply all essential nutrients to people who cannot eat foods.

8 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

who eat a healthful diet do not need such formulas and, with a nutritious diet, most need no dietary supplements at all. Even if a person’s basic nutrient needs are per- fectly understood and met, concoctions of nutrients still lack something that foods provide. Hospitalized clients who are fed nutrient mixtures through a vein often improve dramatically when they can fi nally eat food. Something in real food is important to health—but what is it? What does food off er that cannot be provided through a needle or a tube? Science has some partial explanations, some physical and some psychological.

In the digestive tract, the stomach and intestine are dynamic, living organs, changing constantly in response to the foods they receive—even to just the sight, aroma, and taste of food. When a person is fed through a vein, the digestive organs, like unused muscles, weaken and grow smaller. Lack of digestive tract stimulation may even weaken the body’s defenses against certain infections, such as infections of the respiratory tract. Medical wisdom now dictates that a person should be fed through a vein for as short a time as possible and that real food taken by mouth should be reintroduced as early as possible. Th e digestive organs also release hor- mones in response to food, and these send messages to the brain that bring the eater a feeling of satisfaction: “Th ere, that was good. Now I’m full.” Eating off ers both physical and emotional comfort.

Food does still more than maintain the intestine and convey messages of com- fort to the brain. Foods are chemically complex. In addition to their nutrients, foods contain phytochemicals, compounds that confer color, taste, and other characteris- tics to foods. Some may be bioactive food components that interact with metabolic processes in the body and may aff ect disease risks. Even an ordinary baked potato contains hundreds of diff erent compounds. In view of all this, it is not surprising that food gives us more than just nutrients. If it were otherwise, that would be surprising.

KE Y POINT In addition to nutrients, food conveys emotional satisfaction and hormonal stimuli that contribute to health. Foods also contain phytochemicals that give them their tastes, aromas, colors, and other characteristics. Some phytochemicals may play roles in reducing disease risks.

LO 1.3, 1.4

The Challenge of Choosing Foods Well-planned meals convey pleasure and are nutritious, too, fi tting your tastes, per- sonality, family and cultural traditions, lifestyle, and budget. Given the astounding numbers and varieties available, consumers can lose track of what individual foods contain and how to put them together into health-promoting diets. A few guide- lines can help.

The Abundance of Foods to Choose From A list of the foods available 100 years ago would be relatively short. It would consist of whole foods—foods that have been around for a long time, such as vegetables, fruits, meats, milk, and grains (Table 1-5). Th ese foods have been called basic, un- processed, natural, or farm foods. By whatever name, choosing a suffi cient variety of these foods each day is an easy way to obtain a nutritious diet. On a given day, however, almost three-quarters of our population consume too few vegetables, and two-thirds of us fail to consume enough fruit.10 Also, although people generally consume a few servings of vegetables, the vegetable they most often choose is pota- toes, usually prepared as French fries. Such dietary patterns make development of chronic diseases more likely.

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phytochemicals compounds in plant- derived foods (phyto means “plant”).

bioactive having biological activity in the body. See also the Controversy in Chapter 2.

9T h e C h a l l e n g e o f C h o o s i n g F o o d s

Th e number of foods supplied by the food industry today is astounding. Th ou- sands of foods now line the market shelves—many are processed mixtures of the basic ones, and some are even constructed mostly from artifi cial ingredients. Ironi- cally, this abundance often makes it more diffi cult, rather than easier, to plan a nutritious diet.

Th e food-related terms defi ned in Table 1-5 reveal that all types of food—includ- ing fast foods and processed foods—off er various constituents to the eater. You may also hear about functional foods, a marketing term coined to identify those foods containing substances, natural or added, that might lend protection against chronic diseases. Th e trouble is, scientists trying to single out the most health- promoting foods fi nd that almost every naturally occurring food—even chocolate—

The purpose of this little glossary is to show that good-sounding food names don’t necessarily signify that foods are nutritious. Read the comment at the end of each defi nition.

whole foods• milk and milk products; meats and similar foods such as fi sh and poultry; vegetables, including dried beans and peas; fruits; and grains. These foods are generally considered to form the basis of a nutritious diet. Also called basic foods. enriched foods• and fortifi ed foods foods to which nutrients have been added. If the starting material is a whole, basic food such as milk or whole grain, the result may be highly nutritious. If the starting material is a concentrated form of sugar or fat, the result may be less nutritious. fast foods• restaurant foods that are available within minutes after customers order them—traditionally, hamburgers, French fries, and milkshakes; more recently, salads and other vegeta- ble dishes as well. These foods may or may not meet people’s nutrient needs, depending on the selections made and on the energy allowances and nutrient needs of the eaters. functional foods• whole or modifi ed foods that contain bioac- tive food components believed to provide health benefi ts, such as reduced disease risks, beyond the benefi ts that their nutrients confer. However, all nutritious foods can support health in some ways; Controversy 2 provides details.

medical foods• foods specially manufactured for use by people with medical disorders and prescribed by a physician. natural foods• a term that has no legal defi nition but is often used to imply wholesomeness. nutraceutical• a term that has no legal or scientifi c meaning but is sometimes used to refer to foods, nutrients, or dietary supple- ments believed to have medicinal effects. Often used to sell un- necessary or unproven supplements. organic foods• understood to mean foods grown without synthetic pesticides or fertilizers. In chemistry, however, all foods are made mostly of organic (carbon-containing) compounds. (See Chap- ter 12 for details.) processed foods• foods subjected to any process, such as mill- ing, alteration of texture, addition of additives, cooking, or others. Depending on the starting material and the process, a processed food may or may not be nutritious. staple foods• foods used frequently or daily, for example, rice (in East and Southeast Asia) or potatoes (in Ireland). If well chosen, these foods are nutritious.

Glossary of Food Types table 1-5

Did You Know? In 1900, Americans chose from among 500 or so different foods; today, they choose from more than 50,000.

All foods once looked like this . . .

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10 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

† A person can also take supplements of iron, but as later discussions demonstrate, eating iron-rich foods is preferable.

adequacy the dietary characteristic of pro- viding all of the essential nutrients, fi ber, and energy in amounts suffi cient to maintain health and body weight.

balance the dietary characteristic of provid- ing foods of a number of types in proportion to each other, such that foods rich in some nutrients do not crowd out the diet foods that are rich in other nutrients. Also called proportionality.

calorie control control of energy intake; a feature of a sound diet plan.

moderation the dietary characteristic of providing constituents within set limits, not to excess.

variety the dietary characteristic of providing a wide selection of foods—the opposite of monotony.

legumes (leg-GOOMS, LEG-yooms) beans, peas, and lentils, valued as inexpensive sources of protein, vitamins, minerals, and fi ber that contribute little fat to the diet. Also defi ned in Chapter 6.

is functional in some way with regard to human health.11 Controversy 2 in Chap- ter 2 provides more information about functional foods.

Th e extent to which foods support good health depends on the calories, nutrients, and phytochemicals they contain. In short, to select well among foods, you need to know more than their names; you need to know the foods’ inner qualities. Even more important, you need to know how to combine foods into nutritious diets. Foods are not nutritious by themselves; each is of value only insofar as it contributes to a nutritious diet. A key to wise diet planning is to make sure that the foods you eat daily, your staple foods, are especially nutritious.

KE Y POINT Foods come in a bewildering variety in the market- place, but the foods that form the basis of a nutritious diet are whole foods, such as ordinary milk and milk products; meats, fi sh, and poultry; vegetables and dried peas and beans; fruits; and grains.

How, Exactly, Can I Recognize a Nutritious Diet? A nutritious diet has fi ve characteristics. First is adequacy: the foods provide enough of each essential nutrient, fi ber, and energy. Second is balance: the choices do not overemphasize one nutrient or food type at the expense of another. Th ird is calorie control: the foods provide the amount of energy you need to maintain appropriate weight—not more, not less. Fourth is moderation: the foods do not provide excess fat, salt, sugar, or other unwanted constituents. Fifth is variety: the foods chosen diff er from one day to the next. In addition, to maintain a steady sup- ply of nutrients, meals should occur with regular timing throughout the day.

Adequacy Any nutrient could be used to demonstrate the importance of dietary adequacy. Iron provides a familiar example. It is an essential nutrient: you lose some every day, so you have to keep replacing it; and you can get it into your body only by eating foods that contain it.† If you eat too few of the iron-containing foods, you can develop iron-defi ciency anemia: with anemia you may feel weak, tired, cold, sad, and unenthusiastic; you may have frequent headaches; and you can do very little muscular work without disabling fatigue. Some foods are rich in iron; others are notoriously poor. If you add iron-rich foods to your diet, you soon feel more en- ergetic. Meat, fi sh, poultry, and legumes are in the iron-rich category, and an easy way to obtain the needed iron is to include these foods in your diet regularly.

Balance To appreciate the importance of dietary balance, consider a second es- sential nutrient, calcium. A diet lacking calcium causes poor bone development dur- ing the growing years and increases a person’s susceptibility to disabling bone loss in adult life. Most foods that are rich in iron are poor in calcium. Calcium’s richest food sources are milk and milk products, which happen to be extraordinarily poor iron sources. Clearly, to obtain enough of both iron and calcium, people have to balance their food choices among the types of foods that provide specifi c nutrients. Balancing the whole diet to provide enough but not too much of every one of the 40-odd nutrients the body needs for health requires considerable juggling, however. As you will see in Chapter 2, food group plans that cluster rich sources of nutrients into food groups can help you to achieve dietary adequacy and balance because they recommend specifi c amounts of foods from each group. Balance among the food groups then becomes the goal.

Calorie Control Energy intakes should not exceed energy needs. Nicknamed cal- orie control, this diet characteristic ensures that energy intakes from food balance energy expenditures required for body functions and physical activity. Eating such a diet helps to control body fat content and weight. Th e many strategies that promote this goal appear in Chapter 9.

11T h e C h a l l e n g e o f C h o o s i n g F o o d s

Moderation Intakes of certain food constituents such as fat, cholesterol, sugar, and salt should be limited for health’s sake. A major guideline for healthy people is to keep fat intake below 35 percent of total calories.12 Some people take this to mean that they must never indulge in a delicious beefsteak or hot-fudge sundae, but they are misinformed: moderation, not total abstinence, is the key. A steady diet of steak and ice cream might be harmful, but once a week as part of an other wise moderate diet plan, these foods may have little impact; as once-a-month treats, these foods would have practically no eff ect at all. Moderation also means that limits are neces- sary, even for desirable food constituents. For example, a certain amount of fi ber in foods contributes to the health of the digestive system, but too much fi ber leads to nutrient losses.

Variety As for variety, nutrition scientists agree that people should not eat the same foods, even highly nutritious ones, day after day. One reason is that a varied diet is more likely to be adequate in nutrients.13 In addition, some less-well-known nutrients and phytochemicals could be important to health and some foods may be better sources of these than others. Another reason is that a monotonous diet may deliver large amounts of toxins or contaminants. Such undesirable compounds in one food are diluted by all the other foods eaten with it and are diluted still further if the food is not eaten again for several days. Last, variety adds interest—trying new foods can be a source of pleasure.

A caution is in order. Any one of these dietary principles alone cannot ensure a healthful diet. For example, the most likely outcome of relying solely on variety could easily be a low-nutrient, high-calorie diet consisting of a variety of snack foods and nutrient-poor sweets.14 If you establish the habit of using all of the prin- ciples just described, you will fi nd that choosing a healthful diet becomes as auto- matic as brushing your teeth or falling asleep. Establishing the A, B, C, M, V habit may take some eff ort, but the payoff in terms of improved health is overwhelming. Table 1-6 takes an honest look at some common excuses for not eating well.

KE Y POINT A well-planned diet is adequate in nutrients, is balanced with regard to food types, off ers food energy that matches energy expended in activity, is moderate in unwanted constituents, and off ers a variety of nutritious foods.

Why People Choose Foods Eating is an intentional act. Each day, people choose from the available foods, pre- pare the foods, decide where to eat, which customs to follow, and with whom to dine. Many factors infl uence food-related choices.

A nutritious diet follows the A, B, C, M, V • principles:

Adequacy.•

Balance.•

Calorie control.•

Moderation.•

Variety.•

If you fi nd yourself saying, “I know I should eat well, but I’m too busy” (or too fond of fast food, or have too little money, or a dozen other excuses), take note:

No time to cook.• Everyone is busy. Convenience packages of frozen vegetables, jars of pasta sauce, and prepared meats and salads make nutritious meals in little time. Not a high priority.• Priorities change drastically and instantly when illness strikes—better to spend a little effort now nourishing your body’s defenses than to spend enormous resources later fi ghting illnesses.

Crave fast food and sweets.• Occasional fast-food meals and sweets in moderation are acceptable in a nutritious diet. Too little money.• Eating right costs no more than eating poorly. Chips, colas, fast food, and premium ice cream cost as much or more per serving as nutritious foods.a

Take vitamins instead.• Vitamin pills cannot make up for consistently poor food choices.

aFor a discussion of this topic, see L. M. Lipsky, Are energy-dense foods really cheaper? Reexamining the relation between food price and energy density, American Journal of Clinical Nutrition 90 (2009): 1397–1401.

What’s Today’s Excuse for Not Eating Well? table 1-6

Calorie control

Moderation

Variety

Adequacy

Balance

Calorie control

Moderation

Variety

Adequacy

Balance

Adequacy

Balance

Calorie control

Moderation

Variety

All of these factors help to build a nutritious diet.

12 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

Cultural and Social Meanings Attached to Food Like wearing traditional clothing or speaking a native language, enjoying traditional cuisines and food- ways can be a celebration of your own or a friend’s heritage. Sharing ethnic food can be symbolic: people off ering foods are expressing a willingness to share cherished values with others. People accepting those foods are symbolically ac- cepting not only the person doing the off ering but the person’s culture. Devel- oping cultural competence is particularly important for professionals who help others to achieve a nutritious diet.15

Cultural traditions regarding food are not infl exible; they keep evolving as people move about, learn about new foods, and teach each other. Today some people are ceasing to be omnivores and are becoming vegetarians. Vegetarians often choose this lifestyle because they honor the lives of animals or because they have discovered the health and other advantages associated with diets rich

in beans, whole grains, fruits, nuts, and vegetables.16 Th e Chapter 6 Controversy explores the pros and the cons of both the vegetarian’s and the meat-eater’s diets.

Factors That Drive Food Choices Consumers today value convenience so highly that they are willing to spend over half of their food budget on meals that require little or no preparation. Th ey frequently eat out, bring home ready-to-eat meals, cook meals ahead in commercial kitchens, or have food delivered.17 In their own kitchens, they want to prepare a meal in 15 to 20 minutes, using only four to six in- gredients. Such convenience doesn’t have to mean that nutrition is out the window. Th is chapter’s Food Feature addresses the time, money, and nutrition trade-off s that many busy people face today.

Convenience is only one consideration. Physical, psychological, social, and philosoph- ical factors all infl uence how you choose the foods you generally eat. Th ese include:

Advertising.• Th e media have persuaded you to consume these foods.18

Availability.• Th ey are present in the environment and accessible to you.19

Cost.• Th ey are within your fi nancial means.

Emotional comfort.• Th ey can make you feel better for a while.

Habit.• Th ey are familiar; you always eat them.

Personal preference and genetic inheritance.• You like the way these foods taste, with

some preferences possibly determined by the genes.20

Positive or negative associations.• Positive: Th ey are eaten by people you admire, or

they indicate status, or they remind you of fun. Negative: Th ey were forced on

you or you became ill while eating them.

Region of the country.• Th ey are foods favored in your area.

Social pressure.• Th ey are off ered; you feel you can’t refuse them.

Values or beliefs.• Th ey fi t your religious tradition, square with your political views,

or honor the environmental ethic.

Weight.• You think they will help to control body weight.

Nutrition and health benefi ts.• You think they are good for you.

Just the last two of these reasons for choosing foods assign a high priority to nutri- tional health. Similarly, the choice of where, as well as what, to eat is often based more on social considerations than on nutrition judgments. College students often choose to eat at fast-food and other restaurants to socialize, to get out, to save time, or to date; they are not always conscious of the need to obtain nutritious food.

Nutrition understanding depends upon a fi rm base of scientifi c knowledge. Th e next section describes the nature of such knowledge and addresses one of the “how” ques- tions posed earlier in this chapter: How do we know what we know about nutrition?

KE Y POINT Cultural traditions and social values revolve around food and often fi nd expression through foodways. Many factors other than nutrition drive food choices.

Figure 2-10 in Chapter 2 depicts some eth-• nic foods that have become an integral part of the “American diet.”

Sharing ethnic food is a way of sharing culture.

cuisines styles of cooking.

foodways the sum of a culture’s habits, customs, beliefs, and preferences concerning food.

ethnic foods foods associated with par- ticular cultural subgroups within a population.

cultural competence having an aware- ness and acceptance of one’s own and other cultures and the ability to interact effectively with people of those cultures.

omnivores people who eat foods of both plant and animal origin, including animal fl esh.

vegetarians people who exclude from their diets animal fl esh and possibly other animal products such as milk, cheese, and eggs.

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The Science of Nutrition Nutrition is a science—a fi eld of knowledge composed of organized facts. Unlike sciences such as astronomy and physics, nutrition is a relatively young science. Most nutrition research has been conducted since 1900. Th e fi rst vitamin was identifi ed in 1897, and the fi rst protein structure was not fully described until the mid-1940s. Because nutrition science is an active, changing, growing body of knowledge, scien- tifi c fi ndings often seem to contradict one another or are subject to confl icting in- terpretations. Bewildered consumers complain in frustration, “Th ose scientists don’t know anything. If they don’t know what’s true, how am I supposed to know?”

Yet, many facts in nutrition are known with great certainty. To understand why apparent contradictions sometimes arise in nutrition science, we need to look fi rst at what scientists do.

The Scientifi c Approach In truth, though, it is a scientist’s business not to know. Scientists obtain facts by systematically asking honest objective questions—that’s their job.21 Following the scientifi c method (outlined in Figure 1-3), they attempt to answer scientifi c questions. Th ey design and conduct various exper- iments to test for possible answers (see Figure 1-4 and Table 1-7). When they have ruled out some possibilities and found evidence for others, they submit their fi ndings, not to the news media, but to boards of reviewers composed of other scientists who try to pick the fi ndings apart. Finally, the work is published in scientifi c journals where still more scientists can read it. Th en the news report- ers read it and write about it and you can read it, too. Table 1-8 explains what you can expect to fi nd in a journal article.

KE Y POINT Scientists ask questions and then design research experiments to test possible answers.

Scientifi c Challenge An important truth in science is that one experi- ment does not “prove” or “disprove” anything. Even after publication, other scientists try to du- plicate the work of the fi rst researchers to support or refute the original fi nding.

Only when a fi nding has stood up to rigorous, repeated testing in several kinds of experiments performed by several diff erent researchers is it fi nally considered confi rmed. Even then, strictly speaking, science consists not of facts that are set in stone, but of theories that can always be chal- lenged and revised. Some fi ndings, though, like the theory that the earth revolves about the sun, are so well supported by observations and experi- mental fi ndings that they are generally accepted as facts. What we “know” in nutrition is confi rmed in the same way—through years of replicating

Formulate a hypothesis—a tentative solution to the problem or answer to the question—and make a prediction

that can be tested.

HYPOTHESIS & PREDICTION

Identify a problem to be solved or ask a specific question to be answered.

OBSERVATION & QUESTION

Design a study and conduct the research to collect relevant data.

EXPERIMENT

Summarize, analyze, and interpret the data; draw conclusions.

RESULTS & INTERPRETATIONS

HYPOTHESIS NOT SUPPORTEDHYPOTHESIS SUPPORTED

Develop a theory that integrates conclusions with those from

numerous other studies.

THEORY NEW OBSERVATIONS & QUESTIONS

Research scientists follow the scientifi c method. Note that most research projects result in new questions, not fi nal answers. Thus, research contin- ues in a somewhat cyclical manner.

Animated! The Scientific Method

figure 1-3

14 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

study fi ndings. Th is slow path of repeated studies stands in sharp contrast to the media’s desire for today’s latest news.

To repeat: the only source of valid nutrition information is slow, painstaking, au- thentic scientifi c research. We believe a nutrition fact to be true because it has been supported, time and again, in experiments designed to rule out all other possibili- ties. For example, we know that eyesight depends partly on vitamin A because

In case studies, individuals with blindness report having consumed a steady diet •

devoid of vitamin A, and

In epidemiological studies, populations with diets lacking in vitamin A are •

observed to suff er high rates of blindness, and

In intervention studies (• controlled clinical trials), vitamin A–rich foods

provided to groups of vitamin A–defi cient people reduce their blindness rates

dramatically, and

The type of study chosen for research depends upon what sort of informa- tion the researchers require. Studies of individuals (case studies) yield observations that may lead to pos- sible avenues of research. A study of a man who ate gumdrops and became a famous dancer might suggest that an experiment be done to see if gumdrops contain dance-enhancing power. Studies of whole populations (epide- miological studies) provide another sort of information. Such a study can reveal a correlation. For example, an epide- miological study might fi nd no worldwide correlation of gumdrop eating with fancy footwork but, unexpectedly, might reveal a correlation with tooth decay. Studies in which researchers actively intervene to alter people’s eating habits (intervention studies) go a step further. In such a study, one set of subjects (the experimental group) receive a treatment, and another set (the con- trol group) go untreated or receive a placebo or sham treatment. If the study is a blind experiment, the subjects do not know who among the members receives the treatment and who receives the sham. If the two groups experience different effects, then the treatment’s ef- fect can be pinpointed. For example, an intervention study might show that with- holding gumdrops, together with other candies and confections, reduced the incidence of tooth decay in an experi- mental population compared to that in a control population. Finally, laboratory studies can pin- point the mechanisms by which nutrition acts. What is it about gumdrops that contributes to tooth decay: their size,

shape, temperature, color, ingredients? Feeding various forms of gumdrops to rats might yield the information that sugar, in a gummy carrier, promotes tooth decay. In the laboratory, using animals or plants or cells, scientists can inoculate with diseases, induce defi cien-

cies, and experiment with variations on treatments to obtain in-depth knowledge of the process under study. Intervention studies and laboratory experiments are among the most powerful tools in nutri- tion research because they show the effects of treatments.

Examples of Research Design figure 1-4

North Atlantic Ocean

Mediterranean Sea

Black Sea

France

Spain

Morocco Algeria

Libya

Tunisia

Italy

Greece Turkey

CroatiaSlovenia

Albania

Egypt

Syria

Jordan Israel

Lebanon

Montenegro

Bosnia

Case Study Epidemiological Study

Intervention Study Laboratory Study

“This person eats too little of nutrient X and has illness Y.”

“This country’s food supply contains more nutri- ent X, and these people suffer less illness Y.”

“Let’s add foods containing nutrient X to some people’s food supply and compare their rates of illness Y with the rates of others who don’t receive the nutrient.”

“Now let’s prove that a nutrient X defi ciency causes illness Y by inducing a defi ciency in these rats.”

controlled clinical trial a research study design that often reveals the effects of a treatment in human beings. Health outcomes are observed in a group of people who receive the treatment and are then compared with out- comes in a control group of similar people who received a placebo (an inert or sham treat- ment). Ideally, neither subjects nor researchers know who receives the treatment and who gets the placebo (a double-blind study).

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15T h e S c i e n c e o f N u t r i t i o n

In laboratory studies, animals deprived of vitamin A and only that vitamin begin •

to go blind; when it is restored soon enough in the diet, their eyesight returns, and

Further laboratory studies elucidated the molecular mechanisms for vitamin A •

activity in eye tissues, and

Replication of these studies provides the same results.•

Now we can say with certainty, “eyesight depends upon suffi cient vitamin A.”

KE Y POINT Nutrition knowledge builds slowly through years of research. Single studies must be replicated before their fi ndings can be considered valid.

Can I Trust the Media to Deliver Nutrition News? Th e news media are hungry for new fi ndings, and reporters often latch onto ideas from the scientifi c laboratories before they have been fully tested. Also, a reporter who lacks a strong understanding of science may misunderstand complex scientifi c principles. To tell the truth, sometimes scientists get excited about their fi ndings,

blind experiment• an experiment in which the subjects do not know whether they are members of the experimental group or the control group. In a double-blind experiment, neither the subjects nor the researchers know to which group the members belong until the end of the experiment.

case studies• studies of individuals. In clinical settings, researchers can observe treat- ments and their apparent effects. To prove that a treatment has produced an effect requires simultaneous observation of an untreated similar subject (a case control).

control group • a group of individuals who are similar in all possible respects to the group being treated in an experiment but who receive a sham treatment instead of the real one. Also called control subjects. See also experimental group and intervention studies.

correlation• the simultaneous change of two factors, such as the increase of weight with increasing height (a direct or positive correlation) or the decrease of cancer incidence with increasing fi ber intake (an inverse or negative correlation). A correlation between two factors suggests that one may cause the other but does not rule out the possibility that both may be caused by chance or by a third factor.

epidemiological studies• studies of populations; often used in nutrition to search for correlations between dietary habits and disease incidence; a fi rst step in seeking nutrition-related causes of diseases.

experimental group • the people or animals participating in an experiment who receive the treatment under investigation. Also called experimental subjects. See also control group and intervention studies.

intervention studies• studies of populations in which observation is accompanied by experimental manipulation of some population members—for example, a study in which half of the subjects (the experimental subjects) follow diet advice to reduce fat intakes while the other half (the control subjects) do not, and both groups’ heart health is monitored.

laboratory studies • studies that are performed under tightly controlled conditions and are designed to pinpoint causes and effects. Such studies often use animals as subjects.

placebo• a sham treatment often used in scientifi c studies; an inert harmless medica- tion. The placebo effect is the healing effect that the act of treatment, rather than the treatment itself, often has.

Research Design Terms table 1-7

Here’s what you can expect to fi nd inside a research article:

Abstract.• The abstract provides a brief overview of the article. Introduction.• The introduction clearly states the purpose of the current study. Review of literature.• A review of the literature reveals all that science has uncovered on the subject to date. Methodology.• The methodology section defi nes key terms and describes the procedures used in the study. Results.• The results report the fi ndings and may include summary tables and fi gures. Conclusions.• The conclusions drawn are those supported by the data and refl ect the original purpose as stated in the introduction. Usually, they answer a few questions and raise several more. References.• The references list relevant studies (including key studies several years old as well as current ones).

The Anatomy of a

Research Article

table 1-8

16 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

too, and leak them to the press before they have been through a rigorous review by the scientists’ peers. As a result, the public is often exposed to late-breaking nutri- tion news stories before the fi ndings are fully confi rmed. Th en, when the hypothesis being tested fails to hold up to a later challenge, consumers feel betrayed by what is simply the normal course of science at work.

It also follows that people who take action based on single studies are almost always acting impulsively, not scientifi cally. Th e real scientists are trend watchers. Th ey eval- uate the methods used in each study, assess each study in light of the evidence gleaned from other studies, and modify little by little their picture of what is true. As evidence accumulates, the scientists become more and more confi dent about their ability to make recommendations that apply to people’s health and lives. Th e Consumer Corner in this chapter off ers some tips for evaluating news stories about nutrition.

Sometimes media sensationalism overrates the importance of even true, repli- cated fi ndings. For example, a few years ago the media eagerly reported that oat bran lowers blood cholesterol, a lipid indicative of heart disease risk. Although the reports were true, oat bran is only one of several hundred factors that aff ect blood cholesterol. News reports on oat bran often failed to mention that cutting intakes of certain fats is still the major step to take to lower blood cholesterol.

Also, new fi ndings need refi nements. Oat bran and oatmeal truly are cholesterol reducers, but how much must a person eat to produce the desired eff ects? Do little oat bran pills or powders meet the need? Do oat bran cookies? If so, how many cookies? For oatmeal, it takes a bowl-and-a-half daily to aff ect blood lipids. A few cookies cannot provide nearly so much and certainly cannot undo all the damage from a high-fat meal.

Today, oat bran’s cholesterol-lowering eff ect is established, and labels on food packages can proclaim that a diet high in oats may reduce the risk of heart disease. Th e whole process of discovery, challenge, and vindication took almost 10 years of research. Some other lines of research have taken many years longer. In science, a single fi nding almost never makes a crucial diff erence to our knowledge as a whole, but like each individual frame in a movie, it contributes a little to the big picture. Many such frames are needed to tell the whole story.

KE Y POINT News media often sensationalize single study fi ndings, and are not always trustworthy sources of nutrition information.

National Nutrition Research As you study nutrition, you are likely to hear of fi ndings based on two ongoing national scientifi c research projects. Th e fi rst, the National Health and Nutrition

Lose Weight While You Sleep!

See two students talking about how they learned the truth about nutrition claims made in advertising.

To hear their stories, log on to www.cengage.com/sso.

my turn

Gabriel

Did You Know? Some newspapers, magazines, talk shows, Internet websites, and other media strive for accuracy in reporting, but others specialize in sensationalism that borders on quackery—see this chapter’s Controversy for details.

The links between lipids and heart disease • are discussed in Chapters 5 and 11.

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17T h e S c i e n c e o f N u t r i t i o n

Examination Surveys (NHANES), is a nationwide project that gathers information from about 50,000 people using diet histories, physical examinations and measure- ments, and laboratory tests. Boiled down to its essence, NHANES involves

asking people what they have eaten;•

recording measures of their health status.•

Th e second project is the Continuing Survey of Food Intakes by Individuals (CSFII), which involves

recording what people have actually eaten for two days;•

comparing the foods they have chosen with recommended food selections.•

Nutrition monitoring makes it possible for research scientists to assess the nutrient status, health indicators, and dietary intakes of the U.S. population. Th e agencies involved with these eff orts are listed in the margin.

KE Y POINT Ongoing national nutrition research provides data on food consumption and nutrient status of the U.S. population.

Agencies active in nutrition policy, research, • and monitoring:

Department of Health and Human Services •

(DHHS).

United States Department of Agriculture •

(USDA).

Centers for Disease Control and Prevention •

(CDC).

Ongoing national nutrition research projects:•

National Health and Nutrition Examination •

Surveys (NHANES).

Continuing Survey of Food Intakes by •

Individuals (CSFII).

consumer corner

valid; the reader has no way of know- ing because the study lacks scrutiny by other experts.

The news report should describe the • researchers’ methods; in truth, few provide these details. For example, it matters whether the study par- ticipants numbered 8 or 8,000, and whether researchers personally observed participants’ behaviors or relied on self-reports given over the telephone.

The report should defi ne the study • subjects—single cells, animals, or human beings. If they were human beings, the more you have in com- mon with them (age and gender, for example), the more applicable the fi ndings may be for you.

Valid reports also present new fi ndings • in the context of previous research. Some reporters regularly follow devel- opments in a research area and thus acquire the background knowledge needed to write meaningfully.

Review articles provide a broad per-• spective on a single topic; they appear in journals such as Nutrition Reviews. Review articles describe fi ndings of many studies on the same topic.

A newspaper reader, who had sworn off butter years ago for his heart’s sake, bemoaned this headline: “Margarine as Bad as Butter for Heart Health.” “Do you mean to say that I could have been eating butter all these years? That’s it. I quit. No more diet changes for me.” His response is understandable—diet changes, after all, take effort to make and commitment to sustain. He, like many others, feels betrayed when, years later, science appears to have turned its advice upside down.

It bears repeating: a single study never proves or disproves anything. Study results may support one view or another, but they rarely merit the sort of fi nality implied by journalistic phrases such as “Now we know” or “The answer has been found.” Misinformed readers look- ing for simple answers to complex nutri- tion problems often take such phrases literally.

To read news stories with an educated eye, keep these points in mind:

A scientifi c study under discussion • should be published in a peer- reviewed journal, such as the Ameri- can Journal of Clinical Nutrition. An unpublished study or one from a less credible source may or may not be

Reading Nutrition News with an Educated Eye

Finally, ask yourself if the study makes sense for you. Even if it turns out that the fat of margarine is damaging to the heart, do you eat enough margarine to worry about its effects? Is butter even worse? When a headline touts a shock- ing new “answer” to a nutrition ques- tion, read the story with a critical eye. It may indeed be a carefully researched report, but often it is a sensational story intended to catch the attention of news- paper and magazine buyers, not to offer useful nutrition information.

A person wanting the whole story on a nutrition topic is wise to seek articles from peer- reviewed journals such as these. A review journal examines all available evidence on major topics. Other journals report details of the methods, results, and conclusions of single studies.

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A dietary analysis computer program is • available on the CengageNow website (www.cengage.com/sso) to help you through the process of examining your diet and comparing it to standards.

Stage Characteristics Actions

Precontemplation Not considering a change, have no intention of chang- ing; see no problems with current behavior.

Collect information about health effects of current behavior and potential benefi ts of change.

Contemplation Admit that change may be needed; weigh pros and cons of changing and not changing.

Commit to making a change and set a date to start.

Preparation Preparing to change a specifi c behavior, taking initial steps, and setting some goals.

Write an action plan, spelling out specifi c parts of the change. Set small-step goals; tell others about the plan.

Action Committing time and energy to making a change; following a plan set for a specifi c behavior change.

Perform the new behavior. Manage emotional and physical reactions to the change.

Maintenance Striving to integrate the new behavior into daily life and striving to make it permanent.

Persevere through lapses. Teach others and help them achieve their own goals. (This stage can last for years.)

Adoption/Moving On The former behavior is gone and the new behavior is routine.

After months or a year of maintenance without lapses, move on to other goals.

Stages of Behavior Change table 1-9

Many people need to change their daily routines to include physical activity.

LO 1.7

A Guide to Behavior Change Nutrition knowledge is of little value if it only helps people to make As on tests. Th e value comes when people use it to improve their diets. To act on knowledge, people must change their behaviors, and while this may sound simple enough, behavior change often takes substantial eff ort.

The Process of Change Psychologists describe six stages of behavior change, off ered in Table 1-9.

Knowing these stages can help you to recognize where you stand in relation to your own goals. Table 1-9 also demonstrates how to use this information to move forward in achieving your behavior change goals.

Assessments and Goals To make a change, you must fi rst be aware of a problem. Some problems, such as never consuming a vegetable, can be easy to spot. More subtle dietary problems, such as failing to meet your need for a particular vitamin or mineral, can have seri- ous repercussions but often must be revealed by a study of the diet. Tracking food intakes over several days’ time and then comparing intakes to standards (see Chap- ter 2) is a revealing exercise. Th en, setting small, achievable goals in areas that need changing is the next step to making improvements. Realistic goals for body weight are discussed in Chapter 9.

Obstacles to Change It is a rare person who, upon setting out to change a behavior, encounters only smooth progress toward the fi nal goal. Obstacles that derail plans or cause lapses often arise in these general areas:

Competence—the person lacks needed knowledge or skill to make the change.•

Confi dence—the person possesses the needed knowledge and skills but • believes

that the needed change is beyond the scope of his or her ability or that the prob-

lem lies outside the realm of personal control.

Motivation• —the person possesses both competence and confi dence but lacks

suffi cient reason to change.

lapses times of falling back into former habits, a normal and expected part of behavior change.

motivation the force that moves people to act. Motivation may be either instinctive (inborn drives such as hunger and thirst) or learned (such as the drive to acquire possessions or to improve health).

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19A G u i d e t o B e h a v i o r C h a n g e

Competence Th e fi rst obstacle, competence, is by far the most easily corrected. For example, a student who recognizes a lack of vegetables in her diet and wishes to increase her intake may not know how to prepare vegetables. Seeking information from a family cook can supply the missing knowledge, and trying out some recipes can bolster her skills. To deal with a serious threat, such as an eating disorder or excessive alcohol intake, outside help from reputable agencies may be needed to ac- complish a change.

Confi dence When a task seems insurmountable, confi dence fl ags. Our vegetable- deprived student who sets the broad goal “I will eat all of the vegetables I need every day” might grumble, “I’ll never be able to eat all those vegetables—I give up.” If, instead, she sets a small, specifi c goal, such as “I will purchase carrot sticks tomor- row and eat them for my snacks this week,” she may feel empowered to attempt it. Jotting down records of her snacks allows her to measure her success and identify obstacles to vegetable consumption.

People who take action and often succeed tend to be those with the quality of self-effi cacy, that is, they believe in their own abilities. To boost self-effi cacy, it helps to develop a strong internal locus of control—the belief that the individual has control over life’s events. Th e opposite, an external locus of control, leaves one feeling helpless against outside forces, such as luck or fate. In other words, the more you believe in yourself and your ability to change your life for the better, the more likely that you will succeed in doing so.

Motivation Th e toughest obstacle to changing, however, may be a lack of moti- vation. Even if our student possesses both competence and confi dence, she will not make a change unless she has suffi cient motivation to do so: “I’m healthy now—why should I bother to eat more vegetables?” Motivation arises when the expected ben- efi t or reward of the behavior change outweighs its perceived costs.

The Concept of Rewards Motivation is often based on the concept of rewards— the person making a change must expect that important rewards will follow the altered behaviors. Rewards are aff ected by four factors:

Th e value of the reward. (How big is the reward?)1. Its timing. (How soon will the reward come, or how soon will the price have to 2. be paid?)

Th e costs. (What will be the risks or consequences of seeking the reward?)3. Its probability. (How likely is the reward to occur, and how certain the price?)4.

If motivation to make dietary changes eludes people, the reason is often because of timing, cost, and probability factors. Th ey have to wait too long to receive the reward, or they perceive too high a cost, or they aren’t sure they’ll ever receive it. Here’s an example:

If you enjoy ice cream now (reward now), you won’t notice your weight gain •

until next month (pay later).

If you forgo the pleasure of eating ice cream now (pay now), you can’t expect to •

see any weight loss until next month (reward later).

No wonder so many people fail to change their poor food habits!

Start Now It is natural, as you progress through this text, to contemplate changing some of your own food habits. If you are ready to move beyond contemplation to preparation and action, the CengageNow Internet website off ers some help. Little reminders entitled Start Now that appear at the end of each of this book’s chapters invite you to visit the website to take inventory of your current behaviors, to set goals for a needed change, and to follow through until the new behavior becomes as comfort- able and familiar as the old one once was.

Did You Know? Outside help for making a change may be available from the professionals at a campus health center, counseling center, or community helping agency.

If you wish to make a change during your • study of nutrition, you can find help at the website www.cengage.com/sso. There, a series of exercises can help you to:

Assess your current diet and exercise •

habits.

Identify behaviors to improve.•

Determine your readiness to change.•

Create a plan for change.•

Track your efforts toward making the •

change.

self-effi cacy the belief in one’s ability to take action and successfully perform a specifi c behavior.

locus of control the assigned source of responsibility for one’s life events; an internal locus of control identifi es the individual’s be- haviors as the driving force; an external locus of control blames chance, fate, or some other external factor. Most people’s attitude falls somewhere in between.

http://www.cengage.com/sso

20 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

food feature

According to the experts, people in the United States are not very successful at selecting diets that meet their nutrition needs. In particular, only a tiny percent- age of adults manage to achieve both adequacy and moderation. In trying to control calories while balancing the diet and making it adequate, certain foods are especially useful. These foods are rich in nutrients relative to their energy contents; that is, they are foods with high nutrient density.22 Figure 1-5 is a simple depic- tion of this concept. Consider calcium sources, for example. Ice cream and fat- free milk both supply calcium, but the milk is denser in calcium per calorie. A cup of rich ice cream contributes more than 350 calories, a cup of fat-free milk only 85—and with almost double the calcium. Most people cannot, for their health’s sake, afford to choose foods without re- gard to their energy contents. Those who do very often exceed calorie allowances while leaving nutrient needs unmet.

Nutrient density is such a useful concept in diet planning that this book encourages you to think in those terms. Right away, the next chapter asks you to apply your knowledge of nutrient density while developing skills in meal plan- ning. Watch for tables and fi gures in later chapters that show the best buys among foods, not necessarily in nutrients per dollar, but in nutrients per calorie. Among foods that often rank high in nutrient density are the vegetables, particularly the nonstarchy vegetables such as broccoli, carrots, mushrooms, peppers, and toma- toes. These inexpensive foods take time to prepare, but time invested in this way pays off in nutritional health. Twenty minutes spent peeling and slicing vegetables for a salad is a better investment in nutrition than 20 minutes spent fi xing a fancy, high- fat, high-sugar dessert. Besides, the des- sert ingredients often cost more money and strain the calorie budget, too.23

How Can I Get Enough Nutrients Without Consuming Too Many Calories?

Time, however, is another concern. To- day’s working families, college students, and active people of all ages may have little time to devote to food preparation. Busy chefs should seek out convenience foods that are nutrient-dense, such as bags of ready-to-serve salads, refriger- ated prepared low-fat meats and poultry, canned beans, and frozen vegetables. Dried fruit and dry-roasted nuts require only that they be kept on hand and make a tasty, nutritious topper for salads and other foods. To round out the meal, fat- free milk is both nutritious and conve- nient. Other convenient selections, such as most pot pies, many frozen pizzas, ramen noodles, and “pocket”-style sandwiches, are less nutritious overall because they contain too few vegetables

and too many calories, making them low in nutrient density. The Food Features of later chapters offer many more tips for choosing convenient and nutritious foods.

All of this discussion leads to a princi- ple that is central to achieving nutritional health: It is not the individual foods you choose, but the way you combine them into meals and the way you arrange meals to follow one another over days and weeks that determine how well you are nourishing yourself. Nutrition is a sci- ence, not an art, but it can be used art- fully to create a pleasing, nourishing diet. The remainder of this book is dedicated to helping you make informed choices and combine them artfully to meet all the body’s needs.

nutrient density a measure of nutrients provided per calorie of food.

Higher Nutrient Density Lower Nutrient Density

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Nutritious Breakfast Doughnut Breakfast

Some foods deliver more nutrients for the same number of calories than others do. These two breakfasts provide about 500 calories each, but they differ greatly in the nutrients they provide per calorie. Note that the sausage in the larger breakfast is lower-calorie turkey sausage, not the high-calorie pork variety. Making small choices like this at each meal can add up to large calorie savings, making room in the diet for more servings of nutritious foods and even some treats.

A Way to Judge Which Foods

Are Most Nutritious

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21A G u i d e t o B e h a v i o r C h a n g e

Track Your Diet After each Food Feature section in this text, exercises like this one provide an ongoing diet analysis activity that asks you to apply what you’ve learned in the chapter to your own diet. To do so, use the Diet Analysis Plus (DA�) program that accompanies this book. To get started, do the following:

From the Home page of the DA1. � program (after your personal data has been entered), select the Re- ports tab from the red navigation bar then Profi le DRI Goals. Click Create PDF button. You will now have DRI values for calories, carbohydrates, and fat appropriate for your Profi le.

For the next three days, with pencil 2. and paper, keep track of everything you eat and drink. Be honest and

careful in your record-keeping. Measure or estimate amounts of foods and beverages you consume, as well as margarine or butter, salt, cream sauces, gravies, pasta sauce, ketchup, relish, jams, jellies, and other add-ons. Even a slice of tomato and a lettuce leaf on a sand- wich count toward the day’s intake. Distribute your data among four meals for each day: breakfast, lunch, dinner, and snacks.

Keep track of your physical activity 3. for all three of those days. Record all the minutes spent walking or biking to class, working out, vacuuming rugs, washing cars, playing sports, danc- ing with friends, or any other nonsed- entary behavior. Hold on to this data: you’ll need it in chapters to come.

From the Home page of DA4. �, select the Track Diet tab and enter each food item that you recorded for Day One, Day Two, and Day Three into the Find Foods area. When fi nished, select the Reports tab and go to Intake vs. Goals. Click the Generate Report button and choose all meals. What information on the report most surprised you?

From the Reports tab, go to Energy 5. Balance. Using Day Two (from the three-day diet intake), choose all meals and generate a report. Was your calorie intake over or under the recommended calories (kcals) for your profi le? Was it higher or lower than expected? You will analyze your energy balance in more detail later, in Chapter 9.

Concepts in Action

Throughout this chapter, the CengageNOW logo indicates an opportunity for online self-study, linking you to interactive tutorials and videos based on your level of understanding. Go to www.cengage.com/sso.

Search for “nutrition” at the U.S. Government health and nutrition sites: www.healthfi nder.gov or www.nutrition .gov.

Learn more about basic science research from the National Science Foundation and Research!America: www.nsf.gov and researchamerica.org.

View Healthy People Objectives for the Nation: www .healthypeople.gov.

Visit the food and nutrition center of the Mayo Clinic: www.mayohealth.org.

Create a chart of your family health history at the U.S. Surgeon General’s site: familyhistory.hhs.gov.

media menu

Answers to these Self Check questions are in Appendix G.

Energy-yielding nutrients include all of the following except:1.

vitaminsA.

carbohydratesB.

fatC.

proteinD.

Organic nutrients include all of the following except:2.

mineralsA.

fatB.

self check

http://www.cengage.com/sso

http://www.healthfi

http://www.nutrition

http://www.nsf.gov

http://www.mayohealth.org

22 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

carbohydratesC.

proteinD.

One of the characteristics of a nutritious diet is that the diet 3. provides no constituent in excess. This principle of diet planning is called:

adequacyA.

balanceB.

moderationC.

varietyD.

A slice of peach pie supplies 357 calories with 48 units of 4. vitamin A; one large peach provides 42 calories and 53 units of vitamin A. This is an example of:

calorie controlA.

nutrient densityB.

varietyC.

essential nutrientsD.

Which of the following is an example of a processed food?5.

carrotsA.

breadB.

nutsC.

watermelonD.

Studies of populations in which observation is accompanied 6. by experimental manipulation of some population members are referred to as:

case studiesA.

intervention studiesB.

laboratory studiesC.

epidemiological studiesD.

Both heart disease and cancer are due to genetic causes, 7. and diet cannot infl uence whether they occur. T F

Both carbohydrates and protein have 4 calories per gram.8. T F

People most often choose foods for the nutrients they 9. provide. T F

The belief in one’s own abilities is the quality of self-effi cacy.10. T F

23controversy 1 S o r t i n g t h e I m p o s t e r s f r o m t h e R e a l N u t r i t i o n E x p e r t s

CONTROVERSY

From the time of salesmen selling snake oil from horse-drawn wagons to the Internet sales schemes of today, nutrition quackery has plagued the na- tion. Government attempts at quackery regulation and enforcement over the past decades have largely failed. To protect themselves, consumers must learn to distinguish authentic and useful nutri- tion products and services from the vast array of well- meaning but misinformed advice and outright scams used to steal people’s money.

INFORMATION SOURCES AND COSTS OF WRONG CHOICES Most people say that television is their source for nutrition information, with magazines a close second, and the Internet quickly gaining in popularity.1* Sometimes, these sources provide sound and scientifi c, and therefore trustworthy, information. More often, though, info-

mercials, advertorials, and urban legends (defi ned in Table C1-1) pretend to inform, but in fact aim to sell products by making fantastic promises for health or weight loss with minimal effort and at bargain prices.

When scam products are garden tools or stain removers, hoodwinked consumers may lose a few dollars and some pride. When the products are ineffective, untested, or even hazard- ous “dietary supplements” or “medical devices,” consumers stand to lose the very thing they are seeking: good health. When a sick person wastes time with quack treatments, serious problems can easily advance while proper treatment is delayed.2 And dietary supplements have infl icted liver failure and other dire outcomes on previously well people who took them in hopes of improving their health.

Each year, consumers spend a deluge of dollars on nutrition-related services and products from both legitimate and fraudulent businesses. Each year, nutrition and other health

11 Sorting the Imposters from the Real Nutrition Experts

LO 1.8

*Reference notes are found in Appendix F.

Who is speaking on nutrition?

advertorials• lengthy advertisements in newspapers and magazines that read like feature articles but are written for the purpose of touting the virtues of products and may or may not be accurate. anecdotal evidence• information based on interesting and entertaining, but not scientifi c, personal accounts of events. fraud• or quackery the promotion, for fi nancial gain, of devices, treatments, services, plans, or products (includ- ing diets and supplements) claimed to improve health, well-being, or appear- ance without proof of safety or effective- ness. (The word quackery comes from the term quacksalver, meaning a person who quacks loudly about a miracle product—a lotion or a salve.) infomercials• feature-length television commercials that follow the format of regular programs but are intended to convince viewers to buy products and not to educate or entertain them. The state- ments made may or may not be accurate. Internet (the Net) • a worldwide network of millions of computers linked together to share information. urban legends • stories, usually false, that may travel rapidly throughout the world via the Internet gaining strength of conviction solely on the basis of repetition. websites • Internet resources composed of text and graphic fi les, each with a unique URL (Uniform Resource Locator) that names the site (for example, www .usda.gov). World Wide Web • (the Web, commonly abbreviated www) a graphical subset of the Internet.

Quackery and

Internet Terms

table C1-1

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24 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

Scientists test their ideas by conduct-• ing properly designed scientifi c experi- ments. They report their methods and procedures in detail so that other sci- entists can verify the fi ndings through replication.

Scientists recognize the inadequacy of • anecdotal evidence or testimonials.

Scientists who use animals in their • research do not apply their fi ndings directly to human beings.

Scientists may use specifi c segments • of the population in their research. When they do, they are careful not to generalize the fi ndings to all people.

Scientists report their fi ndings in • respected scientifi c journals. Their work must survive a screening review

a gym, a physician, a health-store clerk, an author of books, or an advocate for juice machines or weight-loss gadgets may all sincerely believe that the nutrition regimens they recommend are benefi cial. But what qualifi es them to give advice? Would fol- lowing their advice be helpful or harmful? To sift the meaningful nutrition information from the rubble, you must fi rst learn to rec- ognize quackery wherever it presents itself.

IDENTIFYING VALID NUTRITION INFORMATION Nutrition derives information from scientifi c research, which has these characteristics:

fraud diverts tens of billions of consumer dollars from legitimate health care.3 Consumers with questions or suspicions about fraud can contact the FDA on the Internet at www.FDA.gov or by telephone at (888) INFO-FDA.

How can people learn to distinguish valid nutrition information from misinforma- tion? Some quackery is easy to identify— like the claims of the salesman in Figure C1-1. Other fraudulent nutrition claims are subtle and so more diffi cult to detect.

Between the extremes of accurate scientifi c data and intentional quackery lies an abundance of less easily recognized nutrition misinformation.4† An instructor at

Too good to be true Enticingly quick and simple answers to complex problems. Says what most people want to hear. Sounds magical.

Testimonials Support and praise by people who “felt healed,” “were younger,” “lost weight,” and the like as a result of using the product or treatment.

Motive: personal gain Those making the claim stand to make a profit if it is believed.

Advertisement Claims are made by an advertiser who is paid to promote sales of the product or procedure. (Look for the word “Advertisement,” in tiny print somewhere on the page.)

Latest innovation/Time-tested Fake scientific jargon is meant to inspire awe. Fake “ancient remedies” are meant to inspire trust.

Fake credentials Uses title “doctor,” “university,” or the like but has created or bought the title—it is not legitimate.

Unpublished studies Scientific studies cited but not published in reliable journals and so are not critically examined.

Suspicions about food supply Urges distrust of the current methods of medicine or suspicion of the regular food supply. Provides “alternatives” for sale under the guise of freedom of choice. May use the term “natural” to imply safety.

A SCIENTIFIC BREAKTHROUGH! FEEL STRONGERSTRONGER, LOSELOSE WEIGHT. IMPROVEIMPROVE YOUR MEMORY ALL WITH THE HELP OF VITE-O-MITE!VITE-O-MITE! OH SURE, YOU MAY HAVE HEARD THAT VITE-O-MITEVITE-O-MITE IS NOT ALL THAT WE SAY IT IS, BUT THAT’S WHAT THE FDA WANTS YOU TO THINK! OUR DOCTORSOUR DOCTORS AND SCIENTISTS SAY IT’S THE ULTIMATE VITAMIN SUPPLEMENT. SAY NO! TO THE WEAKENED VITAMINS IN TODAY’S FOODS. VITE-O-MITEVITE-O-MITE INCLUDES POTENT SECRET INGREDIENTSPOTENT SECRET INGREDIENTS THAT YOU CANNOT GET WITH ANY OTHER PRODUCT! ORDER RIGHT NOW AND WE'LL SEND YOU ANOTHER FOR FREE!

Persecution claims Claims of persecution by the medical establishment or claims that physicians “want to keep you ill so that you will continue to pay for office visits.”

Authority not cited Studies cited sound valid but are not referenced, so that it is impossible to check and see if they were conducted scientifically.

Logic without proof The claim seems to be based on sound reasoning but hasn’t been scientifically tested and shown to hold up.

Earmarks of Nutrition Quackery figure C1-1

†Quackery-related defi nitions are available from the National Counsel Against Health Fraud, www.ncahf .org/pp/defi nitions.html.

http://www.FDA.gov

http://www.ncahf

25controversy 1 S o r t i n g t h e I m p o s t e r s f r o m t h e R e a l N u t r i t i o n E x p e r t s

Hoaxes and scare stories abound on websites and in e-mails. Be suspicious when:

The contents were written by someone • other than the sender or some author- ity you know.

A phrase like “Forward this to every-• one you know” appears anywhere in the piece.

governed Internet “encyclopedia” web- sites allow anyone to post information or change others’ postings on topics.‡ Information on the sites may be correct, but it may not be—readers must evaluate it for themselves. Table C1-3 provides some clues to judging the reliability of nutrition information websites.

by their peers before it is accepted for publication.

With each report from scientists, the fi eld of nutrition changes a little—each fi nding contributes another piece to the whole body of knowledge. Table C1-2 lists some sources of credible nutrition information.

NUTRITION ON THE NET Got a question? The World Wide Web on the Internet has an answer. The Internet offers endless opportunities to obtain high-quality information, but it also delivers an abundance of incomplete, misleading, or inaccurate information.5 Simply put: anyone can publish anything on the Internet. For example, popular self-

To judge whether an Internet site offers reliable nutrition information, answer the following questions.

Who is responsible for the site?• Clues can be found in the three-letter “tag” that fol- lows the dot in the site’s name. For example, “gov” and “edu” indicate government and university sites, usually reliable sources of information. Do the names and credentials of information providers appear? Is an editorial • board identifi ed? Many legitimate sources provide e-mail addresses or other ways to obtain more information about the site and the information providers behind it. Are links with other reliable information sites provided?• Reputable organizations almost always provide links with other similar sites because they want you to know of other experts in their area of knowledge. Caution is needed when you evaluate a site by its links, however. Anyone, even a quack, can link a webpage to a reputable site without the organization’s permission. Doing so may give the quack’s site the appearance of legitimacy, just the effect the quack is hoping for. Is the site updated regularly?• Nutrition information changes rapidly, and sites should be updated often. Is the site selling a product or service?• Commercial sites may provide accurate information, but they also may not, and their profi t motive increases the risk of bias. Does the site charge a fee to gain access to it?• Many academic and government sites offer the best information, usually for free. Some legitimate sites do charge fees, but before paying up, check the free sites. Chances are good you’ll fi nd what you are looking for without paying. Some other credible websites include:•

Government agencies• Department of Agriculture (USDA) www.usda.gov Department of Health and Human Services (DHHS) www.os.dhhs.gov Food and Drug Administration (FDA) www.fda.gov Health Canada www.hc-sc.gc.ca/index-eng.php

Volunteer health agencies• American Cancer Society www.cancer.org American Diabetes Association www.diabetes.org American Heart Association www.americanheart.org

Reputable consumer and professional • groups: American Council on Science and Health www.acsh.org

American Dietetic Association www.eatright.org American Medical Association www.ama-assn.org Dietitians of Canada www.dietitians.ca Federal Citizen Information Center www.pueblo.gsa.gov International Food Information Council www.ific.org

Journals• American Journal of Clinical Nutrition www.ajcn.org Journal of the American Dietetic Association www.adajournal.org New England Journal of Medicine www.nejm.org Nutrition Reviews www.ilsi.org

Is This Site Reliable? table C1-3

Professional health organizations, gov- ernment health agencies, volunteer health agencies, and consumer groups provide consumers with reliable health and nutrition information. Credible sources of nutrition information include:

Professional health organizations, • especially the American Dietetic As- sociation’s National Center for Nutri- tion and Dietetics (NCND), www .eatright.org/ncnd.html, also the Society for Nutrition Education, www .sne.org and the American Diabetes Association, www.diabetes.org Government health agencies such • as the Federal Trade Commis- sion (FTC), www.ftc.gov and the National Institutes of Health Offi ce of Dietary Supplements, www .dietary-supplements.info.nih.gov Certain consumer watchdog agen-• cies such as the National Council Against Health Fraud, www.ncahf .org, Stephen Barrett’s Quackwatch, www.quackwatch.com, and Snopes .com—Rumor Has It, www.snopes .com Reputable consumer groups such • as the Better Business Bureau, www.bbb.org, the Consumers Union, www.consumersunion.org and the American Council on Sci- ence and Health, www.acsh.org

Credible Sources

of Nutrition

Information

table C1-2

‡An example is Wikipedia.

http://www.eatright.org

http://www.ama-assn.org

http://www.dietitians.ca

http://www.pueblo.gsa.gov

http://www.ific.org

http://www.ajcn.org

http://www.adajournal.org

http://www.nejm.org

http://www.ilsi.org

http://www.usda.gov

http://www.os.dhhs.gov

http://www.fda.gov

http://www.hc-sc.gc.ca/index-eng.php

http://www.cancer.org

http://www.diabetes.org

http://www.americanheart.org

http://www.acsh.org

http://www.diabetes.org

http://www.ftc.gov

http://www.ncahf

http://www.quackwatch.com

http://www.snopes

http://www.bbb.org

http://www.consumersunion.org

http://www.acsh.org

26 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

The American Dietetic Association The American Dietetic Association (ADA), the professional association of dietitians, asserts that nutrition education should be part of the curriculum for health- care professionals: physicians’ assistants, dental hygienists, physical and occupa- tional therapists, social workers, and all others who provide services directly to clients. This plan would bring access to re- liable nutrition information to more people.

Physicians who specialized in clinical nutrition in medical school are highly qualifi ed to advise on nutrition. Member- ship in the American Society for Clinical Nutrition, whose journal is cited many times throughout this text, is another sign of nutrition knowledge. Still, few physicians have the knowledge, time, or experience to develop diet plans and provide detailed diet instruction for cli- ents, and they often refer their clients to nutrition specialists. Table C1-4 lists the best specialists to choose.

Registered Dietitians: The Nutrition Specialists Fortunately, the credential that indicates a qualifi ed nutrition expert is easy to spot—you can confi dently call on a registered dietitian (RD). Additionally, some states require that nutritionists and dietitians obtain a license to prac- tice. Meeting state-established criteria in addition to registration with the Ameri- can Dietetic Association certifi es that an expert is the genuine article.

RDs are easy to fi nd in most communi- ties because they perform a multitude of duties in a variety of settings. They work in foodservice operations, phar- maceutical companies, sports nutrition programs, corporate wellness programs, the food industry, home health agen- cies, long-term care institutions, private practice, community and public health settings, cooperative extension offi ces,§ research centers, universities and other educational settings, and hospitals, health maintenance organizations (HMOs), and other health-care facilities.

website, which provides free access to over 10 million abstracts (short descrip- tions) of research papers published in scientifi c journals around the world. Many abstracts provide links to full articles posted on other sites. The site is easy to use and offers instructions for beginners. Figure C1-2 introduces this resource.

WHO ARE THE TRUE NUTRITION EXPERTS? Most people turn to their physicians for dietary advice. Physicians are expected to know all about health-related matters. Only about 30 percent of all medical schools in the United States require students to take a comprehensive nutri- tion course; less than half require the minimum 25 hours of nutrition instruction recommended by the National Acad- emy of Sciences.6 By comparison, most students reading this text are taking a nutrition class that provides an average of 45 hours of instruction.

The piece states “This is not a hoax”; • chances are, it is.

The information seems shocking or • something that you’ve never heard from legitimate sources.

The language is overly emphatic or • sprinkled with capitalized words or exclamation marks.

No references are offered or, if pres-• ent, are of questionable validity when examined.

The message has been debunked on • websites such as www.quackwatch .com or www.urbanlegends.com.

Of course, these hints alone are insuf- fi cient to judge nutrition information from any source. The user must also scrutinize “nutrition experts” who make statements, even when they possess legitimate degrees, as described in the next section.

In contrast, one of the most trust worthy sites for scientifi c investigation is the National Library of Medicine’s PubMed

Refine the search by setting limits

Type search terms here

Use “help” resources to answer questions

The U.S. National Library of Medicine’s PubMed website offers tutorials to help teach the beginner to use the search system effectively. Often, simply visiting the site, typing a query in the “Search for” box, and clicking “Search” will yield satisfac- tory results. For example, to fi nd research concerning calcium and bone health, typing in “calcium bone” nets almost 3,000 results. To refi ne the search, try setting limits on dates, types of articles, languages, and other criteria to obtain a more manageable number of abstracts to peruse.

PubMed (www.ncbi.nlm.nih.gov/pubmed):

Internet Resource for Scientific Nutrition

References

figure C1-2

§Cooperative extension agencies are associated with land grant colleges and universities and may be found in the phone book’s government listings.

http://www.quackwatch

http://www.urbanlegends.com

http://www.ncbi.nlm.nih.gov/pubmed):

27controversy 1 S o r t i n g t h e I m p o s t e r s f r o m t h e R e a l N u t r i t i o n E x p e r t s

DETECTING FAKE CREDENTIALS In contrast to RDs and other credentialed nutrition professionals, thousands of people possess fake nutrition degrees and claim to be nutrition counselors, nutritionists, or “dietists.” These and other such titles may sound meaningful, but most of these people lack the estab- lished credentials of the ADA-sanctioned dietitian. If you look closely, you can see signs that their expertise is fake.

Educational Background Take, for example, a nutrition expert’s educational background. The minimum standards of education for a dietitian specify a bachelor of science (BS) de- gree in food science and human nutrition (or related fi elds) from an accredited

nutritionists play key roles in delivering nutrition services to people in the com- munity. A public health nutritionist may plan, coordinate, administer, and evalu- ate food assistance programs; act as a consultant to other agencies; manage fi nances; and much more.

In some facilities, a dietetic techni- cian assists registered dietitians in both administrative and clinical responsi- bilities. A dietetic technician has been educated and trained to work under the guidance of a registered dietitian; upon passing a national examination, the tech- nician earns the title dietetic technician, registered (DTR).

RDs in hospitals have many subspecial- ties. Administrative dietitians manage the foodservice system; clinical dietitians pro- vide client care and are leaders in disease prevention services (see Table C1-5); and nutrition support team dietitians coor- dinate nutrition care, such as medical nutrition therapy, with the efforts of other health-care professionals.7 A registered dietitian can become a certifi ed diabe- tes educator (CDE), a specialist who educates people with diabetes about the management of their disease.

In the food industry, dietitians conduct research, develop products, and market services. In government, public health

American Dietetic Association (ADA)• the professional organization of dietitians in the United States. The Canadian equivalent is the Dietitians of Canada (DC), which operates similarly. certifi ed diabetes educator (CDE)• a health-care professional who specializes in edu- cating people with diabetes to help them manage their disease through medical and lifestyle means. Extensive training, work experience, and an examination are required to achieve CDE status. dietetic technician• a person who has completed a two-year academic degree from an accredited college or university and an approved dietetic technician program. A dietetic technician, registered (DTR) has also passed a national examination and maintains registration through continuing professional education. dietitian• a person trained in nutrition, food science, and diet planning. See also regis- tered dietitian. license to practice• permission under state or federal law, granted on meeting specifi ed criteria, to use a certain title (such as dietitian) and to offer certain services. Licensed dietitians may use the initials LD after their names. medical nutrition therapy• nutrition services used in the treatment of injury, illness, or other conditions; includes assessment of nutrition status and dietary intake and correc- tive applications of diet, counseling, and other nutrition services. nutritionist• someone who studies nutrition. Some nutritionists are RDs, whereas others are self-described experts whose training is questionable and who are not qualifi ed to give advice. In states with responsible legislation, the term applies only to people who have master of science (MS) or doctor of philosophy (PhD) degrees from properly ac- credited institutions. public health nutritionist• a dietitian or other person with an advanced degree in nutri- tion who specializes in public health nutrition. registered dietitian (RD)• a dietitian who has graduated from a university or college after completing a program of dietetics. The program must be approved or accredited by the American Dietetic Association (or Dietitians of Canada). The dietitian must serve in an approved internship, coordinated program, or preprofessional practice program to practice the necessary skills; pass the fi ve parts of the association’s registration ex- amination; and maintain competency through continuing education.a Many states also require licensing for practicing dietitians. registration• listing with a professional organization that requires specifi c course work, experience, and passing of an examination.

aThe fi ve content areas of the registration examination for dietitians are food and nutrition; clinical and com- munity nutrition; education and research; food and nutrition systems; and management. New emphasis is placed on genetics, cultural competency, complementary care, and reimbursement.

Terms Associated with Nutrition Advice table C1-4

The fi rst six items in this list play essen- tial roles in medical nutrition therapy as part of a medical treatment plan. Dieti- tians also play leading roles in health promotion and disease prevention.

Assesses clients’ nutrition status.• Determines clients’ nutrient • requirements. Monitors clients’ nutrient intakes.• Develops, implements, and evaluates • clients’ medical nutrition therapy. Counsels clients to cope with unique • diet plans. Teaches clients and their families • about nutrition and diet plans. Provides training for other dieti-• tians, nurses, interns, and dietetics students. Serves as liaison between clients and • the foodservice department. Communicates with physicians, • nurses, pharmacists, and other health-care professionals about clients’ progress, needs, and treatments. Participates in professional activities • to enhance knowledge and skill.

Selected

Responsibilities

of a Clinical

Dietition

table C1-5

28 chapter 1 F o o d C h o i c e s a n d H u m a n H e a l t h

Would You Trust a Nutritionist Who Eats Dog Food? In a similar stunt, Mr. Eddie Diekman was named a “professional member” of an association of nutrition “experts.” For his efforts, Eddie received a diploma suit- able for framing and displaying. Eddie is a cocker spaniel. His owner, Connie B. Diekman, then president of the American Dietetic Association, paid Eddie’s tuition to prove that he could be awarded the title “nutritionist” merely by sending in his name.††

Staying Ahead of the Scammers In summary, to stay one step ahead of the nutrition quacks, check a provider’s qualifi cations. First look for the degrees and credentials listed after the person’s name (such as MD, RD, MS, PhD, or LD). Next fi nd out what you can about the reputations of the institutions that awarded the degrees. Then call your state’s health-licensing agency and ask if dietitians are licensed in your state. If they are, fi nd out whether the person giving you dietary advice has a license— and if not, fi nd someone better qualifi ed. Your health is your most precious asset, and protecting it is well worth the time and effort it takes to do so.

State laws do not necessarily help consumers distinguish experts from fakes; some states allow anyone to use the title dietitian or nutritionist. But other states have responded to the need by allowing only RDs or people with certain graduate degrees and state licenses to call themselves dietitians. Licensing pro- vides a way to identify people who have met minimum standards of education and experience.

A Failed Attempt to Fail To dramatize the ease with which anyone can obtain a fake nutrition degree, for $82 one writer enrolled in a nutrition diploma mill that billed itself as a cor- respondence school. She made every attempt to fail, intentionally answering all the examination questions incorrectly. Even so, she received a “nutritionist” cer- tifi cate at the end of the course, together with a letter from the “school” offi cials explaining that they were sure she must have misread the test.

college or university (Table C1-6 defi nes this term). Such a degree generally requires four to fi ve years of study.

In contrast, a fake nutrition expert may display a degree from a six-month course of study; such a degree is simply not the same. In some cases, schools posing as legitimate institutions are actually diploma mills—fraudulent busi- nesses that sell certifi cates of compe- tency to anyone who pays the fees, from under a thousand dollars for a bachelor’s degree to several thousand for a doctor- ate. To obtain these “degrees,” a candi- date need not read any books or pass any examinations, and the only written work is a signature on a check.

Accreditation and Licensure Lack of proper accreditation is the identifying sign of a fake educational institution. To guard educational quality, an accrediting agency recognized by the U.S. Department of Education certifi es that certain schools meet the criteria de- fi ning a complete and accurate school- ing, but in the case of nutrition, quack accrediting agencies cloud the picture. Fake nutrition degrees are available from schools “accredited” by more than 30 phony accrediting agencies.**

accredited• approved; in the case of medical centers or universities, certifi ed by an agency recognized by the U.S. Department of Education. diploma mill• an organization that awards meaningless degrees without requiring its students to meet educational standards.

Terms Describing Institutions of Higher

Learning, Legitimate and Fradulent

table C1-6

Eddie displays his professional credentials.

**To fi nd out whether an online school is accredited, write the Distance Education and Training Council, Accrediting Commission, 1601 Eighteenth Street, NW, Washington, D.C. 20009; call (202) 234-5100; or visit their website (www.detc.org). To fi nd out whether a school is properly accred- ited for a dietetics degree, write the American Dietetic Association, Division of Education and Research, 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606-6995, phone: 800/877-1600; or visit their website (www.eatright.org/caade). The American Council on Education publishes a directory of accredited institutions, professionally accredited programs, and candidates for accredita- tion in Accredited Institutions of Postsecondary Education Programs (available at many libraries). For additional information, write the American Council on Education, One Dupont Circle NW, Suite 800, Washington, D.C. 20036; call (202) 939-9382; or visit their website (www.acenet.edu).

††The stunt described was patterned after that of the late Victor Herbert, whose cat Charlie and poodle Sassafras were also awarded nutritionist credentials by mail.

ou rte

sy o

f e at

rig ht

.o rg

http://www.detc.org

http://www.eatright.org/caade

http://www.acenet.edu

22Nutrition Tools— Standards and Guidelines

do you ever . . . Wonder how scientists decide how • much of each nutrient you need to consume each day?

Dismiss government dietary • recommendations as too simplistic to help you plan your diet?

Consume the portions offered in • restaurants and fast-food places,

believing them to be in keeping with nutrition recommendations?

Wish that your foods could boost • your health by providing substances beyond the nutrients they contain?

Keep reading . . .

LO 2.1 Explain how RDA, AI, DV, and EAR serve different functions in describing nutrient values and discuss how each is used.

LO 2.2 List the major categories of the Dietary Guidelines

for Americans and explain their importance to the population.

LO 2.3 Describe how foods are grouped in the USDA Food Guide and MyPyramid.

LO 2.4 Describe the concept of the discretionary calorie allowance, and explain how it can be used in diet planning.

LO 2.5 Plan a day’s meals that follow the pattern of the USDA Food Guide within a given calorie budget.

LO 2.6 Defi ne the term functional foods, and discuss some potential effects of such foods on human health.

Learning Objectives To find learning objective topics in this chapter, look for text headings with a corresponding “LO” number above the heading. After completing this chapter, you should be able to accomplish the following:

30 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

E ating well is easy in theory—just choose foods that supply appropriate amounts of the essential nutrients, fi ber, phytochemicals, and energy without excess in-

takes of fat, sugar, and salt and be sure to get enough exercise to balance the foods you eat. In practice, eating well proves harder than it appears. Many people are overweight, or undernourished, or suff er from nutrient excesses or defi ciencies that impair their health—that is, they are malnourished. You may not think that this statement applies to you, but you may already have less than optimal nutrient in- takes and activity without knowing it. Accumulated over years, the eff ects of your habits can seriously impair the quality of your life.

Putting it positively, you can enjoy the best possible vim, vigor, and vitality throughout your life if you learn now to nourish yourself optimally. To learn how, you fi rst need some general guidelines and the answers to several basic questions. How much energy and how much of each nutrient should you consume? How much physical activity do you need to balance your energy intake from food? Which types of foods supply which nutrients? How much of each type of food do you have to eat to get enough? And how can you eat all these foods without gaining weight? Th is chapter begins by identifying some ideals for nutrient intakes and ends by showing how to achieve them.

LO 2.1

Nutrient Recommendations Nutrient recommendations are sets of “yardsticks,” or standards, for measuring healthy people’s energy and nutrient intakes. Nutrition experts use the recommen- dations to assess intakes and to off er advice on amounts to consume. Individuals may use them to decide how much of a nutrient they need to consume and how much is too much.

Dietary Reference Intakes Th e standards in use in the United States and Canada are the Dietary Reference Intakes (DRI). A committee of nutrition experts from the United States and Can- ada develops and publishes the DRI.* Th e DRI committee has set values for all of the vitamins and minerals, as well as for carbohydrates, fi ber, lipids, protein, water, and energy. Values for other food constituents that may play roles in health mainte- nance are forthcoming.

Another set of nutrient standards is useful for the person trying to make wise choices among packaged foods. Th ese are the Daily Values, familiar to anyone who has read a food label. Th ese standards—the DRI and Daily Values—are used and referred to so often that they are printed on the inside front and back cover pages of this book.

KE Y POINT The Dietary Reference Intakes are nutrient intake standards set for people living in the United States and Canada. The Daily Values are U.S. standards used on food labels.

Goals of the DRI Committee For each nutrient, the DRI establish a number of values, each serving a diff erent purpose. Most people need to focus on only two kinds of DRI values: those that set nutrient intake goals for individuals (RDA and AI, described next) and those that defi ne an upper limit of safety for nutrient intakes (UL, addressed later). In total, the DRI include:

Estimated Average Requirements (EAR)•

Recommended Dietary Allowances (RDA)•

*This is a committee of the Food and Nutrition Board of the National Academy of Sciences’ Institute of Medicine, working in association with Health Canada.

A directory of recommendations:•

DRI lists—inside front cover pages A, B, •

and C.

Daily Values—see inside back cover, •

page Y.

Dietary Reference Intakes (DRI) a set of four lists of values for measuring the nutrient intakes of healthy people in the United States and Canada. The four lists are Estimated Average Requirements (EAR), Recommended Dietary Allowances (RDA), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL).

Daily Values nutrient standards that are printed on food labels and on grocery store and restaurant signs. Based on nutrient and energy recommendations for a general 2,000- calorie diet, they allow consumers to compare foods with regard to nutrients and calorie contents.

Estimated Average Requirements (EAR) the average daily nutrient intake es- timated to meet the requirement of half of the healthy individuals in a particular life stage and gender group; used in nutrition research and policymaking and is the basis upon which RDA values are set (see below).

Recommended Dietary Allow- ances (RDA) nutrient intake goals for individuals; the average daily nutrient intake level that meets the needs of nearly all (97 to 98 percent) healthy people in a particular life stage and gender group. Derived from the Estimated Average Requirements (see above).

31N u t r i e n t R e c o m m e n d a t i o n s

Adequate Intakes (AI)•

Tolerable Upper Intake Levels (UL)•

Th e following sections address the diff erent DRI values, arranged by the goals of the DRI committee.

Goal #1. Setting Recommended Intake Values—RDA and AI One of the great advantages of the DRI values lies in their applicability to the diets of individu- als.1† Th e committee off ers two sets of values that individuals may use for their own nutrient intake goals: Recommended Dietary Allowances (RDA) and Adequate Intakes (AI).‡

Th e RDA form the indisputable bedrock of the DRI recommended intakes be- cause they derive from solid experimental evidence and reliable observations—they are expected to meet the needs of almost all healthy people. AI values, in contrast, are based as far as possible on the available scientifi c evidence but also on some educated guesswork. Whenever the DRI committee fi nds insuffi cient evidence to generate an RDA, they establish an AI value instead. Th is book refers to the RDA and AI values collectively as the DRI recommended intakes.

Goal #2. Facilitating Nutrition Research and Policy—EAR Another set of values established by the DRI committee, the Estimated Average Requirements (EAR), establishes nutrient requirements for given life stages and gender groups that researchers and nutrition policymakers use in their work. Public health of- fi cials may also use them to assess nutrient intakes of populations and make recommendations.

To set the EAR, the DRI committee decides on criteria for each nutrient based on its roles in the body and in reducing disease risks.2 Th e EAR values form the scientifi c basis upon which the RDA values are set (a later section explains how).

Goal #3. Establishing Safety Guidelines—UL Beyond a certain point, it is un- wise to consume large amounts of any nutrient, so the DRI committee sets the Tolerable Upper Intake Levels (UL) to identify potentially toxic levels of nutrient intake.3 Th e UL are indispensable to consumers who take supplements or consume foods and beverages to which vitamins or minerals have been added—a group that includes almost everyone. Public health offi cials also rely on UL values to set safe upper limits for nutrients added to our food and water supplies.

Nutrient needs fall within a range, and a danger zone exists both below and above that range. Figure 2-1 on page 32 illustrates this point. People’s tolerances for high doses of nutrients vary, so caution is in order when nutrient intakes approach the UL values.

Some nutrients do not have UL values. Th e absence of a UL for a nutrient does not imply that it is safe to consume it in any amount, however. It means only that insuffi cient data exist to establish a value.

Goal #4. Preventing Chronic Diseases Th e DRI committee also takes into ac- count chronic disease prevention, wherever appropriate. For example, the commit- tee set lifelong intake goals for the mineral calcium at the levels believed to lessen the likelihood of osteoporosis-related fractures in the later years.

In addition to the four basic DRI lists just named, the DRI committee also set healthy ranges of intake for carbohydrate, fat, and protein known as Acceptable Ma- cronutrient Distribution Ranges (AMDR). Each of these three energy-yielding nutrients contributes to the day’s total calorie intake, and their contributions can be expressed as a percentage of the total. According to the committee, a diet that pro- vides adequate energy in the following proportions can provide adequate nutrients while reducing the risk of chronic diseases:

45 to 65 percent of calories from carbohydrate.•

†Reference notes are found in Appendix F. ‡For simplicity, this book refers to two sets of nutrient goals (AI and RDA) collectively as the DRI recommended intakes. The AI values are not the scientifi c equivalent of the RDA, however.

Did You Know? The DRI table on the inside front cover, page B distinguishes the RDA from AI values, but both kinds of values are intended as nutrient intake goals for individuals.

Tolerable Upper Intake Levels (UL) are listed • on page C, inside the front cover.

Adequate Intakes (AI) nutrient intake goals for individuals; the recommended aver- age daily nutrient intake level based on intakes of healthy people (observed or experimentally derived) in a particular life stage and gender group and assumed to be adequate. Set whenever scientifi c data are insuffi cient to allow establishment of an RDA value.

Tolerable Upper Intake Levels (UL) the highest average daily nutrient intake level that is likely to pose no risk of toxicity to almost all healthy individuals of a particular life stage and gender group. Usual intake above this level may place an individual at risk of illness from nutrient toxicity.

Acceptable Macronutrient Distri- bution Ranges (AMDR) values for carbohydrate, fat, and protein expressed as percentages of total daily calorie intake; ranges of intakes set for the energy-yielding nutrients that are suffi cient to provide adequate total energy and nutrients while reducing the risk of chronic diseases.

32 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

20 to 35 percent of calories from fat.•

10 to 35 percent of calories from protein.•

Th e chapters on the energy-yielding nutrients come back to these ranges.

KE Y POINT The DRI provide nutrient intake goals for individuals, supply a set of standards for researchers and public policymakers, establish tolerable upper limits for nutrients that can be toxic in excess, and take into account evidence from research on disease prevention. The DRI are composed of the RDA, AI, UL, and EAR lists of values, along with the AMDR ranges for energy-yielding nutrients.

Understanding the DRI Intake Recommendations Nutrient recommendations have been much misunderstood. One young woman posed this question: “Do you mean that some bureaucrat says that I need exactly the same amount of vitamin D as every other young woman in my group? Do they really think that ‘one size fi ts all’?”

DRI for Groups Th e DRI committee acknowledges diff erences between indi- viduals. It has made separate recommendations for specifi c groups of people—men, women, pregnant women, lactating women, infants, and children—and for specifi c age ranges. Children aged 4 to 8 years, for example, have their own DRI recom- mended intakes. Each individual can look up the recommendations for his or her own age and gender group. Within your own age and gender group, the commit- tee advises adjusting nutrient intakes in special circumstances that may increase or decrease nutrient needs, such as illness, smoking, or vegetarianism. Later chapters provide details about which nutrients may need adjustment.

For almost all healthy people, a diet that consistently provides the RDA or AI amount for a specifi c nutrient is very likely to be adequate in that nutrient. On aver- age, you should try to get 100 percent of the DRI recommended intake for every nutrient to ensure an adequate intake over time.

Consuming too much of a nutrient endangers health, just as consuming too little does. The DRI recommended intake values fall within a safety range with the UL marking tolerable upper levels.

The Naïve View Versus the Accurate View

of Optimal Nutrient Intakes

figure 2-1

Naïve view

Tolerable Upper Intake Level (UL)

DRI Recommended

Intakes

Accurate view

Safety

Danger of toxicity

Danger

of deficiency

Danger

Marginal

P ho

to di

sc /G

et ty

Im ag

Don’t let the “alphabet soup” of nutrient intake standards confuse you. Their names make sense when you learn their purposes.

33N u t r i e n t R e c o m m e n d a t i o n s

Other Characteristics of the DRI Th e following facts will help put the DRI recommended intakes into perspective:

Th e values are based on available scientifi c research to the greatest extent pos-•

sible and are updated periodically in light of new knowledge.

Th e values are based on the concepts of probability and risk. Th e DRI recom-•

mended intakes are associated with a low probability of defi ciency for people of

a given life stage and gender group, and they pose almost no risk of toxicity for

that group.

Th e values are recommendations for optimal intakes, not minimum require-•

ments. Th ey include a generous safety margin and meet the needs of virtually all

healthy people in a specifi c age and gender group.

Th e values are set in reference to certain indicators of nutrient adequacy, such as •

blood nutrient concentrations, normal growth, and reduction of certain chronic

diseases or other disorders when appropriate, rather than prevention of defi -

ciency symptoms alone.

Th e values refl ect daily intakes to be achieved, on average, over time. Th ey as-•

sume that intakes will vary from day to day and are set high enough to ensure

that the body’s nutrient stores will meet nutrient needs during periods of inad-

equate intakes lasting several days to several months, depending on the nutrient.

The DRI Apply to Healthy People Only Th e DRI are designed for health main- tenance and disease prevention in healthy people, not for the restoration of health or repletion of nutrients in those with defi ciencies. Under the stress of serious illness or malnutrition, a person may require a much higher intake of certain nutrients or may not be able to handle even the DRI amount. Th erapeutic diets take into account the increased nutrient needs imposed by certain medical conditions, such as recovery from surgery, burns, fractures, illnesses, malnutrition, or addictions.

KE Y POINT The DRI represent up-to-date, optimal, and safe nutrient intakes for healthy people in the United States and Canada.

How the Committee Establishes DRI Values— An RDA Example A theoretical discussion will help to explain how the DRI committee goes about setting DRI values. Suppose we are the DRI committee members with the task of setting an RDA for nutrient X (an essential nutrient).§ Ideally, our fi rst step will be to fi nd out how much of that nutrient various healthy individuals need. To do so, we review studies of defi ciency states, nutrient stores and their depletion, and the factors infl uencing them. We then select the most valid data for use in our work. Of the DRI family of nutrient standards, the setting of an RDA value demands the most rigorous science and tolerates the least guesswork.

Determining Individual Requirements One experiment we would review or conduct is a balance study. In this type of study, scientists measure the body’s in- take and excretion of a nutrient to fi nd out how much intake is required to balance excretion. For each individual subject, we can determine a requirement to achieve balance for nutrient X. With an intake below the requirement, a person will slip into negative balance or experience declining stores that could, over time, lead to defi ciency of the nutrient.

We fi nd that diff erent individuals, even of the same age and gender, have diff er- ent requirements. Mr. A needs 40 units of the nutrient each day to maintain bal- ance; Mr. B needs 35; Mr. C, 57. If we look at enough individuals, we fi nd that their

§This discussion describes how an RDA value is set; to set an AI value, the committee would use some educated guesswork as well as scientifi c research results to determine an approximate amount of the nutrient most likely to support health.

balance study a laboratory study in which a person is fed a controlled diet and the intake and excretion of a nutrient are measured. Balance studies are valid only for nutrients like calcium (chemical elements) that do not change while they are in the body.

requirement the amount of a nutrient that will just prevent the development of specifi c defi ciency signs; distinguished from the DRI recommended intake value, which is a gener- ous allowance with a margin of safety.

34 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

requirements are distributed as shown in Figure 2-2—with most requirements near the midpoint (here, 45) and only a few at the extremes.

Accounting for the Needs of the Population To set the value, we have to decide what intake to recommend for everybody. Should we set it at the mean (45 units in Figure 2-2)? Th is is the Estimated Average Requirement (EAR) for nu- trient X, mentioned earlier as valuable to scientists but not appropriate as an in- dividual’s nutrient goal. Th e EAR value is probably close to everyone’s minimum need, assuming the distribution shown in Figure 2-2. (Actually, the data for most nutrients indicate a distribution that is much less symmetrical.) But if people took us literally and consumed exactly this amount of nutrient X each day, half the popu- lation would begin to develop internal defi ciencies and possibly even observable symptoms of defi ciency diseases. Mr. C (at 57) would be one of those people.

Perhaps we should set the recommendation for nutrient X at or above the ex- treme, say, at 70 units a day, so that everyone will be covered. (Actually, we didn’t study everyone, and some individual we didn’t happen to test might have an even higher requirement.) Th is might be a good idea in theory, but what about a person like Mr. B who requires only 35 units a day? Th e recommendation would be twice his requirement and to follow it he might spend money needlessly on foods contain- ing nutrient X to the exclusion of foods containing other vital nutrients.

The Decision Th e decision we fi nally make is to set the value high enough so that 97 to 98 percent of the population will be covered but not so high as to be excessive (Figure 2-3 illustrates such a value). In this example, a reasonable choice might be 63 units a day. Moving the DRI further toward the extreme would pick up a few additional people, but it would infl ate the recommendation for most people, includ- ing Mr. A and Mr. B. Th e committee makes judgments of this kind when setting the DRI recommended intakes for many nutrients. Relatively few healthy people have requirements that are not covered by the DRI recommended intakes.

KE Y POINT The DRI are based on scientifi c data and are designed to cover the needs of virtually all healthy people in the United States and Canada.

Setting Energy Requirements In contrast to the recommendations for nutrients, the value set for energy, the Esti- mated Energy Requirement (EER), is not generous; instead, it is set at a level pre- dicted to maintain body weight for an individual of a particular age, gender, height, weight, and physical activity level consistent with good health. Th e energy DRI val- ues refl ect a balancing act: enough food energy is critical to support health and life, but too much energy causes unhealthy weight gain. Because even small amounts of excess energy consumed day after day cause weight gain and associated diseases, the DRI committee did not set a Tolerable Upper Intake Level for energy.

People don’t eat energy directly. Th ey derive energy from foods containing car- bohydrate, fat, and protein, each in proportion to the others. Th e Acceptable Ma- cronutrient Distribution Ranges, listed earlier, are designed to provide a healthy balance among these nutrients and minimize a person’s risk of chronic diseases. Th ese ranges resurface in later chapters of this book wherever intakes of the energy- yielding nutrients are discussed with regard to chronic disease risks.

KE Y POINT Estimated Energy Requirements are energy-intake recommendations predicted to maintain body weight and to discourage unhealthy weight gain.

Why Are Daily Values Used on Labels? Most careful diet planners are already familiar with the Daily Values because they appear on U.S. food labels. After learning about the DRI, you may wonder why yet

N u m

b e r

o f p

e o p

Daily requirement for nutrient X (units/day)

30 40 50 60 70

A B

Estimated Average Requirement (EAR)

Each square represents a person. A, B, and C are Mr. A, Mr. B, and Mr. C. Each has a different requirement.

Individuality

of Nutrient

Requirements

figure 2-2

N u

m b

e r

o f

p e

o p

Vitamins and Minerals

Recommended intake (RDA)EAR

Daily requirement for nutrient X (units/day)

30 40 50 60 70

aEstimated Average Requirement

Intake recommendations for most vita- mins and minerals are set so that they will meet the requirements of nearly all people (boxes represent people).

Nutrient

Recommended

Intake: RDA

Example

figure 2-3

The DRI Estimated Energy Requirements • (EER) are found on the inside front cover, page A.

35D i e t a r y G u i d e l i n e s f o r A m e r i c a n s

another set of nutrient standards is needed for food labels. One answer is that while DRI values vary from group to group, values appearing on food labels must apply to the “average” person—someone eating 2,000 to 2,500 calories a day.

While the Daily Values are ideal for allowing comparisons among foods, they cannot serve as nutrient intake goals for individuals. Th e Daily Values are set at the highest nutrient needs among all people, from children of age 4 through aging adults; for example, the Daily Value for iron, 18 mg, an amount that far exceeds a man’s RDA of 8 mg (but that meets a young woman’s high need precisely). Also, DRI values have changed over the years as new data emerged; the Daily Values have remained static. Using the Daily Values appropriately is a topic of this chap- ter’s Consumer Corner.

KE Y POINT The Daily Values are standards used only on food labels to enable consumers to compare the nutrient values among foods.

LO 2.2

Dietary Guidelines for Americans Many countries set forth dietary guidelines, striving to answer the question asked by their citizens, “What should I eat to stay healthy?” Th e guidelines and nutri- ent standards are related: if everyone followed the guidelines for individuals, most people’s nutrient needs would fall into place.

The Guidelines Promote Health Th e U.S. Department of Agriculture’s Dietary Guidelines for Americans (listed in Figure 2-4) off er science-based advice to pro- mote health and to reduce risk of major chronic diseases through diet and physi- cal activity.4 People who balance their energy (calorie) intakes with expenditures, consume diets that meet nutrient recommendations, and engage in regular physical activity most often enjoy optimum health. Th e Dietary Guidelines apply to most healthy people age 2 years or older.

Choose Nutritious Foods and Limit Some Food Components A major rec- ommendation of the Dietary Guidelines for Americans is to choose a healthy diet based on the diet-planning guide, the USDA Food Guide, explained next. To meet its recommendations, most U.S. consumers need to limit calorie intakes and ob- tain more and varied selections among fruits, vegetables, whole grains, and nonfat or low-fat milk or milk products (for reasons that will become clear as you move through this book). A basic premise of both the Dietary Guidelines and of this book is that foods, not supplements, should provide the needed nutrients whenever possible.

Another focus of the Dietary Guidelines is on limiting potentially harmful dietary constituents. A healthful diet is carefully chosen to supply the kinds of carbohy- drates that the body needs, but little sugar, and to off er the needed fats and oils while limiting saturated fat, trans fat, and cholesterol (Chapters 4 and 5 explain these distinctions). People are also asked to consume less salt and to choose sensibly if they use alcohol. Finally, foods should be kept safe from spoilage or contamina- tion (see Chapter 12).

Notice that the Dietary Guidelines do not require that you give up your favorite foods or eat strange, unappealing foods. With a little planning and a few adjust- ments, almost anyone’s diet can approach these recommendations. As for physical activity, this chapter’s Th ink Fitness box spells out some guidelines.

Canada’s Guidelines Canadian Guidelines also recommend many of the same ideals. Canadian readers can fi nd Canada’s 2007 food group plan, Eating Well with Canada’s Food Guide, in Appendix B.

Agencies that put forth nutrient recommen-• dations for the world’s people include the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) of the United Nations.

G et

ty Im

ag es

The Dietary Guidelines recommend that physical activity balance food intake.

Estimated Energy Requirement (EER) the average dietary energy intake predicted to maintain energy balance in a healthy adult of a certain age, gender, weight, height, and level of physical activity consistent with good health.

The Daily Values are found on the inside • back cover, page Y.

36 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

The U.S. Diet and Dietary Guidelines Compared To assess how well a diet meets the Dietary Guidelines and the USDA Food Guide (described next), researchers use the Healthy Eating Index (HEI).5 Th e HEI allows comparison between the recommendations and various aspects of a diet and yields a score. For example, a diet that provides enough grain foods with at least half from whole grains scores 10 out of 10 possible points for the category. A diet with no grains scores a 0 for grains. For diet components that must be limited, such as saturated fat, lower intakes earn higher HEI scores. Th e current American diet scores only 58 out of 100 possible points, and most people’s diets show room for improvement.6

As a nation, Americans eat too few of the foods that supply certain key nutrients (listed in the margin on the next page) and too many that are rich in calories and fats. For most people, then, meeting the diet ideals of the Dietary Guidelines re- quires choosing more of these foods:

Vegetables (especially dark green vegetables, orange vegetables, and legumes).•

Fruits.•

Whole grains.•

Fat-free or low-fat milk and milk products.•

And choosing less of these:

Consume a variety of nutrient-dense foods and beverages within and among the basic food groups; limit intakes of saturated and trans fats, cholesterol, added sugars, salt, and alcohol. Meet recommended intakes within energy needs by adopting a balanced eating pattern, such as the USDA Food Guide (explained in a later section).

•

ADEQUATE NUTRIENTS WITHIN ENERGY NEEDS

To maintain body weight in a healthy range, balance calories from foods and beverages with calories expended (Chapter 9). To prevent gradual weight gain over time, make small decreases in food and beverage calories and increase physical activity.

•

WEIGHT MANAGEMENT

Engage in regular physical activity and reduce sedentary activities to promote health, psychological well-being, and a healthy body weight (Chapter 10). Achieve physical fitness by including cardiovascular conditioning, stretching exercises for flexibility, and resistance exercises or calisthenics for muscle strength and endurance.

•

PHYSICAL ACTIVITY

Consume a sufficient amount of fruits, vegetables, milk and milk products, and whole grains while staying within energy needs. Select a variety of fruits each day. Include vegetables from all five subgroups (dark green, orange, legumes, starchy vegetables, and other vegetables) several times a week. Make at least half of the grain selections whole grains. Select fat-free or low-fat milk products.

•

FOOD GROUPS TO ENCOURAGE

Keep saturated fat, trans fat, and cholesterol consumption low—less than 10 percent of calories from saturated and trans fats and less than 300 milligrams of cholesterol per day (Chapter 5). Keep total fat intake between 20 to 35 percent of calories, mostly from foods that provide unsaturated fats, such as fish, nuts, olives, and vegetable oils. Select and prepare foods that are lean, low-fat, or fat-free.

•

FATS

Choose fiber-rich fruits, vegetables, and whole grains often (Chapter 4). Choose and prepare foods and beverages with little added sugars. Reduce the incidence of dental caries by practicing good oral hygiene and consuming sugar- and starch-containing foods and beverages less frequently.

•

CARBOHYDRATES

Choose and prepare foods with little salt (less than 2,300 milligrams sodium, or approximately 1 tsp salt). At the same time, consume potassium-rich foods, such as fruits and vegetables (Chapter 8).

SODIUM AND POTASSIUM

•

Those who choose to drink alcoholic beverages should do so sensibly and in moderation. Some individuals should not consume alcoholic beverages (Controversy 3).

ALCOHOLIC BEVERAGES

To avoid microbial foodborne illness, keep foods safe: clean hands, food contact surfaces, and fruits and vegetables; separate raw, cooked, and ready-to-eat foods; cook foods to a safe internal temperature; chill perishable food promptly; and defrost food properly (Chapter 12).

FOOD SAFETY

These Guidelines apply to all healthy people over 2 years of age.

Dietary Guidelines for Americans—Key Recommendations figure 2-4

Healthy Eating Index (HEI) a mea- sure that assesses how well a diet meets the recommendations of the Dietary Guidelines for Americans and MyPyramid.

37D i e t P l a n n i n g w i t h t h e U S D A F o o d G u i d e

Refi ned grains.•

Total fats (especially saturated fat, • trans fat, and cholesterol).

Added sugars.•

Salt.•

In addition, many people should reduce total calorie intakes. Th e diet planner can achieve these ideals with the help of the USDA Food Guide.

Our Two Cents’ Worth If the experts who develop the Dietary Guidelines were to ask us, we would add one more recommendation to their lists: take time to enjoy and savor your food. Th e joys of eating are physically benefi cial to the body because they trigger health-promoting changes in the nervous, hormonal, and immune sys- tems. When the food is nutritious as well as enjoyable, then the eater obtains all the nutrients needed for healthy body systems, as well as for the healthy skin, glossy hair, and natural attractiveness that accompany robust health. Remember to enjoy your food.

KE Y POINT The Dietary Guidelines for Americans, Nutrition Recommendations for Canadians, and other such standards address the problems of undernutrition and overnutrition. To implement them requires exercising regularly, following the USDA Food Guide, seeking out vegetables, fruits, whole grains, and low- fat milk while limiting intakes of saturated and trans fats, sugar, and salt, and moderating alcohol intake.

LO 2.3, 2.4

Diet Planning with the USDA Food Guide Diet planning connects nutrition theory with the food on the table, and a few min- utes invested in meal planning can pay off in better nutrition. To help people achieve the goals set forth by the Dietary Guidelines for Americans 2005, the USDA provides a food group plan—the USDA Food Guide.9 Figure 2-5 displays this plan. By

Did You Know? The key nutrients most often lacking in the U.S. diet are:

Fiber.•

Vitamin A.•

Vitamin C.•

Vitamin E.•

Calcium.•

Magnesium.•

Potassium. •

think fitness Recommendations for Daily Physical Activity

The 2008 Physical Activity Guide- lines for Americans set by the USDA and the Department of Health and Human Services sug- gest that to maintain good health, adults should engage in about 2½ hours of moderate physical activ- ity each week.7 A brisk walk at a pace of about 100 steps per min-

ute (1,000 steps over 10 minutes) constitutes “moderate” activity.8 In addition:

Physical activity can be intermit-• tent, 10 minutes here and there, throughout the week.

Resistance activity (such as • weight-lifting) can be included as

part of the exercise total for the week.

For weight control and additional health benefit, more than the mini- mum amount of physical activity is required. Details are found in Chapter 10.

START NOW

Ready to make a change? Consult the online behavior-change planner to plan how you might obtain the recommended 30 minutes of daily physical activity at www.cengage .com/sso.

food group plan a diet-planning tool that sorts foods into groups based on their nutrient content and then specifi es that people should eat certain minimum numbers of servings of foods from each group.

http://www.cengage

38 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

Key:

Foods lower in nutrient density (limit selections)

Foods generally high in nutrient density (choose most often)

Consume a variety of fruits and no more than one-half of the recommended intake as fruit juice.

These foods contribute folate, vitamin A, vitamin C, potassium, and fiber.

1 c fruit is equivalent to 1 c fresh, frozen, or canned fruit; 1⁄2 c dried fruit; 1 c fruit juice..

Apples, apricots, avocados, bananas, blueberries, cantaloupe, cherries, grapefruit, grapes, guava, kiwi, mango, nectarines, oranges, papaya, peaches, pears, pineapples, plums, raspberries, strawberries, tangerines, watermelon; dried fruit (dates, figs, raisins); unsweetened juices.

Canned or frozen fruit in syrup; juices, punches, and fruit drinks with added sugars; fried plantains.

FRUITS

Make at least half of the grain selections whole grains.

These foods contribute folate, niacin, riboflavin, thiamin, iron, magnesium, selenium, and fiber.

1 oz grains is equivalent to 1 slice bread; 1⁄2 c cooked rice, pasta, or cereal; 1 oz dry pasta or rice; 1 c ready-to-eat cereal; 3 c popped popcorn.

Whole grains (amaranth, barley, brown rice, buckwheat, bulgur, millet, oats, quinoa, rye, wheat) and whole-grain, low-fat breads, cereals, crackers, and pastas; popcorn. Enriched bagels, breads, cereals, pastas (couscous, macaroni, spaghetti), pretzels, rice, rolls, tortillas. Biscuits, cakes, cookies, cornbread, crackers, croissants, doughnuts, french toast, fried rice, granola, muffins, pancakes, pastries, pies, presweetened cereals, taco shells, waffles.

GRAINS

Choose a variety of vegetables each day, and choose from all five subgroups several times a week.

These foods contribute folate, vitamin A, vitamin C, vitamin K, vitamin E, magnesium, potassium, and fiber.

1 c vegetables is equivalent to 1 c cut-up raw or cooked vegetables; 1 c cooked legumes; 1 c vegetable juice; 2 c raw, leafy greens.

Vegetable subgroups 1. Dark green vegetables: Broccoli and leafy greens such as arugula, beet greens,

bok choy, collard greens, kale, mustard greens, romaine lettuce, spinach, and turnip greens.

2. Orange and deep yellow vegetables: Carrots, carrot juice, pumpkin, sweet

potatoes, and winter squash (acorn, butternut). 3. Legumes: Black beans, black-eyed peas, garbanzo beans (chickpeas), kidney

beans, lentils, navy beans, pinto beans, soybeans and soy products such as tofu, and split peas. 4. Starchy vegetables: Cassava, corn, green peas, hominy, lima beans, and potatoes. 5. Other vegetables: Artichokes, asparagus, bamboo shoots, bean sprouts, beets,

brussels sprouts, cabbages, cactus, cauliflower, celery, cucumbers, eggplant, green beans, iceberg lettuce, mushrooms, okra, onions, peppers, seaweed,

snow peas, tomatoes, vegetable juices, zucchini.

Baked beans, candied sweet potatoes, coleslaw, french fries, potato salad, refried beans, scalloped potatoes, tempura vegetables.

VEGETABLES

USDA MyPyramid Food Guide figure 2-5

39D i e t P l a n n i n g w i t h t h e U S D A F o o d G u i d e

Select the recommended amounts of oils from among these sources.

These foods contribute vitamin E and essential fatty acids (see Chapter 5), along with abundant calories. 1 tsp oil is equivalent to 1 tbs low-fat mayonnaise; 2 tbs light salad dressing; 1 tsp vegetable oil; 1 tsp soft margarine.

Liquid vegetable oils such as canola, corn, flaxseed, nut, olive, peanut, safflower, sesame, soybean, and sunflower oils; mayonnaise, oil-based salad dressing, soft trans-free margarine.

Unsaturated oils that occur naturally in foods such as avocados, fatty fish, nuts, olives, seeds (flaxseeds, sesame seeds), and shellfish.

Limit intakes of food and beverages with solid fats and added sugars.

Solid fats deliver saturated fat and trans fat, and intake should be kept low. Solid fats and added sugars contribute abundant calories but few nutrients, and intakes should not exceed the discretionary calorie allowance—calories to meet energy needs after all nutrient needs have been met with nutrient-dense foods. Alcohol also contributes abundant calories but few nutrients, and its calories are counted among discretionary calories. See Table 2-2 on page 44 for some discretionary calorie allowances.

Solid fats that occur in foods naturally such as milk fat and meat fat (see in previous lists).

Solid fats that are often added to foods such as butter, cream cheese, hard margarine, lard, sour cream, and shortening.

Added sugars such as brown sugar, candy, honey, jelly, molasses, soft drinks, sugar, and syrup.

Alcoholic beverages include beer, wine, and liquor.

OILS

SOLID FATS AND ADDED SUGARS

Make lean or low-fat choices. Prepare them with little, or no, added fat.

Meat, poultry, fish, and eggs contribute protein, niacin, thiamin, vitamin B6, vitamin B12, iron, magnesium, potassium, and zinc; legumes and nuts are notable for their protein, folate, thiamin, vitamin E, iron, magnesium, potassium, zinc, and fiber. 1 oz meat is equivalent to 1 oz cooked lean meat, poultry, or fish; 1 egg; 1⁄4 c cooked legumes or tofu; 1 tbs peanut butter; 1⁄2 oz nuts or seeds.

Poultry (no skin), fish, shellfish, legumes, eggs, lean meat (fat-trimmed beef, game, ham, lamb, pork); low-fat tofu, tempeh, peanut butter, nuts (almonds, filberts, peanuts, pistachios, walnuts) or seeds (flaxseeds, pumpkin seeds, sunflower seeds).

Bacon; baked beans; fried meat, fish, poultry, eggs, or tofu; refried beans; ground beef; hot dogs; luncheon meats; marbled steaks; poultry with skin; sausages; spare ribs.

MEAT, POULTRY, FISH, LEGUMES, EGGS, AND NUTS

Make fat-free or low-fat choices. Choose lactose-free products or other calcium-rich foods if you don’t consume milk.

These foods contribute protein, riboflavin, vitamin B12, calcium, magnesium, potassium, and, when fortified, vitamin A and vitamin D. 1 c milk is equivalent to 1 c fat-free milk or yogurt; 11⁄2 oz fat-free natural cheese; 2 oz fat-free processed cheese.

Fat-free milk and fat-free milk products such as buttermilk, cheeses, cottage cheese, yogurt; fat-free fortified soy milk.

1% low-fat milk, 2% reduced-fat milk, and whole milk; low-fat, reduced-fat, and whole-milk products such as cheeses, cottage cheese, and yogurt; milk products with added sugars such as chocolate milk, custard, ice cream, ice milk, milk shakes, pudding, sherbet; fortified soy milk.

MILK, YOGURT, AND CHEESE

Matthew Farruggio

USDA MyPyramid Food Guide (continued) figure 2-5

40 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

using it wisely and by learning about the energy-yielding nutrients, vitamins, and minerals in various foods (as you will in coming chapters), you can achieve the goals of a nutritious diet fi rst mentioned in Chapter 1: adequacy, balance, calorie control, moderation, and variety.

If you design your diet around this plan, it is assumed that you will obtain ad- equate and balanced amounts not only of the nutrients of greatest concern but also of the two dozen or so other essential nutrients as well as benefi cial phytochemicals because all of these are distributed among the same food groups. It can also help you to limit potentially harmful dietary constituents and calories.

A diff erent kind of planning tool, the exchange system (see Appendix D), was developed for use by those with diabetes. Th e exchange system focuses on control- ling the carbohydrate, fat, protein, and energy (calories) in the diet. Canada’s Be-

yond the Basics, a similar planning system, is presented in Appendix B.

The Food Groups and Subgroups Figure 2-5 defi nes the major food groups and their subgroups and specifi es por- tions of various foods that are considered equivalents in each group. It also lists the key nutrients provided by foods within each group, information worth noting and remembering. Note also that the fi gure sorts foods within each group by nutrient density (as the key to Figure 2-5 explains).

Key Nutrients in Vegetable Subgroups Th e foods in each group are well-known contributors of the key nutrients listed (but you can count on these foods to supply many other nutrients as well). Vegetables, for example, are sorted into subgroups according to their nutrient contents. All vegetables provide valuable fi ber and the mineral potassium, but the vegetables of each subgroup reliably provide a key nutri- ent as well, such as vitamin A from the “orange and deep yellow vegetables,” the vi- tamin folate from the “dark green vegetables,” abundant carbohydrate energy from the “starchy vegetables,” and iron and protein from “legumes.” Many of the same nutrients but few calories come from “other vegetables.”

Grains and Others Among the grains, whole grains supply nutrients and fi ber lacking from refi ned grains. Th e Food Guide suggests that at least half of the grains in a day’s meals be whole grains, or at least three 1-ounce equivalents of whole grains each day.10

Spices, herbs, coff ee, tea, and diet soft drinks, excluded from the USDA Food Guide, provide few if any nutrients but can add fl avor and pleasure to meals. Th ey can also provide some potentially benefi cial phytochemicals, such as those in tea or certain spices—see this chapter’s Controversy section.

Variety Among and Within the Food Groups Varying your food choices, both among the food groups and within each group, helps to ensure adequate nutrients and also protects against large amounts of toxins or contaminants from any one source, as Chapter 1 made clear. 11 Achieving variety may require some eff ort but knowing the food groups eases the task. Figure 2-6 demonstrates that people in the United States choose too few servings of vegetables, fruits, and milk, and too many of refi ned grains and meats. For health’s sake, U.S. citizens are urged to more closely follow the Food Guide recommendations.

KE Y POINT The USDA Food Guide divides foods into food groups based on key nutrient contents. People who consume the specifi ed amounts of foods from each group achieve dietary adequacy, balance, and variety. Most U.S. diets fail to achieve these amounts.

The Discretionary Calorie Concept To help people control calories to prevent excess weight gain, the USDA devel- oped the concept of the discretionary calorie allowance. Th e concept can also help people to moderate intakes of certain fats and added sugars.

CONCEPT LINK 2-1 The A, B, C, M, V principles were explained in Chapter 1, pages 10–11.

Another eating plan, the DASH eating plan • of Chapter 11, also meets the goals of the Dietary Guidelines for Americans 2005.

CONCEPT LINK 2-2 Phytochemicals and their potential biological actions are explained in Controversy 2.

Legumes were defined in Chapter 1 as dried • beans, peas, and lentils.

exchange system a diet-planning tool that organizes foods with respect to their nutri- ent content and calories. Foods on any single exchange list can be used interchangeably. See the U.S. Exchange System, Appendix D (or Appendix B for Canada), for details.

discretionary calorie allowance the balance of calories remaining in a person’s energy allowance after accounting for the number of calories needed to meet recom- mended nutrient intakes through consumption of nutrient-dense foods.

41D i e t P l a n n i n g w i t h t h e U S D A F o o d G u i d e

Discretionary Calorie Demonstration As Figure 2-7 demonstrates, a person needing 2,000 calories of energy in a day to maintain weight may need only 1,700 calories or so of the most nutrient-dense foods to supply the nutrients required for

Meat and beansVegetables Fruits MilkGrainsa

140

120

100

USDA Food Groups

P e rc

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W ho

R efi

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R efi

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Key: Recommended Intakes

Actual U.S. Intakes

aAt least half of the grain selections should be whole grains.

How Does the U.S. Diet Stack Up? figure 2-6

Energy (calorie) intake required to meet nutrient needs

Discretionary calorie allowance

Energy (calorie) allowance required to maintain weight

500

1000

1500 1,733

267

2000

C a lo

ri e s

A well-chosen diet may leave room in the calorie budget for some discretionary calories. Additional servings of nutritious foods, some fats, or added sugars may be chosen to supply them.

Discretionary Calorie Allowance

in a 2,000-Calorie Diet

figure 2-7

4 2 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

the day. Th e diff erence between the calories needed to maintain weight and those needed to supply nutrients from the most nutrient-dense foods is the person’s dis- cretionary calorie allowance (in this case, 267 calories).

Physically active people use greater numbers of calories each day than do seden- tary people, a fact refl ected in their greater discretionary calorie allowances. People who need fewer calories to maintain their weight have fewer discretionary calories to spend.

Discretionary Calorie Sources A person with a discretionary calorie allowance to spend may choose to do any of the following:

Eat extra servings of the same nutrient-dense foods that make up the base of 1. the diet, for example, an extra piece of skinless chicken, a second ear of corn,

or some added pieces of fruit.

Include some fats from two sources (within the limits recommended for 2. health—see Chapter 5):

Naturally occurring fats, such as the fats in regular hamburger versus lean • hamburger, and in whole milk or reduced-fat milk versus fat-free milk.

Added fats, including solid fats such as butter, hard margarine, lard, and • shortening; or oils in amounts greater than the daily need.

Include some added sugars, such as jams, sugars of sweet baked goods, soft 3. drinks and punches, or honey.

Consume alcohol within limits (some people should 4. not make this choice; read

Controversy 3).

Alternatively, a person wishing to lose weight might choose to omit the dis-5. cretionary calories from the diet. Th is is a safe strategy because discretionary

calories are not essential for delivering needed nutrients to the diet.

Discretionary Calories Versus Calories of Nutritious Foods Discretionary calories are distinguished from the calories of the nutrient-dense foods of which they may be a part. A fried chicken leg, for example, provides discretionary calories from two sources: the naturally occurring fat of the chicken skin and the added fat absorbed during frying. Th e calories of the skinless chicken underneath are not dis- cretionary (unless consumed in excess of need)—they are necessary to provide the nutrients of chicken. Likewise, an oatmeal cookie provides discretionary calories of sugar and shortening, but its oatmeal contributes to the day’s intake of whole grains. Table 2-1 provides additional examples.

Nutrient-Dense Foods To control calories and prevent overweight or obesity, the USDA Food Guide instructs diet planners to choose the most nutrient-dense foods from each group. Unprocessed or lightly processed foods are generally best because some processes strip foods of benefi cial nutrients and fi ber, while others add many calories in the form of sugar or fat. Figure 2-5 identifi ed a few of the most nutrient-dense food selections in each food group and some foods of lower nutrient density to give you an idea of which are which.

Uncooked oil is a notable exception. Oil is pure fat and therefore rich in calories, but a small amount of raw oil from sources such as avocado, olives, nuts, fi sh, or vegetable oil provides vitamin E and other important nutrients that other foods lack. High temperatures used in frying destroy these nutrients, however.

KE Y POINT The USDA Food Guide defi nes discretionary calorie allowances to help people meet their nutrient requirements while controlling calories. It also helps to moderate intakes of potentially harmful saturated fats.

Within calorie limits, small amounts of added • sugars can be enjoyed as part of the discre- tionary calories in a nutrient-dense diet:

3 tsp for 1,600 cal•

5 tsp for 1,800 cal•

8 tsp for 2,000 cal•

9 tsp for 2,200 cal•

12 tsp for 2,400 cal•

CONCEPT LINK 2-3 Nutrient density was explained in Chapter 1, page 20.

Chapter 9 will help you determine your en-• ergy needs. For a quick approximation, find your EER on the inside front cover, page A.

43D i e t P l a n n i n g w i t h t h e U S D A F o o d G u i d e

Notice that foods providing zero discretionary calories are naturally low in fat and have no added fats or sugars. These form the base of the diet in the USDA Food Guide. When choosing foods, pay close attention to portion size. More food means more calo- ries from all sources.

Food Amount Total

Caloriesa Discretionary

Caloriesa

Discretionary Calorie Sources

Milk and Milk Products

Fat-free milk 1 cup 85 0 —

Whole milk 1 cup 145 65 Fat

Low-fat chocolate milk 1 cup 160 75 Fat, sugar

Cheddar cheese 1½ oz 170 90 Fat

Ice cream, vanilla 1 cup 290 205 Fat, sugar

Meat

Extra lean ground beef (95% lean) 3 oz, cooked 165 0 —

Regular ground beef (80% lean) 3 oz, cooked 230 65 Fat

Roast chicken breast (skinless) 3 oz 140 0 —

Fried chicken breast with skin & batter 3 oz 245 105 Fat

Beef bologna 3 slices (1 oz each) 265 100 Fat

Grains

Bread 1 slice (1 oz) 70 0 —

Blueberry muffi n 1 small (2 oz) 185 45 Fat, sugar

Biscuit, plain 1 (2.5˝ diameter) 130 60 Fat

Chocolate chip cookies 2 large 135 70 Fat, sugar

Glazed doughnut, yeast type 1 medium 240 165 Fat, sugar

Vegetables

Potato, boiled or baked 1 (2.5˝ diam) 120 0 —

French fries 1 medium order 460 325 Fat

Onion rings 8 to 9 rings 275 160 Fat

Fruit

Peach slices, fresh 1 cup 60 0 —

Canned peaches, heavy syrup 1 cup 195 135 Sugar

Extras

Diet soda 12 oz 0 0 —

Regular soda 12 oz 155 155 Sugar

Fruit punch 1 cup 115 115 Sugar

Table wine 5 oz 115 115 Alcohol

Beer (regular) 12 oz 145 145 Alcohol

Butter or stick margarine 1 teaspoon 35 35 Fat

Cream cheese 1 tablespoon 50 50 Fat

aEstimated calories

Source: Data from USDA

Examples of Discretionary Calorie Sources table 2-1

This skinless chicken meat, a nutrient-dense food, provides 140 calories.

A cup of plain peaches provides 60 calories of a nutritious food.

The fat in this chicken skin and the oil that soaked into the coating during frying provide over 100 discretion- ary calories.

The added sugars in the heavy canning syrup of these peaches provide 135 discretionary calories.

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4 4 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

Sedentary Women: 51+ Yr

Sedentary Women: 31–50 Yr

Sedentary Women: 19–30 Yr

Active Women: 51+ Yr

Sedentary Men: 51+ Yr

Active Women: 31–50 Yr

Sedentary Men: 31–50 Yr

Active Women: 19–30 Yr

Active Men: 51+ Yr

Sedentary Men: 19–30 Yr

Active Men: 31–50 Yr

Active Men: 19–30 Yr

Caloriesa 1,600 1,800 2,000 2,200 2,400 2,800 3,000

Fruits 1½ c 1½ c 2 c 2 c 2 c 2½ c 2½ c

Vegetablesb 2 c 2½ c 2½ c 3 c 3 c 3½ c 4 c

Grains 5 oz 6 oz 6 oz 7 oz 8 oz 10 oz 10 oz

Meats and legumes 5 oz 5 oz 5½ oz 6 oz 6½ oz 7 oz 7 oz

Milk 3 c 3 c 3 c 3 c 3 c 3 c 3 c

Oilsc 5 tsp 5 tsp 6 tsp 6 tsp 7 tsp 8 tsp 10 tsp

Discretionary calorie allowance 132 cal 195 cal 267 cal 290 cal 362 cal 426 cal 512 cal

Note: In addition to gender, age, and activity levels, energy needs vary with height and weight (see Chapter 9 and Appendix H). aAssumes high nutrient density choices—lean, low-fat, and fat-free with no added sugars. bDivide these amounts among the vegetable subgroups as specifi ed in Table 2-3. cApproximate measures; the gram values are 22, 24, 27, 29, 31, 34, and 36, respectively.

MyPyramid Recommended Daily Intakes from Each Food Group table 2-2

LO 2.5

Diet Planning Application Th e USDA Food Guide specifi es the amounts needed from each food group to create a healthful diet for a given number of calories. Look at the top line of Table 2-2 and fi nd yourself among the people described there (for other calorie levels, see Table E-1 of Appendix E). Th en look at the column of numbers below for amounts from each food group that meet your calorie need. Table 2-2 also specifi es the dis- cretionary calorie allowance for each calorie level. Note that the more energy spent in physical activity in a day, the higher the calorie need and the greater the discre- tionary calorie allowance.

For vegetables, intakes should be divided among all the vegetable subgroups over a week’s time, as shown in Table 2-3. Look across the top row for your calorie level (obtained from Table 2-2)—a healthful diet includes the listed amounts of each type of vegetable each week. It is not necessary to eat vegetables from each subgroup every day.

With judicious selections, the diet can supply all the necessary nutrients and pro- vide some luxury items, as well. A sample diet plan demonstrates how the theory of the USDA Food Guide translates to food on the plate. Th e USDA Food Guide ensures that a certain amount from each of the fi ve food groups is represented in the diet. Th e diet planner begins by assigning each of the food groups to meals and snacks, as shown in Table 2-4. Th en the plan can be fi lled out with real foods to create a menu. For example, the breakfast calls for 1 ounce grains, 1 cup milk, and ½ cup fruit. Here’s one possibility for this meal:

1 cup ready-to-eat cereal = 1 ounce grains.

1 cup fat-free milk = 1 cup milk.

1 medium banana = ½ cup fruit.

45D i e t P l a n n i n g A p p l i c a t i o n

Th en the planner moves on to complete the menu for lunch, supper, and snacks, as shown in Figure 2-8. Th is day’s choices are explored further as “Monday’s Meals” in the Food Feature at the end of the chapter.

KE Y POINT Food patterns for calorie levels can guide food choices in diet planning. Some discretionary calories often fi t into the diet.

MyPyramid: Steps to a Healthier You For consumers with Internet access, the USDA’s MyPyramid online educational tool makes applying the Food Guide easier. Figure 2-9 explains its graphic image. MyPyramid guides users through diet planning to create a diet that more closely meets the ideals of the USDA Food Guide and the recommendations of the Dietary

Guidelines for Americans.

Table 2-2 specifi es the recommended amounts (in cups) of total vegetables per day. This table shows those amounts dispersed among fi ve vegetable subgroups per week.

Vegetable Subgroups 1,600 cal 1,800 cal 2,000 cal 2,200 cal 2,400 cal 2,600 cal 2,800 cal 3,000 cal

Dark green 2 c 3 c 3 c 3 c 3 c 3 c 3 c 3 c

Orange and deep yellow 1½ c 2 c 2 c 2 c 2 c 2½ c 2½ c 2½ c

Legumes 2½ c 3 c 3 c 3 c 3 c 3½ c 3½ c 3½ c

Starchy 2½ c 3 c 3 c 6 c 6 c 7 c 7 c 9 c

Other 5½ c 6½ c 6½ c 7 c 7 c 8½ c 8½ c 10 c

Weekly Amounts from Vegetable Subgroups table 2-3

This diet plan is one of many possibilities for a day’s meals. It follows the amounts suggested for a 2,000-calorie diet (with an extra ½ cup of vegetables).

Food Group

Recommended MyPyramid Amounts Breakfast Lunch Snack Dinner Snack

Fruits 2 c ½ c ½ c 1 c

Vegetables 2½ c 1 c 2 c

Grains 6 oz 1 oz 2 oz ½ oz 2 oz ½ oz

Meat and legumes 5½ oz 2 oz 3½ oz

Milk 3 c 1 c 1 c 1 c

Oils 5½ tsp 1½ tsp 4 tsp

Discretionary calorie allowance 267 cal

Sample Diet Plan table 2-4

46 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

For many, the dietary changes required to do so may seem daunting or even insur- mountable, and taken all at once they may be. However, small steps taken each day can add up to substantial dietary changes over time. If everyone would begin, today, to take such steps, the rewards in terms of less heart disease, less cancer, greater quality of life, and better overall health would prove well worth their eff ort.

Computer-savvy consumers will also fi nd an abundance of MyPyramid support material and diet assessment tools on the Internet (www.MyPyramid.gov). Th ose without computer access can achieve the MyPyramid goals by following the USDA Food Guide principles and working with pencil and paper, as illustrated later.

KE Y POINT The concepts of the USDA Food Guide are conveyed to consumers through the MyPyramid educational tool.

Flexibility of the USDA Food Guide Although it may appear rigid, the USDA Food Guide can actually be very fl exible once its intent is understood. For example, the user can substitute fat-free yogurt for fat-free milk because both supply the key nutrients for the milk, yogurt, and cheese group. Legumes provide many of the nutrients of the meat group, but they also con- stitute a vegetable subgroup, so legumes in a meal can count as a serving of meat or of vegetables. Consumers can adapt the plan to mixed dishes such as casseroles and to national and cultural foods as well, as Figure 2-10 demonstrates.

Note: This plan meets the recommendations to provide 45 to 65 percent of calories from carbohydrate, 20 to 35 percent from fat, and 10 to 35 percent from protein.

1 oz whole grains 1 c milk 1/2 c fruit

2 oz meats, 2 oz whole grains 11/2 tsp oils 1 c vegetables

1 c whole-grain cereal 1 c fat-free milk 1 medium banana (sliced)

108 100 105

272 71 50

86 74 72

8 11 71 76

425

22 67 49

90 100

1 turkey sandwich on whole-wheat roll 11/2 tbs low-fat mayonnaise 1 c vegetable juice

1/2 oz whole grains 1 c milk 1/2 c fruit

4 whole-wheat reduced-fat crackers 11/2 oz low-fat cheddar cheese 1 medium apple

1/2 c vegetables 1/4 c vegetables 1 oz meats 2 tsp oils

1 c raw spinach leaves 1/4 c shredded carrots 1/4 c garbanzo beans 2 tbs oil-based salad dressing and olives

3/4 c vegetables, 21/2 oz meat, 2 oz enriched grains 1/2 c vegetables 2 tsp oils 1 c fruit

Spaghetti with meat and tomato sauce 1/2 c green beans 2 tsp soft margarine 1 c strawberries

1/2 oz whole grains 1 c milk

3 graham crackers 1 c fat-free milk

BREAKFAST

Amounts Sample Menu Energy (Cal)

LUNCH

SNACK

DINNER

SNACK

This sample menu provides about 1,850 calories of the 2,000-calorie plan. About 150 discretionary calories remain available to spend on more nutrient-dense foods or luxuries such as added sugars and fats.

A Sample Menu figure 2-8

To make a start at changing your own diet, • use the Diet Analysis Plus program on this textbook’s website to work through the questions at the end of the Food Feature section on page 59.

http://www.MyPyramid.gov

47D i e t P l a n n i n g A p p l i c a t i o n

Th e USDA Food Guide can help vegetarians in making their food choices, too. Th e food group that includes the meats also includes legumes, nuts, seeds, and products made from soybeans. In the food group that includes milk, soy drinks and soy milk (beverages made from soybeans) can fi ll the same nutrient needs, pro- vided that they are fortifi ed with calcium, ribofl avin, vitamin A, vitamin D, and vitamin B12. Th us, for all sorts of careful diet planners, the USDA Food Guide provides a general road map for designing a healthful diet.

OILSVEGETABLES FRUITS MILK MEAT & BEANSGRAINS

A person climbing steps reminds consumers to be physically active each day.

The narrow slivers of color at the top imply moderation in foods rich in solid fats and added sugars.

The wide bottom represents nutrient-dense foods that should make up the bulk of the diet.

The multiple colors of the pyramid illustrate variety: each color represents one of the five food groups, plus one for oils. Different widths of colors suggest the proportional contribution of each food group to a healthy diet.

Greater intakes of grains, vegetables, fruits, and milk are encouraged by the width of orange, green, red, and blue, respectively.

The name, slogan, and website present a personalized approach.

MyPyramid: Steps to a Healthier You figure 2-9

Right Size—Supersize?

Do you often overeat when you eat out? Listen to two students talk about making healthy choices in restaurants.

To hear their stories, log on to www.cengage.com/sso.

my turn

Chris Stephanie

en ga

ge L

ea rn

in g

en ga

ge L

ea rn

in g

http://www.cengage.com/sso

48 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

KE Y POINT The USDA Food Guide can be used with fl exibility by people with diff erent eating styles.

Portion Control To control calories, the diet planner must learn to control food portions. It’s of- ten hard to judge portion sizes, though. Restaurants may deliver colossal helpings to ensure repeat business; a server on a cafeteria line may be instructed to deliver “about a spoonful”; fast-food burgers range from a 1-ounce mini-sized burger to a ¾-pound triple deluxe. What amount is right to choose?

Colossal Cuisine In the United States, the trend has been toward consuming larger and larger food portions, especially of foods rich in fat and sugar (see Figure 2-11). At the same time, body weights have been creeping upward, suggesting an increasing need for portion control. Consumers need more helpful guidance about portion sizes, and the margin note off ers some notable comparisons among portion sizes and everyday objects.

Tips on Weights and Measures Among volumetric measures, 1 “cup” refers to an 8-ounce measuring cup (not a teacup or drinking glass) fi lled to level (not heaped up, or shaken, or pressed down). Tablespoons and teaspoons refer to mea- suring spoons (not fl atware), fi lled to level (not rounded or heaping). Ounces signify weight, not volume. Two ounces of meat, for example, refers to ⅛ of a pound of cooked meat. One ounce (weight) of crispy rice cereal measures a full cup (volume), but take care: 1 ounce of granola cereal measures only ¼ cup.

Also, some foods are specifi ed as “medium,” as in “one medium apple,” but the word medium means diff erent things to diff erent people. When college students are asked to bring medium-sized foods to class, they reliably bring bagels weighing from 2 to 5 ounces, muffi ns from about 2 to 8 ounces, baked potatoes from 4 to 9 ounces, and so forth. Th e Table of Food Composition, Appendix A, can help in determining serving sizes because it lists both weights and volumes of a wide variety of foods.

Grains Asian

Vegetables Fruits Meats and Legumes Milk

Pita pocket

bread, pastas,

rice, couscous,

polenta, bulgur,

focaccia, Italian

bread

Eggplant,

tomatoes,

peppers,

cucumbers,

grape leaves

Olives,

grapes,

figs

Ricotta,

provolone,

parmesan,

feta,

mozzarella,

and goat

cheeses;

yogurt

Fish and other seafood,

gyros, lamb, chicken,

beef, pork, sausage,

lentils, fava beans

Tortillas (corn

or flour),

taco shells,

rice

Chayote, corn,

jicama, tomato

salsa, cactus,

cassava,

tomatoes,

yams, chilies

Guava,

mango,

papaya,

avocado,

plantain,

bananas,

oranges

Cheese,

custard

Refried beans, fish,

chicken, chorizo, beef,

eggs

Mediterranean

Mexican

Rice, white or

rice noodles,

millet, wheat or

rice wrappers

and crepes

Amaranth, baby

corn, bamboo

shoots, chayote,

bok choy, mung

bean sprouts,

snow peas,

mushrooms, water

chestnuts, kelp

Carambola,

guava,

kumquat,

lychee,

persimmon,

melons,

mandarin

orange

Soy milkSoybeans and soy

products such as miso

and tofu, squid, duck

eggs, pork, poultry, fish

and other seafood,

peanuts, cashews

ec ky

L ui

ga rt-

St ay

ne r/

Co rb

is Ph

ot od

is c/

Ge tty

Im ag

es M

itc h

Hr dl

ic ka

/P ho

to di

sc /

Ge tty

Im ag

es Ethnic Food Choices

figure 2-10

Vegetarians will find more tips for choosing • the right foods to supply the nutrients they need in the chapters to come.

To estimate the size of food portions, re-• member these common objects:

3 ounces of meat = the size of the palm of •

a woman’s hand or a deck of cards.

1 medium piece of fruit or potato = the •

size of a regular (60-watt) lightbulb.

1½ ounces cheese = the size of a 9-volt •

battery.

1 ounce lunch meat or cheese = 1 slice.•

1 pat (1 tsp) butter or margarine = a •

slice from a quarter-pound stick of butter

about as thick as 280 pages of this book

(pressed together).

Did You Know? You can use an ice cream scoop to serve mashed potatoes, pasta, vegetables, rice, ce- reals, or other foods. Most scoops hold ¼ cup. Test the size of your scoop—fi ll it with water and pour the water into a measuring cup.

49D i e t P l a n n i n g A p p l i c a t i o n

KE Y POINT People wishing to avoid overconsuming calories must pay attention to the size of their food portions.

A Note About Exchange Systems Exchange systems, defi ned earlier, can be useful to careful diet planners, especially those wishing to control calories (weight watchers), those who must control carbo- hydrate intakes (people with diabetes), and those who should control their intakes of fat and saturated fat (almost everyone). An exchange system, presented in Ap- pendix D (Appendix B for Canada), lists the estimated carbohydrate, fat, saturated fat, and protein contents of food portions, as well as their calorie values. Th e values in the exchange lists diff er from the exacting values given for individual foods in Appendix A because exchange lists estimate values for whole groups of foods. With these estimates, exchange system users can make an informed approximation of the nutrients and calories in almost any food they might encounter.

Th e exchange system also highlights a fact pointed out by the USDA Food Guide: most foods provide more than just one energy nutrient. Meat, for example, is famous for protein, but meats like bacon and sausage deliver many more calories from fat than from protein. A slice of bread provides most of its calories as carbo- hydrate, but biscuits provide many of their calories as fat, and so on. Th is focus on energy-yielding nutrients leads to some unexpected food groupings in the exchange lists. Th e high-fat meats mentioned here and also many cheeses are listed together as “high-fat meats” because fat constitutes the predominant form of energy in these foods, followed by protein. Potatoes and other vegetables high in starch are listed with the breads because one serving of bread and one serving of a starchy vegetable contain about the same amount of carbohydrate. To explore the usefulness of this powerful aid to diet planning, spend some time studying Appendix D (or B).

KE Y POINT Exchange lists facilitate calorie control by providing an understanding of how much carbohydrate, fat, and protein are in each food group.

Cola

French fries Hamburger Bagel Steak Pasta Baked potato Candy bar Popcorn

10 oz bottle, 120 cal

about 30, 475 cal 3–4 oz meat, 330 cal 2–3 oz, 230 cal 8–12 oz, 690 cal 1 c, 200 cal 5–7 oz, 180 cal 11/2 oz, 220 cal 11/2 c, 80 cal

40–60 oz fountain, 580 cal about 50, 790 cal 6–12 oz meat, 1,000 cal 5–7 oz, 550 cal 16–22 oz, 1,260 cal 2–3 c, 600 cal 1 lb, 420 cal 3–4 oz, 580 cal 8–16 c tub, 880 cal

Note: Calories are rounded values for the largest portions in a given range.

Today’s colossalTypical 1970sFood

1970s Today 1970s Today 1970s Today

o n y F

re e m

a n /P

h o to

E d

a tt h e w

F a rr

u g

g io

( b

o th

)

Chapter 9 discusses the consequences of increasing portion sizes in terms of body fatness.

U.S. Trend Toward Colossal Cuisine figure 2-11

at th

ew F

ar ru

gg io

How much does your bagel weigh?

50 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

consumer corner A potato is a potato and needs no label to tell you so. But what can a package of potato chips tell you about its contents? By law, its label must list the chips’ ingre- dients—potatoes, fat, and salt—and its Nutrition Facts panel must also reveal details about their nutrient composition (see Table 2-5). If the oil is high in satu- rated fat, the label will tell you so (more about fats in Chapter 5). A label may also warn consumers of a food’s potential for causing an allergic reaction (Chapter 14 provides details). In addition to required information, labels may make optional statements about the food being deli- cious, or good for you in some way, or a great value. Some of these comments, especially some that are regulated by the Food and Drug Administration (FDA), are reliable. Many others are based on less convincing evidence.

This Consumer Corner introduces food labels and points out the accurate, tested, regulated, and therefore help- ful information that consumers need to make wise food choices. It then turns the spotlight on claims whose purpose is to attract consumer dollars by treading beyond established nutrition science into

the realm of pure marketing. Consumers must acquire some tools for digging out the truth from among the rubble and then hone their skills by comparing actual labels. This Consumer Corner provides the tools; Chapter 5 presents an oppor- tunity to compare some labels, and for those with Internet access, more practice can be gained at the USDA’s Make Your Calories Count website.*

WHAT FOOD LABELS MUST INCLUDE The Nutrition Education and Labeling Act of 1990 set the requirements for certain label information to ensure that food labels truthfully inform consumers about the nutrients and ingredients in the package. This information remains reliable and true today. According to the law, every packaged food must state the following:

The common or usual name of the • product.

The name and address of the manu-• facturer, packer, or distributor.

The net contents in terms of weight, • measure, or count.

The nutrient contents of the product • (Nutrition Facts panel).

Checking Out Food Labels Then the label must list the following in ordinary language:

The ingredients in descending order of • predominance by weight.

Not every package need display infor- mation about every vitamin and mineral. A large package, such as the box of cereal in Figure 2-12, must provide all of the information just listed. A smaller label, such as the label on a can of tuna, provides some of the information in ab- breviated form. A label on a roll of candy rings provides only a phone number, which is allowed for the tiniest labels. The Canadian version of a food label can be found in Appendix B.

The Nutrition Facts Panel Most food packages are required to display a Nutrition Facts panel, like the one shown in Figure 2-12. Grocers also voluntarily post placards or offer handouts in fresh-food departments to provide consumers with similar sorts of nutrition information for the most popular types of fresh fruits, vegetables, meats, poultry, and seafoods.

When you read a Nutrition Facts panel, be aware that only the top portion of the panel conveys information specifi c to the food inside the package. The bottom portion is identical on every label—it stands as a reminder of the Daily Values.

The highlighted items in this section correspond with those of Figure 2-12, which shows the location of the items that follow.

Serving size.• Common household and metric measures to allow comparison of foods within a food category. This amount of food constitutes a single serving and that portion containing the nutrient amounts listed. A serving of chips may be 10 chips, so if you eat 50 chips, you will have consumed fi ve times the nutrient amounts listed on the label. When you compare nutri- ents or calories in two or more brands of the same food, check the serving size—it may differ.

Servings per container.• Number of servings per box, can, package, or other unit.

health claims• claims linking food constituents with disease states; allowable on labels within the criteria established by the Food and Drug Administration. nutrient claims• claims using ap- proved wording to describe the nutri- ent values of foods, such as a claim that a food is “high” in a desirable constituent or “low” in an undesir- able one. Nutrition Facts• on a food label, the panel of nutrition information required to appear on almost every packaged food. Grocers may also provide the information for fresh produce, meats, poultry, and seafoods. structure-function claim• a legal but largely unregulated claim permitted on labels of dietary supplements and conventional foods.

Food Label Terms table 2-5

*USDA’s Make Your Calories Count website is avail- able at www.cfsan.fda.gov/~ear/hwm/hwmintro.html.

av id

Y ou

ng -W

ol ff/

P ho

to E

di t

Food labels provide clues for nutrition sleuths.

http://www.cfsan.fda.gov/~ear/hwm/hwmintro.html

51D i e t P l a n n i n g A p p l i c a t i o n

Calories/calories from fat.• Total food energy per serving and energy from fat per serving.

Nutrient amounts and percentages • of Daily Values. This section provides the core information concerning these nutrients:

Total fat. ◆ Grams of fat per serving with a breakdown showing grams of saturated fat and trans fat per serving.

Cholesterol. ◆ Milligrams of cholesterol per serving.

Sodium. ◆ Milligrams of sodium per serving.

Total carbohydrate. ◆ Grams of carbo- hydrate per serving, including starch, fi ber, and sugars, with a breakdown showing grams of dietary fi ber and sugars. The sugars include those

that occur naturally in the food plus any added during processing.

Protein. ◆ Grams of protein per serving.

In addition, the label must state the contents of these nutrients expressed as percentages of the Daily Values:

Vitamin A.•

Vitamin C.•

Calcium.•

Iron.•

Other nutrients present in signifi cant amounts in the food may also be listed on the label. The percentages of the Daily Values (see the inside front cover, page Y) are given in terms of a 2,000- calorie diet.

Daily Values and calories-per-gram • reminder. This portion lists the Daily

Values for a person needing 2,000 or 2,500 calories a day and provides a calories-per-gram reminder as a handy reference for label readers.

Ingredients List An often neglected but highly valuable body of information is the list of:

Ingredients.• The product’s ingredients must be listed in descending order of predominance by weight.

Knowing how to read an ingredients list puts you many steps ahead of the naïve buyer. Consider the ingredients list on an orange drink powder whose fi rst three entries are “sugar, citric acid, orange fl avor.” You can tell that sugar is the chief ingredient. Now consider a canned juice whose ingredients list begins with “water, orange juice concentrate, pineapple

No Saturated Fat, No Trans Fat and No Cholesterol

Weston Mills, Maple Wood Illinois 00550

Although many factors affect

heart disease, diets low in

saturated fat and cholesterol

may reduce the risk of this disease.

INGREDIENTS, listed in descending order of predominance:

Corn, Sugar, Salt, Malt flavoring, freshness preserved by BHT.

VITAMINS and MINERALS: Vitamin C (Sodium ascorbate),

Niacinamide , Iron, Vitamin B 6 (Pyridoxine hydrochloride),

Vitamin B 2 (Riboflavin), Vitamin A (Palmitate), Vitamin B

(Thiamin hydrochloride), Folic acid, and Vitamin D.

Total Fat 1 g 2%

*Percent Daily Values are based on

a 2000 calorie diet. Your daily

values may be higher or lower

depending on your calorie needs.

Serving size 3/4 cup (28 g) Servings per container 14

Calories 110

Amount per serving

Calories from fat 9

% Daily Value*

Saturated fat 0 g

Trans fat 0 g

Cholesterol 0 mg 0%

Sodium 250 mg 10%

Protein 3 g

Vitamin A 25% • Vitamin C 25% • Calcium 2% • Iron 25%

2000 2500

Total fat

Sat fat

Cholesterol

Sodium

Total Carbohydrate

Fiber

65 g

20 g

300 mg

2400 mg

300 g

25 g

80 g

25 g

300 mg

2400 mg

375 g

30 g

Less than

Calories:

Calories per gram

Fat 9 • Carbohydrate 4 • Protein 4

Sugars 10 g

Dietary fiber 1.5 g

Total Carbohydrate 23 g

Nutrition Facts

INGREDIENTS, lis ted in

descending order o f p

redominance:

Corn, S ugar, S

alt, Malt f

lavorin g, fr

eshness preserved by BHT.

VITAMINS and M INERALS: V

ita min C (S

odium ascorbate),

Niachamide, Ir on, V

ita min B6

(P yrid

oxine hydrochlorid e),

Vita min B2

(R ibofla

vin), V ita

min A (P alm

ita te), V

ita min B1

(Thiamin hydrochlorid e), F

olic acid, a nd Vita

min D.

Total Fat 1 g

*Percent D aily Values are based on

a 2000 calorie diet. Y our daily

values may be higher or lo wer

depending on your calorie needs.

Serving size

3/4 cup (28 g)

Servings per container

Calories 110Amount per serving

Calories fro m Fat 9

% Daily Value*

Saturated fat 0 g

Cholesterol 0 mg

Sodium 250 mg

10%

Protein 3 g

Vitamin A 25% • Vitamin C 25% • Calcium 2% • Iro n 25%

2000

2500

Total fa t

Sat fa t

Cholesterol

Sodium

Total C arbohydrate

Fiber

65 g

20 g

300 mg

2400 mg

300 g

25 g

80 g

25 g

300 mg

2400 mg

375 g

30 g

Less than

Calories:

Calories per g ram

Fat 9 • C arbohydrate 4 • P

rotein 4

Sugars 10 gDietary fib er 1.5 g

Total C arbohydrate 23 g

Nutrit ion Facts

The name and address of the manufacturer, packer, or distributor

The common or usual product name

Approved nutrient claims if the product meets specified criteria

The net contents in weight, measure, or count

Approved health claims stated in terms of the total diet

The serving size and number of servings per container

Calorie information and quantities of nutrients per serving, in grams (g) and milligrams (mg)

Daily Values reminder for selected nutrients for a 2,000- and a 2,500- calorie diet

Calorie per gram reminder

The ingredients in descending order of predominance by weight

Quantities of nutrients as “% Daily Values” based on a 2,000-calorie energy intake

This cereal label maps out the locations of information needed to make wise purchases. The text provides details about each label section. Labels may also warn consumers of potential allergy risks (see Chapter 14 for details).

Animated! What’s on a Food Label? figure 2-12

52 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

on nutrition labels. This section looks at reliable claims and also describes the unreliable but legal claims that can be made on food labels.

Nutrient Claims on Food Labels If a food meets specifi ed criteria, the label may display certain approved nutrient claims, descriptive terms concerning the product’s nutritive value. The Daily Values serve as the basis for claims that a food is “low” in cholesterol or a “good source” of vitamin A. Table 2-6 provides

food contributes “a little” or “a lot” of a nutrient, whether it contributes “more” or “less” than another food, and how well it fi ts into your overall diet. Consumers may soon see updated Daily Values based on current DRI recommendations—revisions are underway.1

WHAT FOOD LABELS MAY INCLUDE So far, this Consumer Corner has pre- sented the accurate and reliable facts

juice concentrate.” This product is clearly made of reconstituted juice. Water is fi rst on the label because it is the main constituent of juice. Sugar is nowhere to be found among the ingredients be- cause sugar has not been added to the product. Sugar occurs naturally in juice, though, so the label does specify sugar grams; details are in Chapter 4.

Now consider a cereal whose entire list contains just one item: “100 percent shredded wheat.” No question, this is a whole-grain food with nothing added. Finally, consider a cereal whose fi rst three ingredients are “puffed milled corn, sweeteners (sugars: corn syrup, sucrose, honey, dextrose), salt.” If you recognize that sugar, corn syrup, honey, and dex- trose are all different versions of sugar (and you will after Chapter 4), you might guess that this product contains close to half its weight as sugar.

More About Percentages of Daily Values Some of the Daily Values are printed on each label in the Nutrition Facts panel. (The entire list can be found on the inside back cover, page Y.) The calculations used to determine the “% Daily Value” fi g- ures for nutrient contributions from a serv- ing of food are based on a 2,000-calorie diet. For example, if a food contributes 13 milligrams of vitamin C per serving and the Daily Value is 60 milligrams, then a serving of that food provides about 22 percent of the Daily Value for vitamin C.

The Daily Values are of two types. Some, such as those for fi ber, protein, vitamins, and most minerals, are akin to other nutrient intake recommendations. They suggest an intake goal to strive for; below that level, some people’s needs may go unmet. Other Daily Values, such as those for cholesterol, total fat, satu- rated fat, and sodium, constitute healthy daily maximums.

Of course, though the Daily Values are based on a 2,000-calorie diet, people’s actual calorie intakes vary widely; some people need fewer calories and some need many more. This makes the Daily Values most useful for comparing one food with another and less useful as nu- trient intake targets for individuals. Still, by examining a food’s general nutrient profi le, you can determine whether the

Energy Terms

low calorie • 40 calories or fewer per serving. reduced calorie• at least 25% lower in calories than a “regular,” or reference, food. calorie free • fewer than 5 calories per serving.

Fat Terms (Meat and Poultry Products)

extra lean• a

less than 5 g of fat and less than 2 g of saturated fat and trans fat combined, and less than 95 mg of cholesterol per serving. lean• a

less than 10 g of fat and less than 4.5 g of saturated fat and trans fat combined, and less than 95 mg of cholesterol per serving.

Fat Terms (Main Dishes and Prepared Meals)

extra lean• a

less than 5 g total fat and less than 2 g saturated fat and less than 95 mg cholesterol per serving. lean• a

less than 8 g total fat and 3.5 g or less saturated fat and less than 80 mg cholesterol per serving.

Fat and Cholesterol Terms (All Products)

cholesterol free• b

less than 2 mg of cholesterol and 2 g or less saturated fat and trans fat combined per serving. fat free• less than 0.5 g of fat per serving. less saturated fat• 25% or less saturated fat and trans fat combined than the compari- son food. low cholesterol• b

20 mg or less of cholesterol and 2 g or less saturated fat per serving. low fat• 3 g or less fat per serving.a

(continued)

aThe word lean as part of the brand name (as in “Lean Supreme”) indicates that the product contains fewer than 10 grams of fat per serving. bFoods containing more than 13 grams total fat per serving or per 50 grams of food must indicate those contents immediately after a cholesterol claim.

Reliable Nutrient Claims on Food Labels table 2-6

53D i e t P l a n n i n g A p p l i c a t i o n

a list of these regulated, reliable label terms along with their defi nitions. By remembering the meanings of these terms, consumers can make informed choices among foods. For example, any food providing 10 percent or more of the Daily Value for a nutrient can boast that it is “a good source” of the nutrient; a food providing 20 percent is considered “high” in the nutrient.

For nutrients that can be harmful if consumed excessively, such as satu- rated fat or sodium, foods providing less than 5 percent are desirable. For hard- to-get nutrients such as iron or calcium, a reasonable goal might be to choose foods that are “good sources” of or “high” in those nutrients several times a day. (See the Snapshot features of Chapters 7 and 8 for foods qualifying as “good sources” or better for the vitamins and minerals.)

Health Claims: The Reliable and Less Reliable In the past, the FDA held manufactur- ers to the highest standards of scientifi c evidence before allowing them to place health claims (defi ned on page 50) on food labels. When a label stated “Diets low in sodium may reduce the risk of high blood pressure,” for example, consumers could be sure that the FDA had substan- tial scientifi c support for the claim. Such reliable health claims still appear on food labels and they have a high degree of scientifi c validity (see Table 2-7).

Today, however, the FDA also allows other claims backed by weaker evidence to be made on labels. These are “quali- fi ed” claims in the sense that labels bear- ing them must also state the strength of the scientifi c evidence backing them up. Unfortunately, most people cannot distinguish between scientifi cally reliable claims and those that are best ignored.2

Structure/Function Claims A label-reading consumer is much more likely to encounter a structure-function claim on either a food or supplement label than the more heavily regulated health claims just described. For the food manufacturer, printing a health claim stating that a product prevents or cures a disease involves acquiring

Fat and Cholesterol Terms (continued)

low saturated fat • 1 g or less saturated fat and less than 0.5 g of trans fat per serving. percent fat free• may be used only if the product meets the defi nition of low fat or fat free. Requires disclosure of grams of fat per 100 g food. reduced • or less cholesterolb

at least 25% less cholesterol than a reference food and 2 g or less saturated fat per serving. reduced saturated fat• at least 25% less saturated fat and reduced by more than 1 g saturated fat per serving compared with a reference food. saturated fat free• less than 0.5 g of saturated fat and less than 0.5 g of trans fat. trans• fat free less than 0.5 g of trans fat and less than 0.5 g of saturated fat per serving.

Fiber Terms

high fi ber• 5 g or more per serving. (Foods making high-fi ber claims must fi t the defi ni- tion of low fat, or the level of total fat must appear next to the high-fi ber claim.) good source of fi ber • 2.5 g to 4.9 g per serving. more • or added fi ber at least 2.5 g more per serving than a reference food.

Sodium Terms

low sodium• 140 mg or less sodium per serving. reduced sodium• at least 25% lower in sodium than the regular product. sodium free• less than 5 mg per serving. very low sodium• 35 mg or less sodium per serving.

Other Terms

free, without, no, zero • none or a trivial amount. Calorie free means containing fewer than 5 calories per serving; sugar free or fat free means containing less than half a gram per serving. fresh• raw, unprocessed, or minimally processed with no added preservatives. good source• 10 to 19% of the Daily Value per serving. healthy• low in fat, saturated fat, trans fat, cholesterol, and sodium and containing at least 10% of the Daily Value for vitamin A, vitamin C, iron, calcium, protein, or fi ber. high in• 20% or more of the Daily Value for a given nutrient per serving; synonyms include “rich in” or “excellent source.” less, fewer, reduced• containing at least 25% less of a nutrient or calories than a refer- ence food. This may occur naturally or as a result of altering the food. For example, pretzels, which are usually low in fat, can claim to provide less fat than potato chips, a comparable food. light• this descriptor has three meanings on labels: 1. A serving provides one-third fewer calories or half the fat of the regular product. 2. A serving of a low-calorie, low-fat food provides half the sodium normally present. 3. The product is light in color and texture, so long as the label makes this intent clear, as in “light brown sugar.” more, extra• at least 10% more of the Daily Value than in a reference food. The nutrient may be added or may occur naturally.

Reliable Nutrient Claims on Food Labels

(continued)

table 2-6

54 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

dense foods” (USDA Food Guide ad- vice) by searching for the words “low- calorie” or “calorie-reduced” on food labels. Label information about fats and sugars can provide more insight into the nutrient density of foods that bear labels. Our informed consumer can then make meaningful comparisons among the Nutrition Facts panels of selected foods. By making good use of food labels, our consumer can be confi dent that the foods going home in grocery sacks will help to meet the chosen Dietary Guideline, in this case, weight management.

scientifi c evidence and submitting it in advance to petition the FDA for permis- sion, a process costing much effort and expense. Instead, the manufacturer can use a similar-looking structure/function claim requiring no prior approval. Notifi - cation of the FDA is suffi cient.

A problem is that, to a reasonable consumer, the two kinds of claims may seem to be identical:

“Lowers cholesterol.” •

“Helps maintain normal cholesterol • levels.”

The fi rst, because it claims to reverse a disease-related condition (high cho- lesterol), requires FDA evaluation and approval before printing. The second structure/function claim refers only to a healthy body state, and so can be printed without prior approval.

A required label disclaimer (often found in tiny print) states that the FDA has not evaluated the claim and that the product is not intended to diagnose, treat, cure, or prevent any disease.3 Often, however, structure/function claims stretch the truth.

Unfortunately, the presence of valid- appearing but unreliable label claims diminishes the usefulness of all health- related claims. Until laws require solid

These claims of potential health benefi ts are well-supported by research, but other similar-sounding claims may not be.

Calcium and reduced risk of osteoporosis• Sodium and reduced risk of hypertension• Dietary saturated fat and cholesterol and reduced risk of coro-• nary heart disease Dietary fat and reduced risk of cancer• Fiber-containing grain products, fruits, and vegetables and • reduced risk of cancer Fruits, vegetables, and grain products that contain fi ber, particu-• larly soluble fi ber, and reduced risk of coronary heart disease Fruits and vegetables and reduced risk of cancer• Folate and reduced risk of neural tube defects• Sugar alcohols and reduced risk of tooth decay• Soluble fi ber from whole oats and from psyllium seed husk and • reduced risk of coronary heart disease Soy protein and reduced risk of coronary heart disease• Whole grains and reduced risk of coronary heart disease and • certain cancers Plant sterol and plant stanol esters and reduced risk of coronary • heart disease Potassium and reduced risk of hypertension and stroke•

Reliable Health Claims on Labels table 2-7

DIRECTIONS FOR USE: One tablet daily for adults. WARNING: CLOSE TIGHTLY AND KEEP OUT OF REACH OF CHILDREN. CONTAINS IRON, WHICH CAN BE HARMFUL OR FATAL TO CHILDREN IN LARGE DOSES. IN CASE OF ACCIDENTAL OVERDOSE, SEEK PROFESSIONAL ASSISTANCE OR CONTACT A POISON CONTROL CENTER IMMEDIATELY.

Product name

Amount Per Tablet % Daily Value

Vitamin A 5000 IU (40% Beta Carotene) 100%

Vitamin C 60 mg 100%

Vitamin D 400 IU 100%

Vitamin E 30 IU 100%

Thiamin 1.5 mg 100%

Riboflavin 1.7 mg 100%

Niacin 20 mg 100%

Vitamin B6 2 mg 100%

Folate 400 mcg 100%

Vitamin B12 6 mcg 100%

Biotin 30 mcg 10%

Pantothenic Acid 10 mg 100%

Calcium 130 mg 13%

Iron 18 mg 100%

Phosphorus 100 mg 10%

Iodine 150 mcg 100%

Magnesium 100 mg 25%

Zinc 15 mg 100%

Selenium 10 mcg 14%

Copper 2 mg 100%

Manganese 2.5 mg 71%

Chromium 10 mcg 8%

Molybdenum 10 mcg 6%

Chloride 34 mg 1%

Potassium 37.5 mg 1%

Supplement Facts Serving Size 1 Tablet

FOR YOUR PROTECTION, DO NOT USE IF PRINTED FOIL SEAL UNDER CAP IS BROKEN OR MISSING.

Store in a dry place at room temperature (59-86F).

Supplements, Inc. 1234 Fifth Avenue

Anywhere, USA Complete Satisfaction or Your Money Back

Description of product

Nutrient claims if product meets criteria

Contents or weight

The dose

The name, quantity per tablet, and “% Daily Value” for all nutrients listed; nutrients without a Daily Value may be listed below.

All ingredients must be listed on

the label, but not necessarily in

the ingredients list nor in descending

order of predominance; ingredients

named in the Supplement Facts

need not be repeated here.

Name and address of manufacturer

A Dietary Supplement Rich in 11 Essential Vitamins

100 TABLETS

INGREDIENTS: Dicalcium Phosphate, Magnesium Hydroxide, Microcrystalline Cellulose, Potassium Chloride, Ascorbic Acid, Ferrous Fumarate, Modified Cellulose Gum, Zinc Sulfate, Gelatin, Stearic Acid, Vitamin E Acetate, Hydroxypropyl Methylcellulose, Niacinamide, Calcium Silicate, Citric Acid, Magnesium, Stearate, Calcium Pantothenate, Artificial Colors (FD&C Red No. 40, Titanium Dioxide, FD&C Yellow No. 6 and FD&C Blue No. 2), Selenium Yeast, Manganese Sulfate, Polyethylene Glycol, Cupric Sulfate, Molybdenum Yeast, Chromium Yeast, Vitamin A Acetate, Pyridoxine Hydrochloride, Riboflavin, Sodium Lauryl Sulfate, Thiamin Mononitrate, Beta Carotene, Folic Acid, Polysorbate 80, Vitamin D, Potassium Iodide, Gluten, Biotin, Cyanocobalamin.

A Supplement Label figure 2-13

scientifi c backing for all claims on labels, consumers should ignore health-related claims and rely on the Nutrient Facts and Supplement Facts panels for nutrient information, direc- tions, and warnings. Figure 2-13 provides a demonstration of a supplement label.

CONSUMER EDUCATION Because labels are valuable only if peo- ple know how to use them, the FDA has designed several programs to educate consumers. Consumers who understand how to read labels are best able to apply the information to achieve and maintain healthful dietary practices.

By design, the nutrition messages from the Dietary Guidelines for Ameri- cans, the USDA Food Guide/MyPyramid, and food labels coordinate with each other, as Table 2-8 demonstrates. For example, a person striving to improve “Weight Management” (one of the Dietary Guidelines) can “select nutrient-

55D i e t P l a n n i n g A p p l i c a t i o n

convincing scientifi c evidence. In the world of food and supplement marketing, label rulings put the consumer on notice: “Let the buyer beware.”

mation on which consumers can base their food choices. Regrettably, more and more of the health-related claims printed on labels are based on less-than-

CONCLUSION The Nutrition Facts panels and ingredi- ents lists on labels provide reliable infor-

Dietary Guidelines for Americans set goals for nutritional health. The USDA Food Guide/MyPyramid offers a meal pattern to meet them. Food labels can then assist consumers in choosing among packaged foods with these goals and patterns in mind. (Don’t forget that unlabeled fresh fruits, vegetables, and meats often excel in meeting nutrient needs and goals.)

Dietary Guidelines USDA Food Guide/MyPyramid Food Labels

Obtain adequate nutrients within energy needs

Select the recommended amounts from each food group at the energy level appropriate for your energy needs.

Look for foods that describe their vitamin, mineral, or fi ber contents as a good source or high.

Weight management

Select nutrient-dense foods and beverages within and among the food groups.

Limit high-fat foods and foods and beverages with added fats and sugars.

Use appropriate portion sizes.

Look for foods that describe their calorie contents as free, low, reduced, light, or less.

Food groups to encourage

Select a variety of fruits each day.

Include vegetables from all fi ve subgroups (dark green, orange, legumes, starchy vegetables, and other vegetables) several times a week.

Make at least half of the grain selections whole grains.

Select fat-free or low-fat milk products.

Look for foods that describe their fi ber contents as good source or high.

Look for foods that provide at least 10% of the Daily Value for fi ber, vitamin A, vitamin C, iron, and calcium from a variety of sources.

Fats Choose foods within each group that are lean, low- fat, or fat-free.

Choose foods within each group that have little added fat.

Look for foods that describe their fat, saturated fat, trans fat, and cholesterol contents as free, less, low, light, reduced, lean, or extra lean.

Look for foods that provide no more than 5% of the Daily Value for fat, saturated fat, and cholesterol.

Carbohydrates Choose fi ber-rich fruits, vegetables, and whole grains often.

Choose foods and beverages within each group that have little added sugars.

Look for foods that describe their sugar contents as free or reduced.

A food may be high in sugar if its ingredients list begins with or contains several of the following: sugar, sucrose, fructose, malt- ose, lactose, honey, syrup, corn syrup, high-fructose corn syrup, molasses, evaporated cane juice, or fruit juice concentrate.

Sodium and potassium

Choose foods within each group that are low in salt or sodium.

Choose potassium-rich foods such as fruits and vegetables.

Look for foods that describe their salt and sodium contents as free, low, or reduced.

Look for foods that provide no more than 5% of the Daily Value for sodium.

Look for foods that provide at least 10% of the Daily Value for potassium.

Alcoholic Beverages

Use sensibly and in moderation (no more than one drink a day for women and two drinks a day for men).

Light beverages contain fewer calories and less alcohol than regular versions.

Food Safety Follow the safe handling instructions on packages of meat and other safety instructions, such as keep refrigerated, on pack- ages of perishable foods.

From Guidelines to Groceries table 2-8

56 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

food feature

Figures 2-14 and 2-15 illustrate a play- ful contrast between two days’ meals. “Monday’s Meals” were selected ac- cording to the recommendations of this chapter and follow the sample menu of Figure 2-8, shown earlier (page 46). “Tuesday’s Meals” were chosen more for convenience and familiarity than out of concern for nutrition.

COMPARING THE NUTRIENTS How can a person compare the nutrients that these sets of meals provide? One way is to look up each food in a table of food composition, write down the food’s nutrient values, and compare each one to a standard such as the DRI recom- mended intakes for nutrients, as we’ve done in Figures 2-14 and 2-15. By this measure, Monday’s meals are the clear winners in terms of meeting nutrient needs within a calorie budget. Tuesday’s meals oversupply calories and saturated fat while undersupplying fi ber and critical vitamins and minerals.

Another useful exercise is to compare the total amounts of foods provided by a day’s meals with the recommended amounts from each food group. A tally of the cups and ounces of foods consumed is provided in both Figures 2-14 and 2-15. The totals are then compared with MyPyramid recommendations in the tabular portion of the fi gures. The tables also identify whole grains and veg- etable subgroups and tally discretionary

Getting a Feel for the Nutrients in Foods

calories from solid fats and sugars to complete the assessment.

MONDAY’S MEALS IN DETAIL Monday’s meals provide the necessary servings from each food group along with a small amount of oil needed for health, while the energy provided falls well within the 2,000-calorie allowance. A closer look at Monday’s foods reveals that the whole-grain cereal at breakfast, whole-grain sandwich roll at lunch, and whole-grain crackers at snack time meet the recommendation to obtain at least half of the day’s grain servings from whole grains.

For the vegetable subgroups, dark green vegetables, orange vegetables, and legumes are represented in the dinner salad, and “other vegetables” are prominent throughout. To repeat: it isn’t necessary to choose vegetables from each subgroup every day, and the person eating this day’s meals will need to include vegetables from other sub- groups throughout the week. In addition, Monday’s eating plan has room to spare in the discretionary calorie allowance for additional servings of favorite foods or for some sweets or fats.

TUESDAY’S MEALS IN DETAIL Tuesday’s meals, though abundant in oils, meats, and enriched grains, completely lack fruit and whole grains and are too low in vegetables and milk

to provide adequate nutrients. Tuesday’s meals supply too much saturated fat and sugar, as well as excessive meats and refi ned grains, pushing the calorie total well above the day’s allowance. A single day of such fare poses little threat to the eater, but a steady diet of “Tues- day meals” presents a high probability of nutrient defi ciencies and weight gain and greatly increases the risk of chronic diseases in later life.

COMPUTER—OR NOT? If you have access to a computer, it can be a time saver—diet analysis programs perform all of these calculations at light- ning speed. This convenience may make working it out yourself, using paper and a sharp pencil with a big eraser, seem a bit old-fashioned. But there are times when using a laptop or PDA (personal digital assistant) may not be practical—such as standing in line at the cafeteria or at a fast-food counter—where real-life food decisions must be made quickly.

People who work out diet analyses for themselves on paper and those who put extra time into studying, changing, and reviewing their computer results often learn to “see” the nutrients in foods (a skill you can develop by the time you reach Chapter 10). They can quickly assess their food options and make informed choices at mealtimes. People who fail to develop such skills must wait until they can access their computer programs to fi nd out how well they did after the fact.

57D i e t P l a n n i n g A p p l i c a t i o n

Before heading off to class, a student eats breakfast:

1 c whole-grain cold cereal 1 c fat-free milk 1 medium banana (sliced)

Then goes home for a quick lunch:

1 roasted turkey sandwich on 2-oz whole-grain roll with 11/2 tsp low-fat mayonnaise 1 c low-salt vegetable juice

While studying in the afternoon, the student eats a snack:

4 whole-wheat reduced-fat crackers 11/2 oz low-fat cheddar cheese 1 apple

That night, the student makes dinner:

A salad: 1 c raw spinach leaves, shredded carrots 1/4 c garbanzo beans 5 lg olives and 2 tbs oil-based salad dressing

A main course: 1 c spaghetti with meat sauce 1/2 c green beans 2 tsp soft margarine

And for dessert: 1 c strawberries

Later that evening, the student enjoys a bedtime snack:

3 graham crackers 1 c fat-free milk

Totals:

Intakes Compared with MyPyramid Amounts

Foods Energy (cal)

MyPyramid Amounts

Fiber (g)

Calcium (mg)

Saturated Fat (g)

Vitamin C (mg)

DRI recommended intakes:a

Percentage of DRI recommended intakes:

aDRI values for a sedentary woman, age 19–30. Other DRI values are listed on the inside front cover, page B.

bThe 20-gram value listed is the maximum allowable saturated fat for a 2,000-calorie diet. The DRI recommends consuming less than 10 percent of calories from saturated fat.

108 100 105

50 343

74 72

425 22 67

90 100

1,857

19 71

1 oz grains 1 c milk 1/2 c fruit

2 oz meat 2 oz grains 11/2 tsp oils 1 c vegetables

1/2 oz grains

1 c milk 1/2 c fruit

2 oz grains 21/2 oz meat 1 c vegetables 2 tsp oils

1 c fruit

1/2 oz grains 1 c milk

1 c vegetables 1 oz legumes

2 tsp oils

3 — 3

1 2

— 3

5 2

—

— —

2 3

14 2

60 —

—

— 6

15 6

—

— 2

224

18 2

—

— — —

— 4

2 —

3 — 1

—

— —

95 306

27 89

—

176 8

56 29 —

— 306

1,204

61 19

2,000 93%

1,000 120%

<20b

60% 75

299% 25

120%

Breakfast

Lunch

Afternoon snack

Dinner

Bedtime snack

Recommended MyPyramid AmountsFood Group Breakfast Lunch Snack Dinner Snack

Monday’s Totals

Fruits 1/2 c 1/2 c

1/2 oz

Vegetables 1 c

Grains 1 oz 2 oz

Meat and legumes 2 oz

Milk 1 c 1 c

1/2 oz

1 c

Oils 11/2 tsp

1 c

2 c

2 oz

31/2 oz

4 tsp

3 c

2 c

3 c

6 oz

51/2 oz

51/2 tsp

1,857 cal

3 c

2 c

21/2 c

6 oz

51/2 oz

51/2 tsp

2,000 cal Calorie allowance

u e s t P

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Monday’s Meals—Nutrient-Dense Choices figure 2-14

58 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

Tuesday’s Meals—Less Nutrient-Dense Choices figure 2-15

Today, the student starts the day with a fast-food breakfast:

1 c coffee 1 English muffin with egg, cheese, and bacon

Between classes, the student returns home for a quick lunch:

1 peanut butter and jelly sandwich on white bread 1 c whole milk

While studying, the student has:

12 oz diet cola Bag of chips (14 chips)a

That night for dinner, the student eats:

A salad: 1c lettuce 1 tbs blue cheese dressing

A main course: 6 oz steak 1/2 baked potato 1 tbs butter 1 tbs sour creamb

12 oz diet cola

And for dessert: 4 sandwich-type cookies

Later on, a bedtime snack:

2 cream-filled snack cakes 1 c herbal tea

Totals:

Foods Energy (cal)

Fiber (g)

Calcium (mg)

Saturated Fat (g)

Vitamin C (mg)

DRI recommended intakes:c

Percentage of DRI recommended intakes:

436

426 156

— 105

158

250 —

2,263

349 161 102

31 —

MyPyramid Amounts

2 oz grains 2 oz meat 1 c milk

2 oz grains 1 oz legumes 1 c milk

2 oz grains

6 oz meat 1/2 c vegetables

1 oz grains

1/2 c vegetables

—

4 6

— 2

2 —

6 — 7 2

—

3 —

— —

2 —

— 4

— — —

—

— 4

—

— —

— 17 — — —

—

266

93 290

— —

—

20 —

765

27 26

3 17 —

2,000 113%

1,000 77%

<20d

210% 25

52% 75

36%

Breakfast

Lunch

Afternoon snack

Dinner

Bedtime snack

cDRI values for a sedentary woman, age 19–30. Other DRI values are listed on the inside front cover, page B.

dThe 20-gram value listed is the maximum allowable saturated fat for a 2,000-calorie diet. The DRI recommends consuming less than 10 percent of calories from saturated fat.

aThe potato in 14 potato chips provides less than 1/2 cup vegetables.

bThe saturated fats of steak, butter, and sour cream are among the solid fats and do not qualify as oils.

Intakes Compared with MyPyramid Amounts

Recommended MyPyramid AmountsFood Group Breakfast Lunch Snack Dinner Snack

Tuesday’s Totals

Fruits

Vegetables a

Grains 2 oz 2 oz

Meat and legumes 2 oz 2 oz

Milk 1 c 1 c

2 oz

Oils

1 c

1 oz

6 oz

2 c

0 c

1 c

7 oz

9 oz

71/2 tspb

2,263 cal

3 c

2 c

21/2 c

6 oz

51/2 oz

51/2 tsp

2,000 cal Calorie allowance

ic h a e l N

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59D i e t P l a n n i n g A p p l i c a t i o n

Compare Your Intakes with MyPyramid The purpose of this chapter’s exercise is to give you a feel for how your diet compares with MyPyramid and help you consider your discretionary calorie sources.

From the Home page of DA1. �, select the Reports tab and select MyPyramid Analysis. Choose Day Two of your three-day diet intake (from Chapter 1). Choose all meals for that day. Generate a report. Did your intake for that day conform to the MyPyramid pattern? Did you consume too few foods from any particular food group(s)? Which, if any, were lacking? Using Table 2-2 (page 44) and Figure 2-5 (pages 38–39) to guide you, suggest ways that you might realistically change your intake to better conform to the MyPyramid diet pattern.

What about fat? Select the Reports 2. tab then Macronutrient Ranges. Generate a report. Did your fat intake fall between 20–35 percent of your total energy? Did you take in enough raw oils to meet your need (see Table 2-2, page 44)? Which ones? Change your date to include all three days of your record and generate a report to see a fat intake average. How does your single day’s fat intake compare with your three-day average?

Find your discretionary calorie 3. allowance on the bottom line of Table 2-2. Select the Track Diet tab and look over your day’s food list. Which foods provided discretionary calories? (Use Table 2-1 on page 43 as a guide.)

Breaking this information down 4. further, consider that the USDA generally recommends that no more than half of the day’s discre-

tionary calories come from added sugars. Which foods on your food list contribute added sugars? If you consumed substantial amounts of added sugars, suggest realistic ways to reduce your intake.

A great feature of the Diet Analy-5. sis program is its Source Analysis Report that allows you to list food sources of calories (kcal) or specifi c nutrients in order of predominance. From the Reports tab, select Source Analysis, Day Three, and choose all meals. Generate a report. Which foods provided most to your calorie intake on that day? If you consumed vegetables, where did they fall on the list? In later chapters you’ll use this report again to analyze various nutrients in your diet.

Concepts in Action

Throughout this chapter, the Cengage NOW logo indicates an opportunity for online self-study, linking you to interactive tutorials and videos based on your level of understanding. Go to www.cengage.com/sso.

Search for “diet” and “food labels” at the U.S. Government health information site: www.healthfi nder.gov.

Learn more about the Dietary Guidelines for Americans: www.healthierus.gov/dietaryguidelines.

Learn more about the USDA Food Guide and MyPyramid: www.mypyramid.gov.

Get healthy eating tips and ideas of ways of eating more fruits and vegetables: www.fruitsandveggiesmatter.gov.

Find Canadian information on nutrition guidelines and food labels at: www.hc-sc.gc.ca.

media menu

Answers to these Self Check questions are in Appendix G.

The nutrient standards in use today include all of the follow-1. ing except:

Adequate Intakes (AI)A.

Daily Minimum Requirements (DMR)B.

Daily Values (DV)C.

(a) and (c)D.

self check

http://www.cengage.com/sso

http://www.healthfi

http://www.healthierus.gov/dietaryguidelines

http://www.mypyramid.gov

http://www.fruitsandveggiesmatter.gov

http://www.hc-sc.gc.ca

60 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

The Dietary Reference Intakes were devised for which of the 2. following purposes?

to set nutrient goals for individualsA.

to suggest upper limits of intakes, above which toxicity is B. likely

to set average nutrient requirements for use in researchC.

all of the aboveD.

According to the USDA Food Guide, which of the following 3. may be counted among either the meats or the vegetables?

chickenA.

avocadosB.

black beansC.

potatoesD.

The USDA Food Guide recommends a small amount of 4. daily oil from which of these sources?

olivesA.

nutsB.

vegetable oilC.

all of the aboveD.

Which of the following values is found on food labels?5.

Daily ValuesA.

Dietary Reference IntakesB.

Recommended Dietary AllowancesC.

Estimated Average RequirementsD.

The energy intake recommendation is set at a level pre-6. dicted to maintain body weight. T F

The Dietary Reference Intakes (DRI) are for all people, 7. regardless of their medical history. T F

People who choose not to eat meat or animal products 8. need to fi nd an alternative to the USDA Food Guide when planning their diets. T F

By law, food labels must state as a percentage of the Daily 9. Values the amounts of vitamin C, vitamin A, niacin, and thiamin present in food. T F

To be labeled “low fat,” a food must contain 3 grams of fat 10. or less per serving. T F

61controversy 2 A r e S o m e F o o d s “ S u p e r f o o d s ” f o r H e a l t h ?

CONTROVERSY

Headlines these days often focus on the latest “superfoods” for health: “Forgetful? Blueberries sharpen brain function!” “Too many colds? Try immune-boosting soy- beans!” “Worried about cancer? Eat to- matoes!” Can simply eating certain foods accomplish these wondrous things? Although headlines tend to overstate their talents, what these foods and many oth- ers have in common is a rich supply of phytochemicals—nonnutrient compo- nents of plants, introduced in Chapter 1. Phytochemicals often act as bioactive food components, food constituents with the ability to alter body processes (terms are defi ned in Table C2-1).

Just a few of today’s “superfoods” ap- pear here; later chapters address others, such as olive oil and nuts (Controversy 5) and broccoli and its relatives (Chap- ter 11). These are functional foods of the simplest kind—they naturally contain substances having biological activity in the body beyond those of the nutri- ents. Other functional foods arise when manufacturers dose candy bars, juices, margarine, snack chips, and the like with nutrients, phytochemicals, herbs, or other bioactive food components.1* Which kind might be most benefi cial to health and why are topics of the last sec- tion of this Controversy.

A SCIENTIST’S VIEW OF PHYTOCHEMICALS At one time, phytochemicals were known only for their sensory properties in foods, such as taste, aroma, texture, and color. Thank phytochemicals for the burning

sensation of hot peppers, the pungent fl avor of onions and garlic, the bitter tang of chocolate, the aromatic quali- ties of herbs, and the beautiful colors of tomatoes, spinach, pink grapefruit, and watermelon.

Today, phytochemicals are emerging as potential regulators of health: many act as antioxidants that protect DNA and other cellular compounds from oxidative damage; some interact with genes to regulate protein synthesis; some mimic hormones; while others alter the blood chemistry in other ways.2

Of the tens of thousands of phyto- chemicals known to exist, just a few have been researched at all, and only a sampling of those are mentioned in this Controversy—enough to illustrate their potential roles in human health and the wide array of foods that supply them. So far, the most promising results have come from studies of cells or animals; studies of human beings are less encouraging.3

Many phytochemicals belong to the large chemical group known as fl avo- noids. Many plant foods, including many fruits, vegetables, whole grains, nuts, red wine, spices, and even dark choco- late (see Table C2-2), contain them. Such phytochemicals may act at the level of the genes to reduce infl amma- tory processes related to many disease processes.4

Blueberries When researchers feed rats on chow rich in blueberry extracts, they exhibit fewer age-related mental declines than rats on plain chow.5 The

antioxidant phyto chemicals of blueber- ries are credited with the effect because they reduce oxidative stress.6 Oxida- tive stress is a chemical imbalance that promotes infl ammation and damages molecular structures of cells. Chronic oxidative stress worsens the brain’s loss of mental powers as it ages. The brain cannot readily replace its damaged cells, so when oxidative damage builds over time, memory and reasoning, loss of muscle control, and other brain function diminish.7

Are blueberries a brain superfood, then? Although blueberries currently lead the way in antioxidant and brain re- search, it is unknown whether or not they can prevent aging effects in the human brain. Furthermore, antioxidants in other berries, artichokes, coffee, pomegran- ates, spinach, or even seaweed could turn out to play similar or better roles.8 In addition, the brain needs carbohy- drate, certain lipids, and vitamins and minerals for peak performance. Rather than gambling on one particular food’s phytochemical, the wisest course is to choose a variety of phytochemical-rich fruits and vegetables in the context of an adequate, balanced diet needed to sustain brain functioning.

Chocolate Imagine the delight of young research subjects who were paid to eat 3 ounces of dark (bittersweet) choco- late for an experiment. Less appealingly, researchers then drew blood from the subjects to test whether an antioxidant fl avonoid in chocolate was absorbed into

Are Some Foods “Superfoods” for Health?

LO 2.6

*Reference notes are found in Appendix F.

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62 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

the bloodstream. The tests were positive: the fl avonoid had indeed accumulated in their blood. At the same time, the level of potentially harmful oxidizing compounds had dropped by 40 percent.

The heart, vulnerable to damage by oxidation, could benefi t from such fl avonoids and other antioxidants (Table C2-3 lists some contributors).†9 In ad- dition, dark chocolate may reduce the likelihood of blood clots, promote normal

blood pressure, help to relax blood ves- sels, improve blood lipids, and reduce infl ammation, factors associated with heart disease prevention.10 A recent study, however, detected no benefi ts of chocolate in terms of heart risk factors or as an indicator of infl ammation.11 No one yet knows whether chocolate fans actu- ally suffer less heart disease.

If eating chocolate daily sounds ap- pealing, consider another centuries-old medicinal use of chocolate: promoting weight gain. Three ounces of sweetened chocolate candy contain over 400 calo-

ries, a signifi cant portion of most people’s daily calorie allowance. At the same time, chocolate contributes few nutrients, save two—fat and sugar. For most people, antioxidant phytochemicals are best obtained from nutrient-dense, low-calorie fruits and vegetables—with chocolate savored as an occasional treat.

Flaxseed Flaxseed is valued for relieving constipation and digestive distress, but other potential health benefi ts are

antioxidants• (anti-OX-ih-dants) compounds that protect other compounds from damaging reactions involving oxygen by themselves reacting with oxygen (anti means “against”; oxy means “oxygen”). Oxidation is a potentially damaging effect of normal cell chemistry involving oxygen (more in Chapters 5 and 7). bioactive food components• compounds in foods, either nutrients or phytochemicals, that alter physiological processes. broccoli sprouts• the sprouted seed of Brassica italica, or the common broccoli plant; believed to be a functional food by virtue of its high phytochemical content. drug• any substance that when taken into a living organism may modify one or more of its functions. edamame• fresh green soybeans, a source of phytoestrogens. fl avonoids • (FLAY-von-oyds) members of a chemical family of yellow pigments in foods; phytochemicals that may exert physiological effects on the body. Flavus means “yellow.” fl axseed • small brown seed of the fl ax plant; used in baking, cereals, or other foods. Valued in nutrition as a source of fatty acids, lignans, and fi ber. functional foods• whole or modifi ed foods that contain bioactive food components believed to provide health benefi ts, such as reduced disease risks, beyond the benefi ts that their nutrients confer. All whole foods are functional in some ways because they provide at least some needed substances, but certain foods stand out as rich sources of bioactive food components. Also defi ned in Chapter 1. genistein• (GEN-ih-steen) a phytoestrogen found primarily in soybeans that both mimics and blocks the action of estrogen in the body. kefi r• (KEE-fur) a liquid form of yogurt, based on milk, probiotic microorganisms, and fl avorings. lignans • phytochemicals present in fl axseed, but not in fl ax oil, that are converted to phytoestrogens by intestinal bacteria and are under study as possible anticancer agents. lutein• (LOO-teen) a plant pigment of yellow hue; a phytochemical believed to play roles in eye functioning and health. lycopene• (LYE-koh-peen) a pigment responsible for the red color of tomatoes and other red-hued vegetables; a phytochemical that may act as an antioxidant in the body. miso • fermented soybean paste used in Japanese cooking. Soy products are considered to be functional foods. organosulfur compounds• a large group of phytochemicals containing the mineral sulfur. Organosulfur phytochemicals are responsible for the pungent fl avors and aromas of foods belonging to the onion, leek, chive, shallot, and garlic family and are thought to stimulate cancer defenses in the body. phytochemicals• (FIGH-toe-CHEM-ih-cals) compounds in plants that confer color, taste, and other characteristics. Often, the bioactive food components of functional foods. Also defi ned in Chapter 1. Phyto means “plant.” phytoestrogens• (FIGH-toe-ESS-troh-gens) phytochemicals structurally similar to the female sex hormone estrogen. Phytoestrogens weakly mimic estrogen or modulate hormone activity in the human body. phytosterols • phytochemicals that resemble cholesterol in structure, but that lower blood cholesterol by interfering with cholesterol absorption in the intestine. Phytosterols include sterol esters and stanol esters. prebiotic• a substance that may not be digestible by the host, such as fi ber, but that serves as food for probiotic bacteria and thus pro- motes their growth. probiotic• a live microorganism which, when administered in adequate amounts, alters the bacterial colonies of the body in ways be- lieved to confer a health benefi t on the host. resveratrol• (rez-VER-ah-trol) a fl avonoid of grapes under study for potential health benefi ts. soy milk • a milklike beverage made from soybeans, claimed to be a functional food. Soy drinks should be fortifi ed with vitamin A, vitamin D, ribofl avin, and calcium to approach the nutritional equivalency of milk. tofu• a white curd made of soybeans, popular in Asian cuisines, and considered to be a functional food.

Phytochemical and Functional Food Terms table C2-1

†Dark chocolate is rich in fl avonoids; milk chocolate or “Dutch” processed chocolate have reduced fl avonoid content.

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Chemical Name Possible Effects Food Sources

Alkylresorcinols (phenolic lipids)

May contribute to the protective effect of grains in reducing the risks of diabetes, heart disease, and some cancers.

Whole-grain wheat and rye

Allicin (organosulfur compound)

Antimicrobial that may reduce ulcers; may lower blood cholesterol.

Chives, garlic, leeks, onions

Capsaicin Modulates blood clotting, possibly reducing the risk of fatal clots in heart and artery disease.

Hot peppers

Carotenoids (include beta-carotene, lycopene, lutein, and hundreds of related compounds)

Act as antioxidants, possibly reducing risks of cancer and other diseases.

Deeply pigmented fruits and vegetables (apri- cots, broccoli, cantaloupe, carrots, pumpkin, spinach, sweet potatoes, tomatoes)

Curcumin Acts as an antioxidant and anti-infl ammatory agent; may re- duce blood clot formation; may inhibit enzymes that activate carcinogens.

Turmeric, a yellow-colored spice

Flavonoids (include fl avones, fl avonols, isofl avones, catechins, and others)

Act as antioxidants; scavenge carcinogens; bind to nitrates in the stomach, preventing conversion to nitrosamines; inhibit cell proliferation.

Berries, black tea, celery, citrus fruits, green tea, olives, onions, oregano, purple grapes, purple grape juice, soybeans and soy prod- ucts, vegetables, whole wheat, wine

Genistein and daidzein (isofl avones)

Phytoestrogens that inhibit cell replication in GI tract; may reduce or elevate risk of breast, colon, ovarian, prostate, and other estrogen-sensitive cancers; may reduce cancer cell survival; may reduce risk of osteoporosis.

Soybeans, soy fl our, soy milk, tofu, textured vegetable protein, other legume products

Indoles (organosulfur compound)

May trigger production of enzymes that block DNA damage from carcinogens; may inhibit estrogen action.

Cruciferous vegetables such as broccoli, brussels sprouts, cabbage, caulifl ower, horseradish, mustard greens, kale

Isothiocyanates (organo- sulfur compounds that include sulforaphane)

Act as antioxidants; inhibit enzymes that activate carcino- gens; activate enzymes that detoxify carcinogens; may reduce risk of breast cancer, prostate cancer.

Cruciferous vegetables such as broccoli, brussels sprouts, cabbage, caulifl ower, horseradish, mustard greens, kale

Lignans Phytoestrogens that block estrogen activity in cells possibly reducing the risk of cancer of the breast, colon, ovaries, and prostate.

Flaxseed and its oil, whole grains

Monoterpenes (including limonene)

May trigger enzyme production to detoxify carcinogens; inhibit cancer promotion and cell proliferation.

Citrus fruit peels and oils

Phenolic acids May trigger enzyme production to make carcinogens water- soluble, facilitating excretion.

Coffee beans, fruits (apples, blueberries, cherries, grapes, oranges, pears, prunes), oats, potatoes, soybeans

Phytic acid Binds to minerals, preventing free-radical formation, pos- sibly reducing cancer risk.

Whole grains

Resveratrol Acts as antioxidant; may inhibit cancer growth; reduce infl ammation, LDL oxidation, and blood clot formation.

Red wine, peanuts, grapes, raspberries

Saponins (glucosides) May interfere with DNA replication, preventing cancer cells from multiplying; stimulate immune response.

Alfalfa sprouts, other sprouts, green vegeta- bles, potatoes, tomatoes

Tannins Act as antioxidants; may inhibit carcinogen activation and cancer promotion.

Black-eyed peas, grapes, lentils, red and white wine, tea

Phytochemicals—Their Food Sources and Potential Actions table C2-2

64 chapter 2 N u t r i t i o n To o l s — S t a n d a r d s a n d G u i d e l i n e s

Asians consume far more soybeans and soy products, such as edamame, miso, soy milk, tofu, and other soy foods than do Westerners. Soybeans are rich sources of phytoestrogens. How- ever, soy is just one among many diet and lifestyle differences between East and West—and even the forms of soy foods consumed in these areas differ.21 To determine whether soy foods account for differences in disease rates requires clinical evidence, not just correlation.

Soy and Chronic Diseases A small drop in blood cholesterol occurs when subjects, particularly men with elevated cholesterol, replace meat and dairy foods in their diets with soy protein sources.22 It takes a lot of soy to achieve this effect—more than half the daily pro- tein intake must come from soy.23 Also, the effect comes from food; benefi ts are diminished if the phytoestrogen is removed from the soybean matrix.24 As is true for fl axseed, soy foods contain compounds that intestinal bacteria con- vert to biologically active forms.25

With regard to cancer, concerns about breast cancer, colon cancer, and pros- tate cancer involve estrogen-sensitive varieties—cancers that grow when ex- posed to estrogen. Soy phytoestrogens are chemical relatives of the human hor- mone estrogen and may weakly mimic or oppose the hormone’s effects. Age of the eater affects the results: a high soy intake during childhood and adoles- cence seems to reduce breast cancer risk in women before menopause; soy intake by adults may or may not reduce this risk, but more research is needed to

clarify these relationships.26

Soy’s Downsides Low doses of one soy phyto- estrogen, genistein, appear to speed up division of breast

cancer cells in laboratory cultures and in mice, and high doses seemed to do the opposite.27 Still under study is whether consuming soy phy- toestrogens may do the same in living people, but it seems unlikely that moder- ate intakes of soy foods would do so.28 If they did, soy-eating cultures would have higher, not lower, incidences of these cancers. In concentrated supplement

ing a spoonful or two of fl axseed in the diet may not be a bad idea, however. Flaxseed richly supplies linolenic acid, an essential fatty acid often lacking in the U.S. diet (see Chapter 5).

Garlic For thousands of years, people have credited garlic with medicinal properties. Descriptions of its uses for headaches, heart disease, and tumors are recorded in early Egyp- tian medical writings. Scientifi c study of garlic’s properties are ongoing.

Among garlic’s most promising con- stituents are antioxidant organosulfur compounds, reported to inhibit cancer development.16 Oxidizing compounds damage DNA in animal cells and trigger cancerous changes.17 Antioxidants of garlic quench these oxidizing com- pounds, at least in test tubes. Whether garlic prevents cancers in people is unknown.18 Other potential roles for garlic include opposing allergies, heart disease, infections, and ulcers, but these effects remain uncertain.19 However, if you like garlicky foods, you can consume them with confi dence; history and at least some research are on your side.

Often, studies of garlic supplements, such as powders and oil, have been dis- appointing. No one can say with certainty whether large doses of concentrated chemicals from garlic may improve a person’s health, but for those who like garlic, fresh garlic may offer the best hope of obtaining benefi ts.20

Soybeans and Soy Products Compared with people in the West, Asians living in Asia suffer less frequently from heart disease; cancers, especially of the breast, colon, and prostate; and osteo- porosis (adult bone loss). Women in Asia also suffer less from symptoms re- lated to menopause, the midlife decline in women’s estrogen secretion when menstruation ceases. When Asians im- migrate to the United States and adopt Western diets and habits, however, they experience these diseases and problems at the same rates as native Westerners.

emerging from research. Flaxseed contains lignans, compounds converted into biologically active phytoestrogens by bacteria that normally reside in the human intestine. Some evidence about their effects follows:

Flaxseed intake, but not fl axseed oil, • appears to improve blood lipids in ways supportive of heart health, par- ticularly among older women.12

Rats fed chow high in fl axseed de-• velop fewer cancerous changes and reduced tumor growth in mammary tis- sue under experimental conditions.13

In one study, men with prostate cancer • given fl axseed had less cancer cell proliferation than controls.14

Some evidence also suggests that fl axseed may lower blood pressure.15 Some risks are associated with fl axseed overuse, however. Flaxseed contains compounds that interfere with vitamin or mineral absorption, and thus high daily fl axseed intakes could cause nutrient defi ciencies. Large quantities of fl axseed also cause digestive distress. Includ-

Blackberries1. Walnuts2. Strawberries3. Spinach4. Artichokes, prepared5. Cranberries 6. Coffee7. Raspberries8. Pecans9. Blueberries10. Cloves, ground 11. Grape juice, cranberry juice, 12. pomegranate juice

Chocolate, dark, unsweetened 13. Cherries, sour 14. Wine, red15.

Common Foods

Ranked by

Antioxidant

Content

table C2-3

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65controversy 2 A r e S o m e F o o d s “ S u p e r f o o d s ” f o r H e a l t h ?

dose supplements of green tea extract have caused liver toxicity and should be avoided.41

A fl avonoid in purple grape juice and red wine, resveratrol, seems to hold promise as a disease fi ghter, but the amount present in wine or a serving of grape juice may be too small to benefi t human health.** The fl avonoid has been credited with extending the life of yeast cells, worms, fl ies, and fi sh but no one knows if such an effect is plausible for human beings.42 In population studies, people who regularly consume red wine, grapes and their products, and other fl avonoid-rich fruits and vegetables often have a lower incidence of cardiovascular disease than others.43 Scientists have suggested biological mechanisms by which these foods might reduce disease risks but controlled clinical human trials to show that people’s hearts actually benefi t from grape consumption are still lacking.44

In high doses, resveratrol has also demonstrated some anticancer activities, but such doses are larger than those attainable by diet, even with daily red wine intake.45 As for drinking red wine for health, Controversy 3 concludes that the immediate risks from alcoholic bever- ages for young adults may outweigh potential benefi ts.

The juice of the pomegranate fruit ranks high among juices in antioxi- dants. Antioxidants reduce the oxida-

tive stress and tissue infl ammation, conditions associated with many chronic diseases.46 Much is yet to be learned about the bioavailability, metabolism, and health effects of the principal phyto- chemicals of pomegranates.

Flavonoids in whole grains may confer health benefi ts on the eater but also im- part a bitter taste. To please consumers who tend to prefer mild or sweet fl avors, food producers refi ne away fl avonoid- rich plant parts, such as bran or fruit skins. Thus, white bread, white grape juice, and white wine lack the fl avonoid contents of their darker counterparts.

Yogurt Yogurt is a special case among “superfoods.” Although yogurt lacks

with antioxidant activity found in guava, papaya, pink grapefruit, tomatoes (es- pecially cooked tomatoes and tomato products), and watermelon.

Lycopene and some of its chemical relatives fi lter high-energy wavelengths of visible light. In the skin, they may act as a sort of internal sunscreen, protecting skin from damaging sun rays that cause skin cancer.§33 Lycopene and some products of its metabolism also act as antioxidants and, theoretically, could inhibit the growth of cancer cells, but so far, research does not support the idea.34 Something else about tomato-eating peoples may be reducing their risks.

An evidence-based review by the FDA concluded that no or very little credible evidence exists to support an association between lycopene or tomato consump- tion and reduced cancer rates.35 It does appear that lycopene supplements are not as hazardous as those of its chemi- cal cousins, beta-carotene and lutein, which clearly raise the risk of lung cancer in smokers.36

Tea, Wine, Pomegranate, and Whole Grain Diets containing fl avonoid-rich foods are frequently credited with health-promoting quali- ties. For example, a recent study suggests that young women who drink three or more cups of tea each day suffer less breast cancer than others.37 When research- ers reviewed the results of 51 studies, the evidence for green tea and cancer was mixed—sometimes drinking the tea seemed protective but other times it did not, so no conclusion can be drawn.38

People in Japan who drink fi ve cups of green tea each day die less often from a form of stroke than people

who drink less than a cup.39 Green tea consumption has also been associated with reduced oxidative stress and infl am- mation among smokers, lower blood lipids, and even reduced body fatness.40 Whether such associations will hold up under further scrutiny is unknown. High-

form, soy phytoestrogens may interfere with the actions of a drug used in breast cancer treatment, however.29 Also, high doses of genistein given to pregnant mice produced female offspring with a high risk of cancer of the uterus.‡ Preg- nant women should never take chances with unproven supplements of any kind (Chapter 13 explains why).With regard to the biological activity of soy, scientifi c understanding is incomplete.30

As for menopause, no consistent fi nd- ings indicate that soy phytoestrogens can eliminate the common sensations of elevated body temperature known as “hot fl ashes.”31 Some evidence does suggest that soy phytoestrogens may help to pre- serve women’s bone density after meno- pause but more research is required to confi rm or refute this fi nding.32 Hormone replacement therapy, once routinely used in menopause to prevent symptoms and bone loss, involves serious health risks, so alternatives are needed. Phyto- estrogen supplements sold as “natural” hormone therapy are unproven, however, and may pose health risks.

The opposing actions of phytoestro- gens should raise a red fl ag against tak- ing supplements, especially by people who have had cancer or whose close relatives have developed cancer. The American Cancer Society recommends that breast cancer survivors and those under treatment for breast cancer should consume only moderate amounts of soy foods as part of a healthy plant-based diet and should not intentionally ingest very high levels of soy products.

Tomatoes People around the world who eat the most to- matoes, about fi ve tomato-containing meals per week, are less likely to suffer from cancers of the esophagus, prostate, or stomach than those who avoid tomatoes. Among phytochemical candidates for promoting this effect is lycopene, a red pigment

‡The drug is DES, or diethylstilbestrol, once given to pregnant women before discovery of the greatly increased risk of uterine and breast cancer among their daughters.

§The other carotenoid relatives of lycopene are lutein and zeaxanthin—more about them in Chapter 7. **The fl avonoid is resveratrol.

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research to support such claims is generally weak or nonexistent.

Phytochemical researchers conclude that the best-known, most effective, and safest sources for bioactive food compo- nents are foods, not supplements. Even those in foods, however, can interfere with the activities of certain drugs and undermine the medical treatment of serious diseases.55 Such food and drug interactions are of critical importance, and the Controversy section of Chapter 14 is devoted to them.

THE CONCEPT OF FUNCTIONAL FOODS Virtually all whole foods have some spe- cial value in supporting health and are therefore functional foods. Cranberries may help prevent urinary tract infections; garlic may lower blood cholesterol; and green tea may inhibit ulcer infections, just to name a few examples.56 Manufactured functional foods, however, often consist of processed foods that are fortifi ed with nutrients or enhanced with bioactive food components (calcium-fortifi ed orange juice, for example). The creation of these functional foods is a fast-growing trend in the global food supply.57

An example of a popular manufac- tured food is a margarine blended with a phytosterol intended to lower blood cholesterol.58 Such novel functional foods raise questions:

Does the margarine constitute a food • or a drug?59

Which is the better choice for the • health-conscious diet planner: to eat a food with additives that affect body function or to adjust the diet?

Does it make more sense to add • cholesterol-lowering margarine to the diet or to replace butter with unsatu- rated oils and eat more plant foods to supply phytosterols?60

Is it more benefi cial to eat fried snack • foods sprinkled with phytochemicals and candy bars laced with vitamins than to obtain these substances from ordinary foods?

What about smoothies packed with • medicinal herbs—are these foods safe to consume regularly? Are they safe for children?

diseases any given person may suffer, much less whether an isolated supple- ment might be of use. Individual phytochemicals, like actors in a play,

are part of a larger story with intertwin- ing and complementary roles—a fact that reinforces the principle of variety in diet planning.

Supporters of Phytochemical Supplements Users and sellers of phytochemical supplements argue that existing evi- dence is good enough to recommend that people take supplements of puri- fi ed phytochemicals. Users, eager for potential benefi ts, and sellers, hoping for profi ts, tend to discount the potential for harm from “natural” substances. People have been consuming foods containing phytochemicals for tens of thousands of years, they say, and because the body can handle phytochemicals in foods, it stands to reason that supplements of those phytochemicals are safe as well.

Detractors of Phytochemical Supplements Such thinking raises concerns among scientists. They point out that although the body is equipped to handle phyto- chemicals when diluted in the other con- stituents of whole foods, it is not adapted to concentrated supplement doses. Fur- ther, the body absorbs only small amounts of these compounds into the bloodstream and quickly destroys most types with its detoxifying equipment.54 No one knows why the body thus defends itself against these substances, but supplements of them overwhelm the body’s defenses.

Consider these facts about phy- tochemical supplements and health:

Phytochemicals alter body functions, 1. sometimes powerfully, in ways that are only partly understood.

Evidence for the safety of isolated 2. phytochemicals in human beings is lacking.

No regulatory body oversees the 3. safety of phytochemicals sold to consumers. No studies proving their safety or effectiveness are required before they are marketed.

Phytochemical labels may make 4. structure-function claims but existing

phytochemicals from plants, it contains living Lactobacillus or other bacteria that ferment milk into yogurt or a liquid yogurt beverage called kefi r. Such micro- organisms, or probiotics, can set up residence in the digestive tract and alter its functioning in ways that are claimed to reduce diseases such as colon cancer, ulcers, and other digestive problems; reduce allergies; or improve immunity and resistance to infections.47 Lactobacillus organisms may indeed be useful for improving the diarrhea that often occurs from the use of antibiotic drugs or from other causes.48 Reports of increased mortality among patients with diseases of the pancreas and serious infections in those with compromised immunity raise concerns about the safety of probiotic microorganism supplements for some groups of people.49

Certain foods provide prebiotics, nutrients such as certain carbohydrates, that probiotic organisms need to grow. Certain by-products of such bacterial growth appear to decrease infl amma- tion of the colon, a condition related to disease.50 More research is needed to clarify whether probiotics and prebiotics may benefi t or harm human health.51

PHYTOCHEMICAL SUPPLEMENTS No doubt exists that diets rich in whole grains, legumes, vegetables, fruits, and other whole foods reduce the risks of heart disease and cancer, but isolating the responsible food, nutrient, or phy- tochemical has proved diffi cult. Foods deliver thousands of bioactive food components, all within a food matrix that maximizes their availability and effective- ness.52 Broccoli, and particularly broc- coli sprouts, may contain as many as 10,000 different phytochemicals—each with the potential to infl uence some ac- tion in the body. These foods are under study for their potential to defend against cancers at the DNA level, and Chapter 11 comes back to them.53

Even if it were known with certainty which foods protect against which diseases, no one can yet predict what

67controversy 2 A r e S o m e F o o d s “ S u p e r f o o d s ” f o r H e a l t h ?

or phytochemicals for their magical health effects. Instead, take a no- nonsense approach where your health is concerned: choose a wide variety of whole grains, legumes, nuts, fruits, and vegetables in the context of an adequate, balanced, and varied diet to receive all of the health benefi ts these foods can offer.

C2-4 offers some tips for consuming the foods known to provide phytochemicals.

Various benefi cial constituents are widespread among foods, and research indicates that a diverse selection of fruits and vegetables in the diet is more ben- efi cial than an equal number of servings from just a few types.61 In other words, don’t try to single out a few “superfoods”

Critics suggest that the designation “functional foods” may be nothing more than a marketing tool. After all, even the most experienced researchers cannot yet identify the perfect combination of bioactive food components to sup- port optimal health. Yet manufacturers freely generate and distribute such concoctions as if they possessed that knowledge.

THE FINAL WORD In light of all of the evidence for and against phytochemicals and functional foods, it seems clear that a moderate approach is warranted. People who eat the recommended amounts of a variety of fruits and vegetables each day may cut their risk for many diseases by as much as half. Replacing some meat with soy foods and other legumes may also lower heart disease and cancer risks. Choosing green tea or vegetable juice, or fruit juice within bounds, instead of daily soft drinks may also cut risks. In the context of a healthy diet, ordinary foods are time-tested for safety, posing virtu- ally no risk of toxic levels of nutrients or phytochemicals (although some contain natural toxins; see Chapter 12). Table

Functional foods currently on the market promise to “enhance mood,” “promote relaxation and good karma,” “increase alertness,” and “improve memory,” among other claims.

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Eat more fruit. The average U.S. diet provides little more than ½ cup fruit a day. Re-• member to choose juices and raw, dried, or cooked fruits and vegetables at mealtimes as well as for snacks. Choose dried fruit in place of candy. Increase vegetable portions. Double the normal portion of cooked plain, nonstarchy • vegetables to 1 cup. Use herbs and spices. Cookbooks offer ways to include parsley, basil, garlic, hot pep-• pers, oregano, and other benefi cial seasonings. Replace some meat. Replace some of the meat in the diet with grains, legumes, and • vegetables. Oatmeal, soy meat replacer, or grated carrots mixed with ground meat and seasonings make a luscious, nutritious meat loaf, for example. Add grated vegetables. Carrots in chili or meatballs, celery and squash in spaghetti • sauce, etc. add phytochemicals without greatly changing the taste of the food. Try new foods. Try a new fruit, vegetable, or whole grain each week. Walk through • vegetable aisles and visit farmers’ markets. Read recipes. Try tofu, fortifi ed soy drink, or soybeans in cooking.

Tips for Consuming Phytochemicals table

C2-4

The Remarkable Body 33 do you ever . . .

Feel your heart beat and wonder • where the blood goes?

Hear people say “You are what you • eat” and think it is just an old saying?

Wonder how food on the plate • becomes nourishment for your body?

Take antacids to relieve heartburn?•

Keep reading . . .

LO 3.1 Describe the levels of organization in the body, and identify some basic ways in which nutrition supports them.

LO 3.2 Compare the terms mechanical digestion and chemical digestion, and point out where these processes occur along the digestive tract.

LO 3.3 Trace the breakdown and absorption of carbohydrate, fat, and protein from the mouth to the colon.

LO 3.4 Explain how nutrients are transported and stored in the body.

LO 3.5 Defi ne the term moderate alcohol consumption, and discuss the potential health effects, both negative and positive, associated with this level of drinking.

Learning Objectives To find learning objective topics in this chapter, look for the text headings with a corresponding “LO” number above the heading. After reading this chapter, you should be able to accomplish the following:

Art Box Images/Getty Images

69T h e B o d y ’ s C e l l s

3 A t the moment of conception, you received genes in the form of DNA from your

mother and father, who, in turn, had inherited them from their parents, and so on into history. Since that moment, your genes have been working behind the scenes, directing your body’s development and functioning. Many of your genes are ancient in origin and are little changed from genes of thousands of centuries ago, but here you are—living with the food, the luxuries, the smog, the contaminants, and all the other pleasures and problems of the 21st century. Th ere is no guarantee that a diet haphazardly chosen from today’s foods will meet the needs of your “an- cient” body. Unlike your ancestors, who nourished themselves from the wild plants and animals surrounding them, you must learn how your body works, what it needs, and how to select foods to meet its needs.

LO 3.1

The Body’s Cells Th e human body is composed of trillions of cells, and none of them knows any- thing about food. You may get hungry for fruit, milk, or bread but each cell of your body needs nutrients—the vital components of foods. Th e ways in which the body’s cells cooperate to obtain and use nutrients are the subjects of this chapter.

Each of the body’s cells is a self-contained, living entity (see Figure 3-1), but at the same time it depends on the rest of the body’s cells to supply its needs. Among the cells’ most basic needs are energy and the oxygen with which to burn it. Cells also need water to maintain the environment in which they live. Th ey need building blocks and control systems. Th ey especially need the nutrients they cannot make for themselves—the essential nutrients fi rst described in Chapter 1—which must be supplied from food. Th e fi rst principle of diet planning is that the foods we choose must provide energy and the essential nutrients, including water.

CONCEPT LINK 3-1 DNA was defined in Chapter 1 (page 2) as the molecule that encodes genetic information in its structure; genes were defined as units of a cell’s inheritance situated along the DNA strands.

These hairlike projections are typical of cells that absorb nutrients in the intestines (details in Figure 3-13).

Inside the nucleus is the hereditary material, DNA, which contains the genes. The genes control the inheritance of the cell’s character- istics and its day-to-day workings. They are faithfully copied each time the cell duplicates itself.

On these membranes, instructions from the genes are translated into proteins that perform functions in the body.

Many other structures are present. This is a mitochondrion, a structure that takes in nutrients and releases energy from them.

A membrane encloses each cell’s contents.

A separate, inner membrane encloses the cell’s nucleus.

This cell has been greatly enlarged; real cells are so tiny that 10,000 can fi t on the head of a pin.

A Cell (Simplified Diagram) figure 3-1

cells the smallest units in which independent life can exist. All living things are single cells or organisms made of cells.

70 chapter 3 T h e R e m a r k a b l e B o d y

As living things, cells also die off , although at varying rates. Some skin cells and red blood cells must replenish themselves every 10 to 120 days. Cells lining the di- gestive tract replace themselves every three days. Under ordinary conditions, many muscle cells reproduce themselves only once every few years. Liver cells have the ability to reproduce quickly and do so whenever repairs to the organ are needed. Certain brain cells do not reproduce at all; if damaged by injury or disease, they are lost forever.

Th e cells work in cooperation with each other to support the whole body. Gene activity within each cell determines the nature of that work.

Genes Control Functions Each gene is a blueprint that directs the production of one or more proteins, such as an enzyme that performs cellular work. Genes also provide the instructions for all of the structural components cells need to survive (see Figure 3-2). Each cell contains a complete set of genes, but diff erent ones are active in diff erent types of cells. For example, in some intestinal cells, the genes for making digestive enzymes are active; in some of the body’s fat cells, the genes for making enzymes that me- tabolize fat are active.

Genes aff ect the way the body handles its nutrients. Certain variations in some of the genes alter the way the body absorbs, metabolizes, or excretes nutrients from

Nucleus Cell

DNA in chromosomes

Genes

Protein Protein Protein

Living cell

Living tissue

1 1

4 4

5 5

Each cell’s nucleus contains DNA — the material of heredity in all living things.

Long strands of human DNA coil into 23 pairs of chromosomes. If the

strands of DNA in all the body’s

cells were uncoiled and laid end to

end, they would stretch to the sun

and back four hundred times. Yet

DNA strands are so tiny that about

5 million of them could be threaded

at once through the eye of a

needle.

Genes contain instructions for making proteins. Genes are sections along the strands of DNA that serve as templates for the building of

proteins. Some genes are involved in building just one protein; others are involved in building more than one.

Many other steps are required to make a protein. See Figure 6-6 of Chapter 6.

Proteins do the work of living cells. Cells employ proteins to perform essential functions and provide structures.

Communities of functioning cells make up the living tissue.

If the human genome were a book of instructions on how to make a human being, then the 23 chromosomes of DNA would be chapters. Each gene would be a word, and the individual molecules that form the DNA would be letters of the alphabet.

From DNA to Living Cells figure 3-2

enzyme any of a great number of working proteins that speed up a specifi c chemical reaction, such as breaking the bonds of a nu- trient, without undergoing change themselves. Enzymes and their actions are described in Chapter 6.

fat cells cells that specialize in the storage of fat and form the fat tissue. Fat cells also produce fat-metabolizing enzymes; they also produce hormones involved in appetite and energy balance (see Chapter 9).

71T h e B o d y F l u i d s a n d t h e C a r d i o v a s c u l a r S y s t e m

the body. Occasionally, a gene variation can cause a lifelong malady—that is, an inborn error of metabolism—that may require a special diet to minimize its po- tential to harm the body. An example is the inborn error phenylketonuria (PKU), in which a genetic variation compromises the body’s ability to handle the amino acid phenylalanine. People with this condition must carefully limit their intakes of phenylalanine, so food manufacturers are required to print warning labels on foods, such as certain artifi cial sweeteners, that contain it.

Nutrients also aff ect the genes. For example, the concentrations of certain nutri- ents and phytochemicals in the body fl uids and tissues infl uence the genes to make more or less of certain proteins. Th ese changes, in turn, alter body functions and ultimately hold meaning for health and disease. Controversy 11 presents details.

Cells, Tissues, Organs, Systems Cells are organized into tissues that perform specialized tasks. For example, indi- vidual muscle cells are joined together to form muscle tissue, which can contract. Tissues, in turn, are grouped together to form whole organs. In the organ we call the heart, for example, muscle tissues, nerve tissues, connective tissues, and others all work together to pump blood. Some body functions are performed by several related organs working together as part of a body system. For example, the heart, lungs, and blood vessels cooperate as parts of the cardiovascular system to deliver oxygen to all the body’s cells. Th e next few sections present the body systems with special signifi cance to nutrition.

KE Y POINT The body’s cells need energy, oxygen, and nutrients, including water, to remain healthy and do their work. Genes direct the making of each cell’s protein machinery, including enzymes. Genes and nutrients interact in ways that aff ect health. Specialized cells are grouped together to form tissues and organs; organs work together in body systems.

The Body Fluids and the Cardiovascular System Body fl uids supply the tissues continuously with energy, oxygen, and nutrients, in- cluding water. Th e fl uids constantly circulate to pick up fresh supplies and deliver wastes to points of disposal. Every cell continuously draws oxygen and nutrients from those fl uids and releases carbon dioxide and other waste products into them.

Th e body’s circulating fl uids are the blood and the lymph. Blood travels within the arteries, veins, and capillaries, as well as within the heart’s chambers (see Fig- ure 3-3). Lymph travels in separate vessels of its own.

Circulating around the cells are other fl uids such as the plasma of the blood, which surrounds the white and red blood cells, and the fl uid surrounding muscle cells (see Figure 3-4). Th e fl uid surrounding cells (extracellular fl uid) is derived from the blood in the capillaries; it squeezes out through the capillary walls and fl ows around the outsides of cells, permitting exchange of materials.

Some of the extracellular fl uid returns directly to the bloodstream by reentering the capillaries. Th e fl uid remaining outside the capillaries forms lymph, which trav- els around the body by way of lymph vessels. Th e lymph eventually returns to the bloodstream near the heart where a large lymph vessel empties into a large vein. In this way, all cells are served by the cardiovascular system.

Th e fl uid inside cells (intracellular fl uid) provides a medium in which all cell re- actions take place. Its pressure also helps the cells to hold their shape. Th e intracel- lular fl uid is drawn from the extracellular fl uid that bathes the cells on the outside.

Interactions between vitamins and minerals • and the genes are addressed in Chapters 7 and 8; other nutrient and gene interactions are addressed in the chapters on pregnancy and disease prevention.

inborn error of metabolism a genetic variation present from birth that may result in disease.

phenylketonuria (PKU) an inborn error of metabolism that interferes with the body’s handling of the amino acid phenylalanine, with potentially serious consequences to the brain and nervous system in infancy and childhood. Often referred to by its abbreviation, PKU.

tissues systems of cells working together to perform specialized tasks. Examples are muscles, nerves, blood, and bone.

organs discrete structural units made of tis- sues that perform specifi c jobs. Examples are the heart, liver, and brain.

body system a group of related organs that work together to perform a function. Ex- amples are the circulatory system, respiratory system, and nervous system.

blood the fl uid of the cardiovascular system; composed of water, red and white blood cells, other formed particles, nutrients, oxygen, and other constituents.

lymph (LIMF) the fl uid that moves from the bloodstream into tissue spaces and then trav- els in its own vessels, which eventually drain back into the bloodstream (see Figure 3-6).

arteries blood vessels that carry blood con- taining fresh oxygen supplies from the heart to the tissues (see Figure 3-3).

veins blood vessels that carry blood, with the carbon dioxide it has collected, from the tissues back to the heart (see Figure 3-3).

capillaries minute, weblike blood vessels that connect arteries to veins and permit trans- fer of materials between blood and tissues (see Figures 3-3 and 3-4).

plasma the cell-free fl uid part of blood and lymph.

extracellular fl uid fl uid residing outside the cells that transports materials to and from the cells.

intracellular fl uid fl uid residing inside the cells that provides the medium for cellular reactions.

72 chapter 3 T h e R e m a r k a b l e B o d y

All the blood circulates to the lungs, where it picks up oxygen and releases car- bon dioxide wastes from the cells, as Figure 3-5 shows. Th en the blood returns to the heart, where the pumping heartbeats push this fresh oxygenated blood from the lungs out to all body tissues. As the blood travels through the rest of the cardiovas- cular system, it delivers materials cells need and picks up their wastes.

Animated! Blood Flow in the Cardiovascular System figure 3-3

Return blood to heart

Lungs

Heart

Liver

Kidneys

Intestines

Right Left

Heart Right side pumps blood to lungs Left side pumps oxygenated blood to body

Lungs Oxygenate blood Remove carbon dioxide from blood

Head and Arms

Liver Filters toxins from blood Stores, transforms, and mobilizes nutrients

Intestines Absorb nutrients

Kidneys Filter wastes from blood Form urine

Pelvis and Legs

The blood is routed through the body as follows: • Heart to tissues to heart to lungs to heart (repeat).

The portion of the blood that flows through the blood vessels of the intestine travels from: • Heart to intestine to liver to heart.

lungs the body’s organs of gas exchange. Blood circulating through the lungs releases its carbon dioxide and picks up fresh oxygen to carry to the tissues.

intestine the body’s long, tubular organ of digestion and the site of nutrient absorption.

liver a large, lobed organ that lies just under the ribs. It fi lters the blood, removes and pro- cesses nutrients, manufactures materials for export to other parts of the body, and destroys toxins or stores them to keep them out of the circulatory system.

73T h e B o d y F l u i d s a n d t h e C a r d i o v a s c u l a r S y s t e m

As it passes through the digestive system, the blood delivers oxygen to the cells there and picks up most nutrients other than fats and their relatives from the in- testine for distribution elsewhere. Lymphatic vessels pick up most fats from the intestine and then transport them to the blood (see Figure 3-6). All blood leaving the digestive system is routed directly to the liver, which has the special task of chemically altering the absorbed materials to make them better suited for use by other tissues. Later, in passing through the kidneys, the blood is cleansed of wastes (look again at Figure 3-3). Note that the blood carries nutrients from the intestine to the liver, which releases them to the heart, which pumps them to the waiting body tissues.

To ensure effi cient circulation of fl uid to all your cells, you need an ample fl uid intake. Th is means drinking suffi cient water to replace the water lost each day. Car- diovascular fi tness is essential, too, and constitutes an ongoing project that requires attention to both nutrition and physical activity. Healthy red blood cells also play a role, for they carry oxygen to all the other cells, enabling them to use fuels for en- ergy. Since red blood cells arise, live, and die within about four months, your body replaces them constantly, a manufacturing process that requires many essential nu- trients from food. Consequently, the blood is very sensitive to malnutrition and often serves as an indicator of disorders caused by dietary defi ciencies or imbalances of vitamins or minerals.

KE Y POINT Blood and lymph deliver nutrients to all the body’s cells and carry waste materials away from them. Blood also delivers oxygen to cells. The cardiovascular system ensures that these fl uids circulate properly among all organs.

Blood enters tissues by way of artery.

Blood collects into veins for return to heart.

Blood circulates among cells by way of capillaries.

Lymph vessel.

Inside capillary.

Lymph vessel.

Capillary wall has spaces between its flat cells.

Cells of surrounding tissue.

Fluid filters out of blood through the

capillary whose walls are made of

cells with small spaces between

them.

Fluid may flow back into the capillary or

into a lymph vessel. Lymph enters the

bloodstream later through a large lymphatic

vessel that empties into a large vein.

The upper box shows a tiny portion of tissue with blood fl ow- ing through its network of capillaries (greatly enlarged). The lower box illustrates the movement of the extracellular fl uid. Exchange of materials also takes place between cell fl uid and extracellular fl uid.

Animated! How the Body Fluids

Circulate Around Cells

figure 3-4

Chapter 8 offers guidelines for water intake.•

P ur

es to

ck /G

et ty

Im ag

All the body’s cells live in water.

Body tissue

AIR

Lung capillary Air sac in lungTissue capillary

CO2 CO2

In body tissues, red blood cells

give up their oxygen (O2) and

absorb carbon dioxide (CO2).

In the air sacs of the lungs, the red

blood cells give up their load of carbon

dioxide (CO2) and absorb oxygen (O2)

from air to supply to body tissues.

Oxygen–Carbon Dioxide

Exchange in the Lungs

figure 3-5

kidneys a pair of organs that fi lter wastes from the blood, make urine, and release it to the bladder for excretion from the body.

74 chapter 3 T h e R e m a r k a b l e B o d y

The Hormonal and Nervous Systems In addition to nutrients, oxygen, and wastes, the blood carries chemical messengers, hormones, from one system of cells to another. Hormones communicate changing conditions that demand responses from the body organs.

What Do Hormones Have to Do with Nutrition? Hormones are secreted and released directly into the blood by organs known as glands. Glands and hormones abound in the body. Each gland monitors a condition and produces one or more hormones to regulate it. Each hormone acts as a messen- ger that stimulates various organs to take appropriate actions.

For example, when the pancreas (a gland) detects a high concentration of the blood’s sugar, glucose, it releases insulin, a hormone. Insulin stimulates muscle and other cells to remove glucose from the blood and to store it. Th e liver also stores glucose. When the blood glucose level falls, the pancreas secretes another hormone, glucagon, to which the liver responds by releasing into the blood some of the glu- cose it stored earlier. Th us, a normal blood glucose level is maintained.

Nutrition aff ects the hormonal system. Fasting, feeding, and exercise alter hor- monal balances. In people who become very thin, for example, altered hormonal bal- ance causes their bones to lose minerals and weaken. Hormones also aff ect nutrition. Along with the nervous system, hormones regulate hunger and aff ect appetite. Th ey

Blood vessels (veins)

Valve

Lymph vessel joins the blood vessel

Lymph from lungs

Blood to lungs

Blood from lungs

Lymph node

Digestive tract lymph vessel network

Blood vessels (arteries)

Digestive tract blood capillaries

Heart

Nutrients are absorbed via two kinds of vessels in the intestines: blood capillaries and small lymph vessels. The capillaries lead to larger blood vessels that lead to the liver.

The lymph in the lymph vessels carries most of the absorbed dietary fat to the large vein near the heart. Some lymph vessels are depicted in Figure 3-13 (lower right), later on.

Lymph Vessels and the Bloodstream figure 3-6

hormones chemicals that are secreted by glands into the blood in response to condi- tions in the body that require regulation. These chemicals serve as messengers, acting on other organs to maintain constant conditions.

pancreas an organ with two main functions. One is an endocrine function—the making of hormones such as insulin, which it releases directly into the blood (endo means “into” the blood). The other is an exocrine function—the making of digestive enzymes, which it releases through a duct into the small intestine to assist in digestion (exo means “out” into a body cav- ity or onto the skin surface).

insulin a hormone from the pancreas that helps glucose enter cells from the blood (de- tails in Chapter 4).

glucagon a hormone from the pancreas that stimulates the liver to release glucose into the bloodstream.

75T h e H o r m o n a l a n d N e r v o u s S y s t e m s

carry messages to regulate the digestive system, telling the digestive organs what kinds of foods have been eaten and how much of each digestive juice to secrete in response. A hormone produced by the fat tissue informs the brain about the degree of body fatness and helps to regulate appetite. Hormones also regulate the menstrual cycle in women, and they aff ect the appetite changes many women experience dur- ing the cycle and in pregnancy. An altered hormonal state is thought to be at least partially responsible, too, for the loss of appetite that sick people experience. Hor- mones also regulate the body’s reaction to stress, suppressing hunger and the diges- tion and absorption of nutrients. When there are questions about a person’s nutrition or health, the state of that person’s hormonal system is often part of the answer.

KE Y POINT Glands secrete hormones that act as messengers to help regulate body processes.

How Does the Nervous System Interact with Nutrition? Th e body’s other major communication system is, of course, the nervous system. With the brain and spinal cord as central controllers, the nervous system receives and inte- grates information from sensory receptors all over the body—sight, hearing, touch, smell, taste, and others—which communicate to the brain the state of both the outer and inner worlds, including the availability of food and the need to eat. Th e nervous system also sends instructions to the muscles and glands, telling them what to do.

Th e nervous system’s role in hunger regulation is coordinated by the brain. Th e sensations of hunger and appetite are perceived by the brain’s cortex, the thinking, outer layer. Deep inside the brain, the hypothalamus (see Figure 3-7) monitors

Details about hormones, menstruation, and • the bones appear in Controversy 8 and Controversy 9.

Cortex

Hypothalamus

Spinal cord Pituitary gland

The hypothalamus monitors the body’s conditions and sends signals to the brain’s thinking portion, the cortex, which decides on actions. The pituitary gland is called the body’s master gland, referring to its roles in regulating the activities of other glands and organs of the body.

Cutaway Side View of the Brain Showing the

Hypothalamus and Cortex

figure 3-7

cortex the outermost layer of something. The brain’s cortex is the part of the brain where conscious thought takes place.

hypothalamus (high-poh-THAL-uh-mus) a part of the brain that senses a variety of conditions in the blood, such as temperature, glucose content, salt content, and others. It signals other parts of the brain or body to adjust those conditions when necessary.

76 chapter 3 T h e R e m a r k a b l e B o d y

many body conditions, including the availability of nutrients and water. To signal hunger, the physiological need for food, the digestive tract sends messages to the hypothalamus by way of hormones and nerves. Th e signals also stimulate the stom- ach to intensify its contractions and secretions, causing hunger pangs (and gurgling sounds). When your brain’s cortex perceives these hunger sensations, you want to eat. Th e conscious mind of the cortex, however, can override such signals, and a person can choose to delay eating despite hunger or to eat when hunger is absent.

In a marvelous adaptation of the human body, the hormonal and nervous systems work together to enable a person to respond to physical danger. Known as the fi ght- or-fl ight reaction, or the stress response, this adaptation is present with only minor variations in all animals, showing how universally important it is to survival. When danger is detected, nerves release neurotransmitters, and glands supply the com- pounds epinephrine and norepinephrine. Every organ of the body responds and metabolism speeds up. Th e pupils of the eyes widen so that you can see better; the muscles tense up so that you can jump, run, or struggle with maximum strength; breathing quickens and deepens to provide more oxygen. Th e heart races to rush the oxygen to the muscles, and the blood pressure rises so that the fuel the muscles need for energy can be delivered effi ciently. Th e liver pours forth glucose from its stores, and the fat cells release fat. Th e digestive system shuts down to permit all the body’s systems to serve the muscles and nerves. With all action systems at peak effi ciency, the body can respond with amazing speed and strength to whatever threatens it.

In ancient times, stress usually involved physical danger, and the response to it was violent physical exertion. In the modern world, stress is seldom physical, but the body reacts the same way. What stresses you today may be a checkbook out of control or a teacher who suddenly announces a pop quiz. Under these stresses, you are not supposed to fi ght or run as your ancient ancestor did. You smile at the “enemy” and suppress your fear. But your heart races, you feel it pounding, and hor- mones still fl ood your bloodstream with glucose and fat.

Your number-one enemy today is not a saber-toothed tiger prowling outside your cave, but a disease of modern civilization: heart disease. Years of fat and other con- stituents accumulating in the arteries and stresses that strain the heart often lead to heart attacks, especially when a body accustomed to chronic underexertion ex- periences sudden high blood pressure. Daily exercise as part of a healthy lifestyle releases pent-up stress and helps to protect the heart.

KE Y POINT The nervous system joins the hormonal system to regulate body processes through communication among all the organs. Together, the hormonal and nervous systems respond to the need for food, govern the act of eating, regulate digestion, and call for the stress response.

The Immune System Many of the body’s tissues cooperate to maintain defenses against infection. Th e skin presents a physical barrier, and the body’s cavities (lungs, mouth, digestive tract, and others) are lined with membranes that resist penetration by invading mi- crobes and other unwanted substances. Th ese linings are highly sensitive to vitamin and other nutrient defi ciencies, and health-care providers inspect both the skin and the inside of the mouth to detect signs of malnutrition. (Later chapters present details of the signs of defi ciencies.) If an antigen, or foreign invader, penetrates the body’s barriers, the immune system rushes in to defend the body against harm.

Immune Defenses Of the 100 trillion cells that make up the human body, one in every hundred is a white blood cell. Th e actions of two types of white blood cells, the phagocytes and the lymphocytes, known as T-cells and B-cells, are of interest:

fi ght-or-fl ight reaction the body’s instinctive hormone- and nerve-mediated reaction to danger. Also known as the stress response.

neurotransmitters chemicals that are re- leased at the end of a nerve cell when a nerve impulse arrives there. They diffuse across the gap to the next cell and alter the membrane of that second cell to either inhibit or excite it.

epinephrine (EP-ih-NEFF-rin) the major hormone that elicits the stress response.

norepinephrine (NOR-EP-ih-NEFF-rin) a compound related to epinephrine that helps to elicit the stress response.

metabolism the sum of all physical and chemical changes taking place in living cells; includes all reactions by which the body ob- tains and spends the energy from food.

microbes bacteria, viruses, or other organ- isms invisible to the naked eye, some of which cause diseases. Also called microorganisms.

antigen a microbe or substance that is foreign to the body.

immune system a system of tissues and organs that defend the body against antigens, foreign materials that have penetrated the skin or body linings.

lymphocytes (LIM-foh-sites) white blood cells that participate in the immune response; B-cells and T-cells.

77T h e I m m u n e S y s t e m

Phagocytes.• Th ese scavenger cells travel throughout the body and are the fi rst

to defend body tissues against invaders. When a phagocyte recognizes a foreign

particle, such as a bacterium, the phagocyte forms a pocket in its own outer

membrane, engulfi ng the invader. Th e phagocytes may then attack the invader

with oxidizing chemicals in an “oxidative burst” or may otherwise digest or de-

stroy them. Phagocytes also leave a chemical trail that helps other immune cells

to fi nd the infection and join the defense.

T-cells.• Killer T-cells are lymphocytes that “read” and “remember” the chemi-

cal messages put forth by phagocytes to identify invaders. Th e killer T-cells

then seek out and destroy all foreign particles having the same identity. T-cells

defend against fungi, viruses, parasites, some bacteria, and some cancer cells (see

the photo). Th ey also pose a formidable obstacle to a successful organ trans-

plant—the physician must prescribe immunosuppressive drugs following surgery

to hold down the T-cells’ attack against the “foreign” organ. Another group,

helper T-cells, does not attack invaders directly but helps other immune cells

to do so. People suff ering from the disease AIDS (acquired immunodefi ciency

syndrome) are rendered defenseless against other diseases because the virus that

causes AIDS selectively attacks and destroys their helper T-cells.*

B-cells.• B-cells respond rapidly to infection by dividing and releasing invader-

fi ghting proteins, antibodies, into the bloodstream. Antibodies travel to the

site of the infection and stick to the surface of the foreign particles, killing or

inactivating them. Like T-cells, B-cells also retain a chemical memory of each

invader, and if the encounter recurs, the response is swift. Immunizations work

this way: a disabled or harmless form of a disease-causing organism is injected

into the body so that the B-cells can learn to recognize it. Later, if the live in-

fectious organism invades, the B-cells quickly release antibodies to destroy it.

In addition to the phagocytes and lymphocytes, the immune system includes many other categories of white blood cells and many organs and tissues. To func- tion properly, all of these cells and organs depend on a steady fl ow of nutrients, delivered to the bloodstream from the digestive system.

KE Y POINT A properly functioning immune system enables the body to resist diseases.

Infl ammation When tissues become injured or irritated they undergo infl ammation, a condition of increased white blood cells, redness, heat, pain, swelling, and sometimes loss of function of the aff ected body part. Infl ammation is the immune system’s normal, healthy response to cell injury.

Many diseases, particularly chronic diseases of later life, such as heart disease, diabetes, and a severe type of arthritis, involve chronic infl ammation.1† When chronic, low-grade, unrelieved infl ammation exists in chronic diseases, it often foretells of an increase in both the severity of the disease and the risk of death from the disease.2 Infl ammation is a sign that a disease process is underway and wors- ening. Dietary factors, such as lipids and phytochemicals, may promote or inhibit infl ammation, but an important predictor is being overweight.3 Th e links among diet, infl ammatory processes, and diseases are topics of intense current research and they are discussed in later chapters.

KE Y POINT Infl ammation is the normal, healthy response of the immune system to cell injury. Chronic infl ammation may play roles in disease development.

More about oxidation in Chapters 5 and 7.•

*The AIDS virus is the human immunodefi ciency virus (HIV). † Reference notes are found in Appendix F.

T-cell

Cancer cell

A killer T-cell (the smaller cell on the bottom) has recognized a cancer cell and is attacking it with toxic chemicals that punch holes in the cancer cell’s surface.

oe hr

in ge

r I ng

el he

im In

te rn

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m bH

, p ho

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en na

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n/ B

on ni

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Chapter 11 explores the roles of nutrition in • supporting the immune system.

phagocytes (FAG-oh-sites) white blood cells that can ingest and destroy antigens. The process by which phagocytes engulf materi- als is called phagocytosis. The Greek word phagein means “to eat.”

T-cells lymphocytes that attack antigens. T stands for the thymus gland of the neck, where the T-cells are stored and matured.

B-cells lymphocytes that produce antibod- ies. B stands for bursa, an organ in the chicken where B-cells were fi rst identifi ed.

antibodies proteins, made by cells of the immune system, that are expressly designed to combine with and inactivate specifi c antigens.

infl ammation the immune system’s response to cellular injury characterized by an increase in white blood cells, redness, heat, pain, and swelling. Infl ammation plays a role in many chronic diseases.

78 chapter 3 T h e R e m a r k a b l e B o d y

LO 3.2, 3.3

The Digestive System When your body needs food, your brain and hormones alert your conscious mind to the sensation of hunger. Th en, when you eat, your taste buds guide you in judging whether foods are acceptable.

Taste buds contain surface structures that detect four basic chemical tastes: sweet, sour, bitter, and salty.4 A fi fth taste is sometimes included on this list: the taste of monosodium glutamate, sometimes called savory or umami (ooh-MOM-ee), its Asian name.5 Th ese basic tastes, along with aroma, texture, temperature, and other fl avor elements, aff ect a person’s experience of a food’s fl avor. In fact, the human ability to detect a food’s aroma is thousands of times more sensitive than the sense of taste. Th e nose can detect just a few molecules responsible for the aroma of frying bacon, for example, even when they are diluted in several rooms full of air.

Why Do People Like Sugar, Salt, and Fat? Sweet, salty, and fatty foods are almost universally desired, but most people have aversions to bitter and sour tastes (see Figure 3-8).6 Th e enjoyment of sugars en- courages people to consume ample energy, especially in the form of foods contain- ing carbohydrates, which provide the energy fuel for the brain. Th e pleasure of a salty taste prompts eaters to consume suffi cient amounts of two very important minerals—sodium and chloride. Likewise, foods containing fats provide concen- trated energy and essential nutrients needed by all body tissues. Th e aversion to bit- terness discourages consumption of foods containing bitter toxins and also aff ects people’s food preferences.7 People born with great sensitivity to bitter tastes are apt to avoid foods with slightly bitter fl avors, such as turnips and broccoli.

Th e instinctive liking for sugar, salt, and fat can lead to drastic overeating of these substances. Sugar has become widely available in pure form only in the last hundred

This newborn baby is (a) resting, (b) tasting distilled water, (c) tasting sugar, (d) tasting something sour, and (e) tasting something bitter.

The Innate Preference for Sweet Taste figure 3-8

Source: Taste-induced facial expressions of neonate infants from the classic studies of J. E. Steiner, in Taste and Development: The Genesis of Sweet Preference, ed. J. M. Weiffenbach, HHS publica- tion no. NIH 77–1068 (Bethesda, MD: U.S. Department of Health and Human Services, 1977), pp. 173–189, with permission of the author.

(a) (b) (c)

(d) (e)

79T h e D i g e s t i v e S y s t e m

years, so it is relatively new to the human diet. Although salt and fat are much older, today all three substances are added liberally to foods by manufacturers to tempt us to eat their products.

KE Y POINT The preference for sweet, salty, and fatty tastes seems to be inborn and can lead to overconsumption of foods that off er them.

The Digestive Tract Once you have eaten, your brain and hormones direct the many organs of the digestive system to digest and absorb the complex mixture of chewed and swallowed food. A diagram showing the digestive tract and its associated organs appears in Figure 3-9. Th e tract itself is a fl exible, muscular tube extending from the mouth through the throat, esophagus, stom- ach, small intestine, large intestine, and rectum to the anus, for a total length of about 26 feet. Th e human body surrounds this digestive canal. When you swallow something, it still is not inside your body—it is only inside the inner bore of this tube. Only when a nutrient or other substance passes through the wall of the diges- tive tract does it actually enter the body’s tissues. Many things pass into the diges- tive tract and out again, unabsorbed. A baby playing with beads may swallow one, but the bead will not really enter the body. It will emerge from the digestive tract within a day or two.

Th e digestive system’s job is to digest food to its components and then to absorb the nutrients and some nonnutrients, leaving behind the substances, such as fi ber, that are appropriate to excrete. To do this, the system works at two levels: one, me- chanical; the other, chemical.

KE Y POINT The digestive tract is a fl exible, muscular tube that digests food and absorbs its nutrients and some nonnutrients. Ancillary digestive organs aid digestion.

The Mechanical Aspect of Digestion Th e job of mechanical digestion begins in the mouth, where large, solid food pieces such as bites of meat are torn into shreds that can be swallowed without chok- ing. Chewing also adds water in the form of saliva to soften rough or sharp foods, such as fried tortilla chips, to prevent them from tearing the esophagus. Saliva also moistens and coats each bite of food, making it slippery so that it can pass easily down the esophagus.

Nutrients trapped inside indigestible skins, such as the hulls of seeds, must be liberated by breaking these skins before they can be digested. Chewing bursts open kernels of corn, for example, which would otherwise traverse the tract and exit un- digested. Once food has been mashed and moistened for comfortable swallowing, longer chewing times provide no additional advantages to digestion. In fact, for di- gestion’s sake, a relaxed, peaceful attitude during a meal aids digestion much more than chewing for an extended time.

Th e stomach and intestines then take up the task of liquefying foods through various mashing and squeezing actions. Th e best known of these actions is peri- stalsis, a series of squeezing waves that start with the tongue’s movement during a swallow and pass all the way down the esophagus (see Figure 3-10). Th e stomach and the intestines also push food through the tract by waves of peristalsis. Besides these actions, the stomach holds swallowed food for a while and mashes it into a fi ne paste; the stomach and intestines also add water so that the paste becomes more fl uid as it moves along.

digestive system the body system composed of organs that break down complex food particles into smaller, absorbable prod- ucts. The digestive tract and alimentary canal are names for the tubular organs that extend from the mouth to the anus. The whole system, including the pancreas, liver, and gallbladder, is sometimes called the gastrointestinal, or GI, system.

digest to break molecules into smaller mol- ecules; a main function of the digestive tract with respect to food.

absorb to take in, as nutrients are taken into the intestinal cells after digestion; the main function of the digestive tract with respect to nutrients.

peristalsis (per-ri-STALL-sis) the wave- like muscular squeezing of the esophagus, stomach, and small intestine that pushes their contents along.

stomach a muscular, elastic, pouchlike organ of the digestive tract that grinds and churns swallowed food and mixes it with acid and enzymes, forming chyme.

80 chapter 3 T h e R e m a r k a b l e B o d y

Accessory Organs That Aid Digestion

Salivary glands Donate a starch-digesting enzyme. Donate a trace of fat-digesting enzyme (important to infants).

Digestive Tract Organs That Contain the Food

Mouth Chews and mixes food with saliva.

Stomach Adds acid, enzymes, and fluid. Churns, mixes, and grinds food to a liquid mass.

Small intestine Secretes enzymes that digest carbohydrate, fat, and protein. Cells lining intestine absorb nutrients into blood and lymph.

Large intestine (Colon) Reabsorbs water and minerals. Passes waste (fiber, bacteria, any unabsorbed nutrients) and some water to rectum.

Rectum Stores waste prior to elimination.

Anus Holds rectum closed. Opens to allow elimination.

Esophagus Passes food to stomach.

Liver Manufactures bile, a detergent-like substance that facilitates digestion of fats.

Gallbladder Stores bile until needed.

Bile duct Conducts bile to small intestine.

Pancreas Manufactures enzymes to digest all energy- yielding nutrients. Releases bicarbonate to neutralize stomach acid that enters small intestine.

Pancreatic duct Conducts pancreatic juice into small intestine.

Animated! The Digestive System figure 3-9

81T h e D i g e s t i v e S y s t e m

Figure 3-11 shows the muscular stomach. Notice the circular sphincter muscle at the base of the esophagus. It squeezes the opening at the entrance to the stomach to narrow it and prevent the stomach’s contents from creeping back up the esophagus as the stomach contracts. Swallowed food remains in a lump in the stomach’s up- per portion, squeezed little by little to its lower portion. Th ere the food is ground and mixed thoroughly, ensuring that digestive chemicals mix with the entire thick liquid mass, now called chyme. Chyme bears no resemblance to the original food. Th e starches have been partly split, proteins have been uncoiled and clipped, and fat has separated from the mass.

Th e stomach also acts as a holding tank. Th e muscular pyloric valve at the stom- ach’s lower end (look again at Figure 3-11) controls the exit of the chyme, allowing only a little at a time to be squirted forcefully into the small intestine. Within a few hours after a meal, the stomach empties itself by means of these powerful squirts. Th e small intestine contracts rhythmically to move the contents along its length.

By the time the intestinal contents have arrived in the large intestine (also called the colon), digestion and absorption are nearly complete. Th e colon’s task is mostly to reabsorb the water donated earlier by digestive organs and to absorb minerals, leav- ing a paste of fi ber and other undigested materials, the feces, suitable for excretion. Th e fi ber provides bulk against which the muscles of the colon can work. Th e rectum stores this fecal material to be excreted at intervals. From mouth to rectum, the transit of a meal is accomplished in as short a time as a single day or as long as three days.

Some people wonder whether the digestive tract works best at certain hours in the day and whether the timing of meals can aff ect how a person feels. Timing of meals is important to feeling well, not because the digestive tract is unable to digest food at certain times, but because the body requires nutrients to be replenished every few hours. Digestion is virtually continuous, being limited only during sleep and exercise. For some people, eating late may interfere with normal sleep. As for exercise, it is best pursued a few hours after eating because digestion can inhibit physical work (see Chapter 10 for details).

KE Y POINT The digestive tract moves food through its various processing chambers by mechanical means. The mechanical actions include chewing, mixing by the stomach, adding fl uid,

Circular muscles are inside.

Cross section of the digestive tract, showing muscles.

As the circular and longitudinal muscles tighten and relax, the food moves ahead of the constriction.

Swallowed food

Longitudinal muscles are outside.

Peristalsis moves the digestive tract contents.

Peristaltic Wave Passing Down the Esophagus and Beyond figure 3-10

sphincter (SFINK-ter) a circular muscle sur- rounding, and able to close, a body opening.

chyme (KIME) the fl uid resulting from the actions of the stomach upon a meal.

pyloric (pye-LORE-ick) valve the circular muscle of the lower stomach that regulates the fl ow of partly digested food into the small intestine. Also called pyloric sphincter.

small intestine the 20-foot length of small-diameter intestine, below the stomach and above the large intestine, that is the major site of digestion of food and absorption of nutrients.

large intestine the portion of the intestine that completes the absorption process.

colon the large intestine.

feces waste material remaining after diges- tion and absorption are complete; eventually discharged from the body.

82 chapter 3 T h e R e m a r k a b l e B o d y

and moving the tract’s contents by peristalsis. After digestion and absorption, wastes are excreted.

The Chemical Aspect of Digestion Several organs of the digestive system secrete special digestive juices that perform the complex chemical processes of digestion. Digestive juices contain enzymes that break down nutrients into their component parts (Table 3-1 presents some enzyme terms). Th e digestive organs that release digestive juices are the salivary glands, the stomach, the pancreas, the liver, and the small intestine. Th eir secretions were listed previously in Figure 3-9 (on page 80).

In the Mouth Digestion begins in the mouth. An enzyme in saliva starts rapidly breaking down starch, and another enzyme initiates a little digestion of fat, espe- cially the digestion of milk fat (important in infants). Saliva also helps maintain the health of the teeth in two ways: by washing away food particles that would other- wise foster decay and by neutralizing decay-promoting acids produced by bacteria in the mouth.

Food is mixed and churned in this area.

Food is stored for a short time in this area.

Esophagus

Sphincter muscle

The pyloric valve controls the flow of chyme into the small intestine.

Small intestine (duodenum)

Muscle cross section

Folds inside stomach allow it to stretch and contract.

Crisscrossed muscle layers create churning and mixing motions.

inner

middle

outer

The Muscular Stomach figure 3-11

Over 30 digestive enzymes reduce food in the human digestive tract into nutrients that can be absorbed. Naming them all is beyond the scope of this book, but some general enzyme terms may prove useful.

-ase (ACE) a suffix meaning enzyme. Categories of digestive and other enzymes and individual enzyme names often contain this suffix. carbohydrase (car-boh-HIGH-drace) any of a number of enzymes that break the chemical bonds of carbohydrates. lipase (LYE-pace) any of a number of enzymes that break the chemical bonds of fats (lipids). protease (PRO-tee-ace) any of a num- ber of enzymes that break the chemical bonds of proteins.

Digestive Enzyme

Terms

table 3-1

83T h e D i g e s t i v e S y s t e m

In the Stomach In the stomach, protein digestion begins. Cells in the stom- ach release gastric juice, a mixture of water, enzymes, and hydrochloric acid. Th is strong acid mixture is needed to activate a protein-digesting enzyme and to ini- tiate digestion of protein—protein digestion is the stomach’s main function. Th e strength of an acid solution is expressed as its pH. Th e lower the pH number, the more acidic the solution; solutions with higher pH numbers are more basic. As Figure 3-12 demonstrates, saliva is only weakly acidic; the stomach’s gastric juice is much more strongly acidic. Notice on the right side of Figure 3-12 that the range of tolerance for the blood’s pH is exceedingly small.

Upon learning of the powerful digestive juices and enzymes within the diges- tive tract, students often wonder how the tract’s own cellular lining escapes being digested along with the food. Th e answer: specialized cells secrete a thick, viscous substance known as mucus, which coats and protects the digestive tract lining.

In the Intestine In the small intestine, the digestive process gets under way in earnest. Th e small intestine is the organ of digestion and absorption, and it fi nishes what the mouth and stomach have started. Th e small intestine works with the pre- cision of a laboratory chemist. As the thoroughly liquefi ed and partially digested nutrient mixture arrives there, hormonal messengers signal the gallbladder to con- tract and to squirt the right amount of bile, an emulsifi er, into the intestine. Other hormones notify the pancreas to release pancreatic juice containing the alkaline

Did You Know? Alcohol needs no assistance from digestive juices to ready it for absorption; its handling by the body is described in this chapter’s Contro- versy section.

pH of common substances

Concentrated lye14

Household ammonia11

Baking soda9

Pancreatic juice8

Water7

Urine6

Coffee5

Orange juice4

Vinegar3

Lemon juice Gastric juice2

Battery acid0

Milk, saliva

pH neutral

Basic

Acidic

Acidosis (Danger zone)

Normal blood pH range

Alkalosis (Danger zone)

Death

7.35

7.45

8.00

6.8

Bile

Soda water

Blood pH ranges (normal and danger zones)

A substance’s acidity or alkalinity is measured in pH units. Each step down the scale indicates a tenfold increase in concentration of hydrogen particles, which determine acidity. For example, a pH of 2 is 1,000 times stronger than a pH of 5.

pH Values of Digestive Juice and Other

Common Fluids

figure 3-12

hydrochloric acid a strong corrosive acid of hydrogen and chloride atoms, pro- duced by the stomach to assist in digestion.

pH a measure of acidity on a point scale. A solution with a pH of 1 is a strong acid; a solu- tion with a pH of 7 is neutral; a solution with a pH of 14 is a strong base.

mucus (MYOO-cus) a slippery coating of the digestive tract lining (and other body lin- ings) that protects the cells from exposure to digestive juices (and other destructive agents). The adjective form is mucous (same pronun- ciation). The digestive tract lining is a mucous membrane.

bile a cholesterol-containing digestive fl uid made by the liver, stored in the gallbladder, and released into the small intestine when needed. It emulsifi es fats and oils to ready them for enzymatic digestion (described in Chapter 5).

emulsifi er (ee-MULL-sih-fi re) a compound with both water-soluble and fat-soluble portions that can attract fats and oils into water, combin- ing them.

pancreatic juice fl uid secreted by the pancreas that contains both enzymes to digest carbohydrates, fats, and proteins and sodium bicarbonate, a neutralizing agent.

84 chapter 3 T h e R e m a r k a b l e B o d y

bicarbonate a common alkaline chemical; a secretion of the pancreas; also the active ingredient of baking soda.

compound bicarbonate in amounts precisely adjusted to neutralize the stomach acid that has reached the small intestine. All these actions alter the intestinal envi- ronment to perfectly support the work of the digestive enzymes.

Meanwhile, as the pancreatic and intestinal enzymes act on the chemical bonds that hold the large nutrients together, smaller and smaller pieces are released into the intes- tinal fl uids. Th e cells of the intestinal wall also hold some digestive enzymes on their surfaces; these enzymes perform last-minute breakdown reactions required before nu- trients can be absorbed. Finally, the digestive process releases pieces small enough for the cells to absorb and use. Digestion by human enzymes and absorption of carbohy- drate, fat, and protein are essentially complete by the time the intestinal contents enter the colon. Water, fi ber, and some minerals, however, remain in the tract.

Certain kinds of fi ber, which cannot be digested by human enzymes, can often be broken down by the billions of living inhabitants of the human digestive tract, the resident bacteria.8 So active are these inhabitants in breaking down substances from food that they have been likened to an organ of the body specializing in nutrient sal- vage. Th ey also aff ect health in other ways that are just beginning to be understood.9 Th e intestinal cells then absorb the small fat fragments released from the fi ber to pro- vide a tiny bit of energy. Table 3-2 provides a summary of all the processes involved.

KE Y POINT Chemical digestion begins in the mouth, where food is mixed with an enzyme in saliva that acts on carbohydrates. Digestion continues in the stomach, where stomach enzymes and acid break down protein. Digestion progresses in the small intestine; there the liver and gallbladder contribute bile that emulsifi es fat, and the pancreas and small intestine donate enzymes that continue digestion so that absorption can occur. Bacteria in the colon break down certain fi bers.

Are Some Food Combinations More Easily Digested Than Others? People sometimes wonder if the digestive tract has trouble digesting certain foods

in combination—for example, fruit and meat. Proponents of fad “food-combining” diets claim that the digestive tract cannot perform certain digestive tasks at

the same time, but this is a gross underestimation of the tract’s capabilities. Th e digestive system adjusts to whatever mixture of foods is presented to it.

Th e truth is that all foods, regardless of identity, are broken down by enzymes into the basic molecules that make them up.

Scientists who study digestion suggest that some organs of the digestive tract analyze the diet’s nutrient contents and deliver juice and enzymes appropriate for digesting those nutrients. Th e pancreas is especially sensitive in this regard and has been observed to adjust its output of enzymes to digest carbohydrate, fat, or protein to an amazing degree. Th e pancreas of a person who suddenly consumes a meal unusually high in carbohydrate, for example, would begin increasing its output of carbohydrate-digesting enzymes within 24 hours, while reducing outputs of other types. Th is sensitive mechanism ensures that foods of all types are used fully by the body. Th e next section reviews the major processes of digestion by showing how the nutrients in a mixture of foods are handled.

KE Y POINT The healthy digestive system is capable of adjusting to almost any diet and can handle any combination of foods with ease.

If “I Am What I Eat,” Then How Does a Peanut Butter Sandwich Become “Me”? Th e process of rendering foods into nutrients and absorbing them into the body fl uids is remarkably effi cient. Within about 24 to 48 hours of eating, a healthy body

85T h e D i g e s t i v e S y s t e m

digests and absorbs about 90 percent of the carbohydrate, fat, and protein in a meal. Here we follow a peanut butter and banana sandwich on whole-wheat, sesame seed bread through the tract.

In the Mouth In each bite, food components are crushed, mashed, and mixed with saliva by the teeth and the tongue. Th e sesame seeds are crushed and torn open by the teeth, which break through the indigestible fi ber coating so that digestive

Mouth Stomach Small Intestine, Pancreas,

Liver, and Gallbladder Large Intestine (Colon)

SUGAR AND STARCH

The salivary glands secrete saliva to moisten and lubri- cate food; chewing crushes and mixes it with a salivary enzyme that initiates starch digestion.

Digestion of starch con- tinues while food remains in the upper storage area of the stomach. In the lower digesting area of the stomach, hydrochloric acid and an enzyme in the stomach’s juices halt starch digestion.

The pancreas produces a starch-digesting enzyme and releases it into the small intestine. Cells in the intestinal lining pos- sess enzymes on their surfaces that break sugars and starch fragments into simple sugars, which then are absorbed.

Undigested carbohy- drates reach the large intestine and are partly broken down by intestinal bacteria.

FIBER The teeth crush fi ber and mix it with saliva to moisten if for swallowing.

No action. Fiber binds cholesterol and some minerals.

Most fi ber is excreted with the feces; some fi ber is digested by bacteria in the large intestine.

FAT Fat-rich foods are mixed with saliva. The tongue produces traces of a fat-digesting enzyme that accomplishes some break- down, especially of milk fats. The enzyme is stable at low pH and is important to digestion in nursing infants.

Fat tends to rise from the watery stomach fl uid and foods and fl oat on top of the mixture. Only a small amount of fat is digested. Fat is last to leave the stomach.

The liver secretes bile; the gallbladder stores it and releases it into the small intestine. Bile emulsifi es the fat and readies it for en- zyme action. The pancreas produces fat-digesting enzymes and releases them into the small intes- tine to split fats into their component parts (primarily fatty acids), which then are absorbed.

Some fatty materials escape absorption and are carried out of the body with other wastes.

PROTEIN Chewing crushes and soft- ens protein-rich foods and mixes them with saliva.

Stomach acid (hydrochloric acid) works to uncoil pro- tein strands and to activate the stomach’s protein- digesting enzyme. Then the enzyme breaks the protein strands into smaller fragments.

Enzymes of the small intestine and pancreas split protein fragments into smaller fragments or free amino acids. Enzymes on the cells of the intestinal lining break some protein fragments into free amino acids, which then are ab- sorbed. Some protein frag- ments are also absorbed.

The large intestine carries undigested protein residue out of the body. Normally, almost all food protein is digested and absorbed.

WATER The mouth donates watery, enzyme-containing saliva.

The stomach donates acidic, watery, enzyme- containing gastric juice.

The liver donates a watery juice containing bile. The pancreas and small intes- tine add watery, enzyme- containing juices; pancre- atic juice is also alkaline.

The large intestine re- absorbs water and some minerals.

Summary of Chemical Digestion table 3-2

86 chapter 3 T h e R e m a r k a b l e B o d y

enzymes can reach the nutrients inside the seeds. Th e peanut butter is the “extra crunchy” type, but the teeth grind the chunks to a paste before the bite is swal- lowed. Th e carbohydrate-digesting enzyme of saliva begins to break down the starch of the bread, banana, and peanut butter to sugars. Each swallow triggers a peristaltic wave that travels the length of the esophagus and carries one chewed bite of sandwich to the stomach.

In the Stomach Th e stomach collects bite after swallowed bite in its upper stor- age area, where starch continues to be digested until the gastric juice mixes with the salivary enzymes and halts their action. Small portions of the mashed sandwich are pushed into the digesting area of the stomach, where gastric juice mixes with the mass. Acid in gastric juice unwinds proteins from the bread, seeds, and peanut butter; then an enzyme clips the protein strands into pieces. Th e sandwich has now become chyme. Th e watery carbohydrate- and protein-rich part of the chyme enters the small intestine fi rst; a layer of fat follows closely behind.

In the Small Intestine Some of the sweet sugars in the banana require so little digesting that they begin to cross the linings of the small intestine immediately on contact. Nearby, the liver donates bile through a duct into the small intestine. Th e bile blends the fat from the peanut butter and seeds with the watery, enzyme- containing digestive fl uids. Th e nearby pancreas squirts enzymes into the small in- testine to break down the fat, protein, and starch in the chemical soup that just an hour ago was a sandwich. Th e cells of the small intestine itself produce enzymes to complete these processes. As the enzymes do their work, smaller and smaller chemical fragments are liberated from the chemical soup and are absorbed into the blood and lymph through the cells of the small intestine’s wall. Vitamins and min- erals are absorbed here, too. Th ey all eventually enter the bloodstream to nourish the tissues.

In the Large Intestine (Colon) Only fi ber fragments, fl uid, and some minerals are absorbed in the large intestine. Th e fi bers from the seeds, whole-wheat bread, peanut butter, and banana are partly digested by the bacteria living in the colon, and some of the products are absorbed. Most fi ber is not absorbed, however, and it passes out of the colon along with some other components, excreted as feces.

KE Y POINT The mechanical and chemical actions of the digestive tract break down foods to nutrients, and large nutrients to their smaller building blocks, with remarkable effi ciency.

Absorption and Transportation of Nutrients Once the digestive system has broken down food to its nutrient components, the rest of the body awaits their delivery. First, though, every molecule of nutrient must traverse one of the cells of the intestinal lining. Th ese cells absorb nutrients from the mixture within the intestine and deposit the water-soluble compounds in the blood and the fat-soluble ones in the lymph. Th e cells are selective: they recognize that some nutrients may be in short supply in the diet. Take the mineral calcium, for example. Th e less calcium in the diet, the greater the percentage of calcium the intestinal cells absorb from the intestinal contents. Th e cells are also extraordinarily effi cient: they absorb enough nutrients to nourish all the body’s other cells.

The Intestine’s Absorbing Surface Th e cells of the intestinal tract lining are arranged in sheets that poke out into millions of fi nger-shaped projections (villi). Every cell on every villus has a brushlike covering of tiny hairlike projections (mi- crovilli) that can trap the nutrient particles. Each villus (projection) has its own capillary network and a lymph vessel so that, as nutrients move across the cells, they can immediately mingle with the body fl uids. Figure 3-13 provides a close look at these details.

Time in stomach, about 1–2 hours.

Time in mouth, less than a minute.

Time in small intestine, about 7–8 hours.*

Time in colon, about 12–14 hours.*

*Based on a 24-hour transit time. Actual times vary widely.

gastric juice the digestive secretion of the stomach.

villi (VILL-ee, VILL-eye) fi ngerlike projections of the sheets of cells lining the intestinal tract. The villi make the surface area much greater than it would otherwise be (singular: villus).

microvilli (MY-croh-VILL-ee, MY-croh-VILL- eye) tiny, hairlike projections on each cell of ev- ery villus that greatly expand the surface area available to trap nutrient particles and absorb them into the cells (singular: microvillus).

87T h e D i g e s t i v e S y s t e m

Th e small intestine’s lining, villi and all, is wrinkled into thousands of folds, so its absorbing surface is enormous. If the folds, and the villi that poke out from them, were spread out fl at, they would cover a third of a football fi eld. Th e billions of cells of that surface weigh only 4 to 5 pounds, yet they absorb enough nutrients to nour- ish the other 150 or so pounds of body tissues.

Small intestine

The wall of the small intestine is wrinkled into thousands of folds and is carpeted with villi.

Between the villi are tubular glands that secrete enzyme- containing intestinal juice.

Each villus in turn is covered with even smaller projections, the microvilli.

This is a photograph of part of an actual human intestinal cell with microvilli.

Stomach

Folds with villi on them

A villus

Muscle layers beneath folds

Capillaries

Lymphatic vessel

Microvilli

Vein

Artery

Lymphatic vessel

If you have ever watched a sea anemone with its fingerlike projections in constant motion, you have a good picture of how the intestinal villi move.

o n W

. F a w

c e tt

ill C

re w

/S u p

e rS

to c k

Details of the Small Intestine Lining figure 3-13

88 chapter 3 T h e R e m a r k a b l e B o d y

Nutrient Transport in the Blood and Lymph Vessels After the nutrients pass through the cells of the villi, the blood and lymph vessels transport the nutrients to their ultimate consumers, the body’s cells. Th e lymph vessels initially transport most of the products of fat digestion and the fat-soluble vitamins, ultimately conveying them into a large blood vessel near the heart. Th e blood vessels directly transport the products of carbohydrate and protein digestion, most vitamins, and the miner- als from the digestive tract to the liver. Th anks to these two transportation systems, every nutrient soon arrives at the place where it is needed.

Nourishment of the Digestive Tract Th e digestive system’s millions of special- ized cells are themselves exquisitely sensitive to an undersupply of energy, nutrients, or dietary fi ber. In cases of severe undernutrition with too little energy and nutri- ents, the absorptive surface of the small intestine shrinks. Th e surface may be re- duced to a tenth of its normal area, preventing it from absorbing what few nutrients a limited food supply may provide. Without suffi cient fi ber to provide an undigested bulk for the tract’s muscles to push against, the muscles become weak from lack of exercise. Malnutrition that impairs digestion is self-perpetuating because impaired digestion makes malnutrition worse.

Th e digestive system’s needs are few, but important. Th e body has much to say to the attentive listener, stated in a language of symptoms and feelings that you would be wise to study. Th e next section takes a lighthearted look at what your digestive tract might be trying to tell you.

KE Y POINT The digestive system feeds the rest of the body and is itself sensitive to malnutrition. The folds and villi of the small intestine enlarge its surface area to facilitate nutrient absorption through countless cells to the blood and lymph. These transport systems then deliver the nutrients to all the body’s cells.

A Letter from Your Digestive Tract To My Owner, You and I are so close; I hope that I can speak frankly without off ending you. I know that sometimes I do off end with my gurgling noises and belching at quiet times and, oh yes, the gas. But, as you can read for yourself in Table 3-3, when you chew gum, drink carbonated beverages, or eat hastily, you gulp air with each swallow. I can’t help making some noise as I move the air along my length or release it upward in a noisy belch. And if you eat or drink too fast, I can’t help getting hiccups. Please sit and relax while you dine. You will ease my task, and we’ll both be happier.

Also, when someone off ers you a new food, you gobble away, trusting me to do my job. I try. It would make my life easier, and yours less gassy, if you would start with small amounts of new foods, especially those high in fi ber. Th e breakdown of fi ber by bacteria produces gas, so introduce fi ber-rich foods slowly. But please, if you do notice more gas than normal from a specifi c food, avoid it. If the gas becomes exces- sive, check with a physician. Th e problem could be something simple—or serious.

When you eat or drink too much, it just burns me up. Overeating causes heart- burn because the acidic juice from my stomach backs up into my esophagus. Acid poses no problem to my healthy stomach, whose walls are coated with thick mucus to protect them. But when my too-full stomach squeezes some of its contents back up into the esophagus, the acid burns its unprotected surface. Also, those tight jeans you wear constrict my stomach, squeezing the contents upward into the esophagus. Just leaning over or lying down after a meal may allow the acid to escape up the esophagus because the muscular sphincter separating the two spaces is much looser than other sphincters. And if we need to lose a few pounds, let’s get at it—excess body fat can also squeeze my stomach, causing acid to back up. When heartburn is a problem, do me a favor: try to eat smaller meals; drink liquids an hour before or after, but not during, meals; wear reasonably loose clothing; and relax after eating, but sit up (don’t lie down).

What is your digestive tract trying to tell you?

on al

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hiccups spasms of both the vocal cords and the diaphragm, causing periodic, audible, short, inhaled coughs. Can be caused by irritation of the diaphragm, indigestion, or other causes. Hiccups usually resolve in a few min- utes, but can have serious effects if prolonged. Breathing into a paper bag (inhaling carbon dioxide) or dissolving a teaspoon of sugar in the mouth may stop them.

heartburn a burning sensation in the chest (in the area of the heart) caused by backfl ow of stomach acid into the esophagus.

89T h e D i g e s t i v e S y s t e m

Sometimes your food choices irritate me. Specifi cally, chemical irritants in foods, such as the “hot” component of chili peppers, chemicals in coff ee, fat, chocolate, carbonated soft drinks, and alcohol, may worsen heartburn in some people. Avoid the ones that cause trouble. Above all, do not smoke. Smoking makes my heartburn worse—and you should hear your lungs bellyache about it.

By the way, I can tell you’ve been taking heartburn medicines again. You must have been watching those misleading TV commercials. You need to know that antacids are designed only to temporarily relieve pain caused by heartburn by neutralizing stomach acid for a while. But when the antacids reduce my normal stomach acidity, I respond by producing more acid to restore the normal acid condition. Also, the ingre- dients in antacids can interfere with my ability to absorb nutrients. Please check with our doctor if heartburn occurs more than just occasionally and certainly before you decide that we need to take the heavily advertised acid reducers; these restrict my normal ability to produce acid so much that my job of digesting food becomes harder. Th ey may also reduce our defense against serious infections, even pneumonia.10

Given a chance, my powerful stomach acid helps to fi ght off many bacterial in- fections—most disease-causing bacteria won’t survive a bath in my caustic juices.11 Acid-reducing drugs reduce acid (I’ll bet you knew that), and so allow more bacte- ria to pass through. And, even worse, self-prescribed heartburn medicine can mask the symptoms of ulcer, hernia, or the severe destructive form of chronic heartburn known as gastroesophageal refl ux disease (GERD).12 Th is can be serious because, although the bacterium H. pylori that causes most ulcers responds to antibiotic drugs, some ulcers have other causes, such as frequent use of certain painkillers— the cause of the ulcer must be treated as well as its symptoms.‡13 Left untreated, H.

pylori raises the risk of stomach cancer.14 A hernia can cause food to back up into the esophagus, so it can feel like heartburn, but many times hernias require correc- tive treatment by a physician. GERD can feel like heartburn, too, but requires the correct drug therapy to prevent respiratory problems, severe damage to tissues, or even cancer of the throat or esophagus.15 So please don’t wait too long to get medi- cal help for chronic or severe heartburn—it may not be simple indigestion.

Recent experiments have shed light on the causes and prevention of intestinal gas. Here are some recent fi ndings.

Milk intake causes gas in those who cannot digest the milk sugar lactose. Most • people, however, can consume up to a cup of milk without producing excessive gas.

Solution: Drink up to 4 ounces of fluid milk at a sitting, or substitute reduced-fat cheeses or yogurt without added milk solids. Use lactose-reduced products, or treat regular products with lactose-reducing enzyme products.

Beans cause gas because some of their carbohydrates are indigestible by human • enzymes, but are broken down by intestinal bacteria. The amount of gas may not be as much as most people fear, however.

Solution: Use rinsed canned beans or dried beans that are well cooked, because cooked carbohydrates are more readily digestible. Try enzyme drops or pills that can help break down the carbohydrate before it reaches the intestine.

Air swallowed during eating or drinking can cause gas, as can the gas of carbonated • beverages. Each swallow of a beverage can carry three times as much gas as fl uid, which some people belch up.

Solution: Slow down during eating and drinking, and don’t chew gum or suck on hard candies that may cause you to swallow air. Limit carbonated beverages.

Vegetables may or may not cause gas in some people, but research is lacking.• Solution: If you feel certain vegetables cause gas, try eating small portions of the cooked products. Do try the vegetable again: the gas you experienced may have been a coincidence and had nothing to do with eating the vegetable.

Foods and Intestinal Gas table 3-3

‡ Anti-infl ammatory drugs such as aspirin, ibuprofen, and napron sodium.

antacids medications that react directly and immediately with the acid of the stomach, neutralizing it. Antacids are most suitable for treating occasional heartburn.

acid reducers prescription and over- the-counter drugs that reduce the acid output of the stomach; effective for treating severe, persistent forms of heartburn but not for neutralizing acid already present. Side effects are frequent and include diarrhea, other gas- trointestinal complaints, and reduction of the stomach’s capacity to destroy alcohol, thereby producing higher-than-expected blood alcohol levels from each drink (see this chapter’s Con- troversy section). Also called acid controllers.

ulcer an erosion in the topmost, and some- times underlying, layers of cells that form a lining. Ulcers of the digestive tract commonly form in the esophagus, stomach, or upper small intestine.

hernia a protrusion of an organ or part of an organ through the wall of the body chamber that normally contains the organ. An example is a hiatal (high-AY-tal) hernia, in which part of the stomach protrudes up through the dia- phragm into the chest cavity, which contains the esophagus, heart, and lungs.

gastroesophageal (GAS-tro-eh-SOFF- ah-jeel) refl ux disease (GERD) a severe and chronic splashing of stomach acid and enzymes into the esophagus, throat, mouth, or airway that causes injury to those organs. Untreated GERD may increase the risk of esophageal cancer; treatment may require surgery or management with medication.

90 chapter 3 T h e R e m a r k a b l e B o d y

When you eat too quickly, I worry about choking (see Figure 3-14). Please take time to cut your food into small pieces, and chew it until it is crushed and moistened with saliva. Also, refrain from talking or laughing before swallowing, and never at- tempt to eat when you are breathing hard. Also, for our sake and the sake of others, learn fi rst aid for choking as shown in Figure 3-15.

When I’m suff ering, you suff er, too. When constipation or diarrhea strikes, nei- ther of us is having fun. Slow, hard, dry bowel movements can be painful, and fail- ing to have a movement for too long brings on headaches, backaches, stomachaches, and other ills; if chronic, constipation may cause hemorrhoids or other ills.16 Most people suff er occasional harmless constipation, and laxatives may help, but too fre- quent use of laxatives and enemas can lead to dependency; upset our fl uid, salt, and mineral balances; and, with mineral-oil laxatives, can interfere with the absorption of fat-soluble vitamins. (Mineral oil, which is not absorbed, dissolves the vitamins and carries them out of the body with it.)

Instead of relying on laxatives, listen carefully for my signal that it is time to def- ecate, and make time for it even if you are busy. Th e longer you ignore my signal, the more time the colon has to extract water from the feces, hardening them. Also, please choose foods that provide enough fi ber (some high-fi ber foods are listed in Chapter 4, pages 114–115).§ Fiber attracts water, creating softer, bulkier stools that stimulate my muscles to contract, pushing the contents along. Fiber helps my muscles to stay fi t, too, making elimination easier. Be sure to drink enough water because dehydration causes the colon to absorb all the water it can get from the fe- ces. And please make time to be physically active; exercise strengthens not just the muscles of your arms, legs, and torso, but those of the colon, too.17

When I have the opposite problem, diarrhea, my system will rob you of water and salts. In diarrhea my intestinal contents have moved too quickly, drawing water and minerals from your tissues into the contents. When this happens, please rest a while and drink fl uids (I prefer clear juices and broths). However, if diarrhea is bloody, or if it worsens or persists, call our doctor—severe diarrhea can be life-threatening.

To avoid diarrhea, try not to change my diet too drastically or quickly. I’m willing to work with you and learn to digest new foods, but if you suddenly change your

For more information about ulcers and medi-• cation, call the Centers for Disease Control and Prevention at 1-888-MY-ULCER, toll free.

Tongue

Food

Larynx rises Esophagus (to stomach)

Trachea (to lungs)

Epiglottis closes over larynx

A normal swallow. The epiglottis acts as a flap to seal the entrance to the lungs (trachea) and direct food to the stomach via the esophagus.

Choking. A choking person cannot speak or gasp because food lodged in the trachea blocks the passage of air. The red arrow points to where the food should have gone to prevent choking.

Normal Swallowing and Choking figure 3-14

§ Rarely, a spastic, constricted bowel causes constipation; this condition requires medical attention, not fi ber.

constipation infrequent, diffi cult bowel movements often caused by diet, inactivity, dehydration, or medication. Also defi ned in Chapter 4.

diarrhea frequent, watery bowel move- ments usually caused by diet, stress, or irrita- tion of the colon. Severe, prolonged diarrhea robs the body of fl uid and certain minerals, causing dehydration and imbalances that can be dangerous if left untreated.

hemorrhoids (HEM-or-oids) swollen, hardened (varicose) veins in the rectum, usually caused by the pressure resulting from constipation.

91T h e D i g e s t i v e S y s t e m

diet, we’re both in for it. I hate even to think of it, but one likely cause of diarrhea is dangerous food poisoning. (Please read, and use, the tips in Chapter 12 to keep us safe.) Also, if diarrhea lasts longer than a day or two, or if it alternates with constipation, the cause could be irritable bowel syndrome (IBS), and you should go see a physician.18 In IBS, strong contractions speed intestinal contents through quickly, causing gas, bloating, diarrhea, and frequent or severe abdominal discom- fort.19 Weakened and slowed contractions may then follow, causing constipation. You might try eating smaller meals and avoiding onions or other irritating foods, but if that doesn’t work, by all means, call our doctor—IBS often responds to anti- spasmodic drugs or even peppermint oil taken under medical supervision.20

By the way, I trust you not to believe false claims that health troubles can be solved by washing the colon with a powerful enema machine—in fact, this “colonic irrigation” is unnecessary and has caused illness and even death from equipment contamination, electrolyte depletion, and intestinal perforation.

Th ank you for listening. I know we’ll both benefi t from communicating like this because you and I are in this together for the long haul.

Aff ectionately, Your Digestive Tract

KE Y POINT The digestive tract has many ways to communicate its needs. Maintenance of a healthy digestive tract requires preventing or responding to symptoms with a carefully chosen diet and sound medical care.

To lend assistance to a choking person: 1. Stand behind the person. 2. Wrap your arms around him. 3. Place the thumb side of one fist snugly against his body, slightly above the navel and below the rib cage. 4. Grasp your fist with your other hand and give him a sudden strong hug inward and upward. 5. Repeat thrusts as necessary.

If you are choking and alone, you can help yourself: 1. Place the thumb side of one fist slightly above your navel and below your rib cage. 2. Grasp the fist with your other hand. 3. Press inward and upward with a quick motion. 4. If this fails, forcefully press your upper abdomen over any firm surface such as the back of a chair, a countertop, or a railing. 5. Repeat as necessary.

The fi rst-aid strategy most likely to succeed is abdominal thrusts, sometimes called the Heimlich maneuver.a Grabbing the throat is the universal sign for choking.

First Aid for Choking figure 3-15

aThe Heimlich maneuver may not be an effective fi rst-aid measure for unconscious drowning victims.

irritable bowel syndrome (IBS) intermittent disturbance of bowel function, especially diarrhea or alternating diarrhea and constipation, often with abdominal cramp- ing or bloating; managed with diet, physical activity, or relief from psychological stress. The cause is uncertain, but IBS does not perma- nently harm the intestines nor lead to serious diseases.

92 chapter 3 T h e R e m a r k a b l e B o d y

The Excretory System Cells generate a number of wastes, and all of them must be eliminated. Many of the body’s organs play roles in removing wastes. Carbon dioxide waste from the cells travels in the blood to the lungs, where it is exchanged for oxygen. Other wastes are pulled out of the bloodstream by the liver. Th e liver processes these wastes and either tosses them out into the digestive tract with bile, to leave the body with the feces, or prepares them to be sent to the kidneys for disposal in the urine. Organ systems work together to dispose of the body’s wastes, but the kidneys are waste- and water-removal specialists.

Th e kidneys straddle the cardiovascular system and fi lter the passing blood. Waste materials, dissolved in water, are collected by the kidneys’ working units, the nephrons. Th ese wastes become concentrated as urine, which travels through tubes to the urinary bladder. Th e bladder empties periodically, removing the wastes from the body. Th us, the blood is purifi ed continuously throughout the day, and dissolved materials are excreted as necessary. One dissolved mineral, sodium, helps to regu- late blood pressure, and its excretion or retention by the kidneys is a vital part of the body’s blood pressure–controlling mechanism.

Th ough they account for just 0.5 percent of the body’s total weight, the kidneys use up 10 percent of the body’s oxygen supply, indicating intense metabolic activity. Th e kidney’s waste-excreting function rivals breathing in importance to life, but the kidneys act in other ways as well. By sorting among dissolved substances, retaining some while excreting others, the kidneys regulate the fl uid volume and concentra- tions of substances in the blood and extracellular fl uid with great precision. Th rough these mechanisms, the kidneys help to regulate blood pressure (see Chapter 11 for details). As you might expect, the kidneys’ work is regulated by hormones secreted by glands that respond to conditions in the blood (such as the sodium concentra- tion). Th e kidneys also release certain hormones.

Because the kidneys remove toxins that could otherwise damage body tissues, whatever supports the health of the kidneys supports the health of the whole body. A strong cardiovascular system and an abundant supply of water are important to keep blood fl ushing swiftly through the kidneys. In addition, the kidneys need suf- fi cient energy to do their complex sifting and sorting job, and many vitamins and minerals serve as the cogs of their machinery. Exercise and nutrition are vital to healthy kidney function.

KE Y POINT The kidneys adjust the blood’s composition in response to the body’s needs, disposing of everyday wastes and helping remove toxins. Nutrients, including water, and exercise help keep the kidneys healthy.

Extracellular fluid is defined on page 71 and • depicted in Figure 3-4.

Did You Know? The lungs also excrete some small percent- age of ingested alcohol—the basis for the “breathalyzer” test given to drivers to deter- mine if they’ve been drinking.

I Am What I Drink

What do college students think about drinking alcohol? Two students talk about their drinking habits—how much, how often, and where.

To hear their stories, log on to www.cengage.com/sso.

my turn

Ashley Christopher

nephrons (NEFF-rons) the working units in the kidneys, consisting of intermeshed blood vessels and tubules.

bladder the sac that holds urine until time for elimination.

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93C o n c l u s i o n

LO 3.4

Storage Systems Th e human body is designed to eat at intervals of about four to six hours, but cells need nutrients around the clock. Providing the cells with a constant fl ow of the needed nutrients requires the cooperation of many body systems. Th ese systems store and release nutrients to meet the cells’ needs between meals. Among the major storage sites are the liver and muscles, which store carbohydrate, and the fat cells, which store fat and other fat-related substances.

When I Eat More Than My Body Needs, What Happens to the Extra Nutrients? Nutrients collected from the digestive system sooner or later all move through a vast network of capillaries that weave among the liver cells. Th is arrangement ensures that liver cells have access to the newly arriving nutrients for processing. Body tissues store excess energy-containing nutrients in two forms (details will follow in later chapters). Th e liver makes some of the excess into glycogen (a carbohydrate), and some is stored as body fat. Liver glycogen can sustain cell activities when the inter- vals between meals become long. Should no food be available, the liver’s glycogen supply dwindles; it can be eff ectively depleted within as few as three to six hours. Muscle cells make and store glycogen, too, but selfi shly reserve it for their own use.

Whereas the liver stores glycogen, it ships out fat in packages (see Chapter 5) to be picked up by cells that need it. All body cells may withdraw the fat they need from these packages, and the fat cells of the adipose tissue pick up the remainder and store it to meet long-term energy needs. Unlike the liver, fat tissue has virtually infi nite storage capacity. It can continue to supply the body’s cells with fat for days, weeks, or possibly even months when no food is eaten.

Th ese storage systems for glucose and fat ensure that the body’s cells will not go without energy even if the body is hungry for food. Body stores also exist for many other nutrients, each with a characteristic capacity. For example, liver and fat cells store many vitamins, and bones provide reserves of calcium and other minerals. Stores of nutrients are available to keep the blood levels constant and to meet cellular demands.

Variations in Nutrient Stores Some nutrients are stored in the body in much larger quantities than others. For ex- ample, certain vitamins are stored without limit, even if they reach toxic levels within the body. Other nutrients are stored in only small amounts, regardless of the amount taken in, and these can readily be depleted. As you learn how the body handles various nutrients, pay particular attention to their storage so that you can know your tolerance limits. For example, you needn’t eat fat at every meal, because fat is stored abundantly. On the other hand, you normally do need to have a source of carbohydrate at intervals throughout the day because the liver stores less than one day’s supply of glycogen.

KE Y POINT The body’s energy stores are of two principal kinds: glycogen in muscle and liver cells (in limited quantities) and fat in fat cells (in potentially large quantities). Other tissues store other nutrients.

Conclusion In addition to the systems just described, the body has many more: bones, muscles, reproductive organs, and others. All of these cooperate, enabling each cell to carry on its own life. For example, the skin and body linings defend other tissues against microbial invaders, while being nourished and cleansed by tissues specializing in these tasks. Each system needs a continuous supply of many specifi c nutrients to

Later chapters provide details about storage • of energy nutrients.

glycogen a storage form of carbohydrate energy (glucose); described more fully in Chapter 4.

adipose tissue the body’s fat tissue, consisting of masses of fat-storing cells and blood vessels to nourish them.

94 chapter 3 T h e R e m a r k a b l e B o d y

maintain itself and carry out its work. Calcium is particularly important for bones, for example; iron for muscles; glucose for the brain. But all systems need all nutri- ents, and every system is impaired by an undersupply or oversupply of them.

While external events clamor and vie for attention, the body quietly continues its life-sustaining work. Most of the body’s work is directed automatically by the uncon- scious portions of the brain and nervous system, and this work is fi nely regulated to achieve a state of well-being. But you need to involve your brain’s cortex, your con- scious thinking brain, to cultivate an understanding and appreciation of your body’s needs. In doing so, attend to nutrition fi rst. Th e rewards are liberating—ample energy to tackle life’s tasks, a robust attitude, and the glowing appearance that comes from the best of health. Read on, and learn to let nutrition principles guide your food choices.

KE Y POINT To achieve optimal function, the body’s systems require nutrients from outside. These have to be supplied through a human being’s conscious food choices.

Learn more about digestive disorders by searching “digestion” or specifi c diseases by name at www.healthfi nder.gov.

Find out more about digestion, absorption, organs of the gas- trointestinal tract, and digestive diseases at www.nlm.nih.gov/ medlineplus.

Learn more about digestive diseases at www.nal.usda.gov/ fnic (under Browse by Subject, select Diet and Disease, and click on Digestive Diseases and Disorders).

media menu

Answers to these Self Check questions are in Appendix G.

All of the following are correct concerning ulcers 1. except:

they usually occur in the large intestineA.

some are caused by a bacteriumB.

if not treated correctly, they can lead to stomach cancerC.

their symptoms can be masked by using antacids regularlyD.

Which of the following increases the production of intestinal 2. gas?

chewing gumA.

drinking carbonated beveragesB.

eating certain vegetablesC.

all of the aboveD.

Chemical digestion of all nutrients mainly occurs in which 3. organ?

mouthA.

stomachB.

small intestineC.

large intestineD.

Which chemical substance released by the pancreas neu-4. tralizes stomach acid that has reached the small intestine?

mucusA.

enzymesB.

bicarbonateC.

bileD.

Which of the following passes through the large intestine 5. mostly unabsorbed?

starchA.

vitaminsB.

mineralsC.

fi berD.

T-cells are immune cells that ingest and destroy antigens in 6. a process known as phagocytosis. T F

Bile starts the process of protein digestion in the stomach.7. T F

To digest food effi ciently, people should not combine certain 8. foods, such as meat and fruit, at the same meal. T F

The gallbladder stores bile until it is needed to emulsify fat.9. T F

Absorption of the majority of nutrients takes place across 10. the mucus-coated lining of the stomach. T F

self check

http://www.cengage.com/sso

http://www.healthfi

http://www.nlm.nih.gov/

http://www.nal.usda.gov/

95controversy 3 A l c o h o l a n d N u t r i t i o n : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

CONTROVERSY

On average, people in the United States consume from 6 to 10 percent of their total daily energy intake as alcohol. Their drinking habits span a wide spectrum: many drink no alcohol whatsoever, some take a glass of wine only with meals, others drink lightly on social occasions, whereas some are heavy social drinkers, and still others take in large quantities of alcohol daily because of a life- shattering addiction. A third of U.S. col- lege students drink alcohol in a pattern that identifi es them as binge drinkers, though when asked, more than 90 per- cent reject this description. Thirty percent of all binge drinking in the United States involves people aged 18 to 25 years, and white men in particular.1*

Heavy drinkers often pay a high price in terms of their health and safety. Mod- erate drinkers, in contrast, consume less alcohol and so suffer fewer of its effects. Some may even benefi t from small amounts of alcohol but, because alcoholic beverages present many discretionary calories, they may also gain weight.

Alcohol is not just an energy source, however; it is also a psychoactive drug and a toxin to the body. Despite its toxic- ity, many people want to know if there is an amount of alcohol they can drink safely or whether they may derive bene- fi ts, particularly for the health of the heart, by drinking. This Controversy starts by defi ning some terms in Table C3-1. Then, it examines alcohol’s immediate actions within the body and its effects on the brain and other organs. It summarizes the long-term effects of alcohol on the

body and nutrition and concludes with research on moderate drinking. In the end, after learning all of alcohol’s effects, you must choose for yourself how, and if, alcohol fi ts into your own life and health.

WHAT IS ALCOHOL? In chemistry, the term alcohol refers to a class of chemical compounds whose names end in -ol. The glycerol molecule of a triglyceride is an example. Alcohols affect living things profoundly, partly because they act as lipid solvents. Alco- hols can easily penetrate a cell’s outer lipid membrane, and once inside, they denature the cell’s protein structures and kill the cell. Because some alcohols kill microbial cells, they make useful disin- fectants and antiseptics.

The alcohol of alcoholic beverages, ethanol, is somewhat less toxic than others. Suffi ciently diluted and taken in small enough doses, its action in the brain produces euphoria. Used in this way, alcohol is a drug, and like many drugs, alcohol presents both benefi ts and hazards to the taker. Its effects depend on the quantity of alcohol consumed.

WHAT IS A “DRINK”? Alcoholic beverages contain a great deal of water and some other substances, as well as the alcohol ethanol. In beer, wine, and wine coolers, alcohol contributes a relatively low percentage of the bever- age’s volume—about 5 percent in most beers to about 13 to 15 percent in many wines.† Malt beverages, even those with

sugar and fruity fl avors or caffeine added, range from 5 to 10 percent ethanol. In contrast, about 50 percent of the volume of whiskey, vodka, rum, and brandy may be ethanol. The percentage of alcohol is stated as proof. Proof equals twice the percentage of alcohol; for example, 100 proof liquor is 50 percent alcohol.

A serving of an alcoholic beverage, commonly called a drink, delivers ½ ounce of pure ethanol. Figure C3-1 depicts servings of alcoholic beverages that are considered to be one drink. These standard measures may have little in common with the drinks served by enthusiastic bartenders, however. Many wine glasses easily hold 6 to 8 ounces of wine; wine coolers may come packaged 12 ounces to a bottle; a large beer stein can hold 16, 20, or even more ounces; a strong liquor drink may contain 2 or 3 ounces of various liquors.

DEFINING DRINKING When people congregate to enjoy conversation and companionship, bever- ages are usually a part of the scene. How alcohol affects the picture depends on how (and whether) it is consumed.

Social Drinkers Many people are social drinkers—they often choose wine, beer, or mixed drinks over cola, juice, milk, tea, or coffee to ac- company a meal, to celebrate occasions, or to relax with friends. In moderation, alcohol reduces inhibitions, eases social interactions, and produces feelings of eu- phoria, a pleasant sensation that people seek. The term moderation is important in this regard because more alcohol impedes social interactions. Euphoria

Alcohol and Nutrition: Do the Benefi ts Outweigh the Risks?

LO 3.5

*Reference notes are found in Appendix F. † Nonalcoholic beers and wine may contain a small amount of alcohol, up to 0.5 percent.

96 chapter 3 T h e R e m a r k a b l e B o d y

is overwhelmingly negative. For these people, drinking alcohol brings irrational and often dangerous behavior, such as driving a car while intoxicated and regret- table human interactions, such as argu- ments, violence, or unplanned and risky sexual activity.3 With continued drinking, such people face psychological depres- sion, physical illness, severe malnutrition, and demoralizing erosion of self-esteem. A tool for self-analysis for alcohol use disorder is found in Table C3-2.

Defi ning Moderation Moderation is not easily defi ned be- cause tolerance to alcohol differs among individuals, partly because of inherited genetic makeup. In general, women

occurs only with the fi rst few drinks and not with higher alcohol intakes.2

All beverages seem to ease conversa- tion, whether they contain alcohol or not. For example, nonalcoholic beers and wines on the market also elevate mood and encourage social interaction, as do tea, coffee, or sodas. To mimic the look and taste of cocktails (and to minimize social pressure to drink alcohol), spar- kling ciders or ginger ale, tomato juice with a stalk of celery, or cola with a slice of lime can do the trick.

Problem Drinkers and Alcoholism In contrast to moderate social drink- ing, the effect of alcohol on problem drinkers or people with alcoholism

acetaldehyde• (ass-et-AL-deh-hide) a substance to which ethanol is metabolized on its way to becoming harmless waste products that can be excreted. alcohol dehydrogenase• (dee-high-DRAH-gen-ace) (ADH) an enzyme system that breaks down alcohol. The antidiuretic hormone listed below is also abbreviated ADH. alcoholism• a dependency on alcohol marked by compulsive uncontrollable drinking with negative effects on physical health, family relationships, and social health. antidiuretic• (AN-tee-dye-you-RET-ick) hormone (ADH) a hor- mone produced by the pituitary gland in response to dehydration (or a high sodium concentration in the blood). It stimulates the kidneys to reabsorb more water and so to excrete less. (This hormone should not be confused with the enzyme alcohol dehy- drogenase, which is also abbreviated ADH.) beer belly• central-body fatness associated with alcohol consumption. binge drinkers• people who drink four or more drinks in a short period. cirrhosis• (seer-OH-sis) advanced liver disease, often associated with alcoholism, in which liver cells have died, hardened, turned an orange color, and permanently lost their function. congeners• (CON-jen-ers) chemical substances other than alco- hol that account for some of the physiological effects of alcoholic beverages, such as appetite, taste, and aftereffects. drink• a dose of any alcoholic beverage that delivers half an ounce of pure ethanol. ethanol• the alcohol of alcoholic beverages, produced by the action of microorganisms on the carbohydrates of grape juice or other carbohydrate-containing fl uids. euphoria• (you-FOR-ee-uh) an infl ated sense of well-being and pleasure brought on by a moderate dose of alcohol and by some other drugs. fatty liver• an early stage of liver deterioration seen in several diseases, including kwashiorkor and alcoholic liver disease, in which fat accumulates in the liver cells.

fi brosis• (fye-BROH-sis) an intermediate stage of alcoholic liver deterioration. Liver cells lose their function and assume the char- acteristics of connective tissue cells (become fi brous). formaldehyde• a substance to which methanol is metabolized on the way to being converted to harmless waste products that can be excreted. gout• (GOWT) a painful form of arthritis caused by the abnormal buildup of the waste product uric acid in the blood, with uric acid salt deposited as crystals in the joints. methanol• an alcohol produced in the body continually by all cells. moderate drinkers• people who do not drink excessively and do not behave inappropriately because of alcohol. A moderate drinker’s health may or may not be harmed by alcohol over the long term. nonalcoholic• a term used on beverage labels, such as wine or beer, indicating that the product contains less than 0.5% alcohol. The terms dealcoholized and alcohol removed mean the same thing. Alcohol free means that the product contains no detectable alcohol. problem drinkers• or alcohol abusers people who suffer social, emotional, family, job-related, or other problems because of alco- hol. A problem drinker is on the way to alcoholism. proof• a statement of the percentage of alcohol in an alcoholic beverage. Liquor that is 100 proof is 50% alcohol, 90 proof is 45%, and so forth. social drinkers• people who drink only on social occasions. De- pending on how alcohol affects a social drinker’s life, the person may be a moderate drinker or a problem drinker. urethane• a carcinogenic compound that commonly forms in alcoholic beverages. Wernicke-Korsakoff• (VER-nik-ee KOR-sah-koff) syndrome a cluster of symptoms involving nerve damage arising from a defi ciency of the vitamin thiamin in alcoholism. Characterized by mental confusion, disorientation, memory loss, jerky eye move- ments, and staggering gait.

Alcohol and Drinking Terms table C3-1

5 oz wine

12 oz beer, alcoholic lemonade, alcoholic carbonated drink

10 oz wine cooler

1 oz hard liquor (80 proof

whiskey,gin, brandy,

rum,vodka)

1 2

(12% alcohol)

Servings of

Alcoholic

Beverages That

Equal One Drink

figure C3-1

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97controversy 3 A l c o h o l a n d N u t r i t i o n : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

want to seek a professional evaluation.‡ Table C3-4 contrasts some behaviors of moderate drinkers with those of problem drinkers.

Binge Drinking Young adults enjoy parties, sports events, and other social occasions, but these settings often encourage binge drinking (defi ned as at least four drinks in a row for women and fi ve drinks in

week but has seven drinks on Saturday night is not a moderate drinker—instead, that alcohol intake pattern characterizes binge drinking.

Who Should Never Drink Alcohol? Doubtless some people can safely consume slightly more than the alcohol dose called moderate; others, especially those prone to alcohol addiction, cannot handle nearly so much without signifi cant risk. The Dietary Guidelines for Americans advises these and some others not to drink at all (listed in Table C3-3).

If you suspect that your own drinking may not be moderate or if alcohol has caused problems in your life, you may

cannot handle as much alcohol as men and should never try to match drinks with male companions. People of Asian or Na- tive American descent may have lower- than-average tolerance to alcohol, too.

Health authorities defi ne moderation as:

no more than two drinks a day for the • average-sized, healthy man.

no more than one drink a day for the • average-sized, healthy woman.

These amounts are supposed to be enough to elevate mood without incur- ring long-term harm to health—note that these are not average amounts, but 24-hour maximums. In other words, a person who drinks no alcohol during the

A health professional can diagnose and evaluate problem drinking or alcohol addic- tion with the answers to these questions.

In the past year, have you:

Ever ended up drinking more or for longer than you intended?1. Wanted to cut down or stop drinking, or tried to, but couldn’t on more than one 2. occasion?

Endangered yourself more than once while or after drinking (such as driving, swim-3. ming, using machinery, walking in a dangerous area, or having unsafe sex) on more than one occasion?

Found that your usual number of drinks no longer produced the desired effect?4. Continued to drink even though it made you feel depressed or anxious? Or after hav-5. ing had a memory blackout?

Spent a lot of time drinking, or being sick, or getting over other aftereffects?6. Continued to drink even though it was causing trouble with your family or friends?7. Found that drinking—or being sick from drinking—often interfered with taking care of 8. your home or family? Or caused job troubles? Or school problems?

Given up or cut back on activities that were important or interesting to you, or gave 9. pleasure, in order to drink?

Been arrested, been held at a police station, or had other legal problems because of 10. your drinking?

Found that when the effects of alcohol were wearing off, you had withdrawal symp-11. toms, such as trouble sleeping, shakiness, restlessness, nausea, sweating, racing heartbeat, or seizure? Or sensed things that were not there?

If you have any of these symptoms, or if people close to you are concerned about your drinking, then alcohol may be a cause for concern. The more symptoms you have and the more often you have them, the more urgent the need for change. See a health professional.

Note: These questions are based on symptoms for alcohol use disorders in the American Psychiatric Asso- ciation’s Diagnostic and Statistical Manual (DSM) of Mental Disorders, Fourth Edition. The DSM is the most commonly used system in the United States for diagnosing mental health disorders.

Source: Adapted from Rethinking Drinking: Alcohol and Your Health, NIH pub. no. 09-3770, February 2009.

Symptoms of Problem Drinking

and Alcohol Addiction

table C3-2

The Dietary Guidelines for Americans

2005 suggest that these people not drink alcoholic beverages at all:

Children and adolescents.• The earlier in life drinking begins, the greater the risk of alcoholism later on. People of any age who cannot restrict • their drinking to moderate levels. Especially, people recovering from alcoholism, problem drinkers, and people whose family members have alcohol problems. Women who may become pregnant • or who are pregnant or breastfeeding. No safe level of alcohol intake has been established for women during pregnancy (see Chapter 13), and alcohol may be especially hazardous during the fi rst few weeks, before a woman knows she is pregnant. People who plan to drive, oper-• ate machinery, or take part in other activities that require attention, skill, or coordination to remain safe. Alcohol remains in the blood for several hours after taking even a single drink. People taking medications that can • interact with alcohol. Alcohol alters the effectiveness or toxicity of many medications, and some drugs may increase blood alcohol levels. People with medical conditions• worsened by alcohol, such as liver disease.

Source: U.S. Department of Agriculture and U.S. Department of Health and Human Services, 2005 Dietary Guidelines for Americans, 6th ed. (Washington, D.C.: 2005), available at www .usda.gov/cnpp or call (888) 878-3256.

Who Should Not

Drink Alcohol?

table C3-3

‡ The U.S. Center for Facts on Alcohol is the National Clearinghouse for Alcohol and Drug Information: (800) 729-6686.

98 chapter 3 T h e R e m a r k a b l e B o d y

Alcohol Dehydrates the Tissues Any- one who has had an alcoholic drink has experienced one of alcohol’s physical effects: alcohol increases urine output (because alcohol depresses the brain’s production of antidiuretic hormone). Loss of body water leads to thirst. The only fl uid that relieves dehydration is water, so add- ing ice to alcoholic drinks to dilute them and alternating alcoholic beverages with nonalcoholic ones will quench thirst. Oth- erwise, each alcoholic drink may worsen the thirst, leading to more drinking.

The water lost due to hormone de- pression takes with it important miner- als, such as magnesium, potassium, calcium, and zinc, depleting the body’s reserves. These minerals are vital to fl uid balance and to nerve and muscle coor- dination. When drinking results in mineral loss, minerals must be made up in sub- sequent meals to avoid defi ciencies.

If a person drinks slowly enough, the alcohol will be collected by the liver after absorption and processed without much effect on other parts of the body. If a person drinks more rapidly, however, some of the alcohol bypasses the liver and fl ows for a while through the rest of the body and the brain.

ALCOHOL ARRIVES IN THE BRAIN Some people use alcohol as a kind of social anesthetic to help them relax or to relieve anxiety. One drink relieves inhibi- tions, which gives people the impression that alcohol is a stimulant. It gives this impression by sedating the inhibitory nerves, allowing excitatory nerves to take over. This effect is temporary, and ulti-

a crisis, such as a car crash, or until they’ve binged long enough to cause substantial damage to their health.

IMMEDIATE EFFECTS OF ALCOHOL From the moment an alcoholic beverage is swallowed, the body gives it special at- tention. As alcohol passes through body tissues, it affects their functioning.

Alcohol Enters the Body Unlike food, which requires digestion before it can be absorbed, tiny alcohol molecules start diffusing right through the stomach walls and they reach the brain within a minute. As a toxin, a too- high dose of ethanol in the stomach trig- gers one of the body’s primary defenses against poison—vomiting. Many times, though, alcohol arrives gradually, diluted in enough fl uid or food that the vomiting refl ex is delayed and the alcohol passes into the small intestine, which readily absorbs it.10

A drinker can soon become intoxi- cated, especially when drinking on an empty stomach. When the stomach is full of food, molecules of alcohol have less chance of touching the stomach walls and diffusing through, so alcohol reaches the brain more gradually. Also, a full stom- ach delays alcohol’s fl ow into the small intestine, allowing time for a stomach en- zyme to destroy some of it.11 Once in the small intestine, however, alcohol is rapidly absorbed whether food is present or not. A person who wants to drink socially and not become intoxicated should eat the snacks provided by the host (avoid the salty ones, they increase thirst).

a row for men).§4 Alcoholic beverages with caffeine added, either premixed or homemade, appeal to binge drinkers because of a “pep up” effect.5 The FDA is investigating whether such beverages may mask feelings of drunkenness, allow continued drinking, and increase the likelihood of reckless behavior.6

Binge drinkers skew the statistics on alcohol use on college campuses. The median number of drinks consumed by all college students is 1.5 per week, but for binge drinkers, it is 14.5 per week. Some of the heaviest binge drinkers con- sume 8 to 10 drinks on a single drinking occasion.7 Among drinkers under age 21, binge drinking accounts for 90 per- cent of the total alcohol consumed and accounts for most of their alcohol-related problems.8

Harms from Binge Drinking Binge drinking poses serious health and social consequences to drink- ers and nondrinkers alike. Compared with nondrinkers or moderate drinkers, binge drinkers are more likely to dam- age property, to assault other people, to cause fatal automobile accidents, and to engage in risky, unprotected sexual inter- course, resulting in sexually transmitted diseases and unplanned pregnancies.9 Female binge drinkers are more likely to be victims of rape.

Binge drinkers on and off campus may fi nd it diffi cult to recognize themselves as problem drinkers (refer again to Table C3-4) until their drinking behavior causes

Moderate Drinkers Typically Problem Drinkers Typically

Drink slowly, casually.• Eat food while drinking or beforehand.• Don’t binge drink; know when to stop.• Respect nondrinkers.• Avoid drinking when solving problems or making decisions.• Do not admire or encourage drunkenness.• Remain peaceful, calm, and unchanged by drinking.• Cause no problems to others or themselves by drinking.•

Gulp or “chug” drinks.• Drink on an empty stomach.• Binge drink; drink to get drunk.• Pressure others to drink.• Turn to alcohol when facing problems or decisions.• Consider drunks to be funny or admirable.• Become loud, angry, violent, or silent when drinking.• Physically or emotionally harm themselves, family members, or • others when drinking.

Behaviors Typical of Moderate Drinkers and Problem Drinkers table

C3-4

§ This defi nition of binge drinking, without specifi ca- tion of time elapsed, is consistent with standard practice in alcohol research.

99controversy 3 A l c o h o l a n d N u t r i t i o n : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

year, deaths attributed to this effect take place during drinking contests. Before passing out, the drinker drinks fast enough to receive a lethal dose. Figure C3-3 shows blood alcohol levels that correspond with progressively greater

in Figure C3-2, because a person usually passes out before drinking a lethal dose. If a person drinks fast enough, though, the alcohol continues to be absorbed, and its effects continue to accelerate after the person has gone to sleep. Every

mately alcohol acts as a depressant that sedates the nerve cells (see Figure C3-2).

A Lethal Dose of Alcohol It is lucky that the brain centers respond to rising blood alcohol in the order shown

Judgment and reasoning centers are most sensitive to alcohol. When alcohol flows to the brain, it first sedates the brain center responsible for all conscious activity. As the alcohol molecules diffuse into the cells of these areas, they interfere with judgment and reasoning.

Speech and vision

Respiration and heart action are the last to be affected. Finally, the conscious brain is completely subdued, and the person passes out. Now the person can drink no more; this is fortunate because higher doses would anesthetize the deepest brain centers that control breathing and heartbeat, causing death.

Speech and vision centers in the midbrain are affected next. If the drinker drinks faster than the rate at which the liver can oxidize the alcohol, blood alcohol concentrations rise: the speech and vision centers of the brain become sedated.

Voluntary muscular control is then affected. At still higher concentrations, the cells in the brain area responsible for coordination of voluntary muscles are affected, including those used in speech, eye-hand coordination, and limb movements. At this point, people under the influence stagger or weave when they try to walk, or they may slur their speech.

Judgment and reasoning

Respiration and heartbeat

Voluntary muscle control

3 4

Alcohol’s Effects on the Brain figure C3-2

Drinks a Drinks a Body Weight in Pounds—Men Body Weight in Pounds—Women

100 90200 240220120 140 160 180 100 200 240220120 140 160 180

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

.04

.08

.11

.15

.19

.23

.26

.30

.34

.38

.02

.04

.06

.08

.09

.11

.13

.15

.17

.19

.02

.04

.06

.08

.10

.12

.14

.17

.19

.21

.02

.05

.07

.09

.11

.14

.16

.18

.20

.23

.03

.05

.08

.10

.13

.15

.18

.20

.23

.25

.03

.06

.09

.11

.14

.17

.20

.23

.26

.28

.03

.07

.10

.13

.16

.19

.23

.26

.29

.32

.04

.08

.11

.15

.19

.23

.27

.30

.34

.38

.05

.09

.14

.18

.23

.27

.32

.36

.41

.45

.05

.10

.15

.20

.25

.30

.35

.40

.45

.51

.02

.03

.05

.06

.08

.09

.11

.13

.14

.16

.02

.03

.05

.07

.09

.10

.12

.14

.15

.17

.02

.04

.06

.08

.09

.11

.13

.15

.17

.19

.02

.04

.06

.08

.11

.13

.15

.17

.19

.21

.02

.05

.07

.09

.12

.14

.16

.19

.21

.23

.03

.05

.08

.11

.13

.16

.19

.21

.24

.27

.03

.06

.09

.12

.16

.19

.22

.25

.28

.31

ONLY SAFE DRIVING LIMIT

IMPAIRMENT BEGINS

LEGALLY INTOXICATED

DRIVING SKILLS SIGNIFICANTLY

AFFECTED

DRIVING SKILLS SIGNIFICANTLY

AFFECTED

Alcohol Doses and Average Blood Level Percentages for Men and Women figure C3-3

NOTE: In some states, driving under the infl uence is proved when an adult’s blood contains 0.08 percent alcohol, and in others, 0.10. Many states have adopted a “zero-tolerance” policy for drivers under age 21, using 0.02 percent as the limit. aTaken within an hour or so: each drink equivalent to ½ ounce pure ethanol. Source: National Clearinghouse for Alcohol and Drug Information

100 chapter 3 T h e R e m a r k a b l e B o d y

greater amounts of alcohol in the blood. The data were derived from police ac- cident reports about people who were driving after drinking alcohol.

ALCOHOL ARRIVES IN THE LIVER The capillaries that surround the diges- tive tract merge into veins that carry the alcohol-laden blood to the liver. Here the veins branch and rebranch into capil- laries that touch every liver cell, which possess most of the body’s alcohol- processing machinery. The routing of blood through the liver allows the cells to go right to work detoxifying alcohol and other toxins before they reach other sensitive body organs such as the heart and brain.

A Liver Enzyme for Alcohol Breakdown The liver is the primary site of alcohol metabolism—it makes and maintains most of the body’s equipment for me- tabolizing alcohol.13 Its primary tool is an enzyme that removes hydrogens from alcohol to break it down; the enzyme’s name, alcohol dehydrogenase (ADH), almost says what it does (see Figure C3-5).** This enzyme converts about 80 percent of the alcohol in the body to

use, arising from its deleterious effects on the brain. All of the following involve alcohol use:

20 percent of all boating fatalities•

23 percent of all suicides•

39 percent of all traffi c fatalities•

40 percent of all residential fi re • fatalities

47 percent of all homicides•

65 percent of all domestic violence • incidents

Figure C3-4 shows that the risk of having an auto accident rises precipitously with

intoxication, and Table C3-5 shows brain and nervous system responses that oc- cur at these levels.

Alcohol Toxicity, Oxidative Stress, and the Brain Brain cells are particularly sensitive to exposure to alcohol. The working brain tissue shrinks, even in people who drink only moderately. The extent of the shrinkage is proportional to the amount drunk. Alcohol addicts are prone to brain hemorrhages and strokes; postmortem examinations reveal brain cell loss, brain swelling, and diminished functioning of the barrier that protects the brain from toxins. All of these conditions are related to the oxidative stress that accompanies ethanol metabolism.12 Free radicals that arise during ethanol metabolism attack brain cell lipids and cause infl ammation. Then, the working brain cells become injured, die off, and disintegrate.

Abstinence from alcohol, together with good nutrition, reverses some of the brain damage, if heavy drinking has not continued for more than a few years. Prolonged drinking beyond an individual’s capacity to recover, however, can do severe and irreversible harm to vision, memory, learning and reasoning, speech, and other brain functions.

Alcohol and Accidents Accidents constitute an immediate and often severe consequence of alcohol

Blood Alcohol Level (%) Brain Response

0.05a Judgment impaired

0.10 Emotional control impaired

0.15 Muscle coordination and refl exes impaired

0.20 Vision impaired

0.30 Drunk, lacking control

0.35 In a stupor

0.50–0.60 Loss of consciousness, death

a A 0.08 percent level is the legal limit for intoxication according to most states’ highway safety ordinances; however, driving ability may be impaired at blood alcohol levels lower than 0.08 percent.

Blood Alcohol Levels and Brain Responses table

C3-5

0 0 0.08

% BAC

A cc

id en

t p ro

ba bi

lit y

0.02 0.060.04 0.160.1 0.140.12 0.18

The Probability of Causing an Accident Rises

with Blood Alcohol Content (BAC)

figure C3-4

**ADH exists in several variants.

101controversy 3 A l c o h o l a n d N u t r i t i o n : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

metabolism of alcohol. The police say that a cup of coffee only makes a sleepy drunk into a wide-awake drunk. Table C3-6 presents other alcohol myths.

ALCOHOL AFFECTS THE LIVER AND OTHER ORGANS Among energy sources, ethanol receives the body’s highest priority for break- down. Toxic ethanol cannot be stored in body tissues without fi rst being con- verted to something safer. Along the way, however, other harmful chemicals arise. For example, alcohol’s fi rst breakdown product, acetaldehyde, can bind to enzymes and other structures, disrupting their functions.14 Also, as Figure C3-5 showed, alcohol metabolism generates damaging free radicals.15 Free radicals increase oxidative stress (introduced

test that law enforcement offi cers admin- ister to someone suspected of driving while intoxicated accurately reveals the person’s degree of intoxication.

Rate of Alcohol Clearance The liver can process about ½ ounce of blood ethanol (one drink’s worth) per hour, depending on the person’s body size, previous drinking experience, food intake, gender, and general health. Fasting for as little as one day causes degradation of body proteins, including ADH levels, and cuts the rate of alcohol metabolism by half.

The liver’s maximum rate of alcohol clearance cannot be accelerated. This explains why only time restores sobriety. Walking doesn’t help, because muscles cannot metabolize alcohol. Nor will drink- ing a cup of coffee be effective. Caffeine is a stimulant, but it won’t speed up the

acetaldehyde, the major breakdown product of alcohol. Other alcohol- metabolizing enzymes help out too, especially when alcohol levels exceed ADH capacity.

The maximum amount of blood alcohol a person’s body can process in a given time is limited by the amount of ADH residing in the liver. If more alcohol arrives at the liver than the enzymes can handle, the extra alcohol circulates again and again through the brain, liver, and other organs until enzymes are available to degrade it.

Alcohol Breakdown in the Stomach The stomach wall also produces ADH that breaks down some alcohol before it reaches the bloodstream. Research shows that people with alcoholism make less stomach ADH than others and that women make less than men.

Earlier, this Controversy warned that women should not try to keep up with male drinkers, and here are the reasons why: pound for pound of body weight, men have more lean tissue and there- fore a greater volume in which to dilute a given amount of alcohol. In women, the same amount of alcohol becomes more concentrated. Also, with her lower stomach ADH levels, a woman absorbs more alcohol from each drink than a man of equal body weight does.

Excretion in Breath and Urine About 10 percent of blood alcohol is not metabolized at all, but is excreted as is, about half exhaled by the lungs in the breath and the other half excreted by the kidneys in urine. The alcohol in the breath is directly proportional to the alcohol in the blood, so the breathalyzer

Acetate (Aldehyde

dehydrogenase) (Alcohol

dehydrogenase)

Acetaldehyde Alcohol (ethanol)

Used for energy or changed into fat and stored

Energy

Free radicals

Energy

Free radicals

The major route of alcohol breakdown produces acetaldehyde, creates free radicals, and increases oxidative stress in the tissues.

Alcohol Breakdown figure C3-5

Myth: Truth:

A shot of alcohol warms you up. Alcohol diverts blood fl ow to the skin making you feel warmer, but it actually cools the body.

Myth: Truth:

Wine and beer are mild; they do not lead to addiction. Wine and beer drinkers worldwide have high rates of death from alcohol- related illnesses. It’s not what you drink but how much that makes the difference.

Myth: Truth:

Mixing drinks is what gives you a hangover. Too much alcohol in any form produces a hangover.

Myth: Truth:

Alcohol is a stimulant. Alcohol depresses the brain’s activity.

Myth: Truth:

Alcohol is legal; therefore, it is not a drug. Alcohol is legal, but it alters body functions and is medically defi ned as a depressant drug.

Myths and Truths Concerning Alcohol table

C3-6

102 chapter 3 T h e R e m a r k a b l e B o d y

hyde is known to raise the risk for certain cancers; no one knows whether formal- dehyde generated from alcohol does the same.19

Normally, a set of liver enzymes con- verts this methanol to formaldehyde, with a second set immediately converting the formaldehyde to carbon dioxide and water, harmless waste products that can be excreted. But these same two sets of liver enzymes are the very ones that process ethanol to its own intermediate (and highly toxic) waste product, acet- aldehyde, and fi nally to carbon dioxide and water. The enzymes prefer ethanol 20 times over methanol. Both alcohols are metabolized without delay until the excess acetaldehyde monopolizes the second set of enzymes, leaving formal- dehyde to wait for later detoxifi cation. At that point, formaldehyde starts accumu- lating and the hangover begins.

Time alone is the cure for a hangover. Vitamins, tranquilizers, aspirin, drinking more alcohol, breathing pure oxygen, ex- ercising, eating, and drinking something awful are all useless. Fluid replacement can help to normalize the body’s chem- istry. The headache, bad mood, nausea, and other effects of a hangover come simply from drinking too much.

ALCOHOL’S LONG-TERM EFFECTS A couple of drinks set in motion many destructive processes in the body. The next day’s abstinence can reverse them only if the doses taken are moderate, the time between them is ample, and nutrition is adequate. If the doses of alcohol are heavy, however, and the time between them is short, complete recov- ery cannot take place, and repeated onslaughts of alcohol take a toll on the body.

Effects in Pregnancy By far the longest-term effects of alcohol are those felt by the child of a woman who drinks during pregnancy. When a pregnant woman takes a drink, her fetus takes the same drink within minutes and its body is defenseless against the ef- fects. Pregnant women should not drink alcohol—this topic is so important that Chapter 13 devotes a section to it. The

Alcohol also affects other systems and organs. It slows the synthesis of some immune system proteins, weakening the body’s defenses against infection. Synthesis of blood lipids speeds up, increasing the concentration of both triglycerides and high-density lipopro- teins (see Chapter 5). In addition, excess alcohol adds to the body’s acid burden and interferes with normal uric acid me- tabolism, causing symptoms like those of gout. All of these effects point to the wisdom of strictly moderating alcohol intakes.

THE HANGOVER The hangover—the awful feeling of headache, pain, unpleasant sensations in the mouth, and nausea the morning after drinking too much—is a mild form of drug withdrawal. (The worst form is a delirium with severe tremors that pre- sents a danger of death and demands medical management.) Hangovers depress mood, disrupt sleep, increase anxiety, cause fatigue, reduce cognitive ability, and reduce the ability to cope with stress.18

Congeners and Dehydration Hangovers are caused by several fac- tors. One is the toxic effects of con- geners that accompany the alcohol in alcoholic beverages. Mixing or switch- ing drinks will not prevent hangover, because congeners are only one factor. Dehydration of the brain is a second factor: alcohol reduces the water content of the brain cells. When they rehydrate the morning after and swell back to their normal size, nerve pain results.

Formaldehyde and Methanol Another contributor to the hangover is form- aldehyde, the smelly chemical laboratories use to preserve dead animals. Formaldehyde arises from methanol, another alcohol pro- duced in tiny amounts by cellular metabolic processes. Occupational exposure to formalde-

in Controversy 2), a condition linked with infl ammation and the development of diabetes, cancer, and other serious diseases. Together, these factors are thought to greatly contribute to the organ damage, especially to the liver, sustained from drinking ethanol.16

Fatty Liver When presented with alcohol, the liver speeds up its production of fats. The fi rst stage of liver deterioration seen in heavy drinkers is therefore known as fatty liver; it interferes with the distribution of nutrients and oxygen to the liver cells. Fat is known to accumulate in the livers of young men after a single night of heavy drinking and to remain there for more than a day.

Liver Fibrosis If heavy drinking continues for long enough, fi brous scar tissue invades the liver. This is the second stage of liver deterioration, called fi brosis. Fibrosis is reversible with good nutrition and ab- stinence from alcohol, but the next (last) stage, cirrhosis, is not. In cirrhosis, the liver cells harden, turn orange, and die, losing function forever.

Reproductive and Other Organs The reproductive system is vulnerable to alcohol’s effects. Heavy drinking in women may lead to infertility or spon- taneous abortion. Alcohol may also suppress the male reproductive hormone testosterone, leading to decreases in muscle and bone tissue, altered im- munity, abnormal prostate gland, and decreased reproductive ability.17

Left, normal liver; center, fatty liver; right, cirrhosis.

A rth

ur G

la ub

er m

an /P

ho to

R es

ea rc

he rs

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103controversy 3 A l c o h o l a n d N u t r i t i o n : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

also causes direct negative effects on nutrients that the body needs to function.

The Fattening Power of Alcohol Metabolic interactions occur between fat and alcohol in the body. Presented with both fat and alcohol, the body stores the comparatively harmless fat and rids itself of the toxic alcohol by using it preferen- tially for energy.27 Thus alcohol promotes fat storage, and particularly in the central abdominal area—the “beer belly” effect seen in moderate drinkers.28 Excess abdominal fat poses risks, as described in Chapter 9.

Alcoholic drinks can be much more fattening than their nonalcoholic coun- terparts. Ethanol yields 7 calories of energy per gram and drink mixers often present many additional calories. Table C3-7 shows the calorie amounts of typi- cal alcoholic beverages and mixers. A general guideline states that each ounce of ethanol represents the same number of calories as about half an ounce of fat. An observant reader, knowing that in the laboratory, a gram of fat and a gram of alcohol yield 9 and 7 calories, respec- tively, may wonder why alcohol in a drink is worth only half the calorie value of fat. The answer lies in the small amount of alcohol excreted in the breath and urine.

Alcohol’s Effects on Vitamins In addition to alcohol’s direct toxic ef- fects, its abuse damages the body indi- rectly via malnutrition. The more alcohol a person drinks, the less likely he or she will eat enough food to obtain adequate nutrients. Like pure sugar and pure fat, alcohol provides discretionary calories without nutrients; in fact, it displaces other nutritious foods and beverages from the diet.

Alcohol abuse also disrupts every tis- sue’s metabolism of nutrients. Stomach cells oversecrete both acid and hista- mine, the latter, an agent of the immune system that produces infl ammation. Intestinal cells fail to absorb thiamin, folate, vitamin B12, and other vitamins. Liver cells lose effi ciency in activating vitamin D. Cells of the eye’s retina, which normally process the alcohol form of vitamin A (retinol) to the form needed in vision (retinal), must process ethanol instead. Liver cells, too, suffer a reduced

other types—in reality, all colors of wine present identical breast cancer risks.23 In the case of beer, alcohol may be acting together with other compounds formed during brewing to promote the cancer. For example, the compound urethane, often found in alcoholic beverages, is known to cause cancer in animals, but the risk to human beings remains unknown.

Long-Term Effects of Alcohol Abuse While many of the effects just men- tioned may also affect people who drink socially, the long-term effects of alcohol abuse and alcoholism can be devastat- ing. They include the following:

Bladder, kidney, pancreas, and pros-• tate damage.

Bone deterioration and osteoporosis.•

Brain disease, central nervous system • damage, and stroke.

Deterioration of the testicles and adre-• nal glands.

Diabetes (type 2 diabetes).•

Disease of the muscles of the heart.•

Feminization and sexual impotence in • men.

Impaired immune response.•

Impaired memory and balance.•

Increased risks of death from all • causes.

Major psychological depression, pos-• sibly caused by alcohol.24

Malnutrition.•

Nonviral hepatitis.• 25

Skin rashes and sores.•

Ulcers and infl ammation of the stom-• ach and intestines.

This list is by no means all-inclusive. Alcohol abuse exerts direct toxic effects on all body organs. Monetarily, alcohol- ism costs our society an estimated $186 billion every year in medical services, lost wages, criminal offenses, auto crashes, and other losses.26

ALCOHOL’S EFFECT ON NUTRITION Alcohol causes disturbances in nutrition. Its calories are all discretionary calories, often overlooked by drinkers. Alcohol

rest of this section concerns effects on drinkers themselves.

Effects on Heart and Brain Alcohol is directly toxic to skeletal and cardiac muscle, causing weakness and deterioration that is greater, the larger the dose. Alcoholism makes heart disease likely, probably because chronic alcohol use raises blood pressure. At autopsy, the heart of a person with alcoholism ap- pears bloated and weighs twice as much as a normal heart.

Alcohol attacks brain cells directly and heavy drinking can result in dementia. Al- cohol’s metabolic product acetaldehyde and the free radicals arising from alcohol metabolism can adversely affect brain tissues. In people with alcoholism, men- tal functioning remains impaired even between drinking bouts. Women may be particularly vulnerable to such impair- ment despite drinking less alcohol for fewer years than men, but the reasons why are not yet known.20 In the liver, cir- rhosis also develops after 10 to 20 years from the cumulative effects of frequent episodes of heavy drinking.

Cancer Experts include daily ethanol exposure among cancer-causing substances for human beings. Even moderate drinking increases the chances of developing cancers of the breast, colon and rectum, esophagus, liver, mouth, pancreas, prostate gland, stomach, and throat.††21 In smokers, alcohol greatly increases the risk of developing lung cancer. And once cancer is established, alcohol seems to speed up its development. Alcohol’s by-products, acetaldehyde and free radicals, may contribute to cancer risk, as well as ethanol itself.

A convincing body of evidence impli- cates alcohol in the causation of breast cancer in women—even those who drink less than one drink per day elevate their risk slightly and, with greater consump- tion, the risk rises accordingly. In men, moderate drinking increases the risks of cancers at many sites, risks that increase substantially with increasing daily alcohol consumption.22 A popular myth holds that red wine is safer for women than

†† In 2002, 389,100 cases (3.6 percent) of cancer worldwide were attributable to drinking alcohol.

104 chapter 3 T h e R e m a r k a b l e B o d y

DOES MODERATE ALCOHOL USE BENEFIT HEALTH? Among middle-aged people, consuming alcohol in moderation often correlates with certain health benefi ts, including reduced risks of heart attacks, strokes, dementia, diabetes, and osteoporosis.29 In fact, moderate alcohol intake corre- lates with lower mortality from all causes, but only in middle-aged adults over age 35.30 Among younger light drinkers, the risk of dying is greater than among non- drinkers of the same age.31 Then, after middle age, the correlation with health benefi ts disappears again as aging body organs become more sensitive to toxic substances.32

Research Problems Such epidemiological fi ndings of disease prevention would normally trigger the kind of studies that could verify or refute them—that is, controlled clinical human trials. In the case of alcohol, however, the potential for addiction, traffi c and other fatalities, and other harms makes it unethical for researchers to administer alcohol to people over long periods to study its effects.33 Additionally, because alcohol’s effects on the brain are almost immediately detectible, administering it without the knowledge of study subjects (a blind study) is impossible.

Benefi ts Versus Risks As mentioned, young people do not benefi t from any amount of alcohol; rather, they increase their risk of dying from all causes and particularly car crashes, homi- cides, and other violence that account for the great majority of deaths among young people each year.34 In fact, for all U.S. populations, the sum of alcohol-related deaths tops 79,000 annually, making alco- hol a substantial contributor to mortality.35

Young women in particular should not drink alcohol for the sake of their heart. Prior to menopause, the risk of heart disease for women is low, but the risk of breast cancer is substantial and daily alcohol contributes to that risk. As mentioned, even the single drink per day that might provide heart benefi ts to older

in excess. The intestine normally re- leases and retrieves folate continuously, but it becomes so damaged by folate defi ciency and alcohol toxicity that it fails to absorb folate. Alcohol also interferes with the action of what little folate is left, causing a buildup in the blood of a com- pound suspected of involvement with many diseases, including heart disease, stroke, and birth defects.‡‡ This interfer- ence inhibits the production of new cells, especially the rapidly dividing cells of the intestine and the blood.

Nutrient defi ciencies are thus an inevi- table consequence of alcohol abuse, not only because alcohol displaces food but also because alcohol interferes directly with the body’s use of nutrients. People treated for alcohol addiction also need nutrition therapy to reverse defi ciencies and even defi ciency diseases rarely seen in others: night blindness, beriberi, pellagra, scurvy, and protein-energy malnutrition.

capacity to process and use vitamin A. The kidneys excrete needed minerals: magnesium, calcium, potassium, and zinc.

The inadequate food intake and impaired nutrient absorption that accompany chronic alcohol abuse frequently lead to a defi ciency of the B vitamin thiamin. In fact, the cluster of thiamin-defi ciency symptoms commonly seen in chronic alcoholism has its own name—the Wernicke-Korsakoff syn- drome. This syndrome is characterized by paralysis of the eye muscles, poor muscle coordination, impaired memory, and damaged nerves; the syndrome and other alcohol-related memory problems may respond somewhat to treatment with thiamin supplements.

Most dramatic is alcohol’s effect on folate. When an excess of alcohol is present, the body actively expels folate from all of its sites of action and stor- age. The liver, which normally contains enough folate to meet all needs, leaks its folate into the blood. As blood folate rises, the kidneys excrete it, as if it were

Beverage Amount (oz) Energy (cal)

Malt beverage (sweetened) 16a 350

Wine cooler 12 170

Pina colada mix (no alcohol) 4 160

Malt beverage (unsweetened) 16 175

Beer 12 150

Dessert wine 3½ 140

Fruit-fl avored soda, Tom Collins mix 8 115

Gin, rum, vodka, whiskey (86 proof) 1½ 105

Cola, root beer, tonic, ginger ale 8 100

Margarita mix (no alcohol) 4 100

Light beer 12 100

Table wine 3½ 85

Tomato juice, Bloody Mary mix ( no alcohol) 8 45

Club soda, plain seltzer, diet drinks 8 1

aTypical container size, but up to 32-oz containers are common.

Calories in Alcoholic Beverages and Mixers table C3-7

‡‡ The compound is homocysteine; see Chapter 6.

105controversy 3 A l c o h o l a n d N u t r i t i o n : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

unaware that they are hungry. But in peo- ple who are tense and unable to eat or in the elderly who have lost interest in food, a small dose of wine taken 20 minutes before meals may improve appetite. For undernourished people and for people with severely depressed appetites, wine may facilitate eating even when psycho- therapy fails to do so.

Another example of the benefi cial use of alcohol comes from research show- ing that moderate use of wine in later life improves morale, stimulates social interaction, and promotes restful sleep. In nursing homes, improved patient and staff relations have been attributed to greater self-esteem among elderly patients who drink moderate amounts of wine. Researchers hypothesize that chronic fatigue may be responsible for some behaviors associated with old age. The positive effects of wine on sleep may alleviate fatigue.

THE FINAL WORD This discussion has explored some of the ways alcohol affects health and nutrition. In the end, each person must decide individually whether or not to consume alcohol and can change the decision at any time. The surest way to escape the harmful effects of alcohol is, of course, to refuse alcohol altogether. If you do choose to drink, do so with care and strictly in moderation.

The good news: the high potassium • content of grape juice, a heart-healthy constituent, persists when the grape juice is made into wine.

The bad news: alcohol in large amounts • raises blood pressure, so grape juice may be more suitable for those with hypertension and heart disease.

More good news: wine contains phyto-• chemicals that, when metabolized by the body, may help reduce the risk of heart disease or cancers of the colon or rectum.39

More bad news: compared with a diet • rich in foods such as onions, berries, or leafy vegetables, wine delivers only a small amount of such phytochemi- cals. Dealcoholized wine, purple grape juice, and whole grapes also provide phytochemicals and do so more safely.

Good news about alcohol and the • brain: some studies report that mod- erate drinkers may suffer less age- related decline of mental function than abstainers or heavy drinkers.

Bad news: improved cognition among • older people probably results from social, economic, and educational advantages of moderate drinkers, and not from alcohol itself.40

And so it goes.

Alcohol and Appetite Alcoholic beverages affect the appetite. Usually, they reduce it, making people

people also raises breast cancer risk in young women by up to 10 percent.36 More alcohol poses greater risks.

In middle-aged populations, taking one to two drinks (moderate drinking) a day may benefi t the heart, but more than this amount substantially increases the risk of cardiovascular diseases.37 Experts con- clude that the theoretical benefi ts from alcohol consumption to the population as a whole are many times outweighed by the known risks, and a population-wide recommendation to consume alcohol would do more harm than good.38

The Health Effects of Wine Red wine has been credited with special health-supporting properties and, re- cently, white wine has won attention for an antioxidant effect, too. The following two statements concerning wine and health have been approved to appear on U.S. wine labels: “The proud people who made this wine encourage you to consult your family doctor about the health effects of wine consumption.” Or, “To learn the health effects of wine consump- tion, send for the Federal Government’s Dietary Guidelines for Americans, Center for Nutrition Policy and Promotion, USDA, 1120 20th Street, NW, Washing- ton, DC 20036 or visit its website.”

These statements seem to promise that good news about wine and health awaits the information seeker, but the science on wine and health is mixed:

news:the

news:alcohol

news:wine

news:compared

news:improved

Carbohydrates: Sugar, Starch, Glycogen, and Fiber 44 do you ever . . .

Think of carbohydrates as providing • nothing but calories to the body?

Wonder why nutrition authorities • unanimously recommend foods high in fi ber?

Have trouble distinguishing whole-• grain foods from others at the grocery store?

Blame carbohydrates in the diet for • obesity or diseases?

Keep reading . . .

LO 4.1 Describe the major types of carbohydrates, and identify their food sources.

LO 4.2 Describe the various roles of carbohydrates in the body, and explain why avoiding dietary carbohydrates may be ill-advised.

LO 4.3 Summarize how fi ber differs from other carbohydrates and how fi ber may contribute to health.

LO 4.4 Explain how complex carbohydrates are broken down in the digestive tract and absorbed into the body.

LO 4.5 Describe how hormones control blood glucose concentrations during fasting and feasting.

LO 4.6 Explain the term glycemic index and how it may relate to diet planning.

LO 4.7 Describe the scope of the U.S. diabetes problem and educate someone about the long- and short-term effects of untreated diabetes and prediabetes.

LO 4.8 Name components of a lifestyle plan to effectively control blood glucose and describe the characteristics of a diet that can assist in managing type 2 diabetes.

LO 4.9 Compare the symptoms of postprandial hypoglycemia with those of fasting hypoglycemia, and name some diseases associated with the latter type.

LO 4.10 Discuss current research regarding the relationships among dietary carbohydrates, obesity, diabetes, and other ills.

Learning Objectives To find learning objective topics in this chapter, look for the text headings with a corresponding “LO” number above the heading. After completing this chapter, you should be able to accomplish the following:

Tess Stone/Getty Images

107A C l o s e L o o k a t C a r b o h y d r a t e s

4 C arbohydrates are ideal nutrients to meet your body’s energy needs, to feed

your brain and nervous system, to keep your digestive system fi t, and within calorie limits, to help keep your body lean. Digestible carbohydrates, together with fats and protein, add bulk to foods and provide energy and other benefi ts for the body. Indigestible carbohydrates, which include most of the fi bers in foods, yield little or no energy but provide other important benefi ts.

All carbohydrates are not equal in terms of nutrition. Th is chapter invites you to learn the diff erences between foods containing complex carbohydrates (starch and fi ber) and those made of simple carbohydrates (the sugars) and to consider the ef- fects of both on the body. Controversy 4 goes on to explore current theories about how consumption of certain carbohydrates may aff ect human health.

Th is chapter on the carbohydrates is the fi rst of three on the energy-yielding nutri- ents. Chapter 5 deals with the fats and Chapter 6 with protein. Controversy 3 in Chap- ter 3 already addressed one other contributor of energy to the human diet, alcohol.

LO 4.1

A Close Look at Carbohydrates Carbohydrates contain the sun’s radiant energy, captured in a form that living things can use to drive the processes of life. Green plants make carbohydrate through photosynthesis in the presence of chlorophyll and sunlight. In this process, water (H2O) absorbed by the plant’s roots donates hydrogen and oxygen. Carbon dioxide gas (CO2) absorbed into its leaves donates carbon and oxygen. Water and carbon dioxide combine to yield the most common of the sugars, the single sugar glucose. Scientists know the reaction in the minutest detail but have yet to reproduce it— green plants are required to make it happen (see Figure 4-1).1*

Light energy from the sun drives the photosynthesis reaction. Th e light energy becomes the chemical energy of the bonds that hold six atoms of carbon together in the sugar glucose. Glucose provides energy for the work of all the cells of the stem, roots, fl owers, and fruits of the plant. For example, in the roots, far from the energy-giving rays of the sun, each cell draws upon some of the glucose made in the leaves, breaks it down (to carbon dioxide and water), and uses the energy thus released to fuel its own growth and water-gathering activities.

Plants do not use all of the energy stored in their sugars, so it remains available for use by the animal or human being that consumes the plant. Th us, carbohydrates form the fi rst link in the food chain that supports all life on earth. Carbohydrate- rich foods come almost exclusively from plants; milk is the only animal-derived food that contains signifi cant amounts of carbohydrate. Th e next few sections de- scribe the forms assumed by carbohydrates: sugars, starch, glycogen, and fi ber.

KE Y POINT Through photosynthesis, plants combine carbon dioxide, water, and the sun’s energy to form glucose. Carbohydrates are made of carbon, hydrogen, and oxygen held together by energy-containing bonds: carbo means “carbon”; hydrate means “water.”

Sugars Six sugar molecules are important in nutrition. Th ree of these are single sugars, or monosaccharides. Th e other three are double sugars, or disaccharides. All of their chemical names end in ose, which means “sugar.” Although they all sound alike at fi rst, they exhibit distinct characteristics once you get to know them as individuals. Figure 4-2 shows the relationships among the sugars.

carbohydrates compounds composed of single or multiple sugars. The name means “carbon and water,” and a chemical shorthand for carbohydrate is CHO, signifying carbon (C), hydrogen (H), and oxygen (O).

complex carbohydrates long chains of sugar units arranged to form starch or fi ber; also called polysaccharides.

simple carbohydrates sugars, includ- ing both single sugar units and linked pairs of sugar units. The basic sugar unit is a molecule containing six carbon atoms, together with oxygen and hydrogen atoms.

photosynthesis the process by which green plants make carbohydrates from carbon dioxide and water using the green pigment chlorophyll to capture the sun’s energy ( photo means “light”; synthesis means “making”).

chlorophyll the green pigment of plants that captures energy from sunlight for use in photosynthesis.

sugars simple carbohydrates; that is, molecules of either single sugar units or pairs of those sugar units bonded together. By common usage, sugar most often refers to sucrose.

glucose (GLOO-cose) a single sugar used in both plant and animal tissues for energy; sometimes known as blood sugar or dextrose.

monosaccharides (mon-oh-SACK-ah- rides) single sugar units (mono means “one”; saccharide means “sugar unit”).

disaccharides pairs of single sugars linked together (di means “two”).

*Reference notes are found in Appendix F.

108 chapter 4 C a r b o h y d r a t e s

Monosaccharides Th e three monosaccharides are glucose, fructose, and galac- tose. Fructose or fruit sugar, the intensely sweet sugar of fruit, is made by rearrang- ing the atoms in glucose molecules. Fructose occurs mostly in fruits, in honey, and as part of table sugar. Other sources include soft drinks, ready-to-eat cereals, and other products sweetened with high-fructose corn syrup (defi ned later on). Glucose and fructose are the most common monosaccharides in nature.

Th e other monosaccharide, galactose, has the same number and kind of atoms as glucose and fructose but in another arrangement. Galactose is one of two single sugars that are bound together to make up the sugar of milk. Galactose rarely oc- curs free in nature but is tied up in milk sugar until it is freed during digestion.

Disaccharides Th e three other sugars important in nutrition are disaccharides, which are linked pairs of single sugars, or disaccharides. Th ey are lactose, maltose, and sucrose. All three contain glucose. In lactose, the milk sugar just mentioned, glucose is linked to galactose. Malt sugar, or maltose, has two glucose units. Malt- ose appears wherever starch is being broken down. It occurs in germinating seeds and arises during the digestion of starch in the human body.

Th e last of the six sugars, sucrose, is familiar table sugar, the product most people think of when they refer to sugar. In sucrose, fructose and glucose are bonded to-

Glucose

Chlorophyll

Water

Carbon dioxide

Oxygen

Energy

Energy Sun

The sun’s energy becomes part of the glucose molecule—its calories, in a sense. In the molecule of glucose on the leaf here, black dots represent the carbon atoms; bars represent the chemical bonds that contain energy.

Animated! Carbohydrate—Mainly Glucose—

Is Made by Photosynthesis

figure 4-1

Single sugars are monosaccharides.•

Pairs of sugars are disaccharides.•

fructose (FROOK-tose) a monosaccharide; sometimes known as fruit sugar (fruct means “fruit”; ose means “sugar”).

galactose (ga-LACK-tose) a monosac- charide; part of the disaccharide lactose (milk sugar).

lactose a disaccharide composed of glu- cose and galactose; sometimes known as milk sugar (lact means “milk”; ose means “sugar”).

maltose a disaccharide composed of two glucose units; sometimes known as malt sugar.

sucrose (SOO-crose) a disaccharide com- posed of glucose and fructose; sometimes known as table, beet, or cane sugar and, often, as simply sugar.

109A C l o s e L o o k a t C a r b o h y d r a t e s

gether. Table sugar is obtained by refi ning the juice from sugar beets or sugarcane, but sucrose also occurs naturally in many vegetables and fruits. It tastes sweet be- cause it contains the sweetest of the monosaccharides, fructose.

When you eat a food containing monosaccharides, you can absorb them directly into your blood. When you eat disaccharides, though, you must digest them fi rst. Enzymes in your intestinal cells must split the disaccharides into separate monosac- charides so that they can enter the bloodstream. Th e blood delivers all products of digestion fi rst to the liver, which possesses enzymes to modify nutrients, making them useful to the body. Glucose is the most used monosaccharide inside the body, so the liver quickly converts fructose or galactose to glucose or to smaller compounds that can serve as building blocks for glucose, fat, or other needed molecules.

Although it is true that the energy of fruits and many vegetables comes from sugars, this doesn’t mean that eating them is the same as eating concentrated sweets such as candy or drinking cola beverages. From the body’s point of view, fruits are vastly diff erent from purifi ed sugars (as a later section makes clear) except that both provide glucose in abundance.

KE Y POINT Glucose is the most important monosaccharide in the human body. Most other monosaccharides and disaccharides become glucose in the body.

Starch In addition to occurring in sugars, the glucose in food also occurs in long strands of thousands of glucose units. Th ese are the polysaccharides (see Figure 4-3). Starch is a polysaccharide, as are glycogen and most of the fi bers.

Starch is a plant’s storage form of glucose. As a plant matures, it not only provides energy for its own needs but also stores energy in its seeds for the next generation. For example, after a corn plant reaches its full growth and has many leaves manu- facturing glucose, it links glucose together to form starch, stores packed clusters of starch molecules in granules, and packs the granules into its seeds. Th ese giant starch clusters are packed side by side in the kernels of corn. For the plant, starch is useful because it is an insoluble substance that will stay with the seed in the ground and nourish it until it forms shoots with leaves that can catch the sun’s rays. Glucose, in contrast, is soluble in water and would be washed away by the rains while the seed lay in the soil. Th e starch of corn and other plant foods is nutritive for people,

Fructose Glucose Galactosea

Sucrose (fructose—glucose)

Maltose (glucose—glucose)

Lactoseb

(glucose—galactose) . . . join together to make three types of disaccharides.

aGalactose does not occur in foods singly but only as part of lactose. bThe chemical bond that joins the monosaccharides of lactose differs from those of other sugars and makes lactose hard for some people to digest—lactose intolerance (see later section).

Three types of monosaccharides … A note on the glucose symbol:

The glucose molecule is really a ring of 5 carbons and 1 oxygen plus a carbon “flag.”

For convenience, glucose is symbolized as or

Carbons Oxygen

Single sugars are monosaccharides while pairs of sugars are disaccharides.

How Monosaccharides Join to Form Disaccharides figure 4-2

CONCEPT LINK 4-1 The digestive system was introduced in Chap- ter 3 (page 78).

Strands of many monosaccharides are • polysaccharides.

polysaccharides another term for com- plex carbohydrates; compounds composed of long strands of glucose units linked together (poly means “many”). Also called complex carbohydrates.

starch a plant polysaccharide composed of glucose. After cooking, starch is highly digest- ible by human beings; raw starch often resists digestion.

granules small grains. Starch granules are packages of starch molecules. Various plant species make starch granules of varying shapes.

110 chapter 4 C a r b o h y d r a t e s

too, because they can digest the starch to glucose and extract the sun’s energy stored in its chemical bonds. A later section describes starch digestion in detail.

KE Y POINT Starch is the storage form of glucose in plants and is also nutritive for human beings.

Glycogen Just as plant tissues store glucose in long chains of starch, animal bodies store glucose in long chains of glycogen. Glycogen resembles starch in that it consists of glucose molecules linked together to form chains, but its chains are longer and more highly branched (see Figure 4-3). Un- like starch, which is abundant in grains, potatoes, and other foods from plants, glycogen is nearly undetectable in meats because glycogen breaks down rapidly when the animal is slaughtered. A later section describes

how the human body handles its own packages of stored glucose.

KE Y POINT Glycogen is the storage form of glucose in animals and human beings.

Fiber Some of the fi bers of a plant form the supporting structures of its leaves, stems, and seeds. Other fi bers play other roles, for example, to retain water and thus protect

Glucose

GlycogenStarch (branched)Starch (unbranched)

Starch Glucose units are linked in long, occasionally branched chains to make starch. Human digestive enzymes can digest these bonds, retrieving glucose. Real glucose units are so tiny that you can’t see them, even with the highest-power light microscope.

Glycogen Glycogen resembles starch in that the bonds between its glucose units can be broken by human enzymes, but the chains of glycogen are more highly branched.

Cellulose (fiber) The bonds that link glucose units together in cellulose are different from the bonds in starch or glycogen. Human enzymes cannot digest them.

Cellulose

Animated! How Glucose Molecules Join to Form Polysaccharides

figure 4-3

The sugars in fruit are diluted with water and naturally packaged with vitamins, minerals, phytochemicals, and fi ber.

al a/

S up

er S

to ck

111T h e N e e d f o r C a r b o h y d r a t e s

seeds from drying out. Like starch, most fi bers are polysaccharides—chains of sug- ars—but they diff er from starch in that the sugar units are held together by bonds that human digestive enzymes cannot break. Most fi bers therefore pass through the human body without providing energy for its use. Billions of bacteria resid- ing within the human large intestine, however, do possess enzymes that can digest fi bers to varying degrees by fermenting them.2 Th rough this process, the fi bers are broken down to waste products, mainly tiny fat fragments that the large intestine (colon) absorbs. Many animals, such as cattle, depend heavily on their digestive sys- tem’s bacteria to make the energy of glucose available from the abundant cellulose, a form of fi ber, in their fodder. Th us, when we eat beef, we indirectly receive some of the sun’s energy that was originally stored in the fi ber of the plants. Beef itself contains no fi ber, nor do other meats and dairy products.

Researchers often divide fi bers into two general groups by their chemical, physi- cal, and functional properties.†3 In the fi rst group are fi bers that dissolve in water (soluble fi bers). Th ese form gels (are viscous) and are easily digested by bacteria in the human colon (are easily fermented). Commonly found in oats, barley, legumes, and citrus fruits, soluble fi bers often lower blood cholesterol and can help to control blood glucose, thus protecting against heart disease and diabetes.4 In foods, soluble fi bers add pleasing consistency, such as the pectin that puts the gel in jelly and the gums added to salad dressings to thicken them.

Other fi bers (insoluble fi bers) do not dissolve in water, do not form gels (are not viscous), and are less readily fermented. Insoluble fi bers, such as cellulose, are found in the outer layers of whole grains (bran), the strings of celery, the hulls of seeds, and the skins of corn kernels. Th ese fi bers retain their structure and rough texture even after hours of cooking. In the body, they aid the digestive system by easing elimination.

In summary, plants combine carbon dioxide, water, and the sun’s energy to form glucose, which can be stored as the polysaccharide starch. Th en animals or people eat the plants and retrieve the glucose. In the body, the liver and muscles may store the glucose as the polysaccharide glycogen, but ultimately it becomes glucose again. Th e glucose delivers the sun’s energy to fuel the body’s activities. In the process, glucose breaks down to the waste products carbon dioxide and water, which are excreted. Later, these compounds are used again by plants as raw materials to make carbohydrate. Fibers are plant constituents that are not digested directly by human enzymes, but their presence in the diet contributes to the health of the body.

KE Y POINT Human digestive enzymes cannot break the bonds in fi ber, so most of it passes through the digestive tract unchanged. Some fi ber, however, is susceptible to fermentation by bacteria in the colon.

LO 4.2, 4.3

The Need for Carbohydrates Glucose from carbohydrate is an important fuel for most body functions. Only two other nutrients provide energy to the body: protein and fats. Protein-rich foods are usually expensive and, when used to make fuel for the body, they provide no advan- tage over carbohydrates. Moreover, overuse of dietary protein has disadvantages, as explained in Chapter 6. Fats normally are not used as fuel by the brain and central nervous system. Th us, glucose is a critical energy source, particularly for nerve cells, including those of the brain. And starchy whole foods that supply complex carbo- hydrates—and especially the fi ber-rich ones—are the preferred source of glucose in the diet.

†The committee on Dietary Reference Intakes (DRI) proposed other fi ber defi nitions to accommodate products that may con- tain new fi ber sources, but consumers may fi nd these too confusing to be used on food labels.

Fiber characteristics in foods:•

Soluble, viscous, fermentable fibers are •

often gummy or add thickness to foods.

Insoluble, nonviscous, less fermentable •

fibers are often tough, stringy, or gritty in

foods.

Chapter 15 revisits humankind’s relationship • with the earth’s food chain.

glycogen (GLY-co-gen) a highly branched polysaccharide that is made and stored by liver and muscle tissues of human beings and animals as a storage form of glucose. Glycogen is not a signifi cant food source of carbohydrate and is not counted as one of the complex carbohydrates in foods.

fi bers the indigestible parts of plant foods, largely nonstarch polysaccharides that are not digested by human digestive enzymes, although some are digested by resident bacteria of the colon. Fibers include cellulose, hemicelluloses, pectins, gums, mucilages, and the nonpolysaccharide lignin.

soluble fi bers food components that readily dissolve in water and often impart gummy or gel-like characteristics to foods. An example is pectin from fruit, which is used to thicken jellies. Soluble fi bers are indigestible by human enzymes but may be broken down to absorbable products by bacteria in the diges- tive tract.

viscous (VISS-cuss) having a sticky, gummy, or gel-like consistency that fl ows relatively slowly.

insoluble fi bers the tough, fi brous structures of fruits, vegetables, and grains; indigestible food components that do not dis- solve in water.

112 chapter 4 C a r b o h y d r a t e s

Sugars also play vital roles in the functioning of body tissues. For example, sug- ars that dangle from protein molecules, once thought to be mere hitchhikers, are now known to dramatically alter the shape and function of certain proteins. Such a sugar-protein complex is responsible for the slipperiness of mucus, the watery lubricant that coats and protects the body’s internal linings and membranes. Sugars also bind to the outside of cell membranes, aff ecting cell-to-cell communication, nerve and brain cell function, and certain disease processes. Clearly, the body needs carbohydrates for more than just energy.

If I Want to Lose Weight and Stay Healthy, Should I Avoid Carbohydrates? Many popular books and magazines wrongly accuse carbohydrates of being the “fattening” ingredient of foods, thereby misleading millions of weight-conscious people into eliminating nutritious carbohydrate-rich foods from their diets.5 In truth, people who wish to lose fat, maintain lean tissue, and stay healthy can do no better than to attend closely to portion sizes and calorie intakes and to design their diets around carbohydrate-rich whole foods that supply fi ber, other needed nutri- ents, and benefi cial phytochemicals.6

Lower in Calories Gram for gram, carbohydrates donate fewer calories than do dietary fats, and converting glucose into fat for storage is metabolically costly. Still, it is possible to consume enough calories of carbohydrate to exceed the need for energy, which reliably leads to weight gain. To lose weight, the dieter must plan a diet to provide fewer calories from all sources that are needed by the body each day; Chapter 9 describes the roles energy nutrients play in management of body weight.

An Exception: Refi ned Sugars Recommendations to choose carbohydrate-rich foods do not extend to refi ned added sugars. Purifi ed, refi ned sugars (mostly su- crose or fructose) contain no other nutrients—no protein, vitamins, minerals, or fi ber—and thus are low in nutrient density.7 A person choosing 400 calories of sugar in place of 400 calories of whole-grain bread loses the protein, vitamins, min- erals, phytochemicals, and fi ber of the bread. You can aff ord to do this only if you have already met all of your nutrient needs for the day and still have discretionary calories to spend.

Overuse of sugars may have other eff ects as well. Some evidence suggests that, for many obese people, a diet too high in added sugars and other refi ned carbohydrates may alter blood lipids in ways that may worsen their heart disease risk (Controversy 4 comes back to this topic).8 For these people, weight loss on a calorie-controlled diet that provides the recommended amounts of whole grains, legumes, fruits, and vegetables reduces the blood lipid response to sugars and lowers their heart disease risk. In fact, consumption of whole grains consistently lowers the risk of cardiovas- cular diseases, including heart disease, in research studies.9

Guidelines For health’s sake, then, most people should increase their intakes of fi ber-rich whole food sources of carbohydrates and reduce intakes of foods high in refi ned white fl our, added sugars, and the kinds of fats associated with heart disease (see Chapter 5).10 Table 4-1 presents carbohydrate recommendations and guidelines from several authorities. Th is chapter’s Consumer Corner describes various whole- grain foods, and the Food Feature comes back to the sugars in foods. As for weight loss, authorities do not recommend omitting carbohydrates. In fact, many recom- mend the opposite.

KE Y POINT The body tissues use carbohydrates for energy and other functions; the brain and nerve tissues prefer carbohydrate as fuel. Nutrition authorities recommend a diet based on foods rich in complex carbohydrates and fi ber.

Did You Know? Alcohol provides energy but it is a toxin, not a nutrient.

1 gram carbohydrates = 4 calories•

1 gram fat = 9 calories•

CONCEPT LINK 4-2 Chapter 1 defined a gram (g) as a unit of weight used in nutrition (page 6).

CONCEPT LINK 4-3 Chapter 2 describes discretionary calories as the balance of calories remaining in a person’s energy allowance after consuming the nutrient- dense foods sufficient to meet the day’s nutri- ent needs (page 41).

Details about controlling body fatness are in • Chapter 9.

The DRI committee recommends that 45 • to 65 percent of daily calories come from carbohydrate. An example of how to convert this recommendation into grams of carbohy- drate in the diet is found in the Food Feature on page 136.

113T h e N e e d f o r C a r b o h y d r a t e s

Why Do Nutrition Experts Recommend Fiber-Rich Foods? As mentioned, carbohydrate-rich foods off er additional benefi ts if they are also rich in fi ber. Foods such as whole grains, vegetables, legumes, and fruits supply valuable vitamins, minerals, and phytochemicals, along with a healthy dose of fi ber and little or no fat. Fiber’s best-known health benefi ts include:

Recommendations for total carbohydrates1. Dietary Guidelines for Americans

Consume between 45% and 65% of calories from carbohydrate.• Dietary Reference Intakes (DRI)

At a minimum, 130 grams per day for adults and children to provide glucose to the • brain.

For health, most people should consume between 45% and 65% of total calories • from carbohydrate.

USDA Food Guide, MyPyramid Grains, fruit, starchy vegetables, and milk contribute to the day’s total carbohydrate • intake.

Recommendations for added sugars2. Dietary Guidelines for Americans

Choose and prepare foods and beverages with little added sugars.• Dietary Reference Intakes (DRI)

Insuffi cient evidence exists to set an upper limit for added sugars; however, the DRI • committee suggests a high maximum of 25% or less of total calories for people who

otherwise meet their nutrient needs, maintain a healthy body weight, and need ad-

ditional energy.a

USDA Food Guide, MyPyramid Added sugars may provide discretionary calories within the energy recommendation • after meeting all nutrient recommendations with nutritious foods.

The American Heart Association A prudent upper limit of not more than one-half the discretionary calorie allowance • (no more than 100 calories of added sugars for most women or 150 calories for most

men).

Recommendations for fi ber3. USDA Food Guide, MyPyramid

Increase intakes of whole fruits and vegetables, make at least half the grain choices • whole grains, and choose legumes several times per week.

Dietary Reference Intakes (DRI) 38 grams of total fi ber per day for men through age 50; 30 grams for men 51 and • older.

25 grams of total fi ber per day for women through age 50; 21 grams for women 51 • and older.

aAn example might be an athlete in training whose high energy need allows greater amounts of added sugars from sports drinks without compromising nutrient intakes; for most sedentary people, maximums of 3 to 12 teaspoons per day are suggested.

Recommendations Concerning Intakes

of Carbohydrates

table 4-1

114 chapter 4 C a r b o h y d r a t e s

Promotion of normal blood cholesterol concentrations and reduced risk of 1. heart disease.

Control of blood pressure (reduced risk of hypertension).2. 11

Modulation of blood glucose concentrations (reduced risk of diabetes).3. Maintenance of healthy bowel function (reduced risk of bowel diseases).4. Promotion of a healthy body weight.5.

Th e obvious choice for anyone placing a value on health is to obtain fi bers from a variety of sources each day.

Figure 4-4 shows the diverse eff ects of diff erent fi bers, and Figure 4-5 provides a brief guide to fi nding these fi bers in foods. Most unrefi ned plant foods contain a mix of fi ber types. Th e following paragraphs describe health benefi ts associated with daily intakes of these foods.

KE Y POINT Fiber-rich diets benefi t the body by helping to normalize blood cholesterol and blood glucose and by maintaining healthy bowel function. They are also associated with healthy body weight.

Lower Cholesterol and Heart Disease Risk Diets rich in legumes, vegetables, and whole grains—and therefore rich in complex carbohydrates—may protect against heart disease and stroke. Such diets are generally low in saturated fat, trans fat, and cholesterol and high in fi bers, vegetable proteins, and phytochemicals—all factors associated with a lower risk of heart disease.12 Oatmeal was fi rst to be iden- tifi ed among cholesterol-lowering foods; apples, barley, carrots, and legumes are

Barley, oats, oat

bran, rye, fruits

(apples, citrus),

legumes (especially

young green peas

and black-eyed

peas), seaweeds,

seeds and husks,

many vegetables,

fibers used as food

additives

• Gums

• Pectins

• Psyllium

• Some hemicellulose

• Lower blood cholesterol

by binding bile

• Slow glucose absorption

• Slow transit of food

through upper GI tract

• Hold moisture in stools,

softening them

• Yield small fat molecules

after fermentation that the

colon can use for energy

• Increase satiety

• Increase fecal weight

and speed fecal passage

through colon

• Provide bulk and feelings

of fullness

• Lower risk of heart disease

• Lower risk of diabetes

• Lower risk of colon and

rectal cancer

• Increased satiety, and

may help with weight

management

• Alleviate constipation

• Lower risk of diverticulosis,

hemorrhoids, and

appendicitis

• Lower risk of colon and

rectal cancer

• Cellulose

• Lignins

• Resistant starch

• Hemicellulose

Brown rice, fruits,

legumes, seeds,

vegetables

(cabbage, carrots,

brussels sprouts),

wheat bran, whole

grains, extracted

fibers used as food

additives

People who eat these foods . . .

Viscous, soluble, more fermentable

Nonviscous, insoluble, less fermentable

with these actions in the body . . .

obtain these types of fibers . . .

and these probable health benefits . . .

•

S to

c k b

y te

/G e tt y I m

a g

e s

B ri a n L

e a ta

rt /G

e tt y I m

a g

e s

aPsyllium, a soluble fiber derived from seeds, is used as a laxative and food additive.

Characteristics, Sources, and Health Effects of Fibers figure 4-4

Appendix A lists the fiber contents of over • 2,000 foods.

The roles of saturated fat, • trans fat, choles- terol, and other lipids in heart disease are discussed in Chapters 5 and 11. The role of vegetable proteins in heart disease is presented in Chapter 6.

115T h e N e e d f o r C a r b o h y d r a t e s

also rich in the viscous fi bers having a signifi cant cholesterol-lowering eff ect.13 In contrast, diets high in refi ned grains and added sugars may push blood lipids toward elevated heart disease risk; Controversy 4 explores these concerns.

Foods rich in viscous fi bers may lower blood cholesterol by binding with cholesterol- containing compounds in bile. Normally, much of this cholesterol would be re- absorbed from the intestine for reuse, but viscous fi ber carries some of it out with the feces (see Figure 4-6).14 Th ese bile compounds are needed in digestion, so the liver responds to their loss by drawing on the body’s cholesterol stocks to synthesize more. Another way in which fi ber in the diet may reduce cholesterol in the blood is through the actions of one of the small fatty acids released during bacterial fer- mentation of fi ber. Th is fatty acid is absorbed and travels to the liver, where it may help to reduce cholesterol synthesis. Th e net result of either mechanism is lowered blood cholesterol.

Fiber Grams Per Serving

Grains, c

Barley, whole-grain

Oatmeal, instant

Oat bran, dry

Seeds, 1 tbs

Psyllium seedsb

Fruit, 1 med

Apple

Banana

Blackberries, c

Orange, grapefruit

Nectarine

Peach

Pear

Plum, large

Prunes, c

Legumes, c

Black beans

Black-eyed peas

Chickpeas (garbanzo beans)

Kidney beans

Lentils

Lima beans

Navy beans

Northern beans

Pinto beans

Vegetables, c

Broccoli (and many other cooked vegetables)

Brussels sprouts, chopped

Carrots

1 2 3 4 5 6 7 8 9 10

1 2

1 4

1 2

Foodsa

Viscous, soluble fiber Nonviscous, insoluble fiberKey:

CONCEPT LINK 4-4 The benefits of phytochemicals in disease pre- vention are featured in Controversy 2, page 61.

Fiber Composition of Common Foods figure 4-5

aValues are for cooked or ready-to-serve foods unless specifi ed. bPsyllium is used as a fi ber laxative and fi ber-rich food additive. Source: Data from the National Heart, Lung and Blood Institute.Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation and Treat- ment of High Blood Cholesterol in Adults (Adult Treatment Panel 10, NIH publication no. 02-5215, 2002); V-6; ESHA Research, 2004.

116 chapter 4 C a r b o h y d r a t e s

KE Y POINT Foods rich in soluble viscous fi bers help control blood cholesterol and blood glucose.

Blood Glucose Control High-fi ber foods—and especially whole grains—play a key role in reducing the risk of type 2 diabetes.15 Th e soluble fi bers of foods such as oats and legumes can help regulate the blood glucose following a carbohydrate- rich meal. Soluble fi bers trap nutrients and delay their transit through the digestive tract, slowing glucose absorption and preventing the glucose surge and rebound often associated with diabetes onset. In people with established diabetes, high-fi ber foods can modulate blood glucose and insulin levels, thus helping to prevent medi- cal complications. A later section comes back to diabetes and its control.

KE Y POINT Foods rich in viscous fi bers help to modulate blood glucose concentrations.

Maintenance of Digestive Tract Health All kinds of fi bers, along with an am- ple fl uid intake, probably play roles in maintaining proper colon function. Fibers such as cellulose (as in wheat bran and other cereal brans, fruits, and vegetables) enlarge and soften the stools, easing their passage out of the body and speeding up their transit time through the intestine. Th us, foods rich in these fi bers help to al- leviate or prevent constipation.

Large, soft stools ease the task of elimination for the rectal muscles. Pressure is then reduced in the lower bowel (colon), making it less likely that rectal veins will swell (hemorrhoids). Fiber prevents compaction of the intestinal contents, which could obstruct the appendix and permit bacteria to invade and infect it (appendi- citis). In addition, fi ber stimulates the GI tract muscles so that they retain their

Gallbladder stores bile

Liver uses blood cholesterol to

make bile

A little cholesterol in bile reabsorbed

into the blood

Intestine: bile aids digestion; binds to fiber

Fiber and bile excreted in

feces

Gallbladder stores bile

Liver uses blood cholesterol to

make bile

Much of the cholesterol in bile

reabsorbed into the blood

Intestine: bile aids digestion

Little bile excreted

A. High-fiber diet B. Low-fiber diet

In some ways, the liver is like a vacuum cleaner, sucking up cholesterol from the blood, using the cholesterol to make bile, and discharging the bile into its storage bag, the gallbladder. The gallbladder empties its bile into the intestine, where bile performs necessary digestive tasks. In the intestine, some of the cholesterol from bile associates with fi ber and is carried out of the body in feces instead of being reabsorbed into the blood.

Animated! One Way Fiber in Food May Lower Cholesterol in the Blood

figure 4-6

A. When the diet is rich in fi ber, more cholesterol (as bile) is carried out of the body.

B. When the diet is low in fi ber, most of the cholesterol is reabsorbed and returned to the bloodstream.

constipation diffi cult, incomplete, or infrequent bowel movements associated with discomfort in passing dry, hardened feces from the body.

hemorrhoids (HEM-or-oids) swollen, hardened (varicose) veins in the rectum, usually caused by the pressure resulting from constipation.

appendicitis infl ammation and/or infection of the appendix, a sac protruding from the intestine.

117T h e N e e d f o r C a r b o h y d r a t e s

strength and resist bulging out into pouches known as diverticula (illustrated in Figure 4-7 in the margin).16

Evidence Concerning Digestive Tract Cancer and Infl ammation Many stud- ies support a role for fi ber in defending against cancers of the colon and rectum. In a study of over a half-million Europeans, for example, people who ate the most dietary fi ber (35 grams per day) reduced their risk of colon cancer by 40 percent compared with those who ate the least fi ber (15 grams per day).17 In the United States, data from over 3,000 people suggest that men (but not women) who were given a diet high in fi ber had signifi cantly less risk of developing colon or rectal cancers.18 In contrast, a study of almost a half-million older U.S. adults suggests that consumption of whole grains, but not fi ber itself, may off er moderate protec- tion against these cancers.19 When researchers examine other lifestyle factors, fi ber shows some eff ect but alcohol intake, physical activity, red and processed meat in- takes, and other factors emerge as associated with colon and rectal cancers, too.20 More investigation into this important area of research is needed.

Fiber-rich foods may work against colon cancer in a number of ways. Fiber at- tracts water, thereby diluting potential cancer-causing agents and speeding their re- moval from the colon.21 Also, many fi ber-rich foods supply the vitamin folate, and diets rich in folate correlate with low rates of colon cancer (folate supplements have proved ineff ective in this regard, however).22 Another possibility involves the intes- tine’s resident bacteria. In fi ber-rich intestinal contents, feasting bacteria reproduce rapidly, and in doing so, they bind nitrogen and carry it out of the body in the feces. Nitrogen is a suspected contributor to cancer causation.

Additionally, the colon’s bacteria ferment soluble fi bers, forming the small fat molecules mentioned earlier, which activate cancer-killing enzymes and reduce in- fl ammation in the colon.23 Also, the cells of the colon prefer one of these little fats, butyrate, as a source of energy.24 A colon well supplied with butyrate from a diet high in soluble fi bers may resist chemical injury that could otherwise lead to cancer formation. A well-fed colon frequently replaces its own lining, sloughing damaged cells before they can initiate the cancer process.

As research progresses, cancer experts recommend that fi ber in the diet come from fi ve to nine ½-cup servings of vegetables and fruit, along with generous por- tions of whole grains and legumes. Note that fi ber supplements or additives are not substitutes for whole, fi ber-rich foods—the foods provide valuable nutrients and phytochemicals in a structure that benefi ts the body, while the supplements provide only fi ber.

KE Y POINT Fibers in foods help to maintain digestive tract health.

Healthy Weight Management Foods rich in fi bers tend to be low in fat and added sugars and can therefore prevent weight gain and promote weight loss by delivering less energy per bite.25 In addition, fi bers absorb water from the digestive juices; as they swell, they create feelings of fullness, delay hunger, and reduce food intake.26 Soluble fi bers may be especially useful for appetite control. In a recent study, soluble fi ber from barley modifi ed the mix of appetite-stimulating hormones in the blood in ways that may reduce food intake.27 By whatever mechanism, as populations choose foods lower in fi ber, body fat stores creep up.28

Weight-loss products may contain bulky fi bers such as methylcellulose, but pure fi ber compounds are not advised. Instead, consumers should select whole grains, legumes, fruits, and vegetables. High-fi ber foods not only add bulk to the diet but are economical, nutritious, and supply health-promoting phytochemicals—benefi ts that no purifi ed fi ber preparation can match.

KE Y POINT Diets that are adequate in fi ber assist the eater in maintaining a healthy body weight.

Colon

Diverticula

Diverticulum

D a v id

M u s h e r/

P h o to

R e s e a rc

h e rs

, In

c .

Diverticula are abnormally bulging pockets in the colon wall. These pockets can entrap feces and become painfully infected and infl amed, requiring hospital- ization, antibiotic therapy, or surgery.

Diverticula figure 4-7

diverticula (dye-ver-TIC-you-la) sacs or pouches that balloon out of the intestinal wall, caused by weakening of the muscle layers that encase the intestine. The painful infl ammation of one or more of the diverticula is known as diverticulitis.

butyrate (BYOO-tier-ate) a small fat frag- ment produced by the fermenting action of bacteria on viscous, soluble fi bers; the pre- ferred energy source for the colon cells.

Carbohydrate: 4 cal/g•

Fat: 9 cal/g•

118 chapter 4 C a r b o h y d r a t e s

Recommendations and Intakes Few people in the United States or Canada eat a diet providing all of their needed fi ber. To see how fi ber stacks up in two day’s meals, turn back to Figures 2-14 and 2-15 on pages 57–58. Tuesday’s meals, typical of many college students’ intakes, provide abundant calories but only half the needed fi ber. In contrast, the more nu- tritious Monday’s meals provide more than enough fi ber to meet recommendations with calories to spare. Th e American Dietetic Association suggests 20 to 35 grams of fi ber daily, or about two times higher than the average intake of about 14 to 15 grams.29 Th e DRI committee’s fi ber recommendations are based on energy needs and so vary widely among age and gender groups (see the margin).

Fiber recommendations are given in terms of total fi ber without distinction be- tween fi ber types. Th is makes sense because most fi ber-rich foods supply a mixture of fi bers (recall Figure 4-5, page 115). Th is chapter’s Consumer Corner provides de- tailed information about choosing wisely among grain foods. You can make a quick approximation of a day’s fi ber intake by following the instructions in Table 4-2.

An eff ective way to add fi ber while lowering fat is to substitute plant sources of protein (legumes) for some of the animal sources of protein (meats and cheeses) in the diet. Another way is to focus on consuming the recommended amounts of fruits, vegetables, and whole grains each day. People choosing high-fi ber foods are wise to seek out a variety of fi ber sources and to drink extra fl uids to help the fi ber do its job.

Can My Diet Have Too Much Fiber? Adding purifi ed fi bers, such as oat or wheat bran, to foods can be taken to extremes. One enthusiastic eater of purifi ed oat bran in muffi ns required emergency surgery for a blocked intestine; too much oat bran and too little fl uid overwhelmed his digestive system. Th is doesn’t mean that you should avoid bran-containing foods, of course, but that you should approach bran and other purifi ed fi bers with an attitude of moderation and be sure to drink an extra beverage with it.

Purifi ed fi bers are like refi ned sugars in one way: the nutrients that originally ac- companied the fi bers have been lost. Too much purifi ed fi ber can displace nutrients from the diet by taking up space ordinarily dedicated to nutritious foods. Fiber can also cause nutrient loss by binding with nutrients in the digestive tract or speeding up their transit out of the body, both eff ects that prevent nutrient absorption. For health’s sake, purifi ed fi bers may not aff ect the body in the same way as fi ber-rich foods in the diet. Some of the health benefi ts attributed to a fi ber may in fact come from other constituents of fi ber-containing foods.

The Binders in Fiber Binders in some fi bers act as chelating agents. Th is means that they link chemically with important nutrient minerals (iron, zinc, calcium, and others) and then carry them out of the body. Th e mineral iron is mostly absorbed at the beginning of the intestinal tract, and excess insoluble fi bers may limit its absorption by speeding foods through the upper part of the digestive tract. Too much bulk in the diet can also limit the total amount of food consumed and cause defi ciencies of both nutrients and energy. People with marginal intakes, such as the malnourished, the elderly, and children who consume no animal products, are par- ticularly vulnerable to this chain of events. Fibers also carry water out of the body and can cause dehydration. Add an extra glass or two of water to go along with the fi ber added to your diet.

Th e next section focuses on the handling of carbohydrates by the digestive sys- tem. Table 4-3 sums up the points made so far concerning the functions of carbohy- drates in the body and in foods.

KE Y POINT Most adults need between 24 and 38 grams of total fi ber each day, but few consume this amount. Fiber needs are best met with whole foods. Purifi ed fi ber in large doses can have undesirable eff ects. Fluid intake should increase with fi ber intake.

Fiber DRI:

Men, age 19–50: 38 g/day.•

Men, age 51 and up: 30 g/day.•

Women, age 19–50: 25 g/day.•

Women, age 51 and up: 21 g/day.•

No Tolerable Upper Intake Level for fiber has • been established.

To quickly estimate fi ber in a day’s meals:

Multiply servings (½ c cut up or 1. 1 medium piece) of any fruit or veg- etable (excluding juice) by 1.5 g.a

Example: 5 servings of fruits and veg- etables � 1.5 � 7.5 g fi ber

Multiply ½ c servings of refi ned grains 2. by 1.0 g. Example: 4 servings of refi ned grains � 1.0 � 4.0 g fi ber

Multiply ½ c servings of whole grains 3. by 2.5 g. Example: 3 servings of whole grains � 2.5 � 7.5 g fi ber

Add fi ber values for servings of 4. legumes, nuts, seeds, and high-fi ber cereals and breads; look these up in Appendix A. Example: ½ c navy beans � 6.0 g fi ber

Add up the grams of fi ber from the 5. previous lines. Example: 7.5 � 4.0 � 7.5 � 6.0 � 25 g fi ber

Day’s total fi ber � 25 g fi ber

aMost cooked and canned fruits and vegetables contain about this amount, while whole raw fruits and some vegetables contain more.

A Quick Method

for Estimating

Fiber Intake

table 4-2

Did You Know? Chelating agents are often sold by supplement vendors to “remove poisons” from the body. Some valid medical uses, such as treatment of lead poisoning, exist, but most of the chelat- ing agents sold over the counter are based on unproven claims.

chelating (KEE-late-ing) agents mol- ecules that attract or bind with other molecules and are therefore useful in either preventing or promoting movement of substances from place to place.

119F r o m C a r b o h y d r a t e s t o G l u c o s e

Carbohydrates in the Body Carbohydrates in Foods

Energy source.• Sugars and starch from the diet provide energy for many body functions; they provide glucose, the preferred fuel for the brain and nerves. Glucose storage.• Muscle and liver glycogen store glucose. Raw material.• Sugars are converted into other compounds, such as amino acids (the building blocks of proteins), as needed. Structures and functions.• Sugars interact with protein molecules, affecting their structures and functions. Digestive tract health.• Fibers help to maintain healthy bowel func- tion (reduce risk of bowel diseases). Blood cholesterol.• Fibers promote normal blood cholesterol concentrations (reduce risk of heart disease). Blood glucose.• Fibers modulate blood glucose concentrations (help control diabetes). Satiety.• Fibers and sugars contribute to feelings of fullness. Body weight.• A fi ber-rich diet may promote a healthy body weight.

Flavor.• Sugars provide sweetness. Browning.• When exposed to heat, sugars undergo browning reactions, lending appealing color, aroma, and taste. Texture.• Sugars help make foods tender. Cooked starch lends a smooth, pleasing texture. Gel formation.• Starch molecules expand when heated and trap water molecules, forming gels. The fi ber pectin forms the gel of jellies when cooked with sugar and acid from fruit. Bulk and viscosity (thickness).• Carbohydrates lend bulk and increased viscosity to foods. Soluble, viscous fi bers lend thick- ness to foods such as salad dressings. Moisture.• Sugars attract water and keep foods moist. Preservative.• Sugar in high concentrations dehydrates bacteria and preserves the food. Fermentation.• Carbohydrates are fermented by yeast, a pro- cess that causes bread dough to rise and beer to brew, among other uses.

Usefulness of Carbohydrates table 4-3

LO 4.4

From Carbohydrates to Glucose You may eat bread or a baked potato, but the body’s cells cannot use foods or even whole molecules of lactose, sucrose, or starch for energy. Th ey need the glucose in those molecules. Th e various body systems must make glucose available to the cells, not all at once when it is eaten, but at a steady rate all day.

Digestion and Absorption of Carbohydrate To obtain glucose from newly eaten food, the digestive system must fi rst render the starch and disaccharides from the food into monosaccharides that can be absorbed through the cells lining the small intestine. Th e largest of the digestible carbohy- drate molecules, starch, requires the most extensive breakdown. Disaccharides, in contrast, need be split only once before they can be absorbed.

Starch Digestion of most starch begins in the mouth, where an enzyme in saliva mixes with food and begins to split starch into maltose. While chewing a bite of bread, you may notice that a slightly sweet taste develops—maltose is being liber- ated from starch by the enzyme. Th e salivary enzyme continues to act on the starch in the bite of bread while it remains tucked in the stomach’s upper storage area. As each chewed lump is pushed downward and mixed with the stomach’s acid and other juices, the salivary enzyme (made of protein) is deactivated by the stomach’s protein-digesting acid. Not all digestive enzymes are susceptible to digestion in the stomach—one enzyme that digests protein works best in the stomach. Its structure protects it from the stomach’s acid.

With the breakdown of the salivary enzyme in the stomach, starch diges- tion ceases, but it resumes at full speed in the small intestine, where another starch-splitting enzyme is delivered by the pancreas. Th is enzyme breaks starch down into disaccharides and small polysaccharides. Other enzymes lib- erate monosaccharides for absorption.

Some forms of starch are easily digested. Th e starch in bread made of refi ned white fl our, for example, breaks down rapidly to glucose that is absorbed high up in

120 chapter 4 C a r b o h y d r a t e s

consumer corner Refi ned, Enriched, and Whole-Grain Foods

The USDA Food Guide, illustrated in Chapter 2, urges everyone to make at least half of their daily grain choices whole grains, an amount equal to at least three 1-ounce equivalents of whole grains a day.1 To do this, you must distinguish among grain foods that are refi ned, enriched, fortifi ed, and whole grain (see Table 4-4). For many people, bread supplies much of the carbohydrate, or at least most of the starch, in a day’s meals. Bread provides a convenient example, but the principles

demonstrated in this section hold true for cereals, rice, pasta, and, in fact, all grain foods.

FLOUR TYPES The part of a typical grain plant, such as the wheat, that is made into fl our and then into bread, other baked goods, cereals, and pasta noodles is the seed or kernel. The kernel (a whole grain) has four main parts: the germ, the en- dosperm, the bran, and the husk, as shown in Figure 4-8. The germ is the part

that grows into a new plant, in this case wheat, and therefore contains concen- trated food to support the new life—it is especially rich in oils, vitamins, and min- erals. The endosperm is the soft, white inside portion of the kernel, containing starch and proteins that help nourish the seed as it sprouts. The kernel is encased in the bran, a protective coating that is similar in function to the shell of a nut; the bran is also rich in nutrients and fi ber. The husk, commonly called chaff, is the dry outermost layer and is inedible by human beings but can be used in animal feed.

In earlier times, people milled wheat by grinding it between two stones, blowing or sifting out the chaff, and retaining the

bran• the protective fi brous coating around a grain; the chief fi ber donator of a grain. brown bread• bread containing ingredients such as molasses that lend a brown color; may be made with any kind of fl our, including white fl our. endosperm• the bulk of the edible part of a grain, the starchy part. enriched, fortifi ed• refers to the addition of nutrients to a refi ned food product. As defi ned by U.S. law, these terms mean that specifi ed levels of thiamin, ribofl avin, niacin, folate, and iron have been added to refi ned grains and grain products. The terms en- riched and fortifi ed can refer to the addition of more nutrients than just these fi ve; read the label.a

germ• the nutrient-rich inner part of a grain. husk• the outer, inedible part of a grain. refi ned• refers to the process by which the coarse parts of food products are removed. For example, the refi ning of wheat into fl our involves removing three of the four parts of the kernel—the chaff, the bran, and the germ—leaving only the endosperm, composed mainly of starch and a little protein. stone ground• refers to a milling process using limestone to grind any grain, including refi ned grains, into fl our. unbleached fl our• a beige-colored refi ned endosperm fl our with texture and nutritive qualities that approximate those of regular white fl our. wheat bread• bread made with any wheat fl our, including refi ned enriched white fl our. wheat fl our• any fl our made from wheat, including refi ned white fl our. white fl our• an endosperm fl our that has been refi ned and bleached for maximum soft- ness and whiteness. white wheat• a wheat variety developed to be paler in color than common red wheat (most familiar fl ours are made from red wheat). White wheat is similar to red wheat in carbohydrate, protein, and other nutrients, but it lacks the dark and bitter, but poten- tially benefi cial, phytochemicals of red wheat. 100% whole grain• a label term for food in which the grain is entirely whole grain, with no added refi ned grains. whole grain• grains, or foods made from them, that contain all the essential parts and naturally occurring nutrients of the entire grain seed (except the husk); not refi ned. whole-wheat fl our• fl our made from whole-wheat kernels; a whole-grain fl our. Also called graham fl our.

aFormerly, enriched and fortifi ed carried distinct meanings with regard to the nutrient amounts added to foods, but a change in the law has made these terms virtually synonymous.

Terms That Describe Grain Foods table 4-4

Head

Stem

Root

husk (chaff)

bran (14%)

endosperm (83%)

germ (2.5%)

A kernel of wheat

A wheat plant

kernels

beard

A Wheat Plant

and a Single

Kernel of Wheat

figure 4-8

121F r o m C a r b o h y d r a t e s t o G l u c o s e

re di

t t o

co m

colored bread made from a specially bred white wheat.

Whole-grain rice, commonly called brown rice, cannot be judged by color alone. Whole-grain rice comes in red and other colors, too. Also, many rice dishes appear brown because of brown-colored ingredients such as soy sauce, beef broth, or seasonings.

Whole-grain pasta noodles are delicious—but be sure that the ingre- dients list on the label agrees with any

nutrient-rich bran and germ as well as the endosperm. Then milling machinery was “improved,” and it became possible to remove the dark, heavy germ and bran, leaving a whiter, smoother-textured fl our with a higher starch content and far less fi ber. People favored this refi ned soft white fl our more than the crunchy, dark brown, “old-fashioned” fl our.

ENRICHMENT OF REFINED GRAINS In turning to highly refi ned grains, many people suffered defi ciencies of iron, thiamin, ribofl avin, and niacin—nutrients formerly obtained from whole grains. To reverse this tragedy, Congress passed the U.S. Enrichment Act of 1942 requiring that iron, niacin, thiamin, and ribofl avin be added to all refi ned grain products before they were sold. In 1996, the vitamin folate (often called folic acid on labels) was added to the list. Today, all refi ned grain products are enriched with at least the nutrients mandated by the Act.

A single serving of enriched grain food is not “rich” in the enrichment nutrients, but people who eat several servings a day obtain signifi cantly more of these nu- trients than they would from unenriched refi ned products, as the bread example of Figure 4-9 shows.

Enriched grain foods are comparable to whole grain only with respect to the added nutrients; whole grains provide more benefi cial magnesium, zinc, vita- min B6, vitamin E, and chromium. Whole grains also provide more fi ber (see Table 4-5), along with potentially benefi cial phytochemicals and essential oils as- sociated with the bran and germ.

FINDING THE WHOLE GRAINS IN FOODS Notice the distinctions between wheat fl our, whole-wheat fl our, refi ned fl our (often called white fl our), and unbleached fl our among the terms that describe grain foods; also notice that the terms wheat bread, brown bread, and stone ground on a label do not guarantee that the bread has been made entirely of whole-grain fl our (see Figure 4-10). Gaining in popularity is a light-

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0 10 20 30 40 50 60 70 80 90 100

Iron

Thiamin

Riboflavin

Niacin

Vitamin B6

Folate

Fiber

Magnesium

Zinc

Nutrients in bread

Key:

Whole-grain bread

Enriched white bread

Unenriched white bread

100%

21%

100% >100%

26%

100%

>100%

28%

100%

98%

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Percentage of nutrients (100% represents nutrient levels of whole-grain bread)

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Nutrients in Whole-Grain, Enriched White,

and Unenriched White Breads

figure 4-9

Dark rye, 18 g

Whole wheat, 15 g

Light rye, 14 g

Buckwheat, 12 g

Whole-grain cornmeal, 9 g

Enriched white, 3 g

Grams of Fiber in

One Cup of Flour

table 4-5

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122 chapter 4 C a r b o h y d r a t e s

resistant starch the fraction of starch in a food that is digested slowly, or not at all, by human enzymes.

the small intestine. Some starch, such as that of cooked beans, digests more slowly and releases its glucose later in the digestion process. Less digestible starch, called resistant starch, is technically a kind of fi ber because it passes through the small intestine undigested into the colon, and can contribute to the daily fi ber need.30 Th e starch of raw potatoes, for example, resists digestion. So does the resistant starch that forms when foods are overheated as well as the starch tucked inside the unbro- ken hulls of swallowed seeds.31 Barley, chilled cooked potatoes and pasta, cooked dried beans and lentils, oatmeal, and underripe bananas are all sources. Some resis- tant starch may be digested, but slowly, and most remains intact until the bacteria of the colon eventually break it down. Similar to insoluble fi bers, resistant starch may support a healthy colon.32

claims being made for the product.2 For cereals, too, look for whole grains listed as the fi rst ingredients. Food names and marketing claims on labels can be

deceiving, so rely on the ingredients list as your guide.

If you are just now making a change to whole grains in your diet, blends of whole

and refi ned grains can make a good starting point. However you go about it, you are well advised to learn to like the hearty fl avor of whole-grain foods.

Total Fat 1.5g 2%

Serving size 1 slice (30g) Servings Per Container 18

Calories 90

Amount per serving

Calories from Fat 14

% Daily Value*

Sodium 135mg 6%

Protein 4g

Sugars 2g

Dietary fiber 2g

Total Carbohydrate 15g

Nutrition Facts

Total Fat 1.5g 2%

Serving size 1 slice (30g) Servings Per Container 21

Calories 60

Amount per serving

Calories from Fat 15

% Daily Value*

Sodium 135mg 6%

Protein 5g

12%

Sugars 0g

Dietary fiber 3g

Total Carbohydrate 9g

Nutrition Facts

INGREDIENTS: UNBLEACHED ENRICHED WHEAT FLOUR, WATER, WHEAT GLUTEN, CELLULOSE, YEAST, SOYBEAN OIL, CRACKED WHEAT, SALT, BARLEY, NATURAL FLAVOR PRESERVATIVES, MONOCALCIUM PHOSPHATE, MILLET, CORN, OATS, SOYBEAN FLOUR, BROWN RICE, FLAXSEED, SUCRALOSE.

Total Fat 1.5g 2%

Serving size 1 slice (30g) Servings Per Container 15

Calories 90

Amount per serving

Calories from Fat 14

% Daily Value*

Sodium 220mg 9%

Protein 4g

Sugars 2g

15g

Nutrition Facts

Total Carbohydrate

Dietary fiber less than 1g 2%

INGREDIENTS: UNBLEACHED ENRICHED WHEAT FLOUR [MALTED BARLEY FLOUR, NIACIN, REDUCED IRON, THIAMIN MONONITRATE (VITAMIN B1), RIBOFLAVIN (VITAMIN B2), FOLIC ACID], WATER, HIGH FRUCTOSE CORN SYRUP, MOLASSES, PARTIALLY HYDROGENATED SOYBEAN OIL, YEAST, CORN FLOUR, SALT, GROUND CARAWAY, WHEAT GLUTEN, CALCIUM PROPIONATE (PRESERVATIVE), MONOGLYCERIDES, SOY LECITHIN.

MADE FROM: UNBROMATED STONE GROUND 100% WHOLE WHEAT FLOUR, WATER, CRUSHED WHEAT, HIGH FRUCTOSE CORN SYRUP, PARTIALLY HYDROGENATED VEGETABLE SHORTENING (SOYBEAN AND COTTONSEED OILS), RAISIN JUICE CONCENTRATE, WHEAT GLUTEN, YEAST, WHOLE WHEAT FLAKES, UNSULPHURED MOLASSES, SALT, HONEY, VINEGAR, ENZYME MODIFIED SOY LECITHIN, CULTURED WHEY, UNBLEACHED WHEAT FLOUR AND SOY LECITHIN.

Trans Fat 0g Trans Fat 0g Trans Fat 0g

Bread Labels Compared figure 4-10

Although breads may appear similar, their ingredients vary widely. “High-fi ber” breads may derive their fi ber from purifi ed cellulose or more nutritious whole grains. “Low carbohydrate” breads may be regular white bread, thinly sliced to reduce carbohydrates per serving, or may contain soy fl our, barley fl our, or fl axseed to reduce starch content. A trick for estimating a bread’s content of a nutritious ingredient, such as whole-grain fl our, is to read the ingredients list (ingredients are listed in order of predominance). Bread generally contains one teaspoon of salt per loaf. Therefore, when a bulky ingredient, such as whole grain, is listed after the salt, you’ll know that less than a teaspoonful was added to the loaf—not enough to signifi cantly improve the nutrient value of one slice of bread.

123F r o m C a r b o h y d r a t e s t o G l u c o s e

Sugars Sucrose and lactose from food, along with maltose and small polysaccha- rides freed from starch, undergo one more split to yield free monosaccharides before they are absorbed. Th is split is accomplished by enzymes attached to the cells of the lining of the small intestine. Th e conversion of a bite of bread to nutrients for the body is completed when monosaccharides cross these cells and are washed away in a rush of circulating blood that carries them to the waiting liver. Figure 4-11 presents a quick review of carbohydrate digestion.

Th e absorbed carbohydrates (glucose, galactose, and fructose) travel in the blood- stream to the liver, which can convert fructose and galactose to glucose. Th e circula- tory system transports the glucose and other products to the cells. Liver and muscle cells may store circulating glucose as glycogen; all cells may split glucose for energy.

Fiber As mentioned, although molecules of most fi bers are not changed by hu- man digestive enzymes, many of them can be digested (fermented) by the bacterial inhabitants of the human colon. A by-product of this fermentation can be any of several odorous gases. Don’t give up on high-fi ber foods if they cause gas. Instead, start with small servings and gradually increase the serving size over several weeks; chew foods thoroughly to break up hard-to-digest lumps that can ferment in the intestine; and try a variety of fi ber-rich foods until you fi nd some that do not cause the problem. Some people also fi nd relief from excessive gas by using commercial enzyme preparations sold for use with beans. Such products contain enzymes that help to break down some of the indigestible fi bers in foods before they reach the colon. In other people, persistent painful gas may indicate that the digestive tract has undergone a change in its ability to digest the sugar in milk, a condition known as lactose intolerance.

KE Y POINT With respect to starch and sugars, the main task of the various body systems is to convert them to glucose to fuel the cells’ work. Fermentable fi bers may release gas as they are broken down by bacteria in the intestine.

Why Do Some People Have Trouble Digesting Milk? Among adults, the ability to digest the carbohydrate of milk varies widely. As they age, upward of 75 percent of the world’s people lose much of their ability to produce the enzyme lactase to digest the milk sugar lactose.33 In the United States, the in- cidence is estimated to be much lower: about 12 percent.34 Lactase, which is made by the small intestine, splits the disaccharide lactose into its component monosac- charides glucose and galactose, which are then absorbed. Almost all mammals lose some of their ability to produce lactase as they age.

Symptoms of Lactose Intolerance People with lactose intolerance experience some degree of nausea, pain, diarrhea, and excessive gas on drinking milk or eating lactose-containing products. Th e undigested lactose remaining in the intestine de- mands dilution with fl uid from surrounding tissue and the bloodstream. Intestinal bacteria use the undigested lactose for their own energy, a process that produces gas and intestinal irritants.

Sometimes sensitivity to milk is due not to lactose intolerance but to an allergic reaction to the protein in milk. Milk allergy arises the same way other allergies do—from sensitization of the immune system to a substance. In this case, the im- mune system overreacts when it encounters the protein of milk. Food allergies can be serious and should be diagnosed by a specialist (see Chapter 14 for more on food allergies).

Consequences to Nutrition Infants produce abundant lactase, which helps them absorb the sugar of breast milk and milk-based formulas; a very few suff er inborn lactose intolerance and must be fed solely on lactose-free formulas. Because milk is

Whole grains include:•

Amaranth,* a grain of the ancient Aztec •

people.

Barley •

Buckwheat* •

Corn, including whole cornmeal and •

popcorn.

Millet •

Oats, including oatmeal •

Quinoa (KEEN-wah),* a grain of the ancient •

Inca people.

Rice, including brown, red, and others. •

Rye •

Sorghum (also called milo), a drought-•

resistant grain.

Teff, popular in Ethiopia, India, and •

Australia.

Triticale, a cross of durum wheat and rye.•

Wheat, in many varieties such as spelt, •

emmer, farro, einkorn, Kamut®, durum; and

forms such as bulgur, cracked wheat and

wheatberries.

Wild rice•

If some of these sound unfamiliar, why not try them? They could be your new favorites.

*While not botanical grains, these foods are similar to

grains in nutrient contents, preparation, and use.

CONCEPT LINK 4-5 The names of the digestive enzymes were explained in Chapter 3, Table 3-1 (page 82).

Approximate percentages of adults with lac- tose intolerance by ethnicity:

85–100% Asians•

80–100% Native Americans•

70–95% Black Africans•

60–80% African Americans•

20–30% Indians (Northern)•

60–70% Indians (Southern)•

60–80% Ashkenazi Jews•

50–80% Hispanics•

6–22% U.S. Whites•

2–7% Northern Europeans•

Source: Data from S. R. Hertzler and coauthors, Intes-

tinal disaccharidase depletions, Modern Nutrition in Health and Disease (Philadelphia: Lippincott Williams

& Wilkins, 2006), p. 1191.

lactose intolerance impaired ability to digest lactose due to reduced amounts of the enzyme lactase.

lactase the intestinal enzyme that splits the disaccharide lactose to monosaccharides dur- ing digestion.

124 chapter 4 C a r b o h y d r a t e s

Liver

Esophagus

Stomach

Small intestine

Large intestine (colon)

Pancreas

Intestinal wall cells Capillary

Fiber, starch, monosaccharides, and disaccharides enter the stomach and pass into the small intestine. Some of the starch is partially broken down by an enzyme from the salivary glands before it reaches the small intestine.

lactose

sucrose

maltose

fiber

starch

Key:

galactose

An enzyme from the pancreas digests most of the starch to disaccharides.

2 Enzymes on the surface of cells that line the intestine split disaccharides to monosaccharides.

Monosaccharides enter capillaries, and are then delivered to the liver via the portal vein.

The liver can convert galactose and fructose to glucose.

Fiber and resistant starch travel unchanged to the colon.

Animated! How Carbohydrate in Food Becomes Glucose in the Body

figure 4-11

125T h e B o d y ’ s U s e o f G l u c o s e

an almost indispensable source of the calcium every child needs for growth, a milk substitute must be found for any child who becomes lactose intolerant. Disadvan- taged young children of the developing world sustain the most severe consequences of lactose intolerance when it combines with disease, malnutrition, or parasites to produce a loss of nutrients that greatly reduces the children’s chances of survival. And girls everywhere who fail to consume enough calcium may later develop weak bones, so young women must fi nd substitutes if they become unable to tolerate milk.

Milk Tolerance and Strategies Th e failure to digest lactose aff ects people to diff ering degrees. Only a few people cannot tolerate lactose in any amount. Many aff ected people can consume up to 6 grams of lactose (½ cup milk) without symp- toms. Th e most successful strategies seem to be increasing intakes of milk products gradually, consuming them with meals, and spreading them out through the day. Often, people overestimate the severity of their lactose intolerance, blaming it for symptoms most probably caused by something else—a mistake that could cost them the health of their bones.

Aged cheese often causes little trouble for lactose-intolerant people—the bacteria or molds that help create cheese digest lactose as they convert milk to a fermented product. Some kinds of yogurt contain live bacterial cultures that may take up resi- dence in the intestinal tract, where they seem to reduce symptoms of lactose intol- erance. Th is bacterial shift allows some lactose-intolerant people to adapt to con- suming some milk products.35 Yogurts that contain added milk solids also contain extra lactose that can overwhelm the system; such yogurts list milk solids and live cultures among the ingredients on their labels.

Lactose-free milk products that have undergone treatment with lactase are avail- able at most grocery stores. Alternatively, people can treat milk products them- selves with over-the-counter enzyme pills and drops. Th e pills are taken with milk- containing meals, and the drops are added to milk-based foods; both products help to digest lactose by replacing the missing natural enzyme. Th e trick is to fi nd ways of splitting lactose to glucose and galactose so that the body can absorb the products, rather than leaving the lactose undigested to feed the bacteria of the colon. Other choices to replace the calcium of milk are calcium-fortifi ed orange juice, calcium- and vitamin-fortifi ed soy drink, and canned sardines or salmon with the bones.

KE Y POINT In lactose intolerance, the body fails to produce suffi cient amounts of the enzyme needed to digest the sugar of milk. Uncomfortable symptoms result and can lead to milk avoidance. Lactose-intolerant people and those allergic to milk need milk alternatives that contain the calcium and vitamins of milk.

LO 4.5, 4.6

The Body’s Use of Glucose Glucose is the basic carbohydrate unit used for energy by each of the body’s cells. Th e body handles its glucose judiciously—maintaining an internal supply to be used when needed and tightly controlling its blood glucose concentration to ensure a steady supply. Recall that carbohydrates serve functional roles, too, such as forming part of mucus, but they are best known for providing energy.

Splitting Glucose for Energy Glucose fuels the work of every cell in the body to some extent, but the cells of the brain and nervous system depend almost exclusively on glucose, and the red blood cells use glucose alone. When a cell splits glucose for energy, it performs an intricate sequence of maneuvers that are of great interest to the biochemist—and of no inter- est whatever to most people who eat bread and potatoes. What everybody needs to

Chapter 8 and its Controversy examine the • topic of milk in adult diets in relation to the adult bone disease osteoporosis.

Lactose in selected foods:

Whole-wheat bread, 1 slice 0.5 g•

Dinner roll, 1 0.5 g•

Cheese, 1 oz•

Cheddar or American 0.5 g•

Parmesan or cream 0.8 g•

Doughnut (cake type), 1 1.2 g•

Chocolate candy, 1 oz 2.3 g•

Sherbet, 1 c 4.0 g•

Cottage cheese (low-fat), 1 c 7.5 g•

Ice cream, 1 c 9.0 g•

Milk, 1 c 12.0 g•

Yogurt (low-fat, 1 c with • added milk solids) 15.0 g

126 chapter 4 C a r b o h y d r a t e s

understand, though, is that there is no good substitute for carbohydrate. Carbohy- drate is essential, as the following details illustrate.

The Point of No Return At a certain point in the process of splitting glucose en- ergy, glucose itself is forever lost to the body. First, glucose is broken in half, releas- ing some energy. Th en, two pathways open to these glucose halves. Th ey can be put back together to make glucose again, or they can be broken into smaller molecules. If they are broken further, they cannot be reassembled to form glucose.

Th e smaller molecules can also take diff erent pathways. Th ey can continue along the breakdown pathway to yield still more energy and eventually break down com- pletely to just carbon dioxide and water. Or, they can be formed into building blocks of protein or be hitched together into units of body fat. Figure 4-12 shows how glucose is broken down to yield energy and carbon dioxide.

Below a Healthy Minimum Although glucose can be converted into body fat, body fat cannot be converted into glucose to feed the brain adequately. When the body faces a severe carbohydrate defi cit, it has two problems. Having no glucose, it must turn to protein to make some (the body has this ability), diverting protein from its own critical functions, such as maintaining the body’s immune defenses. When body protein is used, it is taken from blood, organ, or muscle proteins; no surplus of protein is stored specifi cally for such emergencies. Protein is indispensable to body functions and carbohydrate should be kept available precisely to prevent the use of protein for energy. Th is is called the protein-sparing action of carbohydrate. As for fat, it cannot regenerate enough glucose to feed the brain and prevent ketosis.

Ketosis Th e second problem with an inadequate supply of carbohydrate concerns a precarious shift in the body’s energy metabolism. Instead of producing energy by following its main metabolic pathway, fat takes another route in which fat frag- ments combine with each other. Th is shift causes an accumulation of the normally scarce acidic products, ketone bodies.36

Ketone bodies can accumulate in the blood (ketosis) to reach levels high enough to disturb the normal acid-base balance. Diets that produce ketosis may also promote de- fi ciencies of vitamins and minerals, increase loss of bone minerals, elevate blood cho- lesterol, set the stage for kidney stones, and impair mood.37 Glycogen stores become too scanty to meet a metabolic emergency or to support vigorous muscular work.

Ketosis isn’t all bad, however. Ketone bodies provide fuel for brain and nerve cells when glucose is lacking, such as in starvation or very-low-carbohydrate diets.38 Not all brain areas use ketones—some rely exclusively on glucose, so the body must still sacrifi ce protein to provide it, but at a slower rate. Some children and adults with epilepsy may benefi t from a therapeutic ketosis-inducing diet, used along with medication, although many fi nd the diet diffi cult to follow for long periods.39

The DRI Minimum Recommendation for Carbohydrate Th e minimum amount of digestible carbohydrate determined by the DRI committee to adequately feed the brain and reduce ketosis has been set at 130 grams a day for an average-sized person.40 Several times this minimum is recommended to maintain health and gly- cogen stores (explained in the next section). Th e amounts of vegetables, fruits, le- gumes, grains, and milk recommended in the USDA Food Guide (see Chapter 2) deliver abundant carbohydrates.

KE Y POINT Without glucose, the body is forced to alter its uses of protein and fats. To help supply the brain with glucose, the body breaks down protein to make glucose and converts its fats into ketone bodies, incurring ketosis.

How Is Glucose Regulated in the Body? Should your blood glucose ever climb abnormally high, you might become confused or have diffi culty breathing. Should your glucose supplies ever fall too low, you

protein-sparing action the action of carbohydrate and fat in providing energy that allows protein to be used for purposes it alone can serve.

ketone (kee-tone) bodies acidic, fat- related compounds that can arise from the incomplete breakdown of fat when carbohy- drate is not available.

ketosis (kee-TOE-sis) an undesirable high concentration of ketone bodies, such as acetone, in the blood or urine.

+ + Energy

+ Energy+

+ Energy

Carbon atoms

Bonds

2-carbon compound

3-carbon compound

Glucose (6-carbon compound)

Carbon dioxide

2 molecules of carbon dioxide

Cell enzymes split the bonds between the carbon atoms in glucose, liberating the energy stored there for the cell’s use. The fi rst split yields two 3-carbon frag- ments. The two-way arrows mean that these fragments can also be rejoined to make glu- cose again. Once they are broken down further into 2-carbon fragments, however, they cannot rejoin to make glucose. The carbon atoms liberated when the bonds split are combined with oxygen and released into the air, via the lungs, as carbon dioxide. Although not shown here, water is also pro- duced at each split.

Animated! The Breakdown of

Glucose Yields Energy

and Carbon Dioxide

figure 4-12

127T h e B o d y ’ s U s e o f G l u c o s e

CONCEPT LINK 4-6 The acid-base balance of the blood was de- scribed in Chapter 3 on page 83.

CONCEPT LINK 4-7 Epinephrine and the body’s stress response were described in Chapter 3, page 76.

‡Epinephrine is also called adrenaline.

insulin a hormone secreted by the pancreas in response to a high blood glucose concen- tration. It assists cells in drawing glucose from the blood.

glucagon (GLOO-cah-gon) a hormone secreted by the pancreas that stimulates the liver to release glucose into the blood when blood glucose concentration dips.

would feel dizzy and weak. Th e healthy body guards against both conditions with two safeguard activities:

siphoning off excess blood glucose into the liver and into the muscles for storage •

as glycogen and to the adipose tissue for storage as body fat.

replenishing diminished blood glucose from liver glycogen stores.•

Two hormones prove critical to these processes. Th e hormone insulin stimulates glucose storage as glycogen while the hormone glucagon helps to release glucose from its glycogen nest.

The Role of Insulin After a meal, as blood glucose rises, the pancreas is the fi rst organ to respond. It releases insulin, which signals the body’s tissues to take up surplus glucose. Muscle and adipose tissue respond by taking up some of this excess glucose to build the polysaccharide glycogen (in muscles) or convert it into fat (in fat cells). Th e liver takes up excess glucose and makes glycogen, too, but it needs no help from insulin to do so.41

Tissue Glycogen Stores Th e muscles hoard two-thirds of the body’s total gly- cogen to use for physical activity. Th e brain stores a tiny fraction of the total as an emergency reserve to fuel the brain for an hour or two in severe glucose depriva- tion.42 Th e liver stores the remainder and is generous with its glycogen, releasing glucose into the bloodstream for the brain or other tissues when the supply runs low. Without carbohydrate from food to replenish it, the liver glycogen stores can be depleted in less than one waking day.

The Release of Glucose from Glycogen Th e glycogen molecule is highly branched with hundreds of ends bristling from each molecule’s surface (review this structure in Figure 4-3 on page 110). When blood glucose starts to fall too low, the hormone glucagon fl oods the bloodstream and triggers the breakdown of liver glycogen to free glucose. Enzymes within the liver cells respond to glucagon by attacking a multitude of glycogen ends simultaneously to release a surge of glucose into the blood for use by all the body’s cells. Th us, the highly branched structure of glycogen uniquely suits the purpose of releasing glucose on demand.

Be Prepared: Eat Carbohydrate Another hormone, epinephrine, also breaks down liver glycogen as part of the body’s defense mechanism in times of danger.‡ To store glucose for emergencies, we are advised to eat carbohydrate at each meal.

You may be asking, “What kind of carbohydrate?” Candy, “energy bars,” and sug- ary beverages are quick sources of abundant sugar energy, but they are not the best choices. Balanced meals and snacks, eaten on a regular schedule, help the body to maintain its blood glucose. Meals with starch and fi ber combined with some pro- tein and a little fat slow digestion so that glucose enters the blood gradually in an ongoing, steady rate.

KE Y POINT Glucose stored as liver glycogen is released and used by the whole body. Muscles store their own glycogen for their own use. Insulin promotes glycogen storage, whereas glucagon acts to liberate glucose from liver glycogen. Healthy people have no problem regulating their blood glucose when they consume mixed meals at regular intervals.

Handling Excess Glucose Suppose you have eaten dinner and are now sitting on the couch, munching pretzels and drinking cola as you watch a ball game on television. Your digestive tract is de- livering molecules of glucose to your bloodstream, and your blood is carrying these

128 chapter 4 C a r b o h y d r a t e s

molecules to your liver and other body cells. Th e body cells use as much glucose as they can for their energy needs of the moment. Excess glucose is linked together and stored as glycogen until the muscle and liver stores are full to overfl owing with glycogen. Still, the glucose keeps coming.

To handle the excess, body tissues shift to burning more glucose for energy in place of fat. As a result, more fat is left to circulate in the bloodstream until it is picked up by the fatty tissues and stored there. If these measures still do not accom- modate all of the incoming glucose, the liver has no choice but to handle the excess. Excess glucose left circulating in the blood can harm the tissues.

Carbohydrate Stored as Fat Th e liver breaks the extra glu- cose into smaller molecules and assembles these into its durable energy-storage compounds—fats. Th ese newly made fats are then released into the blood, carried to the adipose tissues, and deposited. Fat cells also take up some glucose directly and con- vert it to fat. Unlike the liver cells, which store only about 2,000 calories of glycogen, the fat cells of an average-size person store over 70,000 calories of fats, and their capacity to store fat is almost limitless.

Human beings possess enzymes to convert excess glucose to fat, but the process requires many enzymatic steps costing a great deal of energy. Th e body is thrifty by nature, so when presented with both glucose and fat from a mixed meal, it pre- fers to store the fat and use the glucose to meet immediate en- ergy needs. In this way, the maximum available food energy is retained because the dietary fat slips easily into storage with few conversions—its energy is conserved. Moral: You had bet-

ter play the game if you are going to eat the food. (Th e Th ink Fitness feature off ers tips to help you play.)

Carbohydrate and Weight Maintenance A balanced diet that is high in com- plex carbohydrates helps control body weight and maintain lean tissue. Bite for bite, carbohydrate-rich foods contribute less to the body’s available energy than do fat- rich foods, and they best support physical activity to promote a lean body. Th us, if you want to stay healthy and remain lean, you should make every eff ort to choose a calorie-appropriate diet providing 45 to 65 percent of its calories from mostly un- refi ned sources of complex carbohydrates and 20 to 35 percent from the right kind of fats.

You had better play the game if you are going to eat the food.

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sc /G

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glycemic index (GI) a ranking of foods according to their potential for raising blood glucose relative to a standard such as glucose or white bread.

glycemic load (GL) a mathematical expression of both the glycemic index and the carbohydrate content of a food, meal, or diet (glycemic index � carbohydrate).

think fitness What Can I Eat to Make Workouts Easier?

A working body needs carbohy- drate fuel to replenish glycogen, and when it runs low, physical activity can seem more difficult. If your workouts seem to drag and never get easier, take a look at your diet. Are your meals regularly timed? Do they provide abundant carbohydrate from nutritious whole

foods to fill up glycogen stores so they last through a workout and provide nutrients to use that fuel?

Here’s a trick: at least an hour before your workout, eat a small snack of about 300 calories of foods rich in complex carbohy- drates and drink some extra fluid

(see Chapter 10 for ideas). Re- member to cut back your intake at other meals by an equivalent amount. The snack provides glu- cose at a steady rate to spare glycogen, and the fluid helps to maintain hydration.

START NOW

Ready to make a change? Consult the online behavior-change planner to explore a method for changing your current behaviors at www.cengage.com/sso.

http://www.cengage.com/sso

129T h e B o d y ’ s U s e o f G l u c o s e

Th is chapter’s Food Feature provides the fi rst set of tools required for the job of designing such a diet. Once you have learned to identify the carbohydrates in foods, you must then set about learning which fats are which (Chapter 5) and how to ob- tain adequate protein without overdoing it (Chapter 6). By Chapter 9, you can put it all together with the goal of achieving and maintaining a healthy body weight.

KE Y POINT The liver has the ability to convert glucose into fat; under normal conditions, most excess glucose is stored as glycogen or used to meet the body’s immediate needs for fuel.

The Glycemic Index of Food Carbohydrate-rich foods vary in the degree to which they elevate both blood glucose and insulin concentrations. When this eff ect is measured, a food’s average score can be ranked on a scale known as the glycemic index (GI). It can then be compared with the score of a standard food, usually white bread or glucose, taken by the same person.43 A food’s ranking may surprise you. For example, baked potatoes rank higher than ice cream, partly because ice cream contains sucrose. Fructose makes up half of each sucrose molecule, and fructose only slightly elevates blood glucose. Th e starch of the potatoes is all glucose. Figure 4-13 shows where some foods fall on the glycemic index scale on average, but test results vary widely.

Diabetes and the Glycemic Index Th e glycemic index, and its mathematical off shoot, glycemic load (GL), may be of interest to people with diabetes who must regulate their blood glucose to protect their health.44 Th e lower the GL of the diet, the less glucose builds up in the blood and the less insulin is needed to maintain normal blood glucose concentrations. Study subjects given carefully controlled diets of low-glycemic foods may indeed lower their blood glucose levels, and some may improve their blood lipids, too.45

Interpreting studies on the GI and GL proves to be complex because other di- etary factors aff ect the results.46 For example, although popular books claim that consumers can lose weight on a low-GL diet, research is mixed on whether the GL of the diet can truly assist in weight loss.47 Low-GI foods often provide abun- dant soluble fi ber, which slows glucose absorption, sustains feelings of fullness, and improves blood lipids; soluble fi ber may in fact be responsible for some eff ects at- tributed to the GI.48 In any case, the glycemic index is not of primary concern for diabetes control, but modest benefi t may come from choosing foods low on the scale in addition to using primary strategies for controlling blood glucose.49

Limitations of the Glycemic Index Some researchers cast doubt on whether the glycemic index is practical or benefi cial.50 An individual’s blood glucose may rise predictably after eating a particular food, but for groups of people, many problems exist in applying the glycemic index.51 Among them:

the glycemic response to any one food varies widely among individuals. •

a person’s body size and weight, blood volume, and metabolic rate aff ect glyce-•

mic response.52

glycemic responses tend to diff er more between individuals for the same food •

than within one person for diff erent foods.

within the same person, results for a particular food vary with the time of day. •

many • food factors also change glycemic index results, including plant variety,

food ripeness, processing, preparation, and other foods eaten at the same time.53

very few foods have been tested and for those that have, diff erent laboratories •

often yield diff erent results.54

Given these limitations, it becomes clear why researchers dismiss the notion of “good” and “bad” foods based on the glycemic response (see this chapter’s Contro- versy section).

Peanuts

Fructose

Soybeans

Cashews, cherries

Barley

Kidney beans Chickpeas (garbanzo beans)

Butter beans, lentils

Yogurt, milk Soy milk

Tomato juice, navy beans, apples, pears

Apple juice, dates, carrots

Bran cereals, black-eyed peas, peaches, oranges

Chocolate pudding, chocolate candy

Grapes, corn tortillas

Green peas, baked beans, pasta

Rye bread, orange juice Bananas, mangoes

Corn, pound cake

Oatmeal, cooked

Cola, pineapple

Honey

Ice cream

Raisins, brown rice

Couscous, sucrose (table sugar)

Pumpkin, popcorn, bagel White bread, wheat bread, white rice

Watermelon, doughnut

Sports drinks, jelly beans

Baked potato, boiled potato

Oatmeal, instant

Rice milk

Cornflakes

Mashed potato, instant; rice crackers

Glucose

HIGH

LOW

100

Glycemic Index

of Selected Foods figure 4-13

Source: F. S. Atkinson, K. Foster-Powell, and J. C. Brand-Miller, International tables of glycemic index and glycemic load values: 2008, Diabetes Care 31 (2008): 2281–2283.

130 chapter 4 C a r b o h y d r a t e s

KE Y POINT The glycemic index is a measure of blood glucose response to foods relative to the response to a standard food. The glycemic load is the product of the glycemic index multiplied by the carbohydrate content of a food. The concept of good and bad foods based on the glycemic response is an oversimplifi cation.

LO 4.7

Diabetes What happens if the body cannot handle carbohydrates normally? One result is diabetes, which is common in developed nations and can be detected by a blood test. Diabetes affl icts a rapidly growing number of U.S. adults (see Figure 4-14), and diabetes has reached record numbers in children. Almost 24 million people in the United States have been diagnosed with diabetes.55 As many as 57 million U.S. adults 20 years of age and older have prediabetes—their blood glucose is elevated but not to such an extent as to be classifi ed as diabetes.56 Of these, over 6 million are unaware of it and so go untreated.

The Perils of Diabetes Diabetes ranks seventh among all causes of death in the United States.57 For people with diabetes, the risk of heart disease and stroke is doubled, and in the United States diabetes is the leading cause of permanent blindness and of fatal kidney fail- ure.58 Each year, diabetes costs nearly $132 billion in U.S. health-care services.59 Th e common forms of diabetes are type 1 and type 2, both disorders of blood glu- cose regulation; their characteristics are summarized in Table 4-6.60

The Toxic Effects of Excess Glucose Chronically elevated blood glucose associ- ated with diabetes alters metabolism in virtually every cell of the body. Some cells convert excess glucose to toxic alcohols, causing the cells to swell—in the lenses of the eyes, for example, the distended cells distort vision. Other cells respond by at-

Type 1 Type 2

Percentage of cases 5–10% 90–95%

Age of onset <30 years >40 yearsa

Associated characteristics Autoimmune diseases, viral infections, inherited factors

Obesity, aging, inherited factors

Primary problems Destruction of pancre- atic beta cells; insulin defi ciency

Insulin resistance, insulin defi ciency (relative to needs)

Insulin secretion Little or none Varies; may be normal, increased, or decreased

Requires insulin Always Sometimes

Older names Juvenile-onset diabetes Insulin-dependent diabetes mellitus (IDDM)

Adult onset-diabetes Noninsulin-dependent diabetes mellitus (NIDDM)

aIncidence of type 2 diabetes is increasing in children and adolescence; in more than 90 percent of these cases, it is associated with overweight or obesity and a family history of type 2 diabetes.

Types 1 and 2 Diabetes Compared table 4-6

diabetes (dye-uh-BEET-eez) a disease characterized by elevated blood glucose and inadequate or ineffective insulin, which impairs a person’s ability to regulate blood glucose normally. The technical name is diabetes mel- litus (mellitus means “honey-sweet” in Latin, referring to sugar in the urine).

prediabetes condition in which blood glu- cose levels are higher than normal but not high enough to be diagnosed as diabetes; consid- ered a major risk factor for future diabetes and cardiovascular diseases.

Key:

<4%

6%–7.9%

4%–5.9%

8%–9.9%

≥10%

1997: Ten states had a prevalence of diabetes of less than 4% and only five states had a prevalence of 6% or greater.

2007: No state had a prevalence of diabetes of less than 4%; all but three states had a prevalence of 6% or greater, with eight states reporting a prevalence of 10% or greater.

Prevalence of

Diabetes Among

Adults in the

United States

figure 4-14

The maps below depict regional changes in U.S. diabetes incidence.

Source: Centers for Disease Control and Prevention, www.cdc.gov/needphp/aag/aag_ddt.htm.

http://www.cdc.gov/needphp/aag/aag_ddt.htm

131D i a b e t e s

taching excess glucose to protein molecules in abnormal ways; these altered proteins cannot function, causing many problems. Th e structures of the blood vessels and nerves become damaged, leading to loss of circulation and nerve function. Loss of blood fl ow to the kidneys damages them, often resulting in the need to cleanse the blood by means of kidney dialysis, or, in later stages, to undergo kidney transplant.

Infl ammation Chronic infl ammation of body tissues accompanies diabetes and may contribute to insulin resistance, a condition related to diabetes, discussed later.61 Infl ammation also occurs in obesity, heart disease, and cancer, as other chapters point out, and may contribute to disease progression.62

Circulation Problems Poor circulation also increases the likelihood of infections. With loss of both circulation and nerve function, undetected injury and infection may lead to death of tissue (gangrene), necessitating amputation of the limbs (most often the legs or feet).

KE Y POINT Diabetes is an example of the body’s abnormal handling of glucose. It is a major threat to health and life, and its prevalence is rapidly increasing.

Prediabetes and the Importance of Testing Prediabetes, a fasting blood glucose level just slightly higher than normal, presents few or no warning signs (see Table 4-7), but tissue damage may silently progress.63 According to one estimate, 54 million people in the United States have prediabetes, but few are aware of it.64 Yet, treatment can delay or prevent the progression to dia- betes, sparing much misery and pain. Th erefore, the American and Canadian dia- betes associations call for everyone over 45 years of age (40 in Canada), and younger people with risk factors such as overweight, to be tested regularly.

Diagnosis is made when two or more fasting blood glucose tests register positive. In this test, a clinician draws blood after a night of fasting and measures an indicator of blood glucose to determine whether it falls within the normal range (values are listed in the margin). A registered dietitian, a Certifi ed Diabetes Educator, or a phy- sician can help those with prediabetes or diabetes learn to manage their condition.

KE Y POINT Prediabetes silently threatens the health of tens of millions of people in the United States.

Type 1 Diabetes Type 1 diabetes is responsible for 5 to 10 percent of diabetes cases. It commonly occurs in childhood and adolescence but can occur at any age, even late in life.65 Its incidence seems to be on the rise and it currently ranks as the leading chronic disease among children and adolescents.66 An autoimmune disorder infl uenced by genetic inheritance, type 1 diabetes arises when the person’s own immune system misidentifi es the protein insulin as an enemy and attacks the cells of the pancreas that produce it.67 Soon the pancreas can no longer produce insulin. Th en, after each meal, glucose concentration builds up in the blood while body tissues are simulta- neously starving for glucose, a life-threatening situation. Th e person must receive insulin from an external source to assist the cells in taking up the fuels they need from the bloodstream that is carrying too much.

Insulin is a protein and if it were taken orally, the digestive system would digest it. Insulin must therefore be taken as daily shots or pumped from an insulin pump that delivers it through a tiny tube implanted under the skin. Fast-acting and long- lasting forms of insulin allow more fl exibility in managing meals and treatments, but users must still plan ahead to balance blood insulin and glucose concentrations.68 Doing so can make a diff erence to health—those who control their blood glucose suff er less cardiovascular and other diseases than those who do not.69 Experimental

Fasting blood glucose (milligrams per • deciliter)

Normal: 70–99 mg/dL •

Prediabetes: 100–125 mg/dL•

Diabetes: • ≥126 mg/dL

These signs appear reliably in type 1 dia- betes and, often, in the later stages of type 2 diabetes.

Excessive urination and thirst• Glucose in the urine• Weight loss with nausea, easy tiring, • weakness, or irritability Cravings for food, especially for sweets• Frequent infections of the skin, gums, • vagina, or urinary tract Vision disturbances; blurred vision• Pain in the legs, feet, or fi ngers• Slow healing of cuts and bruises• Itching• Drowsiness• Abnormally high glucose in the blood•

Warning Signs

of Diabetes

table 4-7

dialysis (die-AL-ih-sis) in kidney disease, treatment of the blood to remove toxic sub- stances or metabolic wastes; more properly, hemodialysis, meaning “dialysis of the blood.”

insulin resistance a condition in which a normal or high level of circulating insulin pro- duces a less-than-normal response in muscle, liver, and adipose tissues; thought to be a metabolic consequence of obesity.

type 1 diabetes the type of diabetes in which the pancreas produces no or very little insulin; often diagnosed in childhood, although some cases arise in adulthood. Formerly called juvenile-onset or insulin-dependent diabetes.

autoimmune disorder a disease in which the body develops antibodies to its own proteins and then proceeds to destroy cells containing these proteins. Examples are type 1 diabetes and lupus.

132 chapter 4 C a r b o h y d r a t e s

treatments such as surgical transplants of insulin-producing pancreatic cells and a vaccine to prevent type 1 diabetes are under development.70

KE Y POINT Type 1 diabetes is an autoimmune disease that attacks the pancreas. Inadequate insulin leaves blood glucose high and cells undersupplied with glucose energy. People with type 1 diabetes depend on external sources of insulin.

Type 2 Diabetes Th e past few decades have seen a sharp rise in the rate of the predominant type of diabetes mellitus, type 2 diabetes (responsible for 90 to 95 percent of cases).71 In type 2 diabetes, body tissues lose their sensitivity to insulin. Th e insulin-resistant muscle and adipose tissues no longer respond to insulin by increasing their uptake of glucose from the blood. As blood glucose climbs higher, the pancreas compensates by producing larger and larger amounts of insulin. Blood insulin may rise abnormally high, but to no avail. Eventually, the overtaxed cells of the pancreas begin to fail and reduce their insulin output while blood glucose spins further out of control.

Type 2 Diabetes and Obesity Obesity underlies many cases of type 2 diabetes.72 Middle age and physical inactivity also foreshadow its development. Th e greater the accumulation of body fat, particularly around the waistline, the more insulin- resistant the cells become, and the higher the blood glucose rises.73 Even moderate weight gain in adults increases the risk. Among children and adolescents, both obe- sity and type 2 diabetes have increased dramatically during the past two decades.74

One theory of how obesity and type 2 diabetes may worsen each other is depicted in Figure 4-15. Many factors may contribute to obesity but according to the theory, once obesity sets in, infl ammation and other metabolic changes trigger the tissues to resist insulin.75 As insulin resistance develops, glucose builds up in the blood while the tissues are deprived of glucose (type 2 diabetes). Meanwhile, blood lipid levels also rise, resulting in an overabundance of circulating fuels available to be stored as fat in the adipose tissue. Fat mass increases, insulin resistance worsens, and obesity is perpetuated. Given this series of events, is it any wonder that obese people with type 2 diabetes have trouble losing weight?

A person’s genetic inheritance also strongly infl uences the risk of developing type 2 diabetes, and genetic researchers are working steadily toward pinpointing genetic risk factors.76 A goal of this research, to develop genetic tests to identify susceptible people, holds the potential to avert much disease and suff ering.

Preventing Type 2 Diabetes In the great majority of cases today, however, pre- vention is not only possible but is also likely when individuals take action to con- trol their lifestyle choices. Men and women who maintain a healthy body weight; choose a diet high in vegetables, fruit, fi sh, poultry, and whole grains; and exercise regularly, restrict alcohol, and abstain from smoking have a greatly reduced inci-

Did You Know? The fi rst use of genetic engineering was to alter the DNA of a bacterium to produce insulin for treatment of diabetes.

Controversy 13 describes the trends in child-• hood obesity and chronic diseases.

• Obesity

• Reduced glucose use for fuel • Increased fat stores

• Type 2 diabetes • Hormonal imbalance

• Insulin resistance

• Enlarged fat mass • Elevated blood lipids • Inflammation

• Genetic inheritance • Excess food energy • Inadequate physical activity

An Obesity-

Diabetes Cycle

figure 4-15

21st Century Epidemic?

Two young people talk about living with diabetes.

To hear their stories, log on to www.cengage.com/sso.

my turn

Liz Ariela

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133M a n a g e m e n t o f D i a b e t e s

dence of type 2 diabetes compared to those with less healthy lifestyles. It’s never too late—even older adults can lower their diabetes risk by changing their lifestyles.77

KE Y POINT Type 2 diabetes is a growing problem. The risk of developing it rises with weight gain, aging, and physical inactivity and falls with a nutritious diet as part of a healthy lifestyle.

LO 4.8

Management of Diabetes Th e eff ects of diabetes can be severe, but controlling blood glucose can reduce the likelihood of harm.78 Monitoring blood glucose and taking medication often be- come part of the daily routine. A person with diabetes is especially advised to control body fatness because overweight worsens diabetes and its associated conditions. All lifestyle factors that aff ect heart and blood vessel diseases (discussed in Chapter 11) demand special attention from those with diabetes because diabetes greatly elevates the risks for developing those diseases. A person diagnosed with diabetes must es- tablish patterns of eating, exercise, and medication to control blood glucose.

Nutrition A major goal of medical nutrition therapy for diabetes and prediabetes is to keep blood glucose levels in the normal range or as close to normal as is safely and prac- tically possible.79 Controlling carbohydrate intake, in turn, plays a central role in controlling the blood glucose. A common misconception is that people with dia- betes need to avoid sugar and sugar-containing foods. As far as blood glucose is concerned, the amount of carbohydrate often matters more than its source.

How Much Carbohydrate Is Best? Th e amount of carbohydrate recommended for a person with diabetes varies with glucose tolerance. A low-carbohydrate diet (less than 130 grams of carbohydrate per day) is not recommended.80 A dietary pattern that includes carbohydrate from fruits, vegetables, whole grains, legumes, and low-fat milk promotes good health, so long as the carbohydrate in the diet is monitored. Several approaches can be used to plan such diets, but many people with diabetes learn to count carbohydrates using the exchange system that is presented in Appendix D (Appendix B for Canadians). As is true for everyone, people with diabetes should choose at least half of their grains as whole grains.

Lifestyle factors that lower diabetes risk:•

Physical activity.•

Never smoking.•

Diet follows the • Dietary Guidelines for Americans.

Limited alcohol intake.•

Healthy body weight.•

Source: D. Mozaffarian and coauthors, Lifestyle risk

factors and new-onset diabetes mellitus in older

adults: The Cardiovascular Health Study, Archives of Internal Medicine 169 (2009): 798–807.

Monitoring blood glucose is a critical step in learn- ing to manage diabetes.

on y

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di t

Like others, people with diabetes benefi t from fruits, vegetables, whole grains, legumes, and low-fat milk products.

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type 2 diabetes the type of diabetes in which the pancreas makes plenty of insulin but the body’s cells resist insulin’s action; often diagnosed in adulthood. Formerly called adult- onset or noninsulin-dependent diabetes.

134 chapter 4 C a r b o h y d r a t e s

Why Is Timing of Carbohydrate Important? To maintain near-normal blood glucose levels, food should deliver the same amount of carbohydrate each day, spaced evenly throughout the day. Eating too much carbohydrate at one time can raise blood glucose too high, stressing the already compromised insulin-producing cells. Eating too little carbohydrate can lead to abnormally low blood sugar (hypoglycemia). Th e glycemic index of foods is not of primary importance for diabetes control.81

Sugar Alcohols and Artifi cial Sweeteners Products sweetened with sugar alcohols, such as cookies, sugarless gum, hard candies, and jams and jellies, are safe in moderation.82 Th ey provide fewer calories and a lower glycemic response compared with sugars (see margin list). Most sugar alcohols provide about half the calories of sugars. Th e exception, erythritol, cannot be metabolized by human be- ings and so is calorie-free.

Sugar alcohols are safer for teeth than sugars, making them useful in chew- ing gums, breath mints, toothpaste, and other products that people keep in their mouths for a while. Mouth bacteria rapidly metabolize regular sugars into acids that cause dental caries; sugar alcohols resist such metabolism. Side eff ects such as gas, abdominal discomfort, and diarrhea arise from ingesting large quantities of sugar alcohols.

In the same vein, artifi cial sweeteners can sweeten foods without calories but people have concerns about their use. Th eir nature and safety is discussed in Chap- ter 12.

Diet Recommendations in Summary Constructed of a balanced pattern of foods, the same diet that best controls diabetes can also help to control body weight and support physical activity. Th is diet is:

Controlled in total carbohydrate (to regulate glucose concentration).•

Low in saturated and • trans fat (these worsen cardiovascular disease risks) and

should provide some raw unsaturated oils (to provide essential nutrients).83

Adequate in nutrients from food, not supplements (to avoid defi ciencies).•

Adequate in fi ber (from whole grains, fruits, legumes, and vegetables).•

Moderate in added sugars (must be counted among the day’s carbohydrates).•

Adequate but not too high in protein (too much may damage kidneys weakened •

by diabetes).84

Such a diet also has all the characteristics important to prevention of chronic dis- eases and meets most of the recommendations of the United States and Canada. A person at risk for diabetes can do no better than to adopt such a diet long before symptoms appear.

KE Y POINT Diet plays a central role in controlling diabetes and the illnesses that accompany it. The balanced diet recommended for diabetes also supports a healthy body weight and physical activity.

CONCEPT LINK 4-8 Exchange systems, introduced in Chapter 2, provide a valuable tool for estimating the car- bohydrate and other energy nutrients in foods. They are presented in full in Appendix D.

For more on low-carbohydrate, high-protein • diets, see Chapter 9.

Sweeteners, calories per gram:•

Sugars 4•

Artificial •

sweeteners 0

Sugar alcohols:•

Erythritol 0•

Isomalt, lactitol, •

maltitol 2

Mannitol 1.6•

Sorbitol 2.6•

Xylitol 2.4•

Sugar alcohols can protect the teeth against decay.

ra ig

M . M

oo re

Chapter 13 discusses a form of diabe-• tes seen only in pregnancy—gestational diabetes.

hypoglycemia (HIGH-poh-gly-SEE- mee-uh) a blood glucose concentration below normal, a symptom that may indicate any of several diseases, including impending diabetes.

sugar alcohols sugarlike compounds in the chemical family alcohol derived from fruits or the sugar dextrose that are absorbed more slowly than other sugars, are metabo- lized differently, and do not elevate the risk of dental caries. Examples are maltitol, mannitol, sorbitol, xylitol, isomalt, and lactitol.

dental caries decay of the teeth (caries means “rottenness”). Dental caries are a topic of Chapter 14.

artifi cial sweeteners sugar substitutes that provide negligible, if any, energy; also called nonnutritive sweeteners.

135I f I F e e l D i z z y B e t w e e n M e a l s , D o I H a v e H y p o g l y c e m i a ?

Physical Activity Th e role of regular physical activity in preventing and controlling diabetes, particularly type 2 diabetes, cannot be overstated.85 Exercise helps reduce the body’s fatness and also heightens tissue sensitivity to insulin. Even with modest weight loss, increasing physical activity in overweight people seems to delay type 2 diabetes onset; in those with the disease, increased activity, even without weight loss, often helps to con- trol it, sometimes to the degree that medication can be reduced or eliminated.

People with type 1 diabetes should check with a physician before increas- ing their physical activity. Hypoglycemia can occur during or after physical activity.86 Scrupulous monitoring of blood glucose before and after activity can identify needed changes in insulin or food intake, and both carbohydrate- rich foods and insulin should be kept at the ready. Like a juggler who keeps three balls in motion, the person with diabetes must constantly balance three factors—diet, exercise, and medication—to control the blood glucose level.

KE Y POINT Regular physical activity, in addition to diet and medication, contributes to controlling blood glucose in diabetes.

LO 4.9

If I Feel Dizzy Between Meals, Do I Have Hypoglycemia? Th e disease hypoglycemia is rare as a true disease, but many people believe they expe- rience its symptoms at times. Th e term hypoglycemia refers to abnormally low blood glucose.

Postprandial Hypoglycemia People with the condition postprandial hypogly- cemia—literally, “low blood glucose after a meal”—may experience fatigue, weak- ness, dizziness, irritability, a rapid heartbeat, anxiety, sweating, trembling, hunger, or headaches. Th ey may feel confused or fi nd mental work diffi cult. Th ese symptoms are so general and common, however, that people can easily misdiagnose themselves as having postprandial hypoglycemia. A true diagnosis requires a test to detect low blood or tissue glucose while the symptoms are present to confi rm that both occur simultaneously. Most often, however, no correlation is found.87

Fasting Hypoglycemia A person who has symptoms while fasting (overnight, for example) has a diff erent kind of hypoglycemia—fasting hypoglycemia—her- alded by headache, mental dullness, fatigue, confusion, amnesia, and even seizures and unconsciousness. It can arise from serious conditions, such as cancer, pancreatic damage, uncontrolled diabetes, liver infection (hepatitis), and advanced liver damage from alcohol overuse. Fasting hypoglycemia requires immediate medical evaluation.

For Most People To bring on even mild hypoglycemia with symptoms in nor- mal, healthy people requires extreme measures—administering drugs that over- whelm the body’s glucose-controlling hormones, insulin and glucagon. Without such intervention, these hormones hardly ever fail to keep blood glucose within normal limits in healthy people. Still, those who believe their symptoms arise from hypoglycemia may benefi t from eating regularly timed, balanced meals. Minimiz- ing alcohol intake and eliminating smoking can be important because alcohol can injure an otherwise healthy pancreas and smoking makes hypoglycemia likely.88

KE Y POINT Postprandial hypoglycemia is an uncommon medical condition in which blood glucose falls too low. It can be a warning of organ damage or disease.

Physical activity: a key player in controlling diabetes.

P ur

es to

ck /G

et ty

Im ag

postprandial hypoglycemia an unusual drop in blood glucose that follows a meal and is accompanied by symptoms such as anxiety, rapid heartbeat, and sweating; also called reactive hypoglycemia.

fasting hypoglycemia hypoglycemia that occurs after 8 to 14 hours of fasting.

136 chapter 4 C a r b o h y d r a t e s

food feature

To support optimal health, a diet must supply enough of the right kinds of carbohydrate-rich foods. Dietary recom- mendations for a health-promoting, 2,000-calorie diet suggest that carbohy- drates provide in the range of 45 percent and 65 percent of calories, or 225 and 325 grams, respectively, each day. This amount more than meets the minimum DRI amount of 130 grams needed to feed the brain and ward off ketosis.89 People needing more or less energy need proportionately more or less carbohydrate.

If you are curious about your own car- bohydrate need, fi nd your DRI estimated energy requirement (see the inside front cover, page A) and multiply by 45 percent to obtain the bottom of your carbohydrate intake range and then by 65 percent for the top; then divide both answers by 4 calories per gram (see the example in the margin).

Breads and cereals, starchy veg- etables, fruits, and milk are all good contributors of starch and dilute sugars. Many foods also provide fi ber in vary- ing amounts, as Figure 4-16 demon- strates. Concentrated sweets provide sugars but little else, as the last section demonstrates.

FRUITS A fruit portion of ½ cup of juice, a small banana, apple, or orange, ½ cup of most canned or fresh fruit, or ¼ cup of dried fruit supplies an aver- age of about 15 grams of carbohydrate, mostly as sugars, including the fruit sugar fructose. Fruits vary greatly in their water and fi ber contents and in their sugar concentrations. Juices should con-

Finding the Carbohydrates in Foods

tribute no more than one-half of a day’s intake of fruit. Except for avocado and olives, which are high in fat, fruits contain insignifi cant amounts of fat and protein.

VEGETABLES Starchy vegetables are major contribu- tors of starch in the diet. Just one small white or sweet potato or ½ cup of cooked dry beans, corn, peas, plantain, or winter squash provides 15 grams of carbohydrate, as much as in a slice of bread, though as a mixture of sugars and starch. One-half cup of carrots, okra, onions, tomatoes, cooked greens, or most other nonstarchy vegetables or a cup of salad greens provides about 5 grams as a mixture of starch and sugars.

BREADS, GRAINS, CEREALS, RICE, AND PASTA Breads and other starchy foods are fa- mous for their carbohydrate. Nutrition au- thorities encourage people to eat grains often and recommend that half of the grain choices should be whole grains. A slice of bread, half an English muffi n, a 6-inch tortilla, 1/3 cup of rice or pasta, or ½ cup of cooked cereal provides about 15 grams of carbohydrate, mostly as starch.

Not all high-fi ber foods are whole grains. One hundred percent bran cereal and bran muffi ns may be high-fi ber foods, but added bran doesn’t qualify as whole grain. Bran is just one part of the grain, and it may be added to mostly refi ned, enriched white fl our and sugar in cereals and muffi ns. Conversely, puffed

Part of eating right is choosing wisely among the many foods available. As we have discussed, largely without your awareness, the body responds to the carbohy- drates supplied by your diet. Now you take the controls by learning how to integrate carbohydrate-rich foods into a diet that meets your body’s needs for nutrients and phytochemicals.

Example for 45% of calories in a 2,700-• calorie diet:

2,700 cal • � 0.45 = 1,215 cal

1,215 cal • � 4 cal/g = 304 g

Example for 65% of calories in a 2,700-• calorie diet:

2,700 cal • � 0.65 = 1,755 cal

1,775 cal • � 4 cal/g = 439 g

The range of carbohydrate intake recom-• mended in a 2,700-calorie diet ranges be- tween about 300 and 440 grams per day.

Fiber recommendations are listed in the • margin on page 118.

The U.S. Food Exchange System (Ap-• pendix D) lists carbohydrate values for a variety of foods. Gram values listed in this section are from the Exchange System.

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137I f I F e e l D i z z y B e t w e e n M e a l s , D o I H a v e H y p o g l y c e m i a ?

Food Fiber (g) Baked potato with skin, 1 4 Broccoli, chopped, 1/2 c 3 Brussels sprouts, 1/2 c 3 Spinach, 1/2 c 3 Asparagus, 1/2 c 2 Baked potato, no skin, 1 2 Cabbage, red, 1/2 c 2 Carrots, 1/2 c 2 Cauliflower, 1/2 c 2 Corn, 1/2 c 2 Green beans, 1/2 c 2

Food Fiber (g) Lentils, 1/2 c Kidney beans, 1/2 c Pinto beans, 1/2 c Black beans, 1/2 c Black-eyed peas, 1/2 c Lima beans, 1/2 c

Food Fiber (g)

Vegetables

Mashed potatoes, home recipe, 1/2 c Bell peppers, 1/2 c Broccoli, raw, chopped, 1/2 c Carrot juice, 1/2 c Celery, 1/2 c Dill pickle, 1 whole Eggplant, 1/2 c Lettuce, romaine, 1 c Onions, 1/2 c Tomato, raw, 1 medium Tomato juice, canned, 3/4 c

2 1 1 1 1 1 1 1 1 1 1

Meat, Poultry, Fish, Dry Peas and Beans, Eggs, and Nuts

aAll values are for ready-to-eat or cooked foods unless otherwise noted. Fruit values include edible skins. All values are rounded values. bPasta includes spaghetti noodles, lasagna, and other noodles.

Soybeans, 1/2 c Almonds or mixed nuts, 1/4 c Peanuts, 1/4 c Peanut butter, 2 tbs Cashew nuts, 1/4 c Meat, poultry, fish, and eggs

Food Fibera (g) 100% bran cereal, 1 oz Barley, pearled, 1/2 c Cheerios, 1 oz Whole-wheat bread, 1 slice Whole-wheat pasta,b 1/2 c Wheat flakes, 1 oz Brown rice, 1/2 c Light rye bread, 1 slice Muffin, bran, 1 small Oatmeal, 1/2 c Popcorn, 2 c

Pumpernickel bread, 1 slice Shredded wheat, 1 large biscuit Cornflakes, 1 oz Muffin, blueberry, 1 Puffed wheat, 11/2 c White pasta,b 1/2 c Cream of wheat, 1/2 c White bread, 1 slice White rice, 1/2 c

2 2 1 1 1 1

<1 <1 <1

Food Fiber (g)

Grains

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3 3 3 3 3 2 2 2 2 2

8 8 8 7 6 5

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Fooda Fiber (g) Pear, raw, 1 medium 5 Blackberries/raspberries, raw, 1/2 c 4 Prunes, cooked, 1/4 c 4 Figs, dried, 3 3 Apple, 1 medium 3 Apricots, raw, 4 each 3 Banana, raw, 1 3 Orange, 1 medium 3

Food Fiber (g)

Fruits

Other berries, raw, 1/2 c Peach, raw, 1 medium Strawberries, sliced, 1/2 c Cantaloupe, raw, 1/2 c Cherries, raw, 1/2 c Fruit cocktail, canned, 1/2 c Peach half, canned Raisins, dry, 1/4 c Orange juice, 3/4 c

2 2 2 1 1 1 1 1

Fiber in the Food Groups figure 4-16

138 chapter 4 C a r b o h y d r a t e s

advice on added sugars: treat them as discretionary calories.90 That is, added sugars bring only calories, with no other signifi cant nutrients, to the diet; con- versely, the naturally occurring sugars of, say, an orange provide calories but also the vitamins, minerals, fi ber, and phyto- chemicals of oranges. Because current law requires manufacturers to list only total sugars on food labels, consumers remain largely in the dark about how much added sugar, and therefore how many discretionary calories, their foods contain. Added sugars can contribute to nutrient defi ciencies by displacing nutri- tious food from the diet.91 Most people can afford only a little added sugar in their diets if they are to meet nutrient needs within calorie limits. The USDA Food Guide suggests about 9 teaspoons of sugar, or one soft drink’s worth, in a nutrient-dense 2,200-calorie diet (the margin on page 139 lists other amounts).

Whether they come from beets, corn, grapes, honey, or sugar cane, the added sugars in foods are all alike. All arise naturally and, through processing, are purifi ed of most or all of the original plant material—bees process honey and machines process the other types. The health effects of refi ned sugars are discussed in Controversy 4. A strawberry spread sweetened with grape juice con- centrate, for example, may claim to be “100% fruit” but can contain more sugars than regular sucrose-sweetened jam.

THE NATURE OF SUGAR Each teaspoonful of any sweet can be assumed to supply about 16 calories and 4 grams of carbohydrate. You may not think of candy or molasses in terms of teaspoons, but this helps to empha- size that all sugary items are like white sugar—in spite of many people’s belief that some are different or “better.” If you use ketchup liberally, remember that a tablespoon of it contains a teaspoon of sugar. And for the soft-drink user, a 12-ounce can of sugar-sweetened cola contains about 8 or more teaspoons of added sugar, usually in the form of high- fructose corn syrup. Figure 4-17 shows that processed foods contain surpris- ingly large amounts of sugar.

cheeses contain little if any carbohydrate. These foods also contribute high-quality protein (a point in their favor), as well as several important vitamins and minerals. Calcium-fortifi ed soy beverages (soy milk) and soy yogurts approximate the nutrients of milk, providing some amount of added calcium and 14 grams of carbohydrate. Milk and soy milk prod- ucts vary in fat content, an important consideration in choosing among them; Chapter 5 provides the details. Sweet- ened milk and soy products contain added sugars.

Butter and cream cheese, though dairy products, are not equivalent to milk because they contain little or no carbo- hydrate and insignifi cant amounts of the other nutrients important in milk. They are appropriately associated with the solid fats.

OILS, SOLID FATS, AND ADDED SUGARS Oils and solid fats are devoid of carbo- hydrate, but sweets provide almost pure carbohydrate. Most people enjoy sweets, so it is important to learn some- thing of their nature and to account for them in the diet. First, the defi nitions of “sugar” come into play (Table 4-8 defi nes sugar terms).

All sugars originally develop by way of photosynthesis in a plant. A sugar molecule inside a grape (one of the naturally occurring sugars) is chemi- cally indistinguishable from one taken from sugar cane or corn and added at the factory (added sugars) to sweeten grape jam. The term added sugars refers to all sugars that have been extracted from their original source and added to other foods. Honey added to food is also an added sugar. The combined total of naturally occurring and added sugars appears on food labels in the line read- ing “sugars.” The body handles all the sugars in the same way, whatever their source.

The committee on the Dietary Guide- lines for Americans 2005 offers clear

wheat cereal, a whole-grain food, regis- ters low in fi ber per cup because the air that puffs up the grains takes up space in the measuring cup.

Also, do not assume that a brown- colored grain food is a whole grain; rather, rely on ingredient lists organized in descending order of prominence as your guide. Brown-colored baked goods may be made from white fl our with brown coloring and fl ecks of bran added. Also, product names like “multigrain,” “seven- grain,” and the like mean only that the product contains some portion of grains other than wheat, but they say nothing about their degree of refi nement or the amounts added—ingredients lists tell the truth.

Most grain choices should be low in fat and sugar. When extra calories are required to meet energy needs, some selections higher in fat (specifi cally, un- saturated fat; see Chapter 5) and sugar can supply discretionary calories and pleasure in eating. These choices might include biscuits, cookies, croissants, muffi ns, and snack crackers.

MEAT, POULTRY, FISH, DRY BEANS, EGGS, AND NUTS With two exceptions, foods of this group provide almost no carbohydrate to the diet. The exceptions are nuts, which provide a little starch and fi ber along with their abundant fat, and legumes (dried beans), revered by diet-watchers as low-fat sources of both starch and fi ber. Just ½ cup of cooked beans, peas, or lentils provides 15 grams of carbohy- drate, an amount equaling the richest carbohydrate sources. Among sources of fi ber, legumes are peerless, providing as much as 8 grams in ½ cup.

MILK, CHEESE, AND YOGURT A cup of milk or plain yogurt is a generous contributor of carbohydrate, donating about 12 grams. Cottage cheese provides about 6 grams of carbohydrate per cup, but most other

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139I f I F e e l D i z z y B e t w e e n M e a l s , D o I H a v e H y p o g l y c e m i a ?

some of this important nutrient. Molas- ses is less sweet than the other sweet- eners, however, so more molasses is needed to provide the same sweetness as sugar. Also, the iron comes from the iron machinery in which the molasses is

What about the nutritional value of a product such as molasses, honey, or concentrated fruit juice sweetener com- pared to white sugar? Molasses con- tains 1 milligram of iron per tablespoon so, if used frequently, it can contribute

The USDA Food Guide suggests that, • within calorie limits, small amounts of added sugars can be enjoyed as part of the discretionary calories in a nutrient- dense diet:

3 tsp for 1,600 cal•

5 tsp for 1,800 cal•

8 tsp for 2,000 cal•

9 tsp for 2,200 cal•

12 tsp for 2,400 cal•

Note: The term sugars here refers to all of the monosaccharides and disaccharides. On a label’s ingredients list, the term sugar means sucrose. See Chapter 12 for terms related to noncaloric artifi cial sweeteners.

added sugars• sugars and syrups added to a food for any purpose, such as to add sweetness or bulk or to aid in brown- ing (baked goods). Also called carbohydrate sweeteners, they include glucose, fructose, corn syrup, concentrated fruit juice, and other sweet carbohydrates. agave syrup• a carbohydrate-rich sweetener made from a Mexi- can plant; a higher fructose content gives some agave syrups a greater sweetening power per calorie than sucrose. brown sugar• white sugar with molasses added, 95% pure sucrose. concentrated fruit juice sweetener• a concentrated sugar syrup made from dehydrated, defl avored fruit juice, commonly grape juice; used to sweeten products that can then claim to be “all fruit.” confectioner’s sugar• fi nely powdered sucrose, 99.9% pure. corn sweeteners• corn syrup and sugar solutions derived from corn. corn syrup• a syrup, mostly glucose, partly maltose, produced by the action of enzymes on cornstarch. dextrose• an older name for glucose. evaporated cane juice• raw sugar from which impurities have been removed. fructose, galactose, glucose• the monosaccharides. granulated sugar • common table sugar, crystalline sucrose, 99.9% pure. high-fructose corn syrup• a commercial sweetener used in many foods, including soft drinks. Composed almost entirely of the monosaccharides fructose and glucose, its sweetness and caloric value are similar to sucrose.

honey• a concentrated solution primarily composed of glucose and fructose, produced by enzymatic digestion of the sucrose in nectar by bees. invert sugar• a mixture of glucose and fructose formed by the splitting of sucrose in an industrial process. Sold only in liquid form and sweeter than sucrose, invert sugar forms during certain cooking procedures and works to prevent crystallization of sucrose in soft candies and sweets. lactose, maltose, sucrose• the disaccharides. levulose• an older name for fructose. maple sugar• a concentrated solution of sucrose derived from the sap of the sugar maple tree, mostly sucrose. This sugar was once common but is now usually replaced by sucrose and artifi cial maple fl avoring. molasses• a syrup left over from the refi ning of sucrose from sugar cane; a thick, brown syrup. The major nutrient in molasses is iron, a contaminant from the machinery used in processing it. naturally occurring sugars• sugars that are not added to a food but are present as its original constituents, such as the sugars of fruit or milk. raw sugar• the fi rst crop of crystals harvested during sugar pro- cessing. Raw sugar cannot be sold in the United States because it contains too much fi lth (dirt, insect fragments, and the like). Sugar sold as “raw sugar” is actually evaporated cane juice. turbinado• (ter-bih-NOD-oh) sugar raw sugar from which the fi lth has been washed; legal to sell in the United States. white sugar• pure sucrose, produced by dissolving, concentrat- ing, and recrystallizing raw sugar.

Terms That Describe Sugar table 4-8

Did You Know? Sugars on the Nutrition Facts panel of a food label refl ect both added and naturally occur- ring sugars in foods. Sugars listed among the ingredients are all added.

Sugar in Processed Foods figure 4-17

½ c canned corn = 1 tsp sugara

12 oz cola = 10 tsp sugar

1 tbs ketchup = 1 tsp sugar

1 tbs creamer = 2 tsp sugar

8 oz sweetened yogurt = 8 tsp sugar

2 oz chocolate = 8 tsp sugar

aValues based on 1 tsp � 4g. Did You Know? Sugar alcohols protect against tooth decay.©

P ol

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140 chapter 4 C a r b o h y d r a t e s

Add sweet spices such as cinnamon, • nutmeg, allspice, or clove.

Add a tiny pinch of salt; it will make • food taste sweeter.

Try reducing the sugar added to reci-• pes by one-third.

Select fresh fruits or fruit juice, or those • prepared without added sugar.

Use small amounts of sugar substi-• tutes in place of sucrose.

Read food labels for clues on sugar • content.

Finally, enjoy whatever sugar you do eat. Sweetness is one of life’s great sen- sations, so enjoy it in moderation.

form of sugar is any “more healthy” than white sugar, as Table 4-9 shows.

It would be absurd to rely on any sugar for nutrient contributions. A tablespoon of honey (64 calories) does offer 0.1 mil- ligram of iron, but it would take 180 table- spoons of honey—11,500 calories—to provide 100 percent of a young woman’s recommended intake of 18 milligrams of iron. The nutrients of honey just don’t add up as fast as its calories. Thus, if you choose molasses, brown sugar, or honey, choose them not for their nutrient contri- butions, but for the pleasure they give.

These tricks can help magnify the sweetness of foods without boosting their calories:

Serve sweet food warm (heat en-• hances sweet tastes).

made and is in the form of an iron salt not easily absorbed by the body.

Honey is no better for health than sug- ars by virtue of being “natural”—honey is chemically almost indistinguishable from sucrose. Honey contains the two mono- saccharides, glucose and fructose, in approximately equal amounts. Sucrose contains the same monosaccharides but joined together in the disaccharide form. Spoon for spoon, however, sugar contains fewer calories than honey because the dry crystals of sugar take up more space than the sugars of honey dissolved in its water.

As for concentrated juice sweeteners, these are highly refi ned and have lost virtually all of the benefi cial nutrients and phytochemicals of the original fruit. No

At fi rst glance, honey, jelly, and brown sugar look more nutritious than plain sugar, but when compared with a person’s nutrient needs, none contributes anything to speak of. The cola beverage is clearly an empty-calorie item, too.

Food

Sugar (1 tbs) 46 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Honey (1 tbs) 64 0 0 1 0.1 0 11 0 0 0 0 0 0 <1 0

Molasses (1 tbs)

55 0 0 42 1.0 50 300 0.1 0 0 0 0.2 0.1 0 0

Concentrated grape or fruit juice sweet- ener (1 tbs)

30 0 0 0 0 0 0 0 0 0 0 0 0 0

Jelly (1 tbs) 49 0 0 1 0 1 12 0 0 0 0 0 0 0 <1

Brown sugar (1 tbs)

54 0 0 8 0.2 3 31 0 0 0 0 0 0 0 0

Cola beverage (12 fl oz)

153 0 0 11 0.1 4 4 0 0 0 0 0 0 0 0

Daily Values 2,000 56 25 1,000 18 400 3,500 15 1,000 1.5 1.7 20 2 400 60

The Empty Calories of Sugar table 4-9

Energy (cal)

Calcium (m

Iron (m g)

M agnesium

(m g)

Potassium (m

Protein (g)

Fiber (g)

Zinc (m g)

Vitam in A (�g)

Thiam in (m

Ribofl avin (m g)

Niacin (m g)

Vitam in B

6 (m g)

Folate (�g)

Vitam in C (m

141I f I F e e l D i z z y B e t w e e n M e a l s , D o I H a v e H y p o g l y c e m i a ?

Analyze Your Carbohydrate Intake The purpose of this chapter’s exercise is to help you examine the carbohydrate- rich foods in your diet, compare your intakes with recommendations, and help you to obtain the recommended amounts of soluble and insoluble fi ber.

In the DA1. � program, select the Reports tab then select Macronutri- ent Ranges. Using your three-day diet records, choose Day Two and choose all meals. Generate a report. Did your intake meet the recommen- dation to consume between 45 per- cent and 65 percent of total energy calories as carbohydrate?

Determine the distribution of car-2. bohydrate among the day’s foods.

Select Reports, then Source Analy- sis, and then Carbohydrate from the drop-down box. Generate a separate report for each meal: breakfast, lunch, and dinner. At which meal did you consume the most carbohy- drate? Which foods were the great- est contributors?

Did your fi ber intake fall within the 3. recommended range of intake (25–35 grams)? From the Reports tab select Intake vs. Goals. Choose Day One, all meals, and generate a report. Did you meet your fi ber needs?

From Reports, select Source Analy-4. sis. Using Day Three, choose all meals and generate a report. Which foods provided the greatest amounts

of fi ber for the day’s intake? If you are short on fi ber, look at Figure 4-4 (page 114), Figure 4-5 (page 115), and Figure 4-16 (page 137) which suggests fi ber-rich foods to increase your intake of both soluble and insoluble fi bers.

Whole grains provide more than just 5. fi ber. From the Track Diet tab, create a new day (do not alter your three- day record). Enter two food items as a snack: 2.5 cups of Fruit Loops cereal and .5 cup granola (these are equal in calories). Select Reports, Source Analysis, and mineral mag- nesium from the drop-down box. Generate a report for the new snack. Which was the better magnesium source?

Concepts in Action

Learn more about topics like lactose intolerance, tooth decay, diabetes, and artifi cial sweeteners at www.healthfi nder.gov.

Search for “sugars” and “fi ber” at the International Food Infor- mation Council site: www.foodinsight.org.

Search the American Diabetes Association website for informa- tion about diabetes, including research, prevention, and living with diabetes: www.diabetes.org.

Learn more about dental health by searching A-Z Public Topics at www.ada.org.

media menu

Answers to these Self Check questions are in Appendix G.

The dietary monosaccharides include:1.

sucrose, glucose, and lactoseA.

fructose, glucose, and galactoseB.

galactose, maltose, and glucoseC.

glycogen, starch, and fi berD.

The polysaccharide that helps form the supporting struc-2. tures of plants is:

celluloseA.

maltoseB.

glycogenC.

sucroseD.

self check

http://www.cengage.com/sso

http://www.healthfi

http://www.foodinsight.org

http://www.diabetes.org

http://www.ada.org

14 2 chapter 4 C a r b o h y d r a t e s

Digestible carbohydrates are absorbed as _________ 3. through the small intestinal wall and are delivered to the liver, where they are converted to ________.

disaccharides; sucroseA.

glucose; glycogenB.

monosaccharides; glucoseC.

galactose; celluloseD.

When blood glucose concentration rises, the pancreas 4. secretes _______, and when blood glucose levels fall, the pancreas secretes ________.

glycogen; insulinA.

insulin; glucagonB.

glucagon; glycogenC.

insulin; fructoseD.

When the body uses fat for fuel without the help of carbohy-5. drate, this results in the production of _______ .

ketone bodiesA.

glucoseB.

starchC.

galactoseD.

Foods rich in soluble fi ber lower blood cholesterol.6. T F

Type 1 diabetes is most often controlled by successful 7. weight-loss management. T F

Around the world, most people are lactose intolerant.8. T F

By law, enriched white bread must equal whole-grain bread 9. in nutrient content. T F

The fi ber-rich portion of the wheat kernel is the bran layer.10. T F

143controversy 4 A r e C a r b o h y d r a t e s “ B a d ” f o r H e a l t h ?

CONTROVERSY 44 Are Carbohydrates “Bad” for Health?

LO 4.10

Lately, dietary carbohydrates have been the target of some serious accusations. Popular writers proclaim, sometimes persuasively, that juicy apples, baked potatoes, warm muffi ns, blueberry pancakes, freshly baked bread, tasty rice or pasta dishes, and other carbohydrate- rich foods are “bad” for health.1* In the scientifi c realm, researchers have been investigating carbohydrates for potential roles in obesity and heart disease.2 Meanwhile, the current Dietary Guidelines for Americans urge people to consume a variety of carbohydrate-rich whole grains, legumes, fruits, vegetables, and milk to support good health. Who’s right?

This Controversy investigates some of the accusations launched against carbohydrate-rich foods by the popular media. It also demonstrates how authen- tic nutrition researchers pursue answers to questions, step-by-step, via scientifi c inquiry.

ACCUSATION 1: CARBOHYDRATES ARE MAKING US FAT Over the past several decades, people in the United States have grown dramati- cally fatter (Figure C4-1).3 At the same time, their carbohydrate intakes have increased. Does that mean, as some popular writers claim, that carbohydrate- rich foods cause obesity? To examine this conclusion, investigators may begin by looking at national nutrient and energy intake data.

Carbohydrate Intake and Calorie Trends Figure C4-2 presents a summary of energy nutrient intake data over the past three decades. It demonstrates that the percentage of calories from carbohy- drates in the U.S. diet increased from 42 percent in the 1970s to 49 percent today.4 During the same period, the per- centage of calories from fat dropped from 41 percent to 34 percent. The percentage of protein intake stayed about the same.

While percentages among energy nutrients in the U.S. diet shifted some- what, a more signifi cant trend was also taking place: People were consuming many more total calories each day.5 Figure C4-2 shows that since the 1970s, the average food energy intake has

*Reference notes are found in Appendix F.

Years

1976–1980 1988–1994 1999–2000’s 125

150

175

200

B od

y w

ei gh

t ( lb

)

Men

Women

Increases in Adult

Body Weight

over Time

figure C4-1

Carbohydrate

1977–1978 1994–1996

D ai

ly in

ta ke

( %

c al

/d ay

)

1987–1988 2005–2006

Fat Protein

Percentages of Calories from Energy Nutrients,

United States, 1977–2006

figure C4-2

The total daily calories in the U.S. diet are divided into three columns for each time period to reveal the relative contributions of carbohydrate, fat, and protein.

14 4 chapter 4 C a r b o h y d r a t e s

few months of dieting, but the difference disappears over time.10 Chapter 9 pro- vides details, but the punch line seems to be that, over time, people lose about the same amount of weight on any kind of low-calorie diet.11 Weight-loss success refl ects the degree of adherence to a calorie-restricted diet, and not the pro- portion of energy nutrients in that diet.

ACCUSATION 2: CARBOHYDRATES CAUSE DIABETES Diabetes impairs blood glucose regula- tion following a carbohydrate-containing meal. At one time, people thought that eating carbohydrate caused diabetes by “overstraining the pancreas,” but now we know that this is not the case. Body fatness is more closely related to diabetes than diet composition is; high rates of diabetes have not been reported in societies where obesity is rare.

Refi ned Carbohydrates and Diabetes In some people, however, intakes of certain forms of carbohydrates accom- pany diabetes development. Particularly among certain Native Americans, a profound increase in the prevalence of diabetes is observed when refi ned fl our and sugars replace whole foods of tra- ditional diets. In addition, evidence from two studies of over 160,000 U.S. women reports an increased diabetes risk in those who drink one or more sugar- sweetened soft drinks each day com- pared with women consuming less than one per month.12 Other studies report no link between sugar intake and metabolic markers of diabetes when calorie intakes do not exceed calorie needs, however.

Glycemic Load and Diabetes Over a decade ago, a study tracking the dietary habits of over 100,000 men and women revealed a positive cor- relation between diabetes and eating a diet with a high glycemic load based on mashed potatoes, white rice, highly refi ned cold breakfast cereals, and white bread. However, a subsequent study of this nature did not support this fi nding. No effect on diabetes risk from such a diet was detected in almost 36,000

root-consuming peoples eating tradi- tional diets most often stay lean even though most of their daily calories derive from carbohydrate. Also, as people in such societies abandon their traditional diets in favor of “Western” style high-fat, high-protein, and high-calorie foods, obesity and chronic disease rates soar. Obesity rates in China, for example, are quickly approaching those of the West.9 In 1985, less than 2 percent of China’s schoolchildren were overweight; by the year 2002, the number was about 17 percent for boys and 10 percent for girls. During the same period, intakes of animal protein jumped from 8 to 25 per- cent of total calories and fat intakes soared as well.

Finally, the fi rst law of thermodynam- ics comes into play.† Energy (calories) cannot collect as body fat unless it arrives from outside the body—that is, from the diet. Metabolic processes can- not manufacture extra calories from a given amount of food, regardless of how plausible a popular writer may make the idea sound.

Carbohydrates and Weight Loss Of interest to many people is whether eating a low-carbohydrate weight-loss diet might produce faster or greater weight loss than other diets. It is clear from research that people following low- carbohydrate diets do lose weight, and may even lose a little extra during the fi rst

increased by at least 300 calories per day, with other estimates as high as 500 calories per day.6 Another factor was also in play: most people were not active enough to use up those extra calories— physical activity levels declined.7 Not surprisingly, the average body weight for adults over these decades increased by about 20 pounds (see Figure C4-3).

Carbohydrates or Calories? Intriguingly, carbohydrates provided almost all of the national calorie increase in recent decades. This fact has led to speculation that something about dietary carbohydrate itself, and not the calories it provides, may be to blame for people’s weight gain. Plausible-sounding meta- bolic explanations for a special “fatten- ing power” of carbohydrates have been offered by the popular media.

In the realm of science, epidemiologi- cal studies report an inverse relationship between carbohydrate intake and body weight.8 That is, people with higher car- bohydrate intakes may have lower body weights. Some of this association, but not all, may be explained by dietary fi ber intake, which follows whole food sources of carbohydrate into the diet. Whole food diets favor a healthy body weight.

If carbohydrate itself caused over- weight, then people around the world consuming traditional high-carbohydrate rice- or root-based diets, such as the Japanese, Chinese, or many Africans, should have high rates of obesity, dia- betes, and heart disease. The reverse is generally true: the world’s grain- and

2500

2000

1500

1000 1977–1978 1987–1988

E ne

rg y

(c al

/d ay

)

1994–1996 2005–2006

Daily Energy Intake over Time figure C4-3

†The fi rst law of thermodynamics states that energy cannot be created or destroyed.

145controversy 4 A r e C a r b o h y d r a t e s “ B a d ” f o r H e a l t h ?

related diseases rise, too. Before con- cluding that sugars must cause health problems, however, scientists also look exhaustively for other potential causes occurring simultaneously. For example, newly wealthy peoples do buy and eat more sweets but, as in the China example described earlier, they also choose more fats (particularly oils for frying), animal pro- teins, fast foods, and refi ned processed

enough, on average, to provide every man, woman, and child with more than 140 pounds of added sugars per year.14 Figure C4-4 depicts the dramatic upward trend in available added sugars in the U.S. diet and offers the USDA sug- gested upper intake limits for added sugars for comparison.15 Note that the columns in the fi gure represent sugars in the food supply and do not account for waste, such as the syrup drained from sweet pickles or jam that molds and is tossed out. They also do not account for sweetened imported food products, a fast-growing source of added sugars in the United States.16 The great majority of these sugars in U.S. foods and bever- ages are added by manufacturers before consumers purchase them. Most people add little sugar from the sugar bowl at home, so they remain unaware of how much sugar they take in each year.

Added Sugars and Diseases Data from the world’s developing nations seem to clinch the case against added sugars: as a population’s income rises, consumption of added sugars increases, and the rates of obesity, diabetes, and

women. What this study did uncover was a lower incidence of type 2 diabetes and cardiovascular disease in those consum- ing greater amounts of whole grains and other whole foods, a fi nding that has been repeated many times.13

In summary, whenever whole foods provide most of the carbohydrate in a diet of moderate calories, diabetes is rare. Such evidence does not prove that refi ned carbohydrates cause diabetes or that whole foods prevent it, however. The apparent protective effect of whole foods might be due to factors other than carbohydrates, such as fi ber, other nutrients, or the phytochemicals of whole grains, fruits, and vegetables. In addition, people who tend to their diets by choos- ing whole grains probably make other healthy choices, such as being physi- cally active, too. Still, refi ned carbohy- drates easily provide excess calories that contribute to body fat stores, and type 2 diabetes risk rises in direct proportion to body fatness.

ACCUSATION 3: ADDED SUGARS CAUSE OBESITY AND ILLNESS Many vocal carbohydrate opponents point out, rightly, that added sugars (and refi ned grains) are relatively new in the diet of humankind. Then they conclude that these foods must therefore be responsible for the current high rates of obesity and chronic illnesses. Indeed, many carbohydrate-rich foods that people eat today bear little resemblance to the seeds, grains, fruits, and roots that provided almost all of the carbo- hydrate in the early human diet. Today, softer, whiter, and sweeter carbohydrate sources predominate.

Trends in Added Sugars In past centuries, the only concentrated sweetener was honey, a rare addition to the diet. Today, each person in the United States uses up almost three- quarters of a cup (31 teaspoons) of refi ned sugars added to their foods and beverages each day.‡ This amount is

D a ily

t e a s p

o o n s o

f s u g

a rs

1890 1970 1980

Suggested upper limit (men)a

1990 Today

Suggested upper limit (women)a

Added Sugars: Average U.S. Supply per

Person Compared with USDA Prudent

Upper Intake Limits

figure C4-4

aThese USDA suggested upper limits for added sugars refl ect one-half of the average discretionary calorie allow- ance for sedentary men aged 19–30 consuming 2,400 cal/day and sedentary women aged 19–30 consuming 2,000 cal/day. For other people, see Appendix E. The American Heart Association sets a prudent upper limit of 6 tsp of sugar for most women, and 9 tsp for most men.

Sources: USDA Food Guide; R. K. Johnson and coauthors, Dietary sugars intake and cardiovascular health: A Scientifi c Statement from the American Heart Association, Circulation 120 (2009): 1011–1020.

Most people remain unaware of how much added sugar they take in each year.

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‡This estimate from the USDA Economic Research Service includes all caloric sweeteners in the U.S. human food supply, including cane and beet sugars, corn sweeteners, honey, and syrups.

146 chapter 4 C a r b o h y d r a t e s

regulating hormones toward appetite suppression.27 Recall from Chapter 4 that glucose from food stimulates the release of insulin from the pancreas. Fructose, in contrast, does not trigger the release of insulin.28 (Appetite regulation is described in Chapter 9.) Because fructose ingestion fails to stimulate insu- lin release, fructose does not suppress the appetite through this mechanism as glucose does.29 Rats given a solution of glucose, fructose, or sucrose all gain body fatness, but the rats receiving fruc- tose gain the most.30 Theoretically, then, chronic fructose consumption could lead to greater food intakes, which could contribute to the nation’s obesity prob- lem. Although this idea seems plausible, one fl aw exists: hardly anyone eats pure fructose. They eat sucrose or HFCS and both of these sugars contain suffi cient glucose to stimulate the release of insulin and reduce the appetite accordingly.

Researchers tested the fructose-weight gain theory on monkeys. 31 They fed one group large amounts of pure fructose, while another group received glucose. Some changes in energy balance were observed at several points over the course of the study, but at the end of one year body weights of fructose- and glucose- fed monkeys did not differ. Fructose did not cause excess weight gain, even when monkeys consumed almost half of their daily calories from fructose.

Finally, when overweight or obese human subjects consumed large, equally caloric amounts of fructose or glucose with their regular diets, both sugars caused about the same degree of weight gain.32 An important difference in the nature of these gains was evident, however. The fructose group gained more of their fat in the abdominal area, and abdominal body fatness elevates the risks of diabetes and heart disease to a greater degree than fat stored elsewhere in the body. While scientifi cally interest- ing, these results cannot be applied to the entire U.S. population, many of whom are not obese.

Delicious, Economical, Easily Consumed Calories All kinds of sugary foods and beverages taste delicious, cost little money, and are constantly available. These factors make

remains stable in acidic foods and • beverages. Sucrose breaks down in acid.

The decision to sweeten foods with HFCS makes good business sense.

HFCS and Obesity One question of concern is whether indi- viduals who consume large amounts of HFCS, usually in the form of sugary bever- ages, weigh more than people who con- sume less. Overall, fi ndings indicate that people in the United States who consume the most HFCS from sugary sodas, fruit punches, and other sugary beverages do weigh more than people who consume less, and they take in more total calo- ries, too.22 When results of many such studies are compiled, the data confi rm these fi ndings—HFCS consumption and obesity often occur together.23 This cor- relation does not prove that HFCS causes obesity, however. Scientists must also fi nd plausible biological mechanisms through which HFCS might have an effect.

Liquid Sugar and Calorie Control Several such mechanisms involve the body’s appetite control system. The fi rst suggests that the body cannot detect calories of liquid sugars and so does not compensate for them with reduced calorie intakes at later meals.24 To test this idea, some subjects were given jelly beans (solid sugar) before a meal. Later, at mealtime, they ate fewer calories of food—they seemed to compensate for the calories in the earlier jelly bean snack. When researchers substituted liquid sugar as soft drinks for the jelly beans, subjects did not compensate for the calo- ries in the liquid snack—they ate the full meal later on. Later research, however, did not support this fi nding. No difference was reported between food intake follow- ing liquid or solid sugar snacks—both suppressed subsequent food intake.25 It appears that, regardless of its form, sugar before mealtimes spoils the appetite.

Fructose and Appetite Regulation A second idea suggests that fructose may impair appetite regulation, pos- sibly by way of insulin or other appetite- regulating signals.26 Release of insulin causes a shift in the body’s appetite-

foods, all at newly affordable prices.17 And as they increase their calorie intake, they decrease their physical activity. To say that one of these factors alone—in this case, sugar intake—is causing the world’s problems would be naïve. Still, added sugars provide more and more energy to the human diet, so their relation- ships with health are worth exploring.

ACCUSATION 4: HIGH- FRUCTOSE CORN SYRUP HARMS HEALTH In 2004, scientists noted that as high- fructose corn syrup (HFCS) replaced sucrose in many foods and beverages, unprecedented U.S. gains in body fatness were burdening the nation’s health.18 Since then, investigators have been test- ing theories concerning potential roles for HFCS in obesity and disease causation.19 Their results quickly made the news and became popular topics for writers and speakers. With repetition, the villainy of fructose was exaggerated to the point that consumers adopted unproven hypothe- ses as common knowledge. Today, some food manufacturers are replacing HFCS with the more familiar sucrose to boost consumer acceptance of their products. Meanwhile, scientists continue to me- thodically test their ideas, one-by-one, to reveal the effects of HFCS on the body.

The Nature of High-Fructose Corn Syrup HFCS sweetens sugary soft drinks, fruit drinks, candies, salad dressings, breads, other baked goods, canned foods, and other sweetened foods. Its sweetening power is similar to that of sucrose, and it contributes about half of the added sugars in the U.S. food supply.20 Food manufacturers choose HFCS in place of sucrose for several reasons.21 Among them, HFCS:

is cheaper. The price is stable.•

derives from a reliable, plentiful U.S. • crop—corn. Sucrose prices and supplies are affected by political and weather conditions in other cane- growing countries.

is a ready-to-use liquid. Dry sucrose • often must be dissolved in liquid before use.

147controversy 4 A r e C a r b o h y d r a t e s “ B a d ” f o r H e a l t h ?

not exceed the body’s energy need.39 The studies in which sugars produce weight gain invariably add sugars to an already calorie-rich diet. Added prudent amounts of sugars may be enjoyed as part of the discretionary calories in a nu- tritious diet with virtually no risk to health.

ACCUSATION 5: BLOOD INSULIN IS TO BLAME If HFCS cannot be blamed for obesity and disease, perhaps other carbo- hydrates are the villains. Starch, for example, comprised almost entirely of glucose, has been blamed for obe- sity and illness because it causes the release of insulin into the bloodstream. Among its many roles, insulin facilitates the transport of glucose into the cells, the storage of fatty acids as body fat, and the synthesis of cholesterol. When insulin is present, the body tends to store energy nutrients rather than using them up.40 Overweight people commonly suf- fer from insulin resistance—they release excess insulin. Does insulin therefore cause their obesity and can a low- glycemic diet reverse it, as some diet books claim?

Claims Made About Insulin Because insulin promotes storage of body fat, popular writers often assume

Consumers often believe these ideas because they don’t know that foods such as fruits, vegetables, honey, sucrose, and even HFCS provide fructose in about a 50:50 mixture with glucose. The metabolic effects of such mixtures differ substantially from those of the 100 percent fructose compound reported in research (see Figure C4-5). When researchers test HFCS and sucrose against each other, they report virtually identical metabolic effects from these two sweeteners.37 This is expected, given their similar chemical makeup.

In a notable exception, however, hu- man subjects were fed one of the follow- ing: a solution of 100 percent fructose, a 50:50 glucose-to-fructose mixture, HFCS (also about an equal mixture of glucose and fructose), and 100 percent glucose solution. Based on previous results, the researchers expected that fructose would elicit the greatest blood lipid response and glucose the smallest, with other mix- tures falling in between. Curiously, blood lipids rose similarly for all subjects except those receiving 100 percent glucose.38 This evidence warrants further study to clarify the health implications of consum- ing sugars with a similar makeup.

Conclusions of Experts In the end, not even fructose can make a person fat when food energy intake does

overconsumption likely. Also the liquid HFCS of fruit punches and soft drinks is easy to consume quickly—no chew- ing required. Few people realize that a typical 16-ounce carbonated soft drink can easily deliver 200 calories, and soda drinkers often drink several at a sitting.

It may be tempting, then, to close the book on HFCS as just another calorie source. One other link between HFCS and obesity has held researchers’ atten- tion, however. It concerns subtle shifts in lipid metabolism when body tissues encounter fructose.

Effects of Fructose on Lipid Metabolism When laboratory animals are fed puri- fi ed fructose, their metabolism shifts toward fat-making and fat-conserving pathways.33 The same effect is observed in people who consume large amounts (about a third of daily calories) of purifi ed fructose.34 Fructose intake causes fats to accumulate in the blood and liver. Instead of being used immediately for energy, the fructose is readily converted into triglycerides by the liver, the form of fat stored by adipose tissue. High fructose intakes may not be necessary to bring on this effect, however: add- ing a single HFCS-sweetened soft drink at each meal for 10 weeks signifi cantly increases blood triglycerides.35

Nutrition scientists conclude that a diet high in fructose could set into motion metabolic activities leading to excess body fatness and a buildup of blood lipids associated with heart disease.36 In addition, study subjects given fructose had higher concentrations of blood insu- lin but lower tissue insulin sensitivity, two conditions associated with prediabetes.

Fructose in Foods and HFCS On hearing these results about fructose and lipid metabolism, diet book writ- ers and others often conclude that the obvious way to avoid and cure obesity, diabetes, or heart disease is to eliminate fructose from the diet. They single out HFCS (after all, its name even says “fruc- tose”) as an obesity-causing sugar. They urge their readers to avoid the fructose of sucrose and even the natural fructose of fruits and vegetables to avoid the effects of fructose seen in laboratories.

Sucrose

Corn syrup (regular type)

High-fructose

corn syrupa

Fructose Glucose Other sugars

Honey

0% 20% 40%30% 50%10% 60% 80% 100%90%70%

S w

ee te

ne r

Glucose and Fructose in Common Added Sugars figure C4-5

aA typical mixture. Corn syrup purchased for use at home, for example in a pecan pie recipe, is not high-fructose corn syrup; it consists almost entirely of glucose.

Source: Data from J. S. White, Straight talk about high-fructose corn syrup: What it is and what it ain’t, American Journal of Clinical Nutrition 88 (2008): 1716S–1721S.

148 chapter 4 C a r b o h y d r a t e s

might be easily solved by removing an ingredient, HFCS, from the food supply is inviting, but research shows this to be a false hope.44 Today’s larger calorie intakes alone are more than suffi cient to explain why people are fatter today than in the past.45 From the nutritionist’s point of view, fad diets that advise people to avoid sugars provided by fruits and vege- tables should be ignored. As you will see in later chapters, research overwhelm- ingly supports consuming 5 to 9 servings of these health-promoting foods.

Enjoying the pleasure of sweets within the discretionary calorie limit is possible in the context of a nutritious diet.46 How- ever, people who consume many empty calories of daily sugary soft drinks, punches, and other sources of added sugars would do well to replace some of them with water, nonfat milk, vegetable juices, or artifi cially sweetened bever- ages and whole foods that are naturally sweet. (Controversies often arise around the use of artifi cial sweeteners, and Chapter 12 presents the facts.)

Do scientists rule insulin to be innocent in causing weight gain, then? Perhaps not entirely. Individual differences in insulin’s metabolism may affect how effi ciently a person stores food energy. In a 6-year study, people who released normal amounts of insulin following either a high- carbohydrate diet or a low-carbohydrate diet gained about the same amount of weight.42 But those with insulin resistance gained more weight, especially when they ate a high-carbohydrate diet.

Although insulin disturbances may trigger weight gain, this scientifi c truth remains: insulin can only assist in the storage of body fat when calories taken in are in excess of need. In all people, weight gain can occur only when the food energy they take in exceeds the energy they use up each day.43

CONCLUSION Investigation into the potential health effects of carbohydrates is ongoing. The idea that the nation’s obesity problem

that insulin must therefore cause excess body fatness and obesity. They argue that to avoid gains of body fat, people needn’t bother controlling discretionary calories or exercising but should simply eat meats, eggs, cheese, salads, and other nonstarchy vegetables and avoid carbohydrates to avoid stimulating the release of insulin. Alternatively, they rec- ommend choosing foods that trigger a reduced insulin response—foods low on the glycemic index scale. Logically, then, less insulin should lead to less storage of body fat, and less body fatness means less type 2 diabetes and a lower risk of heart disease. Keep in mind, however, that logic is not science.

What Nutrition Experts Say About Insulin When scientists speak on these issues, they agree on this point: insulin regulates carbohydrate and fat storage in the body. However, they disagree that insulin, and not excess calories, causes accumula- tion of excess body fat.41

55 The Lipids: Fats, Oils, Phospholipids, and Sterols

do you ever . . . Think of fats as unhealthy food • constituents that are best eliminated from the diet?

Wonder about the differences • between “bad” and “good” cholesterol?

Choose fi sh for health’s sake without • fully knowing why?

Recognize invisible fats in your • foods?

Keep reading . . .

LO 5.1 Discuss the reasons why a moderate intake of lipids is an essential part of a healthy diet.

LO 5.2 Compare and contrast the physical properties and the sources of saturated, polyunsaturated, and monounsaturated fats.

LO 5.3 Describe how and where dietary lipids are broken down and absorbed during digestion and how they are transported throughout the body.

LO 5.4 Describe the signifi cance of the blood tests for HDL and LDL cholesterol.

LO 5.5 Describe the roles of omega-3 and omega-6 fatty acids in the body, and discuss which may be too low in some people’s diets and how they can increase their intakes.

LO 5.6 Justify the recommendation to eat fatty fi sh instead of relying on fi sh oil supplements, and discuss safety issues surrounding both choices.

LO 5.7 Describe the formation and structure of a trans-fatty acid, and state ways in which consumers may reduce their intakes.

LO 5.8 Develop a diet plan that provides enough of the right kinds of fats within calorie limits.

LO 5.9 Discuss evidence for the benefi ts and drawbacks of specifi c dietary fats in terms of their potential effects on human health.

Rebecca Bradley/Getty Images

150 chapter 5 T h e L i p i d s

Y our bill from a medical laboratory reads “Blood lipid profi le—$250.” A health- care provider reports, “Your blood cholesterol is high.” Your physician advises,

“You must cut down on the saturated fats in your diet and replace them with oils to lower your risk of cardiovascular disease (CVD).” Blood lipids, cholesterol, satu- rated fats, and oils—what are they, and how do they relate to health?

No doubt you are expecting to hear that fat-related compounds have the potential to harm your health, but lipids are also valuable. In fact, lipids are absolutely neces- sary. Th e diet recommended for health is moderate in fats, but it is by no means a “no-fat” diet. Luckily, at least traces of fats and oils are present in almost all foods, so you needn’t make an eff ort to eat any extra so long as your diet is balanced among nutritious foods.

LO 5.1

Introducing the Lipids Th e lipids in foods and in the human body fall into three classes. About 95 percent are triglycerides. Th e other classes of the lipid family are the phospholipids (of which lecithin is one) and the sterols (cholesterol is the best known of these). Some of these names may sound unfamiliar, but most people will recognize at least a few functions of lipids in the body and in food that are listed in Table 5-1. More details on each of the lipid classes follow later.

Usefulness of Fats in the Body When people speak of fat, they are usually talking about triglycerides. Th e term fat is more familiar, though, and we will use it in this discussion. Fat is the body’s chief storage form for the energy from food eaten in excess of need. Th e storage of fat is a valuable survival mechanism for people who live a feast-or-famine existence: stored during times of plenty, fat enables them to remain alive during times of famine. Fat also provides most of the energy needed to perform much of the body’s work, especially muscular work.

Most body cells can store only limited fat, but some cells are specialized for fat storage. Th ese fat cells seem able to expand almost indefi nitely—the more fat they store, the larger they grow. An obese person’s fat cells may be many times the size of a thin person’s. Far from being a collection of inert sacks of fat, however, adipose (fat) tissue secretes hormones that help to regulate appetite and infl uence other body functions in ways critical to good health.1* A fat cell is shown in Figure 5-1.

Fats in the Body Fats in Food

Energy stores• Fats are the body’s chief form of stored energy. Muscle fuel• Fats provide most of the energy to fuel muscular work. Emergency reserve• Fats serve as an emergency fuel supply in times of illness and diminished food intake. Padding• Fats protect the internal organs from shock through fat pads inside the body cavity. Insulation• Fats insulate against temperature extremes through a fat layer under the skin. Cell membranes• Fats form the major material of cell membranes. Raw materials• Fats are converted to other compounds, such as hormones, bile, and vitamin D, as needed.

Nutrient• Fats provide essential fatty acids. Energy• Fats provide a concentrated energy source in foods. Transport• Fats carry fat-soluble vitamins A, D, E, and K along with some phytochemicals and assist in their absorption. Raw materials• Fats provide raw material for making needed products. Sensory appeal• Fats contribute to the taste and smell of foods.• Appetite• Fats stimulate the appetite. Satiety• Fats contribute to feelings of fullness. Texture• Fats help make foods tender.

The Usefulness of Fats table 5-1

*Reference notes are found in Appendix F.

lipid (LIP-id) a family of organic (carbon- containing) compounds soluble in organic sol- vents but not in water. Lipids include triglycer- ides (fats and oils), phospholipids, and sterols.

cholesterol (koh-LESS-ter-all) a member of the group of lipids known as sterols; a soft, waxy substance made in the body for a variety of purposes and also found in animal-derived foods.

fats lipids that are solid at room temperature (70°F or 21°C).

oils lipids that are liquid at room temperature (70°F or 21°C).

cardiovascular disease (CVD) dis- ease of the heart and blood vessels; disease of the arteries of the heart is called coronary heart disease (CHD). Also defi ned in Chapter 11.

triglycerides (try-GLISS-er-ides) one of the three main classes of dietary lipids and the chief form of fat in foods and in the human body. A triglyceride is made up of three units of fatty acids and one unit of glycerol (fatty acids and glycerol are defi ned later). Triglycerides are also called triacylglycerols.

phospholipids (FOSS-foh-LIP-ids) one of the three main classes of dietary lipids. These lipids are similar to triglycerides, but each has a phosphorus-containing acid in place of one of the fatty acids. Phospholipids are present in all cell membranes.

lecithin (LESS-ih-thin) a phospholipid man- ufactured by the liver and also found in many foods; a major constituent of cell membranes.

sterols (STEER-alls) one of the three main classes of dietary lipids. Sterols have a struc- ture similar to that of cholesterol.

151I n t r o d u c i n g t h e L i p i d s

You may be wondering why the carbohydrate glucose is not the body’s major form of stored energy. As mentioned in Chapter 4, glucose is stored in the form of glyco- gen. Because glycogen holds a great deal of water, it is quite bulky and heavy, and the body cannot store enough to provide energy for very long. Fats, however, pack tightly together without water and can store much more energy in a small space. Gram for gram, fats provide more than twice the energy of carbohydrate, making fat an effi cient storage form of energy. Th e body fat found on a normal-weight per- son contains more than enough energy to fuel an entire marathon run or to battle disease should the person become ill and stop eating for a while.

Fat serves many other purposes in the body, too. Pads of fat surrounding the vital internal organs serve as shock absorbers. Th anks to these fat pads, you can ride a horse or a motorcycle for many hours with no serious internal injuries. A fat blanket under the skin also insulates the body from extremes of temperature, thus assisting with internal climate control. Lipids also play critical roles in all of the body’s cells as part of their surrounding envelopes, the cell membranes.

Some essential nutrients are soluble in fat. Th ey are therefore found mainly in foods that contain fat and are absorbed most effi ciently from them. Th ese nutrients are the fat-soluble vitamins: A, D, E, and K. Other essential nutrients, the essential fatty acids, constitute parts of the fats themselves. As a later section explains, the essential fatty acids serve as raw materials from which the body makes molecules it requires. Fat also aids in the absorption of some phytochemicals, plant constituents believed to benefi t health.

Chapter 9 comes back to the hormones of • adipose tissue.

Muscle tissue

Fat tissue

Blood capillaries

Lipids enter from blood

Lipids exit to blood

Cell membrane

Fat cell

Nucleus

Within the fat cell, lipid is stored in a droplet. This droplet can greatly enlarge, and the fat cell membrane will expand to accommodate its swollen contents. More about fat tissue (also called adipose tissue) and body functions in Chapter 9.

A Fat Cell figure 5-1

Thanks to internal fat pads, vital organs are cush- ioned from shock.

M at

th ew

L ee

te /G

et ty

Im ag

essential fatty acids fatty acids that the body needs but cannot make in amounts suffi cient to meet physiological needs.

152 chapter 5 T h e L i p i d s

KE Y POINT Lipids not only serve as energy reserves but also cushion the vital organs, protect the body from temperature extremes, carry the fat-soluble nutrients and phytochemicals, serve as raw materials, and provide the major component of which cell membranes are made.

Usefulness of Fats in Food Th e energy density of fats makes fat-rich foods valuable in many situations. A gram of fat or oil delivers more than twice as many calories as a gram of carbohydrate or protein. A hunter or hiker must consume a large amount of food energy to travel long distances or to survive in intensely cold weather. An athlete must meet often enormous energy needs to avoid weight loss that could impair performance. As Fig- ure 5-2 demonstrates, for such a person fat-rich foods most effi ciently provide the needed energy in the smallest package. But for a person who is not expending much energy in physical work, those same high-fat foods may deliver many unneeded calories in only a few bites.

People naturally like high-fat foods. Fat carries with it many dissolved compounds that give foods enticing aromas and fl avors, such as the aroma of frying bacon or French fries. In fact, when a sick person refuses food, dietitians off er foods fl avored with some fat to tempt that person to eat again. Fat also lends tenderness to foods such as meats and baked goods. Around the world, as fats become less expensive and more available in a given food supply, people consistently choose fatty foods more often.

Fat also contributes to satiety, the satisfaction of feeling full after a meal. Th e fat of swallowed food triggers a series of physiological events that slow down the move- ment of food through the digestive tract and promote satiety.2 Even so, before the sensation of fullness stops them, people can easily overeat on fat-rich foods because the delicious taste of fat stimulates eating and each bite of a fat-rich food delivers many calories. Chapter 9 revisits the topic of appetite and its control.

KE Y POINT Lipids provide more energy per gram than carbohydrate and protein, enhance the aromas and fl avors of foods, and contribute to satiety, or a feeling of fullness, after a meal.

LO 5.2

A Close Look at Lipids Each class of lipids—triglycerides, phospholipids, and sterols—possesses unique characteristics. As mentioned, the term fat refers to triglycerides, the major form of lipid found in the body and in foods. Triglycerides, in turn, are made of fatty acids and glycerol.

Triglycerides: Fatty Acids and Glycerol Very few fatty acids are found free in the body or in foods; most are incorporated into large, complex compounds: triglycerides. Th e name almost explains itself: three fatty acids (tri) are attached to a molecule of glycerol to form a triglyceride molecule (Figure 5-3). Tissues all over the body can easily assemble triglycerides or disassemble them as needed.

Fatty acids can diff er from one another in two ways: in chain length and in de- gree of saturation (explained next). Triglycerides usually include mixtures of various fatty acids. Depending on which fatty acids are incorporated into a triglyceride, the resulting fat will be soft or hard. Triglycerides containing mostly the shorter-chain

CONCEPT LINK 5-1 Controversy 2 describes the current research on phytochemicals (page 61).

Carbohydrate-rich lunch 1 low-fat muffin 1 banana 2 oz carrot sticks 8 oz fruit yogurt

calories = 550 weight (g) = 500

Fat-rich lunch 6 butter-style crackers 11/2 oz American cheese 2 oz trail mix with candy

calories = 550 weight (g) = 115

Both lunches contain the same number of calories, but the fat-rich lunch takes up less space and weighs less.

Two Lunches figure 5-2

CONCEPT LINK 5-2 A reminder from Chapter 1:

1 g carbohydrate = 4 calories• 1 g fat = 9 calories• 1 g protein = 4 calories•

153A C l o s e L o o k a t L i p i d s

fatty acids or the more unsaturated ones are softer and melt more readily at lower temperatures.

Each species of animal (including people) makes its own characteristic kinds of tri glycerides, a function governed by genetics. Fats in the diet, though, can aff ect the types of triglycerides made because dietary fatty acids are often incorporated into triglycerides in the body. For example, many animals raised for food can be fed diets containing specifi c triglycerides to give the meat the types of fats that consumers demand.

KE Y POINT The body combines three fatty acids with one glycerol to make a triglyceride, its storage form of fat. Fatty acids in food infl uence the composition of fats in the body.

Saturated Versus Unsaturated Fatty Acids Saturation refers to whether or not a fatty acid chain is holding all of the hydrogen atoms it can hold. If every available bond from the carbons is holding a hydrogen, the chain forms a saturated fatty acid; it is fi lled to capacity with hydrogen. Th e zigzag structure on the left in Figure 5-4 represents a saturated fatty acid.

Saturation of Fatty Acids Sometimes, especially in the fatty acids of plants and fi sh, the chain has a place where hydrogens are missing: an “empty spot,” or point of unsaturation.† A fatty acid carbon chain that possesses one or more points of unsaturation is an unsaturated fatty acid. With one point of unsaturation, the fatty acid is a monounsaturated fatty acid (see the second structure in Figure 5-4). With two or more points of unsaturation, it is a polyunsaturated fatty acid, some- times abbreviated PUFA (see the third structure in Figure 5-4; other examples are given later in the chapter).

Melting Point and Fat Hardness Th e degree of saturation of the fatty acids in a fat aff ects the temperature at which the fat melts. Generally, the more unsaturated the fatty acids, the more liquid the fat is at room temperature. In contrast, the more saturated the fatty acids, the fi rmer the fat. Th us, looking at three fats—beef tallow

Small amounts of fat offer eaters both pleasure and needed nutrients.

ag e

S ou

rc e/

S up

er S

to ck

Glycerol

3 fatty acids of differing lengths

A triglyceride formed from 1 glycerol + 3 fatty acids

Glycerol, a small, water-soluble carbohydrate derivative, plus three fatty acids equals a triglyceride.

Triglyceride Formation figure 5-3

satiety (sat-EYE-uh-tee) the feeling of full- ness or satisfaction that people experience after meals.

fatty acids organic acids composed of carbon chains of various lengths. Each fatty acid has an acid end and hydrogens attached to all of the carbon atoms of the chain.

glycerol (GLISS-er-all) an organic compound, three carbons long, of interest here because it serves as the backbone for triglycerides.

saturated fatty acid a fatty acid carrying the maximum possible number of hydrogen atoms (having no points of unsaturation). A saturated fat is a triglyceride that contains three saturated fatty acids.

point of unsaturation a site in a mol- ecule where the bonding is such that additional hydrogen atoms can easily be attached.

unsaturated fatty acid a fatty acid that lacks some hydrogen atoms and has one or more points of unsaturation. An unsaturated fat is a triglyceride that contains one or more unsaturated fatty acids.

monounsaturated fatty acid a fatty acid containing one point of unsaturation.

polyunsaturated fatty acid (PUFA) a fatty acid with two or more points of unsaturation.

†These points of unsaturation can also be referred to as double bonds.

154 chapter 5 T h e L i p i d s

(a type of beef fat), chicken fat, and saffl ower oil—beef tallow is the most saturated and the hardest; chicken fat is less saturated and somewhat soft; and saffl ower oil, which is the most unsaturated, is a liquid at room temperature.

If a health-care provider recommends limiting saturated fats or trans fats and us- ing monounsaturated fats or polyunsaturated fats instead to protect your health, you can generally judge by the hardness of the fats which ones to choose. Figure 5-5 compares the percentages of saturated, monounsaturated, and polyunsaturated fatty acids in various fats and oils. To determine the degree of saturation of the fats in the oil you use, place it in a clear container in the refrigerator and watch for cloudiness. Th e least saturated oils remain clear. Olive oil, mostly monounsaturated fat, turns cloudy in the refrigerator while polyunsaturated vegetable oil stays clear. Olive oil is still excellent oil, however, from the standpoint of the health of the heart, as this chapter’s Controversy reveals.

Where the Fatty Acids Are Found Most vegetable and fi sh oils are rich in poly- unsaturated fatty acids; some vegetable oils, olive oil and canola oil in particular, are also rich in monounsaturated fatty acids; animal fats are generally the most satu- rated. But you have to know your oils—it is not enough to choose foods with labels claiming plant oils over those containing animal fats. Some nondairy whipped des- sert toppings use coconut oil in place of cream (butterfat). Coconut oil does come from a plant, but it disobeys the rule that plant oils are less saturated than animal fats; the fatty acids of coconut oil are more saturated than those of cream and may add to heart disease risk. Palm oil, a vegetable oil used in food processing, is also highly saturated and has been shown to elevate blood cholesterol. Likewise, short- enings, stick margarine, and commercially fried or baked products may claim to be “all vegetable fat,” but much of their fat may be of the harmful saturated or trans kind, as a later section makes clear.

When polyunsaturated fat replaces saturated fat and trans fat in the diet, the heart and blood lipids benefi t.3 Olive oil, rich in monounsaturated fatty acids and antioxi- dant phytochemicals, also benefi ts the heart when it replaces butter and other satu-

Fats melt at different temperatures: The more unsaturated a fat, the more liquid it is at room temperature. The more saturated a fat, the higher the temperature at which it melts.

ue st

P ho

to gr

ap hi

c, In

Did You Know? There are three types of fatty acids: saturated, monounsaturated, and polyunsaturated.

Point of unsaturation

Saturated Monounsaturated Polyunsaturated

Points of unsaturation

The more carbon atoms in a fatty acid, the longer it is. The more hydrogen atoms attached to those carbons, the more saturated the fatty acid is.

Three Types of Fatty Acids figure 5-4

Did You Know? Health-care providers recommend replacing saturated fats with the “UN” fats—polyUNsat- urated and monoUNsaturated—to benefi t the heart.

Trans• fats are the topic of a later section.

saturated fats triglycerides in which most of the fatty acids are saturated.

trans fats fats that contain any number of unusual fatty acids—trans-fatty acids—formed during processing.

monounsaturated fats triglycerides in which most of the fatty acids have one point of unsaturation (are monounsaturated).

polyunsaturated fats triglycerides in which most of the fatty acids have two or more points of unsaturation (are polyunsaturated).

155A C l o s e L o o k a t L i p i d s

rated fats in the diet, as it does in many traditional Mediterranean diets (see the Con- troversy section).4 If you are a woman, take note: these observations apply to you as well as to men. By far, more women suff er from heart disease than from breast cancer, and the old myth that heart disease is a “man’s disease” should be put to rest forever. In truth, heart disease kills more women in the United States than any other cause.

KE Y POINT Fatty acids are energy-rich carbon chains that can be saturated (fi lled with hydrogens) or monounsaturated (with one point of unsaturation) or polyunsaturated (with more than one point of unsaturation). The degree of saturation of the fatty acids in a fat determines the fat’s softness or hardness. Health- care providers recommend that both women and men consume unsaturated fats instead of saturated fats for heart health.

Phospholipids and Sterols Th us far we have dealt with the largest of the three classes of lipids—the triglyc- erides and their component fatty acids. Th e other two classes—phospholipids and sterols—play important structural and regulatory roles in the body.

Phospholipids A phospholipid, like a triglyceride, consists of a molecule of glycerol with fatty acids attached, but it contains two, rather than three, fatty acids. In place of the third is a molecule containing phosphorus, which makes the phospholipid

Walnut oil

Coconut oil

Butter

Beef tallow (beef fat)

Palm oil

Animal fats and the tropical oils of coconut and palm contain mostly saturated fatty acids.

Some vegetable oils, such as olive and canola, are rich in monounsaturated fatty acids.

Many vegetable oils are rich in omega-6 polyunsaturated fatty acids.a

Only a few oils provide significant omega-3 polyunsaturated fatty acids.a

Safflower oilb

Sunflower oil

Corn oil

Soybean oil

Cottonseed oil

Flaxseed oil

Fish oil c

Olive oil

Canola oil

Peanut oil

Lard (pork fat)

Chicken fat

Key:

Saturated fatty acids

Monounsaturated fatty acids

Polyunsaturated, omega-6 fatty acids a

Polyunsaturated, omega-3 fatty acids a

aThese families of polyunsaturated fatty acids are explained in a later section. bSalad or cooking type over 70% linoleic acid. cFish oil average values derived from USDA data for salmon, sardine, and herring oils.

Most fats are a mixture of saturated, monounsaturated, and polyunsaturated fatty acids.

Fatty Acid Composition of Common Food Fats figure 5-5

er. e.

yc- nd

156 chapter 5 T h e L i p i d s

soluble in water, while its fatty acids make it soluble in fat. Th is versatility permits any phospholipid to play a role in keeping fats dispersed in water—it can serve as an emulsifi er.

Food manufacturers blend fat with watery ingredients by way of emulsifi cation. Some salad dressings separate to form two layers—vinegar on the bottom, oil on the top. Other dressings, such as mayonnaise, are also made from vinegar and oil but never separate. Th e diff erence lies in a special ingredient of mayonnaise, the emulsi- fi er lecithin in egg yolks. Lecithin, a phospholipid, blends the vinegar with the oil to form the stable, spreadable mayonnaise. Health-promoting properties, such as the ability to lower blood cholesterol, are sometimes attributed to lecithin, but the peo- ple making the claims profi t from selling supplements. Lecithin supplements have no special ability to promote health—the body makes all of the lecithin it needs.

Phospholipids also play key roles in the body. Phospholipids bind together in a strong layer that forms the membranes of cells. Because phospholipids have both water-loving and fat-loving characteristics, they help fats travel back and forth across the lipid-containing membranes of cells into the watery fl uids on both sides. In addition, some phospholipids generate signals inside the cells in response to hor- mones, such as insulin, to help modulate body conditions.

Sterols Sterols such as cholesterol are large, complicated molecules consisting of interconnected rings of carbon atoms with side chains of carbon, hydrogen, and ox- ygen attached. Cholesterol serves as the raw material for making emulsifi ers in bile (see the next section for details), important to fat digestion. Other sterols include vitamin D, which is made from cholesterol, and the familiar steroid hormones, in- cluding the sex hormones.

Cholesterol is important in the structure of cell membranes and so is a part of every cell and necessary to the body’s functioning. Like lecithin, cholesterol can be made by the body, so it is not an essential nutrient. Cholesterol also forms the major part of the plaques that narrow the arteries in atherosclerosis, the underlying cause of heart attacks and strokes. Sterols other than cholesterol exist in plants. Th ese plant sterols resemble cholesterol in structure and can inhibit cholesterol absorption in the human digestive tract, thus lowering blood cholesterol levels.

KE Y POINT Phospholipids, including lecithin, play key roles in cell membranes; sterols play roles as part of bile, vitamin D, the sex hormones, and other important compounds. Plant sterols inhibit cholesterol absorption.

LO 5.3

Lipids in the Body From the moment they enter the body, lipids aff ect the body’s functioning and con- dition. Th ey also demand special handling, because fat separates from water and body fl uids consist largely of water.

Digestion and Absorption of Fats A bite of food in the mouth fi rst encounters the enzymes of saliva. An enzyme pro- duced by the tongue plays a major role in digesting milk fat in infants but is of little importance to digestion in adults.

Fat in the Stomach After being chewed and swallowed, the food travels to the stomach, where droplets of fat separate from the watery components and tend to fl oat as a layer on top. Even the stomach’s powerful churning cannot completely dis- perse the fat in the watery parts, so little fat digestion takes place in the stomach.

Fat in the Small Intestine As the stomach contents empty into the small intes- tine, the digestive system faces a problem: how to thoroughly mix fats, which are

Water

Oil

Without help from emulsifi ers, fats and water separate into layers.

at th

ew F

ar ru

gg io

emulsifi er a substance that mixes with both fat and water and permanently disperses the fat in the water, forming an emulsion.

emulsifi cation the process of mixing lipid with water by adding an emulsifi er.

bile an emulsifi er made by the liver from cholesterol and stored in the gallbladder. Bile does not digest fat as enzymes do but emulsi- fi es it so that enzymes in the watery fl uids may contact it and split the fatty acids from their glycerol for absorption.

157L i p i d s i n t h e B o d y

now separated, with its own watery fl uids. Th e solution is an emulsifi er: bile. Bile contains compounds made from cholesterol that work as emulsifi ers; one end of each molecule attracts and holds fat, while the other end is attracted to and held by water.

By the time fat enters the small intestine, the gallbladder, which stores the liver’s output of bile, has contracted and squirted its bile into the intestine. Bile mixes fat droplets with watery fl uid by emulsifying them (see Figure 5-6) and suspend- ing them in the fl uid until the fat-digesting enzymes contributed by the pancreas can split them into smaller molecules for absorption. To review: fi rst, the digestive system mixes fats with bile-containing digestive juices to emulsify the fats; then, fat-digesting enzymes can break the fats down.

People sometimes wonder how a person without a gallbladder can digest food. Th e gallbladder is just a storage organ. Without it, the liver still produces bile but delivers it into a duct which conducts it into the small intestine instead of into the gallbladder.

Fat Absorption Once the intestine’s contents are emulsifi ed, fat-splitting en- zymes act on triglycerides to split fatty acids from their glycerol backbones. Free fatty acids, phospholipids, and monoglycerides cling together in balls surrounded by bile emulsifi ers. At this point, the fats face another watery barrier, the watery layer of mucus that coats the absorptive lining of the digestive tract. Fats must traverse this layer to enter the cells of the digestive tract lining. Th e solution again depends on bile, this time in the balls of digested lipids. Th e bile shuttles the lipids across the watery mucus layer to the waiting absorptive cells of the intestinal villi. Th e cells then extract the lipids. Th e bile may be absorbed and reused by the body, or it may exit with the feces, as was shown in Figure 4-6 of Chapter 4.

Th e digestive tract absorbs triglycerides from a meal with remarkable effi ciency: up to 98 percent of fats consumed are absorbed. Very little fat is excreted by a healthy system. Th e process of fat digestion takes time, though, so the more fat taken in at a meal, the slower the digestive system action becomes. Th e effi cient series of events just described is depicted in Figure 5-7.

KE Y POINT In the stomach, fats separate from other food components. In the small intestine, bile emulsifi es the fats, enzymes digest them, and the intestinal cells absorb them.

CONCEPT LINK 5-3 Chapter 3 defined bile as a cholesterol- containing digestive fluid made by the liver, stored in the gallbladder, and released into the small intestine when needed (page 83).

In the stomach, the fat and watery digestive juices tend to separate. Enzymes are in the water and can’t get at the fat.

When fat enters the small intestine, the gallbladder secretes bile. Bile

After emulsification, more fat is exposed to the enzymes, and fat digestion proceeds efficiently.

Fat

Enzymes

Watery digestive juices

Fat

Bile compounds

Emulsified fat

Enzyme

Emulsified fat

compounds have an affinity for

both fat and water, so bile can

mix the fat into the water.

Detergents are emulsifi ers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dis- solved out of the spot and suspended in the water, where it can be rinsed away.

The Action of Bile in Fat Digestion figure 5-6

monoglycerides (mon-oh-GLISS-er-ides) products of the digestion of lipids; consist of glycerol molecules with one fatty acid attached (mono means “one”; glyceride means “a com- pound of glycerol”).

158 chapter 5 T h e L i p i d s

Transport of Fats Glycerol and shorter-chain fatty acids pass directly through the cells of the intesti- nal lining into the bloodstream where they travel unassisted to the liver. Th e larger lipids, however, present a problem for the body. As mentioned, fat fl oats in water. Without some mechanism to keep it dispersed, large lipid globules would sepa- rate out of the watery blood as it circulates around the body, disrupting the blood’s normal functions. Th e solution to this problem lies in an ingenious use of proteins: many fats travel from place to place in the watery blood as passengers in lipopro- teins, assembled packages of lipid and protein molecules.

Th e larger digested lipids, monoglycerides and long-chain fatty acids, must form lipoproteins before they can be released into the lymph in vessels that lead to the bloodstream. Inside the cells of the small intestine, they are re-formed into tri- glycerides and clustered together with proteins and phospholipids to form chylo- microns that can safely travel in the watery blood. Chylomicrons form one type of lipoproteins (shown in Figure 5-7); other types are discussed later with regard to their profound eff ects on health.

Digestive enzymes accomplish most fat digestion in the small intestine. There, bile emulsifies fat, making it available for enzyme action. The enzymes cleave triglycerides into free fatty acids, glycerol, and monoglycerides.

Capillary network

Chylomicrons

Lymph

Lymph to blood

Bloodstream

Blood vessels

Note: In this diagram, molecules of fatty acids are shown as large objects, but, in reality, molecules of fatty acids are too small to see even with a powerful microscope, while villi are visible to the naked eye.

Villi

In the small intestine:

At the intestinal lining:

In the large intestine:

Little fat digestion takes place.

In the mouth and stomach:

A small amount of cholesterol trapped in fiber exits with the feces

The parts are absorbed by intestinal villi. Glycerol and short-chain fatty acids enter directly into the bloodstream.

The cells of the intestinal lining convert large lipid fragments, such as monoglycerides and long-chain fatty acids, back into triglycerides and combine them with protein, forming chylomicrons (a type of lipoprotein) that travel in the lymph vessels to the bloodstream.

Liver Esophagus

Stomach

Small intestine

Large intestine (colon)

Pancreas

Animated! The Process of Lipid Digestion and Absorption

figure 5-7

lipoproteins (LYE-poh-PRO-teens, LIH- poh-PRO-teens) clusters of lipids associated with protein, which serve as transport vehicles for lipids in blood and lymph.

chylomicrons (KYE-low-MY-krons), lipoproteins formed when lipids from a meal are combined with carrier proteins in the cells of the intestinal lining. Chylomicrons transport food fats through the watery body fl uids to the liver and other tissues.

159S t o r i n g a n d U s i n g t h e B o d y ’ s F a t

KE Y POINT Glycerol and short-chain fatty acids travel in the bloodstream unassisted. Other lipids are incorporated into chylomicrons for transport in the lymph and blood. Fats need special transport vehicles—the lipoproteins—to carry them in watery body fl uids.

Storing and Using the Body’s Fat Methodically, the body conserves fat molecules not immediately required for en- ergy. Stored fat serves as a sort of “rainy day” fund to fuel the body’s activities at times when food is unavailable, when illness impairs the appetite, or when energy expenditures increase.

The Body’s Fat Stores Many triglycerides eaten in foods are transported by the chylomicrons to the fat depots—muscles, breasts, the external fat layer under the skin, the internal fat pads of the abdomen, and others—where they are stored by the body’s fat cells for later use. When a person’s body starts to run out of available fuel from food, it begins to retrieve this stored fat to use for energy. (It also draws on its stored glycogen, as the last chapter described.)

Th e body can also store excess carbohydrate as fat, but this conversion is not energy-effi cient. Figure 5-8 illustrates a simplifi ed series of conversion steps from carbohydrate to fat. Before excess glucose can be stored as fat, it must fi rst be broken into tiny fragments and then reassembled into fatty acids, steps that require energy to perform. Fat requires fewer chemical steps before storage.

What Happens When the Tissues Need Energy? Fat cells respond to the call for energy by dismantling stored fat molecules (triglycerides) and releasing fatty acids into the blood. Upon receiving these fatty acids, the energy-hungry cells break them down further into small fragments. Finally, each fat fragment is combined with a fragment derived from glucose, and the energy-releasing process continues, liberating energy, carbon dioxide, and water. Th e way to use more of the energy stored as body fat, then, is to create a greater demand for it in the tissues by decreas- ing intake of food energy, by increasing the body’s expenditure of energy, or both.

Carbohydrate in Fat Breakdown When fat is broken down to provide cellular energy, carbohydrate helps the process run most effi ciently. Without carbohydrate, products of incomplete fat breakdown (ketones) build up in the tissues and blood, and they spill out into the urine.

CONCEPT LINK 5-4 The body’s circulatory system and lymphatic system are described and depicted in Chapter 3, pages 71–74.

Glucose is broken down into fragments.

Energy

The fragments can provide immediate energy for the tissues.

Fatty acid

Or, if the tissues need no more energy, the fragments can be reassembled, not back to glucose but into fatty acid chains.

Glucose can be used for energy, or it can be changed into fat and stored.

Glucose to Fat figure 5-8

Chapter 9 discusses health risks of too • much abdominal fat.

Body fat supplies much of the fuel these muscles need to do their work.

ag e

S ou

rc e/

Ju pi

te r I

m ag

160 chapter 5 T h e L i p i d s

For weight-loss dieters who want to use their body fat for energy, knowing these details of energy metabolism is less important than remembering what research and common sense tell us: successful weight loss depends on taking in less energy than the body needs—not on the proportion of energy nutrients in the diet.5 For the body’s health, however, the proportions of certain lipids in the diet matter greatly, as the next section makes clear.

KE Y POINT When low on fuel, the body draws on its stored fat for energy. Carbohydrate is necessary for the complete breakdown of fat.

LO 5.4

Dietary Fat, Cholesterol, and Health High intakes of certain dietary fats are associated with serious diseases. So much research has focused on the links between diet and diseases that an entire chapter, Chapter 11, is devoted to presenting the details of these connections.

Heart and Artery Disease Th e person who chooses a diet too high in saturated fats or trans fats and too low in healthy oil from fi sh invites heart and artery disease (CVD), the number-one killer of adults in the United States and Canada.6 Satu- rated fatty acids and trans-fatty acids both worsen the blood lipid profi le; saturated fatty acids also contribute to blood clotting associated with heart attacks, while oils from fi sh oppose this action.7 Some have questioned whether trans fat made by

ruminant animals might be less harmful to consumers than the manufactured kind, but this idea has not gained support from research.8

Cancer As for cancer, a few studies link a diet high in saturated fats with greater-than-average risk of developing certain cancers.9 However, authori-

ties conclude that saturated fats pose the greatest public health hazard in terms of heart disease, not cancers.10

Obesity Obesity carries serious risks to health. A diet high in energy-rich fatty foods makes overconsumption of calories likely and encourages unneeded weight gain. Chapter 9 provides many details.

Recommendations for Lipid Intakes Some fat in the diet is essential for good health, but too much fat, especially satu- rated fat, increases the risks for chronic diseases. Guidelines aim to keep fat intakes within healthy limits.

A Healthy Range of Fat Intakes Defi ning an exact gram amount of fat, satu- rated fat, or cholesterol that begins to harm people’s health is not possible, so the DRI committee did not set Tolerable Upper Intake Levels for the lipids (see Table 5-2). Instead, the DRI and 2005 Dietary Guidelines set a range of 20 to 35 per- cent of daily energy from total fat and recommend that saturated fat, trans fat, and cholesterol be kept low. Keep in mind that even liquid oils contain some amount of saturated fat (look again at Figure 5-5 on page 155), so when total dietary fat exceeds 35 percent of calories, saturated fat automatically rises to levels associated with chronic diseases.

Today’s average fat intake as a percentage of calories is lower than it was 40 years ago: 34 percent of total daily calories now versus 45 percent then.11 At fi rst glance this appears to be a healthy trend—until grams of fat are inspected. Today, people eat more grams of fat, not less, but they also take in far more grams of carbohydrate than before. Th e shift in the energy nutrient balance toward carbohydrate produced

CONCEPT LINK 5-5 Chapter 4 described the need for carbohydrate in fat breakdown on page 126.

Metabolic interactions among energy • nutrients are of interest to people wanting to manage body weight; Chapter 9 describes them in more detail.

(C rat fat fr

Ob© Colour, 2011/Shutterstock.com

161D i e t a r y F a t , C h o l e s t e r o l , a n d H e a l t h

a misleading mathematical drop in the percentage of fat calories. Bottom line: be- fore fat recommendations in terms of percentages can be of benefi t, total calorie intakes must be brought under control.

In practical terms, for a 2000-calorie diet, 20 to 35 percent represents 400 to 700 calories from fat (roughly 45 to 75 grams, or about 9 to 19 teaspoons). Part of this fat allowance should provide the essential fatty acids linoleic acid and linolenic acid (these are described in a later section). DRI recommended intakes have been set for these two fatty acids, listed in Table 5-2. To supply these fatty acids, the USDA Food Guide of Chapter 2 recommends that people consume a small amount of raw vegetable oils daily. For saturated and trans fat, in contrast, the lower the better.

U.S. Fat and Saturated Fat Intakes According to surveys, people in the United States consume about 34 percent of their total energy from fat, a percentage within bounds. Saturated fat, however, contributes about 12 percent of calories, thus ex- ceeding the Dietary Guidelines limit of 10 percent.12

Some points about fats and heart health are presented next because they form the foundation of lipid intake recommendations. Th e lipoproteins take center stage, because they play important roles concerning the heart.

KE Y POINT Energy from fat should provide 20 to 35 percent of the total energy in the diet; intakes of saturated fat, trans fat, and cholesterol should be kept low.

Lipoproteins and Heart Disease Risk Recall that monoglycerides and long-chain fatty acids from digested food fat de- pend on chylomicrons, a type of lipoprotein, to transport them around the body.

Total fat1. a

Dietary Guidelines for Americans Keep total fat intake between 20 and 35% of calories from • mostly polyunsaturated and monounsaturated fat sources

such as fi sh, nuts, and vegetable oils.

Select and prepare foods that are lean, low-fat, or fat-free.• Dietary Reference Intakes

An acceptable range of fat intake is estimated at 20 to 35% • of total calories.

Saturated fat2. American Heart Association

Limit saturated fat to less than 7% of total energy.• Dietary Guidelines for Americans;b Dietary Reference Intakesc

Keep saturated fat intake low, less than 10% of calories, • within the context of an adequate diet.

Trans3. fat

Dietary Guidelines for Americans Keep • trans fat intake as low as possible.

American Heart Association Limit • trans fat to less than 1% of total energy.

Polyunsaturated fatty acids4. Dietary Reference Intakesc

Linoleic acid (5 to 10% of total calories):• 17 grams per day for young men.

12 grams per day for young women.

Linolenic acid (0.6 to 1.2% of total calories):• 1.6 grams per day for men.

1.1 grams per day for women.

Cholesterol5. American Heart Association, Dietary Guidelines for Americans, and World Health Organization

Limit cholesterol to less than 300 milligrams per day.• d

Dietary Reference Intakesc

Minimize cholesterol intake within the context of a healthy • diet.

aIncludes monounsaturated fatty acids. bThe Dietary Guidelines for Americans, 2005 use the term solid fats to describe sources of saturated fatty acids. Solid fats include milk fat, fats of high-fat meats and cheeses, hard margarines, butter, lard, and shortening. cFor DRI values set for various life stages, see the inside front cover. Linoleic and linolenic acids are defi ned later in this chapter. dPeople with heart disease should aim for less than 200 mg/day.

Lipid Intake Recommendations for Healthy People table 5-2

CONCEPT LINK 5-6 The USDA MyPyramid suggests calorie intakes for groups of people. They can be found in Table 2-2 on page 44.

The • Dietary Guidelines for Americans 2005 urge people to consume less than 10 percent of calories from saturated fatty acids within a healthy diet. Some examples:

1,600-calorie diet: 18 grams•

2,000-calorie diet: 20 grams•

2,200-calorie diet: 24 grams•

2,500-calorie diet: 25 grams•

2,800-calorie diet: 31 grams•

The American Heart Association Diet and • Lifestyle Recommendations are found in Chapter 11.

162 chapter 5 T h e L i p i d s

Chylomicrons and other lipoproteins are clusters of protein and phospholipids that act as emulsifi ers—they attract both water and fat to enable their large lipid pas- sengers to travel dispersed in the watery body fl uids. Th e tissues of the body can extract whatever fat they need from chylomicrons passing by in the bloodstream. Th e remnants are then picked up by the liver, which dismantles them and reuses their parts.

Major Lipoproteins: VLDL, LDL, HDL In addition to the chylomicrons, the body uses three other types of lipoproteins to carry fats:

Very-low-density lipoproteins (VLDL),• which carry triglycerides and other

lipids made in the liver to the body cells for their use.

Low-density lipoproteins (LDL),• which transport cholesterol and other lipids

to the tissues. LDL are made from VLDL after they have donated many of their

triglycerides to body cells.

High-density lipoproteins (HDL),• which are critical in carrying cholesterol

away from body cells to the liver for disposal.

Th e last two of these lipoproteins, LDL and HDL, play major roles in heart health and are the focus of most lipid recommendations aimed at reducing the risk of heart disease. Figure 5-9 depicts typical lipoproteins and demonstrates how a lipopro- tein’s density changes with its lipid and protein contents.

The LDL and HDL Difference Th e separate functions and eff ects of LDL and HDL are worth a moment’s attention because they carry important implications for the health of the heart and blood vessels.

Both LDL and HDL carry lipids in the blood, but LDL are larger, lighter, and •

richer in cholesterol; HDL are smaller, denser, and packaged with more protein.

LDL deliver triglycerides and cholesterol to the tissues; HDL scavenge excess •

cholesterol and other lipids from the tissues to the liver for disposal.

LDL carry lipids that trigger • infl ammation that may contribute to heart dis-

ease; HDL oppose infl ammatory processes and protect against heart attacks.13

100

P e rc

e n t

Protein

Cholesterol

Phospholipid

Triglyceride

HDLLDL (More lipid, less protein)

(Less lipid, more protein)

Lower density Higher density

Protein

Cholesterol

Phospholipid

Triglyceride

A typical lipoprotein

As the graph shows, the density of a lipoprotein is determined by its lipid-to-protein ratio. All lipoproteins contain protein, cho- lesterol, phospholipids, and triglycerides in varying amounts. An LDL has a high ratio of lipid to protein (about 80 percent lipid to 20 percent protein) and is especially high in cholesterol. An HDL has more protein relative to its lipid content (about equal parts lipid and protein).

Lipoproteins figure 5-9

very-low-density lipoproteins (VLDL) lipoproteins that transport triglycer- ides and other lipids from the liver to various tissues in the body.

low-density lipoproteins (LDL) lipo- proteins that transport lipids from the liver to other tissues such as muscle and fat; contain a large proportion of cholesterol.

high-density lipoproteins (HDL) lipoproteins that return cholesterol from the tis- sues to the liver for dismantling and disposal; contain a large proportion of protein.

infl ammation (in-fl am-MAY-shun) an immune defense against injury, infection, or allergens and marked by heat, fever, and pain. Also defi ned in Chapter 3.

oxidation interaction of a compound with oxygen; in this case, a damaging effect by a chemically reactive form of oxygen. Chapter 7 provides details.

dietary antioxidant (anti-OX-ih-dant) a substance in food that signifi cantly decreases the damaging effects of reactive compounds, such as reactive forms of oxygen and nitrogen, on tissue functioning (anti means “against”; oxy means “oxygen”).

163D i e t a r y F a t , C h o l e s t e r o l , a n d H e a l t h

Both LDL and HDL carry cholesterol, but elevated blood LDL concentrations warn of an increased risk of heart attack, whereas elevated HDL concentrations point to a reduced risk. Th us, some people refer to LDL as “bad” cholesterol and HDL as “good” cholesterol—yet they carry the same kind of cholesterol. Th e diff er- ence to health between LDL and HDL lies in the proportions of lipids they contain and the tasks they perform, not in the type of cholesterol they carry.

The Importance of LDL and HDL Cholesterol Th e importance of blood cho- lesterol to heart health cannot be overstated.‡ Th e blood lipid profi le, a medical test mentioned at the beginning of this chapter, tells much about a person’s blood concentrations of cholesterol and the lipoproteins that carry it. High blood LDL cholesterol and low HDL cholesterol account for two major risk factors for CVD (see Table 5-3). And for LDL cholesterol, the lower the better for heart health.14

LDL Oxidation An important detail about LDL concerns its susceptibility to damage by oxidation. Oxidation of the lipid part of LDL may trigger infl amma- tion, thus contributing to the damage to the arteries of the heart. Adequate intakes of dietary antioxidants, such as vitamin C, vitamin E, the mineral selenium, and antioxidant phytochemicals consumed in foods oppose LDL oxidation and corre- late with low heart disease risk; supplements of these compounds generally provide no heart benefi ts and they carry some risks of their own, as Chapter 7 points out.15

KE Y POINT The chief lipoproteins are chylomicrons, VLDL, LDL, and HDL. Blood LDL and HDL concentrations are among the major risk factors for heart disease. LDL are susceptible to oxidation and cause infl ammation.

What Does Food Cholesterol Have to Do with Blood Cholesterol? Th e answer may be “Not as much as most people think.” Most saturated food fats (and trans fats) raise harmful blood cholesterol more than food cholesterol does.

Does Cholesterol Matter? When told that dietary cholesterol doesn’t matter as much as saturated fat, people may then jump to the wrong conclusion—that blood cholesterol doesn’t matter. It does matter. High blood LDL cholesterol and low blood HDL cholesterol are major indicators of CVD risk. Th e main dietary factors associated with such harmful blood cholesterol levels are high saturated fat and trans fat intakes.

Cholesterol Sources and Body Response Dietary cholesterol makes a smaller but still signifi cant contribution to elevated blood cholesterol.16 Cholesterol intakes in the United States average 237 milligrams a day for women and 358 for men. Th e margin note lists the top contributors of cholesterol to the U.S. diet. Th e Dietary Guidelines 2005 recommend a cholesterol intake of below 300 milligrams per day for healthy people.

Genetic inheritance modifi es everyone’s ability to handle dietary cholesterol.17 Most healthy people exhibit little increase in their blood cholesterol when they consume limited amounts of eggs, shellfi sh, liver, and other cholesterol-containing foods because the body slows its cholesterol synthesis when the diet provides cho- lesterol. Cholesterol diff ers from salt and solid fats and added sugar in this respect: it cannot be omitted from the diet without omitting foods that are nutritious and sometimes low in fat. Moderation, not elimination, is key for most people as far as cholesterol-containing foods are concerned. People with high blood cholesterol, however, may benefi t from limiting their cholesterol intake to less than 200 mil- ligrams per day.

Chapter 11 provides details about the effects • of dietary factors on heart disease.

Did You Know? Here’s a trick: Remember HDL is Healthy. LDL is Less healthy.

Standards for blood lipids are found in • Chapter 11.

CONCEPT LINK 5-7 Phytochemicals are discussed in Controversy 2 (page 61).

Did You Know? The best diet to oppose heart disease is low in saturated fats, including trans fats, and high in fruit, vegetables, whole grains, and legumes, with enough polyunsaturated oils to meet nutri- ent needs within energy needs.

These five foods contribute about 70% of the • food cholesterol in the U.S. diet:

eggs•

beef•

poultry•

cheese•

milk•

‡Blood, plasma, and serum all refer to about the same thing; this book uses the term blood cholesterol. Plasma is blood with the cells removed; in serum, the clotting factors are also removed. The concentration of cholesterol is not much altered by these treatments.

The more of these factors present in a person’s life, the more urgent the need for changes in diet and lifestyle to reduce heart disease risk:

High blood LDL cholesterol.• Low blood HDL cholesterol.• High blood pressure (hypertension).• Diabetes (insulin resistance).• Obesity.• Physical inactivity.• Cigarette smoking.• A diet high in saturated fats, including • trans fats, and low in fi sh, vegetables, legumes, fruit, and whole grains.

Family history, older age, and male gender are risk factors that cannot be changed.

Modifiable

Lifestyle Factors

in Heart Disease

Risk

table 5-3

164 chapter 5 T h e L i p i d s

KE Y POINT Elevated blood cholesterol is a risk factor for cardiovascular disease. Among major dietary factors that raise blood cholesterol, saturated fat and trans fat intakes are most infl uential. Dietary cholesterol raises blood cholesterol to a lesser degree. Low-fat cholesterol-containing foods are nutritious and most people can eat them in moderation.

Recommendations Applied In a welcome trend, the number of U.S. citizens with high total and LDL cholesterol is dropping.18 Even so, heart disease still tops the charts of killer diseases in the United States and most people are wise to choose a diet that provides 20 to 35 per-

Sources of monounsaturated fats:•

Olive oil, canola oil, peanut oil•

Avocados•

Sources of polyunsaturated fats: •

Vegetable oils (safflower, sesame, soy, •

corn, sunflower)

Nuts and seeds•

Fatty fish•

Amount Per Serving

Nutrition Facts

o la

ra S

tu d

io s I n c . (a

ll)

54%

65%

43%

Plain potato (5 ounces) Fat-free milk (1 cup)

Pork chop (5 ounces) with 1/2 inch of fat

Total Fat 35g

Cholesterol 130mg

Calories 450 Calories from Fat 315

% Daily Value

Saturated Fat 13g

17%

20%

36%

Pork chop (4 ounces) with fat trimmed off

Total Fat 11g

Cholesterol 107mg

Calories 230 Calories from Fat 100

% Daily Value

Saturated Fat 4g

Total Fat 0g

Cholesterol 0mg

Calories 150 Calories from Fat 0

% Daily Value

Saturated Fat 0g

Total Fat 0g

Cholesterol 5mg

Calories 90 Calories from Fat 0

% Daily Value

Saturated Fat 0g

43%

90%

12%

Total Fat 28g

Cholesterol 37mg

% Daily Value

Saturated Fat 18g

12%

25%

Total Fat 8g

Cholesterol 24mg

% Daily Value

Saturated Fat 5g

Potato (5 ounces) with 1 tablespoon butter and 1 tablespoon sour cream

Calories 400 Calories from Fat 250

Whole milk (1 cup)

Calories 150 Calories from Fat 70

You can fi nd much of the saturated fat and calories in food by looking for the fat. The fats of meat, milk, and added fats are the main contributors of saturated fat to the U.S. diet. When you trim fat, you trim calories and often saturated fat.

Food Fat, Saturated Fat, and Calories figure 5-10

165D i e t a r y F a t , C h o l e s t e r o l , a n d H e a l t h

cent of its calories from mostly unsaturated fats and that keeps saturated fat and trans fat as low as possible (less than 10 percent and 1 percent of calories, respectively).19

Trimming Saturated Fat to Lower LDL To repeat, dietary saturated fat and trans fat are potent in triggering a rise in LDL cholesterol in the blood. A dietary tactic often eff ective against high blood cholesterol is to trim the saturated fat and trans fat from foods and replace them with monounsaturated and polyunsaturated fats, within a reasonable calorie intake.20 Th e Controversy section provides evidence about both monounsaturated and polyunsaturated fats in relation to disease risk.

Th e photos of Figure 5-10 show that food trimmed of fat is also trimmed of satu- rated fat and energy.21 A pork chop trimmed of its border of fat loses almost 70 percent of its saturated fat, 23 milligrams of cholesterol, and 220 calories. A plain baked po- tato has no saturated fat or cholesterol and about 40 percent of the calories of one with butter and sour cream. Choosing fat-free milk over whole milk provides large savings of saturated fat, calories, and cholesterol. Note that much of the cholesterol of the pork chop remained after trimming because cholesterol forms part of the cell membranes of muscle tissue. Figure 5-11 identifi es top sources of saturated fat in the U.S. diet. Fats from animal sources (meat fats and butterfat) contribute about 60 percent of the saturated fats in most people’s diets.22 Trans fat sources are identifi ed later on.

Raising HDL As for HDL cholesterol, dietary measures are generally ineff ective at signifi cantly raising its concentrations. Instead, regular physical activity defends against heart disease partly because it eff ectively raises HDL, as the Th ink Fitness feature on page 166 points out.

KE Y POINT Trimming fat from food trims calories and, often, saturated fat as well. Dietary measures to lower LDL in the blood involve reducing saturated fat and trans fat and substituting monounsaturated and polyunsaturated fats.

0 1062

Percentage of total saturated fat intakea

4 8Food

Cheese

Beef

Milk

Oils

Ice cream/sherbet/frozen yogurt

Cakes/cookies/quick breads/doughnuts

Butter

Other fats (shortening and animal fats)

Salad dressings/mayonnaise

Poultry

Margarine

Sausage

Potato chips/corn chips/popcorn

Yeast bread

Eggs

Candy

Hot dogs

12 14

These foods supply about 80% of the saturated fat in the U.S. diet. The remainder comes from foods supplying less than 2% each, such as cold cuts, pork, cream, bacon, ham, nuts and seeds, pies and cobblers, and nondairy creamers and toppings. Note that fruits, grains, and vegetables are insignifi cant sources, unless saturated fats are added during processing or preparation.

Top Contributors of Saturated Fats to the U.S. Diet figure 5-11

aRounded values

166 chapter 5 T h e L i p i d s

LO 5.5, 5.6

Essential Polyunsaturated Fatty Acids Th e human body needs fatty acids, and it can use carbohydrate, fat, or protein to synthesize nearly all of them. Two are well-known exceptions: linoleic acid and linolenic acid. Body cells cannot make these two polyunsaturated fatty acids from scratch nor can the cells convert one to the other.

The Need for Essential Fatty Acids Linoleic and linolenic acids must be supplied by the diet and are therefore essential nutrients. Th ese two essential fatty acids are indispensible to health.

Functions of Essential Fatty Acids Essential fatty acids serve as raw materials from which the body makes substances known as eicosanoids that act somewhat like hormones. Eicosanoids aff ect a wide range of diverse body functions, such as muscle relaxation and contraction, blood vessel constriction and dilation, blood clot formation, blood lipid regulation, and immune response to injury and infection such as fever, infl ammation, and pain. A familiar drug, aspirin, relieves fever, infl am- mation, and pain by slowing the synthesis of these eicosanoids. Table 5-4 summa- rizes the many established roles of the essential polyunsaturated fatty acids, and new functions continue to emerge. So important are the essential fatty acids that the DRI committee has recommended specifi c intakes to maintain health (see the margin).

Defi ciencies of Essential Fatty Acids A defi ciency of an essential fatty acid in the diet leads to observable changes in cells, some more subtle than others. When the diet is defi cient in all of the polyunsaturated fatty acids, symptoms of reproduc- tive failure, skin abnormalities, and kidney and liver disorders appear. In infants, growth is retarded and vision is impaired. Th e body stores some essential fatty ac- ids, so extreme defi ciency disorders are seldom seen except when intentionally in- duced in research or on rare occasions when inadequate diets have been provided to infants or hospital patients by mistake. Th e DRI recommended intakes for linoleic acid and linolenic acid refl ect U.S. and Canadian average intakes because defi cien- cies severe enough to cause symptoms in otherwise healthy adults in these countries are unknown. Th e story doesn’t end there, however.

think fitness Why Exercise the Body for the Health of the Heart?

Every leading authority recom- mends physical activity to promote and maintain the health of the heart. The blood, arteries, heart, and other body tissues respond to exercise in these ways:

Blood HDL concentration in-• creases, shifting blood lipids in a healthy direction.

The muscles of the heart and • arteries strengthen and circulation improves, easing delivery of blood to the lungs and tissues.

A larger volume of blood is • pumped with each heartbeat, re- ducing the heart’s workload.

The body grows leaner, reduc-• ing overall risk of cardiovascular disease.

START NOW

Ready to make a change? Consult the online behavior-change planner to help plan for enough physical activity each day to strengthen the health of your heart at www.cengage.com/sso.

These roles for the essential fatty acids are known, but others are under investigation.

Provide raw material for eicosanoids.• Serve as structural and functional parts • of cell membranes. Contribute lipids to the brain and • nerves. Promote normal growth and vision.• Assist in gene regulation.• Maintain outer structures of the skin, • thus protecting against water loss. Help regulate genetic activities affecting • metabolism. Support immune cell functions.•

Functions of the

Essential Fatty

Acids

table 5-4

Dietary Reference Intakes

Linoleic acid (5 to 10% of total calories):

17 g per day for young men.•

12 g per day for young women.•

Linolenic acid (0.6 to 1.2% of total calories):

1.6 g per day for men.•

1.1 g per day for women.•

For other life stages, see the inside front cover.

linoleic (lin-oh-LAY-ic) acid and lino- lenic (lin-oh-LEN-ic) acid polyunsaturated fatty acids that are essential nutrients for hu- man beings. The full name of linolenic acid is alpha-linolenic acid.

eicosanoids (eye-COSS-ah-noyds) bio- logically active compounds that regulate body functions.

http://www.cengage.com/sso

167E s s e n t i a l P o l y u n s a t u r a t e d F a t t y A c i d s

KE Y POINT Two polyunsaturated fatty acids, linoleic acid and linolenic acid, are essential nutrients used to make substances that perform many important functions.

Omega-6 and Omega-3 Fatty Acid Families Linoleic acid is the “parent” member of the omega-6 fatty acid family, so named for the chemical structure of these compounds. Given dietary linoleic acid, the body can produce other needed members of the omega-6 family. One of these is arachi- donic acid, notable for its role as a starting material from which a number of eico- sanoids are made. Omega-6 fatty acids are supplied abundantly in vegetable oils.

Linolenic acid is the parent member of the omega-3 fatty acid family. Given di- etary linolenic acid, the body can make other members of the omega-3 series. Two family members of greatest interest to researchers in the fi elds of heart health and human development are EPA and DHA. Th e body makes only limited amounts of these omega-3 fatty acids, but they are found abundantly in the oils of certain fi sh. Because evidence indicates that health benefi ts may result from consuming these two fatty acids, scientists have proposed setting DRI intake values for them and listing them on Nutrition Facts panels of food labels.23

Omega-3 Fatty Acids and Heart Health Years ago, someone thought to ask why the native peoples of Greenland, northern Canada, and Alaska, who eat a diet very high in fat, have such low rates of death from heart disease.24 Th e trail led to the abundant fi sh and other marine life in their diets, then to the oils in fi sh, and fi nally to EPA and DHA in fi sh oils. Since that time, researchers have identifi ed a potential mechanism underlying the heart benefi ts from eating fatty fi sh: dietary EPA and DHA appear to lower blood pressure, prevent blood clot formation, and protect against irregular heartbeats.25 Evidence in animals suggests that they may also reduce the infl ammation associated with heart disease.26

EPA and DHA tend to collect in cell membranes. Unlike saturated fatty acids, which physically stack closely together, unsaturated fatty acids need more elbow room (refer back to Figure 5-4, p. 154). When the highly unsaturated EPA and DHA amass in cell membranes, they profoundly change cellular structures and activities thought to benefi t the heart.27

Today, as younger generations of native peoples of the north abandon traditional marine-based diets for more modern foodways, the incidence of high blood pres- sure, elevated blood lipids, and obesity has soared. Figure 5-12 demonstrates that seafood-consuming populations generally have lower rates of death from cardio- vascular diseases than those that omit it. Based on available evidence, scientists conclude that a lack of marine oils in diet probably contributes to heart disease development.28 For healthy people who want to stay that way, many population studies and controlled clinical trials support the recommendation to eat fatty fi sh.29 Even some hospitalized patients who have suff ered heart failure or heart attack may benefi t from fi sh oil.30 Fish, low in saturated fat while high in protein, contributes many nutrients other than fatty acids to the diet, including selenium, a mineral of concern for heart health (see Chapter 8).31

Brain Function and Vision Human breast milk provides abundant DHA, thought to be essential for normal brain development and for visual acuity in infants and possibly young children.32 Th e brain is a fatty organ, with a quarter of its dry weight as lipid. EPA and DHA readily join other lipids in the brain’s cell mem- branes.33 Evidence so far suggests that these fatty acids may benefi t the production of the brain’s communication molecules, improve signaling processes, and reduce infl ammation.34

Early studies raised hopes that ample DHA may delay the loss of brain functions in aging, but recent population studies report no association.35 In several reports on psychological depression, low fi sh intake seemed to correlate with depression; one study reported improvements in depressive symptoms when subjects received

Cardiovascular deaths occur less often in countries with higher EPA and DHA intakes from seafood. The percentage of total energy supplied by fi sh oils is listed for each country.

Fish Oil Intakes

and Cardiovascular

Death Rates

figure 5-12

C a rd

io v a s c u la

r D

e a th

s p

e r

1 0 0 ,0

0 0 P

o p

u la

ti o n

Ireland USA France Japan

100

200

300

400

500

600

700

800800

0.09%

0.13%

0.14%

0.37%

Fish is a good source of omega-3 fatty acids.

oo d

C ol

le ct

io n/

S to

ck fo

od A

m er

ic a

omega-6 fatty acid a polyunsaturated fatty acid with its endmost double bond six car- bons from the end of the carbon chain. Linoleic acid is an example.

arachidonic (ah-RACK-ih-DON-ik) acid an omega-6 fatty acid derived from linoleic acid.

omega-3 fatty acid a polyunsaturated fatty acid with its endmost double bond three carbons from the end of the carbon chain. Linolenic acid is an example.

EPA, DHA eicosapentaenoic (EYE-cossa- PENTA-ee-NO-ick) acid, docosahexaenoic (DOE-cossa-HEXA-ee-NO-ick) acid; omega-3 fatty acids made from linolenic acid in the tis- sues of fi sh.

168 chapter 5 T h e L i p i d s

supplements of EPA and DHA.36 In contrast, other studies report no eff ect of fi sh oil on mental well-being.37 Further research will reveal the meaning, if any, of such fi ndings for people’s mental health.

Infl ammation Chronic infl ammation occurs with many diseases and may con- tribute to their progression. Omega-3 fatty acids have been reported to reduce indi- cators of infl ammation in some experiments but not in others.38 Whether an anti- infl ammatory eff ect of fi sh oil bears a relation to disease risks is unknown. Other potential benefi cial eff ects of these remarkable lipids are listed in Table 5-5.

KE Y POINT The omega-6 family of polyunsaturated fatty acids includes linoleic acid and arachidonic acid. The omega-3 family includes linolenic acid, EPA, and DHA. DHA from human breast milk plays special roles in early development, and EPA and DHA from marine oils play roles in disease prevention.

Recommendations for Omega-3 Fatty Acid Intake Obtaining the health benefi ts from the essential fatty acids requires consuming enough of both fatty acid families.39 In the body’s cells, both types compete for the same metabolic enzymes, so a fl ood of omega-6 fatty acids prevents the omega-3s from interacting with the enzymes that convert them to needed compounds.40 On av- erage in this country, people take in plenty of omega-6 fatty acids from vegetable oils, margarine, and salad dressings. What they lack is omega-3 fatty acids from fatty fi sh.

A previous theory suggested that a ratio between omega-3 and omega-6 fatty acids best serves the body’s health, but research does not support this idea.41 Most people need simply to increase the omega-3 fatty acids in their diets.42 Th e Ameri- can Heart Association recommends doing so by including two fatty fi sh servings to- taling 8 ounces a week in a heart-healthy diet.43 For pregnant women, two 3-ounce servings of fatty fi sh per week are compatible with good health.44

KE Y POINT Most people consume plenty of the omega-6 fatty acids but need more omega-3 fatty acids from fi sh.

What About Fish Oil Supplements? Fish, not fi sh oil supplements, is the pre- ferred source of omega-3 fatty acids, except for persons with cardiovascular disease who cannot obtain enough EPA and DHA from fi sh and must use supplements, and then only under a physician’s supervision.45 Supplements of 2 grams a day of EPA or more than 3 grams of fi sh oil interfere with blood clotting and cause pro- longed bleeding times.46 In mice, fi sh oil supplements impair immune resistance to fl u viruses.47 Supplements also lack the other benefi cial nutrients that fi sh provides. Some fi sh oil supplements also taste fi shy and people often complain of a lingering or repeating taste for hours after taking them.

Finally, fi sh oil supplements are made from fi sh skins and livers, which can ac- cumulate toxic concentrations of dioxins and other industrial contaminants from polluted waters.§48 Mercury contamination is also a problem in the fl esh of both freshwater and saltwater species; the Consumer Corner section discusses the risks of fi sh consumption. For supplements, newer processing methods can rid fi sh oil of most contaminants but not all supplements are refi ned in this way. In addition to contamination, fi sh liver oil naturally contains high levels of the two most poten- tially toxic vitamins, A and D. Lastly, supplements of fi sh oil are expensive—they must be purchased in addition to food, whereas fatty fi sh replaces other protein foods that would have been purchased instead.

These benefi ts from fi sh or fi sh oil are well- established but researchers are investi- gating many others.

Against heart disease A shift toward omega-3 eicosanoids • by reducing production of omega-6 eicosanoids. This shift may reduce abnormal blood clotting, help sustain more regular heartbeats, and reduce infl ammation of many body tissues, including the arteries of the heart. Reduced blood triglycerides (in some • studies, fi sh oil supplements elevated blood LDL cholesterol, an opposing, detrimental outcome). Retarded hardening of the arteries • (atherosclerosis). Relaxation of blood vessels, mildly • reducing blood pressure.

In infant growth and development Normal brain development in infants. • DHA concentrates in the brain’s cortex, the conscious thinking part. Normal vision development in infants. • DHA helps to form the eye’s retina, the seat of normal vision.

Potential Health

Benefits of Fish Oils

table 5-5

CONCEPT LINK 5-8 Table 2-2 of Chapter 2 (page 44) provides the USDA recommendations for oil intakes.

Chapters 12 and 15 provide more informa-• tion about the contaminants from human activities that end up in the earth’s oceans and lakes, and ultimately, in our food and water. §Contaminants include organically bound arsenic, organochlorines, polychlorinated biphenyls (PCBs), and others.

169E s s e n t i a l P o l y u n s a t u r a t e d F a t t y A c i d s

Omega-3 Enriched Foods and Flaxseed Food products that have been enriched with omega-3 fatty acids can help meet the needs of those people who do not eat fi sh. For example, when laying chickens are fed grains enriched with fi sh oil or algae oil, some of the EPA and DHA from the oils ends up in the eggs. Likewise, fl axseed in chicken feed produces eggs enriched with mostly linolenic acid.49 Omega-3 fatty acids and fi sh oil cannot simply be added to foods such as milk, juice, and bread because they change the taste of the food and because they are rapidly oxidized to rancidity products. Food chemists are working on a way to encapsulate microscopic droplets of fi sh oil in digestible coatings to create a more stable additive, but most omega-3 enriched foods today contain only linolenic acid unless the label specifi es “EPA or DHA added.”50 Eating fl axseed or its oil directly adds linolenic acid to the diet, but its conversion to EPA and DHA in the human body is limited. Some con- version does take place, however, but whether the amount is suffi cient to approach the benefi ts of eating fi sh is unknown.51

People who consume wild game meat or beef from pasture-fed cattle also ob- tain more omega-3 fatty acids and less saturated fat from these sources than from traditional meats. In addition, several forms of marine algae and their oils provide DHA.52 Today’s infant formulas also contain DHA for brain and vision develop- ment, and no law says that adults cannot use the formulas in cooking or in bever- ages.53 No exotic, expensive food choices are necessary, however—common foods chosen wisely can provide a healthy, balanced fatty acid intake (see Table 5-6).54

KE Y POINT Supplements are not recommended and enriched foods are expensive. Ordinary foods can provide the needed essential fatty acids.

Omega-6

Linoleic acid Seeds, nuts, vegetable oils (corn, cottonseed, saffl ower, sesame, soybean, sunfl ower), poultry fat

Omega-3

Linolenic acida Oils (canola, fl axseed, soybean, walnut, wheat germ; liquid or soft margarine made from canola or soybean oil) Nuts and seeds (fl axseeds, walnuts, soybeans) Vegetables (soybeans)

EPA and DHA Human milk

Fish and seafood:

>500 mg per 3.5 oz serving: European seabass (bronzini), herring (Atlantic and Pacifi c), mackerel, oyster (Pacifi c wild), salmon (wild and farmed), sardines, toothfi sh (includes Chilian seabass), trout (wild and farmed)

150–500 mg per 3.5 oz serving: black bass, catfi sh (wild and farmed), clam, cod (Atlantic), crab (Alaskan king), croakers, fl oun- der, haddock, hake, halibut, oyster (eastern and farmed), perch, scallop, shrimp (mixed varieties), sole, swordfi sh, tilapia (farmed)

<150 mg per 3.5 oz serving: cod (Pacifi c), grouper, lobster, mahi- mahi, monkfi sh, red snapper, skate, triggerfi sh, tuna, wahoo

aAlpha-linolenic acid. Also found in the seed oil of the herb evening primrose.

Source for fi sh data: K. L. Weaver and coauthors, The content of favorable and unfavorable polyunsatu- rated fatty acids found in commonly eaten fi sh, Journal of the American Dietetic Association 108 (2008): 1178–1185; P. M. Kris-Etherton, W. S. Harris, and L. J. Appel, Fish consumption, fi sh oil, omega-3 fatty acids, and cardiovascular disease, Circulation 106 (2002): 2747–2757.

Food Sources of Omega-6 and Omega-3

Fatty Acids

table 5-6

170 chapter 5 T h e L i p i d s

consumer corner

Species most heavily contaminated with mercury

Saltwater

Freshwater

King mackerel Shark

Largemouth bass Smallmouth bass Spotted bass

Swordfish Fresh tuna steaksa Tilefish

Species lower in mercury:

Canned light tunaa

Brown trout Rainbow troutChannel catfish

Catfish Pollock Salmon Sardines Shrimp

Seafood Safety—Balancing Risks and Benefi ts

On learning of its contamination with industrial pollutants, consumers may question the safety of eating fi sh.1 Most healthy people, however, can safely consume two 4-ounce servings per week of most cooked ocean fi sh; intakes of freshwater fi sh should be limited to local guidelines. Consuming raw fi sh and shellfi sh is never recommended—it causes many cases of serious or fatal bacterial, viral, and other illness each year (read Chapter 12 for details).

Varying fi sh choices is a good idea to minimize exposure to any single contam-

inant that may accumulate in a favored species. Of particular concern is the toxic metal mercury. When industrial mercury escapes into natural waterways, bacteria in the water convert the mercury into a more toxic form, methylmercury, which often concentrates in large predatory species of both saltwater and freshwater fi sh.2 A recent study reports increasing mercury levels in U.S. women, revealing that once in the body, mercury settles in the liver, immune tissue, brain, and other organs where it accumulates over time.3 Another study linked high intakes of

fi sh oils and fi sh to an increased risk of type 2 diabetes; contaminants typically found in fi sh may raise diabetes risks.4

Children and pregnant or lactat- ing women, especially, should avoid consuming methylmercury and other contaminants. At the same time, these groups benefi t from consuming safer fi sh varieties—the risks from not eating fi sh may outweigh the risks from doing so. For these groups, experts recom- mend two servings of EPA- and DHA-rich fi sh from safer fi sh species each week.5 People with existing heart disease also

Many seafood species that provide benefi cial EPA and DHA (see Table 5-6) are contaminated with mercury from polluted water.

Mercury in Fish Species figure 5-13

aCanned albacore (“white”) tuna generally contains more mercury than light tuna varieties. Source for tuna: S. L. Gerstenberger, A. Martinson, and J. L. Kramer, An evaluation of mercury concentrations in three brands of canned tuna, Environmental Chemistry 29 (2010): 237–242.

171T h e E f f e c t s o f P r o c e s s i n g o n U n s a t u r a t e d F a t s

LO 5.7

The Effects of Processing on Unsaturated Fats Vegetable oils make up most of the added fat in the U.S. diet because fast-food chains use them for frying, food manufacturers add them to processed foods, and consumers tend to choose margarine over butter. Consumers of vegetable oils may feel safe in choosing them because they are generally less saturated than animal fats. If consumers choose a liquid oil, they may be justifi ed in feeling secure. If the choice is a processed food, however, their security may be questionable, especially if the words partially hydrogenated appear on the label’s ingredients list.

What Is “Hydrogenated Vegetable Oil,” and What’s It Doing in My Chocolate Chip Cookies? When manufacturers process foods, they often alter the fatty acids in the fat (triglyc- erides) the foods contain through a process called hydrogenation. Hydrogenation of fats makes them stay fresher longer and also changes their physical properties.

Oxidation of Unsaturated Oils Points of unsaturation in fatty acids are weak spots that are vulnerable to attack by oxygen. Oxidative damage is not confi ned to fats within body tissues but occurs anywhere oxygen mixes with fats. When the un- saturated points in the oils of food are oxidized, the oils become rancid and the food tastes “off .” Th is is why cooking oils should be stored in tightly covered containers that exclude air. If stored for long periods, they need refrigeration to retard oxidation.

Hydrogenation of Oils One way to prevent spoilage of unsaturated fats and also to make them harder and more stable when heated to high temperatures is to change their fatty acids chemically by hydrogenation, as shown on the left side of Figure 5-14. When food producers want to use a polyunsaturated oil such as soybean oil to make a spreadable margarine, for example, they hydrogenate it by forcing hydrogen into the liquid oil. Some of the unsaturated fatty acids become more saturated as they accept the hydrogen, and the oil hardens. Th e resulting product is more satu- rated and more spreadable than the original oil. It is also more resistant to damage from oxidation or breakdown from high cooking temperatures. Hydrogenated oil has a high smoking point, so it is suitable for purposes such as frying.

Hydrogenated oils are thus easy to handle, easy to spread, and store well. Mak- ers of peanut butter often replace a small quantity of the liquid oil from the ground peanuts with hydrogenated vegetable oils to create a creamy paste that does not

pose a concern because mercury may worsen heart disease, while EPA and DHA of fi sh may benefi t the heart. Figure 5-13 lists fi sh species known to be lower in mercury.

Farm-raised fi sh offer an alternative to wild fi sh but the “farms” are often giant ocean cages, exposed to what- ever contaminants fl oat by in the water. Compared with wild fi sh, farm-raised fi sh do tend to collect less methylmercury in their fl esh, and the levels of other harmful industrial pollutants generally test below the maximums set by the U.S. Food and Drug Administration. Pollutants in fi sh

demonstrate that monitoring is essen- tial. They also serve as a reminder that our health is inextricably linked with the health of our planet (see Chapter 15).

After weighing the available evidence, experts conclude that the heart benefi ts from consuming moderate amounts of safer fatty fi sh outweigh the potential risks.6 The greatest health benefi ts can be expected from grilled, baked, or broiled fi sh partly because the species of fi sh prepared this way often contain more EPA and DHA than species used for deep frying in fast-food restaurants or available as frozen fi sh products.7

Also, commercial frying fats are often laden with saturated fat and trans fat, so avoiding commercially fried fi sh reduces heart disease risks in this way, too. Further benefi ts arise when fi sh displaces high-fat meats or other saturated fat-rich foods in the diet.

In the end, the arguments for eating the recommended fatty fi sh each week outweigh those against it. However, the dietary principles of adequacy and mod- eration come into play: choose enough of the safer varieties of fi sh to meet your needs—but don’t go overboard.

methylmercury any toxic compound of mercury to which a characteristic chemical structure, a methyl group, has been added, usually by bacteria in aquatic sediments. Methyl mercury is readily absorbed from the intestine and causes nerve damage in people.

hydrogenation (high-dro-gen-AY-shun) the process of adding hydrogen to unsaturated fatty acids to make fat more solid and resistant to the chemical change of oxidation.

smoking point the temperature at which fat gives off an acrid blue gas.

172 chapter 5 T h e L i p i d s

Points of unsaturation are places on fatty acid chains where hydrogen is missing. The bonds that would normally be occupied by hydrogen in a saturated fatty acid are shared, reluctantly, as a double bond between two carbons that both carry a slightly negative charge.

When a positively charged hydrogen is made available to an unsaturated bond, it readily accepts the hydrogen and, in the process, becomes saturated. The fatty acid no longer has a point of unsaturation.

The hydrogenation process also produces some trans-fatty acids. The trans-fatty acid retains its double bond but takes a twist instead of becoming fully saturated. It resembles a saturated fatty acid both in shape and in its effects on health.

Point of unsaturation

Unsaturated fatty acid

Hydrogenated fatty acid (now fully saturated) Trans-fatty acid

Usual shapea

Trans shape

H H

H+

H+H+

Animated! Hydrogenation Yields Both Saturated and Trans-Fatty Acids

figure 5-14

aThe usual shape of the double bond structure is known as a cis (pronounced sis) formation.

separate into layers of oil and peanuts as the “old-fashioned” types do. Neither type of peanut butter is high in saturated fat, however.

Nutrient Losses Once fully hydrogenated, oils lose their unsaturated character and the health benefi ts that go with it. Hydrogenation may aff ect not only the es- sential fatty acids in oils but also vitamins, such as vitamin K, decreasing their activity in the body. If you, the consumer, are looking for health benefi ts from poly- unsaturated oils, hydrogenated oils such as those in shortening or stick margarine will not meet your need.

An alternative to hydrogenation is to add a chemical preservative that will com- pete for oxygen and thus protect the oil. Th e additives are antioxidants, and they work by reacting with oxygen before it can do damage. Examples are the additives BHA and BHT** listed on snack food labels. Another alternative, already men- tioned, is to keep the product refrigerated.

KE Y POINT Vegetable oils become more saturated when they are hydrogenated. Hydrogenated fats resist rancidity better, are fi rmer textured, and have a higher smoking point than unsaturated oils, but they also lose the health benefi ts of unsaturated oils.

What Are Trans-Fatty Acids, and Are They Harmful? Many consumers now identify trans fats—that is, fats that contain trans-fatty acids—as health risks. Some cities have even set limits on the amount of trans fats

Baked goods often contain hydrogenated fats.

C S

qu ar

ed S

tu di

os /P

ho to

di sc

/G et

ty Im

ag es

**BHA and BHT are butylated hydroxyanisole and butylated hydroxytoluene.

trans-fatty acids fatty acids with unusual shapes that can arise when hydrogens are added to the unsaturated fatty acids of polyunsaturated oils (a process known as hydrogenation).

173T h e E f f e c t s o f P r o c e s s i n g o n U n s a t u r a t e d F a t s

allowed in restaurant meals within city borders.55 Does the villainy of trans fats warrant their bad reputation?

Formation of Trans-Fatty Acids Trans-fatty acids occur only in small amounts in nature, mostly in dairy products, but form generously during hydrogenation. When polyunsaturated oils are hardened by hydrogenation, some of the unsatu- rated fatty acids end up changing their shapes instead of becoming saturated (look at the right side of Figure 5-14). Th is change in chemical structure creates trans unsaturated fatty acids that are similar in shape to saturated fatty acids. Th e change in shape changes their eff ects on the health of the body.

Health Effects of Trans-Fatty Acids Consuming manufactured trans fat poses a risk to the heart and arteries by raising blood LDL cholesterol and, at higher intakes, lowering benefi cial HDL cholesterol.56 Trans-fatty acids may also increase tissue infl ammation, a key player in heart disease development. In addition, when hydrogenation changes essential fatty acids into their saturated or trans counter- parts, the consumer loses the health benefi ts of the original raw oil.57 Compared with the risk to heart health posed by saturated fat, the risk from trans fat is similar or slightly greater.58 Th e Dietary Guidelines 2005 therefore suggest that people keep trans fat intake as low as possible.

Trans Fat in Foods Th e largest contributors of trans fat to the U.S. diet have been commercially fried foods, from doughnuts to chicken, along with baked goods and other commercial foods (see the margin). Food makers have recently responded to the clamor surrounding trans fats by reducing their use, however.59 Newly formu- lated commercial oils and fats can now perform the same jobs as the old hydroge- nated fats, but with fewer trans-fatty acids.60

Are the New Fats Better for Health? Whether the new fats are better for heart health is a valid question. Some new fats merely substitute saturated fat for trans fat—and the risk to the heart and arteries from saturated fats is well established.61 Others use hydrogenated fat made from monounsaturated fatty acids instead of polyunsaturated; monounsaturated fats create far fewer trans-fatty acids during hy- drogenation. Other options are under investigation.62

Intense media coverage has led some consumers to believe that if a food lacks trans fats, it is safe for the heart. But saturated fat matters, too, and it is far more prevalent in foods. On the label shown in Figure 5-15, note that 1 ounce of trans fat–free crackers contains 6 grams of saturated fat, or about a third of the entire day’s allowance. A glance back at Figure 5-5 (page 155) reveals that saturated fats are present even in the vegetable and fi sh oils required to provide essential nutrients to the diet—and saturated fat grams add up quickly in a day’s meals.

Foods most likely to supply • trans-fatty acids:

Fast foods. •

Chips, cookies, crackers. •

Cake products and frostings. •

Breads.•

Stick margarines. •

Commercial fried chicken and fish •

products.

Other commercially prepared foods. •

Guidelines suggest keeping • trans-fatty acid consumption as low as possible.

Did You Know? The Nutrition Facts section of food labels lists the grams of trans-fatty acids in foods.

Consumers must look beyond the trans fat line to judge a food. One serving of these crackers presents no trans fat, but it contains almost a third of the saturated fat allowable for the day, with only small contributions of essential nutrients.

Saturated Fat in

a Trans Fat–Free

Food

figure 5-15

Total Fat 8g 13%

Serving Size 8 Crackers (28g) Servings Per Container about 9

Calories 165

Amount per serving

Calories from Fat 77

% Daily Value*

Cholesterol 0mg 0%

Sodium 290mg 12%

Protein 3g

Sugars 3g

19g

Nutrition Facts

INGREDIENTS: ENRICHED FLOUR (WHEAT FLOUR, NIACIN, REDUCED IRON, THIAMIN MONONITRATE, RIBOFLAVIN, FOLIC ACID), VEGETABLE OIL (CONTAINS ONE OR MORE OF THE FOLLOWING OILS: SAFFLOWER, CANOLA, SOYBEAN, PALM, COTTONSEED, COCONUT), WHEAT GERM, SUGAR, SALT, HIGH FRUCTOSE CORN SYRUP, EXTRACT OF MALTED CORN AND BARLEY, MOLASSES, LEAVENING (BAKING SODA, MONOCALCIUM PHOSPHATE), EXTRACTIVES OF ANNATTO AND TURMERIC FOR COLOR), MALTED BARLEY FLOUR, SODIUM METABISULFITE.

Total Carbohydrate

Dietary fiber less than 1g

Calcium 2%

Vitamin A

Thiamin 15%

Niacin 6%

Trans Fat 0g

Saturated Fat 6g 30%

Vitamin C

8%Iron

8%Riboflavin

8%Folate

•

0% my turn

Jessica Katy

Heart to Heart

How often do you think about the consequences of your food choices now on your heart health later in life? Two people talk about planning heart-healthy meals.

To hear their stories, log on to www.cengage.com/sso.

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http://www.cengage.com/sso

174 chapter 5 T h e L i p i d s

KE Y POINT The process of hydrogenation also creates trans- fatty acids. Trans fats act like saturated fats in the body. Consumers should not lose sight of saturated fats as the main dietary risk factor for heart and artery disease.

LO 5.8

Fat in the Diet Th e remainder of this chapter and its Controversy show you how to choose fats wisely with the goals of providing optimal health and pleasure in eating. As you read, notice which foods off er unsaturated fat and which off er saturated fat and trans fat. Your choices can make a diff erence in the unseen condition of your arteries.

Essential Fat in the Diet Remember that some fat is necessary for essential nutrients. People who take fat recommendations to an extreme and try to eliminate all traces of fat from food do so at their peril. Most people need about 20 percent of their daily energy in the form of unsaturated fat. Th e needed fats of fatty fi sh, nuts, and vegetable oils provide benefi cial EPA and DHA, linoleic acid and linolenic acid, and vitamin E and provide necessary calories, not discretionary, when con- sumed within calorie limits. Th e needed amounts of these fats are small, however, and most people take in many more calories of fats than they need each day.

Visible vs. Invisible Fats Keep in mind that the fat of some foods, such as the rim of fat on a steak, is visible (and therefore removable). Other fats are invisible, such as the fats in the marbling of meat, the fat ground into lunchmeats and ham- burger, the fats blended into sauces of mixed dishes, and the fats in avocados, bis- cuits, cheese, coconuts, other nuts, olives, and fried foods. Invisible fats contribute much of the fat in the U.S. diet.

Added Fats A dollop of dessert topping, a spread of butter on bread, oil or shortening in a recipe, dressing on a salad—all of these are examples of added fats. All sorts of fats can be added to foods during commercial or home preparation or at the table. Th e following amounts of these fats contain about 5 grams of pure fat, providing 45 calories and negligible protein and carbohydrate:

1 teaspoon oil or shortening.•

1½ teaspoon mayonnaise, butter, or margarine.•

1 tablespoon regular salad dressing, cream cheese, or heavy cream.•

1½ tablespoon sour cream.•

Th e majority of added fats in the diet are invisible. Th ey are the hidden fats of fried foods and baked goods, sauces and mixed dishes, and dips and spreads.

KE Y POINT Fats added to foods during preparation or at the table are a major source of fat in the diet.

Meat, Poultry, Fish, Dried Peas and Beans, Eggs, and Nuts Meats conceal a good deal of the fat—and much of the saturated fat—that people consume. To help “see” the fat in meats, it is useful to think of them in four cat- egories according to their fat contents—very lean, lean, medium-fat, and high-fat meats—as the exchange lists do in Appendix D. Meats in all four categories contain about equal amounts of protein, but their fat contents diff er and their saturated fat

CONCEPT LINK 5-9 The concept of discretionary calories was first addressed in Chapter 2 (page 42).

CONCEPT LINK 5-10 The Canadian Food Guide is found in Ap- pendix B.

A serving of ten small olives or a sixth of an avo- cado each provides about 5 grams of mostly monounsaturated fat.

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175F a t i n t h e D i e t

and calorie amounts vary signifi cantly. Figure 5-16 shows fat and calorie data for some ground meats. Table 2-6 in Chapter 2 provided some defi nitions concerning the fat contents of meats. Th e 2005 USDA Food Guide suggests that most adults limit a day’s intake of meats or its equivalents to about 5 or 7 ounces. For compari- son, the smallest fast-food hamburger weighs about 3 ounces. Steaks served in res- taurants often run 8, 12, or 16 ounces, more than a whole day’s meat allowance. You may have to weigh a serving or two of meat to see how much you are eating.

The Hidden Fat of Meats People think of meat as protein food, but calculation of its nutrient contents reveals a surprising fact. A big (4-ounce), fast-food ham- burger sandwich contains 23 grams of protein and 20 grams of fat. Because protein off ers 4 calories per gram and fat off ers 9, the sandwich provides 92 calories from protein but 180 calories from fat. Hot dogs, fried chicken sandwiches, and fried fi sh sandwiches also provide hundreds of fat calories, mostly hidden in the food. Because so much meat fat is hidden from view, meat eaters can easily and unknow- ingly overeat on high-fat, high-calorie food.

Clues to Lower-Fat Meats When choosing beef or pork, look for lean cuts named loin or round from which the fat can be trimmed, and eat small portions. Chicken and turkey fl esh are naturally lean, but commercial processing and frying add fats, especially in “patties,” “nuggets,” “fi ngers,” and “wings.” Watch out for ground turkey or chicken products. Th e skin is often ground in to add moistness when cooked, and these products end up with a higher fat content than lean beef. Also, some people (even famous chefs) misinterpret Figure 5-5, earlier, believing the fats of poultry and pork to be harmless to the heart because they are less saturated than beef fat. Nutri- tion authorities emphatically state, however, that all sources of saturated fat pose a risk to the heart and even the skin of poultry should be removed for heart health.

260 cal/3 ozb 4 tsp fat 8 g saturated fat

1/2 220 cal/3 ozb 3 tsp fat

6 g saturated fat 200 cal/3 ozb 2 tsp fat 3 g saturated fat

1/4 180 cal/3 ozb 1 tsp fat

4 g saturated fat

1/2

Regular ground beef 23% fat

Ground chuck 16% fat

Commercial ground turkeya

(with skin ground in) 13% fat

Ground round 10% fat

Higher in fat Lower in fat

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Only the ground round, at 10 percent fat by raw weight, qualifi es to bear the word lean on its label. To be called “lean,” products must contain fewer than 10 grams of fat, 4 grams of saturated fat, and 95 milligrams of cholesterol per 100 grams of food. The red labels on these packages list rules for safe meat handling, explained in Chapter 12.

Calories, Fat, and Saturated Fat in Cooked Ground Meat Patties figure 5-16

aValues for 3 ounces of cooked turkey breast ground without skin are 108 calories, ½ teaspoon fat, and 1 gram saturated fat. bLarger servings will, of course, provide more fat, saturated fat, and calories than the values listed here.

176 chapter 5 T h e L i p i d s

KE Y POINT Meats account for a large proportion of the hidden fat and saturated fat in many people’s diets. Most people consume meat in larger amounts than recommended and types that present a great deal of fat.

Milk, Yogurt, and Cheese Some milk products contain fat and saturated fat, as Figure 5-17 shows. In homog- enizing whole milk, milk processors blend in the cream, which otherwise would fl oat and could be removed by skimming. A cup of whole milk contains the protein and carbohydrate of fat-free milk, but in addition it contains about 60 extra calories from fat. A cup of reduced-fat (2 percent fat) milk falls between whole and fat-free, with 45 calories of fat. Th e fat of whole milk occupies only a teaspoon or two of the volume but nearly doubles the calories in the milk. Depending on its fat content, milk bears one of the names listed in the margin.

Milk and yogurt appear in the milk group, but cream and butter do not. Milk and yogurt are rich in calcium and protein, but cream and butter are not. Cream and butter are fats, as are whipped cream, sour cream, and cream cheese, so they are

Milk’s names: •

Milk, whole milk.•

Reduced-fat, less-fat, or 2% milk.•

Low-fat, or 1% milk.•

Fat-free, zero-fat, no-fat, skim, or nonfat •

milk.

Fat-free, skim, zero-fat, no-fat, or nonfat milk, 8 oz (<0.5% fat by weight)

Low-fat milk, 8 oz (1% fat by weight)

Low-fat strawberry yogurt, 8 oz

Low-fat cheddar cheese, 1.5 oz

Whole milk, 8 oz (3.3% fat by weight)

Amount Per Serving

Nutrition Facts

Reduced-fat, less-fat milk, 8 oz (2% fat by weight)

Strawberry yogurt, 8 oz Cheddar cheese, 1.5 oz

Total Fat 0g 0%

Calories 80 Calories from Fat 0

% Daily Value*

Saturated Fat 0g 0%

Cholesterol 5mg 2%

Total Fat 2g 3%

Calories 105 Calories from Fat 20

% Daily Value*

Saturated Fat 1.5g 8%

Cholesterol 10mg 3%

Total Fat 2.5g 4%

Calories 240 Calories from Fat 20

% Daily Value*

Saturated Fat 2g 10%

Cholesterol 15mg 5%

Total Fat 3g 5%

Calories 70 Calories from Fat 30

% Daily Value*

Saturated Fat 2g 10%

Cholesterol 10mg 3%

Total Fat 5g 8%

Calories 120 Calories from Fat 45

% Daily Value*

Saturated Fat 2g 10%

Cholesterol 20mg 7%

Total Fat 5g 8%

Calories 250 Calories from Fat 45

% Daily Value*

Saturated Fat 3g 15%

Cholesterol 15mg 5%

Total Fat 8g 12%

Calories 150 Calories from Fat 70

% Daily Value*

Saturated Fat 5g 25%

Cholesterol 24mg 8%

Total Fat 14g 22%

Calories 165 Calories from Fat 130

% Daily Value*

Saturated Fat 9g 45%

Cholesterol 40mg 13%

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tu d

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c .

Red boxes below indicate foods with higher lipid contents that warrant moderation in their use. Green indicates lower-fat choices.

Lipids in Milk, Yogurt, and Cheese figure 5-17

177F a t i n t h e D i e t

grouped together with the solid fats. Cheeses are the single greatest contributor of saturated fat in the diet. Among food fats, only the lipids of palm oil and coconut oil rank higher for saturation than the butterfat in fatty dairy products.

KE Y POINT The choice between whole and fat-free milk products can make a large diff erence to the fat and saturated fat content of a diet. Cheeses are a major contributor of saturated fat.

Grains Grain foods in their natural state are very low in fat, but fat, including saturated and trans fats, may be added during manufacturing, processing, or cooking (see Figure 5-18). Th e fats in these foods can be particularly hard to detect, so diners must

Amount Per Serving

Low-fat granola, 1/ 2 c

Crispy oat bran, 1/ 2 c

Buttery crackers, 5 crackers

Fried rice, 1/ 2 ca

A dinner roll

Fettuccine alfredo, 1/ 2 c

A breakfast bar

A muffin

A homemade waffle

A large biscuit

Total Fat 3g 5%

Calories 195 Calories from Fat 35

% Daily Value*

Saturated Fat 1g 5%

Cholesterol 0mg 0%

Total Fat 5g 8%

Calories 150 Calories from Fat 45

% Daily Value*

Saturated Fat 1.5g 8%

Cholesterol 0mg 0%

Total Fat 4g 6%

Calories 80 Calories from Fat 35

% Daily Value*

Saturated Fat 1g 5%

Cholesterol 0mg 0%

Total Fat 7g 11%

Calories 140 Calories from Fat 65

% Daily Value*

Saturated Fat 1g 5%

Cholesterol 20mg 7%

Total Fat 2g 3%

Calories 80 Calories from Fat 20

% Daily Value*

Saturated Fat 0g 0%

Cholesterol 0mg 0%

Total Fat 14g 22%

Calories 250 Calories from Fat 130

% Daily Value*

Saturated Fat 8g 40%

Cholesterol 60mg 20%

Total Fat 6g 9%

Calories 150 Calories from Fat 55

% Daily Value*

Saturated Fat 2.5g 13%

Cholesterol 0mg 0%

Total Fat 6g 9%

Calories 160 Calories from Fat 54

% Daily Value*

Saturated Fat 1g 5%

Cholesterol 20mg 7%

Total Fat 11g 17%

Calories 220 Calories from Fat 100

% Daily Value*

Saturated Fat 2g 10%

Cholesterol 50mg 17%

Total Fat 11g 17%

Calories 260 Calories from Fat 80

% Daily Value*

Saturated Fat 2.5g 13%

Cholesterol 0mg 0%

Total Fat 14g 22%

Calories 270 Calories from Fat 130

% Daily Value*

Saturated Fat 8g 40%

Cholesterol 45mg 15%

A large croissant

Nutrition Facts

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Red boxes below indicate foods with higher lipid contents that warrant moderation in their use. Green indicates lower-fat choices.

Lipids in Bread, Cereal, Rice, and Pasta figure 5-18

aThe calorie and fat contents of fried rice vary by preparation method.

178 chapter 5 T h e L i p i d s

remember which foods stand out as being high in fat. Notable are granola and cer- tain other ready-to-eat cereals, croissants, biscuits, cornbread, fried rice, pasta with creamy or oily sauces, quick breads, snack and party crackers, muffi ns, pancakes, and homemade waffl es. Packaged breakfast bars often resemble vitamin-fortifi ed candy bars in their fat and sugar contents.

KE Y POINT Fat in breads and cereals can be well hidden. Consumers must learn which foods of this group contain fats.

Now that you know where the fats in foods are found, how can you reduce or elim- inate the harmful ones from your diet? Th e Food Feature provides some pointers.

food feature

Meeting today’s guidelines for reducing solid fats and including raw liquid oils in the diet while controlling their contribu- tions of discretionary calories can be tricky. These feats require not only iden- tifying fatty foods but also recognizing sources of saturated fats and trans fats, and then doing something about them. This can be accomplished by:

Reducing saturated and 1. trans fats in the diet, thereby reducing calorie intakes.

Replacing saturated and 2. trans fats with unsaturated fats, holding calories steady.

Replacing saturated and 3. trans fats with lower-calorie carbohydrate, pro- tein, or other fat replacers, reducing calorie intakes, as well as saturated fats.63

The recommendation to limit daily intakes of saturated and trans fats for the health of the heart applies to all people. To repeat: No amount of these fats is needed for health and to stay healthy. For healthy people, consuming diets that supply over 35 percent of calories as fat presents health and nutrition risks. For people with heart disease or obesity, total dietary fat must be kept even lower to prevent worsening their illnesses.

Although such advice is easily dis- pensed, it is not easily followed. The fi rst step in doing so is to learn which foods contain heavy doses of saturated and

Defensive Dining

trans fats and then keep these foods to a minimum.

PORTION SIZES Perhaps most important for many people is learning to control portion sizes, particularly of fatty foods that can pack hundreds of calories and many grams of saturated fats into just a few bites. Higher-fat foods may be included in the diet, but the calories they provide must fi t within a person’s discretionary calorie allowance and saturated fat limit.

IN THE GROCERY STORE The right choices in the grocery store can save you many grams of fat, saturated fat, and trans fats, while the wrong ones can undermine your efforts. Food labels can reveal much about a processed food’s fat contents. With that knowledge, you can decide whether to use the food as a staple item in your diet or as an occasional treat. Choose foods lowest in harmful fats for everyday use; limit others to occasional use only. For example, choose frozen vegetables (a staple food) without butter or other high-fat sauces, which are often highly saturated and inevitably drive up the calories, as well as the price; add your own fl avorings such as a touch of olive oil or liquid margarine with some herbs, garlic, or lemon pep- per at home. If you choose precooked meats, avoid those that are coated and fried or prepared in fatty sauces. Try

rotisserie chicken from the deli section— rotisserie cooking lets much of the fat and saturated fat drain away.

FAT REPLACERS AND ARTIFICIAL FATS Look for new innovations aimed at re- ducing saturated and trans fats.64 Some foods contain fat replacers—ingredi- ents made from carbohydrate or protein that provide some of the taste and texture of fats, but with fewer calories. Others contain artifi cial fats, synthetic compounds offering the sensory proper- ties of fat but none of the calories. For example, “lite” potato chips and other snack foods contain olestra, an artifi cial fat. Formerly, questions about olestra’s safety limited its popularity but manufac- turers have reformulated their products to remedy the problems. Chapter 12 provides details about artifi cial fats and other food additives.

Keep in mind that “fat-free” versions of normally high-fat foods do not necessar- ily provide fewer calories than the original product, particularly when carbohydrates such as added sugars replace the fats. They may be very low in saturated fats, however; read their labels to evaluate whether they are useful in your diet.

COOKING AT HOME Once at home, minimize solid saturated fats used as seasonings. This means eating cooked vegetables without butter,

179F a t i n t h e D i e t

replaced by unsaturated vegetable oils to maintain a taste and texture close to the original cheese. These cheeses pro- vide the same calories as regular cheese but help to reduce saturated fat intakes.

CHOOSE UNSATURATED OILS When choosing oils, trade off among different types to obtain the benefi ts different oils offer. Peanut and saffl ower oils are especially rich in vitamin E. Olive oil presents the heart with health benefi ts (see the Controversy section for details), and canola oil is rich with monounsatu- rates and the essential fatty acids. High temperatures, such as those used in frying, destroy some omega-3 acids and other benefi cial constituents, so treat your oils gently. Especially important: take care to substitute oils for saturated fats in the diet; do not add oils to an

tutes in recipes. These replacements will not change the taste or appearance of the fi nished product very much, but they will dramatically lower the calories and the saturated fat.

USE FLAVORFUL FATS When you add fats to foods, be sure that they are detectable and that you enjoy them. For example, if you use strongly fl avored fat, a little goes a long way. Sesame oil, peanut butter, nut oils, and the fats of strong cheeses are equal in calories to others, but they are so strongly fl avored that you can use much less. Try small amounts of grated Asiago, Romano, or other hard, intensely fl avored cheeses to replace larger amounts of less fl avorful cheeses. Some cheeses undergo processing to remove saturated butterfat and cholesterol, which are then

bacon, or stick margarine; replacing shortening with oils such as olive or canola oil; omitting high-fat meat gravies and cheese or cream sauces; and leav- ing off most other last-minute fatty addi- tions. As for calories, butter and regular margarine contain the same number of calories (about 35 per teaspoon); diet margarine contains fewer calories because water, air, or fi llers have been added. Imitation butter-fl avored sprinkles contain no fat and few calories.

For snacks, make it a habit to choose lower-fat microwave popcorn, and then sprinkle on butter or cheese fl avoring, if you like it. Keep that fl avoring on hand together with other substitutes such as diet, soft, or liquid margarine (generally low in saturated and trans fats), reduced- fat sauce mixes or recipes, and nonstick spray or olive oil for frying. Table 5-7 provides a list of other possible substi-

Artificial fats and other food additives are • topics of Chapter 12.

In addition to reducing foods high in saturated fat, use these substitutions.

Use Instead of

Fat-free milk products Whole-milk products

Evaporated fat-free (“skim”) milk (canned) Cream

Yogurta or fat-free sour cream replacer Sour cream

Soft or liquid margarine, olive oil, butter replacers Butter

Wine, lemon juice, or broth Butter

Fruit butters, nut butters Butter

Part-skim or fat-free ricotta, low-fat or fat-free cottage cheesea

Whole-milk ricotta

Part-skim or reduced-fat cheeses, “fi lled” cheeses in which vegetable oil has replaced saturated fat, avocado for cold dishes

Regular cheeses

Toasted nuts or seeds (in small amounts) Fried onion or potato chip toppings

Lean ground beef and grain mixture Ground beef

Low-fat frozen yogurt or sherbet Ice cream

Herbs, lemons, spices, fruits, liquid smoke fl avoring, olive oil, liquid margarine, or ham- fl avored bouillon cubes

Butter, bacon, bacon fat

Baked tortilla or potato chips, pretzels Regular chips

aIf the recipe calls for the food to be boiled, the yogurt or cottage cheese must be stabilized with a small amount of cornstarch or fl our.

Substitute Ingredients to Lower

Saturated Fat Intakes

table 5-7

fat replacers ingredients that replace some or all of the functions of fat and may or may not provide energy.

artifi cial fats zero-energy fat replacers that are chemically synthesized to mimic the sensory and cooking qualities of naturally oc- curring fats but are totally or partially resistant to digestion.

olestra a noncaloric artifi cial fat made from sucrose and fatty acids; formerly called sucrose polyester. A trade name is Olean.

180 chapter 5 T h e L i p i d s

Keep these facts about fast food in mind:

Salads are a good choice, but beware • of toppings such as fried noodles, ba- con bits, greasy croutons, sour cream, or shredded cheese that can drive up the calories, saturated fat, and trans fat contents. To reduce calories, avoid mixed salad-bar items, such as maca- roni salad. Use only about a quarter of the dressing provided with fast-food salads or use low-fat dressing.

If you are really hungry, order a small • hamburger or “veggie burger” and a side salad. Hold the cheese; use mus- tard or ketchup as condiments.

A small bowl of chili (hold the cheese • and sour cream) poured over a plain baked potato can also satisfy a bigger appetite. Top with chopped raw onions or hot sauce for spice.

Tacos and other Mexican treats are • delicious topped with salsa instead of cheese and sour cream.

Fast-food fried fi sh or chicken sand-• wiches provide at least as much fat as hamburgers and more trans fat. Broiled sandwiches are far less fatty if you order them made without spreads, dressings, cheese, bacon, or mayonnaise.

Chicken wings are mostly fatty skin, • and the tastiest wing snacks are fried in cooking fat (often a saturated hydro- genated type with trans-fatty acids), smothered with a buttery, spicy sauce, and then dipped in blue cheese dress- ing, making wings an extraordinarily high-fat food. If you snack on wings, plan on eating low-fat foods at several other meals to balance them out.

Because fast foods are short on variety, let them be part of a lifestyle in which they complement the other parts. Eat differently, often, elsewhere.

CHANGE YOUR HABITS By this time you may be wondering if you can realistically make all the changes recommended for your diet. In truth, even small changes yield big dividends

already fat-rich diet. No benefi ts are expected unless oils replace other, more saturated fats.

REVAMP RECIPES Here are some other tips to revise high- fat recipes that contribute excess fat calories and saturated fats:

Grill, roast, broil, boil, bake, stir-fry, • microwave, or poach foods. Don’t fry in solid fats, such as shortening or but- ter. If you must fry, use a little liquid oil for pan frying.

Choose large portions of salad greens • and other vegetables, and dress lightly. Reduce or eliminate “add- ons” such as batter, creamy sauces, cheese, sour cream, and bacon that drive up the calories and saturated fat. Add a small amount of olives, nuts, or avocado for rich fl avor.

Cut recipe amounts of meat in half; • use only lean meats. Fill in the lost bulk with soy meat replacers, shredded vegetables, legumes, pasta, grains, or other low-fat items.65

Replace a thick slice of ham with two • or three wafer-thin slices. The serving will be smaller and thus provide less fat, but the taste will be as satisfying because the ham surface area that im- parts fl avor to the taste buds is greater.

Refrigerate meat pan drippings and • broth, and lift off the fat when it solidi- fi es. Then add the defatted broth to a recipe.

Make prepared mixes, such as rice or • potato mixtures, without the fats called for on the label, or substitute liquid oils for solid fats in preparing them.

FIND LOWER-FAT FAST FOODS All of these suggestions work well when a person plans and prepares each meal at home. But in the real world, people fall behind schedule and don’t have time to cook, so they eat fast food. Figure 5-19 compares some fast-food choices and offers tips to reduce the calories and saturated fat to make fast-food meals healthier.

Did You Know? USDA facts:

70% of teenage males eat meals away • from home each day.

57% of all Americans and 40% of those • over 60 years old eat out daily.

The foods chosen away from home are • higher in fat, saturated fat, trans fat, and cholesterol and lower in vitamins and minerals than meals typically eaten at home.

181F a t i n t h e D i e t

2 “grande” burritos with beef, beans, cheese, and sour cream; salsa

2 bean burritos; salsa

Big double bacon cheeseburger, large fries, regular milkshake

Big broiled chicken breast sandwich, pickle, side salad with low-calorie dressing, fat-free milk

Taco salad with chili, cheese, sour cream, salsa, and taco chips

Taco salad with chili, salsa, and taco chips

Two slices extra cheese pizza with sausage and pepperoni

Two slices cheese pizza with mushrooms, olives, onions, and peppers

When ordering Mexican- style fast food, you can reduce both calories and saturated fat by limiting cheese, meat, and sour cream.

A broiled chicken breast sandwich with spicy mustard is just as tasty as a burger but delivers far less saturated fat and fewer calories. Beware of fried chicken sandwiches or “patties”—these can be as fatty as the hamburger choice.

Don’t let add-ons, such as greasy croutons, chips, bacon bits, full-fat cheese, and sour cream pile the calories and saturated fat onto your otherwise healthy fast- food salad. To cut fats and calories, leave off most of the toppings and use just half the dressing.

Reduce calories and saturated fat even further: try ordering your veggie pizza with half the regular melted cheese and sprinkle it with parmesan cheese, herbs, or hot peppers for flavor.

Burrito choices

Sandwich choices

Salad choices

Pizza choices

Higher in saturated fat Lower in saturated fat

1,000 880

80%

500

1,500

20 16

cal g sat fat cal g sat fat

30 100%

1,000

1,610

135%

500

1,500

30 100%

1,000 670

73%

500

1,500

20 14.5

30 100%

1,000

1,246

170%

500

1,500

30 100%

1,000 750

35%

500

1,500

30 100%

1,000

560

10%

500

1,500

2 0

30 100%

1,000

458 15%

500

1,500

30 100%

1,000 560

30%

500

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Key:

Calories

Grams saturated fat

% Daily Value (DV=20 g saturated fat)

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182 chapter 5 T h e L i p i d s

Analyze Your Lipid Intake The purpose of this exercise is to help you identify fatty foods in your diet, as well as sources of saturated and trans fats. The Diet Analysis Plus (DA�) program will help you learn which foods contain which fats and help you to choose unsaturated fats.

No amount of dietary saturated or 1. trans fat is required for health. Open the DA� Home page. From the Reports tab, select Fat Breakdown. Choose a date, choose all meals, then generate a report. Your report will show a breakdown of your fat in- take for that day as a percentage of total calories. What are the percent- ages for saturated, monosaturated, polyunsaturated, and trans fats in your day’s intake?

Which foods contribute the most fat 2. to your diet? Select Source Analy- sis from the Reports tab. Select a date and choose all meals. Gener-

ate a report for saturated fat and select Create PDF. Do the same for monosaturated, polyunsaturated, and trans fatty acids. What three foods contributed the most saturated and monounsaturated fats? Polyun- saturated and trans? Are any of your foods listed as top saturated fat con- tributors in Figure 5-11 (page 165)?

The Macronutrient Ranges report 3. compares your intakes to the recom- mended intake ranges. From the Reports tab, select the Macronutrient Ranges. Choose a date, choose all meals, and generate a report. Did your intake for fats fall within the rec- ommended range? What percentage of your calories came from fat?

To study your intake of essential 4. fatty acids, select Reports, Intake vs. Goals, select Day One, and all meals. Generate a report. Look for the essential fatty acid (efa) heading. Compared with the DRI goal, how

did your intake stack up? Use the Source Analysis Report to fi nd the sources of omega-3 and omega-6 essential fatty acids in your meals. What foods might you change to improve your intake (see Figure 5-5 on page 155).

Toppings and dressings added to 5. nutritious foods drive up calories and fats. The Food Feature (page 178) gives suggestions for reducing these add-ons. From the Track Diet tab, se- lect the Recipes button, then Create New Recipe to create an appealing heart-healthy salad with little saturated and trans fats. Save, and close your recipe. Select a new day (not from your three-day record) and select only your salad. Click on View: Favorites and then click the “i” icon next to the recipe name to display the nutrients in the salad. How did you do?

Concepts in Action

in terms of reducing harmful fats in the diet. Be assured that most such changes can become habits after a few repetitions. You do not have to give up all high-fat treats, nor should you strive

to eliminate all fats. You need only learn to exercise moderation. You decide what the treats should be and then choose them judiciously, just for pure pleasure. Meanwhile, make sure that your every-

day, ordinary choices are those whole, nutrient-dense foods suggested through- out this book. That way you’ll meet all your body’s needs for nutrients and never feel deprived.

183F a t i n t h e D i e t

Search for information on atherosclerosis, heart disease, and stroke at www.healthfi nder.gov.

Learn more about specifi c cardiovascular diseases or explore tools under the Health Tools tab that allow you to assess your disease risk at www.mayoclinic.com.

Read practical information about diet, exercise, and cardio- vascular risk reduction under the Healthy Lifestyle tab at www.americanheart.org.

media menu

Answers to these Self Check questions are in Appendix G.

Which of the following is 1. not one of the ways fats are useful in foods?

Fats contribute to the taste and smell of foods.A.

Fats carry fat-soluble vitamins.B.

Fats provide a low-calorie source of energy compared to C. carbohydrates.

Fats provide essential fatty acids.D.

Generally speaking, vegetable and fi sh oils are rich in which 2. of these?

polyunsaturated fat A.

saturated fatB.

cholesterolC.

trans-D. fatty acids

A benefi t to health is seen when _______ is used in place 3. of _______ in the diet.

a. saturated fat/monounsaturated fatA.

saturated fat/polyunsaturated fatB.

monounsaturated fat/saturated fatC.

polyunsaturated fat/cholesterolD.

Chylomicrons, a class of lipoproteins, are produced in the:4.

gallbladderA.

small intestinal cellsB.

large intestinal cellsC.

liverD.

The roles of the essential fatty acids include:5.

forming parts of cell membranes.A.

supporting infant growth and vision development.B.

supporting immune function.C.

all of the above.D.

LDL deliver triglycerides and cholesterol from the liver to the 6. body’s tissues. T F

Taking supplements of fi sh oil is recommended for those 7. who don’t like fi sh. T F

Consuming large amounts of 8. trans-fatty acids lowers LDL cholesterol and thus lowers the risk of heart disease and heart attack. T F

Trans9. fatty acids form in foods primarily when saturated fats are heated, as in frying. T F

Fried fi sh from fast-food restaurants and frozen fried fi sh 10. products are often low in omega-3 and high in saturated fatty acids. T F

self check

http://www.cengage.com/sso

http://www.healthfi

http://www.mayoclinic.com

http://www.americanheart.org

184 chapter 5 T h e L i p i d schapter 5 T h e L i p i d s

CONTROVERSY

Good Fats and Bad Fats— Which Are Which?

To consumers, advice about dietary fats appears to change almost daily. “Eat less fat—choose more fatty fi sh.” “Give up butter and margarine—use soft margarine.” “Forget soft margarine— replace it with olive oil.” To researchers, however, the evolution of advice about fats refl ects decades of study to reveal the truth about dietary fats. As scientifi c understanding has grown, dietary guide- lines have become more specifi c and therefore more meaningful.

This Controversy begins with a closer look at today’s guidelines for lipid intakes. It also singles out the Mediter- ranean diet as an eating style famous for supporting the health of the heart despite its inclusion of high-fat foods.1* It concludes with strategies for choosing the right amounts of the right kinds of fats within the context of a heart-healthy diet and lifestyle.

THE OBJECTIONS TO “LOW-FAT” GUIDELINES For years, consumers were urged to cut their fat intakes in everything from hot dogs to salad dressings to preserve their good health. This advice was straight- forward: cut the fat and improve your health. Dietary saturated fat is a well- established culprit behind elevated blood cholesterol, but the guidelines focused on limiting total fat to 30 percent or less of calories. Did this strategy work to cut saturated fat intake? Yes, but only for those few who consistently applied the advice. Most who tried failed, fi nding the

low-fat diet impossible to maintain over months or years.

In addition to poor compliance, low-fat diets present several other problems. For one, a low-fat diet is not necessarily low in calories, and many overweight people with heart disease need to reduce calorie consumption. For another, diets high in refi ned carbohydrates, even if low in fat, can cause blood triglycerides to rise and HDL to fall, a deleterious combina- tion for heart health.2 Finally, taken to the extreme, a low-fat diet may exclude nutritious foods, such as fatty fi sh, nuts, seeds, and vegetable oils, that provide the essential fatty acids along with many phytochemicals, vitamins, and minerals.

Are Low-Fat Diets Helpful for Anyone? It should be said that low-fat diets remain a critical centerpiece of treatment plans for people with elevated blood lipids or heart disease and therefore are impor- tant in nutrition.3 But what about healthy people? Evidence from around the world has led researchers to change population- wide recommendations from a “low-fat” to a “wise-fat” approach to help healthy people to stay healthy.

A classic study of the effects of diet on the world’s people, the Seven Countries Study, fi rst revealed the strong asso- ciation between death rates from heart disease and diets high in saturated fats.4 Even early on, evidence for harm from total fat was weak. In fact, the two countries with the highest fat intakes were Finland and the Greek island of Crete; yet Finland had the highest rate of death from heart disease while Crete had the lowest.

In both countries, fat provided 40 per- cent or more of total calories. Total fat was clearly not to blame for a high rate of heart disease—something else had to be responsible. When researchers more closely examined the diets of these fat-loving peoples, they found that the Cretes ate diets high in olive oil but low in saturated fat (less than 10 percent of calories), a pattern they linked with relatively low disease risks.

Many studies that followed yielded similar results—people who eat tradi- tional “Mediterranean-type” diets typical of the region in the mid-1900s have low rates of heart disease, some cancers, and other chronic diseases and their life expectancy is high. Unfortunately, many busy Mediterranean people today, and especially the young, are trading labor- intensive traditional diets for convenient and fast Western-style foods. At the same time, their health advantages are rapidly disappearing.5

The New Guidelines On reviewing the evidence, the DRI com- mittee concluded that a diet containing a slightly greater percentage of fat—up to 35 percent of total calories—but reduced in saturated fat and trans fat and con- trolled in energy (calories) is compatible with low rates of heart disease, diabetes, obesity, and cancer. The Dietary Guide- lines for Americans 2005 and the Ameri- can Heart Association therefore suggest replacing the “bad” saturated and trans fats with “good” unsaturated fats and enjoying these fats within calorie limits.6 These authorities make clear, however, that the human body requires a diet adequate in nutrients, including the es-

LO 5.9

*Reference notes are found in Appendix F.

185controversy 5 G o o d F a t s a n d B a d F a t s — W h i c h A r e W h i c h ?

Traditional Mediterranean people focus their diets on crusty breads, whole grains, nuts, potatoes, and pastas; a variety of vegetables (including wild greens) and legumes; feta and mozza- rella cheeses and yogurt; and fruits (es- pecially lemons, grapes, and fi gs). They eat some fi sh, other seafood, poultry, a few eggs, and a little meat. Along with ol- ives and olive oil, their principal sources of fat are nuts and fi sh; they rarely use butter or encounter hydrogenated fats. Consequently, traditional Mediterranean diets are:

Low in saturated fat.•

Very low or absent in • trans fat.

Rich in unsaturated fats, including • monounsaturated fats and EPA and DHA.

Rich in carbohydrates from whole • foods, including fi ber.

Rich in nutrients and phytochemicals.•

As a result, lipid profi les improve, infl am- mation diminishes, and the risks of heart disease, stomach cancer, and many other conditions decline.14 Early research even reveals a correlation with preserved mental faculties in old age—and the more stringently the diet is followed, the better.15

In traditional Mediterranean diets, omega-3 fatty acids derive from some atypical foods, such as wild plants and snails unavailable to U.S. consumers. In addition, because food animals graze in fi elds, their meat, dairy products, and eggs are richer in omega-3 fatty acids than those from animals fed grain, as done elsewhere. Apparently, each of the foods in a traditional Mediterranean diet contributes some small benefi t that harmonizes with others to produce a substantial cumulative or synergistic benefi t.

Fish: A Key Mediterranean Food The Mediterranean regions are sur- rounded by the sea, and seafood provides a great deal of the protein in a traditional diet. The preceding chapter made clear that fi sh oils hold the poten- tial to improve health, and particularly the health of the heart. Research studies cited in the preceding chapter lend strong support for increasing omega-3 fatty acids in the diet to lower the risk of heart disease.16 People who eat some

but also their potential for protecting the health of the heart. Treat olive oils gently when cooking—olive oil burns easily.

Other liquid unhydrogenated vegeta- ble oils, such as avocado oil, canola oil, grapeseed oil, walnut oil, and other nut oils, provide little saturated fat with their abundant unsaturated fats. Such oils, when they replace solid, saturated fats in the diet, preserve heart health. In fact, canola oil qualifi es to claim heart benefi ts on its label by virtue of its low saturated fat content.

People who treat olive or nut oil like a magic potion against heart disease are bound to be disappointed. Drizzling olive oil on a high-saturated-fat food, such as a cheese and sausage pizza, does not make the food healthier. Also, like other fats, olive oil delivers 9 calories per gram. Adding oils to foods can easily add hundreds of calories to a day’s intake, making weight gain inevitable in those who fail to balance energy intake with energy output (see Chapter 9).

The Mediterranean Diet Beyond Olive Oil Olive oil alone cannot account for the heart benefi ts associated with the tradi- tional Mediterranean diet. Such features as low intakes of red meats, and higher intakes of nuts, vegetables, and sea- sonal fruits probably also deserve some credit.12 The traditional Mediterranean diet features fresh, whole foods and few processed foods.13 Though each of the countries bordering the Mediterranean Sea has its own culture and dietary tradi- tions, researchers have identifi ed some common characteristics.

sential fatty acids, and that no saturated or trans fats are essential for health.

HIGH-FAT FOODS AND HEART HEALTH Avocados, salami, cheese, walnuts, po- tato chips, and mackerel are all high-fat foods, yet the fats of these foods differ markedly in their health effects. The fol- lowing evidence can help to clarify why some high-fat foods rightly belong in a heart-healthy diet and why others are best left on the shelf.

Olive Oil: The Mediterranean Connection The traditional health-promoting diets of Greece and the Mediterranean region are exemplary in their use of “good” fats, especially olives and their oil. In popula- tion and laboratory studies, use of dark green (virgin) olive oil instead of other cooking fats, especially butter, stick mar- garine, and meat fats, has been linked with numerous potential health benefi ts. When olive oil replaces saturated fats in the diet, such as those of butter, coconut or palm oil, hydrogenated stick mar- garine, lard, or shortening, it may help protect against heart disease by some of these mechanisms:

Lowering total and LDL cholesterol • and not lowering or raising HDL cholesterol.7

Reducing LDL cholesterol’s vulnerabil-• ity to oxidation.8

Reducing blood-clotting factors.•

Providing phytochemicals that act as • antioxidants (see Controversy 2).9

Lowering blood pressure.• 10

Interfering with the infl ammatory • response.11

When choosing olive oil, go for the darker, “extra virgin” kind because it contains the highest levels of potentially benefi cial phytochemicals. When re- searchers studied the effects of olive oils on 200 healthy men, they found that ex- tra virgin oil elevated blood HDL levels to a greater extent than lighter, more refi ned olive oils. When processors lighten the oils, they strip away the intensely fl avored phytochemicals of the olives, thus dimin- ishing not only the bitter fl avor of the oils

Olives and their oil may benefi t heart health.

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186 chapter 5 T h e L i p i d s

choose to include a few nuts each day for their potential health benefi ts.26

Researchers studying nut effects must carefully adjust the calories of test diets to make room for the nuts—that is, they use carefully measured amounts of nuts instead of, not in addition to, other fat sources (such as meats, potato chips, oils, margarine, and butter) to keep calories constant. If you decide to snack on nuts, you should do the same thing. Remember that nuts provide substantially more calories per bite than, say, whole- grain pretzels or crunchy raw vegetables. People struggling to maintain enough body weight can welcome the extra calo- ries of added nuts; all others must adjust for them to avoid unneeded weight gain.

Butter or Margarine: Which to Choose? When news of the possible effects of trans-fatty acids on heart health fi rst emerged, oversimplifi ed reports implied that margarine provides no heart-health advantage over butter. Admittedly, hard margarines and virtually all shortenings are made largely from hydrogenated fats and therefore contain substantial saturated fatty acids. Since the 2006 requirement that trans fat be listed on the Nutrition Facts panel of food labels, margarine makers have reformulated their products to contain much less trans fat.27 Soft or liquid varieties are made from unhydrogenated oils, which are mostly unsaturated and so are less likely to elevate blood cholesterol than the saturated fats of butter. Some contain olive oil or omega-3 fatty acids, making these margarines preferable to butter and other margarines for the heart.

Read the Labels With over 57 types of margarines and spreads on the market in

lipids—even in people whose total and LDL cholesterol were elevated at the outset. In animals, walnuts improve other markers of heart health as well.21

Evidence on Almonds Some observa- tions suggest a reduction of heart dis- ease in people who consume almonds, but the results can be diffi cult to interpret. In one study, subjects with high blood LDL cholesterol added about an ounce of almonds to a low-fat, low-cholesterol diet and also consumed margarine enriched with plant sterols, along with foods rich in soluble fi bers and soy foods each day.22 Most subjects had no prob- lem consuming almonds and margarine but failed to include the fi ber and soy. While the average blood LDL concentra- tion had dropped by 13 percent, no one can say with certainty whether almonds were responsible for the drop. In a recent meta-analysis of studies on almonds and blood lipids, researchers concluded that almonds themselves have a neutral ef- fect on blood lipids.23 If eating almonds lowers heart disease risk, then, another mechanism may be in play.

Potential for Benefi ts from Nuts Nuts may lower heart disease risk be- cause they are:

Low in saturated fats.•

High in fi bers, vegetable protein, and • other valuable nutrients, including the antioxidant vitamin E.

A source of antioxidant phytochemi-• cals that oppose infl ammation related to chronic diseases; antioxidants are concentrated in the brown papery skins that surround the nutmeats.24

A source of plant sterols that block • cholesterol absorption.

Walnuts also supply linolenic acid, a little of which the tissues can convert to mostly EPA and less of DHA. Linolenic acid is currently under study for heart protec- tive effects, anti-infl ammatory roles, and benefi ts to the brain and nerves.25

High-Calorie Foods Nuts and peanuts once had no place in a low-fat or low- calorie diet, with good reason—up to 80 percent of their calories come from fat, and an ounce (¼ c) of nuts provides over 200 calories. Research does not report greater weight gain in those who consume nuts, so even dieters may

fi sh each week lower their risks of heart attack and stroke. Table 5-6 on page 169 of the chapter identifi ed fi sh varieties that supply at least 1 gram of omega-3 fatty acids per serving.

Nuts: More Than a High-Calorie Snack Food Nuts are extraordinarily popular in tradi- tional Mediterranean cuisines and show up in everything from savory sauces to desserts. In fact, nuts are popular with most people around the world. Not only do nuts taste good, they seem to have favorable effects on heart health, too.17

Nuts for the Heart People who eat an ounce of nuts on fi ve or more days a week appear to have lower heart disease risks than those consuming no nuts.18 Even in women with diabetes, whose risks are high, nuts (5 oz per week) or peanut butter (5 tbs per week) were associated with reduced heart disease risk.19 As little as 2 ounces of nuts a week may provide a detectable benefi t.

The nuts under study are the common varieties: almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pistachios, walnuts, even peanuts with skins, and, as mentioned, peanut but- ter.20 On average, such nut varieties contain mostly monounsaturated fat (59 percent), some polyunsaturated fat (27 percent), and just a small amount of saturated fat (14 percent). Walnuts are well-studied. Time and again, walnuts, when substituted for other fats in the diet, produce favorable effects on blood

Fish and other seafood contributes key nutri- ents to the traditional Mediterranean diet.

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187controversy 5 G o o d F a t s a n d B a d F a t s — W h i c h A r e W h i c h ?

saturated fatty acids as well. Diets based on fruits, greens, legumes, nuts, soy products, vegetables, and whole grains can, and often do, deliver less saturated fat than diets based on animal-derived foods, however. Table C5-1 summarizes which foods provide which fats.

CONCLUSION Are some fats “good” and others “bad” from the body’s point of view? Certainly, saturated and trans fats seem mostly bad for the health of the heart. Aside from providing energy, which unsatu- rated fats can do equally well, saturated and trans fats bring no indispensable benefi ts to the body. Furthermore, no harm can come from consuming diets low in saturated fats and trans fats.

In contrast, unsaturated fats are mostly good for the health of the heart when consumed in moderation and within a sensible calorie limit. To date, their one proven fault seems to be that they, like all fats, provide abundant energy and so may promote obesity if they drive calorie intakes higher than energy needs.31 Obesity, in turn, often begets many body ills (see Chapter 9).

Fatty Acids Occur in Mixtures When judging foods by their fatty acids, keep in mind that food fats present the body with a mixture of both saturated and unsaturated fatty acids. As the preceding chapter showed, even olive oil and other vegetable oils deliver some saturated fat. Consequently, even when a person chooses foods with mostly unsaturated fats, saturated fat can still add up if total fat is high.

in energy from saturated fatty acids in the diet produces an estimated 2 percent jump in heart disease risk by way of ele- vating blood LDL cholesterol. Conversely, reducing saturated fat intake by 1 percent is estimated to produce a 2 percent drop in heart disease risk by the same mecha- nism. Even a 2 percent drop in LDL rep- resents a signifi cant improvement for the health of the heart.29 Similarly, trans fats also raise heart disease risk by elevating LDL cholesterol. A heart-healthy diet limits foods rich in these two types of fat.

To limit saturated fat intake, consumers must choose carefully among high-fat foods. Over a third of the fat in most meats is saturated. Over half of the fat in whole milk and other high-fat dairy products, such as cheese, butter, cream, half-and-half, cream cheese, sour cream, and ice cream, is saturated (review Figure 5-5 of the chapter). The saturated fats of palm and coconut oils are rarely used by consumers in the kitchen but their stability and other properties make them useful to food manufacturers, so commercially prepared foods provide these fats in abundance.

To choose among meats, milk prod- ucts, and commercially prepared foods, rely on the Nutrition Facts panels of la- bels to point to those lowest in saturated fat and trans fat. Appendix A lists the saturated fat in thousands of foods that bear no labels.

Designing a diet with zero saturated fat is not possible, even for experts.30 A nutri- tionally adequate diet will always provide some saturated fat because foods that provide the essential polyunsaturated fatty acids also supply some amount of

sticks, tubs, sprays, and liquids contain- ing from 0 percent to 80 percent fat, consumers must educate themselves, read labels, and select margarines that provide the preferred fl avor with the least saturated and trans fat.28 When oils (but not hydrogenated oils) are the fi rst ingredient listed on a margarine label, the margarine is, in all probability, low in saturated and trans fats and therefore a good choice for a healthy heart.

Instead of, Not in Addition to Simply adding margarine that contains plant sterols, olive oil, or fi sh oils to a diet high in saturated fat is unlikely to bring health benefi ts. These substances cannot undo the damage from a diet consistently high in saturated fats. Plant-enriched margarines have drawbacks. They cost much more than regular margarine, they equal regular margarine in calories, and they are not proven safe for use by certain populations, such as growing chil- dren. Recently, plant sterols have been added to juices and candies, foods that appeal to children.

Food manufacturers may soon come to the assistance of consumers wishing to choose unsaturated fats instead of sat- urated and trans fats. Most major snack manufacturers are reducing the saturated and trans fats in some of their products and offering snack foods in smaller pack- ages to reduce serving sizes.

Fats to Avoid: Saturated Fats and Trans Fats The number-one dietary determinant of LDL cholesterol is saturated fat. Figure C5-1 shows that each 1 percent increase

2% decrease in blood LDL cholesterol

1% decrease in dietary saturated fatty acidsa

2% decrease in heart disease riskb

1% increase in dietary saturated fatty acidsa

2% increase in blood LDL cholesterol

2% increase in heart disease riskb

Impact of Change in Saturated Fatty Acid Intake on Blood LDL Cholesterol

and Heart Disease Risk

figure C5-1

aPercentage of change in total energy intake from saturated fatty acids. bThe change in an individual’s risk may compound when blood lipid changes are sustained over time.

188 chapter 5 T h e L i p i d s

The Synergy of a Whole Foods Diet Pattern and Lifestyle While some traditional Mediterranean foods stand out as sources of benefi cial or benign fats, it may not be possible to tease apart the pieces that make up the whole. The health benefi ts results observed in research arise most often from a diet pattern, chosen in various forms, day after day, rather than from a single food’s presence or absence.32 To achieve similar results for yourself, try designing your own diet on traditional Mediterranean principles. That is, dine on vegetables, fruits, whole grains, seafood, and legumes most often, and replace saturated fats with unsaturated sources such as oils from nuts and olives. In addition, reduce intakes of convenience foods and fast foods; choose small portions of meats, fi sh, and poultry; and select portion sizes that do not exceed your energy requirement. Figure C5-2 presents a Mediterranean food pyramid for guidance.

Keep in mind that Mediterranean peoples have traditionally led physically active lifestyles, and physical activity reduces disease risks. Therefore, if you love olive oil and generally want to eat like a Greek, you’d better walk, garden, bicycle, and swim like one, too.

HEALTHFUL FATTY ACIDS

Monounsaturated Omega-6 Polyunsaturated Omega-3 Polyunsaturated

Avocado Nuts (almonds, cashews, fi lberts, hazelnuts,

macadamia nuts, peanuts, pecans, pistachios) Oils (canola, olive, peanut, saffl ower, sesame) Olives Peanut butter (old-fashioned) Seeds (sesame)

Margarine (nonhydrogenated) Mayonnaise Nuts (walnuts) Oils (corn, cottonseed, soybean) Salad dressing Seeds (pumpkin, sunfl ower)

Fatty fi sh (listed in Table 5-6 of the preceding chapter)

Flaxseed Nuts

HARMFUL FATTY ACIDS

Saturated Trans

Commercial baked goods, including cookies, cakes, pies, or other goodies made with margarine or vegetable shortening

Fried foods, particularly restaurant and fast foods Many fried or processed snack foods, including microwave popcorn, chips, and crackers Margarine (hydrogenated or partially hydrogenated) Nondairy creamer Shortening

Note: Keep in mind that foods contain a mixture of fatty acids; see Figure 5-5, p. 155.

Food Sources of Fatty Acids table C5-1

Bacon Butter Cheese Chocolate Coconut Cream, half-and-half Cream cheese

Lard Meat Milk fat (whole milk products) Oils (coconut, palm, palm

kernel) Shortening Sour cream

Be Physically Active; Enjoy Meals with Others

Fruits, Vegetables, Grains (mostly whole), Olive oil, Beans, Nuts, Legumes and Seeds, Herbs and Spices Base every meal on these foods

Fish and Seafood Often, at least two times per week

Meats and Sweets Less often

Poultry and Eggs Moderate portions, every two days or weekly

Cheese and Yogurt Moderate portions, daily to weekly

Wine In moderation

Drink Water

Mediterranean Diet Pyramid A contemporary approach to delicious, healthy eating

A Mediterranean Diet Pyramid figure C5-2

http://www.oldwayspt.org

66The Proteins and Amino Acids

do you ever . . . Wonder why you need protein?•

Find it curious that heating an egg • changes it from a liquid to a solid?

Take amino acid pills?•

Fear that your diet will lack protein • unless you eat at least some meat?

Keep reading . . .

LO 6.1 Describe why some amino acids are essential, nonessential, or conditionally essential to the human body, and state the outcome should any one of them be lacking from the diet.

LO 6.2 Compare the digestion of protein and transport of amino acids with digestion and transport of lipids in the body.

LO 6.3 Discuss the roles that various proteins and amino acids can play in the body.

LO 6.4 Describe the fate of amino acids consumed with a balanced diet versus a carbohydrate-poor diet.

LO 6.5 Discuss the concept of nitrogen balance and compute the amount of protein needed for a healthy college student.

LO 6.6 Identify the major forms of protein malnutrition, and discuss reasons why consuming too much protein is not recommended.

LO 6.7 Summarize the health advantages and nutritional risks of a vegan diet.

LO 6.8 Develop a lacto-ovo vegetarian diet plan that meets all nutrient requirements for a given individual.

190 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

T he proteins are amazing, versatile, and vital cellular working molecules. With- out them, life would not exist. First named 150 years ago after the Greek word

proteios (meaning “of prime importance”), proteins have revealed countless secrets of the processes of life and have helped to answer many questions in nutrition: How do we grow? How do our bodies replace the materials they lose? How does blood clot? What gives us immunity? What makes one person diff erent from another? Understanding the nature of the proteins helps to solve these mysteries.

LO 6.1

The Structure of Proteins Th e structure of proteins enables them to perform many vital functions. One key diff erence from carbohydrates and fats is that proteins contain nitrogen atoms in addition to the carbon, hydrogen, and oxygen atoms that all three energy-yielding nutrients contain. Th ese nitrogen atoms give the name amino (which means “nitro- gen containing”) to the amino acids, the building blocks of proteins. Another key diff erence is that in contrast to the carbohydrates—whose repeating units, glucose molecules, are identical—the amino acids in a strand of protein are diff erent from one another. A strand of amino acids that makes up a protein may contain 20 dif-

ferent kinds of amino acids.

Amino Acids All amino acids have the same simple chemical backbone consisting of a single carbon atom with both an amine group (the nitrogen-containing part) and an acid group attached to it. Each amino acid also has a distinctive chemical side chain attached to the center carbon of the backbone (see Figure 6-1). It is this side chain that gives identity and its chemical nature to each amino acid. About 20 amino acids, each with its own diff erent side chain, make up most of the proteins of living tissue.1* Other rare amino acids appear in a few proteins.

Th e side chains make the amino acids diff er in size, shape, and electrical charge. Some are negative, some are positive, and some have no charge (are neutral). Th e fi rst part of Figure 6-2 is a diagram of three amino acids, each with a diff erent side chain attached to its backbone. Th e rest of the fi gure shows how amino acids link to form protein strands. Long strands of amino acids form large protein molecules, and the side chains of the amino acids ultimately help to determine the protein’s molecular shape and behavior.

Essential Amino Acids Th e body can make about half of the 20 amino acids for itself, given the needed parts: fragments derived from carbohydrate or fat to form the backbones and nitrogen from other sources to form the amine groups. Th e healthy adult body cannot make some amino acids or makes them too slowly to meet its needs. Th ese are the essential amino acids (listed in the margin on page 193). Without these essential nutrients, the body cannot make the proteins it needs to do its work. Because the essential amino acids can only be replenished from foods, a person must frequently eat the foods that provide them.

Under special circumstances, a nonessential amino acid can become essential. For example, the body normally makes tyrosine (a nonessential amino acid) from the essential amino acid phenylalanine. If the diet fails to supply enough phenyl alanine or if the body cannot make the conversion for some reason (as happens in the in- herited disease phenylketonuria; see Chapter 3, page 71), then tyrosine becomes a conditionally essential amino acid.

Recycling Amino Acids Th e body not only makes some amino acids but also breaks protein molecules apart and reuses those amino acids. Both food proteins after digestion and body proteins when they have fi nished their cellular work are dis- mantled to liberate their component amino acids.2 Amino acids from both sources

*Reference notes are found in Appendix F.

Backbone

Side chain

Acid groupAmine group

The “backbone” is the same for all amino acids. The side chain differs from one amino acid to the next. The nitrogen is in the amine group.

An Amino Acid figure 6-1

proteins compounds composed of carbon, hydrogen, oxygen, and nitrogen and arranged as strands of amino acids. Some amino acids also contain the element sulfur.

amino (a-MEEN-o) acids the building blocks of protein. Each has an amine group at one end, an acid group at the other, and a distinctive side chain.

amine (a-MEEN) group the nitrogen- containing portion of an amino acid.

side chain the unique chemical structure attached to the backbone of each amino acid that differentiates one amino acid from another.

essential amino acids amino acids that either cannot be synthesized at all by the body or cannot be synthesized in amounts suf- fi cient to meet physiological need. Also called indispensable amino acids.

conditionally essential amino acid an amino acid that is normally non- essential but must be supplied by the diet in special circumstances when the need for it exceeds the body’s ability to produce it.

191T h e S t r u c t u r e o f P r o t e i n s

provide the cells with raw materials from which they can build the protein molecules they need. Cells can also use the amino acids for energy and discard the nitrogen at- oms as wastes. By reusing intact amino acids to build proteins, however, the body re- cycles and conserves a valuable commodity while easing its nitrogen disposal burden.

Th is recycling system also provides access to an emergency fund of amino acids in times of fuel, glucose, or protein deprivation. At such times, tissues can break down their own proteins, sacrifi cing working molecules before the ends of their normal lifetimes, to supply energy and amino acids to the body’s cells. Th e body employs a priority system in selecting the tissue proteins to dismantle—it uses the most dis- pensable ones fi rst, such as the small proteins of the blood and muscles.3 It guards the structural proteins of the heart and other organs until forced, by dire need, to relinquish them.

KE Y POINT Proteins are unique among the energy nutrients in that they possess nitrogen-containing amine groups and are composed of 20 diff erent amino acid units. Of the 20 amino acids, some are essential and some are essential only in special circumstances.

How Do Amino Acids Build Proteins? In the fi rst step of making a protein, each amino acid is hooked to the next (as shown in Figure 6-2). A chemical bond, called a peptide bond, is formed between the amine group end of one amino acid and the acid group end of the next. Th e side chains bristle out from the backbone of the structure, giving the protein molecule its unique character.

Th e strand of protein does not remain a straight chain. Figure 6-2 shows only the fi rst step in making proteins—the linking of amino acid units with peptide bonds until the strand contains from several dozen to as many as 300 amino acids. Amino acids at diff erent places along the strand are chemically attracted to each other, and this attraction causes some segments of the strand to coil, somewhat like a metal spring. Also, each spot along the coiled strand is attracted to, or repelled from, other spots along its length (demonstrated in Figure 6-3). Th ese interactions cause the entire coil to fold this way and that, forming either a globular structure, as shown in Figure 6-4, or a fi brous structure (not shown).

Th e amino acids whose side chains are electrically charged are attracted to water. Th erefore, in the body’s watery fl uids, they orient themselves on the outside of the protein structure. Th e amino acids whose side chains are neutral are repelled by wa- ter and are attracted to one another; these tuck themselves into the center away from the body fl uids. All these interactions among the amino acids and the surrounding fl uids fold each protein into a unique architecture, a form to suit its function.

One fi nal detail may be needed for the protein to become functional. Several strands may cluster together into a functioning unit, or a metal ion (mineral), a vita- min, or a carbohydrate molecule may join to the unit and activate it.

Valine Leucine Tyrosine Single amino acids with different side chains . . .

can bond to form . . . a strand of amino acids, part of a protein.

This is the basic process by which proteins are assembled.

Different Amino Acids Join Together figure 6-2

Hair, skin, eyesight, and the health of the whole body depend on protein from food.

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peptide bond a bond that connects one amino acid with another, forming a link in a protein chain.

192 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

KE Y POINT Amino acids link into long strands that coil and fold to make a wide variety of diff erent proteins.

The Variety of Proteins Th e particular shapes of proteins enable them to perform diff erent tasks in the body. Th ose of globular shape, such as some proteins of blood, are water-soluble. Some form hollow balls, which can carry and store materials in their interiors. Some pro- teins, such as those of tendons, are more than 10 times as long as they are wide, forming stiff , rodlike structures that are somewhat insoluble in water and very strong. A form of the protein collagen acts somewhat like glue between cells. Th e hormone insulin, a protein, helps to regulate blood glucose. Among the most fas- cinating proteins are the enzymes, which act on other substances to change them chemically. More of the body’s proteins are discussed in a later section.

A portion of a strand of amino acids.

The strand coils, as this “ribbon” demonstrates.

The completed protein.

The first shape of a strand of amino acids is a chain, which can be very long. This shows just a portion of the strand.

Coiling the strand. The strand of amino acids takes on a springlike shape as their side chains variously attract and repel each other.

Once coiled and folded, the protein may be functional as is, or it may need to join with other proteins, or add a carbohydrate molecule or a vitamin or mineral, as the iron of the protein hemoglobin demonstrates in Figure 6-4 (page 193).

Folding the coil. The coil then folds and flops over on itself to take a functional shape.

Animated!

The Coiling and Folding of a Protein Molecule figure 6-3

collagen (KAHL-ah-jen) a type of body protein from which connective tissues such as scars, tendons, ligaments, and the foundations of bones and teeth are made.

enzymes (EN-zimes) proteins that facilitate chemical reactions without being changed in the process; protein catalysts.

hemoglobin the globular protein of red blood cells, whose iron atoms carry oxygen around the body via the bloodstream (more about hemoglobin in Chapter 8).

193T h e S t r u c t u r e o f P r o t e i n s

Some protein strands work alone, while others must associate in groups of strands to become functional. One molecule of hemoglobin—the large, globular protein mole- cule that is packed into the red blood cells by the billions and carries oxygen—is made of four associated protein strands, each holding the mineral iron (see Figure 6-4).

Th e great variety of proteins in the world is possible because an essentially infi nite number of sequences of amino acids can be formed. To understand how so many diff erent proteins can be designed from only 20 or so amino acids, think of how many words are in an unabridged dictionary—all of them constructed from just 26 letters. If you had only the letter “G,” all you could write would be a string of Gs: G–G–G–G–G–G–G. But with 26 diff erent letters available, you can create poems, songs, or novels. Similarly, the 20 amino acids can be linked together in a huge variety of sequences—many more than are possible for letters in a word, which must alternate consonant and vowel sounds. Th us, the variety of possible sequences for amino acid strands is tremendous. A single human cell may contain as many as 10,000 diff erent proteins, each one present in thousands of copies.

Inherited Amino Acid Sequences For each protein there exists a standard amino acid sequence, and that sequence is specifi ed by heredity. Often, if a wrong amino acid is inserted, the result can be disastrous to health.

Sickle-cell disease—in which hemoglobin, the oxygen-carrying protein of the red blood cells, is abnormal—is an example of an inherited variation in the amino acid sequence. Normal hemoglobin contains two kinds of protein strands. In sickle- cell disease, one of the strands is an exact copy of that in normal hemoglobin, but in the other strand, the sixth amino acid is valine rather than glutamic acid. Th is replacement of one amino acid so alters the protein that it is unable to carry and release oxygen. Th e red blood cells collapse from the normal disk shape into cres- cent shapes (see Figure 6-5). If too many crescent-shaped cells appear in the blood, the result is abnormal blood clotting, strokes, bouts of severe pain, susceptibility to infection, and early death.4

You are unique among human beings because of minute diff erences in your body proteins that establish everything from eye color and shoe size to susceptibility to

Iron

A heme structure holds the iron.

The amino acid sequence causes the strands to coil and loop, forming the globular protein structure.

Four highly folded protein strands form the globular hemoglobin protein.

The Structure of Hemoglobin figure 6-4

The essential amino acids:•

Histidine (HISS-tuh-deen).•

Isoleucine (eye-so-LOO-seen).•

Leucine (LOO-seen).•

Lysine (LYE-seen).•

Methionine (meh-THIGH-oh-neen).•

Phenylalanine (fen-il-AL-ah-neen).•

Threonine (THREE-oh-neen).•

Tryptophan (TRIP-toe-fan, TRIP-toe-fane).•

Valine (VAY-leen).•

Other amino acids important in nutrition:•

Alanine (AL-ah-neen).•

Arginine (ARJ-ih-neen).•

Asparagine (ah-SPAR-ah-geen).•

Aspartic acid (ah-SPAR-tic acid).•

Cysteine (SIS-the-een).•

Glutamic acid (GLU-tam-ic acid).•

Glutamine (GLU-tah-meen).•

Glycine (GLY-seen).•

Proline (PRO-leen).•

Serine (SEER-een).•

Tyrosine (TIE-roe-seen).•

NOTE: In special cases, some nonessential amino acids may become conditionally essen- tial (see the text).

194 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

certain diseases.5 Th ese diff erences are determined by the amino acid sequences of your proteins, which are written into the genetic code you inherited from your par- ents and they from theirs. Ultimately, the genes determine the sequence of amino acids in each fi nished protein, and some genes are involved in making more than one protein (how DNA directs protein synthesis is described in Figure 6-6). As scientists completed the identifi cation of the human genome, they recognized a still greater task that lies ahead: the identifi cation of every protein made by the human body.†

Nutrients and Gene Expression When a cell makes a protein, as shown in Fig- ure 6-6, scientists say that the gene for that protein has been “expressed.” Every cell nucleus contains the DNA for making every human protein, but cells do not make them all. Some cells specialize in making certain proteins; for example, cells of the pancreas express the gene for the protein hormone insulin. Th e gene for making insulin exists in all other cells of the body, but it is idle, or silenced.

Nutrients, including amino acids and proteins, do not change DNA structure, but they greatly infl uence genetic expression.6 As research advances, researchers hope to one day use nutrients to infl uence a person’s genes in ways that reduce dis- ease risks but, for now, that day is fi rmly in the future.7 Th e Controversy section of Chapter 11 comes back to this fascinating area of nutrient and gene interactions. Th e Th ink Fitness feature on page 196 addresses a related concern of exercisers and athletes about whether extra dietary protein or amino acids can trigger the synthesis of muscle tissue and increase strength.

KE Y POINT Each type of protein has a distinctive sequence of amino acids and so has great specifi city. Often, cells specialize in synthesizing particular types of proteins in addition to the proteins necessary to all cells. Nutrients can greatly aff ect genetic expression.

†The identifi cation of the entire collection of human proteins, the human proteome (PRO-tee-ohme), is a work in progress.

Normal red blood cellsSickle-shaped blood cells

Amino acid sequence of sickle-cell hemoglobin:

Val His Leu Thr Pro Glu

Amino acid sequence of normal hemoglobin:

Val His Leu Thr Pro GluGlu

Val

What a difference one amino acid can make! ©

D r. S

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U n lim

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Normal red blood cells are disk shaped. In sickle-cell disease, one amino acid in the protein strands of hemoglobin takes the place of another, causing the red blood cell to change shape and lose function.

Normal Red Blood Cells and Sickle Cells figure 6-5

CONCEPT LINK 6-1 Chapters 1 and 3 provided background on DNA, cells, and their fluids (pages 2–3 and 70–71).

195T h e S t r u c t u r e o f P r o t e i n s

The mRNA attaches itself to the protein-making machinery of the cell, the ribosomes. Meanwhile, another form of RNA, transfer RNA (tRNA), collects amino acids from the cell fluid and brings them to the messenger.

The mRNA exits the nucleus through the nuclear membrane. DNA remains inside the nucleus.

Ribosomes (protein-making machinery)

Ribosome

mRNA

DNA

As the amino acids are lined up in the right sequence, and the ribosome moves along the messenger, an enzyme bonds one amino acid after another to the growing protein strand.

Thousands of these tRNAs, each carrying its amino acid, cluster around the ribosomes, like donors bearing gifts to a host. When the messenger calls for an amino acid, the tRNA carrying it snaps into position. Then the next tRNA with its load moves into place, followed by the next tRNA and the next.

mRNA

Completed protein strand

DNA

Cell

Amino acid

tRNA

Finally, the completed protein is released. The mRNA is degraded or reused. The tRNAs are freed to return for more amino acids. It takes many words to describe these events, but in the cell, 40 to 100 amino acids can be added to a growing protein strand in only a second.

The DNA serves as a template to make strands of messenger RNA (mRNA). Each mRNA strand copies exactly the instructions for making some protein the cell needs.

Nucleus

1 2

Animated!

Protein Synthesis

figure 6-6

196 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

Denaturation of Proteins Proteins can be denatured (distorted in shape) by heat, radiation, alcohol, acids, bases, or the salts of heavy metals. Th e denaturation of a protein is the fi rst step in its destruction; thus, these agents are dangerous because they can disrupt a protein’s folded structure, making it unable to function in the body. In digestion, however, denaturation is useful to the body.

During the digestion of a food protein, the stomach acid opens up the protein’s structure, permitting digestive enzymes to make contact with the peptide bonds and cleave them. Denaturation also occurs during the cooking of foods. Cooking an egg denatures the proteins of the egg and makes it fi rm, as the margin photo demonstrates. More important for nutrition is that heat denatures two proteins in raw eggs: one binds the B vitamin biotin and the mineral iron, and the other slows protein digestion. Th us, cooking eggs liberates biotin and iron and aids digestion.

Many well-known poisons are salts of heavy metals like mercury and silver; these denature protein strands wherever they touch them. Th e common fi rst-aid antidote for swallowing a heavy-metal poison is to drink milk. Th e poison then acts on the protein of the milk rather than on the protein tissues of the mouth, esophagus, and stomach. Later, vomiting can be induced to expel the poison that has combined with the milk.

KE Y POINT Proteins can be denatured by heat, acids, bases, alcohol, or the salts of heavy metals. Denaturation begins the process of digesting food protein and can also destroy body proteins.

think fitness Can Eating Extra Protein Make Muscles Grow Stronger?

The answer is mostly “no” but also a qualified “yes.” Athletes and fit- ness seekers cannot stimulate their muscles to gain size and strength simply by consuming more protein or amino acids. Hard work is nec- essary to trigger the genes to build more of the muscle tissue needed for sport. The “yes” part of the answer reflects research suggest- ing that well-timed protein intakes can often further stimulate muscle growth. Protein intake cannot re- place exercise in this regard, how- ever, as many supplement sellers would have people believe. Exer- cise generates cellular messages

that stimulate the DNA to begin synthesizing the muscle proteins needed to perform the work. A protein-rich snack—say, a glass of skim milk or soy milk—consumed immediately before or within an hour or two after resistance exer- cise (such as weight lifting; see Chapter 10) may offer additional stimulus for muscle growth, but only within the context of the work- ing muscle. Athletes may need somewhat more dietary protein than other people do, and exercise authorities recommend higher protein intakes for athletes pursuing various ac-

tivities (Chapter 10 has details).8 Amino acid or protein supplements, however, offer no advantage over food, and amino acid supplements are more likely to cause problems (as this chapter’s Consumer Cor- ner makes clear). Bottom line: The path to bigger muscles is rigorous physical training with adequate en- ergy and nutrients from balanced, well-timed meals and snacks. Many more details about dietary protein and muscles are interesting and important, but this truth remains: extra protein and amino acids with- out physical work add nothing but excess calories.

START NOW

Ready to make a change? Consult the online behavior-change planner to help you plan to provide your muscles with the physical work and nutrients they need to grow stronger at www.cengage.com/sso.

Heat denatures protein, making it fi rm.

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denaturation the irreversible change in a protein’s folded shape brought about by heat, acids, bases, alcohol, salts of heavy metals, or other agents.

http://www.cengage.com/sso

197D i g e s t i o n a n d A b s o r p t i o n o f D i e t a r y P r o t e i n

LO 6.2

Digestion and Absorption of Dietary Protein Each protein performs a special task in a particular tissue of a specifi c kind of ani- mal or plant. When a person eats food proteins, whether from cereals, vegetables, beef, fi sh, or cheese, the body must fi rst alter them by breaking them down into amino acids; only then can it rearrange them into specifi c human body proteins.

Th e whole process of digestion is an ingenious solution to a complex problem. Proteins (enzymes), activated by acid, digest proteins from food, denatured by acid. Th e coating of mucus secreted by the stomach wall protects its own proteins from attack by either acid or enzymes. Th e normal acid in the stomach is so strong (pH 1.5) that no food is acidic enough to make it stronger; for comparison, the pH of vinegar is about 3.

Protein Digestion Other than being crushed and torn by chewing and moistened with saliva in the mouth, nothing happens to protein until it reaches the stomach. Th en, the action begins.

In the Stomach Strong acid produced by the stomach denatures proteins in food. Th is acid helps to uncoil the protein’s tangled strands so that molecules of the stomach’s protein-digesting enzyme can attack the peptide bonds. You might expect that the stomach enzyme, being a protein itself, would be denatured by the stomach’s acid. Unlike most enzymes, though, the stomach enzyme functions best in an acid environment. Its job is to break other protein strands into smaller pieces. Th e stomach lining, which is also made partly of protein, is protected against attack by acid and enzymes by its coat of mucus, secreted by its cells.

In the Small Intestine By the time most proteins slip from the stomach into the small intestine, they are denatured and cleaved into smaller pieces. A few are single amino acids, but the majority remain in large strands called polypeptides. In the small intestine, alkaline juice from the pancreas neutralizes the acid delivered by the stomach. Th e pH rises to about 7 (neutral), enabling the next enzyme team to accomplish the fi nal breakdown of the strands. Protein-digesting enzymes from the pancreas and intestine continue working until almost all pieces of protein are bro- ken into single amino acids or into strands of two or three amino acids, dipeptides and tripeptides, respectively (see Figure 6-7). Figure 6-8 summarizes the whole process of protein digestion.

Common Misconceptions Consumers who fail to understand the basic mecha- nism of protein digestion are easily misled by advertisers of books and other products who urge, “Take enzyme A to help digest your food” or “Don’t eat foods contain- ing enzyme C, which will digest cells in your body.” Th e writers of such statements fail to realize that enzymes (proteins) are digested before they are absorbed, just as all proteins are. Even the stomach’s digestive enzymes are denatured and digested when their jobs are through. Similar false claims are made that predigested proteins (amino acid supplements) are “easy to digest” and can therefore protect the diges- tive system from “overworking.” Of course, the healthy digestive system is superbly designed to digest whole proteins with ease. In fact, it handles whole proteins better than predigested ones because it dismantles and absorbs the amino acids at rates that are optimal for the body’s use.

KE Y POINT Digestion of protein involves denaturation by stomach acid, then enzymatic digestion in the stomach and small intestine to amino acids, dipeptides, and tripeptides.

CONCEPT LINK 6-2 pH, stomach acidity, and the medicines that control it are topics of Chapter 3, pages 83 and 89.

Tripeptide

Dipeptide

A Dipeptide

and Tripeptide

figure 6-7

polypeptides (POL-ee-PEP-tides) protein fragments of many (more than 10) amino acids bonded together (poly means “many”). A peptide is a strand of amino acids. A strand of between 4 and 10 amino acids is called an oligopeptide.

dipeptides (dye-PEP-tides) protein frag- ments that are 2 amino acids long (di means “two”).

tripeptides (try-PEP-tides) protein frag- ments that are 3 amino acids long (tri means “three”).

198 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

What Happens to Amino Acids After Protein Is Digested? Th e cells all along the small intestine absorb single amino acids. As for dipeptides and tripeptides, enzymes on the cells’ surfaces split most of them into single amino acids, and the cells absorb them, too. Dipetides and tripeptides are also absorbed as is into the cells, where they are split into amino acids and join with the others to be

Liver

Esophagus

Stomach

Small intestine

Large intestine (colon)

Pancreas

Intestinal wall cells

Capillary, leading to larger blood vessels

Stomach When swallowed food arrives in the stomach, acid denatures the protein strands, and an enzyme cleaves amino acid strands into polypeptides and a few amino acids.

1 amino acid

Key:

Small Intestine Enzymes on the surface of the small intestine’s lining and within the absorptive cells split tripeptides and dipeptides. The intestinal cells absorb and transfer amino acids to the bloodstream.

Bloodstream The bloodstream transports amino acids to all the body’s cells.

Small Intestine Enzymes from the pancreas and the intestine split peptide strands into tripeptides, dipeptides, and amino acids.

dipeptide

tripeptide

polypeptide

Animated!

How Protein in Food Becomes Amino Acids in the Body

figure 6-8

199T h e I m p o r t a n c e o f P r o t e i n

released into the bloodstream. A few larger peptide molecules can escape the diges- tive process altogether and enter the bloodstream intact. Scientists believe these larger particles may act as hormones to regulate body functions and provide the body with information about the external environment. Th e larger molecules may also stimulate an immune response and thus play a role in food allergy.

Th e cells of the small intestine possess separate sites for absorbing diff erent types of amino acids. Amino acids of the same type compete for the same absorption sites. Consequently, when a person ingests a large dose of any single amino acid, that amino acid may limit absorption of others of its general type. Th e Consumer Corner (page 205) cautions against taking single amino acids as supplements partly for this reason.

Once amino acids are circulating in the bloodstream, they are carried to the liver where they may be used or released into the blood to be taken up by other cells of the body. Th e cells can then link the amino acids together to make proteins that they keep for their own use or liberate into lymph or blood for other uses. When necessary, the body’s cells can also use amino acids for energy.

KE Y POINT The cells of the small intestine complete digestion, absorb amino acids and some larger peptides, and release them into the bloodstream for use by the body’s cells.

LO 6.3, 6.4

The Importance of Protein Amino acids must be continuously available to build the proteins of new tissue. Th e new tissue may be in an embryo; in the muscles of an athlete in training; in a grow- ing child; in new blood cells needed to replace blood lost in menstruation, hemor- rhage, or surgery; in the scar tissue that heals wounds; or in new hair and nails.

Less obvious is the protein that helps to replace worn-out cells and internal cell structures. Each of your millions of red blood cells lives for only three or four months. Th en it must be replaced by a new cell produced by the bone marrow. Th e millions of cells lining your intestinal tract live for only three days; they are constantly being shed and replaced. Th e cells of your skin die and rub off , and new ones grow from underneath. Nearly all cells arise, live, and die in this way, and while they are living, they constantly make and break down their proteins. In ad- dition, cells must continuously replace their own internal working proteins as old ones wear out. Amino acids conserved from these processes provide a great deal of the required raw material from which new structures are built. Th e entire process of breakdown, recovery, and synthesis is called protein turnover.

Each day, about a quarter of the body’s available amino acids are irretrievably diverted to other uses, such as being used for fuel. For this reason, amino acids from food are needed each day to support the new growth and maintenance of cells and to make the working parts within them. Th e following sections spell out some of the critical roles that proteins play in the body.

KE Y POINT The body needs dietary amino acids to grow new cells and to replace worn-out ones.

The Roles of Body Proteins Only a sampling of the many roles proteins play can be described here, but these illustrate their versatility, uniqueness, and importance in the body. One important role was already mentioned: regulation of gene expression. Others range from di- gestive enzymes and antibodies to tendons and ligaments, scars, fi laments of hair, the materials of nails, and more. No wonder their discoverers called proteins the primary material of life.

Providing Structure and Movement A great deal of the body’s protein (about 40 percent) exists in muscle tissue. Specialized muscle protein structures allow the body

protein turnover the continuous break- down and synthesis of body proteins involving the recycling of amino acids.

200 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

to move. In addition, muscle proteins can release some of their amino acids should the need for energy become dire, as in starvation. Th ese amino acids are integral parts of the muscle structure and their loss exacts a cost of functional protein. Other structural proteins confer shape and strength on bones, teeth, skin, tendons, cartilage, blood vessels, and other tissues. All are important to the workings of a healthy body.

Building Enzymes, Hormones, and Other Compounds Among proteins formed by living cells, enzymes are metabolic workhorses. An enzyme acts as a catalyst: it speeds up a reaction that would happen anyway, but much more slowly. Th ousands of enzymes reside inside a single cell, and each one facilitates a specifi c chemical re- action. Figure 6-9 shows how a hypothetical enzyme works—this one synthesizes a compound from two chemical components. Other enzymes break compounds apart into two or more products or rearrange the atoms in one kind of compound to make another. A single enzyme can facilitate several hundred reactions in a second.

Th e body’s hormones are messenger molecules, and many of them are made from amino acids. Various body glands release hormones when changes occur in the in- ternal environment; the hormones then elicit tissue responses necessary to restore normal conditions. For example, the familiar pair of hormones, insulin and gluca- gon, oppose each other to maintain blood glucose levels. Both are built of amino acids. For interest, Figure 6-10 shows how many amino acids are linked in sequence to form human insulin. It also shows how certain side groups attract one another to complete the insulin molecule and make it functional.

In addition to serving as building blocks for proteins, amino acids also perform other tasks in the body. For example, the amino acid tyrosine forms parts of the neurotransmitters epinephrine and norepinephrine, which relay messages through- out the nervous system. Th e body also uses tyrosine to make the brown pigment melanin, which is responsible for skin, hair, and eye color. Tyrosine is also con- verted into the thyroid hormone thyroxine, which regulates the body’s metabolism. Another amino acid, tryptophan, serves as starting material for the neurotransmit- ter serotonin and the vitamin niacin.

Building Antibodies Of all the proteins in living organisms, the antibodies best demonstrate that proteins are specifi c to one organism. Antibodies distinguish for- eign particles (usually proteins) from all the proteins that belong in “their” body. When they recognize an intruder, they mark it as a target for attack. Th e foreign protein may be part of a bacterium, a virus, or a toxin, or it may be present in a food that causes an allergic reaction.

Each antibody is designed to help destroy one specifi c invader. An antibody active against one strain of infl uenza is of no help to a person ill with another strain. Once the body has learned how to make a particular antibody, it remembers. Th e next time the body encounters that same invader, it destroys the invader even more rapidly. In

New compound

Enzyme Enzyme

A B

Enzyme

Enzyme plus two compounds A and B

Enzyme complex with A and B

Enzyme plus new compound AB

Compounds A and B are attracted to the enzyme’s active site and park there for a moment in the exact position that makes the reaction between them most likely to occur. They react by bonding together and leave the enzyme as the new com- pound, AB.

Enzyme Action figure 6-9

CONCEPT LINK 6-3 Insulin and glucagon were topics of Chapter 4, page 127.

Recall from Chapter 5 that other hormones • are made from lipids.

CONCEPT LINK 6-4 Neurotransmitters were introduced in Chap- ter 3, page 76.

The vitamin niacin is discussed in Chapter 7.•

catalyst a substance that speeds the rate of a chemical reaction without itself being perma- nently altered in the process. All enzymes are catalysts.

hormones chemical messengers secreted by a number of body organs in response to conditions that require regulation. Each hormone affects a specifi c organ or tissue and elicits a specifi c response. Also defi ned in Chapter 3.

thyroxine (thigh-ROX-in) a principle peptide hormone of the thyroid gland that regulates the body’s rate of energy use.

serotonin (SARE-oh-TONE-in) a compound related in structure to (and made from) the amino acid tryptophan. It serves as one of the brain’s principal neurotransmitters.

antibodies (AN-te-bod-ees) large proteins of the blood, produced by the immune system in response to an invasion of the body by foreign substances (antigens). Antibodies combine with and inactivate the antigens. Also defi ned in Chapter 3.

201T h e I m p o r t a n c e o f P r o t e i n

other words, the body develops immunity to the invader. Th is molecular memory un- derlies the principle of immunizations, injections of drugs made from destroyed and inactivated microbes or their products that activate the body’s immune defenses. Some immunities are lifelong; others, such as that to tetanus, must be “boosted” at intervals.

Transporting Substances A large group of proteins specialize in transporting other substances, such as lipids, vitamins, minerals, and oxygen around the body. To do their jobs, such substances must travel within the bloodstream, into and out of cells, or around the cellular interiors. Two familiar examples are the protein he- moglobin that carries oxygen from the lungs to the cells and the lipoproteins that transport lipids in the watery blood.

Maintaining Fluid and Electrolyte Balance Proteins help to maintain the fl uid and electrolyte balance by regulating the quantity of fl uids in the compartments of the body. To remain alive, cells must contain a constant amount of fl uid. Too much can cause them to rupture; too little makes them unable to function. Although water can diff use freely into and out of cells, proteins cannot; and proteins attract water.

By maintaining stores of internal proteins and also of some minerals, cells retain the fl uid they need. By the same mechanism, fl uid is kept inside the blood vessels by proteins too large to move freely across the capillary walls. Th e proteins attract wa- ter and hold it within the vessels, preventing it from freely fl owing into the spaces between the cells. Should any part of this system begin to fail, too much fl uid will soon collect in the spaces between the cells of tissues, causing edema.

Cys Leu His Gln

Asn

Val

Phe

GlySerHisLeuValGluAlaLeu

Tyr

Leu

Val

CysGlyGluArgGlyPhePhe

Tyr

Thr

Pro Lys Ala

Cys Tyr Asn Glu Leu Gln Tyr Leu Ser Cys

Val

Asn

Gly Ile Val Glu Gln Cys Cys

Ala

Ser

This picture shows a refi nement of protein structure not mentioned in the text. The amino acid cysteine (cys) has a sulfur-containing side group. The sulfur groups on two cysteine molecules can bond together, creating a bridge between two protein strands or two parts of the same strand. Insulin contains three such bridges.

Amino Acid Sequence of Human Insulin figure 6-10

CONCEPT LINK 6-5 A discussion of the immune system is found in Chapter 3, pages 76–77.

Edema results when body tissues fail to control the movement of water.

S P

L/ P

ho to

R es

ea rc

he rs

, I nc

immunity protection from or resistance to a disease or infection by development of anti- bodies and by the actions of cells and tissues in response to a threat.

fl uid and electrolyte balance the distribution of fl uid and dissolved par- ticles among body compartments (see also Chapter 8).

edema (eh-DEEM-uh) swelling of body tis- sue caused by leakage of fl uid from the blood vessels; seen in protein defi ciency (among other conditions).

The control of water’s location by electro-• lytes is discussed further in Chapter 8.

202 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

Not only is the quantity of the body fl uids vital to life but so also is their compo- sition. Transport proteins in the membranes of cells also help maintain this com- position by continuously transferring substances into and out of cells (see Figure 6-11). For example, sodium is concentrated outside the cells, and potassium is con- centrated inside. A disturbance of this balance can impair the action of the heart, lungs, and brain, triggering a major medical emergency. Cell proteins avert such a disaster by holding fl uids and electrolytes in their proper chambers.

Maintaining Acid-Base Balance Normal processes of the body continually pro- duce acids and their opposite, bases, that must be carried by the blood to the organs of excretion. Th e blood must do this without allowing its own acid-base balance to be aff ected. Th is feat is another trick of the blood proteins, which act as buff ers to maintain the blood’s normal pH. Th e protein buff ers pick up hydrogens (acid) when there are too many in the bloodstream and release them again when there are too few. Th e secret is that negatively charged side chains of amino acids can accommo- date additional hydrogens, which are positively charged.

Blood pH is one of the most rigidly controlled conditions in the body. If blood pH changes too much, acidosis or the opposite basic condition, alkalosis, can cause coma or death. Th ese conditions constitute medical emergencies because of their ef- fect on proteins. When the proteins’ buff ering capacity is fi lled—that is, when they have taken on all the acid hydrogens they can accommodate—additional acid pulls them out of shape, denaturing them and disrupting many body processes.

Blood Clotting To prevent dangerous blood loss, special blood proteins respond to an injury by clotting the blood. In an amazing series of chemical events, these proteins form a stringy net that traps blood cells to form a clot. Th e clot acts as a plug to stem blood fl ow from the wound. Later, as the wound heals, the protein col- lagen fi nishes the job by replacing the clot with scar tissue.

Th e fi nal function of protein, providing energy, depends upon some metabolic adjustments, as described in the next section. Table 6-1 provides a summary of the functions of proteins in the body.

Providing Energy and Glucose Only protein can perform all the functions just described, but protein will be surrendered to provide energy if need be. Under con- ditions of inadequate energy or carbohydrate, protein breakdown speeds up, as the next section explains.9

KE Y POINT Proteins provide structure and movement; serve as enzymes, hormones, and antibodies; provide molecular transport,

Molecule enters protein from inside cell.

Protein changes shape; molecule exits protein outside the cell.

Molecule enters protein from outside cell.

Molecule exits protein; proper balance restored.

Outside cell

Inside cell

Cell membrane

Transport protein

A transport protein within the cell membrane acts as a sort of two-door passageway—substances enter on one side and are re- leased on the other, but the protein never leaves the membrane. The protein differs from a simple passageway in that it actively escorts the substances in and out of cells; therefore, this form of transport is often called active transport.

Animated!

Proteins Transport Substances Into and Out of Cells

figure 6-11

acids compounds that release hydrogens in a watery solution.

bases compounds that accept hydrogens from solutions.

acid-base balance equilibrium between acid and base concentrations in the body fl uids.

buffers compounds that help keep a solu- tion’s acidity or alkalinity constant.

acidosis (acid-DOH-sis) the condition of excess acid in the blood, indicated by a below-normal pH (osis means “too much in the blood”).

alkalosis (al-kah-LOH-sis) the condition of excess base in the blood, indicated by an above-normal blood pH (alka means “base”; osis means “too much in the blood”).

203T h e I m p o r t a n c e o f P r o t e i n

fl uid and electrolyte regulation, buff ers for blood; contribute to blood clotting, energy supplies, and glucose for the body.

Amino Acids to Glucose Th e body must have energy to live from moment to moment, so obtaining that energy is a top priority. Not only can amino acids supply energy but many of them can be converted to glucose, as fatty acids can never be. Th us, if the need arises, protein can help to maintain a steady blood glucose level and serve the glucose need of the brain.

When amino acids are degraded for energy or converted into glucose, their nitrogen-containing amine groups are stripped off and used elsewhere or are in- corporated by the liver into urea and sent to the kidneys for excretion in the urine. Th e fragments that remain are composed of carbon, hydrogen, and oxygen, as are carbohydrate and fat, and can be used to build glucose or fatty acids or can be me- tabolized like them.

Protein Lack and Abundance Glucose is stored as glycogen and fat as triglyc- erides, but no specialized storage compound exists for protein. Body protein is pres- ent only as the active working molecular and structural components of body tissues. When protein-sparing energy from carbohydrate and fat is lacking and the need be- comes urgent, as in starvation, prolonged fasting, or severe calorie restriction, the body must dismantle its tissue proteins to obtain amino acids for building the most essential proteins and for energy. Each protein is taken in its own time: fi rst, small proteins from the blood; then, proteins from the muscles, liver, and other organs. Th us, energy defi ciency (starvation) always incurs wasting of lean body tissue as well as loss of fat.

When amino acids are oversupplied, the body cannot store them. It has no choice but to remove and excrete their amine groups and then use the residues in one of three ways: to meet immediate energy needs, to make glucose for storage as glycogen, or to make fat for energy storage.10 Th e body readily converts amino acids to glucose. Th e body also possesses enzymes to convert amino acids into fat and can produce fatty ac- ids for storage as triglycerides in the fat tissue. An indirect contribution of amino ac- ids to fat stores also exists—the body speeds up its use of amino acids for fuel, burning them instead of fat, which is then abundantly available for storage in the fat tissue.

Th e similarities and diff erences of the three energy-yielding nutrients should now be clear. Carbohydrate off ers energy; fat off ers concentrated energy; and protein can off er energy plus nitrogen (see Figure 6-12).

Acid-base balance.• Proteins help main- tain the acid-base balance of various body fl uids by acting as buffers. Antibodies.• Proteins form the immune system molecules that fi ght diseases. Blood clotting.• Proteins provide the net- ting on which blood clots are built. Energy and glucose.• Proteins provide some fuel for the body’s energy needs. Enzymes.• Proteins facilitate needed chemical reactions. Fluid and electrolyte balance.• Proteins help to maintain the water and mineral composition of various body fl uids. Gene expression.• Proteins associate and interact with DNA, regulating gene expression. Hormones.• Proteins regulate body pro- cesses. Some hormones are proteins or are made from amino acids. Structure.• Proteins form integral parts of most body tissues and confer shape and strength on bones, skin, tendons, and other tissues. Structural proteins of muscles allow body movement. Transportation.• Proteins help transport needed substances, such as lipids, minerals, and oxygen, around the body.

Summary of

Protein Functions

table 6-1

More about the effects of fasting in Chapter 9.•

Energy

Carbohydrate

Fat

Protein

Energy

Nitrogen

+ (4 calories per gram)

(9 calories per gram)

(4 calories per gram)

Carbohydrate offers energy; fat offers concentrated energy; and protein, if neces- sary, can offer energy plus nitrogen. The compounds at the left yield the 2-carbon fragments shown at the right. These fragments oxidize quickly in the presence of oxygen to yield carbon dioxide, water, and energy.

Three Different Energy Sources figure 6-12

urea (yoo-REE-uh) the principal nitrogen- excretion product of protein metabolism; generated mostly by removal of amine groups from unneeded amino acids or from amino acids being sacrifi ced to a need for energy.

204 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

The Fate of an Amino Acid To review the body’s handling of amino acids, let us follow the fate of an amino acid that was originally part of a protein-containing food. When the amino acid arrives in a cell, it can be used in one of several ways, depending on the cell’s needs at the time:

Th e amino acid can be used as is to build part of a growing protein.•

Th e amino acid can be altered somewhat to make another needed compound, •

such as the vitamin niacin.

Th e cell can dismantle the amino acid in order to use its amine group to build a •

diff erent amino acid. Th e remainder can be used for fuel or, if fuel is abundant,

converted to glucose or fat.

In a cell that is starved for energy and has no glucose or fatty acids, the cell strips the amino acid of its amine group (the nitrogen part) and uses the remainder of its structure for energy. Th e amine group is excreted from the cell and then from the body in the urine. In a cell that has a surplus of energy and amino acids, the cell takes the amino acid apart, excretes the amine group, and uses the rest to meet im- mediate energy needs or converts it to glucose or fat for storage.

When not used to build protein or make other nitrogen-containing compounds, amino acids are “wasted” in a sense. Th is wasting occurs under any of four conditions:

When the body lacks energy from other sources.1. When the diet supplies more protein than the body needs.2. When the body has too much of any single amino acid, such as from a 3. supplement.

When the diet supplies protein of low quality, with too few essential amino 4. acids, as described in the next section.

To prevent the wasting of dietary protein and permit the synthesis of needed body protein, the dietary protein must be of adequate quality; it must supply all essential amino acids in the proper amounts; it must be accompanied by enough energy- yielding carbohydrate; and fat must be present to permit the dietary protein to be used as such.

KE Y POINT Amino acids can be metabolized to protein, nitrogen plus energy, glucose, or fat. They will be metabolized to protein only if suffi cient energy is present from other sources. The nitrogen part is removed from each amino acid, and the resulting fragment is oxidized for energy. No storage form of amino acids exists in the body.

LO 6.5

Food Protein: Need and Quality A person’s response to dietary protein depends on many factors. To know whether, say, 60 grams of a particular protein is enough to meet a person’s daily needs, one must consider the eff ects of factors discussed in this section, some pertaining to the body and some to the nature of the protein.

How Much Protein Do People Really Need? Th e DRI recommendation for protein intake is designed to cover the need to replace protein-containing tissue that healthy adults lose and wear out every day. Th erefore, it depends on body size: larger people have a higher protein need. For adults of

Amino acids in a cell can be:•

Used to build protein.•

Converted to other amino acids or small •

nitrogen-containing compounds.

Stripped of their nitrogen, amino acids can • be:

Burned as fuel.•

Converted to glucose or fat.•

Amino acids are wasted when:•

Energy is lacking.•

Protein is overabundant.•

An amino acid is oversupplied in supple-•

ment form.

The protein is of low quality (too few es-•

sential amino acids).

205F o o d P r o t e i n : N e e d a n d Q u a l i t y

consumer corner Protein and Amino Acid Supplements AMINO ACID SUPPLEMENTS Enthusiastic popular reports have led to widespread use of individual amino acids. One such amino acid is lysine, touted to prevent or relieve the infections that cause herpes sores on the mouth or genital organs. Lysine does not cure herpes infections. Whether it reduces outbreaks or even whether it is safe is unknown because scientifi c studies are lacking.

Tryptophan supplements are adver- tised to relieve pain, depression, and insomnia. Tryptophan plays a role as a precursor for the brain neurotransmit- ter serotonin, an important regulator of sleep, appetite, mood, and sensory per- ception. The DRI committee concludes that high doses of tryptophan may induce sleepiness, but they may also cause side effects, such as nausea and skin disorders. A serious blood disorder, EMS, probably caused by contaminants, once threatened takers of tryptophan supplements, but improved regulations have reduced this risk.*3

The body is designed to handle whole proteins best. It breaks them into manageable pieces (dipeptides and tripeptides), then splits these a few at a

Why do people take protein supple- ments? Athletes often take them when trying to build muscle. Dieters may take them in hopes of speeding the process of weight loss or preserving lean tissue. Some women take them to strengthen their fi ngernails. People take individual amino acids, too—to cure herpes, to make themselves sleep better, to lose weight, and to relieve pain and depres- sion. Do protein and amino acid supple- ments really do these things? Probably not. Are they safe? Not always.

In the skilled hands of clinical regis- tered dietitians, formulas with supple- mental protein or amino acids may help to reverse malnutrition in some critically ill patients. Not every patient is a candi- date for such therapy, however, because supplemental amino acids may also stimulate infl ammation and so worsen some illnesses.

PROTEIN SUPPLEMENTS Protein supplements are popular with athletes but well-fed athletes do not need them (see Controversy 10 for details). True, dietary protein is necessary for build- ing muscle tissue and, true, consuming protein in conjunction with resistance ex- ercise helps muscles build new proteins.1 But protein supplements do not improve athletic performance beyond the gains from well-timed meals of ordinary foods. And, if supplements create a surplus of protein or certain amino acids, the excess must be metabolized, placing a burden on the kidneys to excrete excess nitrogen.

Weight-loss dieters may benefi t from making a habit of consuming the needed protein-rich foods because protein often satisfi es the appetite, while insuffi cient protein may increase it.2 However, extra protein from powders, pills, or bever- ages is unlikely to dampen the appetite further, although it contributes unneeded calories—the wrong effect for weight loss. Evidence does not support taking protein supplements for weight loss, and common sense opposes it.

time, simultaneously releasing them into the blood. This slow, bit-by-bit assimila- tion is ideal because groups of chemi- cally similar amino acids compete for the carriers that absorb them into the blood. An excess of one amino acid can tie up a carrier and disturb amino acid absorp- tion, creating a temporary imbalance.4 Amino acids are key players in complex mechanisms for gene regulation, and excesses may affect these processes in unpredictable ways.5 In mice, for ex- ample, excess methionine causes the blood buildup of an amino acid associ- ated with heart disease (homocysteine) and increases infl ammation in the liver. No one knows if the same is true in people.6 Many supplement takers ex- perience digestive disturbances. Amino acids in concentrated supplements cause excess water to fl ow into the digestive tract, causing diarrhea.7

A lack of research prevents the DRI committee from setting Tolerable Upper Intake Levels for amino acids.8 There- fore, no level of amino acid supplemen- tation can be assumed safe; Table 6-2 lists people most likely to be harmed. In fact, Canada bans sales of single amino acids to consumers.† The warning is

Growth or altered metabolism makes these people especially likely to be harmed by self-prescribed amino acid supplements:

All women of childbearing age.• Pregnant or lactating women.• Infants, children, and adolescents.• Elderly people.• People with inborn errors of metabolism that affect their bodies’ handling of amino • acids. Smokers.• People on low-protein diets.• People with chronic or acute mental or physical illnesses.•

People Most Likely to Be Harmed by Amino Acid

Supplements

table 6-2

*EMS is short for eosinophilia-myalgia syndrome.

†Canada only allows single amino acid supplements to be sold as drugs or used as food additives.

this: much is still unknown, and the taker of amino acid supplements cannot be certain of their safety or effectiveness.9

CONCLUSION Many chapters of this book present evidence that whole foods are superior

sources for nutrients and phytochemicals for human health.10 The Consumer Cor- ner in Chapter 4 showed that a nutrition- ally inferior food (refi ned bread) enriched with a few added nutrients is still inad- equate in many others compared with whole grains. The Controversy section in Chapter 7 points out potential dangers

of vitamin and mineral supplements and their lack of effi cacy for preventing any disease except nutrient defi ciencies. The same is true of amino acids—whole food proteins, in balance with other needed foods, best support human health. Even with all that we know about science, it is hard to improve on nature.

healthy body weight, the DRI recommended intake is set at 0.8 gram for each kilo- gram (or 2.2 pounds) of body weight (see inside front cover). Th e minimum amount is set at 10 percent of total calories. As mentioned in the Th ink Fitness feature ear- lier, athletes may need slightly more protein but the increased need is well covered by most people’s diets.11

For infants and growing children, the protein recommendation, like all nutrient recommendations, is higher per unit of body weight. Th e DRI committee set an up- per limit for protein intake of no more than 35 percent of total calories, an amount signifi cantly higher than average intakes. Table 6-3 reviews recommendations for protein intake, and the margin provides a method for determining your own protein need. Th e DRI committee suggests that vegetarians need more iron than the gen- eral population. Th e following factors also modify protein needs.

The Body’s Health Malnutrition or infection may greatly increase the need for protein while making it hard to eat even normal amounts of food. In malnutrition, secretion of digestive enzymes slows as the tract’s lining degenerates, impairing protein digestion and absorption. When infection is present, extra protein is needed for enhanced immune functions.

Other Nutrients and Energy Th e need for ample energy, carbohydrate, and fat has already been emphasized. To be used effi ciently by the cells, protein must also be accompanied by the full array of vitamins and minerals.

Protein Quality Th e remaining factor, protein quality, helps determine how well a diet supports the growth of children and the health of adults. Two factors infl u- ence protein quality: a protein’s digestibility and its amino acid composition, dis- cussed later.

Recommendations for protein intake assume a normal mixed diet, that is, a diet that includes suffi cient nutrients and a combination of animal and plant protein. Because not all proteins are used with 100 percent effi ciency, the recommendation is generous. Many healthy people can consume less than the recommended amount and still meet their bodies’ protein needs. What this means in terms of food selec- tions is presented in this chapter’s Food Feature.

The DRI recommended intake for protein • (adult) = 0.8 g/kg.

To figure out your protein need:•

Find your body weight in pounds.1.

Convert pounds to kilograms (by dividing 2. pounds by 2.2).

Multiply kilograms by 0.8 to find total 3. grams of protein recommended.

For example:

Weight = 130 lb.•

130 lb ÷ 2.2 = 59 kg.•

59 kg × 0.8 = 47 g.•

206 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

DRI Recommended Intakea

0.8 gram protein per kilogram of body • weight per day. Women: 46 grams per day; men: 56 • grams per day. Acceptable intake range: 10 to 30 per-• cent of calories from protein.

USDA Food Guide, MyPyramid

Every day most adults should eat 5- to • 6½-ounce equivalents of lean meat, poultry without skin, fi sh, legumes, eggs, nuts, or seeds. Every day most adults need 3 cups of • fat-free or low-fat milk or yogurt, or the equivalent of fat-free cheese or vitamin- and mineral-fortifi ed soy beverage. Eat a variety of foods to provide small • amounts of protein from other sources.

aProtein recommendations for infants, children, and pregnant and lactating women are higher; see inside front cover, page B.

Protein Intake

Recommendations

for Healthy Adults

table 6-3

Veggin’ Out

Have you ever considered not eating meat? Listen to two students discuss how becoming vegetarian affected their social life.

To hear their stories, log on to www.cengage.com/sso.

my turn

Aira Joshua

en ga

ge L

ea rn

in g

en ga

ge L

ea rn

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http://www.cengage.com/sso

207F o o d P r o t e i n : N e e d a n d Q u a l i t y

KE Y POINT The protein intake recommendation depends on size and stage of growth. The DRI recommended intake for adults is 0.8 gram of protein per kilogram of body weight. Factors concerning both the body and food sources modify an individual’s protein need.

Nitrogen Balance Underlying the protein recommendation are nitrogen balance studies, which compare nitrogen lost by excretion with nitrogen eaten in food. In healthy adults, nitrogen-in (consumed) must equal nitrogen-out (excreted). Scientists measure the body’s daily nitrogen losses in urine, feces, sweat, and skin under controlled condi- tions and then estimate the amount of protein needed to replace these losses.‡12

How Nitrogen Balance Varies Under normal circumstances, healthy adults are in nitrogen equilibrium, or zero balance; that is, they have the same amount of total protein in their bodies at all times. When nitrogen-in exceeds nitrogen-out, people are said to be in positive nitrogen balance; somewhere in their bodies more proteins are being built than are being broken down and lost. When nitrogen-in is less than nitrogen-out, people are said to be in negative nitrogen balance; they are losing protein. Figure 6-13 illustrates these diff erent states.

Positive Nitrogen Balance Growing children add new blood, bone, and muscle cells to their bodies every day, so children must have more protein, and therefore more nitrogen, in their bodies at the end of each day than they had at the begin- ning. A growing child is therefore in positive nitrogen balance. Similarly, when a woman is pregnant, she must be in positive nitrogen balance until after the birth, when she once again reaches equilibrium.

Negative Nitrogen Balance Negative nitrogen balance occurs when muscle or other protein tissue is broken down and lost. Illness or injury triggers the release of powerful messengers that signal the body to break down some of the less vital pro- teins, such as those of the skin and even muscle.§ Th is action fl oods the blood with

‡The average protein is 16 percent nitrogen by weight; that is, each 100 grams of protein contain 16 grams of nitrogen. As a general rule, multiply the nitrogen’s weight by 6.25 to estimate the protein’s weight. §The messengers are cytokines.

nitrogen balance the amount of nitrogen consumed compared with the amount ex- creted in a given time period.

Growing children end each day with more bone, blood, muscle, and skin cells than they had at the beginning of the day.

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Positive Nitrogen Balance

These people—a growing child, a person building muscle, and a pregnant

woman—are all retaining more nitrogen than they are excreting.

Nitrogen Equilibrium

These people—a healthy college student and a young retiree—are in nitrogen equilibrium.

Negative Nitrogen Balance

These people—an astronaut and a surgery patient—are losing more nitrogen than they are taking in.

N N N

N N

NN N

N N N

N N

NN N N

N N N

N N

Nitrogen Balance figure 6-13

208 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

amino acids and energy needed to fuel the body’s defenses and fi ght the illness. Th e result is negative nitrogen balance. Astronauts, too, experience negative nitrogen balance. In the stress of space fl ight, and with no need to support the body’s weight against gravity, the astronauts’ muscles waste and weaken. To minimize the inevi- table loss of muscle tissue, the astronauts must do special exercises in space.

KE Y POINT Protein recommendations are based on nitrogen balance studies, which compare nitrogen excreted from the body with nitrogen ingested in food.

Which Foods Provide High-Quality Protein? Put simply, high-quality proteins provide enough of all the essential amino acids needed by the body to create its own working proteins, whereas low-quality proteins don’t. In making their required proteins, the cells need a full array of amino acids. If a nonessential amino acid (that is, one the cell can make) is unavailable from food, the cell synthesizes it and continues attaching amino acids to the protein strands being manufactured. If the diet fails to provide enough of an essential amino acid (one the cell cannot make), the cells begin to adjust their activities. Th e cells:

Break down more internal proteins to liberate the needed essential amino acid.•

Conserve the essential amino acid by limiting their synthesis of proteins.• 13

As the deprivation continues, tissues make one adjustment after another in the struggle to survive.

Limiting Amino Acids Th e measures just described help the cells to channel the available limiting amino acid to its wisest use: making new proteins. Even so, the normally fast rate of protein synthesis slows to a crawl as the cells make do with the proteins on hand. When the limiting amino acid once again becomes available in abundance, the cells resume their normal protein-related activities. If the shortage becomes chronic, however, the cells begin to break down their protein-making ma- chinery. Consequently, when protein intakes become adequate again, protein synthe- sis lags behind until the needed machinery can be rebuilt. Meanwhile, the cells func- tion less and less eff ectively as their proteins wear out and are only partially replaced.

Th us, a diet that is short in any of the essential amino acids limits protein synthe- sis. An earlier analogy likened amino acids to letters of the alphabet. To be mean- ingful, words must contain all the right letters. For example, a print shop that has no letter “N” cannot make personalized stationery for Jana Johnson. No matter how many Js, As, Os, Hs, and Ss are in the printer’s possession, they cannot replace the missing Ns. Likewise, in building a protein molecule, no amino acid can fi ll another’s spot. If a cell that is building a protein cannot fi nd a needed amino acid, synthesis stops and the partial protein is released.

Partially completed proteins are not held for completion at a later time when the diet may improve. Rather, they are dismantled and the component amino acids are returned to the circulation to be made available to other cells. If they are not soon inserted into protein, their amine groups are removed and excreted and the residues are used for other purposes. Th e need that prompted the call for that particular pro- tein will not be met. Since the other amino acids are wasted, the amine groups are excreted, and the body cannot resynthesize the amino acids later.

Complementary Proteins It follows that if a person does not consume all the essential amino acids in proportion to the body’s needs, the body’s pools of es- sential amino acids will dwindle until body organs are compromised. Consuming the essential amino acids presents no problem to people who regularly eat proteins containing ample amounts of all of the essential amino acids, such as those of meat, fi sh, poultry, cheese, eggs, milk, and most soybean products.

An equally sound choice is to eat a combination of foods from plants so that amino acids that are low in some foods will be supplied by the others. Th e protein-

high-quality proteins dietary proteins containing all the essential amino acids in rela- tively the same amounts that human beings require. They may also contain nonessential amino acids.

limiting amino acid an essential amino acid that is present in dietary protein in an insuffi cient amount, thereby limiting the body’s ability to build protein.

complementary proteins two or more proteins whose amino acid assortments complement each other in such a way that the essential amino acids missing from one are supplied by the other.

mutual supplementation the strategy of combining two incomplete protein sources so that the amino acids in one food make up for those lacking in the other food. Such protein combinations are sometimes called complementary proteins.

Just as each letter of the alphabet is important in forming whole words, each amino acid must be available to build fi nished proteins.

209F o o d P r o t e i n : N e e d a n d Q u a l i t y

rich foods are combined to yield complementary proteins (see Figure 6-14), or proteins containing all the essential amino acids in amounts suffi cient to support health.14 Th is concept, called mutual supplementation, is illustrated in Figure 6-15. Th e fi gure demonstrates that the amino acids of legumes and grains balance each other to provide all of the needed amino acids. Th e complementary proteins need not be eaten together, so long as the day’s meals supply them all and the diet provides enough energy and total protein from a variety of sources.

Protein Digestibility In measuring a protein’s quality, digestibility is important. Simple measures of the total protein in foods are not useful by themselves—even animal hair and hooves would receive a top score by those measures alone. Th ey are made of protein, but not in a form that people can use.

Th e digestibility of protein varies from food to food and bears profoundly on protein quality. Th e protein of oats, for example, is less digestible than that of eggs. In general, amino acids from animal proteins, such as chicken, beef, and pork, are most easily digested and absorbed (over 90 percent). Th ose from legumes are next (about 80 to 90 percent). Th ose from grains and other plant foods vary (from 70 to 90 percent). Cooking with moist heat improves protein digestibility, whereas dry heat methods can impair it.

KE Y POINT Digestibility of protein varies from food to food, and cooking can improve or impair it.

Perspective on Protein Quality Concern about the quality of individual food proteins is of only theoretical interest in settings where food is abundant. Most people in the United States and Canada eat a variety of nutritious foods to meet their energy needs. Healthy adults in these places would fi nd it next to impossible not to meet their protein needs, even if they were to eat no meat, fi sh, poultry, eggs, or cheese products at all. Th ey need not pay attention to mutual supplementation, so long as the diet is varied, nutritious, and adequate in energy and other nutrients— not made up just of, say, cookies, potato chips, or alcoholic beverages. Protein suf- fi ciency follows eff ortlessly behind a balanced, nutritious diet.

For people in areas where food sources are less reliable, protein quality can make the diff erence between health and disease. When food energy intake is limited (where malnutrition is widespread) or when the selection of foods available is severely lim- ited (where a single low-protein food, such as fufu made from cassava root,** provides

1 c rice = 4 g 1 c beans = 16 g

1 c pasta = 11 g 1 c vegetables = 2 g 2 tbs Parmesan cheese = 4 g

1 2/3 4/ c oatmeal = 5 g

Protein total 20 g Protein total 17 g

Protein total 5 g

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Healthful foods like these contribute substantial protein (42 grams total) to this day’s meals without meat. Additional servings of nutritious foods, such as milk, bread, and eggs, can easily supply the remainder of the day’s need for protein (14 additional grams for men and 4 for women).

Complementary Protein Combinations figure 6-14

Lys Met Trp

Legumes

Grains

Together

Ile

Legumes provide plenty of the amino acids isoleucine (Ile) and lysine (Lys), but fall short in methionine (Met) and tryp- tophan (Trp). Grains have the opposite strengths and weaknesses, making them a perfect match for legumes.

How

Complementary

Proteins Work

Together

figure 6-15

legumes (leg-GOOMS, LEG-yooms) plants of the bean, pea, and lentil family that have roots with nodules containing special bacteria. These bacteria can trap nitrogen from the air in the soil and make it into compounds that become part of the plant’s seeds. The seeds are rich in protein compared with those of most other plant foods. Also defi ned in Chapter 1.

fufu a low-protein staple food that provides abundant starch energy to many of the world’s people; fufu is made by pounding or grinding root vegetables or refi ned grains and cooking them to a smooth semisolid consistency.

Cooking with moist heat improves protein di- gestibility, whereas frying makes protein harder to digest.

m an

a Im

ag es

In c.

/A la

m y

**Cassava is also called manioc or yucca.

210 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

90 percent of the calories), the primary food source of protein must be checked be- cause its quality is crucial.

KE Y POINT A protein’s amino acid assortment greatly infl uences its usefulness to the body. Proteins lacking essential amino acids can be used only if those amino acids are present from other sources.

LO 6.6

Protein Deficiency and Excess Protein defi ciencies are well known because, together with energy defi ciencies, they are the world’s leading form of malnutrition. Th e health eff ects of too much protein are far less well known. Both defi ciency and excess are of concern.

What Happens When People Consume Too Little Protein? Protein defi ciency and energy defi ciency go hand in hand. Th is combination— protein-energy malnutrition (PEM)—is the most widespread form of malnutri- tion in the world today. Over 500 million children face imminent starvation and suff er the eff ects of severe malnutrition and hunger. Most of the 33,000 children who die each day are malnourished. PEM is prevalent in Africa, Central Amer- ica, South America, the Middle East, and East and Southeast Asia, but developed countries, including those in North America, are not immune to it.

PEM strikes early in childhood, but it endangers many adults as well. Inadequate food intake leads to poor growth in children and to weight loss and wasting in adults. Stunted growth due to PEM is easy to overlook because a small child can look normal. Th e small stature of children in impoverished nations was once thought to be a normal adaptation to the limited availability of food; now it is known to be an avoidable failure of growth due to a lack of food during the growing years.

PEM takes two diff erent forms, with some cases exhibiting a combination of the two. In one form, the person is shriveled and lean all over—this disease is called marasmus. In the second, a swollen belly and skin rash are present, and the disease is named kwashiorkor.†† In the combination, some features of each type are pres- ent. Marasmus refl ects a chronic inadequate food intake and therefore inadequate energy, vitamins, and minerals as well as too little protein. Kwashiorkor may result from severe acute malnutrition, with too little protein to support body functions.

KE Y POINT Protein-defi ciency symptoms are always observed when either protein or energy is defi cient. Extreme food-energy defi ciency is marasmus; extreme protein defi ciency is kwashiorkor. The two diseases most often overlap and together are called PEM.

Marasmus Marasmus occurs most commonly in children from 6 to 18 months of age in over- populated city slums. Children in impoverished nations subsist on a weak cereal drink with scant energy and protein of low quality; such food can barely sustain life, much less support growth. A starving child often looks like a wizened little old person—just skin and bones.

Muscle Wasting and Other Impairments Without adequate nutrition, muscles, including heart muscle, waste and weaken. Brain development is stunted and learn- ing is impaired. Metabolism is so slow that body temperature is subnormal. Th ere is

The extreme loss of muscle and fat characteristic of marasmus is apparent in this child’s “match- stick” arms.

P /W

id e

W or

ld P

ho to

protein-energy malnutrition (PEM) the world’s most widespread malnu- trition problem, including both marasmus and kwashiorkor and states in which they overlap; also called protein-calorie malnutrition (PCM).

hunger the physiological craving for food; the progressive discomfort, illness, and pain resulting from the lack of food. See also Chap- ters 9 and 15.

marasmus (ma-RAZ-mus) a form of PEM related to protein malnutrition and infections, with a set of recognizable symptoms, such as edema.

kwashiorkor (kwash-ee-OR-core, kwashee-or-CORE) a form of PEM related to protein malnutrition and infections, with a set of recognizable symptoms, such as edema.

††A term gaining acceptance for use in place of kwashiorkor is hypoalbuminemic-type PEM.

211P r o t e i n D e f i c i e n c y a n d E x c e s s

little or no fat under the skin to insulate against cold, and hospital workers fi nd that children with marasmus need to be wrapped up and kept warm. Th ey also need love because they have often been deprived of parental attention as well as food.

Th e starving child faces this threat to life by engaging in as little activity as pos- sible—not even crying for food. Th e body collects all its forces to meet the crisis and so cuts down on any expenditure of energy not needed for the heart, lungs, and brain to function. Growth ceases; the child is no larger at age four than at age two. Th e skin loses its elasticity and moisture, so it tends to crack; when sores develop, they fail to heal. Digestive enzymes are in short supply, the digestive tract lining de- teriorates, and absorption fails. Th e child can’t assimilate what little food is eaten.

Disease Conditions Blood proteins, including hemoglobin, are no longer pro- duced, so the child becomes anemic and weak. If a bone breaks, healing is delayed because the protein needed to heal it is lacking. Antibodies to fi ght off invading bacteria are degraded to provide amino acids for other uses, leaving the child an easy target for infection. Th en dysentery, an infection of the digestive tract, causes diarrhea, further depleting the body of nutrients, especially minerals. Measles, which might make a healthy child sick for a week or two, kills a child with PEM within two or three days. In the marasmic child, once infection sets in, kwashior- kor often follows and the immune response weakens further. Infections that occur with malnutrition are responsible for two-thirds of the deaths of young children in developing countries.

Preventing Death Ultimately, marasmus progresses to the point of no return when the body’s machinery for protein synthesis, itself made of protein, has been degraded. At this point, attempts to correct the situation by giving food or protein fail to prevent death. If caught before this time, however, the starvation of a child can be reversed by careful nutrition therapy. Th e fl uid balances are most critical. Diarrhea will have depleted the body’s potassium and upset other electrolyte bal- ances. Th e combination of electrolyte imbalances, anemia, fever, and infections of- ten leads to heart failure and sudden death. Careful correction of fl uid and electro- lyte balances usually raises the blood pressure and strengthens the heartbeat within a few days. Later, fat-free milk, providing protein and carbohydrate, can safely be given; fat is introduced still later, when body protein is suffi cient to provide carriers. Years after PEM is corrected, a child may experience defi cits in thinking and school achievement compared with well-nourished peers.

KE Y POINT PEM is starvation, in which muscles waste away, growth ceases, brain development is stunted, body temperature falls, diseases set in, and nutrient absorption fails. Without proper and timely nutrition therapy, death ensues.

Kwashiorkor Kwashiorkor is a Ghanaian name for “the evil spirit that infects the fi rst child when the second child is born.” In countries where kwashiorkor is prevalent, each baby is weaned from breast milk as soon as the next one comes along. Th e older baby no longer receives breast milk, which contains high-quality protein designed perfectly to support growth, but is instead given a watery cereal with scant protein of low quality. Small wonder the just-weaned child sickens when the new baby arrives. Th ough rare in the United States and Canada, kwashiorkor is not entirely unknown, usually occurring when fad diets replace sound nutrition in children.

Some kwashiorkor symptoms resemble those of marasmus (see Table 6-4) but often without severe wasting of body fat. Proteins and hormones that previously maintained fl uid balance are now diminished, so fl uid leaks out of the blood and ac- cumulates in the belly and legs, causing edema, a distinguishing feature of kwashi- orkor. Th e kwashiorkor victim’s belly often bulges with a fatty liver, caused by lack of the protein carriers that transport fat out of the liver. Th e fatty liver loses some of

dysentery (DISS-en-terry) an infection of the digestive tract that causes diarrhea.

Did You Know? The term electrolyte balance, defi ned earlier, refers to the proper concentrations of salts (dissolved particles) within the body fl uids (see Chapter 8 for details).

The edema and enlarged liver characteristic of kwashiorkor are apparent in this child’s swollen belly.

au l A

. S ou

de rs

/C or

bi s

212 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

its ability to clear poisons from the body, prolonging their toxic eff ects. Th us, toxins can worsen the condition. Without suffi cient tyrosine to make melanin, the child’s hair loses its normal color; inadequate protein synthesis leaves the skin patchy and scaly; sores fail to heal. Measles or other infections easily penetrate the weakened immune defenses of the protein-defi cient child and often precipitate kwashiorkor.

KE Y POINT Kwashiorkor sets in when too little protein is provided to a growing child. Symptoms include edema, fatty liver, changes in hair color, scaly skin, reduced disease resistance, and sores that fail to heal.

PEM at Home PEM occurs among some groups in the United States and Canada: the poor living on U.S. Indian reservations, in inner cities, and in rural areas; some elderly people; hungry and homeless children; and those suff ering from the eating disorder an- orexia nervosa. Occasionally, well-meaning but misinformed parents infl ict PEM and other serious defi ciency diseases on their infants and toddlers by replacing their formula or milk with unenriched, protein-poor “health-food” soy or rice drinks.15 Also at risk for PEM are those with wasting diseases such as cancer or AIDS and those addicted to drugs and alcohol. In a downward spiral, PEM and serious illness worsen each other, so treating the PEM often reduces medical complications and suff ering even when the underlying disease is untreatable.

Today, in the United States, tens of millions of people who work to support their children earn so little that they cannot aff ord a steady supply of nutritious food. Al- most 14 million U.S. children live in households where hunger threatens or is pain- fully experienced. Hunger, especially in children, harms everyone’s future. Hungry children do not learn as well as fed children, nor are they as competitive. Th ey are ill more often, they have higher absentee rates from school, and when they attend, they cannot concentrate for long. Th e forces driving poverty and hunger will require many great minds working together to fi nd solutions.

KE Y POINT PEM is not unknown in the United States, where millions live on the edge of hunger.

Separating PEM into two classifi cations oversimplifi es the condition, but at the extremes, marasmus and kwashiorkor exhibit marked differences. Marasmus-kwashiorkor mix presents symptoms common to both marasmus and kwashiorkor. In all cases, children are likely to develop diarrhea, infections, and multiple nutrient defi ciencies.

Marasmus Kwashiorkor

Infants and toddlers (less than 2 yr)

Severe deprivation or impaired absorption of protein, energy, vitamins, and minerals

Develops slowly; chronic PEM

Severe weight loss

Severe muscle wasting with fat loss

Growth: <60% weight-for-age

No detectable edema

No fatty liver

Anxiety, apathy

Appetite may be normal or impaired

Hair is sparse, thin, and dry; easily pulled out

Skin is dry, thin, and wrinkled

Older infants and young children (1 to 3 yr)

Inadequate protein intake or, more commonly, infections

Rapid onset; acute PEM

Some weight loss

Some muscle wasting, with retention of some body fat

Growth: 60 to 80% weight-for-age

Edema

Enlarged, fatty liver

Apathy, misery, irritability, sadness

Loss of appetite

Hair is dry and brittle; easily pulled out; changes color; becomes straight

Skin develops lesions

Features of Marasmus and Kwashiorkor in Children table 6-4

Given appropriate nutrition care, this child has successfully recovered from kwashiorkor.

or ld

H ea

lth O

rg an

iz at

io n,

G en

ev a

Turn to Chapter 15 for details concerning the • causes of hunger at home and abroad.

Did You Know? Melanin, a brown pigment of hair, skin, and eyes, was mentioned earlier as a product made from tyrosine.

213P r o t e i n D e f i c i e n c y a n d E x c e s s

Is It Possible to Consume Too Much Protein? Overconsumption of protein-rich foods off ers no benefi ts and may pose health risks, particularly for weakened kidneys.16 Selecting too many protein-rich foods, such as red meats and fat-containing milk products, adds saturated fat and crowds out fruits, vegetables, and whole grains, a problem from the standpoint of chronic disease risks, too.

U.S. Protein Intakes Most people assume that Americans eat too much pro- tein. Research demonstrates that a median protein intake for U.S. adult males is about 16 percent of total calories, an amount well within the DRI suggested range of between 10 and 35 percent of calories.17 Women, children, and some elderly people may typically take in less protein—13 to 15 percent. A small percentage of adolescent girls and elderly women consume insuffi cient pro- tein or barely enough to meet their needs.18

In contrast to the average, some people follow popular diet advice to load up on up to 65 percent or more of calories from protein as a way to lose weight. Obtaining enough protein to meet the DRI recommended intake is important for appetite control and retention of lean body tissue during weight loss.19 However, as Chapter 9 explains, it is calorie reduction, not the proportion of energy nutrients, that produces long-term weight loss.20 Let it suffi ce here to say that the best weight- loss diet is one that provides a health-promoting balance of energy nutrients from a variety of whole foods.

Heart Disease Foods rich in animal protein can also be rich in saturated fats. Consequently, it is not surprising that people who take in a great deal of animal protein (red meats and dairy products) have a greater risk of heart disease.21 In the United States, meat consumption often accompanies higher energy (calorie) intakes and increased abdominal body fatness, and excess abdominal fat raises the risk for heart disease.22 As the Controversy points out, people who substitute vegetable protein for animal protein lower their risk of dying from heart disease.23

Currently, researchers are debating about the meaning of an observed link be- tween an amino acid, homocysteine, and heart disease.24 A high blood level of homocysteine often accompanies heart disease and stroke.25 In addition, people with elevated blood homocysteine less often survive a heart attack than those with lower levels.26 Many suspected factors—including a high-protein diet—can raise homocysteine in the blood, but it is unknown whether elevated homocysteine might be a cause of heart disease or an eff ect of it.27 Research is focused on clarifying these relationships.28

Kidney Disease Animals fed experimentally on high-protein diets often develop enlarged kidneys or livers. In human beings, a high-protein diet increases the kid- neys’ workload, but this alone does not appear to damage healthy kidneys or cause kidney disease.29 In people with kidney stones or other kidney diseases, however, a high-protein diet may speed the kidneys’ decline. One of the most eff ective treat- ments for people with established kidney problems is to limit protein intakes to improve the symptoms of their disease.30 Taken to an extreme, very low protein diets, even when supplemented with essential amino acids, do not delay kidney deterioration further and may increase fatality.31

Adult Bone Loss When human subjects are given increasing doses of purifi ed protein, they spill larger and larger amounts of calcium from the body into the urine. Th is fact raises concerns that a high-protein diet may cause or worsen adult bone loss and the crippling eff ects of osteoporosis. In a recent study, however, re- searchers concluded that, unlike the eff ect of purifi ed protein, high protein intakes from whole food sources, such as meat or milk products, do not appear to increase calcium losses.32 Other factors, such as low intakes of vitamin D and bone miner- als, ultimately harm bone health to a greater degree than high intakes of protein.33

Conversely, too little dietary protein almost certainly weakens the bones, both during young years of bone development and in malnourished elderly individuals.

homocysteine (hoe-moe-SIS-teen) an amino acid produced as an intermediate compound during amino acid metabolism. A buildup of homocysteine in the blood is associated with defi ciencies of B vitamins and may increase the risk of diseases. See also Chapter 7.

osteoporosis (OSS-tee-oh-pore-OH-sis) a disease of older persons characterized by porous and fragile bones that easily break, leading to pain, infi rmity, and death. Also defi ned in Chapter 8.

214 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

Protein defi ciency and hip fractures often occur together, while restoring dietary protein along with calcium and vitamin D supplements improves bone status.‡‡34 In establishing protein recommendations, the DRI committee considered the eff ect of excess protein on the bones but found the evidence insuffi cient to set a Tolerable Upper Intake Level.35

Cancer Th e eff ects of protein on cancer causation cannot be easily separated from the various foods that provide protein to the diet. When researchers consider all sources of animal protein in the diet, for example, no association with cancers of the colon and rectum are evident.36 However, when researchers limit their focus to well-cooked red meats and processed meats (typical protein sources for those on high-protein diets), they often report moderately increased risk for cancers, particu- larly of the colon and rectum.37 Intakes of frankfurters, sausages, ham, luncheon meats, bacon, and other processed meats may best be limited for two other reasons, as well: these foods contain large amounts of saturated fat and salt, factors associ- ated with heart disease and hypertension. Chapter 11 delves deeper into apparent links between diet and cancer.

KE Y POINT Most U.S. protein intakes fall within the DRI recommended protein intake range of 10 and 35 percent of calories. No Tolerable Upper Intake Level exists for protein. Health risks may follow the overconsumption of protein-rich foods.

Chapter 8 and Controversy 8 provide details • about calcium and the bones.

Did You Know? Red meats include beef, pork, mutton, lamb, veal, goat, venison, and others. White meats include poultry, fi sh, and other seafood. (Claims that pork is a “white” meat are scien- tifi cally inaccurate.)

‡‡The calcium supplement was citrate malate.

food feature

People in developed nations usually eat more than ample protein. The DRI recommendation for protein is generous and more than adequately covers the estimated needs of most people, even those with unusually high requirements. Most foods contribute at least some protein to the diet.

PROTEIN-RICH FOODS Foods in the meat, poultry, fi sh, dry peas and beans, eggs, and nuts group and in the milk, yogurt, and cheese group contribute an abundance of high-quality protein. Two others, the vegetable group and the grains group, contribute smaller amounts of protein, but they can add up to signifi cant quantities. What about the fruit group? Don’t rely on fruit for pro- tein—fruit contains only small amounts. Figure 6-16 demonstrates that a wide variety of foods contribute protein to

Getting Enough but Not Too Much Protein

the diet. Figure 6-17 lists the top protein contributors in the U.S. diet.

Protein is critical in nutrition, but too many protein-rich foods can displace other important foods from the diet. Foods richest in protein carry with them a charac- teristic array of vitamins and minerals, in- cluding vitamin B12 and iron, but they lack others—vitamin C and folate, for example. In addition, many protein-rich foods such as meat are high in calories, and to over- consume them is to invite obesity.

In Chapter 2, Figures 2-14 and 2-15 (pages 57–58) demonstrated this effect in two diets. What the fi gure did not show was that Monday’s meals provided 87 grams of protein from a small amount of meat in harmony with all the other foods needed for the day and fell within the calorie budget. The more typical Tuesday’s meals provided 106 grams of protein but fell short of meeting many other needs and exceeded the calorie

allowance. Protein recommendations for adults generally fall between 46 and 56 grams per day, so both these day’s meals provided much more than enough protein. Moral: Protein-rich meats are not always the best, or even the most desir- able, sources of protein in a balanced nutritious diet.

Because American consumption of protein is ample, you can plan meatless or reduced-meat meals with confi dence. Of the many interesting, protein-rich meat equivalents available, one has already been mentioned: the legumes.

THE ADVANTAGES OF LEGUMES The protein of some legumes is of a quality almost comparable to that of meat, an unusual trait in a fi ber-rich vege- table. For practical purposes, the quality of soy protein can be considered equiva- lent to that of meat. Figure 6-18 shows

215P r o t e i n D e f i c i e n c y a n d E x c e s s

Finding the Protein in Foodsafigure 6-16

Food Protein g %DVb

Bagel 2 sm

41/2 8 Pancakes 6 12

Brown rice 1/2 c 3 6 Grain bread 1 sl 3 6 Noodles, pasta 1/2 c 3 6 Oatmeal 1/2 c 3 6 Barley 1/2 c 2 4 Cereal flakes 1 oz 2 4

Grains

Milk, Yogurt, and Cheese

Fruits

Vegetables

Oils, Solid Fats, and Added Sugars

Meat, Poultry, Fish, Dry Peas and Beans,

Eggs, and Nuts

Food Protein g %DVb

Avocado 2 4 Cantaloupe 1 2 Orange sections 1 2 Strawberries 1 2

Food Protein g %DVb

Chicken breast 2 oz 15 30

Roast beef 2 oz 19 33

Pork meat 2 oz 15 30

Turkey leg 2 oz 16 32

Tuna 2 oz 14 28 Lentils, beans, peas 1/2 c 9 18 Peanut butter 2 tbs 8 16 Almonds 1/4 c 8 16

Lunch meat 2 oz 6 12

Cashew nuts 1/4 c 5 10 Egg 1 lg 6 12

Hot dog 1 reg 7 14

Food Protein g %DVb

Corn 3 6

Bean sprouts 1 2

2 4 Collard greens

Sweet potato

2 4

Baked potato 1 2

Broccoli 2 4

Winter squash 1/2 c

1/2 c

1 2

Food Protein g %DVb

Pudding 1 c 5 10

Milk, yogurt 1 c 10 20

Cheese, processed 2 oz 13 26

Not a significant source

aAll foods are prepared and ready to eat. bThe Daily Value (DV) for protein is 50 g, based on an

energy intake of 2,000 calories per day.

o la

ra S

tu d

io s I n c . (a

ll)

1/2 c

216 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

Many of these are intended to match the known nutrient contents of animal protein foods, but they often fall short.*** A wise vegetarian uses such foods sparingly and learns to use combinations of whole foods to supply the needed nutrients. The nutrients of soybeans are also avail- able as bean curd, or tofu, a staple used in many Asian dishes. Thanks to the use of calcium salts when some tofu is

acids can be much improved by using grains and other vegetables with them.

Soybeans are versatile legumes and many nutritious products are made from them. Heavy use of soy products in place of meat, however, inhibits iron absorption. The effect can be alleviated by using small amounts of meat and/or foods rich in vitamin C in the same meal with soy products. Vegetarians and oth- ers sometimes use convenience foods made from textured vegetable protein (soy protein) formulated to look and taste like hamburgers or breakfast sausages.

a legume plant’s special root system that enables it to make abundant protein by obtaining nitrogen from the soil.38 Legumes are also excellent sources of many B vitamins, iron, calcium, and other minerals, making them exceptionally nutritious. On average, a cup of cooked legumes contains about 30 percent of the Daily Values for both protein and iron.§§ Like meats, though, legumes do not offer every nutrient, and they do not make a complete meal by themselves. They contain no vitamin A, vitamin C, or vitamin B12, and their balance of amino

0 1062

% Totala

4 8 Food group

Beef

Poultry

Milk

Yeast bread

Cheese

Fish/shellfish (excluding canned tuna)

Pork (fresh/unprocessed)

Eggs

Pasta

Ham

Cakes/cookies/quick breads/doughnuts

Dried beans/lentils

12 14 16 18

These foods supply about 70 percent of the protein in the U.S. diet. The remainder comes from foods contributing less than 2 percent of the total, such as cold cuts; ready-to-eat cereal; white potatoes; sausage; fl our and baking ingredients; ice cream, sherbet, and frozen yogurt; nuts and seeds; cooked rice and other grains; and canned tuna.

Top Contributors of Protein to the U.S. Diet figure 6-17

aRounded values Source: Data from P. A. Cotton and coauthors, Dietary sources of nutrients among U.S. adults, 1994–1996, Journal of the American Dietetic Association 104 (2004): 921–930.

These root nodules contain bacteria which capture nitrogen

Seed pods (peas), where nitrogen is stored

The legumes include such plants as the kidney bean, soybean, green pea, lentil, black-eyed pea, and lima bean. Bacteria in the root nodules can “fi x” nitrogen from the air, contributing it to the beans. Ultimately, thanks to these bacteria, the plant accumulates more nitrogen than it can get from the soil and also con- tributes more nitrogen to the soil than it takes out. The legumes are so effi cient at trapping nitrogen that farmers often grow them in rotation with other crops to fertilize fi elds. Legumes are included with the meat group in Figure 6-16.

A Legume figure 6-18

Legumes: protein-rich and exceptionally nutritious.

S to

ck by

te /G

et ty

Im ag

§§ Data from the Food Processor Plus, ESHA re- search, version 7.11.

***In Canada, regulations govern the nutrient con- tents of such products.

textured vegetable protein pro- cessed soybean protein used in products formulated to look and taste like meat, fi sh, or poultry.

tofu (TOE-foo) a curd made from soy- beans that is rich in protein, often rich in calcium, and variable in fat content; used in many Asian and vegetarian dishes in place of meat. (Also defi ned in Controversy 2.)

217P r o t e i n D e f i c i e n c y a n d E x c e s s

sweet treats to lower-calorie complex carbohydrates and fi ber-rich choices, such as whole grains, legumes, and vegetables. With these changes, protein totals automatically come into line with the requirements.

most people, however, supply too little fi ber, too much fat, too many calories, and abundant protein. To bring their diets into line with recommendations, then, requires changing the bulk of intake from calorie-rich fried foods, fatty meats, and

made, it can be high in calcium. Check the Nutrition Facts panel on the label.

The Food Features presented so far show that the recommendations for the three energy-yielding nutrients occur in balance with each other. The diets of

Analyze Your Protein Intake The purpose of this exercise is to make you aware of the effects of choosing protein-rich foods in balancing the three energy-yielding nutrients while planning a nutritious diet.

Most people in the United States 1. and Canada eat a variety of foods that provide high-quality protein, making it almost impossible not to meet their protein needs. Do you think that your diet contains adequate protein? From the DA+ Home page, select Reports, then Macronutrient Ranges. Choose Day Three, include the entire day’s meals, and generate a report. Is your intake within the recommended 10–35 percent of total energy intake range, as recommended by the DRI? What percent of your calorie intake consists of protein? If your protein

intake is higher than 35 percent, what foods could you choose less of to bring you within range? If your intake is lower, what foods would you add to your diet?

From the Reports tab, select Intake 2. vs. Goals report, choose Day Two, all meals. Generate a report. Table 6-3 provides protein intake recommen- dations (page 206) against which to compare your intake. Did your protein gram values fall into line with your DRI recommended intake (multiply your weight in kilograms by 0.8 gram)?

Which foods in your meals provide 3. the greatest amounts of protein? From the Reports tab, select Source Analysis, choose Day Two, all meals. Select protein in the drop-down box, then generate a report. This report will help you determine your protein sources.

Using the same report and date from 4. the previous question, break it down further to see how many grams of protein you eat for each meal: break- fast, lunch, and dinner.

Using Figure 6-14 (page 209), 5. Figure 6-16 (page 215), and the Controversy section, create a vegan vegetarian meal that provides one- third of daily requirement for protein for a 19-year-old female vegan. Pick a new date, select Track Diet, and input the foods in the meal; then generate a report on the Intake Spreadsheet. Compare with DRI values on the inside front cover. If the meal fell short of one-third the protein DRI goal, what vegan foods can you change or add to provide the needed protein?

Concepts in Action

To fi nd additional quiz questions, view videos and animations, and explore interactive exercises, go to www.cengage.com/sso.

Search for information on vegetarianism and food allergies at www.healthfi nder.gov.

Also search for information on food allergens and vegetarian diets at www.fda.gov.

Search for more information about protein-energy malnutrition worldwide at www.who.int/nut.

Learn more about sickle-cell anemia from the National Heart, Lung, and Blood Institute or the Sickle Cell Disease Association of America: www.nhlbi.nih.gov or www.sicklecelldisease.org.

media menu

http://www.cengage.com/sso

http://www.healthfi

http://www.fda.gov

http://www.who.int/nut

http://www.nhlbi.nih.gov

http://www.sicklecelldisease.org

218 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

Answers to these Self Check questions are in Appendix G.

The basic building blocks for protein are:1.

glucose unitsA.

amino acidsB.

side chainsC.

saturated bondsD.

Protein digestion begins in the:2.

mouthA.

stomachB.

small intestineC.

large intestineD.

To prevent wasting of dietary protein, which of the following 3. conditions must be met?

Dietary protein must be adequate in quantity.A.

Dietary protein must supply all essential amino acids in the B. proper amounts.

The diet must supply enough calories from carbohydrate and C. fat.

All of the above.D.

For healthy adults, the DRI recommended intake for protein 4. has been set at:

0.8 gram per kilogram of body weightA.

2.2 pounds per kilogram of body weightB.

12 to 15 percent of total caloriesC.

100 grams per dayD.

Which of the following statements is correct regarding pro-5. tein and amino acid supplements?

They help athletes build muscle without exercise.A.

They help dieters lose weight quicker.B.

They can assist in relieving depression.C.

None of the above.D.

Under certain circumstances, protein can be converted to 6. glucose and so serve the energy needs of the brain. T F

Too little protein in the diet can have severe consequences, 7. but excess protein has not been proven to have adverse effects. T F

Although protein energy malnutrition (PEM) is prevalent in 8. underdeveloped nations, it is not seen in the United States. T F

Partially completed proteins are not held for completion at a 9. later time when the diet may improve. T F

An example of a person in positive nitrogen balance is a 10. pregnant woman. T F

self check

219controversy 6 V e g e t a r i a n a n d M e a t - C o n t a i n i n g D i e t s : W h a t A r e t h e B e n e f i t s a n d P i t f a l l s ?

CONTROVERSY

In affl uent countries around the world, people who eat well-planned vegetar- ian diets suffer less often from major chronic diseases than people whose diets center on meat.1* Should everyone consider eating a vegetarian diet, then? If so, should people simply omit meat, or is more demanded of the vegetarian diet planner? What positive contributions do animal products make to the diet? This Controversy looks fi rst at the positive health aspects of vegetarian diets, then at the positive aspects of meat eaters’ diets. It ends with some practical advice for the vegetarian diet planner.

A vegetarian lifestyle may mistakenly be associated with a particular culture, reli- gion, or belief system, but there are many reasons why individuals might choose it:

Health concerns: omitting meats is a • way to reduce saturated fat intakes and increase whole-grain, fruit, veg-

etable, and legume intakes—changes associated with good health.

Moral objections: some believe that • we should not kill animals and so do not consume animal products, such as milk, cheese, eggs, or honey, or use items made from leather, wool, feathers, or silk.

Other animal concerns: many people • object to inhumane treatment of livestock. Some fear diseases, such as food poisoning or “mad cow disease,” associated with meats.

Religious beliefs: some religions pro-• hibit eating meat.

Environmental concerns: producing • meat protein requires a much greater input of resources than does an equal amount of vegetable protein.2 (See Chapter 15 for more on these topics.)

In any case, vegetarians are not categorized by their motivations but by the foods they choose to eat (see Table C6-1).

Why do meat eaters choose to eat meat and other animal products? Some reasons include:

Convenience: some people fi nd that • a hamburger or chicken sandwich makes a convenient lunch.

Vegetarian and Meat- Containing Diets: What Are the Benefi ts and Pitfalls?

LO 6.7, 6.8

Can a diet without animal products supply the needed nutrients?

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Some of the terms below are in common usage, but others are useful only to researchers.

fruitarian• includes only raw or dried fruits, seeds, and nuts in the diet. lacto-ovo vegetarian• includes dairy products, eggs, vegetables, grains, legumes, fruits, and nuts; excludes fl esh and seafood. lacto-vegetarian• includes dairy products, vegetables, grains, legumes, fruits, and nuts; excludes fl esh, seafood, and eggs. macrobiotic diet• a vegan diet composed mostly of whole grains, beans, and certain vegetables; taken to extremes, macrobiotic diets can compromise nutrient status. ovo-vegetarian• includes eggs, vegetables, grains, legumes, fruits, and nuts; excludes fl esh, seafood, and milk products. partial vegetarian• a term sometimes used to mean an eating style that includes seafood, poultry, eggs, dairy products, vegetables, grains, legumes, fruits, and nuts; excludes or strictly limits certain meats, such as red meats. pesco-vegetarian• same as partial vegetarian, but eliminates poultry. vegan• includes only food from plant sources: vegetables, grains, legumes, fruits, seeds, and nuts; also called strict vegetarian. vegetarian• includes plant-based foods and eliminates some or all animal-derived foods.

Terms Used to Describe Vegetarians

and Their Diets

table C6-1

*Reference notes are found in Appendix F.

220 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

those who limit or eliminate these foods, and their blood lipids refl ect it.

Decades of experimentation have revealed that when soy protein replaces animal protein in the diet, a slight but signifi cant decline in LDL cholesterol oc- curs.11 However, to achieve this benefi t requires consuming large amounts of daily soy protein—50 grams, the amount in about fi ve average soy “burgers” or two and a half cups of tofu.12 Half this amount has proved ineffective.13 In con- trast, supplements of soy phytochemi- cals do not seem to benefi t the heart.14 Any protective effect of soy, therefore, may arise from the abundant soy protein, polyunsaturated fatty acids, fi bers, vitamins, and minerals in these foods; they also often displace foods high in saturated fat from the diet.15

Defense Against High Blood Pressure Vegetarians tend to have lower blood pressure and lower rates of hypertension than nonvegetarians. Often, vegetarians maintain a healthy body weight, and ap- propriate body weight helps to maintain healthy blood pressure; so does a diet low in total and saturated fat and high in fi ber, fruits, vegetables, the mineral potassium, and soy protein.16 A low so- dium intake also promotes normal blood pressure, as do lifestyle factors such as not smoking, keeping alcohol intake moderate, and being physically active.

Defense Against Cancer In a 2007 report, cancer authorities made this statement: “Red meat is a convinc- ing cause of colorectal cancer.”17 Stated another way, colon and rectal cancer are reported to occur less frequently among people who eat mostly plant-based diets than among those who regularly con- sume red meat and processed meat.18 The amount of red or processed meat reported to have this effect is surprisingly small—only 120 grams, or a little over 4 ounces per day.

Is the case closed on meat’s culpabil- ity in colon and rectal cancers, then? “Not so fast,” is the answer from a sur- prising study of over 60,000 people in the United Kingdom.19 In this study, people who ate fi sh but not red meats had the lowest overall cancer rates—so far, so

ians more often maintain a healthier body weight than nonvegetarians.6 The converse is also true: meat consumption correlates with increased energy intake and increased obesity.7 The reason for this is not clear, but may refl ect a lifestyle adopted by many vegetarians that makes health a high priority. Obesity impairs health in a number of ways (see Chapter 9), and vegetarians who maintain a healthy weight enjoy a health advantage.

Defense Against Heart Disease Vegetarians die less often from heart disease and related illnesses than do meat-eating people.8 Plant-based diets can be low in saturated fat, and satu- rated fat intake correlates directly with heart disease risk. The unsaturated fats of soybeans, seeds, avocados, nuts, olives, and other unsaturated vegetable oils reduce the risk of heart disease when they replace saturated fat sources in the diet.9 Furthermore, diets that con- tain such foods generally provide more dietary fi ber, a bonus to blood lipids and to the heart.

The lowest blood lipids are found in vegans; the blood lipids of lacto-ovo vegetarians are higher; and the blood lipids of people eating typical, meat-rich Western diets are the highest.10 Vegetar- ians who eat cheese, sour cream, and butter take in more saturated fat than

Nutrients: some people rely on animal • products for the energy and key nutri- ents they supply.

Taste: others enjoy the taste of roasted • chicken, barbecued ribs, or a grilled steak.

Habit: some people wouldn’t know • what to eat without meat; they are ac- customed to seeing it on the plate.

Misguided weight-control efforts: • people may mistakenly think that eat- ing meats instead of grains, potatoes, and breads speeds weight loss (it doesn’t). Conversely, teens may hide an eating disorder under the guise of being “vegetarian” (Chapter 9 takes up the issues of weight-loss dieting and eating disorders).3

Whatever your eating style or reasons for choosing it, choose carefully: the foods that you eat regularly make an impact on your health.

POSITIVE HEALTH ASPECTS OF VEGETARIAN DIETS Today, nutrition authorities state with confi dence that a well-chosen vegetarian diet can meet nutrient needs while sup- porting health superbly.4 Although much evidence links vegetarian diets with reduced incidence of chronic diseases, particularly heart and artery diseases, such evidence is not easily obtained. It would be easy if vegetarians differed from others only in the absence of meat, but they often have increased intakes of whole grains, legumes, nuts, fruits, and vegetables as well.5 Such diets are rich contributors of carbohydrates, fi ber, vita- mins, minerals, and phytochemicals that also correlate with low disease risks.

Also, many vegetarians avoid tobacco, use alcohol in moderation if at all, and are more physically active than other adults. When researchers take into ac- count all of the effects of a total health- conscious lifestyle on disease develop- ment, the evidence weighs in favor of vegetarian diets, as the next sections make clear.

Defense Against Obesity Among both men and women and across many ethnic groups, vegetar-

When consumed in suffi cient quantity, soy foods, such as this roasted tofu, may improve the health of the heart.

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221controversy 6 V e g e t a r i a n a n d M e a t - C o n t a i n i n g D i e t s : W h a t A r e t h e B e n e f i t s a n d P i t f a l l s ?

derived foods provide abundant iron, zinc, vitamin D, and vitamin B12 needed by everyone, but particularly by pregnant women, infants, children, adolescents, and the elderly (details about these needs appear in later chapters).

In Pregnancy and Infancy Women who eat meat, eggs, or milk products can be sure of receiving enough energy, vitamin B12, vitamin D, calcium, iron, and zinc, as well as protein, to support pregnancy and breastfeeding. A woman following a well-planned lacto-ovo vegetarian diet can also relax in the knowledge that she is superbly supplied with energy and all necessary nutrients. And if she also habitually eats abundant veg- etables and fruits, she can relax further, knowing that diet supplies the vitamin folate in amounts needed to protect her developing fetus from certain birth defects. A vegan woman who doesn’t meet her nutrient needs, however, may enter pregnancy too thin and with scant nutrient stores to draw on as the nutrient demands of the fetus grow.

Of particular interest is vitamin B12, a vitamin abundant in foods of animal origin but absent from vegetables. In fact, obtaining enough vitamin B12 poses a challenge to vegans of all ages. For pregnant and lactating women, obtain- ing vitamin B12 is critical. A severe and sometimes fatal disorder is occasionally reported among breastfed infants of vegan mothers who fail to obtain suffi - cient vitamin B12.26 The infant may die or suffer permanent damage if the condition goes untreated.27 If caught in time, death and disability can be averted by adminis- tering the missing vitamin.

In Childhood Children who eat meat, poultry, and fi sh receive abundant protein, iron, zinc, and vitamin B12; such foods are reliable, convenient sources of nutrients needed for growth. Likewise, children eating well- planned lacto-ovo vegetarian diets also receive adequate nutrients and grow as well as their meat-eating peers.28 Child- sized servings of vegan foods, however, can fail to provide suffi cient energy or several key nutrients needed for normal growth. A child’s small stomach can hold

to a healthy diet, can be used wisely to provide benefi cial nutrients, as the next sections point out.

POSITIVE HEALTH ASPECTS OF THE MEAT EATER’S DIET Unlike vegetarians, for whom suitable replacements exist for meat and milk in a healthy diet, meat eaters fi nd no ade- quate substitutes for whole grains, fruits, and vegetables (not even antioxidant supplement pills, as the next chapter points out). A meat eater who excludes or minimizes intakes of these foods imperils health. The following sections consider a balanced, adequate diet, in which lean meat, poultry, seafood, eggs, and milk play a part.

Both meat eaters and lacto-ovo veg- etarians can generally rely on their diets during critical times of life. In contrast, a vegan diet poses challenges. Protein is critical for building new tissues during growth, for fi ghting illnesses, and for building bone during youth and main- taining bone and muscle tissue integrity in old age.25 While protein from plant sources can meet most people’s needs, very young children and very elderly people with small appetites may not con- sume enough legumes, whole grains, or nuts to supply the protein they need.

The chapter made clear that animal protein from meat, fi sh, milk, and eggs is the clear winner in tests of digestibility and availability to the body, with soy protein a close second. Also, animal-

good. Vegetarians also had lower rates than meat eaters for total cancers—also not surprising. However, vegetarians had the highest number of colon and rectal cancers of any group, while fi sh eaters again had the lowest. No one yet knows the meaning of these results, but the fi ndings may refl ect the unusually small meat intakes (2 to 3 ounces per day) or the high vegetable and fruit intakes (just 20 percent lower than in the vegetarians) reported among these particular meat eaters.

The fi nding about fi sh in the study just described brings up questions about the so-called white meats: poultry and fi sh. Did the fi sh eaters in the British study gain some protection from fi sh? A hint comes from a study tracking cancer deaths among a half-million educated, non-Hispanic white men and women over age 50.20 In support of many other fi ndings, those who consumed the least red and processed meat had modestly lower cancer death rates, mostly colon and rectal cancers, than those who ate more meat. Unexpectedly, however, people who ate the most poultry and fi sh suffered the least cancer, making it clear that researchers must take into account types, not just totals, of meats consumed when studying links with cancer. Critics of the study also point out that people who eat less red meat (and choose poul- try and fi sh most often) may also adopt other healthy habits, such as exercising regularly, which may reduce their cancer risks.21 In that case, red meat intake may correlate with, but perhaps not be the cause of, an increased cancer risk.

Colon cancer risk also appears to increase with:

Alcohol (moderate-to-high intakes).• 22

Body and abdominal fatness.• 23

Other Health Benefi ts In addition to obesity, heart disease, high blood pressure, and cancer, vegetar- ian diets may help prevent diabetes, osteoporosis, diverticular disease, and gallstones.24 However, these effects may arise more from what vegetarians include in the diet—abundant fruit, legumes, vegetables, and whole grains—than from omission of meat. Lean meats, poultry, and seafood, while not essential

This 5-ounce steak provides almost all of the meat recommended for an entire day’s intake in a 2,000-calorie diet.

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222 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

ians need to select fortifi ed foods or use supplements daily. Like MyPyramid, this vegetarian food pyramid also encourages physical activity. In planning a vegetarian diet, scrutinize the labels of convenience and prepared vegetarian foods just as you would those of ordinary foods. Some prepared foods constitute a nutritional bargain, such as vegetarian “hot dogs.” Made of soy, these hot dogs look and taste like the original meat product but contain much less fat and saturated fat and no cholesterol. Conversely, banana chips, often sold as “healthy” alternative snack food, are no bargain: a quarter cup of banana chips fried in saturated coco- nut oil provides 150 calories with 7 grams of saturated fat (a big hamburger has 8 grams). A plain banana has 100 calories and practically no fat.

Protein Vegetarians who consume eggs and low-fat milk products receive high- quality complete protein that provides all the essential amino acids required for health. Even vegans are likely to meet protein needs provided that they meet their energy needs with nutritious whole foods and that their protein sources are varied.32

Foods made from textured vegetable protein, usually soybean products, are formulated to look and taste like meat. They may fall short of the nutrients in meats, however, and they may be high in salt, sugar, or other additives. Labels list all of the ingredients in such foods. Vegetarians may also use soybeans in other forms, such as plain tofu (bean curd), edamame (cooked green soy- beans, pronounced ed-eh-MAH-may), or soy fl our, to bolster protein intake without consuming unwanted salt, sugar, or other additives.

Iron Getting enough iron can be a problem even for meat eaters; vegetarians must be vigilant about obtaining iron. The iron in plant foods such as legumes, dark green leafy vegetables, iron-fortifi ed cereals, and whole-grain breads and ce- reals may not be as well absorbed (see Chapter 8 for more details). Such foods also contain inhibitors of iron absorp-

of cures attributed to restrictive eating plans, such as macrobiotic diets, but these diets often severely limit food se- lections and can fail to deliver the energy and nutrients needed for recovery.

PLANNING A VEGETARIAN DIET Most vegetarians easily obtain large quantities of the nutrients that are abun- dant in plant foods: carbohydrate, fi ber, thiamin, folate, and vitamins B6, C, A, and E. Vegetarian food guides help to ensure adequate intakes of the main nu- trients vegetarian diets might otherwise lack: protein, iron, zinc, calcium, vitamin B12, vitamin D, and omega-3 fatty acids. Table C6-2 presents good vegetarian sources of these key nutrients.

If not properly balanced, any diet— vegetarian or otherwise—can lack nutrients. Poorly planned vegetarian diets typically lack iron, zinc, calcium, vitamin B12, and vitamin D; poorly planned meat- eater’s diets may lack vitamin A, vitamin C, folate, and fi ber. Simply put, a diet that omits key foods omits essential nutrients.

Vegetarian Food Guide The MyPyramid resources, introduced in Chapter 2, include tips for planning vege- tarian diets using the USDA Food Guide. In addition, several vegetarian food guides have been developed to address the diet-planning needs of vegetarians.31 Figure C6-1 presents one version.

When selecting from the vegetable and fruit groups, vegetarians should emphasize sources of calcium and iron. Green leafy vegetables provide both calcium and iron. Similarly, dried fruits deserve special notice in the fruit group because they can deliver more iron than other fruits. Note that the milk group features fortifi ed soy milk for those who do not use milk, cheese, or yogurt. Their similarities are demonstrated in Figure C6-2 on page 225. The meat group, called “proteins,” emphasizes legumes, soy products, nuts, and seeds. The oils group encourages the use of vegetable oils, nuts, and seeds rich in unsaturated fats and omega-3 fatty acids.

To ensure adequate intakes of vitamin B12, vitamin D, and calcium, vegetar-

only so much food, and the vegan child may feel full before eating enough to meet his or her nutrient needs. Com- pared with meat-eating children, well-fed vegan children tend to be shorter and lighter in weight but not excessively so.

Small, frequent meals of fortifi ed breads, cereals, or pastas with legumes, nuts, nut butters, and sources of un- saturated fats can help to meet protein and energy needs in a smaller volume at each sitting.29 Because vegan children derive protein only from plant foods, their daily protein requirement may be some- what higher than the DRI indicates for the general meat-eating population.30 Other nutrients of concern for vegan children include vitamin B12, vitamin D, calcium, iron, and zinc. A later section provides tips to help meet these nutrient needs within the context of a vegan diet.

In Adolescence The healthiest vegetarian adolescents choose balanced diets that are heavy in fruits and vegetables but light on the sweets, fast foods, and salty snacks that tempt the teenage palate. These healthy vegetarian teens often meet national di- etary objectives, such as those of Healthy People 2010 (listed in Chapter 1)—a rare accomplishment in the United States.

Other teens, however, adopt poorly planned vegetarian diets lacking in en- ergy, protein, vitamin B12, calcium, zinc, and vitamin D. Omissions of calcium and vitamin D lead to weak bone develop- ment at precisely the time when bones must develop strength to protect them through later life. Also, teens must plan a source of vitamin B12 to avoid serious nerve damage from a defi ciency. If a vegetarian child or teen refuses sound dietary advice, a registered dietitian can help identify problems, dispense ap- propriate guidance, and put unwarranted parental worries to rest.

In Aging and in Illness For elderly people with diminished appe- tites or impaired digestion or for people recovering from illnesses, soft or ground meats can provide a well-liked, well- tolerated concentrated source of nutri- ents. People battling life-threatening dis- eases may encounter testimonial stories

223controversy 6 V e g e t a r i a n a n d M e a t - C o n t a i n i n g D i e t s : W h a t A r e t h e B e n e f i t s a n d P i t f a l l s ?

cally eat many vitamin C–rich fruits and vegetables. Consequently, vegetarians suffer no more iron defi ciency than other people do.

to a vegetarian diet by absorbing iron more effi ciently. Also, iron absorption is enhanced by vitamin C consumed with iron-rich foods, and vegetarians typi-

tion, so the DRI committee suggests that vegetarians need 1.8 times the amount of iron recommended for meat eaters.33 At some point, the body begins to adapt

NUTRIENTS

FOOD GROUPS

Grains Vegetables Fruits Legumes and Other Protein-Rich Foods Milk or Soy Milk Oils

PROTEIN Whole grainsa Legumes, seeds, nuts, soy products (tempeh, tofu, veg- gie burgers)a

Eggs (for ovo- vegetarians)

Milk, cheese, yogurt (for lacto-vegetarians); soy milk, soy yogurt, soy cheeses

IRON Fortifi ed cereals, enriched and whole grains

Dark green leafy vegetables (spin- ach, turnip greens)

Dried fruits (apricots, prunes, raisins)

Legumes (black- eyed peas, kidney beans, lentils), soy products

ZINC Fortifi ed cereals, whole grains

Legumes (garbanzo beans, kidney beans, navy beans), nuts, seeds (pump- kin seeds)

Milk, cheese, yogurt (for lacto-vegetarians); soy milk, soy yogurt, soy cheeses

CALCIUM Fortifi ed cereals Dark green leafy vegetables (bok choy, broccoli, col- lard greens, kale, mustard greens, turnip greens, watercress)

Fortifi ed juices, fi gs

Fortifi ed soy products, nuts (almonds), seeds (sesame seeds)

Milk, cheese, yogurt (for lacto-vegetarians); fortifi ed soy milk, fortifi ed soy yogurt, fortifi ed soy cheese

VITAMIN B12 Fortifi ed cereals Eggs (for ovo-

vegetarians); forti- fi ed soy products

Milk, cheese, yogurt (for lacto-vegetarians); fortifi ed soy milk, fortifi ed soy yogurt, fortifi ed soy cheese

VITAMIN D Fortifi ed cereals Milk, cheese, yogurt (for lacto-vegetarians); fortifi ed soy milk, fortifi ed soy yogurt, fortifi ed soy cheese

OMEGA-3 FATTY ACIDS

Marine algae and its oils

Flaxseed, walnuts, soybeans, fortifi ed margarine,b fortifi ed eggs (for ovo- vegetarians)b

Flaxseed oil, walnut oil, soy- bean oil

aMany plant proteins lack certain essential amino acids or contain them in insuffi cient amounts for human health. A variety of daily plant protein sources, such as grains and legumes, can meet protein needs when energy intake is suffi cient. bFortifi cation sources of EPA and DHA may be fi sh oil or marine algae oil; read the ingredients list on the label.

Vegetarian Sources of Key Nutrients table

C6-2

224 chapter 6 T h e P r o t e i n s a n d A m i n o A c i d s

eggs, these foods are reliable sources. For vegans, fermented soy products may contain some vitamin B12 from the bacte- ria that did the fermenting, but much of it may be an inactive form. Seaweeds such as nori and chlorella supply just a trace of vitamin B12, and excessive intakes of these foods can lead to iodine toxicity. For a reliable supply of vitamin B12, veg- ans can use vitamin B12–fortifi ed foods (such as soy milk or breakfast cereals) or take a supplement that contains it.

Vitamin D Overall, vegetarians are similar to nonvegetarians in their vitamin D status; factors such as taking supplements, skin color, and sun exposure have a greater infl uence on vitamin D than diet.35 Peo- ple who do not use vitamin D–fortifi ed foods and do not receive enough expo- sure to sunlight to synthesize adequate vitamin D may need supplements to

legumes, some green vegetables (broc- coli, kale, and turnip greens, but not spinach—see Chapter 8), some nuts such as almonds, and certain seeds such as sesame seeds.† One cup of cooked kale, for example, provides about 90 milligrams of calcium and 1.2 milligrams of iron, or about 7 percent of both the daily calcium and iron needs of an adolescent girl.34 The choices should be varied because calcium absorption from some plant foods is limited and the amounts present may be insuf- fi cient to meet many people’s calcium requirements.

Vitamin B12 The requirement for vitamin B12 is small, but this vitamin is critical, as already men- tioned. Found naturally only in animal- derived foods, such as meats, milk, and

Zinc Zinc is similar to iron in that meat is its richest food source, and zinc from plant sources is not as well absorbed. Zinc can be a problem for growing children, but few vegetarian adults eating nutrient- dense diets are zinc defi cient.

Calcium The calcium intakes of vegetarians who use milk and milk products are similar to those of the general population. For vegans, ample quantities of calcium- fortifi ed foods, such as juices, soy milk, and breakfast cereals, are required regularly. Not all such products are well endowed with calcium, however, so label reading must become a passion. This is especially important when feeding chil- dren and adolescents whose developing bones demand ample calcium.

Some absorbable calcium is also present in fi gs, calcium-set tofu, some

Review Figure 2-5 on page 38 and Table 2-2 on page 44 of Chapter 2 to fi nd the recommended daily amounts from each food group, serving size equivalents, and examples of foods within each group. Tips for planning a vegetarian diet can be found at MyPyramid.gov.

My Vegetarian Food Pyramid figure C6-1

Source: © GC Nutrition Council, 2006, adapted from USDA 2005 Dietary Guidelines and www.mypyramid.gov

†Calcium salts are often added to tofu during pro- cessing to coagulate it.

http://www.mypyramid.gov

225controversy 6 V e g e t a r i a n a n d M e a t - C o n t a i n i n g D i e t s : W h a t A r e t h e B e n e f i t s a n d P i t f a l l s ?

diet should include small amounts of fl axseed, walnuts, and their oils, as well as soybeans and canola oil to provide essential fatty acids.

CONCLUSION This comparison has shown that both a meat-eater’s diet and a vegetarian’s diet are best approached scientifi cally. Some people make much of the distinctions among types of vegetarians; and al- though these distinctions are useful aca- demically, they do not represent uncross- able lines. Some people use meat as a condiment or seasoning for vegetable or grain dishes. Some people eat meat only once a week and use plant protein foods the rest of the time. Many people rely mostly on milk products to meet their protein needs but eat fi sh twice weekly, and so forth. To force people into the categories of “vegetarians” and “meat eaters” leaves out all these in-between styles of eating that have much to rec- ommend them.

If you are just beginning to study nutri- tion, consider adopting the attitude that the choice to make is not whether to be a meat eater or a vegetarian, but where along the spectrum to locate yourself. Your preferences should be honored with only these caveats: that you plan your own diet and the diets of those in your care to be adequate, balanced, and varied and that you use moderation when choosing foods high in saturated fat or calories.

products can provide EPA and DHA, but all of these sources ultimately derive from fi sh, an unacceptable food for veg- ans.37 Alternatively, certain marine algae and their oils provide DHA and more foods are being fortifi ed with such oils, which are listed among the ingredients on a food’s label.‡38 A vegetarian’s daily

fend off bone loss. Of particular concern are infants, children, and older adults in northern climates during winter months.

Omega-3 Fatty Acids Vegetarian diets typically provide enough of the essential fatty acids linoleic acid and linolenic acid, but they lack a dietary source of EPA and DHA.36 Fatty fi sh and DHA-fortifi ed eggs and other fortifi ed

Total Fat 0g 0%

Serving Size 1 cup (240mL) Servings Per Container About 8

Calories 80 Calories from Fat 0

Amount Per Serving

% Daily Value*

Sodium 100mg

Cholesterol 5mg

Potassium 380mg

11%

Protein 8g

Saturated Fat 0g

Trans Fat 0g

Total Carbohydrate 13g

Nutrition Facts

Polyunsaturated Fat 0g

Monounsaturated Fat 0g

0%Dietary Fiber 0g

Sugars 12g

Total Fat 0g 0%

Serving Size 1 cup (240mL) Servings Per Container About 8

Calories 70 Calories from Fat 0

Amount Per Serving

% Daily Value*

Sodium 120mg

Cholesterol 0mg

Potassium 300mg

Protein 6g

Saturated Fat 0g

Trans Fat 0g

Total Carbohydrate 8g

Nutrition Facts

Polyunsaturated Fat 0g

Monounsaturated Fat 0g

4%Dietary Fiber 1g

Sugars 6g

Vitamin A 10% • Vitamin C 0%

Calcium 30% • Iron 0%

Vitamin D 25% • Riboflavin 30%

Vitamin B12 20%

Vitamin A 10% • Vitamin C 0%

Calcium 30% • Iron 6%

Vitamin D 30% • Riboflavin 30%

Vitamin B12 50%

Manufacturers of soy milk often fortify it with many of the nutrients that milk provides.

Nutrients in Nonfat Milk and Light Soy Milk figure C6-2

‡The algae are Cryptherodinium cohnii and Schizochytrium spp.

The Vitamins 77 do you ever . . .

Wonder how vitamins work in the body?•

Associate sunshine with good health?•

Take vitamin C tablets to ward off a cold?•

Eat vitamin-fortifi ed foods and take • supplements as a harmless form of health insurance?

Keep reading . . .

LO 7.1 List the fat-soluble and water-soluble vitamins, and describe how solubility affects the absorption, transport, storage, and excretion of each type.

LO 7.2 Explain how vitamins and minerals work in combination to maintain the health of the bones.

LO 7.3 Name some functions of vitamin D not associated with the bones.

LO 7.4 Defi ne the term antioxidant, and name the vitamins that act as antioxidants in the body.

LO 7.5 Discuss the roles of B vitamins in body tissues, and explain in a general way how B vitamins assist with energy metabolism.

LO 7.6 Present arguments both for and against vitamin fortifi cation of foods.

LO 7.7 Suggest foods that can help to ensure adequate vitamin intakes without providing too many calories.

LO 7.8 Justify this statement: “It is better to get vitamins from food than from supplements.”

LO 7.9 List some valid reasons why supplements may be required by some people.

227D e f i n i t i o n a n d C l a s s i f i c a t i o n o f V i t a m i n s

E arly in the 20th century, the thrill of the discovery of the fi rst vitamins cap- tured the world’s imagination. Seemingly miraculous cures took place—a whole

group of people were unable to walk (or were going blind or bleeding profusely) until an alert scientist stumbled onto the substance missing from their diets. Th e scientist confi rmed the discovery by feeding vitamin-defi cient feed to laboratory animals, which responded by becoming unable to walk (or going blind or bleeding profusely). When the missing vitamin was restored to their diets, both people and animals soon recovered.

In the decades that followed, advances in chemistry, biology, and genetics al- lowed scientists to isolate the vitamins, defi ne their chemical structures, and reveal their functions in maintaining health and preventing defi ciency diseases. Today, research hints that certain vitamins may be linked with the development of two major scourges of humankind: cardiovascular disease (CVD) and cancer. Defi cien- cies of some vitamins may mimic radiation in their disruption of cellular genetic functioning.1* Many other conditions, from infections to cracked skin, bear relation to vitamin nutrition, details that unscrupulous sellers of vitamins often use to mar- ket their wares (see the Controversy section).

Can foods rich in vitamins protect us from life-threatening diseases? What about vitamin pills? For now, we can say this with certainty: the only disease a vitamin will cure is the one caused by a defi ciency of that vitamin. As for chronic disease prevention, research is ongoing but evidence so far supports the conclusion that vitamin-rich foods, but not vitamin supplements, are protective.2

LO 7.1

Definition and Classification of Vitamins A child once defi ned a vitamin as “what, if you don’t eat, you get sick.” Although the grammar left something to be desired, the defi nition was accurate. Less imagi- natively, a vitamin is defi ned as an essential, noncaloric, organic nutrient needed in tiny amounts in the diet. Th e role of many vitamins is to help make possible the processes by which other nutrients are digested, absorbed, and metabolized or built into body structures. Although small in size and quantity, the vitamins accomplish mighty tasks.

As each vitamin was discovered, it was given a name and some were given letters and numbers—vitamin A came before B vitamins, then came vitamin C, and so forth. Th is led to the confusing variety of vitamin names that still exists today. Th is chapter uses the names in Table 7-1; alternative names are given in Tables 7-6 and 7-7 at the end of the chapter.

The Concept of Vitamin Precursors Some of the vitamins occur in foods in a form known as precursors, or provitamins. Once inside the body, these are transformed chemically to one or more active vitamin forms. Th us, to measure the amount of a vitamin found in food, we often must count not only the amount of the true vitamin but also the vitamin activity potentially available from its precursors. Tables 7-6 and 7-7 specify which vitamins have precursors.

Two Classes of Vitamins: Fat-Soluble and Water-Soluble Th e vitamins fall naturally into two classes: fat-soluble and water-soluble (listed in Table 7-1). Solu- bility confers on vitamins many of their characteristics. It determines how they are absorbed into and transported around by the bloodstream, whether they can be stored in the body, and how easily they are lost from the body.

In general, like other lipids, fat-soluble vitamins are absorbed into the lymph, and they travel in the blood in association with protein carriers. Fat-soluble vitamins can be stored in the liver or with other lipids in fatty tissues, and some can build up

7 If we could give every individual the right

amount of nourishment and exercise, not too

little and not too much, we would have found

the safest way to health.

—Hippocrates

*Reference notes are found in Appendix F.

Did You Know? The only disease a vitamin can cure is the one caused by a defi ciency of that vitamin.

Vitamin intake recommendations are found • on the inside front cover, page B.

Fat-Soluble Vitamins

Vitamin A

Vitamin D

Vitamin E

Vitamin K

Water-Soluble Vitamins

B vitamins

Thiamin (B1) Riboflavin (B2) Niacin (B3) Folate Vitamin B12 Vitamin B6 Biotin Pantothenic acid

Vitamin C

aVitamin names established by the International Union of Nutritional Sciences Committee on Nomenclature. Other names are listed in Tables 7-6 and 7-7 (pp. 260, 261).

Vitamin Namesatable 7-1

vitamins organic compounds that are vital to life and indispensable to body functions but are needed only in minute amounts; noncaloric essential nutrients.

precursors, provitamins compounds that can be converted into active vitamins.

228 chapter 7 T h e V i t a m i n s

to toxic concentrations. Th e water-soluble vitamins are absorbed directly into the bloodstream, where they travel freely. Most are not stored in tissues to any great extent; rather, excesses are excreted in the urine. Th us, the risks of immediate tox- icities are not as great as for fat-soluble vitamins.

Table 7-2 sums up the general features of the fat-soluble and water-soluble vita- mins. Th is chapter examines the fat-soluble vitamins fi rst and then the water-soluble ones. Th e tables at the end of the chapter present basic facts about all of them.

KE Y POINT Vitamins are essential, noncaloric nutrients that are needed in tiny amounts in the diet and help to drive cell processes in the body. Vitamin precursors in foods are transformed into active vitamins by the body. The fat-soluble vitamins are vitamins A, D, E, and K; the water-soluble vitamins are vitamin C and the B vitamins.

LO 7.2, 7.3, 7.4

The Fat-Soluble Vitamins Th e fat-soluble vitamins—A, D, E, and K—are found in the fats and oils of foods and require bile for absorption. Once absorbed, these vitamins are stored in the liver and fatty tissues until the body needs them. Because they are stored, you need not eat foods containing these vitamins every day. If the diet provides suffi cient amounts of the fat-soluble vitamins on average over time, the body can survive for weeks without consuming them. Th is capacity to be stored also sets the stage for toxic buildup if you take in too much. Excesses of vitamins A and D from supple- ments and highly fortifi ed foods are especially likely to reach toxic levels.

Defi ciencies of the fat-soluble vitamins occur when the diet is consistently low in them. We also know that any disease that produces fat malabsorption (such as

Vitamins fall into two classes—fat-soluble and water-soluble.

While each of the vitamins have unique functions and features, a few generaliza- tions about the fat-soluble and water-soluble vitamins can aid understanding.

Fat-Soluble Vitamins: Vitamins A, D, E, and K

Water-Soluble Vitamins: B Vitamins and Vitamin C

ABSORPTION Absorbed like fats, fi rst into the lymph, then the blood.

Absorbed directly into the blood.

TRANSPORT AND STORAGE

Must travel with protein carriers in watery body fl uids; stored in the liver or fatty tissues.

Travel freely in watery fl uids; most are not stored in the body.

EXCRETION Not readily excreted; tend to build up in the tissues.

Readily excreted in the urine.

TOXICITY Toxicities are likely from supplements, but occur rarely from food.

Toxicities are unlikely but possible with high doses from supplements.

REQUIREMENTS Needed in periodic doses (perhaps weeks or even months) because the body can draw on its stores.

Needed in frequent doses (perhaps 1 to 3 days) because the body does not store most of them to any extent.

Characteristics of the Fat-Soluble

and Water-Soluble Vitamins table 7-2

CONCEPT LINK 7-1 Look back at Figure 5-6, page 157, to see how bile acts in lipid absorption.

229V i t a m i n A

liver disease that prevents bile production) can cause the loss of vitamins dissolved in undigested fat and so bring on defi ciencies. In the same way, a person who uses mineral oil (which the body cannot absorb) as a laxative risks losing fat-soluble vi- tamins because they readily dissolve into the oil and are excreted. Defi ciencies are also likely when people eat diets that are extraordinarily low in fat because such diets interfere with absorption of these vitamins.

Fat-soluble vitamins play diverse roles in the body. Vitamins A and D act some- what like hormones, directing cells to convert one substance to another, to store this, or to release that. Th ey also directly infl uence the genes, thereby regulating protein production. Vitamin E fl ows throughout the body, guarding the tissues against harm from destructive oxidative reactions. Vitamin K is necessary for blood to clot and is thought to aff ect bone health. Each is worth a book in itself.

Vitamin A Vitamin A has the distinction of being the fi rst fat-soluble vitamin to be recog- nized. Today, after a century of scientifi c investigation, vitamin A and its plant- derived precursor, beta-carotene, are still very much a focus of research.

Th ree forms of vitamin A are active in the body; one of the active forms, retinol, is stored in specialized cells of the liver. Th e liver makes retinol available to the bloodstream and thereby to the body’s cells. Th e cells convert retinol to its other two active forms, retinal and retinoic acid, as needed.

Foods derived from animals provide forms of vitamin A that are readily absorbed and put to use by the body. Foods derived from plants provide beta-carotene, which must be converted to active vitamin A before it can be used as such.

Roles of Vitamin A and Consequences of Defi ciency Vitamin A is a versatile vitamin, with roles in gene expression, vision, maintenance of body linings and skin, immune defenses, growth of bones and of the body, and normal development of cells. It is of critical importance for reproduction. In short, vitamin A is needed everywhere (its chief functions in the body are listed in the Snapshot on page 233 and in Table 7-6 on page 260).

Gene Regulation Vitamin A exerts considerable infl uence on body functions through its regulation of genes.3 Genes direct the synthesis of proteins, including enzymes, and enzymes perform the metabolic work of the tissues. Hence, factors that infl uence gene expression also aff ect the metabolic activities of the tissues, and, in turn, the health of the body. Hundreds of genes are regulated by the retinoic acid form of vitamin A.4

Researchers have long known that the presence of genetic equipment needed to make a particular protein does not guarantee that the protein will be made, any more than owning a car guarantees you a ride across town. To get the car rolling, you must also use the right key to trigger the events that start up its engine and, to prevent its racing out of control, to turn it off at the appropriate times. Some dietary components, including the retinoic acid form of vitamin A, are now known to act like such keys—they help activate or deactivate genes and thus aff ect the produc- tion of proteins essential to body functions and health.5

Eyesight Th e most familiar function of vitamin A is to sustain normal eyesight. Vitamin A plays two indispensable roles: in the process of light perception at the retina and in the maintenance of a healthy, crystal-clear outer window, the cornea (see Figure 7-1).

When light falls on the eye, it passes through the clear cornea and strikes the cells of the retina, bleaching many molecules of the pigment rhodopsin that lie within those cells.6 Vitamin A is a part of the rhodopsin molecule. When bleaching occurs, the vitamin is broken off , initiating the signal that conveys the sensation of

CONCEPT LINK 7-2 Gene expression, protein synthesis, and the work of proteins in the body were topics of Chapter 6 (pages 194–195).

This eye is sectioned to reveal its inner structures.

An Eye figure 7-1

Pupil

Cornea

Retina

Macula

Lens

Nerve

beta-carotene an orange pigment with antioxidant activity; a vitamin A precursor made by plants and stored in human fat tissue.

retinol one of the active forms of vitamin A made from beta-carotene in animal and human bodies; an antioxidant nutrient. Other active forms are retinal and retinoic acid.

retina (RET-in-uh) the layer of light-sensitive nerve cells lining the back of the inside of the eye.

cornea (KOR-nee-uh) the hard, transparent membrane covering the outside of the eye.

rhodopsin (roh-DOP-sin) the light-sensitive pigment of the cells in the retina; it contains vitamin A (opsin means “visual protein”).

230 chapter 7 T h e V i t a m i n s

sight to the optic center in the brain. Th e vitamin then reunites with the pigment, but a little vitamin A is destroyed each time this reaction takes place, and fresh vitamin A must replenish the supply.

Night Blindness If the vitamin A supply begins to run low, a lag occurs before the eye can see again after a fl ash of bright light at night (see Figure 7-2). Th is lag in the recovery of night vision, termed night blindness, often indicates a vita- min A defi ciency.7 A bright fl ash of light can temporarily blind even normal, well- nourished eyes, but if you experience a long recovery period before vision returns, your health-care provider may want to check your vitamin A intake.

Xerophthalmia and Blindness A more profound defi ciency of vitamin A is ex- hibited when the protein keratin accumulates and clouds the eye’s outer vitamin A– dependent part, the cornea. Th e condition is known as keratinization, and if the defi ciency of vitamin A is not corrected, it can worsen to xerosis (drying) and then progress to thickening and permanent blindness, xerophthalmia. Tragically, a half million of the world’s vitamin A–deprived children become blind each year from this often preventable condition; about half die within a year after losing their sight. Vitamin A supplements given early to children developing vitamin A defi ciency can reverse the process and save lives.8 Better still, a child fed a variety of fruits and vegetables regularly is virtually assured protection.

Cell Differentiation Vitamin A is needed by all epithelial tissue (external skin and internal linings), not just by the cornea. Th e skin and all of the protective lin- ings of the lungs, intestines, vagina, urinary tract, and bladder serve as barriers to infection and other threats.

An example of vitamin A’s health-supporting work is the process of cell diff er- entiation, in which each type of cell develops to perform a specifi c function. For example, when goblet cells (cells populating the linings of internal organs) mature, they specialize in synthesizing and releasing mucus to protect delicate tissues from toxins or bacteria and other microbial invaders. In the body’s outer layers, vitamin A helps to protect against skin damage from sunlight.

If vitamin A is defi cient, the cell diff erentiation is impaired and goblet cells fail to mature, then fail to make protective mucus, and eventually die off . Goblet cells are then displaced by cells that secrete keratin, mentioned earlier with regard to the eye. Keratin is the same protein that provides toughness in hair and fi ngernails, but in the wrong place, such as skin and body linings, keratin makes the tissue surfaces dry, hard, and cracked. As dead cells accumulate on the surface, the tissue becomes vulnerable to infection (see Figure 7-3). In the cornea, keratinization leads

This is one of the earliest signs of vitamin A defi ciency.

Night Blindness figure 7-2

In dim light, you can make out the details in this room.

A flash of bright light momentarily blinds you as the pigment in the retina is bleached.

You quickly recover and can see the details again in a few seconds.

With inadequate vitamin A, you do not recover but remain blind for many seconds; this is night blindness.

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Did You Know? Using new technologies, researchers are close to developing a vitamin A–rich rice to serve as a staple food for the world’s children who lack vitamin A. See the Controversy section of Chapter 12 for details.

night blindness slow recovery of vision after exposure to fl ashes of bright light at night; an early symptom of vitamin A defi ciency.

keratin (KERR-uh-tin) the normal protein of hair and nails.

keratinization accumulation of keratin in a tissue; a sign of vitamin A defi ciency.

xerosis (zeer-OH-sis) drying of the cornea; a symptom of vitamin A defi ciency.

xerophthalmia (ZEER-ahf-THALL-me-uh) progressive hardening of the cornea of the eye in advanced vitamin A defi ciency that can lead to blindness (xero means “dry”; ophthalm means “eye”).

epithelial (ep-ith-THEE-lee-ull) tissue the layers of the body that serve as selective barriers to environmental factors. Examples are the cornea, the skin, the respiratory tract lining, and the lining of the digestive tract.

cell differentiation (dih-fer-en-she-AY- shun) the process by which immature cells are stimulated to mature and gain the ability to per- form functions characteristic of their cell type.

231V i t a m i n A

to xerophthalmia; in the lungs, the displacement of mucus-producing cells makes respiratory infections likely; in the urinary tract, the same process leads to urinary tract infections.9

Immune Function Vitamin A has gained a reputation as an “anti-infective” vi- tamin because so many of the body’s defenses against infection depend on an ad- equate supply.10 Much research supports the need for vitamin A in the regulation of the genes involved in immunity. Without suffi cient vitamin A, these genetic inter- actions produce an altered response to infection that weakens the body’s defenses.

When the defenses are weak, especially in vitamin A–defi cient children, an ill- ness such as measles can become severe. A downward spiral of malnutrition and infection can set in. Th e child’s body must devote its scanty store of vitamin A to the immune system’s fi ght against the measles virus, but this destroys the vitamin. As vitamin A dwindles further, the infection worsens. Measles takes the lives of more than 500 of the world’s children every day.11 Even if the child survives the infection, blindness is likely to occur. Th e corneas, already damaged by the chronic vitamin A shortage, degenerate rapidly as their meager supply of vitamin A is di- verted to the immune system.

Growth Vitamin A is essential for normal growth of bone (and teeth). Normal children’s bones grow longer, and the children grow taller, by remodeling each old bone into a new, bigger version. To do so, the body dismantles the old bone struc- tures and replaces them with new, larger bone parts. Growth cannot take place just by adding on to the original small bone; vitamin A must be present for critical dismantling steps. Failure to grow is one of the fi rst signs of poor vitamin A status in a child. Restoring vitamin A to such children is imperative, but correcting di- etary defi ciencies may be more eff ective than giving vitamin A supplements alone because many other nutrients from nutritious foods are also needed for children to gain weight and grow taller.

Vitamin A Defi ciency Around the World Vitamin A defi ciency presents a vast problem worldwide, placing a heavy burden on society. Between 3 and 10 million of the world’s children suff er from signs of severe vitamin A defi ciency—not only xerophthalmia and blindness but diarrhea, appetite loss, and reduced food intake that rapidly worsen their condition.12 A staggering 275 million more children suff er from milder defi ciency that impairs immunity, leaving them open to infections.

In countries where children receive vitamin A supplements, childhood rates of blindness and death have declined dramatically.13 Even in the United States, vita- min A supplements are recommended for certain groups of infants and for children with measles. Vitamin A supplementation may also off er some protection against the complications of other life-threatening infections, including malaria, lung dis- eases, and HIV. Th e World Health Organization (WHO) and UNICEF (United Nations International Children’s Emergency Fund) are working to eliminate vita- min A defi ciency; achieving this goal would improve child survival throughout the developing world.

Vitamin A Toxicity For people who take excess active vitamin A in supplements or fortifi ed foods, tox- icity is a real possibility.14 Figure 7-4 shows that toxicity compromises the tissues just as defi ciency does and is equally dangerous. Th e many symptoms of vitamin A toxicity include nausea, vomiting, diarrhea; joint pain; loss of coordination; rashes; hair loss; stunted growth; possibly irreversible damage to the liver; and enlargement of the spleen. Th e earliest symptoms of overdoses include appetite loss, dizziness, blurred vision, headache, itching of the skin, and irritability. Over the years, even relatively small vitamin A excesses may silently weaken the bones and contribute to hip fractures later in life.15

The Skin in

Vitamin A

Deficiency

figure 7-3

The hard lumps on the skin of this per- son’s arm refl ect accumulations of keratin in the epithelial cells.

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World hunger is a topic of Chapter 15.•

232 chapter 7 T h e V i t a m i n s

Ordinary vitamin supplements taken in the context of today’s heavily fortifi ed food supply can easily add up to small daily excesses of vitamin A. Even fortifi ed candy bars and bubble gum supply substantial amounts (see Table 7-3). Some ex- perts are asking whether this level of fortifi cation is doing more harm than good in the population.

Pregnant women, especially, should be wary—excessive vitamin A during preg- nancy can injure the spinal cord of the developing fetus, causing birth defects.16 Even a single massive vitamin A dose (100 times the need) can do so. Children, too, can be easily hurt by vitamin A excesses; they often mistake chewable vitamin pills and vitamin bubble gum for treats.17 Even misinformed adolescents put themselves at risk when they take high doses of vitamin A in misguided attempts to cure acne. An eff ective acne medicine, Accutane, and topical prescription acne creams are derived from vitamin A but are chemically altered—vitamin A itself has no eff ect on acne.18

Vitamin A Recommendations Th e ability of vitamin A to be stored in the tissues means that, although the DRI recommendation is stated as a daily amount, you need not consume vitamin A ev- ery day. An intake that meets the daily need when averaged over several months is suffi cient. Th e vitamin A recommendation is based on body weight. According to the DRI committee, a man needs a daily average of about 900 micrograms of ac- tive vitamin A; a woman, who typically weighs less, needs about 700 micrograms. During lactation, her need is higher. Children need less. A regular balanced diet that includes the recommended fruits and vegetables each day supplies more than adequate amounts.

As for vitamin A supplements, the DRI committee recommends against exceed- ing the Tolerable Upper Intake Level of 3,000 micrograms (for adults over age 18). Th e best way to ensure a safe intake of vitamin A is to steer clear of supplements that contain it and rely on food sources instead.

Food Sources of Vitamin A Active vitamin A is present in foods of animal origin. Th e richest sources are liver and fi sh oil but milk and milk products and other fortifi ed foods such as cereals, to

Vitamin A intake, Toxic

3,000 and over

Normal

500–3,000

Deficient

0–500

Overstimulated cell division

Normal cell division and development

Death

Skin rashesNormal body functioning

Decreased cell division and deficient cell development

Night blindness

Keratinization

Xerophthalmia

Impaired immunity

Reproductive and growth abnormalities

Exhaustion

Death

Effects on cells

Health consequences

Effects on cells

Health consequences

Effects on cells

Health consequences

Hemorrhages

Hair loss

Bone abnormalities

Birth defects

Fractures

Liver failure

μg/day

Danger lies both above and below a normal range of intake of vitamin A.

Vitamin A Deficiency and Toxicity figure 7-4

Vitamin A from highly fortifi ed foods and other rich sources can add up. The UL for vitamin A is 3,000 µg per day.

High-potency vitamin pill 3,000 µg

Calf’s liver, 1 oz cooked 2,300 µg

Regular multivitamin pill 1,500 µg

Vitamin gumball, 1 1,500 µg

Chicken liver, 1 oz cooked 1,400 µg

“Complete” liquid supple- ment drink, 1 serving 350–1,500 µg

Instant breakfast drink, 1 serving 600–700 µg

Cereal breakfast bar, 1 350–400 µg

“Energy” candy bar, 1 350 µg

Milk, 1 c 150 µg

Vitamin-fortifi ed cereal, 1 serving 150 µg

Margarine, 1 tsp 55 µg

Sources of Active

Vitamin A

table 7-3

The effects of excessive vitamin A intakes dur-• ing pregnancy are discussed in Chapter 13.

The U.S. and Canadian standard for vitamin • A intake is the DRI, listed on the inside front cover, page B.

233V i t a m i n A

which active vitamin A is added, can also be good sources. Even butter and eggs provide some vitamin A.

Can Fast Foods Provide Vitamin A? Th e defi nitive fast-food meal—a ham- burger, fries, and cola—lacks vitamin A. Many fast-food restaurants, however, now off er salads with cheese and carrots, fortifi ed milk, and other vitamin A–rich foods. Th ese selections greatly improve the nutritional quality of fast food.

Liver: A Lesson in Moderation Foods naturally rich in vitamin A pose little risk of toxicity, with the possible exception of liver. When young laboratory pigs eat daily chow made from salmon parts, including the livers, their growth halts and they fall ill from vitamin A toxicity. Inuit people and Arctic explorers know that polar bear livers are a dangerous food source because the bears eat whole fi sh (with the livers) and in turn concentrate large amounts of vitamin A in their own livers.

An ounce of ordinary beef or pork liver delivers 3 times the Dietary Reference In- take (DRI) recommendation for vitamin A, and a common portion is 4 to 6 ounces. An occasional serving of liver can provide abundant nutrients and boost nutrient status. Daily use invites vitamin A toxicity, however, especially in young children and pregnant women who eat other fortifi ed foods or take supplements.19 Snapshot 7-1 is the fi rst of a series of fi gures that show a sampling of foods that provide more than 10 percent of the Daily Value for a vitamin in a standard-size portion and therefore qualify as “good” or “rich” sources.

KE Y POINT Vitamin A is essential to vision, integrity of epithelial tissue, bone growth, reproduction, and more. Vitamin A defi ciency causes blindness, sickness, and death and is a major problem worldwide. Overdoses are possible and cause many serious symptoms. Foods are preferable to supplements for supplying vitamin A.

Vitamin A and Beta-Carotene DRI Recommended Intakes Men: 900 µg/daya

Women: 700 µg/daya

Tolerable Upper Intake Level Adults: 3,000 µg vitamin A/day

Chief Functions Vision; maintenance of cornea, epithelial cells, mucous mem- branes, skin; bone and tooth growth; regulation of gene expres- sion; reproduction; immunity

Defi ciency Night blindness, corneal drying (xerosis), and blindness (xe- rophthalmia); impaired bone growth and easily decayed teeth; keratin lumps on the skin; impaired immunity

Toxicity Vitamin A: Increased activity of bone-dismantling cells causing reduced bone density and pain; liver abnormalities; birth defects Beta-carotene: Harmless yellowing of skin

*These foods provide 10 percent or more of the vitamin A Daily Value in a serving. For a 2,000-calorie diet, the DV is 900 µg/day. aVitamin A recommendations are expressed in retinol activity equivalents (RAE). bThis food contains preformed vitamin A. cThis food contains the vitamin A precursor, beta-carotene.

snapshot 7-1

GOOD SOURCES*

FORTIFIED MILKb

1 c = 150 µg

CARROTSc (cooked) ½ c = 671 µg

SWEET POTATOc (baked) ½ c = 961 µg

SPINACHc (cooked) ½ c = 472 µg

BOK CHOYc (cooked) ½ c = 180 µg

BEEF LIVERb (cooked) 3 oz = 6,582 µg

APRICOTSc

3 apricots = 100 µg

Colorful foods are often rich in vitamins.

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234 chapter 7 T h e V i t a m i n s

Beta-Carotene In plants, vitamin A exists only in its precursor forms. Beta-carotene, the most abundant of these carotenoid precursors, has the highest vitamin A activity. While not vitamins, other carotenoids may play other roles in human health.20 Diets that lack dark green, leafy vegetables, rich sources of carotenoids, are associated with the most common form of age-related blindness, macular degeneration.†21 Th e macula, a yellow spot of pigment at the focal center of the retina (identifi ed in Fig- ure 7-1 on page 229), loses integrity, impairing the most important fi eld of vision, the central focus. Several other nutrients are under study for roles in preventing this cause of blindness, as well.22

Does Eating Carrots Really Promote Good Vision? Bright orange fruits and vegetables derive their color from beta-carotene and are so colorful that they deco- rate the plate. Carrots, sweet potatoes, pumpkins, mango, cantaloupe, and apricots are all rich sources of beta-carotene—and therefore contribute vitamin A to the eyes and to the rest of the body—so, yes, eating carrots does promote good vision. Another colorful group, dark green vegetables, such as spinach, other greens, and broccoli, owe their deep dark green color to the blending of orange beta-carotene with the green leaf pigment chlorophyll. As mentioned, they provide the other ca- rot enoids needed for eye health, as well.

Beta-Carotene, an Antioxidant Beta-carotene is one of many dietary antioxi- dants present in foods—others include vitamin E, vitamin C, the mineral selenium, and many phytochemicals. Dietary antioxidants are just one class of a complex array of constituents in whole foods that seem to benefi t health synergistically.23 Foods supply all of these factors and more in ideal amounts and combinations that supple- ments cannot duplicate.

Measuring Beta-Carotene Th e conversion of beta-carotene to retinol in the body entails losses, however, so vitamin A activity for precursors is measured in retinol activity equivalents (RAE). It takes about 12 micrograms of beta-carotene from food to supply the equivalent of 1 microgram of retinol to the body. Some food tables and supplement labels express beta-carotene and vitamin A contents using IU (international units). When comparing vitamin A in foods, be careful to notice whether a food table or supplement label uses micrograms or IU. To convert one to the other, use the factor in the margin.

Toxicity Beta-carotene from food is not converted to retinol effi ciently enough to cause vitamin A toxicity. A steady diet of abundant pumpkin, carrots, carrot juice, and the like, however, has been known to turn light-skinned people bright yellow because beta-carotene builds up in the fat just beneath the skin and imparts a harm-

Take Your Vitamins?

Two students talk about vitamins and minerals in campus foods and in supplements.

To hear their stories, log on to www.cengage.com/sso.

my turn

Claudio Steve

†The carotenoids associated with protection from macular degeneration are lutein (LOO-tee-in) and its close chemical relative zeaxanthin (zee-ZAN-thin).

Funct ional Group Key antioxidant vitamins:

Beta-carotene, vitamin E, and vitamin C.•

A key antioxidant mineral:

Selenium.•

1 IU = 0.3 µg retinol•

The Aids to Calculations appendix (Appen-• dix C) provides factors for converting many kinds of units used in nutrition.

carotenoid (CARE-oh-ten-oyd) a member of a group of pigments in foods that range in color from light yellow to reddish orange and are chemical relatives of beta-carotene. Many have a degree of vitamin A activity in the body. Also defi ned in Controversy 2.

macular degeneration a common, progressive loss of function of the part of the retina that is most crucial to focused vision (the macula is shown on page 229). This degenera- tion often leads to blindness.

dietary antioxidants compounds typically found in plant foods that signifi cantly decrease the adverse effects of oxidation on living tissues. The major antioxidant vitamins are vitamin E, vitamin C, and beta-carotene.

retinol activity equivalents (RAE) a new measure of the vitamin A activity of beta- carotene and other vitamin A precursors that refl ects the amount of retinol that the body will derive from a food containing vitamin A precur- sor compounds.

IU (international units) a measure of fat-soluble vitamin activity sometimes used in food composition tables and on supplement labels.

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235V i t a m i n D

less yellow cast; see Figure 7-5. Concentrated beta-carotene supplements, however, may have adverse eff ects of their own, as a later section points out.

Food Sources of Beta-Carotene Plants contain no active vitamin A, but many vegetables and fruits provide the vitamin A precursor, beta-carotene. Snapshot 7-1 shows good sources of beta-carotene. Other colorful vegetables, such as red beets, red cabbage, and yellow corn, can fool you into thinking they contain beta-carotene, but these foods derive their colors from other pigments and are poor sources of beta-carotene. As for “white” plant foods such as grains and potatoes, they have none. Concerning the term yam: a white-fl eshed Mexican root vegetable called “yam” is devoid of beta-carotene, but the orange-fl eshed sweet potato called “yam” in the United States is one of the richest beta-carotene sources known. In choosing fruits and vegetables, follow the guidance of the USDA Food Guide of Chapter 2.

KE Y POINT The vitamin A precursor in plants, beta-carotene, is an eff ective antioxidant in the body. Brightly colored plant foods are richest in beta-carotene, and diets containing these foods are associated with good health.

Vitamin D Vitamin D is unique among nutrients in that the body can synthesize all it needs with the help of sunlight. Th erefore, in a sense, vitamin D is not an essential nutri- ent. Given enough sun each day, most people need consume no vitamin D at all from foods. Whether made from sunlight or obtained from food, vitamin D under- goes chemical transformations in the liver and kidneys to activate it.24

As simple as it may sound to obtain vitamin D, recent surveys indicate that many people, particularly African Americans and Mexican Americans, border on insuf- fi ciency of this critical nutrient.25 By one estimate, two-thirds of U.S. residents over 1 year of age take in too little vitamin D.26

Roles of Vitamin D Vitamin D is the best-known member of a large cast of nutrients and hormones that interact to regulate blood calcium and phosphorus levels, and thereby maintain bone integrity.27 Calcium is indispensable to the proper functioning of cells in all body tissues, including muscles, nerves, and glands, which draw calcium from the blood as they need it. To replenish blood calcium, vitamin D acts at three body sites to raise the calcium level.28 First, the skeleton serves as a vast warehouse of stored calcium that can be tapped when blood calcium begins to fall. Only two other or- gans can increase blood calcium: the digestive tract, where food brings calcium in, and the kidneys, which recycle calcium that would otherwise be lost in urine.

Vitamin D functions as a hormone, that is, a compound manufactured by one organ of the body that acts on other organs or tissues.29 Beyond bone regulation, vitamin D acts at the genetic level, aff ecting how cells grow, multiply, and special- ize. Vitamin D infl uences over 30 body tissues, from hair follicles, to reproductive system cells, to cells of the immune system.30

Research is hinting (sometimes strongly) that to incur a defi cit of vitamin D is to invite problems of many kinds, including high blood pressure, cardiovascular dis- eases, some common cancers, infections such as tuberculosis or fl u, high blood pres- sure, infl ammatory conditions, and autoimmune diseases such as type 1 diabetes, rheumatoid arthritis, the skin disease psoriasis (so-RYE-ah-sis), multiple sclerosis, and even a higher risk of dying.31* Th e well-established vitamin D roles, however, concern calcium balance and the bones during growth and throughout life.

CONCEPT LINK 7-3 Potential roles for carotenoids and other phy- tochemicals in human health were topics of Controversy 2 on page 61.

Excess

Beta-Carotene

Symptom:

Discoloration

of the Skin

figure 7-5

The hand on the right shows skin dis- coloration from excess beta-carotene. Another person’s normal hand (left) is shown for comparison.

00 2

M as

sa ch

us et

ts M

ed ic

al S

oc ie

The sunshine vitamin: vitamin D.

an dy

B ox

P ho

to /F

ot ol

Funct ional Group Key bone vitamins:

Vitamin A, vitamin D, vitamin K, vitamin C, •

other vitamins

Key bone minerals:

Calcium, phosphorus, magnesium, fluo-•

ride, other minerals

Key bone protein:

Collagen•

*Read more about these preliminary fi ndings in the articles cited in note 31, Appendix F.

236 chapter 7 T h e V i t a m i n s

Too Little Vitamin D—A Danger to Bones Th e most obvious sign of vitamin D defi ciency occurs in early life—the abnormality of the bones in the disease rickets is shown in Figure 7-6. Children with rickets develop bowed legs because they are unable to mineralize newly forming bone ma- terial, a rubbery protein matrix. As gravity pulls their body weight against these weak bones, the legs bow. Many such children also have a protruding belly because of lax abdominal muscles.

As early as the 1700s, rickets was known to be curable with cod-liver oil, which is rich in vitamin D. More than a hundred years later, a Polish physician linked sun- light exposure to prevention and cure of rickets. Today, in some areas of the world, such as Mongolia, Tibet, and the Netherlands, more than half of the children suff er the bowed legs, knock-knees, beaded ribs, and protruding (pigeon) chests of rick- ets.32 In the United States, over 58 million children are reported to be vitamin D– defi cient or insuffi cient, but rickets itself is uncommon.33 When it occurs, black children and adolescents—especially females and overweight teens—are most likely to be aff ected.34 To prevent rickets, the American Academy of Pediatrics recom- mends a minimum daily intake of 400 IU vitamin D for all infants, children, and adolescents.35 Adolescents, who often abandon vitamin D–fortifi ed milk in favor of soft drinks and punches, may also prefer indoor pastimes such as video games to outdoor activities during daylight hours. Such teens often lack vitamin D and so fail to develop the bone density needed to prevent bone loss in later life.36

In adults, the poor mineralization of bone results in the painful bone disease os- teomalacia.37 Th e bones become increasingly soft, fl exible, brittle, and deformed. Older people can suff er painful joints and muscles if their vitamin D levels are low, although the condition is easily missed during examinations and may be mistaken for arthritis or other painful conditions. Inadequate vitamin D also sets the stage for a loss of calcium from the bones, which can result in fractures from osteoporo- sis. Th e simple act of taking a combined vitamin D and calcium supplement could easily save the life of an elderly person who might otherwise suff er dangerous bone fractures and falls.38 Vitamin D alone seems ineff ective in this regard, however.39

Too Much Vitamin D—A Danger to Soft Tissues Vitamin D is the most potentially toxic vitamin. In excess, vitamin D raises the concentration of blood calcium, which can then collect in the soft tissues, forming stones.40 Th e kidneys, which must concentrate calcium in order to excrete it, are particularly vulnerable to forming stones.41 Calcifi cation may also harden the blood vessels, a condition that may be fatal when it aff ects major arteries of the brain, heart, and lungs. Early symptoms of toxicity include pain, chills, appetite loss, nausea, vomiting, and increased urination and thirst. Among people taking vitamin D sup- plements, infants and older people are most often reported to develop toxicities.42

Vitamin D from Sunlight Most of the world’s people rely on exposure to sunlight for vitamin D. When ul- traviolet (UV) B light rays from the sun shine on a cholesterol compound in hu- man skin, the compound is transformed into a vitamin D precursor and is absorbed directly into the blood. Slowly, over the next day and a half, the liver and kidneys fi nish converting the precursor to the active form of vitamin D. Diseases that aff ect either the liver or the kidneys can impair the conversion of the inactive precursor to the active vitamin and therefore produce symptoms of vitamin D defi ciency. People who wear concealing clothing for religious reasons, particularly girls and women, may also lack vitamin D. Th e factors listed in Table 7-4 can all interfere with vita- min D synthesis, as well.

Is Sunlight Exposure a Safe Source of Vitamin D? Sunlight presents no risk of vitamin D toxicity; the sun itself begins breaking down excess vitamin D made in the skin. Sunbathers run other risks, however, such as

This child has the bowed legs of the vitamin D–defi ciency disease rickets.

Rickets figure 7-6

This child displays the beaded ribs common in rickets.

B io

ph ot

o A

ss oc

ia te

s/ S

ci en

ce S

ou rc

e/ P

ho to

R es

ea rc

he rs

, I nc

. P

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C ou

rte sy

o f D

r. N

or m

an C

ar va

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at C

hi ld

re n’

s H

ea lth

ca re

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tla nt

Chapter 8 and Controversy 8 present more • about bone minerals and their regulation and about osteoporosis, the bone-weaken- ing disease of aging.

Did You Know? Too much vitamin D causes high blood cal- cium, but a high calcium intake does not (see the next chapter).

237V i t a m i n D

premature skin wrinkling and skin cancers. UV radiation from the sun, including UVB that promotes vitamin D synthesis, is carcinogenic, contributing to about a million skin cancers per year in the United States alone.43 Successful public health campaigns to promote sunscreen use (sun protection factor, or SPF, of 15 and above) and to avoid sun exposure, along with an increasingly indoor, sedentary lifestyle may be responsible for a recent downturn in serum vitamin D among people in the United States (Figure 7-7).44

Th e pigments of dark skin protect against UV radiation, but dark-skinned people require up to 3 hours of direct sun (depending on the climate) for several days’ worth of vitamin D. Light-skinned people need much less time (an estimated 5 minutes without sunscreen or 10 to 30 minutes with sunscreen).45 Tanning booths may or may not promote vitamin D synthesis but they, like the sun, deliver UV radiation that promotes skin cancer. Given that any amount of UV exposure increases the risk of skin cancer, some experts conclude that dietary vitamin D may be the safer source.46

Intake Recommendations Advancing age increases the risk of vitamin D defi ciency, so intake recommenda- tions increase with age: 5 micrograms per day for adults 19 to 50 years, 10 micro- grams for those 51 to 70 years, and 15 micrograms for those over 70. Th e DRI committee has set a Tolerable Upper Intake Level for vitamin D at 50 micrograms per day (2,000 IU on supplement labels). Some experts are calling for signifi cant increases in both the target vitamin D intakes (up to 125 micrograms per day) and in the Tolerable Upper Intakes.47

Food Sources Snapshot 7-2 shows the few signifi cant naturally occurring food sources of vitamin D. Butter, cream, and fortifi ed margarine also contribute small amounts. In the United States and Canada, milk, whether fl uid, dried, or evaporated, is fortifi ed with vitamin D. Yogurt and cheese products are often not fortifi ed, so read the labels.

The more of these factors present in a person’s life, the more critical it becomes to obtain vitamin D from food or supplements.

Factor Effect on Vitamin D Synthesis

Advanced age With age, the skin loses some of its capacity to synthesize vitamin D.

Air pollution Particles in the air screen out the sun’s rays.

City living Tall buildings block sunlight.

Clothing Most clothing blocks sunlight.

Geography Sunlight exposure is limited:

September through March at latitudes above 50 degrees (most of • Canada) November through February at latitudes between 35 and 50 degrees • (most U.S. locations)

In locations south of 35 degrees (much of the southern United States), direct sun exposure is suffi cient for vitamin D synthesis year-round.

Homebound Living indoors prevents sun exposure.

Season Warmer seasons of the year bring more direct sun rays.

Skin pigment Darker-skinned people synthesize less vitamin D per minute than lighter-skinned people.

Sunscreen Use reduces or prevents skin exposure to sun’s rays.

Time of day Midday hours bring maximum direct sun exposure.

Factors Affecting Vitamin D Synthesis table 7-4

rickets the vitamin D–defi ciency disease in children; characterized by abnormal growth of bone and manifested in bowed legs or knock- knees, outward-bowed chest, and knobs on the ribs.

osteomalacia (OS-tee-o-mal-AY-shuh) the adult expression of vitamin D–defi ciency disease, characterized by an overabundance of unmineralized bone protein (osteo means “bone”; mal means “bad”). Symptoms include bending of the spine and bowing of the legs.

osteoporosis a weakening of bone mineral structures that occurs commonly with advancing age. Also defi ned in Chapter 8.

1988–1994a

2001–2004a

White Black Mexican American

Other

A v e

ra g

e b

lo o

d v

it a

m in

D ,

n g

/m lb

Downturn in

Vitamin D Blood

Levels Among

Population Groups,

1988–2004

figure 7-7

aNHANES data. bNanograms per milliliter of blood serum. Source: Adapted from A. A. Ginde and coauthors, Demographic differences and trends of vitamin D insuffi ciency in the US population, 1988–2004, Archives of Internal Medicine 169 (2009): 626–632.

238 chapter 7 T h e V i t a m i n s

Young adults who drink 3 cups of milk a day receive half of their daily require- ment; the other half comes from exposure to sunlight and other food sources. Without adequate sunshine, fortifi cation, or supplementation, strict vegetarians cannot meet vitamin D needs. Vegan sources include vitamin D–fortifi ed soy milk and cereals. Importantly, feeding infants and young children unfortifi ed “health beverages” instead of milk or infant formula can create severe nutrient defi ciencies, including rickets.

KE Y POINT Vitamin D raises mineral levels in the blood, notably calcium and phosphorus, permitting bone formation and maintenance. A defi ciency can cause rickets in childhood or osteomalacia in later life. Vitamin D is the most toxic of all the vitamins, and excesses cause health problems. People exposed to the sun make vitamin D from a cholesterol-like compound in their skin, but skin cancer arises from sun exposure; fortifi ed milk is an important source.

Vitamin E Almost a century ago, researchers discovered a compound in vegetable oils essen- tial for reproduction in rats.48 Th is compound was named tocopherol from tokos, a Greek word meaning “off spring.” A few years later, the compound was named vitamin E.

Four tocopherol compounds have been identifi ed, and each is designated by one of the fi rst four letters of the Greek alphabet: alpha, beta, gamma, and delta. Of these, alpha-tocopherol is the gold standard for vitamin E activity. For this reason, DRI intake recommendations are expressed as alpha-tocopherol. Although not readily

tocopherol (tuh-KOFF-er-all) a kind of alcohol. The active form of vitamin E is alpha- tocopherol.

Vitamin D DRI Recommended Intakes Adults: 5 µg/day (19–50 yr) 10 µg/day (51–70 yr) 15 µg/day (�70 yr)

Tolerable Upper Intake Level Adults: 50 µg/day

Chief Functions Mineralization of bones and teeth (raises blood calcium and phos- phorus by increasing absorption from digestive tract, withdrawing calcium from bones, stimulating retention by kidneys)

Defi ciency Abnormal bone growth resulting in rickets in children, osteomala- cia in adults; malformed teeth; muscle spasms

Toxicity Elevated blood calcium; calcifi cation of soft tissues (blood ves- sels, kidneys, heart, lungs, tissues of joints), excessive thirst, headache, nausea, weakness

*These foods provide 10 percent or more of the vitamin D Daily Value in a serving. For a 2,000-calorie diet, the DV is 10 µg/day. aAvoid prolonged exposure to sun.

snapshot 7-2

GOOD SOURCES*

FORTIFIED MILK 1 c = 3.2 µg

TUNA (light, canned) 3 oz = 5.7 µg

SUNLIGHT Promotes vitamin D synthesis in the skin.a

SALMON 3 oz = 15.3 µg

ENRICHED CEREAL (ready-to-eat) ¾ c = 1 µg

SARDINES 3 oz = 5.8 µg

COD LIVER OIL 1 tsp = 11 µg

239V i t a m i n E

converted to alpha-tocopherol, the other tocopherols are of interest to researchers for potentially benefi cial roles in the body.‡49

Roles of Vitamin E Vitamin E is an antioxidant and thus acts as a bodyguard against oxidative dam- age.50 Such damage occurs when highly unstable molecules known as free radicals, formed during normal cell metabolism, run amok and disrupt the structures of lip- ids in cell membranes, of lipoproteins (LDL), of DNA in genetic material, and of proteins that perform cellular work. Free radicals, left unchecked, cause infl amma- tion that may contribute to some cancers, heart disease, or other diseases.51 Vita- min E, by being oxidized itself, quenches free radicals and reduces infl ammation.52 Figure 7-8 provides an overview of the activity of vitamin E and its potential role in disease prevention.

Th e protection of vitamin E is especially crucial in the lungs, where high oxygen concentrations would otherwise disrupt vulnerable membranes. Red blood cells also need protection as they transport oxygen from the lungs to other tissues, and vitamin E defends their cell membranes, too. White blood cells that fi ght diseases also depend on vitamin E, and sensitive brain tissues rely on its antioxidant nature, as well.53

Vitamin E Defi ciency A defi ciency of vitamin E produces a wide variety of symptoms in laboratory ani- mals, but these are almost never seen in healthy human beings. Defi ciency of vi- tamin E, which dissolves in fat, may occur in people with diseases that cause fat malabsorption or in infants born prematurely. Disease or injury of the liver (which makes bile, necessary for digestion of fat), the gallbladder (which delivers bile into the intestine), or the pancreas (which makes fat-digesting enzymes) make vitamin E defi ciency likely. In people without diseases, low blood levels of vitamin E are most likely when diets extremely low in fat are consumed for years.

A classic vitamin E defi ciency occurs in premature babies born before the trans- fer of the vitamin from the mother to the infant, which takes place late in preg- nancy. Without suffi cient vitamin E, the infant’s red blood cells rupture (erythro- cyte hemolysis), and the infant becomes anemic. Th e few symptoms of vitamin E

‡Other tocopherols may also function as antioxidants.

A chemically reactive oxygen free radical attacks fatty

acid, DNA, protein, or cholesterol molecules, which form other free radicals in turn.

This initiates a rapid, destructive chain reaction.

Antioxidants, such as vitamin E, stop the chain reaction by changing the nature of the free radical.

The result is: • cell membrane lipid damage. • cellular protein damage. • DNA damage. • oxidation of LDL cholesterol. • inflammation. These changes may initiate steps leading to diseases such as heart disease, cancer, macular degeneration, and others.

Susceptible

molecules

Oxygen free

radical

Antioxidant

Free radicals cause chain reactions that damage cellular structures.

Antioxidants quench free radicals and protect cellular structures.

4 4

Free-radical formation occurs during metabolic processes, and it accelerates when diseases or other stresses strike.

Free-Radical Damage and Antioxidant Protection figure 7-8

free radicals atoms or molecules with one or more unpaired electrons that make the atom or molecule unstable and highly reactive

erythrocyte (eh-REETH-ro-sight) hemolysis (HEE-moh-LIE-sis, hee-MOLL- ih-sis) rupture of the red blood cells, caused by vitamin E defi ciency (erythro means “red”; cyte means “cell”; hemo means “blood”; lysis means “breaking”). The anemia produced by the condition is hemolytic (HEE-moh-LIT-ick) anemia.

240 chapter 7 T h e V i t a m i n s

defi ciency observed in adults include loss of muscle coordination and refl exes and impaired vision and speech. Vitamin E corrects all of these symptoms.

People with low blood vitamin E concentrations but without overt symptoms die more often from chronic diseases and other causes than do people with higher blood levels.54 Th e Controversy section provides details, but you should know right away that experts do not recommend taking vitamin E to ward off chronic diseases.55

Toxicity of Vitamin E Vitamin E in foods is safe to consume. Reports of vitamin E toxicity symptoms are rare across a broad range of intakes.56 However, vitamin E in supplements augments the eff ects of anticoagulant medication used to oppose unwanted blood clotting, so people taking such drugs risk uncontrollable bleeding if they also take vitamin E. Vi- tamin E prolongs blood clotting times by interfering with the activity of vitamin K by a mechanism yet to be defi ned.57An increase in brain hemorrhages, a form of stroke, has also been noted among smokers taking just 50 milligrams of vitamin E per day.

Recently, the pooled results from 67 experiments involving almost a quarter-million people suggested that taking vitamin E supplements may slightly increase mortality in both healthy and sick people.58 Other studies fi nd no eff ect or a slight decrease in mortality among certain groups.59 To err on the safe side, people who use vitamin E supplements should probably keep their dosages low, and they should not exceed the Tolerable Upper Intake Level of 1,000 milligrams alpha-tocopherol per day.

Vitamin E Recommendations and U.S. Intakes Th e DRI recommended intake (inside front cover, page B) for vitamin E is 15 milli- grams a day for adults. Th is amount seems suffi cient to maintain healthy, normal blood values for vitamin E for most people. Smokers may have higher needs. On average, U.S. intakes of vitamin E fall substantially below the recommendation (see Figure 7-9).60 Th e need for vitamin E rises as people consume more polyunsaturated oil because the oil requires antioxidant protection by the vitamin. Luckily, most raw oils also contain vitamin E, so people who eat raw oils also receive the vitamin.

Food Sources of Vitamin E Vitamin E is widespread in foods (see Snapshot 7-3). Much of the vitamin E in the diet comes from vegetable oils and products made from them, such as margarine

Did You Know? Cooking methods using high heat, such as frying, destroy vitamin E. Uncooked oils supply vitamin E to the diet.

Vitamin E DRI Recommended Intake Adults: 15 mg/day

Tolerable Upper Intake Level Adults: 1,000 mg/day

Chief Functions Antioxidant (protects cell membranes, regulates oxidation reactions, protects polyunsaturated fatty acids)

Defi ciency Red blood cell breakage, nerve damage

Toxicity Augments the effects of anticlotting medication

*These foods provide 10 percent or more of the vitamin E Daily Value in a serving. For a 2,000-calorie diet, the DV is 30 IU or 20 mg/day. aCooking destroys vitamin E.

snapshot 7-3

GOOD SOURCES*

SAFFLOWER OILa (raw) 1 tbs = 4.6 mg

WHEAT GERM 1 oz = 4.5 mg

CANOLA OILa (raw) 1 tbs = 2.3 mg

MAYONNAISE (saffl ower oil)

1 tbs = 3.0 mg

SUNFLOWER SEEDSa (raw kernels)

2 tbs = 5.8 mg

M ill

ig ra

m s v

it a m

in E

DRI recommendation

Men

Women

U.S. intakes

Vitamin E

Recommendations

and U.S. Intakes

Compared

figure 7-9

Source: USDA Agricultural Research Service, Table 1, Nutrient Intakes from Food: Mean Amounts Consumed per Individual, One Day, 2005–2006, What We Eat in America: NHANES, available at www.ars.usda.gov.

http://www.ars.usda.gov

241V i t a m i n K

and salad dressings. Wheat germ oil is especially rich in vitamin E. Animal fats have almost none.

Vitamin E is readily destroyed by heat and oxidation, so fresh, raw oils or lightly processed foods are the best sources. As people choose more highly processed foods, fried fast foods, or “convenience” foods, they lose vitamin E because little vitamin E survives the heating and other processes used to make these foods.

KE Y POINT Vitamin E acts as an antioxidant in cell membranes and is especially important for the integrity of cells that are constantly exposed to high oxygen concentrations. Vitamin E defi ciency is rare in human beings, but it does occur in newborn premature infants. The vitamin is widely distributed in plant foods; it is destroyed by high heat. Toxicity is rare but supplements may carry risks.

Vitamin K Have you ever thought about how remarkable it is that blood can clot? Th e liquid turns solid in a life-saving series of reactions—if blood did not clot, wounds would just keep bleeding, draining the blood from the body.

Roles of Vitamin K Th e main function of vitamin K is to help activate proteins that help clot the blood. Hospitals measure the clotting time of a person’s blood before surgery and, if needed, administer vitamin K to reduce bleeding during the operation. Vitamin K is of value only if a vitamin K defi ciency exists. Vitamin K does not improve clotting in those with other bleeding disorders, such as the inherited disease hemophilia.

Some people with heart problems need to prevent the formation of clots within their circulatory system—this is popularly referred to as “thinning” the blood. One of the best-known medicines for this purpose is warfarin, which interferes with vitamin K’s clot-promoting action. Vitamin K therapy may be needed for people on warfarin if uncontrolled bleeding should occur. People taking warfarin who self- prescribe vitamin K supplements risk interfering with the action of the drug.61

Vitamin K is also necessary for the synthesis of key bone proteins. Without vi- tamin K, the bones produce an abnormal protein that cannot bind the minerals that normally form bones, causing low bone mineral density.62 People who con- sume abundant vitamin K in the form of green leafy vegetables suff er fewer hip fractures than those with lower intakes. Vitamin K supplements seem ineff ective against bone loss, however.63 Vitamin K is also under investigation for roles in heart disease prevention.64

Defi ciency of Vitamin K Few U.S. adults are likely to experience vitamin K defi ciency, even if they seldom eat vitamin K–rich foods. Th is is because, like vitamin D, vitamin K can be ob- tained from a nonfood source—in this case, the intestinal bacteria. Billions of bac- teria normally reside in the intestines, and some of them synthesize vitamin K.

Newborn infants present a unique case with regard to vitamin K because they are born with a sterile intestinal tract, and the vitamin K–producing bacteria take weeks to establish themselves. To prevent hemorrhage, the newborn is given a single dose of vitamin K at birth. People who have taken antibiotics that have killed the bacteria in their intestinal tracts also may develop vitamin K defi ciency. In certain other medical conditions, bile production falters, making lipids, including all of the fat-soluble vitamins, unabsorbable. Supplements of the vitamin are needed in these cases because a vitamin K defi ciency can be fatal.

Raw vegetable oils contain substantial vitamin E but high temperatures destroy it.

ar y

H ou

ld er

/C or

bi s

Did You Know? K stands for the Danish word koagulation (clotting).

CONCEPT LINK 7-4 The roles of protein in blood clotting were described in Chapter 6 on page 202.

Warfarin is pronounced WAR-fuh-rin.•

Soon after birth, newborn infants receive a dose of vitamin K.

S im

on F

ra se

r/P ho

to R

es ea

rc he

rs , I

nc .

24 2 chapter 7 T h e V i t a m i n s

Vitamin K Toxicity Reports of vitamin K toxicity among healthy adults are rare, and the DRI commit- tee has not set a Tolerable Upper Intake Level. For infants and pregnant women, however, vitamin K toxicity can result when supplements of a synthetic version of vitamin K are given too enthusiastically.§ Toxicity induces breakage of the red blood cells and release of their pigment, which colors the skin yellow. A toxic dose of synthetic vitamin K causes the liver to release the blood cell pigment (bilirubin) into the blood (instead of excreting it into the bile) and leads to jaundice.

Requirements and Sources of Vitamin K Th e vitamin K requirement for men is 120 micrograms a day; women require 90 micrograms. As Snapshot 7-4 shows, vitamin K’s richest plant food sources include dark green, leafy vegetables such as cooked spinach and other greens, which pro- vide an average of 300 micrograms per half-cup serving. Lettuces, broccoli, brussels sprouts, and other members of the cabbage family are also good sources.

Only one rich animal food source of vitamin K exists: liver. Canola and soybean oils (unhydrogenated liquid oils) provide smaller but still signifi cant amounts, while fortifi ed cereals can be rich sources of added vitamin K. One egg and a cup of milk contain about equal amounts, or 25 micrograms each. Tables of food composition do not include the vitamin K contents of foods because they are not well enough known.

KE Y POINT Vitamin K is necessary for blood to clot; defi ciency causes uncontrolled bleeding. The bacterial inhabitants of the digestive tract produce vitamin K. Toxicity causes jaundice.

LO 7.5, 7.6

The Water-Soluble Vitamins Vitamin C and the B vitamins dissolve in water, which has implications for their handling in food and by the body. In food, water-soluble vitamins easily dissolve and drain away with cooking water, and some are destroyed on exposure to light,

Vitamin K DRI Recommended Intakes Men: 120 µg/day Women: 90 µg/day

Chief Functions Synthesis of blood-clotting proteins and bone proteins

Defi ciency Hemorrhage; abnormal bone formation

Toxicity Opposes the effects of anti-clotting medication

*These foods provide 10 percent or more of the vitamin K Daily Value in a serving. For a 2,000-calorie diet, the DV is 80 µg/day. Data from USDA.

snapshot 7-4

GOOD SOURCES*

CABBAGE (steamed) ½ c = 41 µg

SPINACH (steamed) ½ c = 444 µg

SOYBEANS (dry roasted) ½ C = 32 µg

CANOLA OIL 1 tbs = 17 µg

CAULIFLOWER (steamed)

½ c = 11 µg

SALAD GREENS 1 c = 63 µg

§The version of vitamin K responsible for this effect is menadione.

jaundice (JAWN-dis) yellowing of the skin due to spillover of the bile pigment bilirubin (bill-ee-ROO-bin) from the liver into the general circulation.

243V i t a m i n C

heat, or oxygen during processing.65 Later sections examine vitamin vulnerability and provide tips for retaining vitamins in foods.

In the body, water-soluble vitamins are easily absorbed and just as easily excreted in the urine. A few of the water-soluble vitamins can remain in the lean tissues for a month or more, but these tissues actively exchange materials with the body fl uids all the time. At any time, the vitamins may be picked up by the extracellular fl uids, washed away by the blood, and excreted in the urine.

Advice for meeting the need for these nutrients is straightforward: choose foods rich in water-soluble vitamins to achieve an average intake that meets the recom- mendation over a few days’ time. Th e Snapshots in this section can help to guide your choices. Foods never deliver toxic doses of the water-soluble vitamins, but the large doses concentrated in some vitamin supplements can reach toxic levels. Normally, though, the most likely hazard to the supplement taker is to the wallet: “If you take supplements of the water-soluble vitamins, you may have the most expensive urine in town.” Th e Th ink Fitness feature asks whether athletes need vitamin supplements.

KE Y POINT Water-soluble vitamins are easily absorbed and excreted from the body and must be consumed frequently in the diet. They are easily lost or destroyed during food preparation and processing.

Vitamin C More than 200 years ago, any man who joined the crew of a seagoing ship knew he had only half a chance of returning alive—not because he might be slain by pirates or die in a storm, but because he might contract scurvy, a disease that often killed as many as two-thirds of a ship’s crew on a long voyage. Ships that sailed on short voy- ages, especially around the Mediterranean Sea, were safe from this disease. Th e spe- cial hazard of long ocean voyages was that the ship’s cook used up the fresh fruits and vegetables early and relied on cereals and live animals for the duration of the voyage.

Th e fi rst nutrition experiment to be conducted on human beings was devised 250 years ago to fi nd a cure for scurvy. A physician divided some British sailors with scurvy into groups.** Each group received a diff erent test substance: vinegar, sulfuric acid, seawater, oranges, or lemons. Th ose receiving the citrus fruits were

The Food Feature section of Chapter 12 pro-• vides details about the effects of processing on vitamins and other nutrients in foods.

Recall characteristics of water-soluble vita-• mins from Table 7-2:

Dissolve in water.•

Are easily absorbed and excreted.•

Are not stored extensively in tissues.•

Seldom reach toxic levels.•

think fitness Vitamins for Athletes

Do athletes who strive for top per- formance need more vitamins than foods can supply? Competitive ath- letes who choose their diets with reasonable care almost never need nutrient supplements. The reason is elegantly simple. The need for

energy to fuel exercise requires that people eat extra calories of food, and if that extra food is of the kind shown in this chapter’s Snap- shots—fruits, vegetables, milk, eggs, whole or enriched grains, lean meats, and some oils—then

the extra vitamins needed to sup- port the activity follow naturally into the body. Chapter 10 comes back to the roles of vitamins in physical activity.

START NOW

Ready to make a change? Consult the online behavior-change planner to plan how you might change your food selections to better meet the needs of your active body at www.cengage.com/sso.

scurvy the vitamin C–defi ciency disease.

Long voyages without fresh fruits and vegetables spelled death by scurvy for the crew.

**The physician was James Lind.

http://www.cengage.com/sso

24 4 chapter 7 T h e V i t a m i n s

cured within a short time. Sadly, it took 50 years for the British navy to make use of the information and require all its vessels to provide lime juice to every sailor daily. British sailors were mocked with the term limey because of this requirement. Th e name later given to the vitamin that the fruit provided, ascorbic acid, literally means “no-scurvy acid.” It is more commonly known today as vitamin C.

The Roles of Vitamin C Vitamin C performs a variety of functions in the body. It is best known for two of them: its work in maintaining the connective tissues and as an antioxidant.

A Cofactor for Enzymes Vitamin C assists several enzymes in performing their jobs. In particular, the enzymes involved in the formation and maintenance of

the protein collagen depend on vitamin C for their activity. Collagen forms the base for all of the connective tissues: bones, teeth, skin, and tendons. Collagen forms the scar tissue that heals wounds, the reinforcing structure

that mends fractures, and the supporting material of capillaries that prevents bruises. Vitamin C also acts as a cofactor in other synthetic reactions, such as in

the production of carnitine, an important compound for transporting fatty acids within the cells and in the creation of certain hormones.66

An Antioxidant In addition to assisting enzymes, vitamin C also acts in a more general way as an antioxidant. Vitamin C protects substances found in foods and in the body from oxidation by being oxidized itself. For example, cells of the immune system maintain high levels of vitamin C to protect themselves from free radicals generated during assaults on bacteria and other invaders. Some oxidized vitamin C is degraded irretrievably and must be replaced by the diet, but much more is not lost but recycled back to the active form for reuse. Th is recycling plays a key role in maintaining suffi cient vitamin C in the cells to allow it to perform its critical work.

In the intestines, vitamin C protects iron from oxidation and so promotes its absorption. In the blood, vitamin C protects sensitive blood constituents from oxi- dation, reduces infl ammation, and helps to protect vitamin E and recycle it to its active form. Th e antioxidant roles of vitamin C are the focus of extensive study, es- pecially in relation to disease prevention.67 Unfortunately, research has yielded only disappointing results: vitamin C supplements seem useless against heart disease, cancer, and other diseases, unless they are prescribed to treat a defi ciency.68

In test tubes, a high concentration of vitamin C has the opposite eff ect from an- tioxidants; that is, it acts as a prooxidant by activating oxidizing elements, such as iron and copper. A few studies suggest that this may happen in people, too, under some conditions. Th e question of what, if anything, such fi ndings may mean for hu- man health remains unanswered.

Defi ciency Symptoms Most of the symptoms of scurvy can be attributed to the breakdown of collagen in the absence of vitamin C: loss of appetite, growth cessation, tenderness to touch, weakness, bleeding gums (shown in Figure 7-10), loose teeth, swollen ankles and wrists, and tiny red spots in the skin where blood has leaked out of capillaries (also shown in the fi gure).69 One symptom, anemia, refl ects an important role worth repeating—vitamin C helps the body to absorb and use iron. Table 7-7 at the end of the chapter summarizes defi ciency symptoms and other information about vitamin C.

In the United States, vitamin C status has been improving but people who smoke or have low incomes continue to be at risk for defi ciency.70 Th e disease scurvy is seldom seen today except in a few elderly people, people addicted to alcohol or other drugs, and a few infants who are fed only cow’s milk.71 Breast milk and infant formula sup- ply enough vitamin C, but infants who are fed cow’s milk and receive no vitamin C in formula, fruit juice, or other outside sources are at risk. Low intakes of fruits and vegetables and a poor appetite overall lead to low vitamin C intakes and are not un- common among people aged 65 and older. Vitamin C also supports immune system

Funct ional Group Key antioxidant vitamins:

Vitamin C, vitamin E, beta-carotene•

Key antioxidant mineral:

Selenium•

ascorbic acid one of the active forms of vitamin C (the other is dehydroascorbic acid); an antioxidant nutrient.

collagen (COLL-a-jen) the chief protein of most connective tissues, including scars, liga- ments, and tendons, and the underlying matrix on which bones and teeth are built.

prooxidant (pro-OX-ih-dant) a compound that triggers reactions involving oxygen.

245V i t a m i n C

functions and so protects against infection. A long-claimed relationship between vi- tamin C and the common cold is the topic of this chapter’s Consumer Corner.

Vitamin C Toxicity Th e easy availability of vitamin C in pill form and the publication of books recom- mending vitamin C to prevent and cure colds and cancer have led thousands of people to take huge doses of vitamin C (see the margin drawing). Th ese “volunteer” subjects enabled researchers to study potential adverse eff ects of large vitamin C doses. One eff ect observed with a 2-gram dose is alteration of the insulin response to carbohydrate in people with otherwise normal glucose tolerances. People tak- ing anticlotting medications may unwittingly counteract the eff ect if they also take massive doses of vitamin C. Th ose with kidney disease, a tendency toward gout, or a genetic abnormality that alters vitamin C’s breakdown to its excretion products are prone to forming kidney stones if they take large doses of vitamin C.†† Vitamin C supplements in any dosage may be dangerous for people with an overload of iron in the body because vitamin C increases iron absorption from the intestine and re- leases iron from storage. Other adverse eff ects are mild, including digestive upsets, such as nausea, abdominal cramps, excessive gas, and diarrhea.

Th e safe range of vitamin C intakes seems to be broad, from the absolute mini- mum of 10 milligrams a day to the Tolerable Upper Intake Level of 2,000 milli- grams (2 grams). Doses approaching 10 grams can be expected to be unsafe. Vita- min C from food is always safe.

Vitamin C Recommendations Th e adult DRI intake recommendation for vitamin C is 90 milligrams for men and 75 milligrams for women. Th ese amounts are far higher than the 10 or so mil- ligrams per day needed to prevent the symptoms of scurvy. In fact, they are close to the amount at which the body’s pool of vitamin C is full to overfl owing: about 100 milligrams per day.

Tobacco use introduces oxidants that deplete the body’s vitamin C. Th us, smok- ers generally have lower blood vitamin C levels than nonsmokers.72 Even “passive smokers” who live and work with smokers and those who regularly chew tobacco need more vitamin C than others. Intake recommendations for smokers are set high, at 125 milligrams for men and 110 milligrams for women, in order to maintain blood levels comparable to those of nonsmokers. Importantly, vitamin C cannot reverse other damage caused by tobacco use. Physical stressors including infections,

Vitamin C defi ciency causes the break- down of collagen, which supports the teeth.

Scurvy Symptoms—Gums and Skin figure 7-10

Small pinpoint hemorrhages (red spots) appear in the skin indicating that invisible internal bleeding may also be occurring.

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††Vitamin C is inactivated and degraded by several routes, and oxalate, which can form kidney stones, is sometimes produced along the way. People may also develop oxalate crystals in their kidneys regardless of vitamin C status.

60 75

100 90

110

200

125

400

600

800

1,000

4,000

2,000

Nutraceutical

recommendation

Tolerable Upper

Intake Level

Maintains full body pool

DRI recommended intake for women

DRI recommended intake for men

DRI recommended intake for smokers (men)

DRI recommended intake for smokers (women)

Daily Value on food and supplement labels

Supports metabolism

Prevents scurvy

Vitamin C Tower of Recommendations

The DRI Tolerable Upper Intake Level for • vitamin C is set at 2,000 mg (2 g) a day.

246 chapter 7 T h e V i t a m i n s

burns, fever, toxic heavy metals such as lead, and certain medications also increase the body’s use of vitamin C.

Food Sources of Vitamin C Fruits and vegetables are the foods to remember for vitamin C, as Snapshot 7-5 shows. A cup of orange juice at breakfast, a salad for lunch, a stalk of broccoli and a potato for dinner easily provide 300 milligrams, making pills unnecessary. People commonly identify citrus fruits and juices as sources of vitamin C, but they often overlook other rich sources that may be lower in calories.

Vitamin C is vulnerable to heat and destroyed by oxygen, so for maximum vitamin C, consumers should treat their fruits and vegetables gently. Losses occurring when a food is cut, processed, and stored may be large enough to reduce vitamin C’s activ- ity in the body. Fresh, raw, and quickly cooked fruits, vegetables, and juices retain the most vitamin C, and they should be stored properly and consumed within a week after purchase. Table 7-5 gives tips for maximizing vitamin retention in foods.

Because of their enormous popularity, white potatoes contribute signifi cantly to vitamin C intakes, despite providing less than 10 milligrams per half-cup serv- ing. Th e sweet potato, often ignored in favor of its paler cousin, is a gold mine of nutrients: a single half-cup serving provides about a third of many people’s recom- mended intake for vitamin C, in addition to its lavish contribution of vitamin A.

Did You Know? The term nutraceutical is used to market vita- min supplements as having pharmacological effects.

consumer corner

Why do so many people take vitamin C supplements to relieve colds? Does any research support this practice? While the term “common cold” does not precisely defi ne any one condition, researchers generally defi ne it as a group of viral up- per respiratory infections untreatable by antibiotics.1

In a recent review, 30 trials of over 11,350 people reported no relationship between routine vitamin C supplemen- tation and prevention of the common cold.2 A few others report modest benefi ts—fewer colds, fewer days, and shorter duration of severe symptoms, especially for those exposed to physical and environmental stresses.3

For treatment of colds once they set in, studies reveal a signifi cant but slight benefi t—a shorter duration of less than a day per cold in those taking at least 1 gram of vitamin C per day.4 The term signifi cant means that statistical analy- sis suggests that the fi ndings probably didn’t arise by chance, but from the experimental treatment being tested. The effect may be greater in children than in adults; in adults, doses teetering on the edge of the Tolerable Upper Intake Level

(2 grams a day) may be required to produce an effect.

Vitamin C (2 grams taken daily for two weeks) seems to reduce blood histamine. Anyone who has ever had a cold knows the effects of hista- mine: sneezing, a runny or stuffy nose, and swollen sinuses. In druglike doses, vitamin C may work like a weak antihista- mine drug, familiar to those who have taken them to treat a cold, by reducing histamine levels. Vitamin C supplements are not recommended as a cold remedy, but, for people who choose to take them, they may slightly reduce the duration and severity of some colds.5

One other effect of vitamin C supple- ments might also provide relief—the placebo effect. Half of the experimental

subjects in one study received a placebo but were told they were receiving vitamin C. These subjects reported having fewer colds than the group who had in fact received vitamin C but thought they were receiving the placebo. At work was the powerful healing effect of faith in treat- ment. One thing is certain—no drug is risk-free, and vitamin C in large doses may have side effects.6

Vitamin C and the Common Cold

Can vitamin C ease the suffering of a person with a cold?

es te

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er gm

an /C

or bi

247V i t a m i n C

Vitamin C DRI Recommended Intakes Men: 90 mg/day Women: 75 mg/day Smokers: add 35 mg/day

Tolerable Upper Intake Level Adults: 2,000 mg/day

Chief Functions Collagen synthesis (strengthens blood vessel walls, forms scar tis- sue, provides matrix for bone growth), antioxidant, restores vitamin E to active form, supports immune system, boosts iron absorption

Defi ciency Scurvy, with pinpoint hemorrhages, fatigue, bleeding gums, bruises; bone fragility, joint pain; poor wound healing, frequent infections

Toxicity Nausea, abdominal cramps, diarrhea; rashes; interference with medical tests and drug therapies; in susceptible people, aggrava- tion of gout or kidney stones

*These foods provide 10 percent or more of the vitamin C Daily Value in a serving. For a 2,000-calorie diet, the DV is 60 mg/day.

snapshot 7-5

GOOD SOURCES*

SWEET RED PEPPER (raw) ½ C = 142 mg

BRUSSELS SPROUTS (cooked) ½ c = 48 mg

GRAPEFRUIT ½ cup = 36 mg

SWEET POTATO ½ c = 20 mg

GREEN PEPPERS (raw)

½ c = 60 mg

ORANGE JUICE ½ c = 62 mg

BROCCOLI (cooked) ½ c = 51 mg

STRAWBERRIES ½ c = 42 mg

BOK CHOY (cooked) ½ c = 22 mg

KE Y POINT Vitamin C helps to maintain collagen, the protein of the connective tissue; it protects against infection; it acts as an antioxidant; and it helps in iron absorption. Taking high vitamin C doses may be unwise. Ample vitamin C can be easily obtained from foods.

Each of these tactics saves a small percentage of the vitamins in foods, but repeated each day this can add up to signifi cant amounts in a year’s time.

Prevent enzymatic destruction: Refrigerate most fruits, vegetables, and juices to slow breakdown of vitamins.•

Protect from light and air: Store milk and enriched grain products in opaque containers to protect ribofl avin. • Store cut fruits and vegetables in the refrigerator in airtight wrappers; reseal opened • juice containers before refrigerating.

Prevent heat destruction or losses in water: Wash intact fruits and vegetables before cutting or peeling to prevent vitamin losses • during washing. Cook fruits and vegetables in a microwave oven, or quickly stir fry, or steam them over • a small amount of water to preserve heat-sensitive vitamins and to prevent vitamin loss in cooking water. Recapture dissolved vitamins by using cooking water for soups, stews, or gravies. Avoid high temperatures and long cooking times.•

Minimizing Nutrient Losses table 7-5

248 chapter 7 T h e V i t a m i n s

The B Vitamins in Unison Th e B vitamins function as part of coenzymes. A coenzyme is a small molecule that combines with an enzyme and activates it. Figure 7-11 shows how a coenzyme enables an enzyme to do its job. Sometimes the vitamin part of the enzyme is the active site, where the chemical reaction takes place. Th e substance to be worked on is attracted to the active site and snaps into place; the reaction proceeds instanta- neously. Th e shape of each enzyme predestines it to accomplish just one kind of job. Without its coenzyme, however, the enzyme is as useless as a car without wheels.

Each of the B vitamins has its own special nature, and the amount of detail known about each one is overwhelming. To simplify things, this introduction describes the teamwork of the B vitamins and emphasizes the consequences of defi ciencies. Many of these nutrients are so interdependent that it is sometimes diffi cult to tell which vitamin defi ciency is the cause of which symptom; the presence or absence of one aff ects the absorption, metabolism, and excretion of others. Later sections present a few details about the vitamins as individuals.

B Vitamin Roles in Metabolism Figure 7-12 shows some body organs and tissues in which the B vitamins help the body metabolize carbohydrates, lipids, and amino acids. Th e purpose of the fi gure is not to present a detailed account of metabolism, but to give you an impression of where the B vitamins work together with enzymes in the metabolism of energy nutrients and in the making of new cells.

Many people mistakenly believe that B vitamins supply the body with energy. Th ey do not, at least not directly. Th e B vitamins are “helpers.” Th e energy-yielding nutrients—carbohydrate, fat, and protein—give the body fuel for energy; the B vi- tamins help the body use that fuel. More specifi cally, active forms of fi ve of the B vitamins—thiamin, ribofl avin, niacin, pantothenic acid, and biotin—participate in the release of energy from carbohydrate, fat, and protein. Vitamin B6 helps the body use amino acids to synthesize proteins; the body then puts the protein to work in many ways—to build new tissues, to make hormones, to fi ght infections, or to serve as fuel for energy, to name only a few.

Folate and vitamin B12 help cells to multiply, which is especially important to cells with short life spans that must replace themselves rapidly. Such cells include both the red blood cells (which live for about 120 days) and the cells that line the digestive tract (which replace themselves every 3 days). Th ese cells absorb and de- liver energy to all the others. In short, each and every B vitamin is involved, directly or indirectly, in energy metabolism.

B Vitamin Defi ciencies As long as B vitamins are present, their presence is not felt. Only when they are missing does their absence manifest itself in a lack of energy and a multitude of other symptoms, as you can imagine after looking at Figure 7-13. Th e reactions by which B vitamins facilitate energy release take place in every cell, and no cell can do its work without energy. Th us, in a B vitamin defi ciency, every cell is aff ected. Among the symptoms of B vitamin defi ciencies are nausea, severe exhaustion, ir- ritability, depression, forgetfulness, loss of appetite and weight, pain in muscles, impairment of the immune response, loss of control of the limbs, abnormal heart action, severe skin problems, swollen red tongue, cracked skin at the corners of the mouth, and teary or bloodshot eyes. Figure 7-13 shows some of these signs. Because cell renewal depends on energy and protein, which in turn depend on the B vitamins, the digestive tract and the blood are invariably damaged. In children, full recovery may be impossible. In the case of a thiamin defi ciency during growth, permanent brain damage can result.

In academic discussions of the B vitamins, diff erent sets of defi ciency symptoms are given for each one. Such clear-cut sets of symptoms are found only in laboratory animals that have been fed fabricated diets that lack just one vitamin. In real life, a

The reaction is completed with the formation of a new product. In this case the product is AB.

With the coenzyme in place, compounds A and B are attracted to the active site on the enzyme, and they react.

Without the coenzyme, compounds A and B don’t respond to the enzyme.

The product AB is released.

A B

Compounds

Active site

Enzyme

A VitaminB

Enzyme

Coenzyme

Enzyme

A B

Enzyme

A B New product

Animated! Coenzyme Action

figure 7-11

CONCEPT LINK 7-5 Recall from Chapter 6, page 200, that enzymes are large proteins that do the body’s building, dismantling, and other work.

To memorize the names of the eight B vita-• mins, try remembering this silly sentence or make up one of your own:

Tender (thiamin)

romance (riboflavin)

never (niacin)

fails (folate)

with 6 or 12 (B6 and B12)

beautiful (biotin)

pearls. (pantothenic acid)

249T h e B V i t a m i n s i n U n i s o n

defi ciency of any one B vitamin seldom shows up by itself because people don’t eat nutrients singly; they eat foods that contain mixtures of nutrients. A diet low in one B vitamin is likely low in other nutrients, too. If treatment involves giving whole- some food rather than a single supplement, subtler defi ciencies and impairments

CoenzymeKey: Vitamin

Muscles and other tissues metabolize protein.

Brain and other tissues metabolize carbohydrates.

Bone tissues make new blood cells.

Digestive tract lining replaces its cells.

Liver and other tissues metabolize fat.

thiamin

riboflavin

niacin

vitamin B6

folate

pantothenic acid

biotin

vitamin B12

TPP

FAD

NAD

NAD NAD

NAD

FMN

NADP

PLP

PLP PLP

PLP THF

THF

THF THF

THF

CoA

Bio

B12

This fi gure does not attempt to teach intricate biochemical pathways or names of B vitamin– containing enzymes. Its sole purpose is to show a few of the many tissue functions that depend on a host of B vitamin–containing enzymes working together in harmony. The B vitamins work in every cell, and this fi gure displays less than a thousandth of what they actually do. Every B vitamin is part of one or more co- enzymes that make possible the body’s chemi- cal work. For example, the niacin, thiamin, and ribo fl avin coenzymes are important in the energy pathways. The folate and vitamin B12 coenzymes are necessary for making RNA and DNA and thus new cells. The vitamin B6 coenzyme is necessary for processing amino acids and, therefore, pro- tein. Many other relationships are also critical to metabolism.

Some Roles of the B Vitamins in Metabolism: Examples figure 7-12

A healthy tongue has a rough and somewhat bumpy surface.

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In a B vitamin deficiency, the corners of the mouth become inflamed and cracked.

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In a B vitamin deficiency, the tongue becomes smooth and swollen.

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B Vitamin Deficiency Symptoms

of the Tongue and Mouth

figure 7-13

coenzyme (co-EN-zime) a small molecule that works with an enzyme to promote the enzyme’s activity. Many coenzymes have B vitamins as part of their structure (co means “with”).

250 chapter 7 T h e V i t a m i n s

will be corrected along with the major one. Th e symptoms of B vitamin defi ciencies and toxicities are listed in Table 7-7 at the end of the chapter.

KE Y POINT As part of coenzymes, the B vitamins help enzymes do their jobs. The B vitamins facilitate the work of every cell. Some help generate energy; others help make protein and new cells. B vitamins work everywhere in body tissues to help metabolize carbohydrate, fat, and protein.

The B Vitamins as Individuals Although the B vitamins all work as part of coenzymes and share other characteris- tics, each B vitamin has special qualities. Th e next sections provide a few details.

Thiamin Roles Th iamin plays a critical role in the energy metabolism of all cells. Th iamin also occupies a special site on nerve cell membranes. Consequently, nerve processes and their responding tissues, the muscles, depend heavily on thiamin.

Thiamin Defi ciency Th e classic thiamin-defi ciency disease, beriberi, was fi rst observed in East Asia, where rice provided 80 to 90 percent of the total calories most people consumed and was therefore their principal source of thiamin. When the custom of polishing rice (removing its brown coat, which contained the thia- min) became widespread, beriberi swept through the population like an epidemic. Scientists wasted years of eff ort hunting for a microbial cause of beriberi before they realized that the cause was not something present in the environment, but some- thing absent from it. Figure 7-14 depicts beriberi and describes its two forms.

Just before 1900, an observant physician working in a prison in East Asia discov- ered that beriberi could be cured with proper diet. Th e physician noticed that the chickens at the prison had developed a stiff ness and weakness similar to that of the prisoners who had beriberi. Th e chickens were being fed the rice left on prisoners’ plates. When the rice bran, which had been discarded in the kitchen, was given to the chickens, their paralysis was cured. Th e physician met resistance when he tried to feed the rice bran, the “garbage,” to the prisoners, but it worked—it pro- duced a miracle cure like those described at the beginning of the chapter. Later, extracts of rice bran were used to prevent infantile beriberi; still later, thiamin was synthesized.

In developed countries today, alcohol abuse often leads to a severe form of thia- min defi ciency, Wernicke-Korsakoff syndrome, defi ned in Controversy 3. Alcohol contributes energy but carries almost no nutrients with it and often displaces food in the diet. In addition, alcohol impairs absorption of thiamin from the digestive tract and hastens its excretion in the urine, tripling the risk of defi ciency. Th e syn- drome is characterized by symptoms almost indistinguishable from alcohol abuse itself: apathy, irritability, mental confusion, disorientation, memory loss, jerky eye movements, and a staggering gait. Unlike alcohol toxicity, the syndrome responds quickly to an injection of thiamin, and some experts recommend a precautionary dose for any patients suspected of having it.73

Recommended Intakes and Food Sources Th e DRI committee set the thiamin intake recommendation at 1.2 milligrams per day for men and at 1.1 milligrams per day for women. Pregnancy and lactation demand somewhat more thiamin (see the DRI, inside front cover, page B). Th iamin occurs in small amounts in many nutri- tious foods. Ham and other pork products, sunfl ower seeds, enriched and whole- grain cereals, and legumes are especially rich in thiamin (see Snapshot 7-6). If you

Beriberi takes two forms: wet beriberi, characterized by edema (fl uid accumula- tion), and dry beriberi, without edema. This person’s ankle retains the imprint of the physician’s thumb, showing the edema of wet beriberi.

Beriberi figure 7-14

M S

B /C

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m M

ed ic

al S

to ck

P ho

thiamin (THIGH-uh-min) a B vitamin in- volved in the body’s use of fuels.

beriberi (berry-berry) the thiamin-defi ciency disease; characterized by loss of sensation in the hands and feet, muscular weakness, ad- vancing paralysis, and abnormal heart action.

251T h e B V i t a m i n s a s I n d i v i d u a l s

keep empty-calorie foods to a minimum and focus your meals on nutritious foods each day, you will easily meet your thiamin needs.

KE Y POINT Thiamin works in energy metabolism and in nerve cells. Its defi ciency disease is beriberi. Many foods supply small amounts of thiamin.

Ribofl avin Roles and Sources Like thiamin, ribofl avin plays a role in the energy metabolism of all cells. When thiamin is defi cient, ribofl avin may be lacking, too, but its defi ciency symptoms, such as cracks at the corners of the mouth, sore throat, or hypersensitivity to light, may go undetected because those of thiamin defi ciency are more severe. World- wide, ribofl avin defi ciency has been documented among children whose diets lack milk products and meats, and researchers suspect that it occurs among some U.S. elderly as well.74 A diet that remedies ribofl avin defi ciency invariably contains some thiamin and so clears up both defi ciencies.

Ribofl avin recommendations are listed in Snapshot 7-7. People in this country obtain over a quarter of their ribofl avin from enriched breads, cereals, pasta, and other grain products, while milk and milk products supply another 20 percent. Cer- tain vegetables, eggs, and meats contribute most of the rest (see Snapshot 7-7).75 Ultraviolet light and irradiation destroy ribofl avin. For these reasons, milk is sold in cardboard or opaque plastic containers, and precautions are taken if milk is pro- cessed by irradiation. Ribofl avin is stable to heat, so cooking does not destroy it.

KE Y POINT Ribofl avin works in energy metabolism. It is destroyed by ordinary light.

Thiamin DRI Recommended Intakes Men: 1.2 mg/day Women: 1.1 mg/day

Chief Functions Part of coenzyme active in energy metabolism

Defi ciencya

Beriberi with possible edema or muscle wasting; enlarged heart, heart failure, muscular weakness, pain, apathy, poor short-term memory, confusion, irritability, diffi culty walking, paralysis, an- orexia, weight loss

Toxicity None reported

*These foods provide 10 percent or more of the thiamin Daily Value in a serving. For a 2,000-calorie diet, the DV is 1.5 mg/day. aSevere thiamin defi ciency is often related to heavy alcohol consumption.

snapshot 7-6

GOOD SOURCES*

ENRICHED PASTA ½ c = 0.14 mg

PORK CHOP (lean only) 3 oz = 0.95 mg

GREEN PEAS (cooked) ½ = 0.23 mg

WAFFLE 1 waffl e = 0.25 mg

ENRICHED CEREAL (ready-to-eat)

¾ c = 0.38 mg

WHOLE WHEAT BAGEL ½ bagel = 0.22 mg

SUNFLOWER SEEDS (raw kernels)

2 tbs = 0.26 mg

BAKED POTATO 1 whole potato

= 0.22 mg

BLACK BEANS (cooked)

½ C = 0.21 mg

Table 7-7 on page 262 lists the symptoms of • riboflavin deficiency.

ribofl avin (RIBE-o-fl ay-vin) a B vita- min active in the body’s energy-releasing mechanisms.

252 chapter 7 T h e V i t a m i n s

Niacin Functions Th e vitamin niacin, like thiamin and ribofl avin, participates in the energy metabo- lism of every cell. Its absence causes serious illness.

Niacin Defi ciency Th e niacin-defi ciency disease pellagra appeared in Europe in the 1700s when corn from the New World became a staple food. In the early 1900s in the United States, pellagra was devastating lives throughout the South and Midwest. Hundreds of thousands of pellagra victims were thought to be suff ering from a contagious disease until this dietary defi ciency was identifi ed. Th e disease still occurs among poorly nourished people living in urban slums and particularly in those with alcohol addiction. Pellagra is also still common in parts of Africa and Asia. Its symptoms are known as the four “Ds”: diarrhea, dermatitis, dementia, and, ultimately, death.

Figure 7-15 shows the skin disorder (dermatitis) associated with pellagra. For comparison, Figure 7-3 (page 231) and Figure 7-18 (page 257) show skin disorders associated with vitamin A and vitamin B6 defi ciency, respectively, a reminder that any nutrient defi ciency aff ects the skin and all other cells. Th e skin just happens to be the organ you can see. Table 7-7 at the end of the chapter lists the symptoms of niacin defi ciency.

Niacin Toxicity Physicians may administer large doses of a form of niacin as part of a treatment regimen to improve blood lipids associated with cardiovascular disease.‡‡76 When used this way, niacin leaves the realm of nutrition to become a pharmacological agent—a drug. Ordinary niacin supplements do not improve blood lipids, and large doses can cause low blood pressure, liver injury, peptic ulcers, or vi- sion loss.77 Some niacin supplements taken in large amounts create a “niacin fl ush,” a dilation of the capillaries of the skin with perceptible tingling that, if intense, can be painful. For safety’s sake, anyone considering taking large doses of niacin should consult a physician, who may prescribe safe, eff ective alternatives.78

Ribofl avin DRI Recommended Intakes Men: 1.2 mg/day Women: 1.1 mg/day

Chief Functions Part of coenzyme active in energy metabolism

Defi ciency Cracks and redness at corners of mouth; painful, smooth, purplish red tongue; sore throat; infl amed eyes and eyelids, sensitivity to light; skin rashes

Toxicity None reported

*These foods provide 10 percent or more of the ribofl avin Daily Value in a serving. For a 2,000-calorie diet, the DV is 1.7 mg/day.

snapshot 7-7

GOOD SOURCES*

BEEF LIVER (cooked) 3 oz = 2.9 mg

COTTAGE CHEESE 1 c = 0.38 mg

ENRICHED CEREAL (ready-to-eat) ½ c = 0.43 mg

SPINACH (cooked) ½ c = 0.21 mg

YOGURT (plain) 1 c = 0.57 mg

MILK 1 c = 0.45 mg

PORK CHOP (lean only)

3 oz = 0.23 mg

MUSHROOMS (cooked)

½ c = 0.23 mg

The typical “fl aky paint” dermatitis of pel- lagra develops on skin that is exposed to light. The skin darkens and fl akes away.

Pellagra figure 7-15

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‡‡The form of niacin is nicotinic acid.

253T h e B V i t a m i n s a s I n d i v i d u a l s

Niacin Recommendations and Food Sources Niacin recommendations are listed in Snapshot 7-8. Th e key nutrient that prevents pellagra is niacin, but any protein containing suffi cient amounts of the amino acid tryptophan will serve in its place. Tryptophan, which is abundant in almost all proteins (but is limited in the protein of corn), is converted to niacin in the body, and it is possible to cure pellagra by administering tryptophan alone. Th us, a person eating adequate protein (as most people in developed nations do) will not be defi cient in niacin. Th e amount of niacin in a diet is stated in terms of niacin equivalents (NE), a measure that takes avail- able tryptophan into account.

Early workers seeking the cause of pellagra observed that well-fed people never got it. From there the researchers defi ned a diet that reliably produced the disease— one of cornmeal, salted pork fat, and molasses. Corn not only is low in protein but also lacks tryptophan. Salt pork is almost pure fat and contains too little protein to compensate; and molasses is virtually protein-free. Snapshot 7-8 shows some good food sources of niacin. Research into optimal intakes and sources of niacin are ongoing.79

KE Y POINT The infamous niacin defi ciency disease pellagra can be prevented by adequate dietary protein because the amino acid tryptophan can be converted to niacin in the body.

Folate Roles To make new cells, tissues must have the vitamin folate. Each new cell must be equipped with new genetic material—copies of the parent cell’s DNA—and folate helps to synthesize DNA. Folate also plays critical roles in the normal metabolism of several amino acids.

Folate Defi ciency Folate defi ciencies may result from consuming a diet too low in folate or from illnesses that impair its absorption, increase its excretion, require

Niacin DRI Recommended Intakes Men: 16 mg/daya

Women: 14 mg/day

Tolerable Upper Intake Level Adults: 35 mg/day

Chief Functions Part of coenzymes needed in energy metabolism

Defi ciency Pellagra, characterized by fl aky skin rash (dermatitis) where exposed to sunlight; mental depression, apathy, fatigue, loss of memory, headache; diarrhea, abdominal pain, vomiting; swollen, smooth, bright red or black tongue

Toxicity Painful fl ush, hives, and rash (“niacin fl ush”); excessive sweating; blurred vision; liver damage, impaired glucose tolerance

*These foods provide 10 percent or more of the niacin Daily Value in a serving. For a 2,000-calorie diet, the DV is 20 mg/day. The DV values are for preformed niacin, not niacin equivalents. aNiacin DRI Recommended Intakes are expressed in niacin equivalents (NE); the Tolerable Upper Intake Level refers to preformed niacin.

snapshot 7-8

GOOD SOURCES*

CHICKEN BREAST 3 oz = 8.9 mg

PORK CHOP 3 oz = 3.9 mg

BAKED POTATO 1 whole potato = 3.3 mg

TUNA (in water) 3 oz = 11.3 mg

ENRICHED CEREAL (ready-to-eat) ¾ c = 5.0 mg

MUSHROOMS (cooked) ½ c = 3.5 mg

niacin a B vitamin needed in energy me- tabolism. Niacin can be eaten preformed or can be made in the body from tryptophan, one of the amino acids. Other forms of niacin are nicotinic acid, niacinamide, and nicotinamide.

pellagra (pell-AY-gra) the niacin-defi ciency disease (pellis means “skin”; agra means “rough”). Symptoms include the “4 Ds”: diar- rhea, dermatitis, dementia, and, ultimately, death.

niacin equivalents (NE) the amount of niacin present in food, including the niacin that can theoretically be made from its precursor tryptophan that is present in the food.

folate (FOH-late) a B vitamin that acts as part of a coenzyme important in the manufac- ture of new cells. The form added to foods and supplements is folic acid.

254 chapter 7 T h e V i t a m i n s

medication that interacts with folate, or otherwise increase the body’s folate need. However it occurs, folate defi ciency has wide-reaching eff ects.

Immature red and white blood cells and the cells of the digestive tract divide most rapidly and therefore are most vulnerable to folate defi ciency. Defi ciencies of folate cause anemia, diminished immunity, and abnormal digestive function. Th e anemia of folate defi ciency is related to the anemia of vitamin B12 malabsorption because the two vitamins work as teammates in producing red blood cells—see Figure 7-17 later in the chapter. Research suggests that a diet defi cient in folate also elevates the risk of cancer of the cervix (in women infected with a sexually transmitted virus, HPV§§), breast cancer (in women who drink alcohol), and pancreatic cancer.80 In a strange twist, however, folate may enhance the progression of some cancers once they have begun.81

Of all the vitamins, folate is most likely to interact with medications. Many drugs, including antacids and aspirin and its relatives, have been shown to interfere with the body’s use of folate. Occasional use of these drugs to relieve headache or upset stomach presents no concern, but frequent users may need to pay attention to their folate intakes. Th ese include people with chronic pain or ulcers who rely heav- ily on aspirin or antacids as well as those who smoke or take oral contraceptives or anticonvulsant medications.

Birth Defects and Folate Enrichment By consuming enough folate during preg- nancy, a woman can reduce her child’s risk of having one of the devastating birth defects known as neural tube defects (NTD).82 NTD range from slight problems in the spine to mental retardation, severely diminished brain size, and death shortly after birth. NTD arise in the fi rst days or weeks of pregnancy, long before most women suspect that they are pregnant.

Most young women eat too few fruits and vegetables from day to day to supply even half the folate needed to prevent NTD. In the late 1990s, the FDA ordered all enriched grain products such as bread, cereal, rice, and pasta sold in the United States to be fortifi ed with an absorbable synthetic form of folate, folic acid. Since this fortifi cation began, typical folate intakes from fortifi ed foods have increased dramatically, along with average blood folate values.83 Among women of childbear- ing age, for example, prevalence of low serum folate concentrations dropped from 21 percent before fortifi cation to less than 1 percent after fortifi cation was introduced.84 During the same period, the U.S. incidence of NTD dropped by 25 percent, even among women receiving late or no prenatal care (see Figure 7-16).85 Miscarriages and certain other birth defects, such as cleft lip, have diminished as well.86

Folate Toxicity As for folate toxicity, a Tolerable Upper Intake Level for syn- thetic folic acid from supplements and enriched foods is set at 1,000 micrograms a day for adults. A question raised about the wisdom of fortifying the nation’s food supply with folic acid concerns folate’s ability to mask defi ciencies of vitamin B12 (more about this eff ect later).87 Among other suspected but unconfi rmed potential harms from high blood folic acid levels are suppression of normal immune func- tioning and increased cancer risks.88 Except for people taking supplements of more than 400 micrograms of folic acid, few (less than 3 percent of the U.S. population) exceed the Tolerable Upper Intake Level for folate.89 Th us, researchers conclude that the current level of fortifi cation of the food supply appears to be safe.

Folate Recommendations Th e DRI recommended intake for folate for healthy adults is set at 400 micrograms per day. Th e DRI committee also advises all women of childbearing age to consume 400 micrograms of folic acid from supplements or en- riched foods each day in addition to the folate that occurs naturally in their foods.

Food Sources of Folate Th e name folate is derived from the word foliage, and sure enough, leafy green vegetables such as spinach and turnip greens provide

§§Human papilloma virus.

Drug and nutrient interactions are the topic • of the Controversy that follows Chapter 14.

Did You Know? The B vitamins thiamin, ribofl avin, niacin, and folate (as folic acid) are among the enrichment nutrients added to grain foods such as breads and cereals sold in the United States.

CONCEPT LINK 7-6 More details on enrichment of grain foods were in Chapter 4, page 120.

neural tube defects (NTD) abnor- malities of the brain and spinal cord apparent at birth and believed to be related to a wom- an’s folate intake before and during pregnancy. Also defi ned in Chapter 13.

255T h e B V i t a m i n s a s I n d i v i d u a l s

abundant folate (see Snapshot 7-9). Fresh, uncooked vegetables and fruits are often superior sources because the heat of cooking and the oxidation that occurs during storage destroy much of the folate in foods. Eggs also provide some folate.

A diff erence in absorption between naturally occurring food folate and the syn- thetic folic acid necessitates compensation when measuring folate. Th e unit of mea- sure, dietary folate equivalent, or DFE, converts all forms of folate into micrograms that are equivalent to the folate in foods. Some food and supplement labels still ex- press folate values in micrograms, not DFE; Appendix C off ers a conversion factor.

Rate per 100,000

Key:

1991 15

1996 2001 2005

Neural tube defects have declined since folate fortifi cation began in 1996.

Incidence of a Common Neural Tube Defect,

Spina Bifida, Over Time figure 7-16

Folate DRI Recommended Intake Adults: 400 µg/daya

Tolerable Upper Intake Level Adults: 1,000 µg/day

Chief Functions Part of a coenzyme needed for new cell synthesis

Defi ciency Anemia, smooth, red tongue; depression, mental confusion, weak- ness, fatigue, irritability, headache; a low intake increases the risk of neural tube birth defects

Toxicity Masks vitamin B12–defi ciency symptoms

*These foods provide 10 percent or more of the folate Daily Value in a serving. For a 2,000-calorie diet, the DV is 400 µg/day. aFolate recommendations are expressed in dietary folate equivalents (DFE). Note that for natural folate sources, 1 µg = 1 DFE; for enrichment sources, 1 µg = 1.7 DFE. bSome highly enriched cereals may provide 400 or more micrograms in a serving.

snapshot 7-9

GOOD SOURCES*

BEEF LIVER (cooked) 3 oz = 221 µg

PINTO BEANS (cooked) ½ c = 146 µg

ASPARAGUS ½ c = 134 µg

AVOCADO ½ c = 105 µg

LENTILS (cooked) ½ c = 179 µg

SPINACH (raw) 1 c = 58 µg

ENRICHED CEREAL (ready-to-eat)b

¾ c = 82 µg

BEETS ½ c = 68 µg

dietary folate equivalent (DFE) a unit of measure expressing the amount of folate available to the body from naturally oc- curring sources. The measure mathematically equalizes the difference in absorption between less absorbable food folate and highly absorb- able synthetic folate added to enriched foods and found in supplements.

Source: National Vital Statistics System, National Center for Health Statistics, Centers for Disease Control, December 2007.

256 chapter 7 T h e V i t a m i n s

KE Y POINT Folate is added to enriched foods as folic acid and occurs naturally in leafy green vegetables and fruits. Low intakes of folate cause birth defects. High intakes can mask the blood symptom of vitamin B12 defi ciency.

Vitamin B12 Roles Vitamin B12 and folate are closely related: each depends on the other for activation. By itself vitamin B12 also helps to maintain the sheaths that surround and protect nerve fi bers.

Vitamin B12 Defi ciency Without suffi cient vitamin B12, nerves become dam- aged and folate fails to do its blood-building work, so vitamin B12 defi ciency causes an anemia identical to that caused by folate defi ciency. Th e blood symptoms of a defi ciency of either folate or vitamin B12 include the presence of large, immature red blood cells. Administering extra folate often clears up this blood condition but allows the defi ciency of vitamin B12 to continue undetected. Vitamin B12’s other functions then become compromised, and the results can be devastating: dam- aged nerve sheaths, creeping paralysis, and general malfunctioning of nerves and muscles.

Diagnosing a vitamin B12 problem is diffi cult, and often the damage will proceed unchecked. In an eff ort to prevent excessive folate intakes that could mask symp- toms of a vitamin B12 defi ciency, the FDA specifi es the exact amounts of folic acid that can be added to enriched foods.

A Special Case: Vitamin B12 Absorption Absorption of vitamin B12 requires an intrinsic factor, a compound made by the stomach with instructions from the genes. With the help of the stomach’s acid to liberate vitamin B12 from the food proteins that bind it, intrinsic factor attaches to the vitamin and the complex is absorbed into the bloodstream.

A few people have an inherited defect in the gene for intrinsic factor, which makes vitamin B12 absorption abnormal, beginning in mid-adulthood. In later years, many others lose the ability to produce enough stomach acid and intrinsic factor to allow effi cient absorption of vitamin B12.***90 In these cases, vitamin B12 must be supplied by injection to bypass the defective absorptive system. Th e anemia of the vitamin B12 defi ciency caused by lack of intrinsic factor is known as pernicious anemia (see Figure 7-17).

Food Sources of Vitamin B12 As Snapshot 7-10 shows, vitamin B12 is present only in foods of animal origin, so vitamin B12 defi ciency poses a threat to strict veg- etarians. Controversy 6 discussed vitamin B12 sources for vegetarians.

Perspective Th e way folate masks the anemia of vitamin B12 defi ciency under- scores a point about supplements. It takes a skilled professional to correctly diag- nose and treat a nutrient defi ciency, and self-diagnosis or acting on advice from self-proclaimed experts poses serious risks. A second point: Since vitamin B12 defi - ciency in the body may be caused by either a lack of the vitamin in the diet or a lack of the intrinsic factor necessary to absorb the vitamin, a change in diet alone may not correct the defi ciency; a professional diagnosis can identify such problems.

KE Y POINT Vitamin B12 occurs in animal products. A defi ciency anemia that mimics folate defi ciency arises with low intakes or poor absorption. This defi ciency also causes nerve damage.

Controversy 6 describes vitamin B• 12 defi- ciency in infants born to women who lacked the vitamin during pregnancy and lactation.

C ar

ol in

a B

io lo

gi ca

l/V is

ua ls

nl im

ite d

E d

R es

ch ke

/P et

er A

rn ol

The anemia of folate defi ciency is indis- tinguishable from that of vitamin B12 defi ciency.

Anemic and

Normal Blood Cells

figure 7-17

Blood cells of pericious anemia. The cells are larger than normal and irregular in shape.

Normal blood cells. The size, shape, and color of these red blood cells show that they are normal.

***The condition is atrophic gastritis (a-TROH-fi k gas-TRY-tis), a chronic infl ammation of the stomach accompanied by a diminished size and functioning of the stomach’s mucous membrane and glands.

vitamin B12 a B vitamin that helps to convert folate to its active form and also helps maintain the sheath around nerve cells. Vitamin B12’s scientifi c name, not often used, is cyanocobalamin.

intrinsic factor a factor found inside a system. The intrinsic factor necessary to prevent pernicious anemia is now known to be a compound that helps in the absorption of vitamin B12.

pernicious (per-NISH-us) anemia a vitamin B12–defi ciency disease, caused by lack of intrinsic factor and characterized by large, immature red blood cells and damage to the nervous system (pernicious means “highly injurious or destructive”).

257T h e B V i t a m i n s a s I n d i v i d u a l s

Vitamin B6 Roles Vitamin B6 participates in over 100 reactions in body tissues and is needed to help convert one kind of amino acid, which cells have in abundance, to other nonessential amino acids that the cells lack. In addition, vitamin B6 functions in these ways:

Aids in the conversion of tryptophan to niacin.•

Plays important roles in the synthesis of hemoglobin and neurotransmitters, •

the communication molecules of the brain. For example, vitamin B6 assists the

conversion of the amino acid tryptophan to the neurotransmitter serotonin.

Assists in releasing stored glucose from glycogen and thus contributes to the •

regulation of blood glucose.

Has roles in immune function and steroid hormone activity.•

Is critical to the developing brain and nervous system of a fetus; defi ciency dur-•

ing this stage causes behavioral problems later.

Is under investigation for roles in maintaining DNA integrity and thus reducing •

cancer risk.91

Vitamin B6 Defi ciency Because of these diverse functions, vitamin B6 defi ciency is expressed in general symptoms, such as weakness, psychological depression, con- fusion, irritability, and insomnia. Other symptoms include anemia, the greasy der- matitis depicted in Figure 7-18, and, in advanced cases of defi ciency, convulsions. A shortage of vitamin B6 may also weaken the immune response. Some evidence sug- gests that low vitamin B6 intakes may also be related to increased incidence of heart disease. Some people have taken vitamin B6 supplements to relieve carpal tunnel syndrome and sleep disorders even though such treatment seems to be ineff ective.

Vitamin B6 Toxicity Large doses of vitamin B6 from supplements can be danger- ous. Years ago it was generally believed that, like most of the other water-soluble vitamins, vitamin B6 could not reach toxic concentrations in the body. Th en a re- port told of women who took more than 2 grams of vitamin B6 daily (the Tolerable Upper Intake Level is set at 100 milligrams, or 0.1 gram) for two months or more, attempting to cure premenstrual syndrome (science doesn’t support this use). Th e women developed numb feet, then lost sensation in their hands, and eventually

Vitamin B12 DRI Recommended Intake Adults: 2.4 µg/day

Chief Functions Part of coenzymes needed in new cell synthesis; helps to maintain nerve cells

Defi ciency Pernicious anemia;a anemia (large-cell type);b smooth tongue; tingling or numbness; fatigue, memory loss, disorientation, degen- eration of nerves progressing to paralysis

Toxicity None reported

*These foods provide 10 percent or more of the vitamin B12 Daily Value in a serving. For a 2,000-calorie diet, the DV is 6 µg/day. aThe name pernicious anemia refers to the vitamin B12 defi ciency caused by a lack of stomach intrinsic factor, but not to anemia from inadequate dietary intake. bLarge cell–type anemia is known as either macrocytic or megaloblastic anemia.

snapshot 7-10

GOOD SOURCES*

CHICKEN LIVER 3 oz = 18.0 µg

SIRLOIN STEAK 3 oz = 2.0 µg

COTTAGE CHEESE 1 c = 2.0 µg

PORK ROAST (lean) 3 oz = 1.0 µg

SARDINES 3 oz = 3.0 µg

TUNA (in water) 3 oz = 3.0 µg

SWISS CHEESE 1½ oz = 1.5 µg

In this dermatitis, the skin is greasy and fl aky, unlike the skin affected by the der- matitis of pellagra.

Vitamin B6

Deficiency

figure 7-18

eo rg

e L.

B la

ck bu

rn , M

.D .,

P h.

D .,

H ar

va rd

ed ic

al S

ch oo

vitamin B6 a B vitamin needed in protein metabolism. Its three active forms are pyridox- ine, pyridoxal, and pyridoxamine.

serotonin (SER-oh-TONE-in) a neurotrans- mitter important in sleep regulation, appetite control, and mood regulation, among other roles. Serotonin is synthesized in the body from the amino acid tryptophan with the help of vitamin B6.

carpal tunnel syndrome a pinched nerve at the wrist, causing pain or numbness in the hand. It is often caused by repetitive mo- tion of the wrist.

258 chapter 7 T h e V i t a m i n s

became unable to walk or work. Since the fi rst report of vitamin B6 toxicity, re- searchers have seen toxicity symptoms in more than 100 women who took vitamin B6 supplements for more than fi ve years. Th e women recovered after they stopped taking the supplements.

Th e potential for a toxic dose from supplements seems clear, but food sources are safe. Consider that one small capsule can easily deliver 2 grams of vitamin B6, but it would take almost 3,000 bananas, more than 1,600 servings of liver, or more than 3,800 chicken breasts to supply an equivalent amount. Moral: Stick with food. Table 7-7 on page 263 lists common defi ciency and toxicity symptoms of vitamin B6 and other water-soluble vitamins.

People may take supplements of vitamin B6 and other B vitamins in hopes of pre- venting heart disease by lowering an amino acid, homocysteine, in the blood. People who suff er a rare disorder of high blood homocysteine almost invariably develop cardiovascular disease (CVD).††† Also, CVD suff erers without the inherited dis- order sometimes accumulate homocysteine in the blood. When healthy men with elevated homocysteine take supplements of vitamin B6, vitamin B12, and folate, their homocysteine values drop signifi cantly. However, the real prize, a drop in CVD oc- currence by lowering homocysteine in healthy people, has yet to be demonstrated.92

Intake Recommendations and Food Sources Vitamin B6 plays so many roles in protein metabolism that the body’s requirement for vitamin B6 is roughly proportional to protein intakes. Th e DRI committee set the vitamin B6 intake recommendation high enough to cover most people’s needs, regardless of diff erences in protein intakes (see the inside front cover, page B). Meats, fi sh, and poultry (protein-rich foods), pota- toes, leafy green vegetables, and some fruits are good sources of vitamin B6 (see Snap- shot 7-11). Other foods such as legumes and peanut butter provide smaller amounts.

KE Y POINT Vitamin B6 works in amino acid metabolism.

Vitamin B6 DRI Recommended Intake Adults (19–50 yr): 1.3 mg/day

Tolerable Upper Intake Level Adults: 100 mg/day

Chief Functions Part of a coenzyme needed in amino acid and fatty acid metabo- lism; helps to convert tryptophan to niacin and to serotonin; helps to make hemoglobin for red blood cells

Defi ciency Anemia, depression, confusion, abnormal brain wave pattern, convulsions; greasy, scaly dermatitis

Toxicity Depression, fatigue, impaired memory, irritability, headaches, nerve damage causing numbness and muscle weakness pro- gressing to an inability to walk and convulsions; skin lesions

*These foods provide 10 percent or more of the vitamin B6 Daily Value in a serving. For a 2,000-calorie diet, the DV is 2 mg/day.

snapshot 7-11

GOOD SOURCES*

BEEF LIVER (cooked) 3 oz = 0.87 mg

BANANA 1 banana = 0.43 mg

SWEET POTATO (cooked) ½ c = 0.29 mg

BAKED POTATO 1 whole potato

= 0.70 mg

CHICKEN BREAST 3 oz = 0.46 mg

SPINACH (cooked) ½ c = 0.22 mg

†††Although chemically an amino acid, homocysteine is not incorporated into body proteins, but is metabolized to other compounds.

259T h e B V i t a m i n s a s I n d i v i d u a l s

Biotin and Pantothenic Acid Two other B vitamins, biotin and pantothenic acid, are, like thiamin, ribofl a- vin, and niacin, important in energy metabolism. Biotin is a cofactor for several enzymes in the metabolism of carbohydrate, fat, and protein. Recently, scientists have revealed roles for biotin in gene expression. No adverse eff ects from high bio- tin intakes have been reported, but some research indicates that high-dose biotin supplementation may damage DNA. No Tolerable Upper Intake Level has yet been set for biotin. Pantothenic acid is a component of a key coenzyme that makes pos- sible the release of energy from the energy nutrients. It also participates in more than 100 steps in the synthesis of lipids, neurotransmitters, steroid hormones, and hemoglobin.

Although rare diseases may precipitate defi ciencies of biotin and pantothenic acid, both vitamins are readily available in foods. A steady diet of raw egg whites, which contain a protein that binds biotin, can produce biotin defi ciency, but you would have to consume more than two dozen raw egg whites daily to produce the eff ect. Cooking eggs denatures the protein. Healthy people eating ordinary diets are not at risk for defi ciencies.

KE Y POINT Biotin and pantothenic acid are important to the body and are abundant in food.

Non-B Vitamins In addition to the B vitamins just discussed, a few compounds that are topics of de- bate among researchers deserve mention. Choline might be called a conditionally essential nutrient because when the diet is devoid of choline, the body cannot make enough of the compound to meet its needs, and it plays important roles in fetal de- velopment.93 Choline is common in foods, though, and defi ciencies are practically unheard of outside the laboratory. DRI intake recommendations have been set for choline (see inside front cover, page B).

Th e compounds carnitine, inositol, and lipoic acid might appropriately be called nonvitamins because they are not essential nutrients for human beings. Carnitine, sometimes called “vitamin BT,” is an important piece of cell machinery, but it is not a vitamin. Although defi ciencies can be induced in laboratory animals for ex- perimental purposes, these substances are abundant in ordinary foods. Even if these compounds were essential in human nutrition, supplements would be unnecessary for healthy people eating a balanced diet. Vitamin companies often include these substances to make their formulas appear more “complete,” but there is no physi- ological reason to do so.

Other substances have been mistakenly thought to be essential in human nu- trition because they are needed for growth by bacteria or other life-forms. Th ese substances include PABA (para-aminobenzoic acid), biofl avonoids (“vitamin P” or hesperidin), and ubiquinone (coenzyme Q ). Other names you may hear are “vita- min B15” and pangamic acid (hoaxes) or “vitamin B17” (laetrile or amygdalin, not a cancer cure as claimed and not a vitamin by any stretch of the imagination).‡‡‡

KE Y POINT Choline is needed in the diet, but it is not a vitamin and defi ciencies are unheard of outside the laboratory. Many other substances that people claim are B vitamins are not. Among these substances are carnitine, inositol, and lipoic acid.

Th is chapter has addressed all 13 of the vitamins. Th e basic facts about each one are summed up in Tables 7-6 and 7-7.

The DRI recommended intakes for biotin • and pantothenic acid are listed on the inside front cover, page B.

biotin (BY-o-tin) a B vitamin; a coenzyme necessary for fat synthesis and other metabolic reactions.

pantothenic (PAN-to-THEN-ic) acid a B vitamin.

choline (KOH-leen) a nonessential nutrient used to make the phospholipid lecithin and other molecules.

carnitine a nonessential nutrient that func- tions in cellular activities.

inositol (in-OSS-ih-tall) a nonessential nutri- ent found in cell membranes.

lipoic (lip-OH-ic) acid a nonessential nutrient.

‡‡‡Read about these and many other claims at the website of the National Council Against Health Fraud, www.ncahf.org.

http://www.ncahf.org

260 chapter 7 T h e V i t a m i n s

VITAMIN A

Other Names Retinol, retinal, retinoic acid; main precur- sor is beta-carotene

Chief Functions in the Body Vision; health of cornea, epithelial cells, mucous membranes, skin; bone and tooth growth; regulation of gene expres- sion; reproduction; immunity

Beta-carotene: antioxidant

Defi ciency Disease Name Hypovitaminosis A

Signifi cant Sources Retinol: fortifi ed milk, cheese, cream, but- ter, fortifi ed margarine, eggs, liver

Beta-carotene: spinach and other dark, leafy greens; broccoli; deep orange fruits (apricots, cantaloupe) and vegetables (winter squash, carrots, sweet potatoes, pumpkin)

Defi ciency Symptoms Toxicity Symptoms

Blood Anemia (small-cell type)a Red blood cell breakage, cessation of menstruation, nosebleeds

Bones/Teeth Cessation of bone growth, painful joints; impaired enamel formation, cracks in teeth, tendency toward tooth decay

Bone pain; growth retardation; increased pressure inside skull; headaches; possible bone mineral loss

Digestive System Diarrhea, changes in intesti- nal and other body linings

Abdominal pain, nausea, vomit- ing, diarrhea, weight loss

Immune System Frequent infections Overreactivity

Nervous/Muscular System

Night blindness (retinal) Mental depression

Blurred vision, muscle weak- ness, fatigue, irritability, loss of appetite

Skin and Cornea Keratinization, corneal degeneration leading to blindness,b rashes

Dry skin, rashes, loss of hair; cracking and bleeding lips, brittle nails; hair loss

Other Kidney stones, impaired growth

Liver enlargement and liver damage; birth defects

VITAMIN D

Other Names Calciferol, cholecalciferol, dihydroxy vita- min D; precursor is cholesterol

Chief Functions in the Body Mineralization of bones (raises blood calcium and phosphorus via absorption from digestive tract and by withdrawing calcium from bones and stimulating reten- tion by kidneys)

Defi ciency Disease Name Rickets, osteomalacia

Signifi cant Sources Self-synthesis with sunlight; fortifi ed milk or margarine, liver, sardines, salmon, shrimp

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Raised blood calcium; calci- fi cation of blood vessels and heart tissues

Bones/Teeth Abnormal growth, misshapen bones (bowing of legs), soft bones, joint pain, malformed teeth

Calcifi cation of tooth soft tis- sues; thinning of tooth enamel

Nervous System Muscle spasms Excessive thirst, headaches, irritability, loss of appetite, weakness, nausea

Other Kidney stones; calcifi cation of soft tissues (kidneys, lungs, joints); mental and physical retardation of offspring

aSmall-cell anemia is termed microcytic anemia; large-cell type is macrocytic or megaloblastic anemia. bCorneal degeneration progresses from keratinization (hardening) to xerosis (drying) to xerophthalmia (thickening, opacity, and irreversible blindness).

The Fat-Soluble Vitamins—Functions, Deficiencies, and Toxicities table 7-6

261T h e B V i t a m i n s a s I n d i v i d u a l s

VITAMIN E

Other Names Alpha-tocopherol, tocopherol

Chief Functions in the Body Antioxidant (quenching of free radicals), stabilization of cell membranes, sup- port of immune function, protection of polyunsaturated fatty acids; normal nerve development

Defi ciency Disease Name (No name)

Signifi cant Sources Polyunsaturated plant oils (margarine, salad dressings, shortenings), green and leafy vegetables, wheat germ, whole-grain products, nuts, seeds

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Red blood cell breakage, anemia

Augments the effects of anti- clotting medication

Digestive System Nerve degeneration, weak- ness, diffi culty walking, leg cramps

General discomfort, nausea

Eyes Blurred vision

Nervous/Muscular System

Fatigue

VITAMIN K

Other Names Phylloquinone, naphthoquinone

Chief Functions in the Body Synthesis of blood-clotting proteins and proteins important in bone mineralization

Defi ciency Disease Name (No name)

Signifi cant Sources Bacterial synthesis in the digestive tract; green leafy vegetables, cabbage-type vegetables, soybeans, vegetable oils

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Hemorrhage Interference with anticlotting medication

Bones Poor skeletal mineralization

The Fat-Soluble Vitamins—Functions, Deficiencies, and Toxicities (continued) table 7-6

The Water-Soluble Vitamins—Functions, Deficiencies, and Toxicities table 7-7

VITAMIN C

Other Names Ascorbic acid

Chief Functions in the Body Collagen synthesis (strengthens blood vessel walls, forms scar tissue, matrix for bone growth), antioxidant, restores vita- min E to active form, hormone synthesis, supports immune cell functions, helps in absorption of iron

Defi ciency Disease Name Scurvy

Signifi cant Sources Citrus fruits, cabbage-type vegetables, dark green vegetables, cantaloupe, strawberries, peppers, lettuce, tomatoes, potatoes, papayas, mangoes

Defi ciency Symptoms Toxicity Symptoms

Digestive System Nausea, abdominal cramps, diarrhea, excessive urination

Immune System Immune suppression, fre- quent infections

Mouth, Gums, Tongue Bleeding gums, loosened teeth

Nervous/Muscular System

Muscle degeneration and pain, depression, disorientation

Headache, fatigue, insomnia

Skeletal System Bone fragility, joint pain Aggravation of gout

Skin Pinpoint hemorrhages, rough skin, blotchy bruises

Rashes

Other Failure of wounds to heal Interference with medical tests; kidney stones in susceptible people

262 chapter 7 T h e V i t a m i n s

THIAMIN

Other Names Vitamin B1

Chief Functions in the Body Part of a coenzyme needed in energy metabolism, supports normal appetite and nervous system function

Defi ciency Disease Name Beriberi (wet and dry)

Signifi cant Sources Occurs in all nutritious foods in moderate amounts; pork, ham, bacon, liver, whole and enriched grains, legumes, seeds

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Edema, enlarged heart, ab- normal heart rhythms, heart failure

(No symptoms reported)

Nervous/Muscular System

Degeneration, wasting, weakness, pain, apathy, irri- tability, diffi culty walking, loss of refl exes, mental confusion, paralysis

Other Anorexia; weight loss

RIBOFLAVIN

Other Names Vitamin B2

Chief Functions in the Body Part of a coenzyme needed in energy metabolism, supports normal vision and skin health

Defi ciency Disease Name Aribofl avinosis

Signifi cant Sources Milk, yogurt, cottage cheese, meat, liver, leafy green vegetables, whole-grain or enriched breads and cereals

Defi ciency Symptoms Toxicity Symptoms

Mouth, Gums, Tongue Cracks at corners of mouth,a

smooth magenta tongueb; sore throat

(No symptoms reported)

Nervous System and Eyes

Hypersensitivity to light, red- dening of cornea

Skin Skin rash

NIACIN

Other Names Nicotinic acid, nicotinamide, niacinamide, vitamin B3; precursor is dietary tryptophan

Chief Functions in the Body Part of coenzymes needed in energy metabolism

Defi ciency Disease Name Pellagra

Signifi cant Sources Synthesized from the amino acid tryp- tophan; milk, eggs, meat, poultry, fi sh, whole-grain and enriched breads and cereals, nuts, and all protein-containing foods

Defi ciency Symptoms Toxicity Symptoms

Digestive System Diarrhea; vomiting; abdomi- nal pain

Nausea, vomiting

Mouth, Gums, Tongue Black or bright red swollen smooth tongueb

Nervous System Irritability, loss of appetite, weakness, headache, diz- ziness, mental confusion progressing to psychosis or delirium

Skin Flaky skin rash on areas exposed to sun

Painful fl ush and rash, sweating

Other Liver damage; impaired glu- cose tolerance

aCracks at the corners of the mouth are termed cheilosis (kee-LOH-sis). bSmoothness of the tongue is caused by loss of its surface structures and is termed glossitis (gloss-EYE-tis).

Th e Water-Soluble Vitamins—Functions, Defi ciencies, and Toxicities (continued) table 7-7

263T h e B V i t a m i n s a s I n d i v i d u a l s

FOLATE

Other Names Folic acid, folacin, pteroyglutamic acid

Chief Functions in the Body Part of a coenzyme needed for new cell synthesis

Defi ciency Disease Name (No name)

Signifi cant Sources Asparagus, avocado, leafy green veg- etables, beets, legumes, seeds, liver, en- riched breads, cereal, pasta, and grains

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Anemia (large-cell type),a elevated homocysteine

Masks vitamin B12 defi ciency

Digestive System Heartburn, diarrhea, constipation

Immune System Suppression, frequent infections

Mouth, Gums, Tongue Smooth red tongueb

Increased risk of neural tube birth defects

Nervous System Depression, mental confu- sion, fatigue, irritability, headache

VITAMIN B12

Other Names Cyanocobalamin

Chief Functions in the Body Part of coenzymes needed in new cell synthesis, helps maintain nerve cells

Defi ciency Disease Name (No name)c

Signifi cant Sources Animal products (meat, fi sh, poultry, milk, cheese, eggs)

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Anemia (large-cell type)a (No toxicity symptoms known)

Mouth, Gums, Tongue Smooth tongueb

Nervous System Fatigue, nerve degeneration progressing to paralysis

Skin Tingling or numbness

VITAMIN B6

Other Names Pyridoxine, pyridoxal, pyridoxamine

Chief Functions in the Body Part of a coenzyme needed in amino acid and fatty acid metabolism, helps convert tryptophan to niacin and to serotonin, helps make red blood cells

Defi ciency Disease Name (No name)

Signifi cant Sources Meats, fi sh, poultry, liver, legumes, fruits, potatoes, whole grains, soy products

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Anemia (small-cell type)a Bloating

Nervous/Muscular System

Depression, confusion, abnormal brain wave pattern, convulsions

Depression, fatigue, impaired memory, irritability, head- aches, numbness, damage to nerves, diffi culty walking, loss of refl exes, restlessness, convulsions

Skin Rashes; greasy, scaly dermatitis

Skin lesions

aSmall-cell anemia is termed microcytic anemia; large-cell type is macrocytic or megaloblastic anemia. bSmoothness of the tongue is caused by loss of its surface structures and is termed glossitis (gloss-EYE-tis). cThe name pernicious anemia refers to the vitamin B12 defi ciency caused by lack of intrinsic factor, but not to that caused by inadequate dietary intake.

The Water-Soluble Vitamins—Functions, Deficiencies, and Toxicities (continued) table 7-7

264 chapter 7 T h e V i t a m i n s

PANTOTHENIC ACID

Other Names (None)

Chief Functions in the Body Part of a coenzyme needed in energy metabolism

Defi ciency Disease Name (No name)

Signifi cant Sources Widespread in foods

Defi ciency Symptoms Toxicity Symptoms

Digestive System Vomiting, intestinal distress Water retention (infrequent)

Nervous/Muscular System

Insomnia, fatigue

Other Hypoglycemia, increased sensitivity to insulin

BIOTIN

Other Names (None)

Chief Functions in the Body A cofactor for several enzymes needed in energy metabolism, fat synthesis, amino acid metabolism, and glycogen synthesis

Defi ciency Disease Name (No name)

Signifi cant Sources Widespread in foods

Defi ciency Symptoms Toxicity Symptoms

Blood/Circulatory System

Abnormal heart action (No toxicity symptoms reported)

Digestive System Loss of appetite, nausea

Nervous/Muscular System

Depression, muscle pain, weakness, fatigue, numb- ness of extremities

Skin Dry around eyes, nose, and mouth

Th e Water-Soluble Vitamins—Functions, Defi ciencies, and Toxicities (continued) table 7-7

food feature

On learning how important the vitamins are to their health, most people want to choose foods that are vitamin-rich. How can they tell which are which? Not by food labels—these are required to list only two of the vitamins—vitamin C and vitamin A—of a food’s contents. A way to fi nd out more about the vitamin contents of foods is to look down the columns of vitamins and calories in a table of food composition, such as Appendix A at the end of this book, to identify some of the vitamin-rich foods in your diet. If you are interested in folate, for instance, you can see that cornfl akes are an especially good source (folic acid is added to corn- fl akes), as is orange juice (folate occurs naturally in this food).

Another way of looking at such data appears in Figure 7-19—the long bars

Choosing Foods Rich in Vitamins LO 7.7

show some foods that are rich sources of a particular vitamin and the short or nonexistent bars indicate poor sources. The colors of the bars represent the vari- ous food groups.

WHICH FOODS SHOULD I CHOOSE? After looking at Figure 7-19, don’t think that you must memorize the richest sources of each vitamin and eat those foods daily. That false notion would lead you to limit your variety of foods while overemphasizing the components of a few foods. Although it is reassuring to know that your carrot-raisin salad at lunch provided more than your entire day’s need for vitamin A, it is a mistake to think that you must then select equally rich

sources of all the other vitamins. Such rich sources do not exist for many vitamins— rather, foods work in harmony to provide most nutrients. For example, a baked po- tato, not a star performer among vitamin C providers, contributes substantially to a day’s need for this nutrient and contrib- utes some thiamin, too. By the end of the day, assuming that your food choices were made with reasonable care, the bits of thiamin, vitamin B6, and vitamin C from each serving of food have accumulated to make a more-than-adequate total diet.

A VARIETY OF FOODS WORKS BEST With a few exceptions, nutritious foods provide small quantities of thiamin, as shown in Figure 7-19. Members of the

265T h e B V i t a m i n s a s I n d i v i d u a l s

well, but its high fat and calorie contents call for moderation in its use.

The vitamin B6 data provide another in- sight to support the argument for variety. From just the few foods listed here, you can see that no one source can provide

good, low-fat sources, and they provide benefi cial fi ber and nutrients lacking from meats. Beans lack the vitamin B12 pro- vided by meats, however. Peanut butter is a good source of thiamin, and of most other B vitamins (except vitamin B12) as

pork family are an exceptionally good thiamin source with one small pork chop (275 calories) providing over half of the Daily Value for thiamin—but again, this does not suggest that you eat pork every day. Legumes and grains are also

Food Amount (Energy) g

VITAMIN A

Beef liver 3 oz fried (184 cal)

Sweet potato 1 whole boiled (159 cal)

Carrots 1/2 c boiled (35 cal)

Cantaloupe 1/2 melon (97 cal)

Spinach 1/2 c boiled (21 cal)

Butternut squash 1/2 c baked (41 cal)

Milk, fat-free 1 c (85 cal)

Tomatoes 1/2 c boiled (33 cal)

Peach

Orange juice

1 fresh medium (42 cal)

1 c (fresh)

Summer squash 1/2 c boiled (18 cal)

Apple 1 fresh medium (81 cal)

Sirloin steak 3 oz lean (171 cal)

Whole-wheat bread 1 slice (70 cal)

Baked potato 1 whole (220 cal)

mg VITAMIN E

Sunflower seeds 2 tbs dry (103 cal)

Sunflower seed oil 1 tbs (124 cal)

Wheat germ 1 oz (117 cal)

Safflower oil 1 tbs (124 cal)

Cottonseed oil 1 tbs (124 cal)

Peanuts 1 oz dry roasted (166 cal)

Corn oil 1 tbs (124 cal)

Peanut butter 2 tbs (190 cal)

Canola oil 1 tbs (124 cal)

Shrimp 3 oz boiled (84 cal)

Parsley 1/2 c fresh chopped (11 cal)

Apple 1 fresh medium (81 cal)

Sweet potato 1 baked (117 cal)

Cheddar cheese 11/2 oz (170 cal)

Whole-wheat bread 1 slice (70 cal)

mgTHIAMIN

Pork chop 3 oz broiled (275 cal)

Black beans 1 c cooked (228 cal)

Sunflower seeds 2 tbs dry (103 cal)

Watermelon 1 slice (91 cal)

Green peas 1/2 c cooked (67 cal)

Orange juice 3/4 c fresh (84 cal)

Oysters 5 oysters simmered (125 cal)

Oatmeal 1/2 c cooked (73 cal)

Sirloin steak 3 oz lean (171 cal)

Whole-wheat bread 1 slice (70 cal)

Milk, fat-free 1 c (85 cal)

Cabbage 1/2 c cooked (33 cal)

Summer squash 1/2 c cooked (18 cal)

Apple 1 fresh medium (81 cal)

Cheddar cheese 11/2 oz (170 cal)

Daily Value (30 IU, or 20 mg) 50% 100%

50% 100%

Daily Value (1.5 mg) 50% 100%

THIAMIN The mix of colors in this table’s bars shows that many kinds of foods supply some thiamin, but few are rich sources. Together, a day’s nutrient-dense foods helps supply the needed amounts of thiamin.

VITAMIN E Orange and blue bars show that vegetable oils and nuts are good sources of vitamin E.

= Milk and milk products = Meats = Vegetables = Fruits = Legumes, nuts, seeds = Grains = Miscellaneous

VITAMIN A The abundant green bars indicate that vegetables are rich sources of vitamin A in the form of beta-carotene. The top sources supply much more than the Daily Value in a single serving.

9,092

1,287

957

860

369

361

161

0.98

0.42

0.41

0.23

0.17

0.16

0.13

0.11

0.10

0.09

0.04

0.02

9.6

6.5

6.0

5.0

3.0

2.9

1.0

0.4

0.3

0.2

0.0

Daily Value (900 μg)

Food Sources of Vitamins Selected to Show a Range of Values figure 7-19

266 chapter 7 T h e V i t a m i n s

These nutrients are both richly supplied by fruits and vegetables. The richest source of either may be only a moder- ate source of the other, but the recom-

and fruits consumed throughout the day work together to supply it.

The last two graphs of Figure 7-19 show sources of folate and vitamin C.

the whole day’s requirement for vitamin B6, but that many small servings of a variety of meats, fi sh, and poultry along with potatoes and a few other vegetables

Food Amount (Energy) mgVITAMIN B6

Baked potato 1 whole (220 cal)

Banana 1 peeled (109 cal)

Turkey breast 3 oz (133 cal)

Watermelon 1 slice (91 cal)

Sirloin steak 3 oz lean (171 cal)

Pork roast 3 oz lean (175 cal)

Spinach 1/2 c cooked (21 cal)

Salmon 3 oz broiled/baked (183 cal)

Navy beans 1/2 c cooked (129 cal)

Broccoli 1/2 c cooked (22 cal)

Milk, fat-free 1 c (85 cal)

Orange juice 3/4 c fresh (84 cal)

Apple 1 fresh medium (81 cal)

Summer squash 1/2 c boiled (18 cal)

Whole-wheat bread 1 slice (69 cal)

Cheddar cheese 11/2 oz (170 cal)

gFOLATE

Beef liver 3 oz fried (184 cal)

Spinach 1/2 c cooked (21 cal)

Asparagus 4 spears cooked (14 cal)

Turnip greens 1/2 c cooked (15 cal)

Winter squash 1/2 c cooked (48 cal)

Beets 1/2 c cooked (37 cal)

Orange juice 3/4 c fresh (84 cal)

Cantaloupe 1/2 melon (97 cal)

Broccoli 1/2 c cooked (22 cal)

Lima beans 1/2 c cooked (85 cal)

Summer squash 1/2 c cooked (18 cal)

Whole-wheat breada 1 slice (70 cal)

Milk, fat-free 1 c (85 cal)

Sirloin steak 3 oz lean (171 cal)

Cheddar cheese 11/2 oz (170 cal)

Apple 1 fresh medium (81 cal)

mg VITAMIN C

Cantaloupe 1/2 melon (97 cal)

Orange juice 3/4 c fresh (84 cal)

Green peppers 1/2 c (20 cal)

Broccoli 1/2 c cooked (26 cal)

Brussels sprouts 1/2 c cooked (30 cal)

Tomato juice 3/4 c canned (31 cal)

Baked potato 1 whole (220 cal)

Cabbage 1/2 c cooked (17 cal)

Apple 1 fresh medium (81 cal)

Oysters 3 oz (69 cal)

Milk, fat-free 1 c (85 cal)

Whole-wheat bread 1 slice (69 cal)

Sirloin steak 3 oz lean (171 cal)

Cheddar cheese

a Unenriched.

1 oz (170 cal)

Daily Value (400 μg) 50% 100%

Daily Value (60 mg) 50% 100%

Daily Value (2.0 mg) 50% 100%

VITAMIN B6 The array of color bars here show that many types of foods contribute some vitamin B6. Variety best meets the need.

FOLATE Green bars show that vegetables, especially green leafy vegetables, are good sources of folate. Liver is the only folate-rich meat. One serving of these provides substantial folate; certain other foods donate smaller amounts; many foods provide almost no folate.

VITAMIN C Fruits (purple) and vegetables (green) head the list. One serving of any of the top suppliers exceeds the Daily Value; meeting vitamin C needs without fruits and vegetables is almost impossible.

= Milk and milk products = Meats = Vegetables = Fruits = Legumes, nuts, seeds = Grains = Miscellaneous

0.70

0.68

0.46

0.41

0.38

0.29

0.22

0.19

0.15

0.11

0.10

0.08

0.07

0.06

0.05

0.03

185

131

116

Food Sources of Vitamins Selected to Show a Range of Values (continued) figure 7-19

267T h e B V i t a m i n s a s I n d i v i d u a l s

aim for a diet that meets the recommen- dations of Chapter 2. Even supplements cannot duplicate the benefi ts of such a diet, a point made in this chapter’s Controversy section.

ing nutrients includes a wide variety of whole foods and it provides more than just isolated nutrients.94 Phytochemi- cals are widespread among fruits and vegetables, and may play roles in human health, as does fi ber and other constitu- ents of whole foods. When aiming for adequate intakes of vitamins, therefore,

mended amounts of fruits and vegetables in the USDA Food Guide of Chapter 2 cover both needs amply. As for vitamin E, vegetable oils and some seeds and nuts are the richest sources, and vegetables and fruits contribute a little, too.

By now, you should recognize a pat- tern in nutrition. The diet best for provid-

Analyze Your Vitamin Intake The purpose of this exercise is to help you identify your food sources of water- soluble and fat-soluble vitamins. Many foods rich in vitamins work in harmony to provide a full complement of nutri- ents, which ultimately contributes to a health-promoting diet.

Determine whether your food pro-1. vides enough vitamins. From the Reports tab, select Intake vs. Goals. Choose Day Two, all meals. Gener- ate a report. Did your actual intakes on that day meet your DRI recom- mended intake values for vitamins? If not, list the vitamins which have not met the DRI goals. Did your intakes exceed any DRI values? If so, list them.

Some fruits and vegetables are good 2. sources of fat-soluble vitamins (see the Snapshots on pages 233, 238,

240, and 242). From the Reports tab, select MyPyramid Analysis and include all meals. Generate a report. Have you met your minimum recom- mended fruit and vegetable intake? What percentage of your goal have you met for fruits and vegetables? Did you consume any fruits and veg- etables listed in the Snapshots for the fat-soluble vitamins? Which ones?

From the Reports tab, select Source 3. Analysis, choose any day, and include all meals. From the drop- down box, select vitamin C, then folate, and generate a report for each vitamin. What is your best food source for vitamin C? And for folate? Were your best sources shown in the Snapshots on pages 247 and 255?

After viewing the Intake vs. Goals 4. report in question 1, if you fell short on any vitamin, what foods could you

add to your diet that would bring you up to the DRI recommended intake value? If you exceeded the DRI val- ues, which foods were responsible?

The MyPyramid patterns suggest 5. that a person who requires 2,000 cal- ories per day should aim to consume 3 cups of a variety of dark green, 2 cups of orange, 3 cups of starchy, and 6.5 cups of other vegetables each week. Create a dish from vegetables or fruits that you enjoy. Get some ideas by using Figure 7-19 (pages 265–266). From the Track Diet tab, select Source Analysis, and select one water-soluble, then one fat-soluble vitamin from the drop- down menu. Generate a report for each. Identify the vitamin-rich foods from the report. What does the bar graph show?

Concepts in Action

To fi nd additional quiz questions, view videos and animations, and explore interactive exercises, go to www.cengage.com/sso.

Search for information on individual vitamins at www .healthfi nder.gov.

Visit the World Health Organization to learn more about “vita- min defi ciencies” around the world: www.who.int.

Learn more about dietary supplements as well as individual vitamins and minerals at www.fda.gov.

Under Browse by Subject, select Dietary Supplements at www.nutrition.gov.

Search for information about herbal dietary supplements, vita- mins, and minerals at www.nlm.nih.gov/medlineplus.

media menu

http://www.cengage.com/sso

http://www.who.int

http://www.fda.gov

http://www.nutrition.gov

http://www.nlm.nih.gov/medlineplus

268 chapter 7 T h e V i t a m i n s

Answers to these Self Check questions are in Appendix G.

Which of the following vitamins are classifi ed as fat-soluble?1.

vitamins B, DA.

vitamins A, D, E, and KB.

vitamins B, E, D, and CC.

vitamins B and CD.

Night blindness and xerophthalmia are the result of a defi -2. ciency of which vitamin?

niacinA.

vitamin CB.

vitamin AC.

vitamin KD.

Which of the following foods is (are) rich in beta-carotene?3.

sweet potatoesA.

pumpkinB.

spinachC.

all of the aboveD.

A defi ciency of niacin may result in which disease?4.

pellagraA.

beriberiB.

scurvyC.

ricketsD.

Which of the following describes the fat-soluble vitamins?5.

vitamins B and CA.

easily absorbed and excretedB.

stored extensively in tissuesC.

(a) and (c)D.

Which vitamin(s) is (are) present only in foods of animal 6. origin?

the active form of vitamin AA.

vitamin BB. 12

ribofl avinC.

(a) and (b)D.

The theory that vitamin C prevents or cures colds is well 7. supported by research. T F

Xerophthalmia results from advanced vitamin A defi ciency 8. and can lead to permanent blindness. T F

Vitamin D functions as a hormone to help maintain bone 9. integrity. T F

Vitamin A supplements can help treat acne.10. T F

self check

269controversy 7 V i t a m i n S u p p l e m e n t s : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

CONTROVERSY

At least half of the U.S. population dose themselves with dietary supplements, spending tens of billions of dollars a year to do so.1* Most take a daily multivitamin and mineral pill to make up for dietary shortfalls. Some take single nutrient supplements to ward off diseases.2 Do people need these supplements? Which ones prevent diseases? Is someone ensuring their safety? Finally, if people do need supplements, which ones are best? This Controversy examines evidence sur- rounding these questions and concludes with some advice for those choosing to take a supplement.

ARGUMENTS IN FAVOR OF TAKING SUPPLEMENTS Indisputably, the people listed in Table C7-1 need supplements. For them, nutri- ent supplements can prevent or reverse illnesses. Because supplements are not risk-free, these people should consult a health-care provider who is alert to po- tential adverse effects and nutrient–drug interactions.3

People with Defi ciencies In the United States and Canada, few adults suffer nutrient defi ciency diseases such as scurvy, pellagra, and beriberi but the conditions still occasionally occur, as

the preceding chapter made clear. When they do, prescribed supplements of the missing nutrients quickly stop or reverse most defi ciency diseases (exceptions include vitamin A–defi ciency blindness, some vitamin B12–defi ciency nerve dam- age, and birth defects caused by folate defi ciency in pregnant women).

People with Increased Nutrient Needs Nutrient needs increase during certain stages of life, and many people fi nd it diffi cult or impossible to meet some of those needs without supplements. For example, women who lose a lot of blood and therefore a lot of iron during

Vitamin Supplements: Do the Benefi ts Outweigh the Risks?

LO 7.8, 7.9

Which is the best source of vitamins to support good health: supplements or food?

C hr

is te

l R os

en fe

ld /S

to ne

/G et

ty Im

ag es

om C

ar te

r/P ho

to E

di t

These People May Need Supplements:

People with nutrient defi ciencies.• Women in their childbearing years (supplemental or enrichment sources of folic acid • are recommended to reduce risk of neural tube defects in infants). Pregnant or lactating women (they may need iron and folate).• Newborns (they are routinely given a vitamin K dose).• Infants (they may need various supplements, see Chapter 13).• Those who are lactose intolerant (they need calcium to forestall osteoporosis).• Habitual dieters (they may eat insuffi cient food).• Elderly people often benefi t from some of the vitamins and minerals in a balanced • supplement (they may choose poor diets, have trouble chewing, or absorb or metabo- lize nutrients less effi ciently; see Chapter 14). Victims of AIDS or other wasting illnesses (they lose nutrients faster than foods can • supply them). Those addicted to drugs or alcohol (they absorb fewer and excrete more nutrients; • nutrients cannot undo damage from drugs or alcohol). Those recovering from surgery, burns, injury, or illness (they need extra nutrients to help • regenerate tissues). Strict vegetarians (they may need vitamin B• 12, vitamin D, iron, and zinc). People taking medications that interfere with the body’s use of nutrients.•

Some Valid Reasons for Taking Supplements table C7-1

*Reference notes are found in Appendix F.

270 chapter 7 T h e V i t a m i n s

toxic heavy metals, bacteria, and other substances have also shown up in a wide variety of dietary supplements. Even some children’s chewable vitamins have contained appreciable lead, a de- structive heavy metal that harms young children.11 While hazardous products are quickly removed from the market upon discovery, many others remain on store shelves because current regulations make the supplement market diffi cult to monitor and control.12 Plain multivitamin and mineral supplements from reputable sources, without herbs or add-ons, often test free from contamination.

Life-Threatening Misinformation Another problem arises when people who are ill come to believe that self- prescribed high doses of vitamins or minerals can be therapeutic. For ex- ample, a man who suffered from mental illness arrived at an emergency room with dangerously low blood pressure.13 He had ingested 11 grams of niacin on the advice of an Internet website that falsely touted niacin as an effective therapy for schizophrenia. The DRI sets a Tolerable Upper Intake Level for niacin at 35 milligrams.

Supplements are rarely effective for purposes other than those already listed in Table C7-1. This doesn’t stop mar- keters from making enticing claims in materials of all kinds—in print, on labels, and on television or the Internet. These claims often fall far short of the FDA standard that claims should be “truthful and not misleading.”

Unknown Needs Another argument against the use of supplements is that no one knows exactly how to formulate the “ideal” supplement. What nutrients should be included? Which, if any, of the phyto- chemicals should be included? How much of each? On whose needs should the choices be based? Surveys have repeatedly shown that the nutrients in the supplements people take are ones that they do not actually need. Most people taking vitamins or minerals in supplements already receive those nu- trients from food, while people with low nutrient intakes rarely take supplements at all.

People’s tolerances for high doses of nu- trients vary, just as their risks of defi cien- cies do, and amounts tolerable for some may be harmful for others. No one knows who falls where along the spectrum, so determining just how much of a nutrient is enough—or too much—for a particular person is diffi cult. The Tolerable Upper Intake Levels of the DRI defi ne the high- est amount that appears safe for most healthy people. A few sensitive people may experience toxicities at lower doses, however. Table C7-2 presents these suggested Upper Levels for selected vitamins and minerals and also lists nutri- ent doses in typical supplements.

Toxicity Supplement users are more likely to have excessive intakes of certain nutrients— notably iron, zinc, vitamin A, and niacin.7 The true extent of supplement toxicity in this country is unknown, but many ad- verse events are reported each year from vitamins, minerals, essential oils, herbs, and other supplements.8 Reported toxicities may greatly underestimate the true occurrence because only an alert health-care professional knowledgeable in nutrition can reliably recognize nutrient toxicity and report it to the Food and Drug Administration (FDA). A chronic, subtle toxicity that progresses slowly of- ten goes unrecognized and unreported.

Toxic overdoses of vitamins and miner- als in children are more readily recog- nized and, unfortunately, fairly common.9 Fruit-fl avored, chewable vitamins shaped like cartoon characters entice youngsters to eat them like candy, thus poison- ing themselves.10 High-potency iron supplements have been known to cause accidental poisoning deaths among children, and even mild iron overdoses cause nausea and black diarrhea that refl ects internal bleeding. Some authori- ties suggest that supplements should bear labels to warn consumers of their potential for harm.

Supplement Contamination The U.S. Food and Drug Administra- tion recently identifi ed over 140 dietary supplements sold on the U.S. market that were contaminated with pharmaceu- tical drugs, such as steroid hormones and stimulants. Toxic plant material,

menstruation each month may need an iron supplement. In women of child- bearing age, supplements of folic acid reduce the risks of neural tube defects.4 Similarly, pregnant and breastfeeding women have exceptionally high nutrient needs and often must rely on special supplements to meet them. Even new- borns require a dose of vitamin K at birth, as the preceding chapter pointed out. (Details about nutrient needs through life are found in Chapters 13 and 14.)

People with Low Nutrient Status Subtle borderline defi ciencies that do not cause classic symptoms are easily overlooked or misdiagnosed—and they often occur. People who diet habitually or elderly people with diminished appetite may eat so little nutritious food that they teeter on the edge of defi ciency, with no reserve to handle any increase in de- mand.5 Similarly, people who omit entire food groups without planning to replace the missing nutrients will fail to meet nutrient needs; people who are too busy, lack knowledge, lack money, or for any reason fail to obtain the nutritious foods they need also fail to meet their needs.6 If correcting nutrient shortfalls with nutri- tious food is not feasible, then vitamin- mineral supplements can help prevent the worst of the defi ciency diseases they might otherwise face.

People Coping with Physical Stress Any interference with a person’s appe- tite, ability to eat, or ability to absorb or use nutrients will impair nutrient status. Prolonged illnesses, extensive injuries, surgery, and addictions to alcohol or other drugs all have these effects, and such stressors increase nutrient require- ments of the tissues, too. In addition, medications used to treat such condi- tions often increase nutrient needs further or impair their absorption or use by the body. In all these cases, supple- ments are appropriate.

ARGUMENTS AGAINST TAKING SUPPLEMENTS Foods rarely cause nutrient imbalances or toxicities, but supplements easily can. The higher the dose, the greater the risk.

271controversy 7 V i t a m i n S u p p l e m e n t s : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

per and calcium absorption, iron hinders zinc absorption, and calcium hinders magnesium and iron absorption. Among vitamins, vitamin C supplements en- hance iron absorption, making iron over- load likely in susceptible people. High doses of vitamin E interfere with vitamin K functions, delaying blood clotting and possibly raising the risk of brain hemor- rhage (a form of stroke).15 The vitamin A precursor beta-carotene interferes with vitamin E metabolism. These and other interactions present drawbacks to supplement use.

Whole Foods Are Best for Nutrients In general, the body absorbs nutrients best from foods that dilute and dis- perse them among other substances to facilitate their absorption and use by the body.14 Taken in pure, concentrated form, nutrients are likely to interfere with one another’s absorption or with the absorption of other nutrients from foods eaten at the same time. Such effects are particularly well known among the minerals. For example, zinc hinders cop-

False Sense of Security Another argument against supplement use is that it may lull people into a false sense of security. A person might eat irresponsibly, thinking, “My supplement will cover my needs.” Or, experiencing a warning symptom of a disease, a person might postpone seeking a diagnosis, thinking, “I probably just need a supple- ment to make this go away.” Such self-diagnosis can postpone effective medical treatment and give their disease a chance to worsen.

Tolerable Upper Nutrient Intake Levelsa Daily Values

Typical Multivitamin-Mineral

Supplement

Average Single-Nutrient

Supplement

Vitamins

Vitamin A 3,000 µg (10,000 IU) 5,000 IU 5,000 IU 8,000 to 10,000 IU

Vitamin D 50 µg (2,000 IU) 400 IU 400 IU 400 IU

Vitamin E 1,000 mg (1,500 to 2,200 IU)b 30 IU 30 IU 100 to 1,000 IU

Vitamin K —c 80 µg 40 µg —e

Thiamin —c 1.5 mg 1.5 mg 50 mg

Ribofl avin —c 1.7 mg 1.7 mg 25 mg

Niacin (as niacinamide) 35 mgb 20 mg 20 mg 100 to 500 mg

Vitamin B6 100 mg 2 mg 2 mg 100 to 200 mg

Folate 1,000 µgb 400 µg 400 µg 400 µg

Vitamin B12 —c 6 µg 6 µg 100 to 1,000 µg

Pantothenic acid —c 10 mg 10 mg 100 to 500 mg

Biotin —c 300 µg 30 µg 300 to 600 µg

Vitamin C 2,000 mg 60 mg 10 mg 500 to 2,000 mg

Choline 3,500 mg — 10 mg 250 mg

Minerals

Calcium 2,500 mg 1,000 mg 160 mg 250 to 600 mg

Phosphorus 4,000 mg 1,000 mg 110 mg —e

Magnesium 350 mgd 400 mg 100 mg 250 mg

Iron 45 mg 18 mg 18 mg 18 to 30 mg

Zinc 40 mg 15 mg 15 mg 10 to 100 mg

Iodine 1,100 µg 150 µg 150 µg —e

Selenium 400 µg 70 µg 10 µg 50 to 200 µg

Fluoride 10 mg — — —e

Copper 10 mg 2 mg 0.5 mg —e

Manganese 11 mg 2 mg 5 mg —e

Chromium —c 120 µg 25 µg 200 to 400 µg

Molybdenum 2,000 µg 75 µg 25 µg —e

aUnless otherwise noted, Upper Levels represent total intakes from food, water, and supplements. bUpper Levels represent intakes from supplements, fortifi ed foods, or both. cThese nutrients have been evaluated by the DRI Committee for Tolerable Upper Intake Levels, but none were established because of insuffi cient data. No adverse effects have been reported with intakes of these nutrients at levels typical of supplements, but caution is still advised, given the potential for harm that accompanies excessive intakes. dUpper Levels represent intakes from supplements only. eAvailable as a single supplement by prescription.

Intake Guidelines (Adults) and Nutrient Supplement Values table C7-2

272 chapter 7 T h e V i t a m i n s

evidence exists to suggest that the same is true in people.

Vitamin C: Intervention Studies Population studies, animal studies, and cell studies of the type just discussed lack the power to state conclusively whether a nutrient may affect the health of human beings. To follow up these forms of evidence, researchers must give supplements to a group of people and then compare their rates of chronic dis- eases with those of others who received a placebo. Such studies indicate no effect of vitamin C and other antioxidant nutrients on chronic diseases.22

The results are different for one group, however. People who test low for blood levels of antioxidant nutrients and who then consume foods that supply the missing nutrients often resist chronic diseases better than people whose defi ciencies go untreated. People eat- ing diets low in fruits and vegetables that supply the antioxidant nutrients are clearly more likely to suffer chronic dis- eases, but whether this effect is caused by a lack of antioxidant nutrients, a lack of phytochemicals, or a combination of other lifestyle choices that may accom- pany such diets is unknown.23

Vitamin E Supplements and Heart Disease In the past decade, much scientifi c re- search has focused on vitamin E supple- ments in the hope of fi nding an acces- sible, safe agent to reduce heart disease risks. Early studies seemed promising: people who reported taking vitamin E supplements were observed to have lower rates of death from heart disease than others.24 In laboratory studies, vitamin E opposes oxidation of blood lipids (LDL), tissue infl ammation, injury to arteries, and blood clotting. In principle, it makes sense that vitamin E might reduce disease risks.

With these clues in hand, researchers undertook the fi nal studies needed to establish or refute the idea that vitamin E supplements prevent heart disease: controlled clinical human trials involving thousands of people, some of whom agreed to take a supplement, and some to take a placebo. After years of record- ing health data, scientists found no pro- tective effect from vitamin E supplements

example, people consuming a diet low in vitamin C can silently incur an increase in oxidative stress in the tissues long before the symptoms of scurvy appear.16

Convincing evidence exists linking high intakes of antioxidant-rich fruits and vegetables with good health and disease prevention (see Chapter 11).17 Results from epidemiological studies draw the link to human health, while cell and animal studies demonstrate that reduced oxidative stress is a plausible mecha- nism. In our vitamin C example, at nor- mal doses from foods, vitamin C clearly acts as an antioxidant in the tissues.

Logically, it might seem that higher vitamin C doses might offer even greater protection.18 However, such a ben- efi t is not observed when mice receive supplemental vitamin C throughout their lives. The presence of surplus vitamin C causes the animals’ tissues to compen- sate by reducing their production of their own native antioxidant enzymes.19 In human research, lower levels of native antioxidant enzymes correlate with el- evated risk of heart disease.20 In the end, no net reduction in oxidative damage is gained by regular supplementation with vitamin C, and supplements may lower native antioxidant protection.

The preceding chapter mentioned that acute, high doses of vitamin C act as a prooxidant, generating free radicals. This action sounds destructive, but it may not be entirely detrimental: research suggests that free radicals from pharma- ceutical doses of vitamin C, administered under controlled conditions, may help to destroy cancer cells in mice.21 No

CAN SUPPLEMENTS PREVENT HEART DISEASE OR CANCER? Many people take supplements, and antioxidant supplements in particular, in the belief that antioxidant nutrients can prevent heart disease and cancer. Can taking a supplement prevent these killers?

Oxidative Stress, Marginal Defi ciencies, and Chronic Diseases Central to the idea that antioxidant nu- trients might fi ght diseases is the theory of oxidative stress (terms are defi ned in Table C7-3). Body cells use oxygen to produce energy, and in this and other processes, they produce free radicals (highly unstable molecules of oxygen). Oxidative stress results when free-radical activity in the body exceeds its antioxi- dant defenses. Then, a destructive chain reaction of oxidation damages cellular lipids, DNA, LDL cholesterol, and other structures. When such damage accumu- lates, this triggers infl ammation, which may lead to heart disease and cancer, among other conditions. Antioxidant nu- trients help to quench these free radicals, rendering them harmless to cellular struc- tures and stopping the chain of events.

Vitamin C: Population, Animal, and Cell Studies According to the theory, even subclinical defi ciencies with no observable defi - ciency symptoms can allow free-radical damage to accumulate in the tissues. For

antioxidant nutrients • vitamins and minerals that oppose the effects of oxidants on human physical functions. The antioxidant vitamins are vitamin E, vitamin C, and beta- carotene. The mineral selenium also participates in antioxidant activities. electrons • parts of an atom; negatively charged particles. Stable atoms (and mol- ecules, which are made of atoms) have even numbers of electrons in pairs. An atom or molecule with an unpaired electron is an unstable free radical. oxidants • compounds (such as oxygen itself) that oxidize other compounds. Com- pounds that prevent oxidation are called antioxidants, whereas those that promote it are called prooxidants (anti means “against”; pro means “for”). oxidative stress • damage infl icted on living systems by free radicals. subclinical, • or marginal, defi ciency a nutrient defi ciency that has no outward clini- cal symptoms. The term is often used to market unneeded nutrient supplements to consumers.

Antioxidant Terms table C7-3

273controversy 7 V i t a m i n S u p p l e m e n t s : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

Ordinary doses (400 IU) of vitamin E • taken daily may slightly increase the risk of death from all causes.34

Supplements of vitamin A, vitamin • E, beta-carotene, or combinations produce no benefi t and may increase mortality.35

Vitamin C supplements may • increase markers of oxidation in the blood or the risk of cataracts in the eyes.36

High doses of vitamin C taken by • women with diabetes may increase their likelihood of dying of cardio- vascular disease.37

Biotin-supplemented cell cultures suf-• fer DNA damage of a type related to cancer formation.38

Daily supplements of beta-carotene • may increase lung cancer in smokers or in people exposed to asbestos.

Vitamin A supplements reliably and • quickly produce liver injury at doses greater than 10,000 micrograms, but liver problems can appear with much lower doses taken regularly over many years.

Vitamin A intakes of only about twice • the DRI taken over years are as- sociated with osteoporosis and hip fractures.39

Supplements of vitamin D and many • minerals can be toxic in large doses.

For most people, foods, not supple- ments, are the best sources of nutrients. While an orange and a pill may both contain vitamin C, the orange presents a balanced array of nutrients, phytochemi- cals, and fi ber that modulate vitamin C’s effects. The pill provides only vitamin C, a lone chemical. However, most people can safely consume an ordinary daily multiple vitamin and mineral supplement, when they follow the directions.40 And for those who need them, nutrient supple- ments constitute a modern-day miracle.

SELECTION OF A MULTINUTRIENT SUPPLEMENT If you fall into one of the categories listed earlier in Table C7-1 and if you absolutely cannot meet your nutrient needs from foods, a supplement containing nutrients

The unscientifi c-minded may fi nd such research reversals frustrating or shocking, but scientists expect them as research unfolds. In this case, scientists have rediscovered a long-known basic nutrition principle: lower disease risks follow a diet of nutritious whole foods that presents a balance of nutrients to the body.

SUPPLEMENTS MUST BE SAFE, OR THE GOVERNMENT WOULD NOT ALLOW THEIR SALE, RIGHT? The spectacular fall from favor of anti- oxidant supplements reinforces the prin- ciple that consumers who take needless supplements are at best wasting money, or at worst risking their health. Many con- sumers wrongly believe that government scientists, in particular those of the Food and Drug Administration (FDA), test each new dietary supplement (see Table C7-4) to ensure their safety and effective- ness before allowing it on the market.

Under current law, the FDA is re- sponsible only for taking action against unsafe dietary supplements already on the market. No advance registration or approval by the FDA is needed before a manufacturer can put a supplement on store shelves.32 To act against unsafe supplements, the FDA must receive manufacturers’ reports concerning seri- ous adverse health effects reported to them by consumers.33 Manufacturers do list contact information on supplement labels for this purpose, but many symp- toms of adverse reactions are easily mistaken for something else—stomach fl u or headache or fatigue. Consumers can also report adverse reactions directly to the FDA via its hotline or website, but few people know how to do so.†

WHAT ARE THE RISKS OF TAKING NUTRIENT SUPPLEMENTS? Supplements of single nutrients may en- danger the taker’s health in these ways:

against heart attack incidence, hospi- talization, or death from heart failure.25 In fact, when results from high-quality studies were pooled, a slight but alarm- ing increased risk for death emerged for people taking vitamin E supplements.26

Such studies have been criticized for testing too low a dose or failing to account for differences such as illness, ra- diation exposure, or smoking—conditions that create excess free radicals.27 Some people’s genetic makeup causes their tissues to produce more free radicals, and this reduces vitamin E in their tissues; such people may benefi t from vitamin E supplements.28 Also, the fact that most people in the United States fail to obtain enough vitamin E in the diet causes some to conclude that supplements may be benefi cial.29 New investigations in the fi eld of nutritional genomics may soon provide more clarity about whether some individu- als may benefi t from extra vitamin E.

The Story of Beta-Carotene It is well known that people whose diets are rich in fruits and vegetables have low rates of many cancers, and this is particularly true for beta-carotene. Based on such evidence, the popular media hailed beta-carotene as a powerful anticancer substance and consumers eagerly bought and took beta-carotene supplements.

A sudden reversal crumbled the beta- carotene theory overnight. Not only did the early results from controlled clinical human trials reveal no benefi t from beta- carotene, but major clinical trials around the world were abruptly stopped upon fi nding a 28 percent increase in lung can- cer among smokers taking beta-carotene compared with placebos. Supplements of another common carotenoid, lutein, may also raise lung cancer risk, along with supplements of vitamin A itself.30 Evidence is mixed on whether smokers may be at particular risk in this regard.

Three mechanisms have been pro- posed to explain these connections. Carotenoid supplements may increase DNA damage by free radicals, they may interfere with other micronutrients, or they may interfere with the benefi cial produc- tion of reactive oxygen species needed by the healthy immune defenses that kill cancer cells.31

†Consumers should report suspected harm from dietary supplements to their health providers or to the FDA’s MedWatch program at (800) FDA-1088 or on the Internet at www.fda.gov/medwatch/.

http://www.fda.gov/medwatch/

274 chapter 7 T h e V i t a m i n s

vanced formula,” “Maximum power,” and the like. Avoid “extras” such as herbs (see Chapter 11). And don’t be misled into buying and taking unneeded supple- ments, because none are risk-free (Table C7-5 provides some invalid reasons for taking supplements in which the risks clearly outweigh the benefi ts).

Reading the Label Now all you have left is the Supplement Facts panel that lists the nutrients, a list of ingredients, the form of the supplement, and the price—the plain facts. You have two basic questions to answer. The fi rst question: What form do you want—chew- able, liquid, or pills? If you’d rather drink your vitamins and minerals than chew them, fi ne. If you choose a fortifi ed liquid meal replacer or “energy bar” (a candy bar to which vitamins and other nutrients are added), you must then proportion- ately reduce the calories you consume as food, or you may gain unwanted weight. If you choose chewable pills, be aware that vitamin C can erode tooth enamel. Swallow promptly and fl ush the teeth with a drink of water. Avoid vitamin-fortifi ed bubble gum to protect both the teeth and gum-loving children who may chew a whole boxful and receive too large a dose for their small bodies.

Targeting Your Needs The second question: Who are you? What vitamins and minerals do you actually need? Compare the DRI nutrient intake recommendations listed for your age and gender (the tables are on the in- side front cover, page B) with the supple-

vitamin supplements often approach the realm of quackery because the profi ts are high and the industry is largely free of oversight. To escape the clutches of the health hustlers, use your imagination and delete the picture on the label of sexy people on the beach and the meaning- less, glittering generalities stating “Ad-

only, with no added extras such as herbs, can prevent serious problems. In these cases, the benefi ts probably outweigh the risks.

Choosing a Type Which supplement to choose? The fi rst step is to remain aware that sales of

aristolochic acid • a Chinese herb ingredient known to attack the kidneys and to cause cancer; U.S. consumers have required kidney transplants and must take lifelong anti- rejection medication after use. Banned by the FDA but available in supplements sold on the Internet. coenzyme Q-10 • an enzyme made by cells and important for its role in energy me- tabolism. With diminished coenzyme Q-10 function, oxidative stress increases, as may occur in aging. Preliminary research suggests that it may be of value for treating certain conditions; toxicity in animals appears to be low. No safe intake levels for human be- ings have been established. DHEA• a a hormone secretion of the adrenal gland whose level falls with advancing age. DHEA may protect antioxidant nutrients. Real DHEA is available only by prescription; the herbal DHEA imitator for sale in health-food stores is not active in the body. No safety information exists for either. dietary supplement • a product, other than tobacco, that is added to the diet and contains one of the following ingredients: a vitamin, mineral, herb, botanical (plant ex- tract), amino acid, metabolite, constituent, or extract, or a combination of any of these ingredients. ephedrine • one of a group of compounds with dangerous amphetamine-like stimulant effects; extracted from the herb ma huang and recently banned by the FDA but still available from Internet sources. The most severe reported side effects of ephedrine include heart attack, stroke, and sudden death. garlic oil • an extract of garlic; may or may not contain the chemicals associated with garlic; claims for health benefi ts unproved. green pills, fruit pills • pills containing dehydrated, crushed vegetable or fruit matter. An advertisement may claim that each pill equals a pound of fresh produce, but in real- ity a pill may equal one small forkful—minus nutrient losses incurred in processing. kelp tablets • tablets made from dehydrated kelp, a kind of seaweed used by the Japa- nese as a foodstuff. ma huang • an evergreen plant that supposedly boosts energy and helps with weight control. Ma huang, also called ephedra, contains ephedrine (see above) and is espe- cially dangerous in combination with kola nut or other caffeine-containing substances. melatonin • a hormone of the pineal gland believed to help regulate the body’s daily rhythms, to reverse the effects of jet lag, and to promote sleep. Claims for life extension or enhancement of sexual prowess are without merit. nutritional yeast • a preparation of yeast cells, often praised for its high nutrient content. Yeast is a source of B vitamins as are many other foods. Also called brewer’s yeast; not the yeast used in baking. organ and glandular extracts • dried or extracted material from brain, adrenal, pitu- itary, or other glands or tissues providing few nutrients but posing a theoretical risk of “mad cow disease.” See Chapter 12. SAM-e • an amino acid derivative that may have an antidepressant effect on the brain in some people, but it is not recommended as a substitute for standard antidepressant therapy. thousands of others.•

aDehydroepiandrosterone.

Note: According to legal defi nitions, all of the substances listed qualify as dietary supplements, even though some appear to have the effects of drugs, not nutrients. Table 11-9 in Chapter 11 describes many more medicinal herbs, including their effects and their hazards.

Dietary Supplement Terms table C7-4

IE TARY SUPPLEM

N T

V E R I F I E D

This symbol means that a supplement contains the nutrients stated and that it will dissolve in the digestive system—the symbol does not guaran- tee safety, or health advantages.

275controversy 7 V i t a m i n S u p p l e m e n t s : D o t h e B e n e f i t s O u t w e i g h t h e R i s k s ?

“Time release.” Medications such as • some antibiotics or pain relievers often must be sustained at a steady concen- tration in the blood to be effective, but nutrients are incorporated into the tis- sues where they are needed whenever they arrive.

“Stress formulas.” Although the stress • response depends on certain B vita- mins and vitamin C, the recommended amount provides all that is needed of these nutrients. If you are under stress (and who isn’t?), generous servings of fruits and vegetables will more than cover your need.

Pills containing extracts of alfalfa, • berries, parsley, or other vegetable or fruit components (these are generally safe but a serving of the original food brings benefi ts that pills can’t match).

Geriatric “tonics.” They are generally • poor in vitamins and minerals and yet may be so high in alcohol as to threaten inebriation.

Any supplement sold with claims that • today’s foods lack suffi cient nutri- ents to support health. Plants make vitamins for their own needs, not ours. Nutrient levels may vary from season to season and among varieties, but a plant lacking a mineral or failing to make a needed vitamin dies before it can bear food for our consumption.

To get the most from a supplement of vitamins and minerals, take it with food. A full stomach retains and dissolves the pill with its churning action.

CONCLUSION People in developed nations are far more likely to suffer from overnutrition and poor lifestyle choices than from nutrient defi ciencies. People wish that swallowing vitamin pills would boost their health. The truth—that they need to improve their eating and exercise habits—is harder to swallow.

Don’t waste time and money trying to single out a few nutrients to take as supplements. Invest energy in eating a wide variety of fruits and vegetables in generous quantities, along with the recommended daily amounts of whole grains, lean meats, and milk products every day, and take supplements only when they are truly needed.

than 10 milligrams per day) except for menstruating women. People who men- struate need more iron, but people who don’t, don’t. Warning: Expect to reject about 80 percent of available prepara- tions when you choose according to these criteria; be choosy where your health is concerned.

Going for Quality If you see a USP symbol on the label, it means that a manufacturer has volun- tarily paid an independent laboratory to test the product and affi rm that it con- tains the ingredients listed and that it will dissolve or disintegrate in the digestive tract to make the ingredients available for absorption. The symbol does not imply that the supplement has been tested for safety or effectiveness with regard to health, however.

A high price also does not ensure the highest quality; generic brands are often as good as or better than expensive name-brand supplements. If they are less expensive, it may mean that their price doesn’t have to cover the cost of national advertising. In any case, buy from a well-known retailer who keeps stocks fresh and stores them properly.

Avoiding Marketing Traps In addition, avoid these:

“For low-carb diets.” Preparations con-• taining extra biotin are claimed to better metabolize the excessive protein these diets present, but no evidence supports these claims and, as mentioned, high doses of biotin may damage DNA.

“Organic” or “natural” preparations • with added substances. They are no better than standard types, but they cost much more and the substances added may also hold risks.

“High-potency” or “therapeutic dose” • supplements. More is not better.

Items not needed in human nutrition, • such as carnitine and inositol. These particular items won’t harm you, but they reveal a marketing strategy that makes the whole mix suspect. The manufacturer wants you to believe that its pills contain the latest “new” nutri- ent that other brands omit, but, in fact, for every valid discovery of this kind, there are 999,999 frauds.

ment choices. The DRI values meet the needs of all reasonably healthy people.

Choosing Doses As for doses of nutrients, for most peo- ple, an appropriate supplement provides all the vitamins and minerals in amounts smaller than, equal to, or very close to the intake recommendations. For those who require a higher dose, such as young women who need supplemental folate in the childbearing years, choose a supplement with just the needed nutrient or in combination with a reasonable dose of others.

Avoid any preparation that in a daily dose provides more than the DRI recom- mended intake of vitamin A, vitamin D, or any mineral or more than the Tolerable Upper Intake Level for any nutrient. In addition, avoid high doses of iron (more

Watch out for plausible-sounding, but false, reasons given by marketers trying to convince you, the consumer, that you need supplements. The invalid reasons listed below have gained strength by repetition among friends, on the Inter- net, and by the media:

You fear that foods grown on today’s • soils lack nutrients (a common false statement made by sellers of supplements). You feel tired and falsely believe that • supplements can provide energy. You hope that supplements can help • you cope with stress. You wish to build up your muscles • faster or without physical exercise. You want to prevent or cure self-• diagnosed illnesses. You hope excess nutrients will pro-• duce unnamed mysterious benefi cial reactions in your body.

People who should never take supple- ments without a physician’s approval include those with kidney or liver ail- ments (they are susceptible to toxicities), those taking medications (nutrients can interfere with their actions), and smokers (who should avoid products with beta- carotene).

Some Invalid

Reasons for Taking

Supplements

table C7-5

Water and Minerals 88 do you ever . . .

Buy bottled water because you think • it is safer than tap water?

Blame “water weight” when you’ve • gained a few pounds?

Skip milk products, believing that • your adult bones no longer need the nutrients they supply?

Feel tired and wonder if you need an • iron supplement?

Keep reading . . .

LO 8.1 Identify the best beverage choices to obtain enough water for the body’s needs.

LO 8.2 Describe the body’s water sources and routes of water loss, and name factors that infl uence the need for water.

LO 8.3 Compare and contrast various sources of drinking water for safety.

LO 8.4 Discuss why electrolyte balance is critical for the health of the body.

LO 8.5 Describe the nutrients needed to maintain blood calcium levels, and explain why this is important.

LO 8.6 Describe a diet that follows the DASH principles, and specify who might benefi t from such a diet and in what ways.

LO 8.7 Compare the availability of iron from plant and animal sources.

LO 8.8 Discuss the function and importance of copper, zinc, chromium, fl uoride, and selenium in the body.

LO 8.9 Describe a diet that a young woman can follow to help prevent osteoporosis later in life.

277W a t e r a n d M i n e r a l s

A shes to ashes and dust to dust”—it is true that when the life force leaves the body, what is left behind becomes nothing but a small pile of ashes. Carbohy-

drates, proteins, fats, vitamins, and water are present at fi rst, but they soon disap- pear. Th e carbon atoms in all the carbohydrates, fats, proteins, and vitamins combine with oxygen to produce carbon dioxide, which vanishes into the air; the hydrogens and oxygens of those compounds unite to form water; and this water, along with the water that made up a large part of the body weight, evaporates. Th e ashes left behind are the minerals, a small pile that weighs only about 5 pounds. Th e pile may not be impressive in size, but the work of those minerals is critical to living tissue.

Consider calcium and phosphorus. If you could separate these two minerals from the rest of the pile, you would take away about three-fourths of the total. Crystals made of these two minerals, plus a few others, form the structure of bones and so provide the architecture of the skeleton.

Run a magnet through the pile that remains and you pick up the iron. It doesn’t fi ll a teaspoon, but it consists of billions and billions of iron atoms. As part of he- moglobin, these iron atoms are able to attach to oxygen and make it available at the sites inside the cells where metabolic work is taking place.

If you then extract all the other minerals from the pile of ashes, leaving only cop- per and iodine, close the windows fi rst. A slight breeze would blow these remaining bits of dust away. Yet the copper in the dust enables iron to hold and to release oxy- gen, and iodine is the critical mineral in the thyroid hormones. Figure 8-1 shows the amounts of the seven major minerals and a few of the trace minerals in the human body. Other minerals such as gold and aluminum are present in the body but are not known to have nutrient functions.

Th e distinction between major and trace minerals doesn’t mean that one group is more important in the body than the other. A daily defi ciency of a few micro- grams of iodine is just as serious as a defi ciency of several hundred milligrams of calcium. Th e major minerals are simply present in larger quantities in the body and are needed in greater amounts in the diet.1*

Th is chapter begins with a discussion of water. Water is unique among the nutri- ents—standing alone as the most indispensable of all. Th e body needs more water

Calcium

0 100

Amount (g)

200 300 400 500 600 700 800 900 1000 1100 1200

Phosphorus

Potassium

Sulfur

Sodium

Chloride

Magnesium

Iron

Zinc

Copper

Manganese

Iodine

Selenium

600

2.4

2.0

0.09

210

0.02

150

1150

NOTE: A pound is about 454 g; thus only calcium and phosphorus appear in amounts larger than a pound.

Major minerals

Trace minerals

The major minerals are needed by the body in larger amounts than the trace miner- als and, as shown in the graph, they are present in larger amounts, too.

Minerals in a 60-Kilogram (132-Pound)

Person (Grams)

figure 8-1

The DRI Recommended Intakes and Toler-• able Upper Intake Levels for minerals appear on the inside front cover, pages B and C.

minerals naturally occurring, inorganic, ho- mogeneous substances; chemical elements.

major minerals essential mineral nutrients required in the adult diet in amounts greater than 100 milligrams per day. Also called macrominerals.

trace minerals essential mineral nutrients required in the adult diet in amounts less than 100 milligrams per day. Also called microminerals.

*Reference notes are found in Appendix F.

“

278 chapter 8 W a t e r a n d M i n e r a l s

each day than any other nutrient—50 times more water than protein and 5,000 times more water than vitamin C. You can survive a defi ciency of any of the other nutri- ents for a long time, in some cases for months or years, but you can survive only a few days without water. In less than a day, a lack of water alters the body’s chemistry and metabolism.

Our discussion begins with water’s many functions. Next we examine how water and the major minerals mingle to form the body’s fl uids and how cells regulate the distri- bution of those fl uids. Th en we take up the specialized roles of each of the minerals.

LO 8.1, 8.2

Water You began as a single cell bathed in a nourishing fl uid. As you became a beautifully organized, air-breathing body of trillions of cells, each of your cells had to remain next to water to stay alive.

Water makes up about 60 percent of an adult person’s weight—that’s almost 80 pounds of water in a 130-pound person. All this water in the body is not simply a river coursing through the arteries, capillaries, and veins. Some of the water is in- corporated into the chemical structures of compounds that form the cells, tissues, and organs of the body. For example, proteins hold water molecules within them, water that is locked in and not readily available for any other use. Water also par- ticipates actively in many chemical reactions.

Why Is Water the Most Indispensable Nutrient? Water brings to each cell the exact ingredients the cell requires and carries away the end products of the cell’s life-sustaining reactions. Th e water of the body fl uids is thus the transport vehicle for all the nutrients and wastes. Without water, cells quickly die.

Solvent Water is a nearly universal solvent: it dissolves amino acids, glucose, minerals, and many other substances needed by the cells. Fatty substances, too, can travel freely in the watery blood and lymph because they are specially packaged in water-soluble proteins.

Cleansing Agent Water is also the body’s cleansing agent. Small molecules, such as the nitrogen wastes generated during protein metabolism, dissolve in the wa- tery blood and must be removed before they build up to toxic concentrations. Th e kidneys fi lter these wastes from the blood and excrete them, mixed with water, as urine. When the kidneys become diseased, as can happen in diabetes and other disorders, toxins can build to life-threatening levels. A kidney dialysis machine must then take over the task of cleansing the blood by fi ltering wastes into water contained in the machine.

Lubricant and Cushion Water molecules resist being crowded together. Th anks to this incompressibility, water can act as a lubricant and a cushion for the joints, and it can protect sensitive tissue such as the spinal cord from shock. Th e fl uid that fi lls the eye serves in a similar way to keep optimal pressure on the retina and lens. From the start of human life, a fetus is cushioned against shock by the bag of amniotic fl uid in the mother’s uterus. Water also lubricates the digestive tract, the respiratory tract, and all tissues that are moistened with mucus.

Coolant Yet another of water’s special features is its ability to help maintain body temperature. Th e water of sweat is the body’s coolant. Heat is produced as a by- product of energy metabolism and can build up dangerously in the body. To rid itself of this excess heat, the body routes its blood supply through the capillaries just under the skin. At the same time, the skin secretes sweat and its water evaporates. Converting water to vapor takes energy; therefore, as sweat evaporates, heat energy dissipates, cooling the skin and the underlying blood. Th e cooled blood then fl ows

Water is the most indispensable nutrient.

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Did You Know? The brain is composed of approximately 80% water.

Boasting scientist: “I’m working on discover-• ing the universal solvent.”

Skeptic: “Is that so? Well, when you’ve got it, • what are you going to keep it in?”

Human life begins in water.

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279W a t e r

back to cool the body’s core. Sweat evaporates continuously from the skin, usually in slight amounts that go unnoticed; thus, the skin is a major organ through which water is lost from the body. Lesser amounts are lost by way of exhaled breath and the feces.2

To sum up, water:

carries nutrients throughout the body.•

serves as the solvent for minerals, vitamins, amino acids, glucose, and other •

small molecules.

cleanses the tissues and blood of wastes.•

actively participates in many chemical reactions.•

acts as a lubricant around joints.•

serves as a shock absorber inside the eyes, spinal cord, joints, and amniotic sac •

surrounding a fetus in the womb.

aids in maintaining the body’s temperature.•

KE Y POINT Water makes up about 60 percent of the body’s weight. Water provides the medium for transportation, acts as a solvent, participates in chemical reactions, provides lubrication and shock protection, and aids in temperature regulation in the human body.

The Body’s Water Balance Water is such an integral part of us that people seldom are conscious of water’s im- portance, unless they are deprived of it. Since the body loses some water every day, a person must consume at least the same amount to avoid life-threatening losses, that is, to maintain water balance. Th e total amount of fl uid in the body is kept bal- anced by delicate mechanisms. Imbalances such as dehydration and water intoxi- cation can occur, but the balance is restored as promptly as the body can manage it. Th e body controls both intake and excretion to maintain water equilibrium.

Th e amount of the body’s water varies by pounds at a time, especially in women who retain water during menstruation. Eating a meal high in salt can temporarily increase the body’s water content; the body sheds the excess over the next day or so as the sodium is excreted. Th ese temporary fl uctuations in body water show up

An extra drink of water benefi ts both young and old.

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solvent a substance that dissolves another and holds it in solution.

dialysis (dye-AL-ih-sis) a medical treatment for failing kidneys in which a person’s blood is circulated through a machine that fi lters out toxins and wastes and returns cleansed blood to the body. Also called hemodialysis.

water balance the balance between water intake and water excretion, which keeps the body’s water content constant.

dehydration loss of water. The symptoms progress rapidly, from thirst to weakness to exhaustion and delirium, and end in death.

water intoxication a dangerous dilution of the body’s fl uids resulting from excessive ingestion of plain water. Symptoms are head- ache, muscular weakness, lack of concentra- tion, poor memory, and loss of appetite.

280 chapter 8 W a t e r a n d M i n e r a l s

on the scale, but gaining or losing water weight does not refl ect a change in body fat. Fat weight takes days or weeks to change noticeably, whereas water weight can change overnight.

KE Y POINT A change in the body’s water content can bring about a temporary change in body weight.

Quenching Thirst and Balancing Losses Th irst and satiety govern water intake.3 When the blood is too concentrated (hav- ing lost water but not salt and other dissolved substances), the molecules and par- ticles in the blood attract water out of the salivary glands, and the mouth becomes dry. Th e brain center known as the hypothalamus senses the concentrated blood particles, low blood volume, or low blood pressure and initiates nerve impulses to the brain that register as “thirst.” Th e hypothalamus also signals the pituitary gland to release a hormone that directs the kidneys to shift water back into the blood- stream from the fl uid destined to become urine. Th e kidneys themselves respond to the sodium concentration in the blood passing through them and secrete regulatory substances of their own. Th e net result is that the more water the body needs, the less it excretes. Figure 8-2 shows how intake and excretion naturally balance out.

Dehydration Th irst lags behind a lack of water. When too much water is lost from the body and is not replaced, dehydration can threaten survival. A fi rst sign of dehydration is thirst, the signal that the body has already lost up to 2 cups of its total fl uid and that the need to obtain fl uid is urgent. But suppose a thirsty person is unable to obtain fl uid or, as in many elderly people, fails to perceive the thirst message. Instead of “wasting” precious water in sweat, the dehydrated body diverts most of its water into the blood vessels to maintain the life-supporting blood pres- sure. Meanwhile, body heat builds up because sweating has ceased, creating the possibility of serious consequences (see Table 8-1). A water defi ciency that develops slowly can switch on drinking behavior in time to prevent serious dehydration, but one that develops quickly may not.

To ignore the thirst signal is to invite dehydration. With a loss of just 1 percent of body weight as fl uid, perceptible symptoms appear: headache, fatigue, confusion or forgetfulness, and an elevated heart rate. A loss of 2 percent impairs physical func- tioning and impedes a wide range of physical activities.4 People should stay attuned to thirst and drink whenever they feel thirsty to replace fl uids lost throughout the day.5 Older adults in whom thirst is blunted should drink regularly throughout the day, regardless of thirst.

Water Intoxication At the other extreme from dehydration, water intoxication occurs when too much plain water fl oods the body’s fl uids and disturbs their normal composition. Most adult victims have consumed several gallons of plain water in a few hours’ time. Water intoxication is rare, but when it occurs, immediate action is needed to reverse dangerously diluted blood before death ensues.

KE Y POINT Water losses from the body necessitate intake equal to output to maintain balance. The brain regulates water intake; the brain and kidneys regulate water excretion. Dehydration and water intoxication can have serious consequences.

How Much Water Do I Need to Drink in a Day? Water needs vary greatly depending on the foods a person eats, the air temperature and humidity, the altitude, the person’s activity level, and other factors (see Table 8-2). Fluid needs vary widely among individuals and also within the same person

CONCEPT LINK 8-1 The hypothalamus was described in Chapter 3, page 75.

Did You Know? A 150-lb person contains 90 lb of water; a 5% loss of body fl uid for this person amounts to about 4½ lb of water.

For more about water intoxication, see • Chapter 10.

The DRI Recommended Intakes for water • are listed on the inside front cover, page A.

Water Balance—

A Typical Example

figure 8-2

Each day, water enters the body in liquids and foods, and some water is created in the body as a by-product of meta- bolic processes. Water leaves the body through the evaporation of sweat, in the moisture of exhaled breath, in the urine, and in the feces.

Foods (700–1,000 ml)

Water input (Total = 1,450–2,800 ml)

Water created by metabolism (200–300 ml)

Liquids (550–1,500 ml)

Water output (Total = 1,450–2,800 ml)

Lungs (350 ml)Feces (150 ml)

Kidneys (500–1,400 ml)

Skin (450–900 ml)

281W a t e r

in various environmental conditions, so a specifi c water recommendation is hard to pin down.

Water from Fluids and Foods A wide range of fl uid intakes can maintain ade- quate hydration. As a general guideline, however, the DRI committee recommends that, given a normal diet and moderate environment, the reference man needs about 13 cups of fl uid from beverages including drinking water, and the reference woman needs about 9 cups.6 Th is amount of fl uid provides about 80 percent of the body’s daily water need. On average, most people in the United States consume close to these amounts.7

Most of the rest of the body’s daily water comes from the water in foods. Nearly all foods contain some water: water constitutes up to 95 percent of the volume of most fruits and vegetables and at least 50 percent of many meats and cheeses (see the margin on the next page and Appendix A). A small percentage of the day’s fl uid is generated in the tissues themselves as energy-yielding nutrients release metabolic water as a product of chemical breakdown.

The Effect of Sweating on Fluid Needs Sweating increases water needs. Espe- cially when performing physical work outdoors in hot weather, people can lose 2 to 4 gallons of fl uid in a day. An athlete training in the heat can sweat out more than a half-gallon of fl uid each hour. Th e importance of maintaining hydration for athletes exercising in the heat cannot be overemphasized, and Chapter 10 provides detailed instructions on exactly how to hydrate the exercising body.

Which Fluids to Choose? Which beverages are best? Any beverage can readily meet the body’s fl uid needs, but those with few or no calories do so without con- tributing to weight gain. Beverages contribute more than 20 percent of the total energy intake in the United States, so for controlling body weight, water may be the superior choice.8 Other choices include tea, coff ee, nonfat and low-fat milk and soy milk, artifi cially sweetened beverages, and fruit and vegetable juices. By far, carbon- ated soft drinks are chosen most often (see Figure 8-3) but this choice often crowds

Mild Dehydration (Loss of <5% Body Weight)

Severe Dehydration (Loss of >5% Body Weight)

Chronic Low Fluid Intake May Increase the Likelihood of:a

Thirst Sudden weight loss Rough, dry skin Dry mouth, throat, body linings Rapid pulse Low blood pressure Lack of energy; weakness Impaired kidney function Reduced quantity of urine; concentrated urine Decreased mental functioning Decreased muscular work and athletic

performance Fever or increased internal temperature Fainting

Pale skin Bluish lips and fi ngertips Confusion; disorientation Rapid, shallow breathing Weak, rapid, irregular pulse Thickening of blood Shock; seizures Coma; death

Cardiac arrest (heart attack) and other heart problems

Constipation Dental disease Gallstones Glaucoma (elevated pressure in the eye) Hypertension Kidney stones Pregnancy/childbirth problems Stroke Urinary tract infections

aEvidence for bladder and colon cancer is inconsistent.

Source: K. M. Kolasa, C. J. Lacky, and A. C. Grandjean, Hydration and health promotion, Nutrition Today 44 (2009): 190–201; F. Manz, Hydration and disease, Journal of the American College of Nutrition 26 (2007): 535S–541S, Standing Committee on the Scientifi c Evaluation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine, Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate (Washington, D.C.: National Academies Press, 2004): 4-31–4-48.

Effects of Mild Dehydration, Severe Dehydration, and Chronic Lack of Fluid table 8-1

These conditions increase a person’s need for fl uids:

Alcohol consumption• Cold weather• Dietary fi ber• Diseases that disturb water balance, • such as diabetes and kidney diseases Forced-air environments, such as air-• planes and sealed buildings Heated environments• High altitude• Hot weather, high humidity• Increased protein, salt, or sugar intakes• Ketosis• Medications (diuretics)• Physical activity• Pregnancy and breastfeeding (see • Chapter 13) Prolonged diarrhea, vomiting, or fever• Surgery, blood loss, or burns• Very young or old age•

Factors That

Increase Fluid

Needs

table 8-2

metabolic water water generated in the tissues during the chemical breakdown of the energy-yielding nutrients in foods.

282 chapter 8 W a t e r a n d M i n e r a l s

more nutritious beverages out of the diet, and the regular sugar-sweetened varieties provide a great deal of added sugar to the day’s discretionary calorie intake.9

A word about caff eine: People who drink caff einated beverages lose a little more fl uid than when they drink water because caff eine acts as a diuretic. Th e DRI Com- mittee considered such fi ndings in their recommendations for water intake and con- cluded: “Caff einated beverages contribute to the daily total water intake similar to that contributed by non-caff einated beverages.”10 In other words, the mild diuretic eff ect of moderate caff eine intake doesn’t seem to prevent people from meeting their fl uid needs. Th e Controversy section of Chapter 14 comes back to the eff ects of caff eine.

KE Y POINT Many factors infl uence a person’s need for water. The water of beverages and foods meets nearly all of the need for water, and a little more is supplied by the water formed during cellular breakdown of energy nutrients.

Are Some Kinds of Water Better for My Health Than Others? Water occurs as hard water or soft water, a distinction that aff ects your health with regard to three minerals. Hard water has high concentrations of calcium and magnesium. Soft water’s principal mineral is sodium. In practical terms, soft water makes more bubbles with less soap; hard water leaves a ring on the tub, a jumble of rocklike crystals in the teakettle, and a gray residue in the wash.

Soft water may seem more desirable, and some homeowners purchase water soft- eners that remove magnesium and calcium and replace them with sodium. Th e so- dium of soft water, even when it bubbles naturally from the ground, may aggravate hypertension, however. Soft water also more easily dissolves certain contaminant metals, such as cadmium and lead, from pipes. Cadmium can harm the body, af- fecting enzymes by displacing zinc from its normal sites of action. Lead, another

Water content of various foods and • beverages:

100% = water, diet soft drinks, seltzer •

(unflavored), plain tea.

95–99% = sugar-free gelatin dessert, clear •

broth, Chinese cabbage, celery, cucumber,

lettuce, summer squash, black coffee.

90–94% = Gatorade, grapefruit, fresh •

strawberries, broccoli, tomato.

80–89% = sugar-sweetened soft drinks, •

milk, yogurt, egg white, fruit juices, low-fat

cottage cheese, cooked oatmeal, fresh

apple, carrot.

60–79% = low-calorie mayonnaise, instant •

pudding, banana, shrimp, lean steak, pork

chop, baked potato, cooked rice.

40–59% = diet margarine, sausage, •

chicken, macaroni and cheese.

20–39% = bread, cake, cheddar cheese, •

bagel.

10–19% = butter, margarine, regular •

mayonnaise.

5–9% = peanut butter, popcorn.•

1–4% = ready-to-eat cereals, pretzels.•

0% = cooking oils, meat fats, shortening, •

white sugar.

CONCEPT LINK 8-2 Discretionary calories were a topic of Chapter 2; the health effects of added sugars were discussed in Controversy 4, page 145.

Water in foods

Water in beverages

Plain drinking water (including carbonated and bottled water)

Key:

O u n c e s

Daily fluid

intake

100

120

Carbonated soft drinks

36%

Alcoholic beverages

18%

Coffee/tea 17%

Milk 14%

Fruit beverages

Sports drinks

Others, including vegetable juices

diuretic (dye-you-RET-ic) a compound, usu- ally a medication, causing increased urinary water excretion; a “water pill.”

hard water water with high calcium and magnesium concentrations.

soft water water with a high sodium concentration.

Source: Data from A. K. Kant, B. I. Graubard, and E. A. Atchison, Intakes of plain water, moisture in foods and beverages, and total water in the adult US population—nutritional, meal pattern, and body weight correlates: National Health and Nutrition Examination Surveys 1999–2006, American Journal of Clinical Nutrition 90 (2009): 655-663; American Beverage Association, What America Drinks, available at www.ameribev.org.

U.S. Fluid Sources figure 8-3

http://www.ameribev.org

283S a f e t y a n d S o u r c e s o f D r i n k i n g W a t e r

toxic metal, is absorbed more readily from soft water than from hard water, possibly because the calcium in hard water protects against its absorption. Old plumbing may contain cadmium or lead, so people living in old buildings should run the cold water tap a minute to fl ush out harmful minerals before drawing water for the fi rst use in the morning and whenever no water has been drawn for more than six hours.11

KE Y POINT Hard water is high in calcium and magnesium. Soft water is high in sodium, and it dissolves cadmium and lead from pipes.

LO 8.3

Safety and Sources of Drinking Water Remember that water is practically a universal solvent: it dissolves almost anything it encounters to some degree. Hundreds of contaminants—including disease-causing bacteria and viruses from human wastes, toxic pollutants from highway fuel runoff , spills and heavy metals from industry, organic chemicals such as pesticides from agriculture, and manure bacteria from farm animals—have been detected in public drinking water.

Safety of Public Water Public water systems remove many hazards. Th ey add disinfectant (usually chlo- rine) to kill most microorganisms and may expose the water to other treatments to purify it. Private well water is usually not chlorinated, so the 40 million Americans who drink water from private wells should have them tested regularly for harmful microorganisms.

Testing and Reporting All public drinking water must be tested regularly for contamination. Th e Environmental Protection Agency (EPA) ensures that public water systems meet minimum standards for health. Public utility customers receive a yearly statement, written in plain language, listing the chemicals and bacteria found in local water. Th is document makes fascinating reading for those interested in the purity of their tap water.

Chlorination and Cancer By-products of water chlorination have been found to cause cancer-related changes in human cells and cancer in laboratory animals.12 In- vestigators acknowledge the possibility of a connection between chlorinated drink- ing water and cancer incidence.13 Even so, they also passionately defend chlorina- tion as a benefi t to public health. In areas of the world without chlorination, an estimated 25,000 people die each day from diseases caused by organisms carried by water and easily killed by chlorine. Substitutes for chlorine exist but they are too expensive or too slow to be practical for treating a city’s water, and some may create by-products of their own.14

Water Sources Meanwhile, what is a consumer to drink? Th e fi rst option is to drink tap water because municipal water is held to minimum standards for purity, as described. It comes from any of several sources.

Surface Water Surface water fl owing from lakes, rivers, and reservoirs fi lls about half of the nation’s need for drinking water, mostly in major cities. Surface water is exposed to contamination by acid rain, petroleum products, pesticides, fer- tilizer, human and animal wastes, and industrial wastes that run directly from pave- ments, septic tanks, farmlands, and industrial areas into streams that feed surface

Did You Know? Lead is exceptionally harmful to children (details in Chapter 14).

surface water water that comes from lakes, rivers, and reservoirs.

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284 chapter 8 W a t e r a n d M i n e r a l s

water bodies. Surface water generally moves faster than groundwater and stays above ground where aeration and exposure to sunlight can cleanse it. Th e plants and microorganisms that live in surface water also fi lter it. Th ese processes can remove some contaminants, but others stay in the water.

Groundwater Groundwater comes from protected aquifers, deep underground rock formations saturated with water. People in rural areas rely mostly on ground- water pumped from private wells, and some cities tap this resource, too. Ground- water can become contaminated from hazardous waste sites, dumps, oil and gas pipelines, and landfi lls, as well as downward seepage from surface water bodies. Groundwater moves slowly and is not aerated or exposed to sunlight, so contami- nants break down more slowly than in surface water. To mingle with water in the aquifer, surface water must fi rst “percolate,” or seep, through soil, sand, or rock, which fi lters out some contaminants.

Home Water Purifi cation A second option is to further purify tap water with home purifying equipment, which ranges in price from about $20 to $5,000. Some home systems do an adequate job of removing lead, chlorine, and other contami- nants, but others only improve the water’s taste. Many are not designed to remove microorganisms that are not aff ected by chlorine. Each system has advantages and drawbacks, and all require periodic maintenance or fi lter replacements that vary in price. Not all companies or representatives are legitimate—some perform water tests that yield dramatic-appearing but meaningless results to sell unneeded systems. Ver- ify all claims of contamination by checking reports from local municipal water agen- cies or by independently testing well water before buying any purifying system.

Bottled Water A third option is to use bottled water. Many people turn to bot- tled water as an alternative to tap water. Read the Consumer Corner for more about bottled water. Whether water comes from the tap or is poured from a bottle, all water comes from the same sources—surface water and groundwater.

Given water’s importance in the body, the world’s supply of clean, wholesome water is a precious resource to be guarded. Th e remainder of this chapter addresses other important nutrients—the minerals.

KE Y POINT Public drinking water is tested and treated for safety. All drinking water originates from surface water or groundwater, which are vulnerable to contamination from human activities.

LO 8.4

Body Fluids and Minerals Most of the body’s water weight is contained inside the cells, and some water bathes the outsides of the cells. Th e remainder fi lls the blood vessels. How do cells keep themselves from collapsing when water leaves them and from swelling up when too much water enters them?

Water Follows Salt Th e cells cannot regulate the amount of water directly by pumping it in and out because water slips across membranes freely. Th e cells can, however, pump minerals across their membranes. Th e major minerals form salts that dissolve in the body fl uids; the cells direct where the salts go, and this determines where the fl uids fl ow because water follows salt.

When mineral (or other) salts dissolve in water, they separate into single, electri- cally charged particles known as ions. Unlike pure water, which conducts electric- ity poorly, ions dissolved in water carry electrical current; for this reason, these elec- trically charged ions are called electrolytes.

Did You Know? If electric service fails in your community, the water supply may become contaminated; use bottled water during emergencies. Alterna- tively, follow these directions:

Boil the available water for 1 to 3 minutes.•

If you cannot boil it, add 8 drops of clean • household bleach (regular strength) per gallon of water; stir it well, and let it sit for 30 minutes before using it.

More information is available at the EPA • website: www.epa.gov.

groundwater water that comes from underground aquifers.

aquifers underground rock formations con- taining water that can be drawn to the surface for use.

bottled water drinking water sold in bottles.

salts compounds composed of charged particles (ions). An example is potassium chloride (K+Cl–).

ions (EYE-ons) electrically charged particles, such as sodium (positively charged) or chlo- ride (negatively charged).

electrolytes compounds that partly disso- ciate in water to form ions, such as the potas- sium ion (K+) and the chloride ion (Cl–).

http://www.epa.gov

285B o d y F l u i d s a n d M i n e r a l s

consumer corner

The FDA is currently studying U.S. BPA intake levels, but estimated previously that the highest intakes were 100 times lower than potentially harmful levels.4

CHOOSING AMONG BOTTLED WATERS Gaining in popularity is water spiked with colors, fl avors, sweeteners, caf- feine, herbal extracts, vitamins, minerals, protein, or oxygen, often sold in swanky- looking bottles. These “fi tness” waters are really just liquid supplements, and those with caffeine and herbs may present some risks (explained in Chapter 11 and the Controversy section of Chapter 14).

As a consumer who wants pure bottled water, what should you look for? Look for the trademark of the International Bottled Water Association (IBWA), a trade orga- nization supporting the FDA’s regulations and enforcement efforts. Next, look for the water’s place of origin. Water bottled in another state might be the safest choice because only water sold across state lines must meet the FDA’s sanita- tion and safety requirements.

Then try to determine the water’s source. At least a quarter of bottled water is drawn directly from the tap and has met the stricter standards of public water supplies. If the water you buy is from a spring or a stream in your state, is the area agricultural, residential, industrial, or undeveloped? Agricultural, industrial, and residential activities can expose

About 1 in 15 households uses bottled water as its main drinking water source, believing it to taste better and be safer than tap water and therefore worth its substantial cost—typically 250 to 10,000 times the price of tap water. As for taste, most water-bottling plants disinfect their products with ozone, which, unlike chlo- rine, leaves no fl avor or odor in the water.

With regard to safety, when a con- sumer group tested bottled water, it disproved the notion of superiority: of 1,000 bottles and 103 brands tested, about a third were contaminated with bacteria, arsenic, or synthetic organic chemicals.*1 In another analysis, lead exceeded accepted limits in about half of the bottles tested.2

BOTTLED WATER REGULATION AND SAFETY Only bottled water that is sold across state lines is regulated by the Food and Drug Administration (FDA). This regu- lated water must pass yearly tests for purity and adherence to sanitation stan- dards, but the standards are less rigor- ous than those applied to U.S. tap water. For example, bottled water need not be tested for the presence of asbestos contamination as tap water sources must be. Water sold within state lines escapes FDA oversight. In response to research fi ndings, the FDA has strengthened its regulation of bottled water to include yearly tests for fecal bacteria, arsenic, uranium, disinfectants, and certain other contaminants. If contamination is found, it must be eliminated at its source before the water is bottled and sold.3

In addition to the water itself, some people question the safety of BPA, a chemical used to make refi llable hard clear-plastic water bottles and baby bottles (but not thinner fl exible dispos- able water bottles).† Such chemicals migrate into the bottle’s contents and are consumed along with the water. Some manufacturers have stopped using BPA.

water sources to contamination. Finally, ask whether your state strictly enforces standards for purity and sanitation of bottled water—many states have un- enforced rules on the books.

Table 8-3 defi nes some terms that appear on labels. What you are unlikely to fi nd on the label is the water’s mineral content. Some bottling companies will provide mineral information if a con- sumer requests it. For nutrition’s sake, the best choice is water rich in calcium and magnesium but low in sodium. Most bottled waters lack needed minerals, however, unless they are identifi ed as “mineral water” on the label.5 As for fl uo- ride, an important mineral for children’s teeth and bones, bottled water is an unpredictable source.

SMALL BOTTLES, BIG BOTTLES Consumers may be shifting away from individual water bottles as they learn more about them. Considerable fossil

Bottled Water

*The group was the National Resources Defense Council. Read its report, Bottled Water: Pure Drink or Pure Hype?; available at www.nrdc.org/water/ drinking/nbw.asp. †BPA is bisphenol A.

The label on a water bottle may imply purity, but what counts is the purity of the product inside.

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286 chapter 8 W a t e r a n d M i n e r a l s

fuels and many gallons of water are required to create and transport plastic water bottles. Billions of empties now pose a serious disposal problem for communities and the environment.

Water delivered in large refi llable bottles must be kept safe from bacteria to avert illness. If your water is dispensed from a water cooler, cleanse the cooler once a month by running half a gallon of white vinegar through it. Remove the vinegar residue by rinsing the cooler with 4 or 5 gallons of tap water. For individual bottles of water, be aware that bacteria from the mouth enter the water with the fi rst sip from the bottle. There- after, keep the unfi nished remainder of water in the refrigerator to minimize bacterial growth.6

CONCLUSION In the end, the choice to drink water from any source instead of sugary soft drinks can help to meet fl uid needs with fewer calories, a step in the right direction for many people. The choice of where to obtain that water—public water sup- plies, disposable bottles, or refi llable bulk water bottles—is also important. It can affect the environment for better or worse long after your thirst is satisfi ed (see Chapter 15).

artesian water• water drawn from a well that taps a confi ned aquifer in which the water is under pressure. baby water• ordinary bottled water treated with ozone to make it safe but not sterile. caffeine water• bottled water with caffeine added. carbonated water• water that contains carbon dioxide gas, either naturally occurring or added, that causes bubbles to form in it; also called bubbling or sparkling water. Seltzer, soda, and tonic waters are legally soft drinks and are not regulated as water. distilled water• water that has been vaporized and recondensed, leaving it free of dis- solved minerals. fi ltered water• water treated by fi ltration, usually through activated carbon fi lters that reduce the lead in tap water, or by reverse osmosis units that force pressurized water across a membrane, removing lead, arsenic, and some microorganisms from tap water. fi tness water• lightly fl avored bottled water enhanced with vitamins, supposedly to enhance athletic performance. mineral water• water from a spring or well that typically contains 250 to 500 parts per million (ppm) of minerals. Minerals give water a distinctive fl avor. Many mineral waters are high in sodium. natural water• water obtained from a spring or well that is certifi ed to be safe and sani- tary. The mineral content may not be changed, but the water may be treated in other ways such as with ozone or by fi ltration. public water• water from a municipal or county water system that has been treated and disinfected. purifi ed water• water that has been treated by distillation or other physical or chemical processes that remove dissolved solids. Because purifi ed water contains no minerals or contaminants, it is useful for medical and research purposes. spring water• water originating from an underground spring or well. It may be bubbly (carbonated) or “fl at” or “still,” meaning not carbonated. Brand names such as “Spring Pure” do not necessarily mean that the water comes from a spring. vitamin water• bottled water with a few vitamins added; does not replace vitamins from a balanced diet and may worsen overload in people receiving vitamins from enriched food, supplements, and other enriched products such as “energy” bars. well water• water drawn from groundwater by tapping into an aquifer.

Water Terms That May Appear on Labels table 8-3

As Figure 8-4 shows, when dissolved particles, such as electrolytes, are present in unequal concentrations on either side of a water-permeable membrane, water fl ows toward the more concentrated side to equalize the concentrations. Cells and their surrounding fl uids work in the same way. Th ink of a cell as a sack made of a water- permeable membrane. Th e sack is fi lled with watery fl uid and suspended in a dilute solution of salts and other dissolved particles. Water fl ows freely between the fl uids inside and outside the cell but generally moves from the more dilute solution toward the more concentrated one (the photo of salted eggplant slices shows this eff ect).

KE Y POINT Cells regulate water movement by pumping minerals across their membranes. Water follows.

Fluid and Electrolyte Balance To control the fl ow of water, the body must spend energy moving its electrolytes from one compartment to another (Figure 8-5). Transport proteins form the pumps that move mineral ions across cell membranes. Th e result is fl uid and electrolyte balance, the proper amount and kind of fl uid in every body compartment.

If the fl uid balance is disturbed, severe illness can develop quickly because fl uid can shift rapidly from one compartment to another. For example, in vomiting or diarrhea, the loss of water from the digestive tract pulls fl uid from between the

The slices of eggplant on the right were sprin- kled with salt. Notice their beads of “sweat,” formed as cellular water moves across each cell’s membrane (water-permeable divider) to- ward the higher concentration of salt (dissolved particles) on the surface.

ra ig

M . M

oo re

287B o d y F l u i d s a n d M i n e r a l s

cells in every part of the body. Fluid then leaves the cell interiors to restore balance. Meanwhile, the kidneys detect the water loss and attempt to retrieve water from the pool destined for excretion. To do this, they raise the sodium concentration outside the cells, and this pulls still more water out of them. Th e result is fl uid and electro- lyte imbalance, a medical emergency. Water and minerals lost in vomiting or diar- rhea ultimately come from all the body’s cells. Th is loss disrupts the heartbeat and threatens life. It is a cause of death among those with eating disorders.

KE Y POINT Mineral salts form electrolytes that help keep fl uids in their proper compartments and buff er these fl uids, permitting all life processes to take place.

Acid-Base Balance Th e minerals help manage still another balancing act, the acid-base balance, or pH of the body’s fl uids. In pure water, a small percentage of water molecules (H2O) exist as positive (H) and negative (OH) ions, but they exist in equilibrium—the positive charges exactly equal the negatives. When dissolved in watery body fl uids, some of the major minerals give rise to acids (H, or hydrogen, ions), and others to bases (OH). Excess H ions in a solution make it an acid; they lower the pH. Excess OH ions in a solution make it a base; they raise the pH.

Maintenance of body fl uids at a nearly constant pH is critical to life. Even slight changes in pH drastically change the structure and chemical functions of most biologically important molecules. Th e body’s proteins and some of its mineral salts help prevent changes in the acid-base balance of its fl uids by serving as buff ers— molecules that gather up or release H ions as needed to maintain the correct pH. Th e kidneys help to control the pH balance by excreting more or less acid (H ions). Th e lungs also help by excreting more or less carbon dioxide. (Dissolved in the blood, carbon dioxide forms an acid, carbonic acid.) Th is tight control of the acid- base balance permits all other life processes to continue.

KE Y POINT Minerals act as buff ers to help maintain body fl uids at the correct pH.

CONCEPT LINK 8-3 Chapter 6 explained how transport proteins work, moving substances into and out of cells (page 202).

CONCEPT LINK 8-4 Figure 3-12 showed the pH of common sub- stances (page 83); Figure 3-4 depicted fluid movement in and around cells (page 73).

1 With equal numbers of dissolved particles on both sides of a water- permeable divider, water levels remain equal.

2 Now additional particles are added to increase the concentration on side B. Particles cannot flow across the divider. In the case of a cell, the divider (cell membrane) partitions fluids inside and outside the cell.

3 Water can flow both ways across the divider but tends to move from side A to side B, where the concentration of dissolved particles is greater. The volume of water increases on side B, and the particle concen- trations on sides A and B become equal.

A B A B A B

Water fl ows in the direction of the more highly concentrated solution.

Animated!

How Electrolytes Govern Water Flow

figure 8-4

fl uid and electrolyte balance main- tenance of the proper amounts and kinds of fl uids and minerals in each compartment of the body.

fl uid and electrolyte imbalance fail- ure to maintain the proper amounts and kinds of fl uids and minerals in every body compart- ment; a medical emergency.

acid-base balance maintenance of the proper degree of acidity in each of the body’s fl uids.

buffers molecules that can help to keep the pH of a solution from changing by gathering or releasing H ions.

Transport protein

Inside cell

Outside cell

Cell membrane

Potassium Sodium

Key

Transport proteins in cell membranes maintain the proper balance of sodium (mostly outside the cells) and potassium (mostly inside the cells).

Electrolyte Balance figure 8-5

288 chapter 8 W a t e r a n d M i n e r a l s

LO 8.5, 8.6

The Major Minerals All the major minerals help to maintain the fl uid balance, but each one also has some special duties of its own. Table 8-8 on pages 310–311 summarizes the roles of the minerals discussed below.

Calcium As Figure 8-1 showed, calcium is by far the most abundant mineral in the body. Th e roles of calcium are critical to body functioning, but only about a third of the U.S. population meet the DRI recommended intake for this mineral.15

Nearly all (99 percent) of the body’s calcium is stored in the bones and teeth, where it plays two important roles. First, it is an integral part of bone structure. Second, bone calcium serves as a bank that can release calcium to the body fl uids if even the slightest drop in blood calcium concentration occurs. Many people think that once deposited in bone, calcium (together with the other minerals of bone) stays there forever—that once a bone is built, it is inert, like a rock. Not so. Th e minerals of bones are in constant fl ux, with formation and dissolution taking place every minute of the day and night (see Figure 8-6).

Calcium in Bone and Tooth Formation Calcium and phosphorus are both es- sential to bone formation: calcium phosphate salts crystallize on a foundation material composed of the protein collagen. Th e resulting hydroxyapatite crystals invade the collagen and gradually lend more and more rigidity to a youngster’s maturing bones until they are able to support the weight they will have to carry. During and after

Major minerals:•

Calcium•

Chloride•

Magnesium•

Phosphorus•

Potassium•

Sodium•

Sulfate•

The major minerals are also called macro-

minerals. The need for each of these is greater than 100 milligrams per day, often far greater.

Blood enters the bone in an artery here.

Blood leaves the bone by way of a vein.

Bone is active, living tissue. Blood travels in capillaries throughout the bone, bringing nutrients to the cells that maintain the bone’s structure and carrying away waste materials from those cells. It picks up and deposits minerals as instructed by hormones.

Bone derives its structural strength from the lacy network of crystals that lie along its lines of stress. If minerals are withdrawn to cover deficits elsewhere in the body, the bone will grow weak and ultimately will bend or crumble.

A Bone figure 8-6

Did You Know? If you could remove all of the minerals from bones, the protein structures that remained (mostly the protein collagen) would be so fl ex- ible that you could tie them in a knot.

hydroxyapatite (hi-DROX-ee-APP-uh- tight) the chief crystal of bone, formed from calcium and phosphorus.

289T h e M a j o r M i n e r a l s

the bone-strengthening processes, fl uoride may displace the “hydroxy” parts of these crystals, making fl uorapatite, a compound that resists bone-dismantling forces.16

Teeth are formed in a similar way: hydroxyapatite crystals form on a collagen matrix to create the dentin that gives strength to the teeth (see Figure 8-7). Th e turnover of minerals in teeth is not as rapid as in bone, but some withdrawal and redepositing do take place throughout life. As a later section makes clear, fl uoride hardens and stabilizes the crystals of teeth.

Calcium in Body Fluids Th e fl uids that bathe and fi ll the cells contain 1 percent of the body’s calcium, but this tiny amount is vital to life. It plays these major roles:

regulates the transport of ions across cell membranes and is particularly impor-•

tant in nerve transmission.

helps maintain normal blood pressure.• 17

plays an essential role in the clotting of blood.•

is essential for muscle contraction and therefore for the heartbeat.•

allows secretion of hormones, digestive enzymes, and neurotransmitters.•

activates cellular enzymes that regulate many processes.•

Because of its importance, blood calcium is tightly controlled. Other roles for calcium are emerging as well. Calcium may protect against hyper-

tension. Some research also suggests protective relationships between calcium and blood cholesterol, diabetes, and colon and rectal cancers.18 Calcium from low-fat milk and milk products (but not from supplements) has been linked with having a healthy body weight in some, but not all, studies.19 Large, well-designed clinical studies are needed to clarify any eff ects of dietary calcium on body weight.20

Calcium Balance Th e key to bone health lies in the body’s calcium balance, a sys- tem of hormones and vitamin D.21 Cells need continuous access to calcium, so the body maintains a constant calcium concentration in the blood. Th e skeleton serves as a bank from which the blood can borrow and return calcium as needed. Th us, a person whose calcium intake is inadequate maintains normal blood calcium but at the expense of bone density. Th e body is sensitive to an increased need for calcium but sends no signals to the conscious brain indicating calcium need. Instead, three organ systems quietly respond:

Th e intestines increase absorption of calcium from the intestine.1. Th e bones release more calcium into the blood.2. Th e kidneys prevent its loss in the urine.3.

Bone Loss Despite the body’s adjustments, some bone loss is an inevitable conse- quence of aging. Sometime around age 30, or 10 years after adult height is achieved, the skeleton no longer adds signifi cantly to bone density.22 After about age 40, regard- less of calcium intake bones begin to lose density but the loss can be slowed somewhat by a diet that provides adequate calcium along with regular physical activity.

A person whose calcium savings account is not suffi cient is more likely to develop the fragile bones of osteoporosis, or adult bone loss. Osteoporosis constitutes a major health problem for many older people—its possible causes and prevention are the topics of this chapter’s Controversy. To protect against bone loss, attention to calcium intakes during early life is crucial. A diet too low in calcium-rich foods during the growing years may prevent a person from achieving peak bone mass (Figure 8-8 illustrates the timing).23 Supplements of calcium seem to be less suc- cessful than foods for building strong bones.24 Vitamin D, vitamin A, other vita- mins, magnesium, phosphorus, other minerals, and protein all play metabolic roles necessary for building the bones.25

Calcium Absorption On average, adults absorb about 30 percent of the calcium they ingest. Th e stomach’s acidity helps to keep calcium soluble, and vitamin D

The inner layer of dentin is bonelike mate- rial that forms on a protein (collagen) ma- trix. The outer layer of enamel is harder than bone. Both dentin and enamel contain hydroxyapatite crystals (made of calcium and phosphorus). The crystals of enamel may become even harder when exposed to the trace mineral fl uoride.

A Tooth figure 8-7

Nerve Bone Blood vessel

Gum

Pulp (blood vessels, nerves)

Enamel Dentin

Funct ional Group Key bone vitamins:

Vitamin A, vitamin D, vitamin K, vitamin C, •

other vitamins.

Key bone minerals:

Calcium, phosphorus, magnesium, fluo-•

ride, other minerals.

fl uorapatite (fl oor-APP-uh-tight) a crystal of bones and teeth, formed when fl uoride dis- places the “hydroxy” portion of hydroxyapatite. Fluorapatite resists being dissolved back into body fl uid.

bone density a measure of bone strength, the degree of mineralization of the bone matrix.

osteoporosis (OSS-tee-oh-pore-OH-sis) a reduction of the bone mass of older persons in which the bones become porous and fragile (osteo means “bones”; poros means “po- rous”); also known as adult bone loss. (Also defi ned in Chapter 6).

peak bone mass the highest attainable bone density for an individual; developed dur- ing the fi rst three decades of life.

290 chapter 8 W a t e r a n d M i n e r a l s

helps calcium absorption. When the body needs more calcium, proteins in the intes- tinal lining increase its absorption.26 Th e result is obvious in the case of a pregnant woman, who absorbs 50 percent of the calcium from the milk she drinks. Similarly, growing children and teens absorb 50 to 60 percent of the calcium they consume.27

Th e body also absorbs a higher percentage of the available calcium when the rou- tine daily diet provides less calcium. 28 Deprived of the mineral for months or years, an adult may double the calcium absorbed; conversely, when supplied for years with abundant calcium, the same person may absorb only about one-third the normal amount. Despite these adjustments, increased calcium absorption cannot fully compensate for a reduced intake. A person who cuts back on calcium is likely to lose calcium from the bones.

How Much Calcium Do I Need? Setting recommended intakes for calcium is diffi cult because absorption varies (the Food Feature comes back to calcium absorp- tion). Th e DRI committee took such variations into account and set recommenda- tions for calcium at levels that produce maximum calcium retention (see the inside front cover, page B). At lower intakes, the body does not store calcium to capacity; at greater intakes, the excess calcium is excreted and thus is wasted.

Snapshot 8-1 provides a look at some foods that are good or excellent sources of calcium, and the Food Feature at the end of the chapter focuses on foods that can help to meet calcium needs. Fiber and the binders phytate (in whole grains) and oxalate (in vegetables) interfere with calcium absorption, but their eff ects are only minor in a typical U.S. diet.

High intakes of calcium from supplements may have adverse eff ects, such as kid- ney stone formation, and supplements may not provide all of the benefi cial eff ects of calcium-rich foods on the bones.29 Because adverse eff ects are possible, an Upper Level has been established (see inside front cover, page C).

10Bone density

20 30 40 50 60 70 80

Peak bone mass

Active growth Bone loss

Time (years)

From birth to about age 20, the bones are actively growing. Between the ages of 12 and 30 years, the bones achieve their maximum mineral density for life—the peak bone mass. Beyond those years, bone resorption exceeds bone formation, and bones lose density.

Bone Throughout Life figure 8-8

CONCEPT LINK 8-5 The importance of vitamin D in calcium absorption was described in Chapter 7, page 235.

Did You Know? In osteoporosis, bones of older adults become brittle and fragile.

Drink Your Milk!

Listen to two students talk about how they learned about the importance of calcium.

To hear their stories, log on to www.cengage.com/sso.

my turn

Kathryn Cynthia

en ga

ge L

ea rn

in g

en ga

ge L

ea rn

in g

http://www.cengage.com/sso

291T h e M a j o r M i n e r a l s

KE Y POINT Calcium makes up bone and tooth structure and plays roles in nerve transmission, muscle contraction, and blood clotting. Calcium absorption rises when there is a dietary defi ciency or an increased need such as during growth.

Phosphorus Phosphorus is the second most abundant mineral in the body, next to calcium. About 85 percent of the body’s phosphorus is found combined with calcium in the crystals of the bones and teeth. Th e rest is everywhere else.

Roles in the Body All body cells rely on phosphorus for these functions:

Phosphorous salts are critical buff ers, helping to maintain the acid-base balance •

of cellular fl uids.

Phosphorus is part of the DNA and RNA of every cell and thus is essential for •

growth and renewal of tissues.

Phosphorous compounds carry, store, and release energy in the metabolism of •

energy nutrients.

Phosphorous compounds assist many enzymes and vitamins in extracting the •

energy from nutrients.

Phosphorus forms part of the molecules of the phospholipids that are principal •

components of cell membranes (discussed in Chapter 5).

Phosphorus is present in some proteins.•

Recommendations and Food Sources Luckily, the body’s need for phosphorus is easily met by almost any diet, defi ciencies are unlikely, and most people in the United States meet their need.30 As Snapshot 8-2 shows, animal protein is the best source of phosphorus (because phosphorus is abundant in the cells of animals). Milk

Calcium DRI Recommended Intakes Adults: 1,000 mg/day (19–50 yr) 1,200 mg/day (>51 yr)

Tolerable Upper Intake Level Adults: 2,500 mg/day

Chief Functions Mineralization of bones and teeth; muscle contraction and relax- ation, nerve functioning, blood clotting

Defi ciency Stunted growth and weak bones in children; bone loss (osteo- porosis) in adults

Toxicity Constipation; interference with absorption of other minerals; increased risk of kidney stone formation

*These foods provide 10 percent or more of the calcium Daily Value in a serving. For a 2,000-calorie diet, the DV is 1,000 mg/day. aBroccoli, kale, and some other cooked green leafy vegetables are also important sources of bioavailable calcium. Almonds also supply calcium. Spinach and chard contain calcium in an unabsorbable form. Some calcium-rich mineral waters may also be good sources.

snapshot 8-1

GOOD SOURCES*

SARDINES (with bones) 3 oz = 325 mg

MILK 1 c = 300 mg

TOFU (calcium set) ½ c = 275 mg

BROCCOLIa (cooked) 1½ c = 93 mg

TURNIP GREENS (cooked)

1 c = 198 mg

CHEDDAR CHEESE 1½ oz = 288 mg

WAFFLE (whole grain)

1 WAFFLE = 196 mg

292 chapter 8 W a t e r a n d M i n e r a l s

and cheese are also rich sources. Food additives, such as modifi ed starches used in gravies, prepared meals, creamy desserts, and other processed foods and phosphates added to colas also contribute phosphorus to the diet.

KE Y POINT Phosphorus is abundant in bones and teeth. Phosphorus helps maintain acid-base balance, is part of the genetic material in cells, assists in energy metabolism, and forms part of cell membranes. Under normal circumstances, defi ciencies of phosphorus are unlikely.

Magnesium Magnesium qualifi es as a major mineral by virtue of its dietary requirement, but only about 1 ounce is present in the body of a 130-pound person, over half of it in the bones. Most of the rest is in the muscles, heart, liver, and other soft tissues, with only 1 percent in the body fl uids. Th e supply of magnesium in the bones can be tapped to maintain a constant blood level whenever dietary intake falls too low. Th e kidneys can also act to conserve magnesium.

Roles in the Body Like phosphorus, magnesium is critical to many cell func- tions. Magnesium:

assists in the operation of more than 300 enzymes.•

is needed for the release and use of energy from the energy-yielding nutrients.•

directly aff ects the metabolism of potassium, calcium, and vitamin D.•

is critical to normal heart functioning.•

Magnesium and calcium work together for proper functioning of the muscles: cal- cium promotes contraction, and magnesium helps the muscles relax afterward. In the teeth, magnesium promotes resistance to tooth decay by holding calcium in tooth enamel.

Magnesium Defi ciency A magnesium defi ciency may occur as a result of in- adequate intake, vomiting, diarrhea, alcoholism, or protein malnutrition. It may

Phosphorus DRI Recommended Intake Adults: 700 mg/day

Tolerable Upper Intake Level Adults (19–70 yr): 4,000 mg/day

Chief Functions Mineralization of bones and teeth; part of phospholipids, important in genetic material, energy metabolism, and buffering systems

Defi ciency Muscular weakness, bone paina

Toxicity Calcifi cation of soft tissues, particularly the kidneys

*These foods provide 10 percent or more of the phosphorus Daily Value in a serving. For a 2,000-calorie diet, the DV is 1,000 mg/day. aDietary defi ciency rarely occurs, but some drugs can bind with phosphorus, making it unavailable.

snapshot 8-2

GOOD SOURCES*

MILK 1 c = 229 mg

COTTAGE CHEESE 1 c = 368 mg

SALMON (canned) 3 oz = 280 mg

NAVY BEANS (cooked) ½ c = 131 mg

SIRLOIN STEAK (lean)

3 oz = 209 mg

Did You Know? The mineral is phosphorus. The adjective form is spelled with an -ous (as in phosphorous

salts).

293T h e M a j o r M i n e r a l s

also occur in hospital clients who have been fed magnesium-poor fl uids through a vein for too long or in people who are using diuretics. People whose drinking water provides adequate magnesium experience a lower incidence of sudden death from heart failure than other people, probably because magnesium defi ciency makes the heart unable to stop spasms once they start. Magnesium solution given in a vein can often correct an abnormal heartbeat.31 A defi ciency also causes hallucinations that can be mistaken for mental illness or drunkenness. Although almost half the U.S. population has intakes below those recommended, defi ciency symptoms are rare in healthy people.32

Magnesium Toxicity Magnesium toxicity is rare, but it can be fatal. Toxicity occurs only with high intakes from nonfood sources such as supplements or mag- nesium salts. Accidental poisonings may occur in children with access to medicine chests and in older people who abuse magnesium-containing laxatives, antacids, and other medications. Th e consequences can be severe diarrhea, acid-base imbal- ance, and dehydration. For safety, be mindful of the UL for magnesium when using magnesium-containing medications.

Recommendations and Food Sources Magnesium DRI recommendations vary slightly among adult age groups (see the inside front cover, page B).33 Snapshot 8-3 shows magnesium-rich foods. Magnesium is easily washed and peeled away from foods during processing, so slightly processed or unprocessed foods are the best sources. In some parts of the country, water contributes signifi cantly to magnesium intakes, so people living in those regions need less from food.

KE Y POINT Most of the body’s magnesium is in the bones and can be drawn out for all the cells to use in building protein and using energy. Many people in the United States choose diets that lack suffi cient magnesium.

Magnesium DRI Recommended Intakes Men (19–30 yr): 400 mg/day Women (19–30 yr): 310 mg/day

Tolerable Upper Intake Level Adults: 350 mg/daya

Chief Functions Bone mineralization, protein synthesis, enzyme action, muscle contraction, nerve function, tooth maintenance, and immune function

Defi ciency Weakness, confusion; if extreme, convulsions, uncontrollable muscle contractions, hallucinations, and diffi culty in swallowing; in children, growth failure

Toxicity From nonfood sources only; diarrhea, pH imbalance, dehydration

*These foods provide 10 percent or more of the magnesium Daily Value in a serving. For a 2,000-calorie diet, the DV is 400 mg/day. aFrom nonfood sources, in addition to the magnesium provided by food. bWheat bran provides magnesium, but refi ned grain products are low in magnesium. cMagnesium in oysters varies.

snapshot 8-3

GOOD SOURCES*

SPINACH (cooked) ½ c = 78 mg

BLACK BEANS (cooked) ½ c = 60 mg

SOY MILK 1 c = 46 mg

BRAN CEREALb

(ready-to-eat) 1 c = 60 mg

OYSTERSc (steamed) 3 oz = 81 mg

YOGURT (plain) 1 c = 43 mg

294 chapter 8 W a t e r a n d M i n e r a l s

Sodium Salt has been known and valued throughout recorded history. “You are the salt of the earth” means that you are valuable. If “you are not worth your salt,” you are worthless. Even our word salary comes from the Latin word for salt. Chemically, sodium is the positive ion in the compound sodium chloride (table salt) and makes up 40 percent of its weight: a gram of salt contains 400 milligrams of sodium.

Roles of Sodium Sodium is a major part of the body’s fl uid and electrolyte bal- ance system because it is the chief ion used to maintain the volume of fl uid outside cells. Sodium also helps maintain acid-base balance and is essential to muscle con- traction and nerve transmission. Scientists think that 30 to 40 percent of the body’s sodium is stored on the surface of the bone crystals, where the body can easily draw on it to replenish the blood concentration.

Sodium Defi ciency A defi ciency of sodium would be harmful, but no known human diets lack sodium.34 Most foods include more salt than is needed, and the body absorbs it freely. Th e kidneys fi lter the surplus out of the blood into the urine. Th ey can also sensitively conserve sodium. In the rare event of a defi ciency, they can return to the bloodstream the exact amount needed. Small sodium losses occur in sweat, but the amount of sodium excreted in a day equals the amount ingested that day. But, if sodium is so well controlled by the body, why do authorities urge people to limit their intakes? To understand why, you must fi rst understand how sodium interacts with body fl uids.

How Are Salt and “Water Weight” Related? Blood sodium levels are well con- trolled.35 If blood sodium begins to rise, as it will after a person eats salted foods, a series of events trigger thirst and ensure that the person will drink water until the sodium-to-water ratio is restored. Th en the kidneys excrete the extra water along with the extra sodium.

Dieters sometimes think that eating too much salt or drinking too much water will make them gain weight, but they do not gain fat, of course. Th ey gain water, but a healthy body excretes this excess water immediately. Excess salt is excreted as soon as enough water is drunk to carry the salt out of the body. From this perspec- tive, then, the way to keep body salt (and “water weight”) under control is to control salt intake and drink more, not less, water.

If blood sodium drops, body water is lost, and both water and sodium must be replenished to avert an emergency. Overly strict use of low-sodium diets in the treatment of hypertension, kidney disease, or heart disease can deplete the body of needed sodium; so can vomiting, diarrhea, or extremely heavy sweating.

Sodium Recommendations and Intakes Th e DRI intake recommendation for sodium has been set at 1,500 milligrams for healthy, active young adults; at 1,300 for people ages 51 through 70; and at 1,200 for the elderly.36 Th ese amounts are suffi cient to ensure an overall diet that provides adequate amounts of other needed nutrients.

Figure 8-9 shows that the average U.S. sodium intake tops 3,400 mg per day, an amount that far exceeds the DRI UL of 2,300 mg per day (equal to approxi- mately 1 tsp of salt).37 Th ree groups of people encompassing about 70 percent of U.S. adults—persons with hypertension, all middle-aged and older adults, and all African Americans—are urged to limit their sodium intakes for the sake of their blood pressure and heart health (see Table 8-4).38

Sodium and Blood Pressure High intakes of salt among the world’s people cor- relates with high rates of hypertension, heart disease, and cerebral hemorrhage, a hypertension-related stroke.39 An estimated 29 percent of U.S. adults have hyperten- sion (that is, high blood pressure), and another 28 percent have prehypertension.40

In many people, the relationship between salt intake and blood pressure is im- mediate and direct—as sodium intakes increase, blood pressure rises with them in a stepwise fashion in just days or weeks of exposure.41 And with high blood pressure, the heart becomes damaged and risk of death from stroke and heart disease climbs

Did You Know? To the chemist, a salt results from the reaction between a base and an acid. Sodium chloride, table salt, arises when the base sodium hy- droxide reacts with hydrochloric acid.

Base + acid = salt + water.

Sodium hydroxide + hydrochloric acid = sodium chloride + water.

Did You Know? Too little sodium can pose a danger to endur- ance athletes performing in hot, humid condi- tions (see Chapter 10).

Chapter 11 presents more details about • blood pressure and lists standard ranges for blood pressure readings.

hypertension high blood pressure; also defi ned in Chapter 11.

prehypertension blood pressure values that predict hypertension. See Chapter 11.

Sodium Intakes

of U.S. Adults

figure 8-9

D a ily

a v e ra

g e s (

m ill

ig ra

m s )

Men Women

3,500

3,000

2,500

2,000

1,500

1,000

500

2,300 a

4,000

aDRI Tolerable Upper Intake Level (UL).

295T h e M a j o r M i n e r a l s

steeply.42 In a large 15-year intervention study, when people with prehypertension reduced their sodium intakes, they reduced their risk of developing heart disease or dying from it by 25 to 30 percent.43

A diff erent form of hypertension, so far observed in rats, baboons, and chimpan- zees, occurs slowly over a lifetime of high sodium intakes. Th is progressive form of hypertension is particularly sinister because it proves irreversible when sodium is reduced.44 If the same holds true for human beings, as population evidence suggests that it does, some people in apparent good health may be on the road to developing an irreversible form of hypertension, making it all the more urgent to cut sodium intakes early on before disease sets in. More human research is needed in this area.

Variations among people’s blood pressure responses to sodium can be partly ex- plained by their genetic inheritance.45 Th e relationships are complex but research- ers suspect that the genes that aff ect blood pressure do so by altering the kidneys’ handling of sodium.

Can Diet Lower Blood Pressure? Luckily, most people can modify their salt response by consuming more potassium-rich foods, especially fruits and vegetables, in the context of a nutritious diet. One proven eating pattern can help people to reduce their sodium and increase potassium intakes, thereby reducing their disease risks.46 Th is dietary approach can lower blood pressure in salt-sensitive and non– salt-sensitive people alike. Th e DASH (Dietary Approaches to Stop Hypertension) diet often achieves a lower blood pressure than restriction of sodium intake alone. It calls for greatly increased intakes of potassium-rich fruits and vegetables, with ad- equate amounts of nuts, fi sh, whole grains, and low-fat dairy products. At the same time, red meat, butter, and other high-fat foods and sweets are held to occasional small portions. Th e diet not only often lowers elevated blood pressure but may pre- vent it from occurring in the fi rst place.47

Other Reasons to Cut Salt Intakes Many Americans have much to gain in terms of cardiovascular health and nothing to lose from cutting back on salt as part of an overall lifestyle strategy to reduce blood pressure. Physical activity should also be part of that lifestyle because regular moderate exercise reliably lowers blood pressure.

Other valid reasons exist for most people to hold their salt intakes at or below the recommended maximum. For example, older people without clinical hypertension often die of stroke, and reducing dietary sodium may lower their blood pressure enough to reduce their stroke risk. Excess salt in the diet also increases calcium excretion, an eff ect that could potentially compromise the integrity of the bones.48 Excessive salt may also directly stress a weakened heart or aggravate kidney prob- lems, and high salt intakes among many Asian peoples have been linked with their high rates of stomach cancer.49

Controlling Salt Intake Cutting down on salt and sodium may be easier than people believe, and Table 8-5 demonstrates how, with a few thoughtful food choices, a meal’s sodium can be drastically reduced. Notice that in the meal in the left-hand column, sauces, dressings, and the salt added to corn, chips, pickles, and piecrust and sprinkled on foods are the major modifi able sources of sodium. Notice, too, that even without added sauces and salt, most foods contain enough sodium to easily meet most people’s needs. Foods eaten without salt may seem less tasty at fi rst, but with repetition, tastes adjust and the natural fl avor becomes the preferred taste. Also, remember that the recommendation is to consume little sodium, not eliminate it altogether. Many experts today are calling for legislation to reduce the sodium in the food supply.50

While an obvious step is to control the saltshaker, this source may contribute as little as 15 percent of the total salt consumed. As Figure 8-10 indicates, a more productive step is to cut down on processed and fast foods, the source of almost 75 percent of salt in the U.S. diet. Often, the least processed foods in each food group are not only lowest in sodium but also highest in potassium. Low potassium may equal high sodium in its eff ects on blood pressure, so processed foods have two strikes against them.51 Th e margin list on page 296 provides the FDA’s guidelines for judging sodium in processed foods.52

DRI Recommendations Recommended intakes for sodium:•

Adults: (19–50 years): 1,500 mg per day. Adults: (51–70 years): 1,300 mg per day. Adults: (71 years and older): 1,200 mg per day.

Tolerable Upper Intake Level for sodium • and salt:

Adults (19 years and older): 2,300 mg sodium, or 5.6 g salt (sodium chloride) per day.

The Centers for Disease Control and Prevention urge these groups of people to consume no more than 1,500 mg of sodium per day:

People 40 years of age or older• African Americans• People with high blood pressure•

Sodium and Salt

Intake Guidelines

table 8-4

The DASH diet is presented in full in the • Food Feature of Chapter 11.

Herbs add delicious fl avors to foods without add- ing salt.

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296 chapter 8 W a t e r a n d M i n e r a l s

In addition to salt, sodium-containing additives are listed among the ingredients: sodium benzoate, monosodium glutamate, sodium nitrite, or sodium ascorbate, to name a few.

Many people are unaware that foods high in sodium do not always taste salty.

Who could guess by taste alone that half a cup of instant chocolate pudding pro- vides almost one-fi fth of the daily upper limit for sodium? Moral: Read the Nutri- tion Facts labels.

KE Y POINT Sodium is the main positively charged ion outside the body’s cells. Sodium attracts water. Sodium chloride is table salt. Too much dietary salt raises blood pressure and aggravates hypertension. Diets rarely lack sodium.

Potassium Outside the body’s cells, sodium is the principal positively charged ion. Inside the cells, potassium takes the role of the principal positively charged ion.

Roles in the Body Potassium plays a major role in maintaining fl uid and electro- lyte balance and cell integrity, and it is critical to maintaining the heartbeat. During nerve impulse transmission and muscle contraction, potassium and sodium briefl y trade places across the cell membrane. Th e cell then quickly pumps them back into place. Controlling potassium distribution is a high priority for the body because it aff ects many aspects of homeostasis, including a steady heartbeat.

Low potassium intakes, especially when combined with high sodium intakes, raise blood pressure and increase the risk of death from heart disease.53 Diets pro- viding ample potassium, especially those also low in sodium, appear to both prevent and correct hypertension.

Potassium Defi ciency In healthy people, almost any reasonable diet provides enough potassium to prevent the dangerously low blood potassium that indicates a severe defi ciency. However, dehydration leads to a loss of potassium from inside cells. Th is condition is dangerous because when the cells of the brain lose potas- sium, the person loses the ability to notice the need for water. Th e sudden deaths that occur during fasting, with severe diarrhea, in children with kwashiorkor, or in people with eating disorders may be due to heart failure caused by potassium loss. Adults are warned not to take diuretics (water pills) that cause potassium loss or to give them to children, except under a physician’s supervision. Physicians prescribing diuretics will tell clients to eat potassium-rich foods to compensate for the losses.

Lunch #1 exceeds the whole day’s Tolerable Upper Intake Level of 2,300 milligrams sodium. With careful substitutions, the so- dium drops dramatically in the second lunch, but it still provides over 40 percent of the suggested maximum intake. In lunch #3, just three small changes—omitting the sauce, coleslaw dressing, and salt—cut the sodium by half again.

Lunch #1: Highest Sodium (mg) Lunch #2: Lower Sodium (mg) Lunch #3: Lowest Sodium (mg)

Chopped pork sandwich, • sauce and meat mixture

950 Sliced pork sandwich, • with 1 tbs sauce

400 Sliced pork sandwich • (no sauce)

210

Creamed corn, ½ c• 460 Corn, 1 cob, soft margarine, salt 190• Corn, 1 cob, soft margarine 50• Potato chips, 2.5 oz• 340 Coleslaw, ½ c• 180 Green salad, oil and vinegar 10• Dill pickle, ½ medium• 420 Watermelon, slice• 10 Watermelon, slice• 10

Milk, low-fat, 1 c• 120 Milk, low-fat, 1 c• 120 Milk, low-fat, 1 c• 120

Pecan pie, slice• 480 Ice cream, low-fat, ½ c• 80 Ice cream, low-fat, ½ cup 80• Total 2,770 Total 980 Total 480

How to Cut Sodium from a Barbecue Lunch table 8-5

Food labels help consumers evaluate so-• dium in foods:

Low-sodium foods provide 5% or less of •

the Daily Value.

Moderate-sodium foods provide 6% to •

20% of the Daily Value.

High-sodium foods provide above 20% of •

the Daily Value.

CONCEPT LINK 8-6 Kwashiorkor was described in Chapter 6 (page 211).

297T h e M a j o r M i n e r a l s

Potassium Toxicity Potassium from foods is safe, but potassium injected into a vein can stop the heart. Potassium chloride pills are available over the counter and are sold in health-food stores without a warning label, but they should not be used except on a physician’s advice. Potassium overdoses normally are not life-threatening as long as they are taken by mouth because the presence of excess potassium in the stomach triggers a vomiting refl ex that expels the unwanted substance. A person with a weak heart, however, should not go through this trauma, and a baby may

Those that are low in sodium contribute less than 10 percent of the total sodium in the U.S. diet.

Salt added at home, in cooking or at the table, contributes 15 percent of the total sodium in the U.S. diet. Many seasonings and sauces also contribute salt and sodium.

These contribute 75 percent of the sodium in the U.S. diet.

Unprocessed Foods Salt Processed Foods

Fresh foods higher in sodium Milk, 120 mg per 1 c Scallops, 260 mg per 3 oz Fresh meats, about 30 to 70 mg per 3 oz Chicken, beef, fish, lamb, pork Fresh vegetables, about 30 to 50 mg per 1/2 c Celery, Chinese cabbage, sweet potatoes Fresh vegetables, about 10 to 20 mg per 1/2 c Broccoli, brussels sprouts, carrots, corn, green beans, legumes, potatoes, salad greens Grains (cooked without salt), about 0 to 10 mg per 1/2 c Barley, oatmeal, pasta, rice

Salts, about 2,000 mg per teaspoon Salt, sea salt, seasoned salt, onion salt, garlic salta

Soy sauce, about 300 mg per teaspoon Condiments and sauces, about 100 to 200 mg per tablespoon Barbecue sauce, ketchup, mustard, salad dressings, sweet pickle relish, taco sauce, Worcestershire sauce

Dry soup mixes (prepared), about 1,000 to 2,000 mg per 1 c Bouillon cube, noodle soups, onion soup, ramen Smoked and cured meats, about 700 to 2,000 mg per 2 oz Canned ham products, corned or chipped beef, ham, lunchmeats Fast foods and TV dinners, about 700 to 1,500 mg per serving Breakfast biscuit (cheese, egg, and ham), cheeseburger, chicken wings (10 spicy wings), frozen TV dinners, pizza (2 slices), taco, vegetarian soy burger (on bun) Canned soups (prepared), about 700 to 1,500 mg per 1 c Bean soup, beef or chicken soups, broths,“hearty” soups, tomato soup, vegetable soup Canned pasta, about 800 to 1,000 mg per serving Beefaroni, macaroni and cheese, ravioli Hot dogs, about 500 to 700 mg per 2 oz Hot dogs, smoked sausages Foods prepared in brine, about 300 to 800 mg per serving Anchovies (2 fillets), dill pickles (1), olives (5), sauerkraut 1/2 c Cheeses, processed, about 550 mg per 11/2 oz American, cheddar, Swiss Pudding, instant, about 420 mg per 1/2 c All flavors Canned vegetables, about 200 to 450 mg per 1/2 c Carrots, corn, green beans, legumes, peas, potatoes Cereals, dry ready-to-eat, about 180 to 260 mg per 1 oz Cheerios, cornflakes, corn bran, Cocoa Puffs, Total, others

aNote that herb seasoning blends may or may not contain substantial sodium; read the labels.

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Sources of Sodium in the U.S. Diet figure 8-10

298 chapter 8 W a t e r a n d M i n e r a l s

Did You Know? Unlike sodium, potassium may exert a positive effect against hypertension and related ills.

not be able to withstand it. Several infants have died when well-meaning parents overdosed them with potassium supplements.

Potassium Recommendations and Food Sources A typical U.S. diet, with its low intakes of fruits and vegetables, provides only about half of the daily 4,700 milligrams of potassium recommended by the DRI committee.54 Although blood potassium may remain normal on such a diet, chronic diseases are more likely to occur. Low potassium intakes raise blood pressure, whereas high potassium intakes, especially when combined with low sodium intakes, appear to both prevent and correct hypertension.55 In addition, low potassium intakes may worsen glucose intolerance, increase metabolic acidity, accelerate calcium losses from bones, and make kidney stone formation more likely.

Potassium is found inside all living cells and cells remain intact unless foods are processed; therefore, the richest sources of potassium are fresh, whole foods (see Snapshot 8-4). Most vegetables and fruits are outstanding. Bananas, despite their fame as the richest potassium source, are only one of many rich sources, which also include spinach, cantaloupe, and almonds. Nevertheless, bananas are readily avail- able, are easy to chew, and have a sweet taste that almost everyone likes, so health- care professionals often recommend them.

Th e amount of fruits and vegetables recommended in both the USDA Food Guide and the DASH diet provide all the needed potassium. Potassium chloride, a salt substitute for people with hypertension who must strictly limit salt, provides potassium but does not reverse many of the conditions associated with diets that lack potassium-rich foods. 56

KE Y POINT Potassium, the major positive ion inside cells, is important in many metabolic functions. Fresh, whole foods are the best sources of potassium. Diuretics can deplete the body’s potassium and so can be dangerous; potassium excess can also be dangerous.

Chloride In its elemental form, chlorine forms a deadly green gas. In the body, the chloride ion plays important roles as the major negative ion. In the fl uids outside the cells, it

Potassium DRI Recommended Intake Adults: 4,700 mg/day

Chief Functions Maintains normal fl uid and electrolyte balance; facilitates chemical reactions; supports cell integrity; assists in nerve functioning and muscle contractions

Defi ciencya

Muscle weakness, paralysis, confusion

Toxicity Muscle weakness; vomiting; for an infant given supplements, or when injected into a vein in an adult, potassium can stop the heart

*These foods provide 10 percent or more of the potassium Daily Value in a serving. For a 2,000-calorie diet, the DV is 3,500 mg/day. aDefi ciency accompanies dehydration.

snapshot 8-4

GOOD SOURCES*

ORANGE JUICE 1 c = 496 mg

BANANA 1 whole banana = 422 mg

LIMA BEANS (cooked) ½ c = 485 mg

BAKED POTATO whole potato

= 844 mg

SALMON (cooked) 3 oz = 377

HONEYDEW MELON 1 cup = 406 mg

AVOCADO ½ avocado = 534 mg

299T h e T r a c e M i n e r a l s

accompanies sodium and so helps to maintain the crucial fl uid balances (acid-base and electrolyte balances). Th e chloride ion also plays a special role as part of hydro- chloric acid, which maintains the strong acidity of the stomach necessary to digest protein. Th e principal food source of chloride is salt, both added and naturally oc- curring in foods, and no known diet lacks chloride.

KE Y POINT Chloride is the body’s major negative ion; it is responsible for stomach acidity and assists in maintaining proper body chemistry. No known diet lacks chloride.

Sulfate Sulfate is the oxidized form of sulfur as it exists in food and water. Th e body requires sulfate for synthesis of many important sulfur-containing compounds. Sulfur- containing amino acids play an important role in helping strands of protein assume their functional shapes. Skin, hair, and nails contain some of the body’s more rigid proteins, which have high sulfur contents.

Th ere is no recommended intake for sulfate, and defi ciencies are unknown. Too much sulfate in drinking water, either naturally occurring or from contamination, causes diarrhea and may damage the colon. Th e summary table at the end of this chapter presents the main facts about sulfate and the other major minerals.

KE Y POINT Sulfate is a necessary nutrient used to synthesize sulfur-containing body compounds.

LO 8.7, 8.8

The Trace Minerals People require only miniscule amounts of the trace minerals but these quantities are vital for health and life. Intake recommendations have been established for nine trace minerals—see Table 8-6. Others are recognized as essential nutrients for some animals but have not been proved to be required for human beings.

Iodine Th e body needs only traces of iodine, but this amount is indispensable to life. Once absorbed, the form of iodine that does the body’s work is the ionic form, iodide.

The DRI committee set recommended intake • values for chloride; see the inside front cover, page B.

Human Intake Recommendations

Established

Known Essential for Animals; Human

Requirements Under Study

Known Essential for Some Animals; No Evidence That Intake by Humans Is Ever

Limiting

Iodine Iron Zinc Selenium Fluoride Chromium Copper Manganese Molybdenum

Arsenic Boron Nickel Silicon Vanadium

Cobalt

Note: The evidence for requirements and essentiality is weak for the trace minerals cadmium, lead, lithium, and tin.

Trace Minerals table 8-6

300 chapter 8 W a t e r a n d M i n e r a l s

Iodide Roles Iodide is a part of the hormone thyroxine, made by the thyroid gland. Th yroxine regulates the body’s metabolic rate, temperature, reproduction, growth, heart functioning, and more.57 Iodine must be available for thyroxine to be synthesized.

Iodine Defi ciency Th e ocean is the world’s major source of iodine. In coastal areas, kelp, seafood, water, and even iodine-containing sea mist are dependable io- dine sources. In many inland areas of the world, however, misery caused by iodine defi ciency is all too common. In iodine defi ciency, the cells of the thyroid gland enlarge in an attempt to trap as many particles of iodine as possible. Sometimes the gland enlarges making a visible lump in the neck, a goiter. People with iodine de- fi ciency this severe become sluggish and may gain weight. Goiter affl icts about 200 million people the world over, many of them in South America, Asia, and Africa, almost all due to iodine defi ciency.

Iodine defi ciency during pregnancy causes fetal death and reduced infant sur- vival; extreme and irreversible mental and physical retardation in the infant, known as cretinism; and it constitutes one of the world’s most common and preventable causes of mental retardation.† In iodine-poor areas of the world, families that fail to use iodized foods are often those who suff er child malnutrition and mortality.58 Much of the mental retardation can be averted if the woman’s defi ciency is detected and treated within the fi rst six months of pregnancy, but if treatment comes too late or not at all, the child may have an IQ as low as 20 (100 is average).59 Children with even a mild iodine defi ciency typically have goiters and may perform poorly in school; many times, treatment with iodine relieves the defi ciency.60

Iodine Toxicity Excessive intakes of iodine can enlarge the thyroid gland just as a defi ciency can.61 Although U.S. intakes are above the recommended intake of 150 micrograms, they are still below the Tolerable Upper Intake Level of 1,100 micro- grams per day for an adult.62 Like chlorine and fl uorine, iodine is a deadly poison in large amounts.

Food Sources of Iodine Th e iodine in food varies with the amount in the soil in which plants are grown or on which animals graze. Because iodine is plentiful in the ocean, seafood is a dependable source. In the central parts of the United States that were never beneath an ocean, the soil is poor in iodine. In those areas, once widespread iodine defi ciencies have been wiped out by the use of iodized salt and the consumption of foods shipped in from iodine-rich areas. Surprisingly, sea salt delivers little iodine because iodine becomes a gas and fl ies off into the air during the salt-drying process. In the United States, salt labels state whether the salt is iodized; in Canada, all table salt is iodized. Less than a half-teaspoon of iodized salt meets the entire recommendation, but U.S. consumers rarely need extra iodine; most people exceed the DRI recommended intake but fall short of the UL.

Much of the iodine in U.S. diets comes from iodized salt added liberally to fast food and prepared foods and from bakery products and milk. Commercial bakeries often use iodine-rich dough conditioners, and most dairies feed iodized grain to dairy cows, which passes iodine into the milk.63 When researchers in Massachu- setts measured the iodine in bread, they were astonished to fi nd from 10 micro- grams (mcg) to 587 mcg per slice. Just two slices of the highest-iodine bread exceeds the iodine UL for both adults and pregnant women and presents almost 4 times the UL for children. In the same study, a single cup of milk contained nearly the entire adult DRI intake value for iodine; thus, people drinking the required three cups of milk from this source each day obtained 3 times their iodine requirement from milk alone. Th e meaning of these results goes beyond a few bakeries and dairies near Boston. Currently, U.S. consumers cannot gauge their iodine intakes against the DRI standards because food labels list neither iodine quantities nor specify ingredi- ents that contain iodine in plain language.64

†Collectively, the problems caused by iodine defi ciency are sometimes referred to as iodine defi ciency disorder.

In iodine defi ciency, the thyroid gland enlarges—a condition known as simple goiter.

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goiter (GOY-ter) enlargement of the thyroid gland due to iodine defi ciency is simple goiter; enlargement due to an iodine excess is toxic goiter.

cretinism (CREE-tin-ism) severe mental and physical retardation of an infant caused by the mother’s iodine defi ciency during pregnancy.

The iodine UL for adults is 1,100 mcg; the • UL for pregnant women is 900 mcg; the UL for young children is 300 mcg.

301T h e T r a c e M i n e r a l s

KE Y POINT Iodine is part of the hormone thyroxine, which infl uences energy metabolism. The defi ciency diseases are goiter and cretinism. Iodine occurs naturally in seafood and in foods grown on land that was once covered by oceans; it is an additive in milk and bakery products. Large amounts are poisonous. Label information needs improvement.

Iron Every living cell, whether plant or animal, contains iron. Most of the iron in the body is a component of two proteins: hemoglobin in red blood cells and myoglobin in muscle cells.

Roles of Iron Iron-containing hemoglobin in the red blood cells carries oxygen from the lungs to tissues throughout the body. Iron in myoglobin holds and stores oxygen in the muscles for their use.

All the body’s cells need oxygen to combine with the carbon and hydrogen at- oms released from energy nutrients during their metabolism. Th is generates carbon dioxide and water waste products that are then removed from the cells; thus, body tissues constantly need fresh oxygen to keep the cells cleansed and functioning. As cells use up their oxygen, iron (in hemoglobin) shuttles fresh oxygen into the tissues from the lungs. In addition to this major task, iron is part of dozens of enzymes, particularly those involved in energy metabolism. Iron is also needed to make new cells, amino acids, hormones, and neurotransmitters.

Iron Stores Iron is clearly the body’s gold, a precious mineral to be hoarded. Th e liver packs iron sent from the bone marrow into new red blood cells, and ships them out to the bloodstream. Red blood cells live for about three to four months. When they die, the spleen and liver break them down, salvage their iron for recycling, and send it back to the bone marrow to be kept until it is reused. Th e body does lose iron from the digestive tract, in nail and hair trimmings, and in shed skin cells but only in tiny amounts.65 Bleeding, however, can cause signifi cant iron loss from the body.

Special measures are needed to contain iron in the body. Left free, iron is a pow- erful oxidant that generates free-radical reactions.66 Free radicals increase oxidative stress and infl ammation and damage cell structures in ways that may underlie dis- eases such as diabetes, heart disease, and cancer.67 Consequently, the body guards against iron’s renegade nature. Special proteins transport and store the body’s iron, keeping it away from vulnerable body compounds and preventing damaging reac- tions. Iron’s actions are thus tightly controlled.

Absorbing Iron Th e body also has special provisions for absorbing iron. Only about 10 to 15 percent of dietary iron is absorbed, but if the body’s supply of iron is diminished or if the need increases (say, during pregnancy), absorption can increase several-fold.68 Th e reverse is also true: absorption declines when iron is abundant.

Iron occurs in two forms in foods. Some is bound into heme, the iron-containing part of hemoglobin and myoglobin in meat, poultry, and fi sh. Some is nonheme iron, in plants and also in meats. Th e form aff ects absorption. Healthy people with adequate iron stores absorb heme iron at a rate of about 23 percent over a wide range of meat intakes. People absorb nonheme iron at rates of 2 to 20 percent, depending on dietary factors and iron stores.

Meat, fi sh, and poultry also contain a factor (MFP factor) that promotes the absorption of nonheme iron from other foods eaten at the same time.69 Vitamin C also improves absorption of nonheme iron, tripling iron absorption from foods eaten in the same meal. Th e bit of vitamin C in dried fruit, strawberries, or watermelon helps absorb the nonheme iron in these foods. Overall, the body absorbs an average of about 18 percent of the iron in a mixed meal.

Some substances impair iron absorption. Th ey include the tannins of tea and coff ee, the calcium and phosphorus in milk, and the phytates that accompany fi - ber in lightly processed legumes and whole-grain cereals. Ordinary black tea excels

CONCEPT LINK 8-7 To read about the damage caused by free radi- cals and oxidation, see Chapter 7 (page 239).

CONCEPT LINK 8-8 Figure 6-4 in Chapter 6 (page 193) de- picted the iron-containing heme molecule of hemoglobin.

Forms of iron affect absorption:•

Heme iron is easily absorbed.•

Nonheme iron is less easily absorbed.•

hemoglobin (HEEM-oh-globe-in) the oxygen-carrying protein of the blood; found in the red blood cells (hemo means “blood”; globin means “spherical protein”).

myoglobin (MYE-oh-globe-in) the oxygen- holding protein of the muscles (myo means “muscle”).

heme (HEEM) the iron-containing portion of the hemoglobin and myoglobin molecules.

nonheme iron dietary iron not associated with hemoglobin; the iron of plants and other sources.

MFP factor a factor present in meat, fi sh, and poultry that enhances the absorption of nonheme iron present in the same foods or in other foods eaten at the same time.

tannins compounds in tea (especially black tea) and coffee that bind iron. Tannins also denature proteins.

phytates (FYE-tates) compounds present in plant foods (particularly whole grains) that bind iron and may prevent its absorption.

The chili dinner provides iron and MFP factor from meat, iron from legumes, and vitamin C from to- matoes. The combination of heme iron, nonheme iron, MFP factor, and vitamin C helps to achieve maximum iron absorption.

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302 chapter 8 W a t e r a n d M i n e r a l s

at reducing iron absorption—clinical dietitians advise people with iron overload to drink it with their meals. For those who need more iron, the opposite advice applies—drink tea between meals, not with food.

Th us, the amount of iron absorbed from a regular meal depends partly on the interaction between promoters and inhibitors. When you eat meat with legumes (for example, a ham sandwich and baked beans or chili with beans and meat), the iron from the meat is well absorbed and MFP factor enhances iron absorption from the beans. If the sandwich and chili also contain some tomato, the vitamin C will enhance iron absorption from the bread or beans. Cooking in an old-fashioned iron pan also adds iron salts, somewhat like the iron found in supplements. Th e iron content of 100 grams of spaghetti sauce simmered in a glass pan is 3 milligrams, but it increases to 87 milligrams when the sauce is cooked in a black iron pan. Th is iron salt is not as well absorbed as iron from meat, but some does get into the body, especially if the meal also contains MFP factor or vitamin C.

What Happens in Iron Defi ciency? If absorption cannot compensate for losses or low dietary intakes, then iron stores are used up and iron defi ciency sets in. Iron defi ciency and iron-defi ciency anemia are not one and the same, though they of- ten occur together. Iron defi ciency develops in stages, and the distinction between iron defi ciency and its anemia is a matter of degree. People may be iron defi cient, meaning that they have depleted iron stores, without being anemic; with worsening iron defi ciency, they may become anemic.

A body severely deprived of iron becomes unable to make enough hemoglobin to fi ll new blood cells, and anemia results. A sample of iron-defi cient blood examined under the microscope shows cells that are smaller and lighter red than normal (see Figure 8-11). Th ese cells contain too little hemoglobin to deliver suffi cient oxygen to the tissues. As iron defi ciency limits the cells’ oxygen and energy metabolism, the person develops fatigue, apathy, and a tendency to feel cold. Th e blood’s lower concentration of its red pigment hemoglobin also explains the pale appearance of fair-skinned iron-defi cient people and the paleness of the normally pink tongue and eye linings of those with darker skin.

Mental Symptoms of Iron Defi ciency Long before the red blood cells are af- fected and anemia is diagnosed, a developing iron defi ciency aff ects behavior.70 Even slightly lowered iron levels cause fatigue, mental impairments, and impaired physical work capacity and productivity.71 Symptoms associated with iron defi ciency are eas- ily mistaken for behavioral or motivational problems (see Table 8-7). With reduced energy, people work less, play less, and think or learn less eagerly. Lack of energy does not always indicate a need for iron, however—see the Th ink Fitness feature. Taking supplements for fatigue without a defi ciency will not increase energy levels.

Dietary factors that increase iron absorption:•

Vitamin C.•

MFP factor.•

Factors that hinder iron absorption:•

Tea.•

Coffee.•

Calcium and phosphorus.•

Phytates, tannins, and fiber.•

The old-fashioned iron skillet adds supplemen- tal iron to foods.

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ar d

Normal red blood cells. Both size and color are normal.

Normal and Anemic Blood Cells figure 8-11

Blood cells in iron-defi ciency anemia. These cells are small and pale because they contain less hemoglobin.

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Apathy, listlessness

Behavior disturbances

Clumsiness

Hyperactivity

Irritability

Lack of appetite

Learning disorders (vocabulary, perception)

Low scores on latency and associative reactions

Lowered IQ

Reduced physical work capacity

Repetitive hand and foot movements

Shortened attention span

Note: These symptoms are not caused by anemia itself but by iron defi ciency in the brain. Children with much more severe anemias from other causes, such as sickle-cell anemia and thalas- semia, show no reduction in IQ when compared with children without anemia.

The Mental

Symptoms

of Anemia

table 8-7

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303T h e T r a c e M i n e r a l s

Children deprived of iron become restless, irritable, unwilling to work or play, and unable to pay attention, and they may fall behind their peers academically. Some symptoms in children, such as irritability, disappear when iron intake im- proves. Others, such as academic failure, may linger after iron repletion, although more studies are needed to clarify this association.72 In iron-defi cient adults, men- tal symptoms clear up reliably when iron is restored.73

A poorly understood behavior seen among some iron-defi cient people, particu- larly low-income women and children, is pica—the craving and consumption of ice, chalk, starch, clay, soil, and other nonfood substances. Th ese substances cannot remedy a defi ciency; in fact, ingested clay inhibits iron absorption, and may cause or worsen iron defi ciency. Researchers hypothesize that pica may result from hunger, nutrient defi ciencies, or attempts at self-treatment of medical conditions.74

Causes of Iron Defi ciency and Anemia Iron defi ciency is usually caused by in- adequate iron intake, either from sheer lack of food or from a steady diet of iron-poor foods. In developed nations, high-calorie foods that are rich in refi ned carbohydrates and fats and poor in nutrients often displace nutritious iron-rich foods from the diet. Th is may explain why obesity and iron defi ciency often occur together in the United States—a steady diet of such foods presents too many calories with too few nutrients.75 In contrast, Snapshot 8-5 shows some foods that are good or excellent sources of iron.

Th e number-one nonnutritional factor that can cause anemia is blood loss. Be- cause the majority of the body’s iron is in the blood, losing blood means losing iron. Menstrual losses increase women’s iron needs to more than double that of men. Digestive tract problems such as ulcers and infl ammation can also cause blood loss severe enough to cause anemia.

Who Is Most Susceptible to Iron Defi ciency? Women of childbearing age can easily develop iron defi ciency because they not only need more iron but they also eat less food than men, on average. In addition to menstruation, pregnancy demands additional iron to support the added blood volume, growth of the fetus, and blood loss during childbirth. Infants and toddlers receive little iron from their high-milk diets, yet need extra iron to support their rapid growth. Th e rapid growth of adoles- cence, especially for males, and the menstrual losses of females also demand extra iron that a typical teen diet may not provide. An adequate iron intake is especially important during these stages of life.

In the United States, 2.4 million young children suff er from iron defi ciency while almost a half-million are diagnosed with iron-defi ciency anemia. Most often, the children are from urban, low-income, and Hispanic families, but children from all groups can develop these conditions.76 As for women in childbearing years, the percentage of iron defi ciency remains 3 times higher than the goal of Healthy

P eople Objectives for the Nation. To combat iron defi ciency, the Special Supplemental

think fitness Exercise-Defi ciency Fatigue

On hearing about symptoms of iron deficiency, tired people may jump to the conclusion that they need to take iron supplements to restore their pep. More likely, they

can obtain help by simply getting to bed on time and getting enough exercise. Few realize that too little exercise over weeks and months is as exhausting as too much—the

less you do, the less you’re able to do, and the more fatigued you feel. The condition even has a name: “sedentary inertia.”

START NOW

Ready to make a change? Consult the online behavior-change planner to set goals to obtain suffi cient physical activity to energize your days at www.cengage.com/sso.

Feeling fatigued, weak, and apathetic does • not necessarily mean that you need iron supplements. Three actions are called for:

Get your diet in order.1.

Get some exercise.2.

If symptoms persist for more than a 3. week or two, consult a physician for a diagnosis.

Did You Know? Iron defi ciency makes children more suscep- tible to lead poisoning.

iron defi ciency the condition of having depleted iron stores, which, at the extreme, causes iron-defi ciency anemia.

iron-defi ciency anemia a form of ane- mia caused by a lack of iron and characterized by red blood cell shrinkage and color loss. Ac- companying symptoms are weakness, apathy, headaches, pallor, intolerance to cold, and inability to pay attention. (For other anemias, see the index.)

anemia the condition of inadequate or impaired red blood cells; a reduced number or volume of red blood cells along with too little hemoglobin in the blood. The red blood cells may be immature and, therefore, too large or too small to function properly. Anemia can result from blood loss, excessive red blood cell destruction, defective red blood cell formation, and many nutrient defi ciencies. Anemia is not a disease, but a symptom of another problem; its name literally means “too little blood.”

pica (PIE-ka) a craving for nonfood sub- stances. Also known as geophagia (gee-oh- FAY-gee-uh) when referring to clay eating and pagophagia (pag-oh-FAY-gee-uh) when refer- ring to ice craving (geo means “earth”; pago means “frost”; phagia means “to eat”).

http://www.cengage.com/sso

304 chapter 8 W a t e r a n d M i n e r a l s

Feeding Program for Women, Infants, and Children (WIC) provides low-income families with credits redeemable for high-iron foods.

Worldwide, iron defi ciency is the most common nutrient defi ciency, aff ecting more than 1.6 billion people.77 In developing countries, parasitic infections of the digestive tract cause people to lose blood daily. For their entire lives, they may feel fatigued and listless but never know why. Almost half of the preschool children and pregnant women in these countries suff er from iron-defi ciency anemia.78 Iron sup- plements can reverse iron-defi ciency anemia from dietary causes in short order.79 Th ey may, however, create digestive upsets, oxidative damage in the digestive tracts of some people, and worse problems in others.

Can a Person Take in Too Much Iron? Iron is toxic in large amounts, largely due to increased oxidative stress in body tissues.80 Once absorbed inside the body, iron is diffi cult to excrete. Th e healthy body defends against iron overload by con- trolling its entry: the intestinal cells trap some of the iron and hold it within their boundaries. When they are shed, these cells carry out of the intestinal tract the excess iron that they collected during their brief lives.

In healthy people, when iron stores fi ll up, less iron is absorbed, protecting them against iron overload. In people with a tendency to absorb too much iron, mostly Caucasian men, excess iron builds up in the tissues.81 Early symptoms include fa- tigue, mental depression, or abdominal pain; untreated, the condition can cause liver failure, bone damage, diabetes, and heart failure.82 Infections are also likely because bacteria thrive on iron-rich blood.83 Alcohol abusers often suff er severe eff ects because the alcohol-damaged intestine can no longer defend against absorb- ing too much iron. Anyone with the condition must monitor and limit their iron intakes and avoid supplemental iron.

Iron-containing supplements can easily cause accidental poisonings in young children.84 As few as fi ve ordinary iron tablets have proved fatal in young children. Keep iron-containing supplements out of children’s reach.

These people are at higher risk for iron • deficiency:

Women in their reproductive years.•

Pregnant women.•

Infants and toddlers.•

Teenagers.•

Iron DRI Recommended Intakes Men: 8 mg/day Women (19–50 yr): 18 mg/day Women (51+): 8 mg/day

Tolerable Upper Intake Level Adults: 45 mg/day

Chief Functions Carries oxygen as part of hemoglobin in blood or myoglobin in muscles; required for cellular energy metabolism

Defi ciency Anemia: weakness, fatigue, headaches; impaired mental and physical work performance; impaired immunity; pale skin, nail- beds, and mucous membranes; concave nails; chills; pica

Toxicity GI distress; with chronic iron overload, infections, fatigue, joint pain, skin pigmentation, organ damage

*These foods provide 10 percent or more of the iron Daily Value in a serving. For a 2,000-calorie diet, the DV is 18 mg/day. Note: Dried fi gs contain 0.6 mg per ¼ cup; raisins contain 0.8 mg per ¼ cup. aSome clams may contain less, but most types are iron-rich foods. bLegumes contain phytates that reduce iron absorption. cEnriched cereals vary widely in iron content.

snapshot 8-5

GOOD SOURCES*

CLAMSa (steamed) 3 oz = 23.8 mg

BEEF STEAK 3 oz = 1.8 mg

NAVY BEANSb (cooked) ½ c = 2.3 mg

BLACK BEANS (cooked) ½ c = 1.8 mg

SPINACH (cooked) ½ c = 3.2 mg

ENRICHED CEREALc

(ready-to-eat) 1 c = 8.1 mg

SWISS CHARD (cooked)

½ c = 2.0 mg

BEEF LIVER (cooked) 3 oz = 5.24 mg

Chapter 14 offers guidance for preventing • iron deficiency in young children.

Table 8-8 on pages 310–311 summarizes the • effects of iron toxicity.

iron overload the state of having more iron in the body than it needs or can handle, usually arising from a hereditary defect. Also called hemochromatosis.

305T h e T r a c e M i n e r a l s

Iron Recommendations and Sources Th e usual diet in the United States pro- vides about 6 to 7 milligrams of iron for every 1,000 calories. Men need 8 milligrams of iron each day, and so do women past age 51, so these people have little trouble meeting their iron needs. For women of childbearing age, the recommendation is higher—18 milligrams—to replace menstrual losses. During pregnancy, a woman needs even more—27 milligrams a day; pregnant women need a supplement. If a man has a low hemoglobin concentration, his health-care provider should examine him for a blood-loss site. Vegetarians, because vegetable sources of iron are poorly absorbed, should aim for 1.8 times the normal requirement (see the margin).

Iron fortifi cation of foods helps some to fend off iron defi ciency but it can be a problem for people who tend toward iron overload. A single ounce of fortifi ed ce- real for breakfast, an ordinary ham sandwich at lunch, and a cup of chili with meat for dinner present almost twice the iron a man needs in a day but only about 800 calories. Most men need about 3,000 calories, and more food means still more iron. Th e U.S. love aff air with vitamin C supplements makes matters worse because vita- min C enhances iron absorption. For healthy people, however, fortifi ed foods pose virtually no risk for iron toxicity.

KE Y POINT Most iron in the body is contained in hemoglobin and myoglobin or occurs as part of enzymes in the energy- yielding pathways. Iron-defi ciency anemia is a problem worldwide; too much iron is toxic. Iron is lost through menstruation and other bleeding; reduced absorption and the shedding of intestinal cells protect against overload. Meat and vitamin C enhance iron.

Zinc Zinc occurs in a very small quantity in the human body, but it works with proteins in every organ, helping nearly 100 enzymes to:

make parts of the cells’ genetic material.•

protect cell structures against damage from oxidation.• 85

make heme in hemoglobin.•

assist the pancreas with its digestive and insulin functions.•

help metabolize carbohydrate, protein, and fat.•

liberate vitamin A from storage in the liver.•

Besides helping enzymes to function, several hundred zinc-containing proteins associate with DNA, where it is indispensible for synthesis of proteins and cell divi- sion critical to normal growth before and after birth.86 Zinc is also needed to pro- duce the active form of vitamin A in visual pigments. Even a mild zinc defi ciency can impair immunity, taste perception, and night vision. Zinc also:

aff ects behavior, learning, and mood.•

assists in proper immune functioning.• 87

is essential to wound healing, sperm production, taste perception, normal meta-•

bolic rate, nerve and brain functioning, bone growth, normal development in

children, and others.88

When zinc defi ciency—even a slight defi ciency—occurs, it packs a wallop to the body, impairing all these functions.

Problem: Too Little Zinc Zinc defi ciency in human beings was fi rst observed a half-century ago in children and adolescent boys in the Middle East who failed to grow and develop normally. Th eir native diets were typically low in animal protein and high in whole grains and beans; consequently, the diets were high in fi ber and phytates, which bind zinc as well as iron. Furthermore, the bread was not leavened; in leavened bread, yeast breaks down phytates as the bread rises. Since that time, zinc defi ciency has been identifi ed as a substantial contributor to illness throughout the developing

Did You Know? The iron Daily Value used on food labels, 18 milligrams, is more than double the DRI recommended intake for men.

To calculate the amount of daily iron • needed by vegetarians, multiply the DRI intake recommendation for the age and gender group (listed on the inside front cover, page B) by a factor of 1.8:

Vegetarian men: 8 mg A 1.8 = 14 mg/day.

Vegetarian women (19 to 50 yr): 18 mg A 1.8 = 32 mg/day.

leavened (LEV-end) literally, “lightened” by yeast cells, which digest some carbohydrate components of the dough and leave behind bubbles of gas that make the bread rise.

306 chapter 8 W a t e r a n d M i n e r a l s

world and responsible for almost a half-million deaths each year.89 Marginal zinc sta- tus also causes widespread problems in pregnancy, infancy, and early childhood.90 Zinc defi ciency alters digestive function profoundly and causes diarrhea, which worsens the malnutrition already present, not only of zinc but of all nutrients. It drastically impairs the immune response, making infections likely.91 Infections of the intestinal tract then worsen the malnutrition and further increase susceptibility to infections—a classic cycle of malnutrition and disease. Zinc therapy often reduces diarrhea and death in malnourished children but often fails to restore normal weight and height.92

Although zinc defi ciencies are not common in developed countries, they do occur among some groups, including pregnant women, young children, the elderly, and the poor. When pediatricians or other health workers note poor growth accompa- nied by poor appetite in children, they should think zinc.

Problem: Too Much Zinc Zinc is toxic in large quantities. High doses (over 50 milligrams) of zinc may cause vomiting, diarrhea, headaches, exhaustion, and other symptoms. A UL for adults was set at 40 milligrams—an amount based on degen- eration of the heart muscle in animals.

High doses of zinc inhibit iron absorption from the digestive tract. A blood pro- tein that carries iron from the digestive tract to tissues also carries some zinc. If this protein is burdened with excess zinc, little or no room is left for iron to be picked up from the intestine. Th e opposite is also true: too much iron also inhibits zinc ab- sorption. Zinc and iron are often found together in foods but, unlike supplements, food sources never cause imbalances in the body. Zinc from cold-relief lozenges, nasal gels, and throat spray products may or may not relieve a cold, but they contrib- ute zinc to the body and the FDA has reported permanent loss of the sense of smell in people who used nasal zinc products.93

Food Sources of Zinc Meats, shellfi sh, poultry, and milk and milk products are among the top providers of zinc in the U.S. diet (see Snapshot 8-6).94 Among plant sources, some legumes and whole grains are rich in zinc, but the zinc is not as well absorbed as it is from meat.95 Most people meet the recommended 11 milligrams

How old does the boy in the picture appear to be? He is 17 years old but is only 4 feet tall, the height of a 7-year-old in the United States. His reproductive organs are like those of a 6-year-old. The retardation is rightly ascribed to zinc defi ciency because it is partially reversible when zinc is restored to the diet. The photo was taken in Egypt.

. S an

st ea

d, U

ni ve

rs ity

o f T

ex as

-G al

ve st

Zinc DRI Recommended Intakes Men: 11 mg/day Women: 8 mg/day

Tolerable Upper Intake Level Adults: 40 mg/day

Chief Functions Activates many enzymes; associated with hormones; synthesis of genetic material and proteins, transport of vitamin A, taste percep- tion, wound healing, reproduction

Defi ciencya

Growth retardation, delayed sexual maturation, impaired immune function, hair loss, eye and skin lesions, loss of appetite

Toxicity Loss of appetite, impaired immunity, reduced copper and iron absorption, low HDL cholesterol (a risk factor for heart disease)

*These foods provide 10 percent or more of the zinc Daily Value in a serving. For a 2,000-calorie diet, the DV is 15 mg/day. aA rare inherited form of zinc malabsorption causes additional and more severe symptoms. bSome oysters contain more or less than this amount, but all types are zinc-rich foods. cEnriched cereals vary widely in zinc content.

snapshot 8-6

GOOD SOURCES*

OYSTERSb (steamed) 3 oz = 154.4 mg

BEEF STEAK (lean) 3 oz = 4.9 mg

YOGURT (plain) 1 c = 2.2 mg

SHRIMP (cooked) 3 oz = 1.5 mg

ENRICHED CEREALc

(ready-to-eat) 1 c = 3.8 mg

PORK CHOP 3 oz = 2 mg

307T h e T r a c e M i n e r a l s

Find the DRI intake recommendation for • selenium on the inside front cover, page B.

per day for men and 8 milligrams per day for women. Vegetarians are advised to eat varied diets that include zinc-enriched cereals or whole-grain breads well leavened with yeast, which helps make zinc available for absorption.96

KE Y POINT Zinc assists enzymes in all cells. Defi ciencies in children cause growth retardation with sexual immaturity. Zinc supplements can reach toxic doses, but zinc in foods is nontoxic. Foods from animals are the best sources.

Selenium Selenium is a nutrient in the news. Hints of its relationships with chronic diseases, as described below, make fascinating reading.

Roles in the Body Selenium-containing enzymes are necessary for the proper functioning of the iodine-containing thyroid hormones that regulate metabolism.97 Selenium has also attracted the attention of the world’s scientists for its role in pro- tecting vulnerable body chemicals against oxidative destruction.98 Selenium is an essential constituent of a group of enzymes that, in concert with vitamin E, work to limit the formation of free radicals and oxidative harm to cells and tissues.99

Relationship with Chronic Diseases Evidence is mixed on whether selenium plays a role in common forms of heart disease.100 Low blood selenium does seem to correlate with the development of cardiovascular diseases, but this evidence is insuffi cient to conclude that low selenium contributes to heart disease.101 In fact, elevated blood selenium also correlates with high blood cholesterol and diabetes, two factors that raise the risk for heart disease.102 As for cancer, men with adequate selenium in their bloodstreams contract prostate cancer less often than men whose blood measures are low.103 Should all men, then, take selenium supplements to ward off prostate cancer? No. Research has yet to establish whether extra selenium may benefi t or harm healthy, well-fed people.104

Defi ciency Without an adequate supply of selenium, the body’s ability to make the needed selenium-containing molecules is compromised. Severe defi ciencies cause muscle disorders with weakness and pain in people and animals. A specifi c type of heart disease is brought on by selenium defi ciency. Th is condition, identi- fi ed in selenium-defi cient regions of China, prompted researchers to place selenium among the essential nutrients.

More subtle defi ciencies may also adversely aff ect body tissues. For example, a short- age of selenium in cells of the immune system may unleash harmful levels of free radi- cals, increasing infl ammation and weakening immune defenses against infections.105

Toxicity Toxicity is possible when people take selenium supplements over a long period. Selenium toxicity brings on symptoms such as hair loss, diarrhea, and nerve abnormalities. Th e Tolerable Upper Intake Level for selenium is set at 400 micro- grams per day.

Sources Clearly, adequate selenium is important, but research does not support taking selenium supplements. If you eat a normal diet composed of mostly unpro- cessed foods, you need not worry about selenium. It is widely distributed in foods such as meats and shellfi sh and in vegetables, nuts, and grains grown on selenium- rich soil.106 As few as two Brazil nuts a day can improve selenium status.107 Soils in the United States and Canada vary in selenium, but foods from many regions mingle on supermarket shelves, ensuring that consumers are well supplied with selenium.

KE Y POINT Selenium works with an enzyme system to protect body compounds from oxidation. A defi ciency induces disease of muscles and other tissues. Defi ciencies are rare in developed countries, but toxicities can occur from overuse of supplements. Selenium in foods varies by region.

308 chapter 8 W a t e r a n d M i n e r a l s

Fluoride Fluoride is not essential to life. It is benefi cial in the diet, however, because of its ability to inhibit the development of dental caries in both children and adults.

Roles in the Body Only a trace of fl uoride occurs in the human body, but the crys- talline deposits in bones and teeth are larger and more perfectly formed because this fl uoride replaces the hydroxy portion of hydroxyapatite, forming the more decay- resistant fl uorapatite in developing teeth. Once teeth have erupted through the gums, fl uoride helps prevent dental caries by promoting the remineralization of early lesions of the enamel that might otherwise progress to form caries. Fluoride also acts directly on the bacteria of plaque, suppressing their metabolism and reduc- ing the amount of acid they produce.

Defi ciency Where fl uoride is lacking, dental decay is common, and fl uoridation of water is recommended for public dental health. Based on evidence of its ben- efi ts, fl uoridation has been endorsed by the National Institute of Dental Health, the American Dietetic Association, the American Medical Association, the National Cancer Institute, and the Centers for Disease Control and Prevention as benefi cial and presenting virtually no risk.

Toxicity In communities where the water contains too much fl uoride—2 to 8 mil- ligrams per million—discoloration of the teeth, or fl uorosis, may occur.108 Fluoro- sis occurs only during tooth development, never after the teeth have formed—and it is irreversible. Widespread availability of fl uoridated toothpaste and mouthwash, foods made with fl uoridated water, and fl uoride-containing supplements has led to an increase in the mildest form of fl uorosis. In this condition, characteristic white spots form in the tooth enamel; a more severe form is shown in Figure 8-12.

To prevent fl uorosis, people in areas with fl uoridated water should limit other sources, such as fl uoride-enriched formula for infants and fl uoride supplements for infants or children, unless prescribed by a physician. Children younger than six years should use only a pea-sized squeeze of toothpaste and should be told not to swallow their toothpaste when brushing their teeth. Th e Tolerable Upper Intake Level for fl uoride for all people older than eight years is 10 mg per day.

Sources of Fluoride Drinking water is the usual source of fl uoride. Almost 70 percent of the U.S. population has access to water with an optimal fl uoride con- centration, which typically delivers about 1 milligram per person per day, or about 1 part per million.109 Figure 8-13 shows the percentage of the population in each state with access to fl uoridated water. Fluoride is rarely present in bottled waters unless it was added at the source, as in bottled municipal tap water.

KE Y POINT Fluoride stabilizes bones and makes teeth resistant to decay. Excess fl uoride discolors teeth; large doses are toxic.

Chromium Chromium is an essential mineral that participates in carbohydrate and lipid me- tabolism. Chromium in foods is safe and essential to health. Industrial chromium is toxic, a known carcinogen that damages the DNA.110

Roles in the Body Chromium helps maintain glucose homeostasis by enhancing the activity of the hormone insulin. When chromium is lacking, a diabetes-like condition may develop with elevated blood glucose and impaired glucose tolerance, insulin response, and glucagon response. Some research fi ndings suggest that chro- mium supplements improve glucose or insulin responses in diabetes, but these rela- tionships are uncertain.111

Chromium Recommendations and Sources Chromium is present in a variety of foods. Th e best sources are unrefi ned foods, particularly liver, brewer’s yeast, and whole grains. Th e more refi ned foods people eat, the less chromium they receive.

Fluoride helps prevent caries in three ways:•

In developing teeth:•

Forms decay-resistant crystals.1.

In erupted teeth:•

Promotes remineralization.2.

Reduces acidity of plaque.3.

To prevent fl uorosis, young children should not swallow toothpaste.

ar ol

in e

Fl ei

sc he

The brown mottled stains on these teeth indicate exposure to high concentrations of fl uoride during development.

Fluorosis figure 8-12

D r.

P. M

ar az

zi /S

ci en

ce P

ho to

L ib

ra ry

/ P

ho to

R es

ea rc

he rs

, I nc

fl uorosis (fl oor-OH-sis) discoloration of the teeth due to ingestion of too much fl uoride dur- ing tooth development.

309T h e T r a c e M i n e r a l s

Chromium Supplements Supplement advertisements may convince consumers that they can lose fat and build muscle by taking chromium picolinate. Chromium supplements probably do not reduce body fat or improve muscle strength more than diet and exercise alone, however.

KE Y POINT Chromium works with the hormone insulin to control blood glucose concentrations. Chromium is present in a variety of unrefi ned foods.

Copper One of copper’s most vital roles is helping to form hemoglobin and collagen. In addition, many enzymes depend on copper for its oxygen-handling ability. Copper plays roles in the body’s handling of iron and, like iron, assists in reactions leading to the release of energy. One copper-dependent enzyme helps to control damage from free-radical activity in the tissues.‡ Researchers are investigating the possibil- ity that a low-copper diet may contribute to heart disease by suppressing the activity of this enzyme.

Copper defi ciency is rare but not unknown: it has been seen in severely malnour- ished infants fed a copper-poor milk formula. Defi ciency can severely disturb growth and metabolism, and in adults, it can impair immunity and blood fl ow through the arteries. Excess zinc interferes with copper absorption and can cause defi ciency.

Copper toxicity from foods is unlikely, but supplements can cause it. Th e Toler- able Upper Intake Level for adults is set at 10,000 micrograms (10 milligrams) per day. Th e best food sources of copper include organ meats, seafood, nuts, and seeds. Water may also supply copper, especially where copper plumbing pipes are used. In the United States, copper intakes are thought to be adequate.112

KE Y POINT Copper is needed to form hemoglobin and collagen and assists in many other body processes. Copper defi ciency is rare.

Other Trace Minerals and Some Candidates DRI intake recommendations have been established for two other trace minerals, molybdenum and manganese. Molybdenum functions as part of several metal- containing enzymes, some of which are giant proteins. Manganese works with doz- ens of diff erent enzymes that facilitate body processes and is widespread among whole grains, vegetables, fruits, legumes, and nuts.

Several other trace minerals are now recognized as important to health. Boron in- fl uences the activity of many enzymes and may play a key role in bone health, brain activities, and immune response.113 Th e richest food sources of boron are noncitrus fruits, leafy vegetables, nuts, and legumes. Cobalt is the mineral in the vitamin B12 molecule; the alternative name for vitamin B12, cobalamin, refl ects cobalt’s pres- ence. Nickel is important for the health of many body tissues; defi ciencies harm the liver and other organs. Silicon is known to be involved in bone calcifi cation in ani- mals. Future research may reveal key roles played by other trace minerals, including barium, cadmium, lead, lithium, mercury, silver, tin, and vanadium. Even arsenic, a known poison and carcinogen, may turn out to be essential in tiny quantities.

All trace minerals are toxic in excess, and Tolerable Upper Intake Levels exist for boron, nickel, and vanadium (see the inside front cover, page C). Overdoses are most likely to occur in people who take multiple nutrient supplements. Th e way to obtain the trace minerals is from food, which is not hard to do—just eat a variety of whole foods in the amounts recommended in Chapter 2.

Research on the trace minerals is uncovering many interactions among them: an excess of one may cause a defi ciency of another. A slight manganese overload, for example, may aggravate an iron defi ciency. A defi ciency of one mineral may open

Key:

<49%

50%–74%

>75%

U.S. Population

with Access to

Fluoridated Water

Through Public

Water Systems

figure 8-13

‡The enzyme is superoxide dismutase.

310 chapter 8 W a t e r a n d M i n e r a l s

the way for another to cause a toxic reaction. Iron defi ciency, for example, makes the body much more susceptible to lead poisoning. Good food sources of one are poor food sources of another, and factors that cooperate with some trace elements oppose others. Th e continuous outpouring of new information about the trace minerals is a sign that we have much more to learn, but the basics of diet planning remain valid. Table 8-8 sums up what this chapter has said about the minerals and fi lls in some additional information.

KE Y POINT Many diff erent trace elements play important roles in the body. All of the trace minerals are toxic in excess.

MINERAL AND CHIEF FUNCTIONS IN THE BODY

Major Minerals Defi ciency Symptoms Toxicity Symptoms Signifi cant Sources

Calcium The principal mineral of bones and teeth. Also acts in normal muscle contraction and relaxation, nerve func- tioning, regulation of cell activities, blood clotting, blood pressure, and immune defenses.

Stunted growth in chil- dren; adult bone loss (osteoporosis).

Constipation; urinary tract stone formation; kidney dysfunction; interference with absorption of other minerals.

Milk and milk products, oys- ters, small fi sh (with bones), calcium-set tofu (bean curd), certain leafy greens, broc- coli, legumes.

Phosphorus Mineralization of bones and teeth; important in cells’ genetic material, in cell membranes as phospholipids, in energy transfer, and in buffering systems.

Appetite loss, bone pain, muscle weakness, impaired growth, and rickets in infants.a

Calcifi cation of nonskel- etal tissues, particularly the kidney.

Foods from animal sources, some legumes.

Magnesium A factor involved in bone mineraliza- tion, the building of protein, enzyme action, normal muscular function, transmission of nerve impulses, proper immune function and mainte- nance of teeth.

Weakness; muscle twitches; appetite loss; confusion; if extreme, convulsions, bizarre movements (especially of eyes and face), hallucinations, and diffi culty in swallowing. In children, growth failure.b

Excess magnesium from abuse of laxatives (Epsom salts) causes diarrhea with fl uid and electrolyte and pH imbalances.

Nuts, legumes, whole grains, dark green vegetables, sea- foods, chocolate, cocoa.

Sodium Sodium, chloride, and potassium (electrolytes) maintain normal fl uid balance and acid-base balance in the body. Sodium is critical to nerve impulse transmission.

Muscle cramps, mental apa- thy, loss of appetite.

Hypertension. Salt, soy sauce, seasoning mixes, processed foods, condiments, fast foods.

Potassium Potassium facilitates reactions, including the making of protein; the maintenance of fl uid and electrolyte balance; the support of cell integrity; the transmission of nerve impulses; and the contraction of muscles, including the heart.

Defi ciency accompanies dehydration; causes muscular weakness, paralysis, and con- fusion; can cause death.

Causes muscular weakness; triggers vomiting; if given into a vein, can stop the heart.

All whole foods: meats, milk, fruits, vegetables, grains, legumes.

aSeen only rarely in infants fed phosphorus-free formula or in adults taking medications that interact with phosphorus. bA still more severe defi ciency causes tetany, an extreme, prolonged contraction of the muscles similar to that caused by low blood calcium.

The Minerals—A Summary table 8-8

311T h e T r a c e M i n e r a l s

Major Minerals Defi ciency Symptoms Toxicity Symptoms Signifi cant Sources

Chloride Chloride is part of the hydrochloric acid found in the stomach, necessary for proper digestion. Helps maintain normal fl uid and electrolyte balance.

Growth failure in children; muscle cramps, mental apathy, loss of appetite; can cause death (uncommon).

Normally harmless (the gas chlorine is a poison but evaporates from water); can cause vomiting.

Salt, soy sauce; moderate quantities in whole, unpro- cessed foods, large amounts in processed foods.

Sulfate A contributor of sulfur to many impor- tant compounds, such as certain amino acids, antioxidants, and the vitamins biotin and thiamin; stabilizes protein shape by forming sulfur-sulfur bridges (see Figure 6-10 in Chapter 6, p. 201).

None known; protein defi - ciency would occur fi rst.

Would occur only if sulfur amino acids were eaten in excess; this (in animals) depresses growth.

All protein-containing foods.

Iodine A component of the thyroid hormone thyroxine, which helps to regulate growth, development, and metabolic rate.

Goiter, cretinism. Depressed thyroid activ- ity; goiter-like thyroid enlargement.

Iodized salt, seafood, bread, plants grown in most parts of the country and animals fed those plants.

Iron Part of the protein hemoglobin, which carries oxygen in the blood; part of the protein myoglobin in muscles, which makes oxygen available for muscle contraction; necessary for the use of energy.

Anemia: weakness, fatigue, pale skin and mucous mem- branes, pale concave nails, headaches, inability to con- centrate, impaired cognitive function (children), lowered cold tolerance.

Iron overload: fatigue, abdominal pain, infections, liver injury, joint pain, skin pigmentation, growth retarda- tion in children, bloody stools, shock.

Red meats, fi sh, poultry, shellfi sh, eggs, legumes, green leafy vegetables, dried fruits.

Zinc Associated with hormones; needed for many enzymes; involved in making genetic material and proteins, immune cell activation, transport of vitamin A, taste perception, wound healing, the making of sperm, and normal fetal development.

Growth failure in children, dermatitis, sexual retardation, loss of taste, poor wound healing.

Nausea, vomiting, diarrhea, loss of appetite, headache, immune suppression, de- creased HDL, reduced iron and copper status.

Protein-containing foods: meats, fi sh, shellfi sh, poultry, grains, yogurt.

Selenium Assists a group of enzymes that defend against oxidation.

Predisposition to a form of heart disease characterized by fi brous cardiac tissue (uncommon).

Nausea; abdominal pain; nail and hair changes; nerve, liver, and muscle damage.

Seafoods, organ meats, other meats, whole grains, and vegetables depending on soil content.

Fluoride Helps form bones and teeth; confers decay resistance on teeth.

Susceptibility to tooth decay. Fluorosis (discoloration) of teeth, nausea, vomiting, diar- rhea, chest pain, itching.

Drinking water if fl uoride- containing or fl uoridated, tea, seafood.

Chromium Associated with insulin; needed for energy release from glucose.

Abnormal glucose metabolism.

Possibly skin eruptions. Meat, unrefi ned grains, veg- etable oils.

Copper Helps form hemoglobin; part of sev- eral enzymes.

Anemia; bone abnormalities. Vomiting, diarrhea; liver damage.

Organ meats, seafood, nuts, seeds, whole grains, drinking water.

The Minerals—A Summary (continued) table 8-8

312 chapter 8 W a t e r a n d M i n e r a l s

food feature

Many people act as though calcium nutrition is of little consequence to their health and neglect to meet their need.114 Yet, a low calcium intake is associated with all sorts of major illnesses, including adult bone loss (see the Controversy that follows this chapter), high blood pres- sure and colon cancer (see Chapter 11), kidney stones, and even lead poisoning (Chapter 14).

Consumption of one of the best sources of calcium—milk—has declined in recent years while consumption of other beverages, such as sweet soft drinks and fruit drinks, has increased dramatically.115 This Food Feature focuses on food and beverage sources of calcium and provides guidance about how to include them in the diet to meet the need for calcium.

MILK, YOGURT, AND CHEESE GROUP Milk and milk products are traditional sources of calcium for people who can tolerate them (see Figure 8-14). Table 8-9 shows the current milk recommendations that help to meet the calcium needs of various age groups. People who shun milk products because of lactose intoler- ance, allergy, or other aversions can obtain calcium from other sources, but care is needed—wise substitutes must be chosen.116 This is especially true for children. Children who don’t drink milk often have lower calcium intakes and poorer bone health than those who drink milk regularly, and they may also be smaller in stature. Most of milk’s many relatives are recommended choices: yo- gurt, kefi r, buttermilk, cheese (especially the low-fat or fat-free varieties), and, for people who can afford the calories, ice milk. Cottage cheese and frozen yogurt desserts contain about half the calcium of milk; 2 cups are needed to provide the amount of calcium in 1 cup of milk. But- ter, cream, and cream cheese are almost pure fat and contain negligible calcium.

Tinker with milk products to make them more appealing. Add cocoa to milk and fruit to yogurt, make your own fruit smoothies from milk or yogurt, or add

Meeting the Need for Calcium

fat-free milk powder to any dish. The cocoa powder added to make chocolate milk does contain a small amount of oxalic acid, which binds with some of milk’s calcium and inhibits its absorption, but the effect is insignifi cant. Sugar lends

both sweetness and calories to choco- late milk, so mix your chocolate milk at home where you control the amount of sugary chocolate added to the milk.

VEGETABLES Absorption of calcium varies among foods, and it affects the body’s calcium economy (see Figure 8-15). Among vegetables, rutabaga, broccoli, beet greens, turnip greens, mustard greens, bok choy (a Chinese cabbage), and kale are good sources of available calcium. So are collard greens, green cabbage, kohlrabi, watercress, parsley, and prob- ably some seaweeds, such as the nori popular in Japanese cookery. Certain other foods, including spinach, Swiss chard, and rhubarb, appear equal to milk in calcium content but provide very little or no calcium to the body because they contain binders that prevent calcium’s absorption (see Figure 8-16). The pres- ence of calcium binders does not make spinach an inferior food. Spinach is also rich in iron, beta-carotene, and dozens of other essential nutrients and potentially helpful phytochemicals. Just don’t rely on it for calcium. Dark greens of all kinds are superb sources of ribofl avin and indispensable for the vegan or anyone else who does not drink milk.

Other sourcesa

37% Cakes,

cookies, quick breads,

doughnuts

Ice cream, sherbet,

frozen yogurt

Yeast bread

Cheese

20%

Milk 28%

aOther sources include foods contributing at least 1% in descending order: yogurt, ready-to-eat cereal, soft drinks, tortillas, eggs, dried beans and lentils, canned tomatoes, meal replacements and protein supple- ments, corn bread and corn muffi ns, hot breakfast cereal, and coffee. Source: Data from P. A. Cotton and coauthors, Dietary sources of nutrients among US adults, 1994–1996, Journal of the American Dietetic Association 104 (2004): 921–930, supplemental Table 21 from www.eatright.org.

Food Sources of

Calcium in the

U.S. Diet

figure 8-14

Milk and milk products contribute over half of the calcium in a typical U.S. diet.

Young Children (2–8 years) 2 cups

Older children (9 years +) 3 cups

Adults 3 cups

Pregnant or lactating women

3 cups

Women past menopause 3 cups

Suggested

Minimum

Daily Fluid

Milk Intakes

table 8-9

Chocolate milk is an excellent source of calcium for those who can afford the extra calories.

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http://www.eatright.org

313T h e T r a c e M i n e r a l s

milk into almost everything. The added calorie value is small, changes to the taste and texture of the dish are practi- cally nil, but each 2 tablespoons adds about 100 extra milligrams of calcium (see Figure 8-17). Dried buttermilk pow- der can also add fl avor and calcium to baked goods and other dishes. Here are some more tips for including calcium- rich foods in your meals:

At Breakfast

Choose calcium-fortifi ed orange or • vegetable juice.

Lighten tea or coffee, hot or iced, with • milk or calcium-rich replacement such as soy milk.

Eat cereals, hot or cold, with milk.•

of calcium. One-third cup of almonds supplies about 100 milligrams of calcium along with almost 300 calories—a high-energy cal- cium source. Calcium-rich mineral water may also be a useful calcium source.117 Recent evidence seems to indicate that the calcium from mineral water, includ- ing hard tap water, may be as absorbable as the cal- cium from milk. Many other foods contribute smaller, but still signifi cant, amounts of calcium to the diet.

CALCIUM-FORTIFIED FOODS Next in order of preference among nonmilk sources

of calcium are foods that contain large amounts of calcium salts by an accident of processing or by intentional fortifi ca- tion. In the processed category are soy- bean curd, or tofu (calcium salt is often used to coagulate it, so check the label); canned tomatoes (fi rming agents donate 63 milligrams per cup of tomatoes); stone-ground fl our and self-rising fl our; stone-ground cornmeal and self-rising cornmeal; and blackstrap molasses.

Milk with extra calcium added can be an excellent source; it provides more calcium per cup than any natural milk, 500 milligrams per 8 ounces. Then comes calcium-fortifi ed orange juice, with 300 milligrams per 8 ounces, a good choice because the bioavailability of its calcium is comparable to that of milk. Calcium-fortifi ed soy milk can also be prepared so that it contains more calcium than whole cow’s milk.

Finally, calcium supplements are avail- able, sold mostly to people hoping to ward off osteoporosis. The Controversy following this chapter points out, however, that, while often useful, supplements are not magic bullets against bone loss.

MAKING MEALS RICH IN CALCIUM For those who tolerate milk, many cooks slip extra calcium into meals by sprin- kling a tablespoon or two of fat-free dry

CALCIUM IN OTHER FOODS For the many people who cannot use milk and milk products, small fi sh such as canned sardines and other canned fi shes prepared with their bones are rich sources

Urine, feces

Skin, hair

Sweat

Menopause (women)

180 mg

60 mg

30 mg

Total loss 300 mg

-or-

1,200 mg/day (at 25% absorption)

1,000 mg per day (at 30% absorption)

Calcium Intake to Offset Losses

Typical Daily Calcium Losses

Calcium Economy figure 8-15

The lefthand box shows typical daily calcium losses. The right-hand box shows that calcium intakes must be higher when calcium is not well absorbed to offset losses.

Source: Data from K. Rafferty and R. P. Heaney, Nutrient effects on the calcium economy: Emphasizing the potassium contro- versy, Journal of Nutrition 138 (2008): 166S–171S.

≥ 50% absorbed

bok choy, broccoli, brussels sprouts, cauliflower, Chinese cabbage, head cabbage, kale, kolhrabi, mustard greens, rutabaga, turnip greens, watercress

≃ 30% absorbed

calcium-fortified foods and beverages, calcium-fortified soy milk, calcium-set tofu, cheese, milk, yogurt

≃ 20% absorbed

almonds, beans (pinto, red, and white), sesame seeds

≤ 5% absorbed

rhubarb, spinach, Swiss chard

Calcium

Absorption from

Food Sources

figure 8-16

Milk, Yogurt, and

Cheese Group

Average Intakesa

figure 8-17

On average, people in the United States fall far short of the recom- mended intake of milk, yogurt, or cheese (or replacements) each day. The picture is worse for the dark green vegetables that supply calcium—only 3% of the vegetables consumed each day meet this description.

aIncludes all forms of milk, yogurt, cheese, and frozen dairy desserts. bRecommended amount for adults from the 2005 USDA Food Guide. Details in Figure 2-5 of Chapter 2. Source: Intake data from U.S. Department of Agriculture, Economic Research Service.

S e

rv in

g s p

e r

p e

rs o

n p

e r

d a

1970 1980

1990 Present

Recommendation: 3 cups

(or the equivalent) b

Average daily intake

314 chapter 8 W a t e r a n d M i n e r a l s

1 point = 4 ounces canned fi sh with • bones.

½ point = 1 cup ice cream, cottage • cheese, or calcium-rich vegetables (see the text).

Also, because bits of calcium are pres- ent in many foods, (a bagel has about 50 milligrams, for example):

1 point = a well-balanced, adequate, • and varied diet.

Example: Say a day’s calcium-rich foods include cereal and a cup of milk, a ham and cheese sandwich, and a broccoli and pasta salad.

1 point (cup of milk) + 1 point (cheese) + ½ point (broccoli) = 2½ points

Add 1 point for the other foods eaten that day.

1 point + 2½ points = 3½ points

This day’s foods provided a calcium intake approximately equal to the lower of the DRI committee’s recommendation. The tips in this section offer many ways to aim higher.

At Supper

Toss a handful of thinly sliced green • vegetables, such as kale or young turnip greens, with hot pasta; the greens wilt pleasingly in the steam of the freshly cooked pasta.

Serve a green vegetable every night • and try new ones—how about kohl- rabi? It tastes delicious when cooked like broccoli.

Learn to stir-fry Chinese cabbage and • other Asian foods.

Try tofu (the calcium-set kind); this • versatile food has inspired whole cookbooks devoted to creative uses.

Add fat-free powdered milk to almost • anything—meat loaf, sauces, gravies, soups, stuffi ngs, casseroles, blended beverages, puddings, quick breads, cookies, brownies. Be creative.

Choose frozen yogurt, ice milk, or • custards for dessert.

Here is a shortcut for tracking the amount of calcium in a day’s meals. To start, memorize these two facts:

A cup of milk provides about 300 milli-1. grams of calcium.

Adults need 1,000 to 1,200 milligrams 2. each day. Broken down in terms of “cups of milk,” the need is 31⁄3 to 4 cups each day.

To estimate calcium from an entire day’s foods, not just milk, assign “cups of milk” points to various calcium sources. The goal is to achieve 3½ to 4 points per day:

1 point = 1 cup milk, yogurt, calcium-• fortifi ed beverage, or 1½ ounces cheese.

Cook hot cereals with milk instead of • water, then mix in 2 tablespoons of fat-free dry milk.

Make muffi ns or quick breads with milk • and extra fat-free powdered milk or dried buttermilk powder.

Add milk to scrambled eggs.•

Moisten cereals with fl avored yogurt.•

At Lunch

Add low-fat cheeses to sandwiches, • burgers, or salads.

Use a variety of green vegetables, • such as watercress or kale, in salads and on sandwiches.

Drink fat-free milk or calcium-fortifi ed • soy milk as a beverage or in a smoothie. For tartness and extra calcium, add 2 tbs dried buttermilk powder.

Drink calcium-rich mineral water as a • beverage.

Marinate cabbage shreds or broc-• coli spears in low-fat Italian dressing for an interesting salad that provides calcium.

Choose coleslaw over potato and • macaroni salads.

Mix the mashed bones of canned • salmon into salmon salad or patties.

Eat sardines with their bones.•

Stuff potatoes with broccoli and low-fat • cheese.

Try pasta such as ravioli stuffed with • low-fat ricotta cheese instead of meat.

Sprinkle parmesan cheese on pasta • salads.

kefi r a yogurt-based beverage.

nori a type of seaweed popular in Asian, particularly Japanese, cooking.

stone-ground fl our fl our made by grinding kernels of grain between heavy wheels made of limestone, a kind of rock derived from the shells and bones of marine animals. As the stones scrape together, bits of the limestone mix with the fl our, enriching it with calcium.

315T h e T r a c e M i n e r a l s

Analyze Your Calcium Intakes Many people do not meet their daily requirement for calcium. The purpose of this exercise is to make you aware of your calcium intake and to give you ideas about how you might meet your DRI recommended intake. Using the Diet Analysis program that accompa- nies this book, complete the following.

From the Reports tab, select Profi le 1. DRI Goals. Find your calcium infor- mation. What is the DRI Adequate Intake for calcium for your profi le?

From the Reports tab, select Intake 2. vs. Goals. Choose Day One (from your three-day diet intake record) and include all meals. What percent- age of your calcium DRI did you meet on that day? Was this intake typical?

From the Reports tab, select Source 3. Analysis. Choose Day One, include all meals, select calcium from the drop-down box, and generate a report. What were the top three food sources of calcium that day? What were your three lowest sources? Which of your top sources matched those of the calcium Snapshot on page 291?

From the Reports tab, select Intake 4. Spreadsheet, choose Day Three, choose breakfast, and then generate a report. Look at the Calcium column. Did the calcium values of any of the foods surprise you? If so, which ones? How many milligrams of cal- cium did you consume for breakfast?

Using the same Intake Spreadsheet, 5. choose Day Three, and choose

lunch, then dinner. At which meal did you consume the most calcium? Which meal had the least calcium: breakfast, lunch, or dinner?

Many nondairy foods can provide 6. calcium. Using the Food Feature, create a calcium-rich side dish with- out milk or milk products. Select the Track Diet tab and enter the ingre- dients for your side dish. From the Reports tab, select Source Analysis, select calcium from the drop-down menu, and generate a report. Did you raise your intake of calcium by choosing nondairy calcium sources? How absorbable was the calcium in these foods? (Check Figure 8-16, page 313.)

Concepts in Action

To fi nd additional quiz questions, view videos and animations, and explore interactive exercises, go to www.cengage.com/sso.

Search for information on individual minerals at www.healthfi nder.gov.

Read the latest calcium and nutrition research at www.nationaldairycouncil.org.

Search the National Women’s Health Information Center for information about bone health: www.4women.gov.

Learn more about the DASH Eating Plan by clicking on the brochure “Lowering Your Blood Pressure with DASH” from this government website: www.nhlbi.nih.gov/health/public/heart/ hbp/dash.

Find tips and recipes for including more milk in your diet at www.whymilk.com.

media menu

http://www.cengage.com/sso

http://www.healthfi

http://www.nationaldairycouncil.org

http://www.4women.gov

http://www.nhlbi.nih.gov/health/public/heart/

http://www.whymilk.com

316 chapter 8 W a t e r a n d M i n e r a l s

Answers to these Self Check questions are in Appendix G.

Water balance is governed by the:1.

liverA.

kidneysB.

brainC.

(b) and (c)D.

Which two minerals are the major constituents of bone?2.

calcium and zincA.

phosphorus and calciumB.

sodium and magnesiumC.

magnesium and calciumD.

All of the following are correct concerning zinc except:3.

it is needed for vitamin A activity in the eyeA.

in high doses it may inhibit iron absorption from the digestive B. tract

fruits and vegetables are the best sources for zincC.

defi ciencies in children retard growthD.

A defi ciency of which mineral is a leading cause of mental 4. retardation worldwide?

ironA.

iodineB.

zincC.

chromiumD.

Which mineral supplement is a likely cause of accidental 5. poisonings of U.S. children under 6 years old?

ironA.

sodiumB.

chlorideC.

potassiumD.

After about 50 years of age, bones begin to lose density.6. T F

The best way to control salt intake is to cut down on pro-7. cessed and fast foods. T F

The most abundant mineral in the body is iron.8. T F

Dairy foods such as butter, cream, and cream cheese are 9. good sources of calcium, whereas vegetables such as broccoli are poor sources. T F

Bottled water must meet higher standards for purity and 10. sanitation than U.S. tap water. T F

self check

317controversy 8 O s t e o p o r o s i s : C a n L i f e s t y l e C h o i c e s R e d u c e t h e R i s k s ?

CONTROVERSY

An estimated 52 million people in the United States, the majority of them women over 50, have or are developing osteoporosis.1* Each year, a million and a half people, 30 percent of them men, break a hip, leg, arm, hand, ankle, or other bone as a result of having osteoporosis. Of these, hip fractures prove most seri- ous. The break is rarely clean—the bone explodes into fragments that cannot be reassembled. Just removing the pieces is a struggle, and replacing them with an artifi cial joint requires major surgery. Many elderly people with hip fracture never walk or live independently again. About a fi fth die from related complications within a year. By the year 2020, the number of hip fractures could double or even triple in the United States.2 Both men and women are urged to do whatever they can to prevent fractures related to osteoporosis.

Fractures from osteoporosis occur during the later years, but osteoporo- sis itself develops silently much earlier. Younger adults are rarely aware of the strength sapping out of their bones but then suddenly, 40 years later, a hip gives way. People say, “She fell and broke her hip,” but in fact the hip may have been so fragile that it broke before she fell.

The causes of osteoporosis are tan- gled, and most are beyond a person’s control. Insuffi cient dietary calcium and vitamin D certainly play roles, but age, gender, physical activity, genetics, and other factors are also major players. Cer- tain actions people can take undoubt- edly reduce the risk of developing it. No controversy exists as to the nature and

victims of osteoporosis; more controver- sial, however, are its causes and what people should do about it.

DEVELOPMENT OF OSTEOPOROSIS To understand how the skeleton loses minerals in later years, you must fi rst know a few things about bones. Table C8-1 offers defi nitions of relevant terms. The photograph on this page shows a human leg bone sliced lengthwise, ex- posing the lattice of calcium-containing crystals (the trabecular bone) inside that are part of the body’s calcium bank. Invested as savings during the milk- drinking years of youth, these deposits provide a nearly inexhaustible fund of calcium. Cortical bone is the dense, ivorylike bone that forms the exterior shell of a bone and the shaft of a long bone (look closely at the photograph). Both types of bone are crucial to overall bone strength. Cortical bone forms a sturdy outer wall, and trabecular bone provides strength along the lines of stress.

The two types of bone handle calcium in different ways. The lacy crystals of the trabecular bone are tapped to raise blood calcium when the supply from the day’s diet runs short; the calcium crys- tals are redeposited in bone when dietary calcium is plentiful.

Trabecular bone, generously supplied with blood vessels, readily gives up its minerals at the necessary rate whenever blood calcium needs replenishing. Loss of trabecular bone begins to be signifi - cant for men and women around age 30. Calcium in cortical bone can also be withdrawn, but more slowly, beginning around age 40.

As bone loss continues (Figure C8-1), bone density declines. Soon, osteo- porosis sets in, and bones become so fragile that the body’s weight can overburden the spine. Vertebrae may suddenly disintegrate and crush down, painfully pinching major nerves.3 Or they may compress into wedges, forming what is insensitively called “dowager’s

Osteoporosis: Can Lifestyle Choices Reduce the Risks?

LO 8.9

*Reference notes are found in Appendix F. A sectioned bone.

on al

d Fa

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su al

s U

nl im

ite d

cortical bone• the ivorylike outer bone layer that forms a shell sur- rounding trabecular bone and that comprises the shaft of a long bone. trabecular• (tra-BECK-you-lar) bone the weblike structure composed of calcium-containing crystals inside a bone’s solid outer shell. It provides strength and acts as a calcium stor- age bank.

Osteoporosis

Terms

table C8-1

318 chapter 8 W a t e r a n d M i n e r a l s

cans, for example, use and conserve calcium more effi ciently than do Cauca- sians.9 African American women may lose bone at just half the rate of white women as they age, and an 80-year-old white woman is 3 times more likely to fracture her hip than is a black woman of the same age.

Some ethnic groups have even lower bone densities than do Caucasians. Asian people from China and Japan, Hispanic people from Central and South America, and Inuit people from St. Law- rence Island all have lower bone density. Do lower bone densities forecast a higher rate of hip fractures in these groups? Not always. Chinese people living in Singa- pore have low bone density, but their hip fracture rates are among the lowest in the world. No one really knows why.

Your genes set a tendency for strong or weak bones. Your environment, includ-

and increased risk of fractures.4 The human genome is under investigation in this regard, and a number of genes may interact with vitamin D and calcium nutrition, or may otherwise affect bone den- sity.5 Genes exert infl uence over:

the activities of bone-forming • cells and bone-dismantling cells.

the cellular mechanisms that • make collagen (the major struc- tural protein of bones).

the mechanisms for absorbing • and employing vitamin D.

and many other contributors to • bone metabolism.6

Researchers hope that, once unsnarled, this tangle of genetic leads will help to answer some of the questions still surrounding the development and prevention of osteoporosis.

Genetic inheritance appears to most strongly infl uence the maximum bone mass attainable during growth. It also infl uences the extent of a woman’s bone loss during menopause, the time when women’s estrogen production de- clines and menstruation ceases.7

Risks of osteoporosis differ by race and ethnicity.8 African Ameri-

hump,” the bent posture of many older men and women as they “grow shorter” (see Figure C8-2). Wrists may break as trabecula-rich bone ends weaken, and teeth may loosen or fall out as the trabecular bone of the jaw recedes. As the cortical bone shell weakens as well, breaks often occur in the hip.

TOWARD PREVENTION— UNDERSTANDING THE CAUSES OF OSTEOPOROSIS Scientists are searching for ways to prevent osteoporosis, but they must fi rst establish its causes. Gender and advanced age are clearly associated, but genetic inheritance and factors in the environment are also in play. Some of these may include:

Poor calcium and vitamin D nutrition.•

Estrogen defi ciency in women.•

Lack of physical activity.•

Body thinness.•

Smoking and alcohol abuse.•

Others.•

Bone Density and the Genes A strong genetic component contrib- utes to osteoporosis, bone density,

Losses of Trabecular Bone figure C8-1

Electron micrograph of healthy trabecular bone.

Electron micrograph of trabecular bone affected by osteoporosis.

re d

H os

sl er

/V is

ua ls

U nl

im ite

na B

oy de

/V is

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im ite

Loss of Height

in a Woman Caused

by Osteoporosis

figure C8-2

The woman on the left is about 50 years old. On the right, she is 80 years old. Her legs have not grown shorter; only her back has lost length, due to collapse of her spinal bones (vertebrae). When collapsed vertebrae cannot protect the spinal nerves, the pressure of bones pinching the nerves causes excruciating pain.

6 inches lost

80 years old50 years old

319controversy 8 O s t e o p o r o s i s : C a n L i f e s t y l e C h o i c e s R e d u c e t h e R i s k s ?

body weight and bone mass (more about leptin in Chapter 9).17 Also, fat tissue serves as a storage depot for hormones, and the more abundant the body fat stores, the greater amount of hormones.

Physical Activity Physical activity supports bone growth during adolescence and may protect the bones later on.18 When combined with adequate calcium intake, the effect is greater still.

When people lie idle—for example, when they are confi ned to bed—the bones lose strength just as the muscles do. Astronauts who live without gravity for days or weeks experience rapid and extensive bone loss. The harm to the bones from a sedentary lifestyle equals that of nutrient defi ciencies and cigarette smoking (Table C8-2). The best exercises to keep bones healthy and prevent falls seem to be the weight-bearing kinds, such as calisthenics, dancing, jogging, vigorous walking, or weight training on most days throughout life. Preventing falls is becoming a new focus for fracture prevention in the elderly.19

menopause. Accelerated losses continue for six to eight years following meno- pause and then taper off, so women again lose bone at the same rate as their male counterparts. Losses of bone minerals continue throughout the remainder of a woman’s lifetime but not at the free-fall pace of the menopause years (refer again to Figure C8-3).

Should young women fail to produce enough estro- gen, they lose bone rapidly, too. Diseased ovaries are often to blame, but estro- gen may be low because the woman suffers from an eating disorder with a dan- gerously low body weight (see Controversy 9). Even with treatment, the bone loss remains long after the eating disorder has been resolved.

If estrogen defi ciency is a major cause of osteo- porosis in women, what is the cause of bone loss in men? Men produce only a little estrogen, yet they resist osteopo- rosis better than women. Does the male sex hormone testosterone play a role? Probably, because elderly men in whom testosterone production has fallen off suffer more fractures than others.†15

Body Weight After age and gender, the next risk factor for osteoporosis is being underweight or losing weight (see Table C8-2). Weight loss reduces bone density and increases the risk of fractures—in part because energy restriction diminishes calcium absorption, tipping the scale toward bone loss.

Women who are thin throughout life, and especially those who lose 10 percent or more of their body weight after the age of menopause, face a hip fracture rate twice as high as that of most other women. Heavier body weight may lead to stronger bones, even when dietary calcium is low.16 An appetite-regulating hormone, leptin, may be a link between

ing diet and other life choices, infl uences the fi nal outcome.

Calcium and Vitamin D In the later years, an adequate calcium intake alone cannot protect against bone fractures.10 Bone strength later in life de- pends most on how well the bones were built during childhood and adolescence. Preteen children who consume enough calcium and vitamin D lay more calcium into the structure of their bones than chil- dren with less adequate intakes. Unfor- tunately, most girls in their bone-building years fail to meet their calcium needs.11

When people reach the bone-losing years of middle age, those who formed dense bones during youth have more bone tissue to lose before suffering ill effects—see Figure C8-3. Building strong bones in youth helps prevent or delay osteoporosis later on.12

Milk is not the only food rich in cal- cium, but milk and milk products supply most of the calcium to the U.S. diet and they are fortifi ed with vitamin D. Children who do not consume milk do not meet their calcium needs unless they use calcium-fortifi ed foods or supplements.13

Dietary calcium and vitamin D in later life cannot make up for earlier defi cien- cies, but they may help to slow the rate of bone loss. Additionally, calcium absorp- tion declines with age, and older bodies become less effi cient at making and activating vitamin D. Unfortunately, older people take in less calcium and vitamin D than do others, and they may fail to go outdoors for the sunlight necessary to form vitamin D and their skin becomes less effi cient in synthesizing it. For these people, supplements may be of benefi t.

Gender and Hormones Gender is a powerful predictor of osteo- porosis: men have greater bone density than women at maturity, and women of- ten lose a great deal of bone in the years surrounding menopause. On hearing this, some men believe that osteoporosis is a “woman’s disease.” However, each year, millions of men suffer fractures from osteoporosis. Their fractures are treated, but their underlying disease often goes unrecognized.14

In women, bone dwindles rapidly when the hormone estrogen diminishes in

Age 30

Menopause Age 60

Higher peak bone mass

Lower peak bone mass

Osteoporosis

Bone mass danger zonea

Age 70

In c re

a s in

g b

o n e m

a s s

Time

Woman A

Woman B

Two Women’s Bone Mass

History Compared

figure C8-3

Woman A entered adulthood with enough calcium in her bones to last a lifetime. Woman B had less bone mass starting out and so suffered ill effects from bone loss later on.

aPeople with a moderate degree of bone mass reduction are said to have osteopenia and are at increased risk of fractures. Source: Data from Standing Committee on the Scientifi c Evalu- ation of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine, Dietary Reference Intakes for Calcium, Phos- phorus, Magnesium, Vitamin D, and Fluoride (Washington, D.C.: National Academies Press, 1997), pp. 71–145.

†The condition is known as hypogonadism.

320 chapter 8 W a t e r a n d M i n e r a l s

mineral crystals of bone form on a pro- tein matrix—collagen. Restoring protein sources to the diet can often improve bone status and reduce the incidence of hip fractures even in the elderly. How- ever, a diet lacking protein no doubt also lacks other critical bone nutrients, such as vitamin D, vitamin K, and calcium, so restoring protein to the diet brings other needed nutrients into play, as well.

An opposite possibility, that a high- protein diet causes bone loss, has also re- ceived attention.23 Excess dietary protein causes urinary calcium losses. Previously, researchers suspected that this extra urinary calcium might have come from the bones, but it appears that a high-protein diet may also stimulate calcium absorp- tion, offsetting urinary calcium losses.24

Animal Versus Vegetable Protein Sources Soy foods may help stem the rapid bone losses of the menopause years by virtue of their protein content—as mentioned, a negative correlation is evident between dietary protein intake and bone loss re- ported.25 Soy phytochemicals may or may not affect bone loss—research is mixed.26

Some protein-rich foods from animals may benefi t calcium balance. Milk is a good example. A milk-rich diet provides high-quality protein, vitamin D, and cal- cium, and also potassium and phospho- rus, minerals that may help to oppose withdrawal of calcium from the skele- ton.27 It follows, then, that vegan vegetar- ians, who do not consume milk products, would have lower bone mineral density than people who consume milk and milk products—and they generally do.28

Sodium, Caffeine, Soft Drinks A high sodium intake is also associ- ated with urinary calcium excretion, and lowering sodium intakes seems to lessen calcium losses.29 In study subjects eat- ing the DASH diet, a controlled sodium diet that provides all of the foods in the USDA MyPyramid plan, urinary calcium losses are reduced.30 In addition, the DASH diet is higher in calcium than most diets, a critical feature that stands against bone loss.

Long-term evidence is lacking to show that a reduced sodium intake prevents

Tobacco Smoke and Alcohol Smoking is hard on the bones. The bones of smokers are less dense than those of nonsmokers of similar body weight, age, and physical activity lev- els.20 Fortunately, quitting can reverse much of the damage. With time, the bone density of former smokers ap- proaches that of nonsmokers.

People who are addicted to alcohol also experience more frequent fractures.21 Alcohol may induce calcium losses in urine through its diuretic effect. It may also upset the hormonal balance that main- tains healthy bones: it is also directly toxic to the bone-building cells. Finally, drinking contributes to accidents and falls.

Protein When elderly people take in too little pro- tein, their bones suffer.22 Recall that the

Risk Factors Protective Factors

HIGH CORRELATION

Advanced age Alcoholism, heavy drinking Chronic steroid use Female gender Rheumatoid arthritis Surgical removal of ovaries or testes Thinness or weight loss White race

Black race Estrogens, long-term use

MODERATE CORRELATION

Diabetes (insulin-dependent, type 1) Early natural menopause Excessive antacid use Family history of osteoporosis Low-calcium diet Low-milk diet (in children) Low-protein diet (in elderly) Low-vitamin D status Sedentary lifestyle Smoking Hypogonadism (in men)

Adequate dietary calcium Adequate dietary protein (in later years) Adequate vitamin D Having given birth High body weight High-calcium diet Regular physical activity

MAY BE IMPORTANT BUT NOT YET PROVED

Caffeine intake High-fi ber diet High blood homocysteine High-protein diet Lactose intolerance

Adequate vitamin K intake Low-sodium diet (later years) Other dietary factors, including bicarbonate,

omega-3 fatty acids, potassium, vitamin C

Risk and Protective Factors That Correlate

with Osteoporosis

table C8-2

These young people are putting bone in the bank.

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321controversy 8 O s t e o p o r o s i s : C a n L i f e s t y l e C h o i c e s R e d u c e t h e R i s k s ?

its. Others stimulate the bone-building cells, resulting in greater bone formation. Such drugs, alone or in combination, have worked minor miracles in reversing even severe bone loss in some people, but for others they are ineffective or their side effects prove intolerable.

Estrogen replacement therapy can help nonmenstruating women prevent further bone loss. However, the National Institutes of Health concludes that hor- mone therapy should not be used to pre- vent disease in healthy postmenopausal women because of increased risks for heart disease and cancers.40

CALCIUM RECOMMENDATIONS Adequate calcium nutrition during the growing years is essential to achiev- ing optimal peak bone mass. Yet only 10 percent of girls and 25 percent of boys meet the recommendation for calcium during their bone-forming years. The DRI committee recommends 1,300 milligrams of calcium, the amount in about 4 cups of milk, each day for ev- eryone 9 through 18 years of age, 1,000 milligrams through age 50, and 1,200 milligrams thereafter.

How should you obtain this calcium? Nutritionists strongly recommend foods and beverages as your source of calcium and that you take supple- ments only when advised to do so by a physician.41 Healthy children, especially, should receive a carefully planned diet that provides the calcium they need from foods—calcium supplements only mar- ginally increase children’s bone density, at best.42 People can best support the health of their bones by following the lifetime recommendations for healthy bones in Table C8-3. Calcium supple- ments cannot equal any of the actions listed in the table.

Bone loss is not a calcium-defi ciency disease comparable to iron-defi ciency anemia, in which iron intake reliably reverses the condition. Calcium alone cannot reverse bone loss. For those who are unable to consume enough calcium- rich foods, however, taking calcium supplements—especially in combination with vitamin D—may help to enhance bone density and protect against bone

also help preserve bone integrity.38 Fluo- ride may oppose bone fractures, although some debate exists on this point.39

Clearly, a well-balanced diet that sup- plies abundant fruits and vegetables and a full array of nutrients is central to bone health. In contrast, diets containing too much salt, candy, or colas and possibly caffeine are associated with bone losses. Additional research points to the bone benefi ts not of a specifi c nutrient, but of a diet rich in fruits and vegetables.

Review Table C8-2 and the risk factors covered here. The more risk factors that apply to you, the greater your chances of developing osteoporosis in the future and the more seriously you should take the advice offered in this Controversy.

DIAGNOSIS AND MEDICAL TREATMENT Diagnosis of osteoporosis includes mea- suring bone density using an advanced form of X ray (DEXA, see the photo below) or ultrasound.‡ Men with osteopo- rosis risk factors and all women should have a bone density test after age 50. A thorough examination also includes factors such as race, family history, and physical activity level.

Several drug therapies can reverse bone loss. Some inhibit the activities of the bone-dismantling cells, thus allowing the bone-building cells to slowly shore up bone tissue with new calcium depos-

osteoporosis, however. Still, no harm can come from recommending that people reduce their sodium intakes.31 Also, increasing potassium may help—some research shows that potassium may counteract the effects of sodium on cal- cium excretion. The person who wishes to lower sodium and increase potassium should choose a diet rich in unprocessed or lightly processed foods such as fruits and vegetables while restricting heavily processed, convenience, or fast foods.

Heavy users of caffeinated beverages, such as coffee, tea, and colas, should be aware that some evidence links caffeine use and osteoporosis, although other fi ndings tend to absolve caffeine use from posing a risk. It may be that ordinary caffeine intakes, say the amount in two cups of coffee, increase calcium losses only when calcium intakes are low. Such losses may be so small that the calcium in just one or two tablespoons of milk is enough to replace them.

About cola beverages—they may also have adverse effects on calcium and bone density, although the reasons why are unclear.32 For one thing, they contain phosphoric acid (many other soft drinks do not), and high dietary phosphorus and cola beverages both seem to speed bone dismantling.33 For another, all soft drinks displace milk from the diet, espe- cially in children and adolescents. More research is needed to determine whether cola beverages might pose a unique risk to the bones.

Other Nutrients Important to Bones Vitamin K, because it plays roles in the production of at least one bone protein important in bone maintenance, has been investigated for links with osteopo- rosis. In fact, people with hip fractures often have low intakes of vitamin K–rich vegetables. However, giving people vitamin K does not appear to prevent bone loss.34 It may be that increased vegetable intakes may improve both vitamin K status and skeletal health, but by unrelated mechanisms.35

Vitamin A is needed in the bone- remodeling process, and vitamin C may slow bone losses.36 Magnesium may help to maintain bone mineral density.37 Suf- fi cient omega-3 fatty acids in the diet may

A DEXA scan measures bone density to help detect the early stages of bone loss, assess fracture risks, and measure the responses to bone-building treatments. (DEXA stands for dual-energy X-ray absorptiometry.)

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322 chapter 8 W a t e r a n d M i n e r a l s

Question 1: How much calcium does the supplement provide? Most provide between 250 and 1,000 milligrams of cal- cium, as stated on the label. To be safe, calcium from foods and supplements should provide less than the Tolerable Up- per Level for calcium of 2,500 milligrams.

Question 2: How digestible is the sup- plement? No matter how much calcium a supplement contains, the body cannot use it unless the tablet disintegrates in the digestive tract. Manufacturers compress large quantities of calcium into small pills, which must be penetrated by the stom- ach acid. To test a supplement’s ability to dissolve, drop a pill into 6 ounces of vinegar and stir occasionally. A digestible pill will dissolve within half an hour.

CALCIUM SUPPLEMENTS Selecting a calcium supplement requires fi nding the answers to some questions about each type. Calcium supplements are often sold as calcium compounds, such as calcium carbonate (as in some antacids), citrate, gluconate, lactate, malate, or phosphate, and compounds of calcium with amino acids (called amino acid chelates). Others are powdered, calcium-rich materials such as bone meal, powdered bone, oyster shell, or dolomite (limestone). Calcium from calcium-rich mineral waters also provides some amount of calcium that appears to be highly absorbable.47 See Table C8-5 for supplement terms.

loss and fractures.43 In a recent trial of over 36,000 postmenopausal women, supplements improved hip bone density, but, unfortunately, did not reduce hip fractures and increased the women’s risk of developing kidney stones.44

Taking self-prescribed calcium supple- ments entails a few risks (see Table C8-4) and cannot take the place of sound food choices and other healthy habits.45 One study’s fi nding that calcium supplements may increase the risk of heart attacks is a matter of controversy among research- ers.46 Much more research is needed to support or refute this idea before its meaning can be known. The next section provides some details about the variety of calcium supplements.

CHILDHOOD

Ages Goal Guidelines

2 through 12 or 13 years (sexual maturity)

Grow strong bones. Use milk as the primary beverage to meet the need for cal-• cium within a balanced diet that provides all nutrients. Play actively in sports or other activities. • Limit television and other sedentary entertainment.• Do not start smoking or drinking alcohol.• Drink fl uoridated water.•

ADOLESCENCE THROUGH YOUNG ADULTHOOD

Ages Goal Guidelines

13 or 14 through 30 years Achieve peak bone mass. Choose milk as the primary beverage, or if milk causes • distress, include other calcium sources. Commit to a lifelong program of physical activity.• Do not smoke or drink alcohol—if you have started, quit.• Drink fl uoridated water.•

MATURE ADULT

Ages Goal Guidelines

31 through 50 years Maximize bone retention. Continue as for 13- to 30-year-olds. • Adopt bone-strengthening exercises.• Obtain the recommended amount of calcium from food. • Take calcium supplements only if calcium needs cannot be • met through foods.

MATURE ADULT

Ages Goal Guidelines

51 years and above Minimize bone loss. Continue as for 13- to 30-year-olds. • Continue striving to meet the calcium need from diet.• Continue bone-strengthening exercises.• Obtain a bone density test; follow physician’s advice con-• cerning bone-restoring medications and supplements.

Note: The exact ages of cessation of bone accretion and onset of loss vary among people, but in general, data indicate that the skeleton continues to accrete mass for approximately 10 years after adult height is achieved and begins to lose bone around age 35.

A Lifetime Plan for Healthy Bones table C8-3

323controversy 8 O s t e o p o r o s i s : C a n L i f e s t y l e C h o i c e s R e d u c e t h e R i s k s ?

is insuffi cient. The authors of this book are so impressed with the importance of using abundant, calcium-rich foods that we have worked out ways to do so at ev- ery meal. Seldom do nutritionists agree so unanimously.

American Society for Bone and Mineral Research recommends calcium-rich foods in preference to supplements. The National Institutes of Health concludes that foods are best and recommends supplements only when intake from food

Question 3: How absorbable is the form of calcium in the supplement? Most healthy people absorb calcium equally well (and as well as from milk) from any of these forms: calcium carbon- ate, citrate, or phosphate. To improve absorption, take smaller doses (less than 500 milligrams) twice a day instead of 1,000 milligrams all at once. Table C8-6 lists some sources of supplemental calcium, the amount of calcium deliv- ered, and the form of the calcium along with the number of calories in a dose or serving.

One last pitch: Think one more time before you decide to take supplements instead of including calcium-rich foods in your diet. The Consensus Conference on Osteoporosis recommends milk. The

amino acid chelates• (KEY-lates) compounds of minerals (such as calcium) combined with amino acids in a form that favors their absorption. A chelating agent is a molecule that surrounds another molecule and can then either promote or prevent its movement from place to place (chele means “claw”). antacids• acid-buffering agents used to counter excess acidity in the stomach. Calcium- containing preparations (such as Tums) contain available calcium. Antacids with alumi- num or magnesium hydroxides (such as Rolaids) can accelerate calcium losses. bone meal• or powdered bone crushed or ground bone preparations intended to sup- ply calcium to the diet. Calcium from bone is not well absorbed and is often contami- nated with toxic materials such as arsenic, mercury, lead, and cadmium. calcium compounds• the simplest forms of purifi ed calcium. They include calcium carbonate, citrate, gluconate, hydroxide, lactate, malate, and phosphate. These supplements vary in the amount of calcium they contain, so read the labels carefully. A 500-milligram tablet of calcium gluconate may provide only 45 milligrams of calcium, for example. dolomite• a compound of minerals (calcium magnesium carbonate) found in limestone and marble. Dolomite is powdered and is sold as a calcium-magnesium supplement but may be contaminated with toxic minerals, is not well absorbed, and interacts ad- versely with absorption of other essential minerals. oyster shell• a product made from the powdered shells of oysters that is sold as a calcium supplement but is not well absorbed by the digestive system.

Calcium Supplement Terms table

C8-5

Calcium Source Typical Amount

per Serving Calories

Antacid medication, regular strength (“Tums” type)

500 mg per 2 tablets 10

Breads with “more” calciuma 80 mg per slice 70

Calcium-fortifi ed candies or chewable candy supplements

500 mg per dose 20

Calcium-fortifi ed or “100% nutrient” cereals 1,000 mg per serving 110

Calcium-fortifi ed fat-free milk and milk products 500 mg per 8-oz serving 100

Calcium-fortifi ed orange juice or other fruit beverages

350 mg per 8-oz serving 110

Calcium pills A wide variety of pills provide varying doses. Read the label.

Negligible

Meal replacer: cereal bars “with milk” 250 mg 160

Meal replacer: “complete nutrition” drinks 200–350 mg per 8-oz drink 360

Meal replacer: “energy” bars 300 per one bar 230

aBread, though not rich in calcium, is heavily consumed and may contribute signifi cantly to many people’s intakes.

A Sampling of Supplemental Calcium Sources table

C8-6

People who take calcium supplements risk:

GI distress. • Constipation, intesti- nal bloating, and excess gas are common. Impaired iron status.• Calcium inhibits iron absorption. Urinary tract stones or kidney damage • in susceptible individuals. People who have a history of kidney stones should be monitored by a physician and choose calcium citrate if they must take supplements. Exposure to contaminants. • Some preparations of bone meal and dolomites are contaminated with haz- ardous amounts of arsenic, cadmium, mercury, and lead. Vitamin D toxicity.• Vitamin D, which is present in many calcium supple- ments, can be toxic. Users must eliminate other concentrated vitamin D sources. Excess blood calcium.• This com- plication is seen only with doses of calcium fourfold or more greater than customarily prescribed. Other nutrient interactions.• Calcium inhibits absorption of magnesium, phosphorus, and zinc. Drug interactions.• Calcium and tet- racycline form an insoluble complex that impairs both mineral and drug absorption.

Calcium

Supplement Risks

table C8-4

Energy Balance and Healthy Body Weight 99 do you ever . . .

Wish you could control your body • weight, once and for all?

Feel tempted by a favorite treat when • you don’t feel hungry?

Wonder how extra calories from food • become fat in your body?

Try popular diets to lose weight?•

Keep reading . . .

LO 9.1 Delineate the health risks of too little and too much body fatness, with emphasis on central obesity and its associated health risks.

LO 9.2 Describe the roles of BMR and several other factors in determining an individual’s daily energy needs.

LO 9.3 Calculate the BMI when given height and weight information for various people, and describe the health implications of any given BMI value.

LO 9.4 Compare and contrast the roles of the hormones ghrelin and leptin in appetite regulation, and name several other infl uences on both hunger and satiety.

LO 9.5 Discuss the potential impact of “outside the body” factors on weight-control efforts.

LO 9.6 Develop a weight-loss plan that includes controlled portions of nutrient-dense foods to produce gradual weight loss while meeting nutrient needs.

LO 9.7 Discuss the role of physical activity in maintaining a healthy body composition.

LO 9.8 Defend the importance of behavior modifi cation in weight loss and weight maintenance over the long term.

LO 9.9 Compare and contrast the characteristics of anorexia nervosa and bulimia nervosa, and provide strategies for combating eating disorders.

Farida Zaman/Stock Illustration Source/Getty Images

325T h e P r o b l e m s o f To o L i t t l e o r To o M u c h B o d y F a t

A re you pleased with your body weight? If you answered yes, you are a rare individual. Nearly all people in our society think they should weigh more or

less (mostly less) than they do. Th eir primary concern is usually appearance but they often perceive, correctly, that physical health is somehow related to weight. Both overweight and underweight present risks to health and life.1*

People also think of their weight as something they should control, once and for all. Th ree misconceptions in their thinking frustrate their eff orts, however—the focus on weight, the focus on controlling weight, and the focus on a short-term en- deavor. Simply put, it isn’t your weight you need to control; it’s the fat, or adipose tissue, in your body in proportion to the lean—your body composition. And con- trolling body composition directly isn’t possible—you can only control your behav-

iors. Sporadic bursts of activity, such as “dieting,” are not eff ective; the behaviors that achieve and maintain a healthy body weight take a lifetime of commitment. Luckily, with time, these behaviors become second nature.

Th is chapter starts by presenting problems associated with defi cient and excessive body fatness and then examines how the body manages its energy budget. Th e fol- lowing sections show how to judge body weight on the sound basis of health. Th e chapter then explores some theories about causes of obesity and reveals how the body gains and loses weight. It goes on to present science-based lifestyle strategies for achieving and maintaining a healthy body weight, and it closes with a Contro- versy section on eating disorders.

LO 9.1

The Problems of Too Little or Too Much Body Fat Both defi cient and excessive body fat present risks to health, but in the United States, too little body fat is not a widespread problem. Obesity, in contrast, is an epidemic—see Figure 9-1.2 In 1960, about 13 percent of U.S. adults were obese. Today, 66 percent are overweight while about a third of the population is obese. Even severe obesity increased alarmingly, although some welcomed recent news reports a slowdown in the rate of increase.†3 Among children and adolescents, 33 percent are overweight or are on their way to becoming overweight.4 Figure 9-2 shows that overweight and obesity stand far above the Healthy People target of 15 percent of the population. Th e problem reaches around the globe, in urban and rural areas alike.5

Th e problem of underweight, while aff ecting fewer than 2 percent of adults in the United States, also poses health threats to those who drop below a healthy minimum.6

People at either extreme of body weight face increased risks (see Figure 9-3).7

What Are the Risks from Underweight? Th in people die fi rst during a siege or in a famine. Overly thin people are also at a disadvantage in the hospital, where their nutrient status can easily deteriorate if they have to go without food for days at a time while undergoing tests or sur- gery.8 Underweight also increases the risk for any person fi ghting a wasting disease. People with cancer often die not from the cancer itself, but from starvation. Th inner people may also have worse outcomes when they develop heart disease (but heavier people develop it far more often).9 Th us, excessively underweight people are urged to gain body fat as an energy reserve and to acquire protective amounts of all the nutrients that can be stored.

KE Y POINT Defi cient body fatness threatens survival during a famine or when a person has a disease.

*Reference notes are found in Appendix F. †Defi ned as more than 100 pounds overweight.

Key:

10%–14%

15%–19%

20%–24%

25%–29%

≥ 30%

1998: Most states had obesity prevalence rates of less than 20 percent.

2008: Most states had prevalence rates of greater than 25 percent, with six states reporting prevalence rates greater than or equal to 30 percent.

Most states had prevalence rates of greater than 25 percent, with six states reporting prevalence rates greater than or equal to 30 percent.

Animated!

Increasing

Prevalence

of Obesity

figure 9-1

Source: www.cdc.nccdphp/dnpa/obesity/trend/ maps/index.htm

overweight body weight above a healthy weight; BMI 25 to 29.9 (BMI is defi ned later). underweight body weight below a healthy weight; BMI below 18.5. adipose tissue the body’s fat tissue. Adi- pose tissue performs several functions, includ- ing the synthesis and secretion of the hormone leptin involved in appetite regulation. body composition the proportions of muscle, bone, fat, and other tissue that make up a person’s total body weight. obesity overfatness with adverse health effects, as determined by reliable measures and interpreted with good medical judgment. Obesity is offi cially defi ned as a body mass index of 30 or higher. wasting the progressive, relentless loss of the body’s tissues that accompanies certain diseases and shortens survival time.

http://www.cdc.nccdphp/dnpa/obesity/trend/

326 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

What Are the Risks from Too Much Body Fat? If tomorrow’s headlines read, “Obesity gone! U.S. Population Loses Excess Fat!” tens of millions of people would be freed from obesity-related illnesses—heart dis- ease, diabetes, arthritis, cancer, and others.10 In just one year, an estimated 300,000 lives could be saved, along with the estimated $147 billion spent on obesity-related health care.11

Chronic Diseases To underestimate the threat from obesity is to invite calamity. Th e risk of dying young increases proportionally with increasing body weight.12 With extreme obesity, the risk of dying equals that from smoking.13

Over 70 percent of obese people suff er from at least one other major health prob- lem. Excess body fatness causes up to half of all cases of hypertension, increasing the risk of heart attack and stroke.14 Obesity triples a person’s risk of developing diabetes, and even modest weight gain raises the risk. Chapter 4 presented maps (page 130) depicting increasing U.S. rates of diabetes over the last decade, which bear a striking resemblance to the obesity maps of Figure 9-1. Central obesity, dis- cussed in a moment, particularly elevates these risks.

Other Risks Obese adults also face these threats: abdominal hernias, arthritis, complications in pregnancy and surgery, fl at feet, gallbladder disease, gout, high blood lipids, kidney stones, nonalcoholic fatty liver disease, reproductive disorders, respiratory problems, skin problems, sleep disturbances, sleep apnea (dangerous abnormal breathing during sleep), varicose veins, and even a high accident rate.15 Some of these maladies start to improve with the loss of just 5 percent of body weight, and risks improve markedly after a 10 percent loss. So great are the harms from obesity that obesity itself is classifi ed as a chronic disease.16

KE Y POINT Most obese people suff er illnesses. Obesity is considered a chronic disease.

What Are the Risks from Central Obesity? Fat that collects deep within the central abdominal area of the body, called visceral fat, poses the greatest risks with regard to:

diabetes.•

heart disease.• 17

hypertension.•

gallbladder stones.•

stroke.• 18

some types of cancer.• 19

In fact, this central obesity elevates the risk of death from all causes to a greater extent than does excess fat lying just beneath the skin (subcutaneous fat) of the abdomen, thighs, hips, and legs (Figure 9-4).20

Central Obesity and Infl ammation Why should fat in the abdomen bring extra risk to the heart? Part of the answer may involve adipokines, hormones released by visceral adipose tissue. Adipokines help to regulate infl ammatory processes and energy metabolism in the tissues.21

In central obesity, a shift occurs in the balance of adipokines favoring those that increase both infl ammation and insulin resistance of tissues.22 Th e resulting chronic infl ammation and insulin resistance contribute to diabetes, atherosclerosis (a cause of heart disease), and other chronic diseases.23 With weight loss, the adipokine bal- ance is restored, and infl ammation and insulin resistance are relieved.24 Chronic disease risks drop in response.

In addition to infl ammation, visceral adipose tissue produces more free fatty acids than other types of fat tissue, contributing to a blood lipid profi le associated with

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99 4

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P er

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Years

Obese

Obese or overweight

Healthy People target for obesity

Adult Obesity

and Overweight

Compared with

Healthy People

Target

figure 9-2

Source: National Center for Health Statistics

M o rt

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R is

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M I d

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Body mass index

15 20 25 30 35 40

R is

k i n c re

a s e s

a s B

M I ri s e s

Underweight,

Overweight,

and Mortality

figure 9-3

This J-shaped curve describes the rela- tionship between body mass index (BMI) and mortality. It shows that both under- weight and overweight present risks of a premature death.

Obesity elevates the risk of these major • conditions:

Hypertension•

Heart disease•

Stroke•

Diabetes•

Certain cancers•

327T h e P r o b l e m s o f To o L i t t l e o r To o M u c h B o d y F a t

metabolic syndrome that predicts heart disease (see Chapter 11).25 Also, when fat is deposited in the abdomen, it collects in the liver and around the heart, as well.26 Both these fat depots are under investigation for increasing disease risks.

Who Develops Central Obesity? Men of all ages and women who are past menopause are more prone to develop the “apple” profi le that characterizes cen- tral obesity, whereas women in their reproductive years typically develop more of a “pear” profi le (fat around the hips and thighs). Some women change profi les at menopause, and life-long “pears” may suddenly face the increased disease risks as- sociated with central obesity.

Two other factors also aff ect body fat distribution. Moderate-to-high intakes of alcohol associate directly with central obesity, while higher levels of physical activ- ity correlate with leanness.27 A later section explains how to judge whether a person carries too much fat around the middle.

KE Y POINT Central obesity is more hazardous to health than other forms of obesity. Adipokines are hormones produced by visceral adipose tissue that contribute to infl ammation and diseases. Certain factors aff ect body fat distribution.

How Fat Is Too Fat? People want to know exactly how much body fat is too much. Th e answer is not the same for everyone, but scientists have developed guidelines.

Evaluating Risks from Body Fatness Obesity experts commonly evaluate the health risks of obesity by way of three indicators (each is described more fully later on). Th e fi rst is a person’s BMI, or body mass index. Th e BMI, which defi nes av- erage relative weight for height in people older than 20 years, generally (but not always) correlates with body fatness and disease risks.28

Th e second indicator is waist circumference, refl ecting the degree of visceral fat- ness, or central obesity, in proportion to total body fat (see Table 9-1).29 Th e third indicator is the person’s disease risk profi le, which takes into account other per- sonal factors, such as a diagnosis of hypertension, type 2 diabetes, or elevated blood

CONCEPT LINK 9-1 Diabetes and its damaging effects on the body were discussed in Chapter 4, pages 130–131.

Leptin, an appetite-controlling hormone • discussed in a later section, is another adipokine.

Visceral Fat and

Subcutaneous Fat

figure 9-4

The fat deep within the body’s abdominal cavity may pose an especially high risk to health.

Subcutaneous fat

Abdominal muscle layer

Visceral fat

Intestines

The degree of risk is heightened by the presence of specifi c diseases, other risk factors (such as elevated blood LDL cholesterol, as described in Chapter 11), or smoking.

BMI

Waist � 40 in. (Men)

or � 35 in. (Women)

Waist � 40 in. (Men)

or � 35 in. (Women)

18.5 or less Underweight Low —

18.5–24.9 Normal Low —

25.0–29.9 Overweight Increased High

30.0–34.9 Obese, class I High Very high

35.0–39.9 Obese, class II Very high Very high

40 or greater Extremely obese, class III Extremely high Extremely high

aRisk for type 2 diabetes, hypertension, and cardiovascular disease.

Source: National Heart, Lung, and Blood Institute, National Institutes of Health, The Practical Guide: Identifi - cation, Evaluation, and Treatment of Overweight and Obesity in Adults, NIH publication no. 00-4084.

Chronic Disease Risks According to

BMI Values and Waist Circumferencea

table 9-1

visceral fat fat stored within the abdominal cavity in association with the internal abdomi- nal organs; also called intra-abdominal fat.

central obesity excess fat in the abdo- men and around the trunk.

subcutaneous fat fat stored directly un- der the skin (sub means “beneath”; cutaneous refers to the skin).

adipokines (AD-ih-poh-kynz) protein hor- mones made and released by adipose tissue (fat) cells.

body mass index (BMI) an indicator of obesity or underweight, calculated by dividing the weight of a person by the square of the person’s height.

328 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

cholesterol; whether the person smokes; and so forth (see Table 9-2). Th e more of these factors a person has and the greater the degree of obesity, the greater the ur- gency to control body fatness.

Why, then, do some obese people remain healthy and live long lives and some average-weight people die young of diseases? Genetic inheritance, smoking habits, and level of physical activity may help to explain why some such individuals stay well while others fall ill.30 Th ese factors are discussed in later sections.

Social and Economic Costs of Body Fatness Although a few overfat people escape health problems, no one who is fat in our society quite escapes the social and economic handicaps. Our society places enormous value on thinness, especially for women, and fat people are less sought after for romance, less often hired, and less often admitted to college.31 Th ey pay higher insurance premiums, and they pay more for clothing. An estimated 30 to 40 percent of all U.S. women (and 20 to 25 percent of U.S. men) are trying to lose weight at any given time, spending $50 bil- lion each year, with little long-term success.

Prejudice defi nes people by their appearance rather than by their abilities and char- acters. Obese people suff er emotional pain when others treat them with insensitivity, hostility, and contempt, and they may internalize a sense of guilt and self-deprecation. Health-care professionals, even dietitians, can be among the off enders without real- izing it.32 To free our society of its obsession with body fatness and prejudice against obese people, activists are promoting respect for individuals of all body weights.

KE Y POINT Health risks from obesity are refl ected in BMI, waist circumference, and a disease risk profi le. Fit people are healthier than unfi t people of the same body fatness. Overweight people face social and economic handicaps and prejudice.

LO 9.2

The Body’s Energy Balance What happens inside the body when you eat too much or too little food? Th e body ends up with an unbalanced energy budget—you have taken in more or less food energy than you spent. Th e body’s energy budget works somewhat like a cash bud-

CONCEPT LINK 9-2 Inflammation was discussed in Chapter 3 (page 77) and Chapter 5 (page 162).

Factors affecting body fat distribution:

Gender.•

Menopause in women.•

Smoking.•

Alcohol intake.•

Physical activity.•

If you are wondering about your own BMI, • find it on the inside back cover, page Z.

Three indicators used to evaluate risks from obesity:

Body mass index.•

Waist circumference.•

Disease risk profile and family medical • history.

The National Heart, Lung, and Blood Institute states that aggressive treatment may be needed for extremely obese people who also have any of the following:

Established cardiovascular disease (CVD).• Established type 2 diabetes or impaired glucose tolerance.• Sleep apnea, a disturbance of breathing in sleep, including temporary stopping of • breathing.

The same urgency for treatment exists for an obese person with any three of the following:

Hypertension.• High LDL.• Smoking.• Low HDL cholesterol.• Sedentary lifestyle.• Age older than 45 years (men) or 55 years (women).• Heart disease of an immediate family member before age 55 (male) or 65 (female).•

Indicators of an Urgent Need for Weight Loss table 9-2

Being active—even if overweight—is healthier than being sedentary. Weight loss itself, how- ever, best reduces disease risks.

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329T h e B o d y ’ s E n e r g y B a l a n c e

get that grows and dwindles in proportion to the fl ow of currency. When more food energy is consumed than is needed, excess fat accumulates in the fat cells in the body’s adipose tissue where it is stored. When energy supplies run low, stored fat is withdrawn. Th e daily energy balance can therefore be stated like this:

Change in energy stores equals food energy taken in minus energy spent on metabolism and muscle activities.

More simply:

Change in energy stores � energy in � energy out.

Too much or too little fat on the body today does not necessarily refl ect today’s en- ergy budget. Small imbalances in the energy budget compound over time.

Energy In and Energy Out Th e energy in foods and beverages is the only contributor to the “energy in” side of the energy balance equation. Before you can decide how much food will supply the energy you need in a day, you must fi rst become familiar with the amounts of energy in foods and beverages. One way to do so is to look up calorie amounts as- sociated with foods and beverages in the Table of Food Composition (Appendix A). Alternatively, computer programs can provide this information at a touch of a key. Such numbers are always fascinating to people concerned with managing body fat- ness. For example, an apple gives you 70 calories from carbohydrate; a regular-size candy bar gives you about 250 calories mostly from fat and carbohydrate. You may already know that for each 3,500 calories you eat in excess of expenditures, you store approximately 1 pound of body fat.‡

On the “energy out” side of the equation, no easy method exists for determin- ing the energy an individual spends and therefore needs. Energy expenditures vary so widely among individuals that estimating an individual person’s need requires knowing something about the person’s lifestyle and metabolism.

KE Y POINT The “energy in” side of the body’s energy budget is measured in calories taken in each day in the form of foods and beverages. No easy method exists for determining the “energy out” side of a person’s energy balance equation.

How Many Calories Do I Need Each Day? Simply put, you need to take in enough calories to cover your energy expenditure each day—your energy budget must balance. One way to estimate your energy need is to monitor your food intake and body weight over a period of time in which your activities are typical and are suffi cient to maintain your health. If you keep an ac- curate record of all the foods and beverages you consume and if your weight is in a healthy range and has not changed during the past few months, you can conclude that your energy budget is balanced. Your average daily calorie intake is suffi cient to meet your daily output—your need, therefore, is the same as your current intake.33 At least three, and preferably seven, days, including a weekend day, of honest record keeping are necessary because intakes and activities fl uctuate from day to day.

An alternative method of determining energy need is based on energy output. Th e two major ways in which the body spends energy are (1) to fuel its basal metab- olism and (2) to fuel its voluntary activities. Basal metabolism requires energy to support the body’s work that goes on all the time without our conscious awareness. A third energy component, the body’s metabolic response to food, or the thermic eff ect of food, uses up about 10 percent of a meal’s energy value in stepped-up me- tabolism in the fi ve or so hours after fi nishing a meal.34

Basal metabolism consumes a surprisingly large amount of fuel, and the basal metabolic rate (BMR) varies from person to person (Figure 9-5). Depending on activity level, a person whose total energy need is 2,000 calories a day may spend as

‡Pure fat is worth 9 calories per gram. A pound of it (450 g), then, would store 4,050 calories. A pound of body fat is not pure fat, though; it contains water, protein, and other materials of living tissue—hence the lower calorie value.

Did You Know? 1 lb body fat = 3,500 cal.

Balancing food energy intake with physical activity can add to life’s enjoyment.

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basal metabolism the sum total of all the involuntary activities that are necessary to sustain life, including circulation, respiration, temperature maintenance, hormone secretion, nerve activity, and new tissue synthesis, but excluding digestion and voluntary activities. Basal metabolism is the largest component of the average person’s daily energy expenditure.

voluntary activities intentional activities (such as walking, sitting, or running) con- ducted by voluntary muscles.

thermic effect of food (TEF) the body’s speeded-up metabolism in response to having eaten a meal; also called diet-induced thermogenesis.

basal metabolic rate (BMR) the rate at which the body uses energy to support its basal metabolism.

330 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

many as 1,000 to 1,600 of them to support basal metabolism. Th e iodine-dependent hormone thyroxine directly controls basal metabolism—the less secreted, the lower the energy requirements for basal functions. Th e rate is lowest during sleep.§ Many other factors also aff ect the BMR (see Table 9-3).

People often wonder whether they can speed up their metabolism to spend more daily energy. You cannot increase your BMR very much today. You can, however, amplify the second component of your energy expenditure—your voluntary activi- ties. If you do, you will spend more calories today, and if you keep doing so day after day, your BMR will also increase as you build lean tissue. Lean tissue is more metabolically active than fat tissue, so a way to speed up your BMR is to make muscle-building physical activities a daily habit to nudge your body composition toward the lean. Energy spent on voluntary activities depends largely on two fac- tors. In general, the heavier the weight of the body parts you move and the longer the time you invest in moving them, the more calories you expend.

Be aware that some ads for weight-loss diets claim that certain substances, such as grapefruit or herbs, can elevate the BMR and thus promote weight loss. Th is claim is false. Any meal temporarily steps up energy expenditure due to the thermic eff ect of food, and grapefruit or herbs are not known to accelerate it further.

KE Y POINT Two major components of the “energy out” side of the body’s energy budget are basal metabolism and voluntary activities. A third component of energy expenditure is the thermic eff ect of food. Many factors infl uence the basal metabolic rate.

Estimated Energy Requirements (EER) A person wishing to know how much energy he or she needs in a day to main- tain weight might look up his or her Estimated Energy Requirement (EER) value listed on the inside front cover of this book. Th e numbers listed there seem to imply that for each age and gender group, the number of calories needed to meet the daily requirement is known as precisely as, say, the recommended intake for vitamin A. Th e printed EER values, however, refl ect the needs of only those people who ex-

25–50% physical activitya

5–10% thermic effect of food 50–65% BMR

Components

of Energy

Expenditure

figure 9-5

Typically, basal metabolism represents a person’s largest expenditure of energy, followed by physical activity and the ther- mic effect of food.

aFor a sedentary person, physical activities may account for less than half as much energy as basal metabolism, whereas a very active person’s activities may equal the energy cost of basal metabolism.

§A measure of energy output taken while the person is awake but relaxed yields a slightly higher number called the resting metabolic rate, sometimes used in research.

CONCEPT LINK 9-3 Thyroxine contains the mineral iodine, as explained in Chapter 8, page 300.

To estimate basal energy output:•

Men: kg body weight • A 24 = cal/day.

Women: kg body weight • A 23 = cal/day.

(To convert pounds to kilograms [kg], divide pounds by 2.2.)

Factor Effect on BMR

Age The BMR is higher in youth; as lean body mass declines with age, the BMR slows. Physical activity may prevent some of this decline.

Height Tall people have a larger surface area, so their BMRs are higher.

Growth Children and pregnant women have higher BMRs.

Body composition The more lean tissue, the higher the BMR. A typical man has greater lean body mass than a typical woman, making his BMR higher.

Fever Fever raises the BMR.

Stress Stress hormones raise the BMR.

Environmental temperature

Adjusting to either heat or cold raises the BMR.

Fasting/starvation Fasting/starvation hormones lower the BMR.

Malnutrition Malnutrition lowers the BMR.

Thyroxine The thyroid hormone thyroxine is a key BMR regulator; the more thyroxine produced, the higher the BMR.

Factors That Affect the BMR table 9-3

Estimated Energy Requirement (EER) the DRI recommendation for energy intake, accounting for age, gender, weight, height, and physical activity. Also defi ned in Chapter 2.

331B o d y W e i g h t V e r s u s B o d y F a t n e s s

actly match the characteristics of the “reference man and woman” (see the margin). People who deviate in any way from these characteristics must use other methods for determining their energy needs, and almost everyone deviates.

Taller people need proportionately more energy than shorter people to balance their energy budgets because their greater surface area allows more energy to escape as heat. Older people generally need less than younger people due to slowed me- tabolism and reduced muscle mass, which occur in part because of reduced physical activity. (As Chapter 14 points out, these losses may not be inevitable for people who stay active.) On average, energy need diminishes by 5 percent per decade be- yond the age of 30 years.

In reality, no one is average. In any group of 20 similar people with similar activ- ity levels, one may expend twice as much energy per day as another. A 60-year-old person who bikes, swims, or walks briskly each day may need as many calories as a sedentary person of 30. Clearly, with such a wide range of variation, a necessary step in determining any person’s energy need is to study that person.

KE Y POINT The DRI committee sets Estimated Energy Requirements for a reference man and woman. People’s energy needs vary greatly.

The DRI Method of Estimating Energy Requirements Th e DRI committee provides a way of estimating EER values for individuals. Th ese calculations take into account the ways in which energy is spent, and by whom. Th e equation includes:

Gender.• Women generally have less lean body mass than men; in addition, women’s

menstrual hormones infl uence the BMR, raising it just prior to menstruation.

Age. • Th e BMR declines by an average of 5 percent per decade, as mentioned, so

age is a determining factor when calculating EER values.

Physical activity.• To help in estimating the energy spent on physical activity each

day, activities are grouped according to their typical intensity.

Body size and weight.• Th e higher BMR of taller and heavier people calls for

height and weight to be factored in when estimating a person’s EER.

Growth.• Th e BMR is high in people who are growing, so pregnant women and

children have their own sets of energy equations.

Full instructions for determining your own EER are presented in Appendix H. Alternatively, the margin note off ers a quick-and-easy but more approximate way to determine your energy need and suggests a range of energy intakes that covers most people’s needs based on the EER.

KE Y POINT The DRI committee has established a method for determining an individual’s approximate energy requirement.

LO 9.3

Body Weight Versus Body Fatness For most people, weighing themselves on a scale provides a convenient and accessi- ble way to monitor body fatness, but researchers and health-care providers must rely on more accurate assessments. Th is section describes some of the preferred methods to assess overweight and underweight.

The DRI committee sets EER for a reference • man and woman:

Reference man:• “Active” physical activity

level, 22.5 BMI, 5 ft 10 in. tall, weighing

154 lb.

Reference woman:• “Active” physical activ-

ity level, 21.5 BMI, 5 ft 4 in. tall, weighing

126 lb.

Instructions for determining whether you are • sedentary, lightly active, active, or very active are provided in Appendix H.

Did You Know? About 80% of people in the United States and Canada fall into the sedentary or lightly active categories.

A quick-and-easy estimate of energy need:•

First, look up the EER listed for your age •

and gender group (inside front cover).

Then, calculate a range of energy needs. •

For most people, the energy requirement

falls within these ranges: (Men) EER � 200

cal. (Women) EER � 160 cal.

Virtually everyone’s energy requirement •

falls within these larger ranges: (Men) EER

� 400 cal. (Women) EER � 320 cal.

332 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

Body Mass Index (BMI) BMI values correlate signifi cantly with body fatness, and experts use them to help evaluate a person’s health risks associated with underweight or overweight. Th e inside back cover of this book provides tables in which to fi nd and evaluate BMI values for adults and adolescents. A formula for determining your BMI is given in the margin.

No one can tell you exactly how much you should weigh; but with health as a value, you have a starting framework in the BMI table. Your weight should fall within the range that best supports your health. As a general guideline, under- weight for adults is defi ned as BMI of less than 18.5, overweight as BMI of 25.0 through 29.9, and obesity as BMI of 30 or more.

Health risks associated with BMI values often follow racial lines—the risks as- sociated with a high BMI appear to be greater for white people than for black peo- ple, perhaps because, pound for pound, blacks often have a greater bone density and more lean tissue than whites.35 Likewise, health risks appear to be greater for Asians than for Caucasians at the same BMI.

Th e BMI values have two major drawbacks: they fail to indicate how much of a person’s weight is fat and where that fat is located. Th ese drawbacks limit the value of the BMI for use with:

Athletes (because their highly developed musculature falsely increases their •

BMI values).

Pregnant and lactating women (because their increased weight is normal during •

childbearing).

Adults over age 65 (because BMI values are based on data collected from •

younger people and because people “grow shorter” with age).

In addition, BMI values may overestimate the rates of overweight and obesity among some racial groups.36

Th e athletic man in the margin proves this point: with a BMI over 30, he would be classifi ed as obese by BMI standards alone. However, a clinician would fi nd that his percentage of body fat is well below average and his waist circumference is within a healthy range. A diagnosis of obesity or overweight requires a BMI value plus some measure of body composition and fat distribution. Th ere is no easy way to look inside a living person to measure bones and muscles, but several indirect measures can provide an approximation.

Waist circumference measurements indicate visceral fatness (Figure 9-6); above a certain girth, disease risks rise.37 Health professionals often use both BMI and waist circumference to assess a person’s health risks and monitor changes over time.38

KE Y POINT The BMI values mathematically correlate heights and weights with risks to health. They are especially useful for evaluating health risks of obesity but fail to measure body composition or fat distribution. They are not equally useful in all populations. Central adiposity can be assessed by measuring waist circumference.

Measures of Body Composition and Fat Distribution A person who stands about 5 feet 10 inches tall and weighs 150 pounds carries about 30 of those pounds as fat. Th e rest is mostly water and lean tissues: muscles; organs such as the heart, brain, and liver; and the bones of the skeleton (see Figure 9-7). Th is lean tissue is vital to health. Th e person who seeks to lose weight wants to lose fat, not this precious lean tissue. And for someone who wants to gain weight, it is desirable to gain lean and fat in proportion, not just fat.

Researchers needing precise measures of body composition may choose any of several techniques to estimate body fat, including the skinfold test, underwater

To determine your BMI:•

(In pounds and inches)

weight (lb) A 703 BMI =

height (in2)

(In kilograms and meters)

weight (kg) BMI =

height (in2)

A table of BMI values is provided on the • inside back cover, page Z.

At 6 feet 3 inches tall and 245 pounds, Mike O’Hearn would be judged to be obese by BMI standards alone. Further measures reveal that his body contains only 8% of its weight as fat, less than the average fat percentage for men, and that his waist circumference is within a healthy range.

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333B o d y W e i g h t V e r s u s B o d y F a t n e s s

weighing, or bioelectrical impedance; body fat distribution can be determined by radiographic techniques, such as dual-energy X-ray absorptiometry (see Figure 9-8). Mastering these and other sophisticated techniques requires proper instruc- tion and practice to ensure reliability. Each method has advantages and disadvan- tages with respect to cost, technical diffi culty, and precision of estimating body fat.

KE Y POINT A clinician can determine the percentage of fat in a person’s body by measuring skinfolds, underwater weight, or other parameters. Distribution of fat can be estimated by radiographic techniques.

How Much Body Fat Is Ideal? After you have a body fatness estimate, the question arises: What is the “ideal” amount of fat for a body to have? Th is prompts another question: Ideal for what? If the answer is “society’s perfect body shape,” be aware that fashion is fi ckle and today’s popular body shapes are not achievable by most people.

If the answer is “health,” then the ideal depends partly on your gender and your age. For people in the healthy BMI range:

A man should have between 12 and 20 percent of his body weight as fat.•

A woman should have between 20 and 30 percent of her body weight as fat.•

Researchers draw the line and declare a person overly fat when body fat exceeds these values:

22 percent in men age 40 and younger.•

25 percent in men over age 40.•

32 percent in women age 40 and younger.•

35 percent in women over age 40.•

Besides gender and age, standards diff er because of lifestyle and stage of life. For example, competitive endurance athletes need just enough body fat to provide fuel,

Measuring Waist

Circumference

figure 9-6

Using a nonstretching tape measure, measure around the body near the belly button. (The skeleton shows the tape position relative to the hip bone.) Exhale normally while taking the measurement. Then compare your measurement with these cutoff points: • Men: 102 cm (40 in.). • Women: 88 cm (35 in.). Anyone with a waist measurement larger than these standards may have an in- creased risk of disease.

45% muscle

25% organs

15% fat

15% bone

36% muscle

24% organs

27% fat

13% bone

The substantially greater fat tissue of women is normal and necessary for reproduction

Average Body Composition of Men and Women figure 9-7

skinfold test measurement of the thick- ness of a fold of skin on the back of the arm (over the triceps muscle), below the shoulder blade (subscapular), or in other places, using a caliper (depicted in Figure 9-8); also called fatfold test.

underwater weighing a measure of density and volume used to determine body fat content.

bioelectrical impedance (im-PEE- dense) a technique for measuring body fatness by measuring the body’s electrical conductivity.

dual-energy X-ray absorptiom- etry (ab-sorp-tee-OM-eh-tree) a noninvasive method of determining total body fat, fat distribution, and bone density by passing two low-dose X-ray beams through the body. Also used in evaluation of osteoporosis. Abbrevi- ated DEXA.

Andersen Ross/Blend Images/Getty Images

334 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

insulate the body, and permit normal hormone activity, but not so much as to weigh them down. An Alaskan fi sherman, in contrast, needs a blanket of extra fat to insu- late against the cold. For a woman starting pregnancy, the outcome may be compro- mised if she begins with too much or too little body fat. Below a threshold for body fat content set by heredity, some individuals become infertile, develop depression or abnormal hunger regulation, or become unable to keep warm. Th ese thresholds are not the same for each function or in all individuals, and much remains to be learned about them.

KE Y POINT No single body composition or weight suits everyone; needs vary by gender, lifestyle, and stage of life.

LO 9.4, 9.5

The Mystery of Obesity Why do some people get fat while others stay thin? Does fatness depend more on inherited metabolic factors or on environmental infl uences? Is it a matter of eating habits? If so, what directs eating behaviors—internal controls or a person’s free will? Many factors, some of them confl icting, correlate with obesity (for interest, the mar- gin lists some of them), but obesity’s cause remains elusive. One component under intense scientifi c study is the appetite and its controls.

Hunger and Appetite—”Go” Signals Food is critical to the body, so the brain and digestive tract communicate about the need for food and food suffi ciency. Th eir means of communication, hormones and sensory nerve signals, fall roughly into two broad functional categories: “go” mech- anisms that stimulate eating and “stop” mechanisms that suppress it. One view of the whole process of food intake regulation is summarized in Figure 9-9.

Three Methods of Assessing Body Fatnessafigure 9-8

Skinfold measures can yield accu- rate results when a trained technician measures body fat by using a caliper to gauge the thickness of a fold of skin. Measurements are taken on the back of the arm (over the triceps), below the shoulder blade (subscapular), and in other places (including lower body sites) and are then compared with standards.

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Bioelectrical impedance is accurate when properly administered; the method determines body fatness by measuring conductivity. Lean tissue conducts a mild, painless electric cur- rent; fat tissue does not.

Dual-energy X-ray absorptiometry (DEXA) employs two low-dose X rays that differentiate among fat-free soft tissue (lean body mass), fat tissue, and bone tissue, providing a precise mea- surement of total fat and its distribution in all but extremely obese subjects.

a Other methods include underwater weighing (hydrodensitometry), computed tomography, and magnetic resonance imaging.

More about optimal weight for pregnancy in • Chapter 13.

Research links obesity with:•

Birth order, number of brothers.•

Divorced/single parents, nonprofessional •

or unemployed parents.

Early menstruation.•

Ethnicity (being black or Mexican American •

elevates risk).

Exposure to a variety of foods; fast-food •

and soft-drink consumption.

Fat intake, protein intake, sugar intake.•

Increased wealth (in developing nations).•

Lower economic status (in developed •

nations).

Less frequent alcohol intake; high alcohol •

intake.

Less leisure time, international travel, geo-•

graphic location.

Maternal starvation or obesity during •

gestation.

Meal skipping (particularly breakfast), •

meals eaten away from home.

Napping habits, sleep deprivation.•

Sedentary behavior, television viewing.•

Substandard housing.•

Many more.•

335T h e M y s t e r y o f O b e s i t y

Hunger Beats Satiety Th e regulation of the human appetite is unbalanced, tip- ping in favor of food consumption.39 Hunger commands food seeking and eating behaviors in a life-or-death drive for survival. In comparison, satiation and satiety are weaker suggestions to curb eating-related behaviors that are easily overruled.

Hunger Most people recognize hunger as a strong, unpleasant sensation that sig- nals the need to seek and eat food. Hunger, the response to a physiological need for food, makes itself known roughly four to six hours after eating, after the food has left the stomach and much of the nutrient mixture has been absorbed by the intestine.

Hunger arises in part from chemical messengers acting on or originating in the brain’s hypothalamus.40 Th e physical contractions of an empty stomach trigger hun- ger signals, as does the stomach hormone ghrelin, a powerful appetite-stimulating hormone. Ghrelin is just one of many appetite-regulating messengers that inform the brain of the need for food. Th e brain itself produces a neurotransmitter that potently stimulates hunger sensations.**

Th e body’s hunger response adapts quickly to changes in food intake. A person who suddenly eats smaller meals may feel extra hungry for a few days, but then hunger may diminish for a time. During this period, a large meal may make the person feel uncomfortably full, partly because the stomach’s capacity has adapted to a smaller quantity of food. At this time a dieter may report “My stomach has shrunk,” but the stomach has simply adjusted to smaller meals. At some point in food deprivation, hunger returns with a vengeance and can lead to bouts of exten- sive overeating.

Physiological influences

• Empty stomach. • Gastric contractions. • Absence of nutrients in small intestine and bloodstream. • Digestive system hormones and neural signals create appetite.

Postingestive influences

(after food enters the digestive tract)

• Food in stomach triggers stretch receptors.

• Nutrients in small intestine elicit nervous and hormonal signals informing the brain of the fed state.

Postabsorptive influences (after nutrients enter the blood)

• Nutrients in the blood signal the brain

(via nerves and hormones) about their availability, use, and storage. • As nutrients dwindle, so does satiety. • Hunger develops.

Sensory influences

Cognitive influences

• Presence of others, social stimulation.

• Perception of hunger, awareness of fullness.

• Favorite foods, foods with special meanings.

• Time of day.

• Abundance of available food.

Hunger and Appetite

5 Satiety: Several hours of other activities

Keep eating

Satiation: End meal

Seek food and start meal

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• Endorphins (the brain’s pleasure chemicals) are triggered by the smell, sight, or taste of foods, enhancing the desire for them.

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Hunger, Appetite, Satiation, and Satiety figure 9-9

**The neurotransmitter is neuropeptide Y.

CONCEPT LINK 9-4 Chapter 3 described the brain’s hypothalamus (page 75).

hunger the physiological need to eat, experienced as a drive for obtaining food; an unpleasant sensation that demands relief.

satiation (SAY-she-AY-shun) the percep- tion of fullness that builds throughout a meal, eventually reaching the degree of fullness and satisfaction that halts eating. Satiation gener- ally determines how much food is consumed at one sitting.

satiety (sah-TIE-eh-tee) the perception of fullness that lingers in the hours after a meal and inhibits eating until the next mealtime. Satiety generally determines the length of time between meals.

ghrelin (GREL-in) a hormone released by the stomach that signals the hypothalamus of the brain to stimulate eating.

336 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

Just as the stomach’s capacity can adapt to small meals, it quickly adapts to larger ones until a meal of normal size no longer satisfi es. Th is observation may partly explain the increasing U.S. calorie intakes: popular demand and food industry mar- keting have led to larger and larger food portions, while stomachs across the nation have adapted to accommodate them.

Appetite In addition to hunger, appetite initiates eating, and sometimes over- eating.41 A person can experience appetite without hunger. For example, seeing and smelling a freshly baked apple pie after fi nishing a big meal can stimulate release of the brain’s endorphins, pleasure molecules that create an appetite for the pie despite an already full stomach. In contrast, a person who is ill or under

stress may physically need food but have no appetite. Other factors aff ecting ap- petite include:

appetite stimulants or depressants and mood-altering drugs.•

customary eating habits (cultural or religious acceptability of foods or the expec-•

tation of dessert with dinner).

environmental conditions (people often prefer hot foods in cold weather and vice •

versa).

hormones (for example, sex hormones).•

inborn appetites (inborn preferences for fatty, salty, and sweet tastes).• 42

learned preferences, aversions, and timings (cravings for favorite foods, fear of •

trying new foods, eating according to the clock).

social interactions (companionship, peer infl uences).• 43

some disease states (obesity may be associated with increased taste sensitivity, •

whereas colds, fl u, and zinc defi ciency reduce taste sensitivity).

KE Y POINT Hunger is a physiologic response to an absence of food in the digestive tract. The stomach hormone ghrelin contributes to feelings of hunger. Appetite can occur with or without hunger, and many factors aff ect it. Hunger outweighs satiety in the appetite control system.

Satiation and Satiety—“Stop” Signals To balance energy in with energy out, eating behaviors must be counterbalanced with ending meals and fasts between meals. As with the “go” signals for food in- take, a series of hormones and sensory nerve messages infl uence these processes.44

Satiation At some point during a meal, the brain receives signals that enough food has been eaten. Th e resulting satiation limits the size of the meal (consult Figure 9-9 again). Food in the digestive tract triggers satiation, starting in the mouth. Greater exposure of the mouth to food triggers increased satiation.45 When the stomach stretches to accommodate a meal, nerve receptors in the stomach fi re, sending a signal to the brain that the stomach is full.46 As nutrients from the meal enter the small intestine, they stimulate receptor nerves and trigger the release of hormones, signaling the hypothalamus about the size and nature of the meal.47 Th e brain also detects absorbed nutrients delivered by the bloodstream, and it responds by releasing neurotransmitters that suppress food intake.

Together, stomach distention and the presence of nutrients trigger nervous and hormonal signals to inform the brain’s hypothalamus that a meal has been con- sumed. Satiation occurs; the eater feels full and stops eating.48

Satiety After a meal, the feeling of satiety continues to suppress hunger over a period of hours, regulating the frequency of meals. Hormones, nervous signals, and the brain work in harmony to sustain feelings of fullness. At some later point, sig- nals from the digestive tract once again sound the alert that more food is needed.

Did You Know? Satiation regulates meal size; satiety regulates meal frequency.

appetite the psychological desire to eat; a learned motivation and a positive sensation that accompanies the sight, smell, or thought of appealing foods.

endorphins brain compounds that reduce pain and produce pleasure in ways similar to opiate drugs. In appetite control, endorphins are released on seeing, smelling, or tasting delicious food and may enhance the drive to eat or continue eating.

337T h e M y s t e r y o f O b e s i t y

Leptin: An Adiposity Regulating Hormone Lep- tin, one of the adipokine hormones, is produced pri- marily by the adipose tissue in direct proportion to body fat.††49 Leptin travels via the bloodstream to the brain, where it acts as part of the brain’s appetite-regulating chemistry to suppress the appetite. Leptin operates on a feedback mechanism—a gain in body fatness stimu- lates leptin production, which in turn reduces food consumption, resulting in fat loss.50 Fat loss brings the opposite eff ect—suppression of leptin production and an increase in appetite. Th us, the fat tissue that pro- duces leptin is ultimately controlled by it.

A rare form of severe obesity arises from an inher- ited inability to produce leptin.51 In those cases, restor- ing the missing hormone quickly produces weight and fat loss and reversal of the insulin resistance that fol- lows obesity.52 More commonly, obese people produce plenty of leptin but they fail to respond to it, a condi- tion called leptin resistance.53 Providing more leptin is therefore useless against most people’s obesity.

Energy Nutrients and Satiety Th e composition of a meal also aff ects satiation and satiety. Of the three energy-yielding nutrients, protein seems to be the most satiating, an eff ect that may be due to elevated blood concentrations of certain amino acids in the bloodstream.54 Carbohydrates in food also contribute to satiation and satiety, however, while fat triggers a hormone that contributes longer-term satiety.55

Among carbohydrates, those ranking low on the glycemic index may lend greater satiety to the diet than those ranking higher.56 Low-glycemic foods, such as le- gumes or barley, are often high in soluble fi bers, and soluble fi bers appear to increase satiation.57 Can a low-glycemic diet produce a lower body weight, then? Not unless the diet also presents a calorie defi cit; the glycemic load alone is not correlated with body weight in research.58

Researchers have also reported increased satiety from foods high in water and even from foods that have been puff ed up with air. As dieters await news of foods that might be useful against hunger, researchers have not yet identifi ed any one food, nutrient, or attribute that is especially eff ective for weight loss and its maintenance.

KE Y POINT Satiation ends a meal when the nervous and hormonal signals inform the brain that enough food has been eaten. Satiety postpones eating until the next meal. The adipokine leptin suppresses the appetite and regulates body fatness.

Inside-the-Body Causes of Obesity Findings about appetite regulation, the “energy in” side of the energy budget, do not fully explain why some people gain too much body fatness while others stay lean. On the opposite “energy out” side of the energy budget, many theories have emerged to explain obesity in terms of metabolic function. And whenever discus- sions turn to metabolism, topics in genetics follow closely behind.

Selected Metabolic Theories of Obesity Metabolic theories attempt to explain variations in the ease with which individuals gain or lose body fat. When given a constant number of excess calories over a period of weeks, some people gain many pounds of body fat while other people gain far fewer. Th e former use calories ef- fi ciently: they seem to have a “thrifty” metabolism.

Table 9-4 provides some theories about how metabolic variations may aff ect weight gain. For example, during metabolism, enzymes “waste” a small percentage

The mouse on the right is genetically obese—it lacks the gene for producing leptin. The mouse on the left is also genetically obese but remains lean because it receives leptin injections.

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CONCEPT LINK 9-5 Chapter 4 described the glycemic index and glycemic load, and Controversy 4 discussed the relationships among various carbohydrate sources and body fatness (pages 128–129 and 145).

††Leptin is also produced in the stomach, where it helps to regulate digestion and contributes to satiation.

leptin an appetite-suppressing hormone produced in the fat cells that conveys informa- tion about body fatness to the brain; believed to be involved in the maintenance of body composition (leptos means “slender”).

338 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

of energy. Th e energy is radiated away as heat in a process called thermogenesis. Some enzymes, however, expend copious energy in thermogenesis, producing abun- dant heat but performing no other useful work. In radiating more energy away as heat, the body spends more, rather than storing more, excess energy.

One tissue extraordinarily gifted in performing thermogenesis is brown adipose tissue (BAT). Formerly detected only in animals and human infants, functional BAT has recently been identifi ed in many young adult human subjects, too.59 Intriguingly, subjects with the greatest body fatness in these studies had the least BAT.60

Is it wise, then, to strive to stimulate metabolic enzymes to step up thermogen- esis? Probably not. In rats, upping the rate of thermogenesis has no eff ect on overall energy expenditure or body fatness.61 Also, at a level of activity not far beyond that of normal functioning, energy-wasting activity causes cell death. Sham “metabolic” diet products may claim to increase energy expenditures, but no tricks of metabo- lism can produce eff ortless fat loss.

Genetics and Obesity If genes carry the instructions for making enzymes, and enzymes are involved in energy metabolism, then genetic variations might reason- ably be expected to explain why some people get fat and some stay lean. Indeed, genomic researchers have identifi ed hundreds of genes likely to play roles in obesity development but have not so far identifi ed genetic causes of common obesity.62 In- herited genes clearly do infl uence a person’s tendency to gain weight or stay lean. For someone with at least one obese parent, the chance of becoming obese is esti- mated to fall between 30 and 70 percent.63

Exceptionally complex relationships exist among the many genes related to en- ergy metabolism and obesity, and they each interact with environmental factors, too.64 Although an individual’s genetic inheritance may make obesity likely, the disease of obesity cannot develop unless the environment—factors that lie outside the body—provides the means of doing so.65

Theory Mechanism of Action

Enzyme theory Excess fat storage may stem from elevated concentrations of an enzyme, lipoprotein lipase (LPL), that enables fat cells to store triglycerides. The more LPL, the more easily fat cells store lipid. The fat cells of obese people contain more LPL than the fat cells of lean people.

Fat cell number theory Body fatness is determined by both the number and the size of fat cells. Fat cells increase in number during the growing years, tapering off in adulthood.

Fetal programming theory The children of mothers who either starved or were obese during their pregnancies more often grow to be overweight or obese themselves. An energy-lean or an energy-rich prenatal environment may infl u- ence fetal genetic expression for enzymes involved in energy metabolism: the underfed fetus adapts by producing more energy-conserving metabolic systems; the richly supplied fetus may adapt by producing more fat-storing enzymes and cells.

Thermogenesis I: Energy-wasting proteins and brown fat theory

Proteins control the body’s heat production, or thermogenesis. A type of adipose tissue, brown fat, has abundant energy-wasting proteins that specialize in converting chemical energy to heat. Brown fat is more abundant in lean animals than in fat ones. Human infants have abundant brown fat. In 2009, functional brown fat was identifi ed in human adults.

Thermogenesis II: Adaptive thermogenesis theory

Many tissues, such as muscle, spleen, and bone marrow, convert stored energy into heat in response to cold temperature, physical conditioning, overfeeding, starvation, trauma, and other stress. Genetic inheritance is thought to determine the effi ciency of this system.

Thermogenesis III: Diet-induced thermogenesis theory

The thermic effect of food varies between obese and nonobese people. In lean people who have just eaten a meal, energy use speeds up for a while, but in many obese people, no change in energy use occurs after eating. In theory, this small difference in energy expenditure may account for an accu- mulation of body fat, but overweight people often spend more energy each day than lean people do because their heavier bodies require more energy to move and maintain.

Selected Theories of Metabolic Causes of Obesity table 9-4

thermogenesis the generation and release of body heat associated with the breakdown of body fuels. Adaptive thermo- genesis describes adjustments in energy expenditure related to changes in environment such as cold and to physiological events such as underfeeding or trauma.

brown adipose tissue (BAT) a type of adipose tissue abundant in hibernating animals and human infants and recently identi- fi ed in human adults. Abundant pigmented en- zymes of energy metabolism give BAT a dark appearance under a microscope; the enzymes release heat from fuels without accomplishing other work. Also called brown fat.

339T h e M y s t e r y o f O b e s i t y

KE Y POINT Metabolic theories attempt to explain obesity on the basis of molecular functioning. A person’s genetic inheritance greatly infl uences, but does not ensure, the development of obesity.

Outside-the-Body Causes of Obesity Food is a source of pleasure. Being creatures of free will, people can easily override satiety signals and eat whenever they wish, especially when tempted with delicious treats and large servings. People also value physical ease and seek out labor-savers, such as automobiles and elevators. Over past decades, the abundance of food has increased enormously while the daily demand for physical activity for survival has all but disappeared.66 By some counts, today’s food energy intakes alone account for the rise in U.S. obesity rates.67

External Cues to Overeating Almost everyone has had the experience of walk- ing into a food store, feeling not particularly hungry, and, after viewing an array of goodies, walking out snacking on a favorite treat. A classic experiment showed that rats, known to precisely maintain body weight when fed standard chow, overeat and rapidly become obese when fed “cafeteria style” on a variety of rich, palatable foods. People may also overconsume foods when off ered a delicious smorgasbord, often without realizing they are doing so.68 Like the rats, they respond to external cues.

Overeating behavior also occurs in response to complex human sensations such as loneliness, yearning, craving, addiction, or compulsion.69 Any kind of stress can also cause overeating and weight gain.70 (“What do I do when I’m worried? Eat. What do I do when I’m concentrating? Eat!”).

People also overeat when given large portions of food. In a classic study, movie- goers given large buckets of popcorn consumed proportionately more than when given small bags of popcorn.71 In an amusing twist, researchers dispensed large and small containers of stale 14-day-old popcorn; moviegoers still ate more from the larger size, despite complaining about the taste. Th is phenomenon seems unaff ected by prior knowledge of it. Graduate students in nutrition who had been taught about the “big bowl” eff ect on portion size, were invited to a party and off ered snack mix from big and small bowls. Despite superior education, they ate bigger portions of snack mix from big bowls than from small ones.72

Physical Inactivity Some people may be obese not because they eat too much, but because they move too little. In as little as one month of inactivity, muscles shrink measurably and collect small deposits of fat.73 Conversely, sustained exercise is known to stimulate muscle cells to develop more fat-metabolizing equipment that uses up fat and other fuels during and after activity.74

In addition to intentional physical activity, a spontaneous kind of activity produces nonexercise activity thermogenesis (NEAT). Lean people tend to be more spon- taneously active, both at work and at leisure, and so expend more NEAT energy.75

Did You Know? Quacks often sell “genetic tests” and diets that promise to “reset your genetic code to be thin. Beware.

Controversy 11 provides a look into the sci-• ence of nutritional genomics.

my turn

Jackie Lauren

How Many Calories?

Two students talk about portion control, physical activity, and dessert.

To hear their stories, log on to www.cengage.com/sso.

CONCEPT LINK 9-6 The rise in U.S. calorie intakes was depicted in Figure C4-3, page 144.

CONCEPT LINK 9-7 Figure 2-11 in Chapter 2 (page 49) demon- strated how portion sizes have increased over recent decades.

nonexercise activity thermogen- esis (NEAT) energy expenditure associ- ated with everyday spontaneous activities, as opposed to consciously undertaken physical activities.

The war on muscular work has been a

remarkable success.

—C. Bouchard, Physical Activity and Obesity (Champaign, Ill: Human Kinetics Publishers, Inc., 2000).

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http://www.cengage.com/sso

340 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

Th eir brains somehow signal them to stand up more, walk around, and fi dget.80 Col- lectively, NEAT expenditures may contribute to energy balance to some degree.81

Th e United States seems locked in an epidemic of inactivity. Television and sed- entary video and computer entertainment have all but replaced outdoor play for many people.82 In addition, most people work at sedentary jobs. A hundred years ago, 30 percent of the energy used in farm and factory work came from human muscle power; today, only 1 percent does. Th e same trend follows at home, at work, at school, and in transportation. Th e more hours spent sitting still, the higher the risk of dying from heart disease and other causes.83 Th e Th ink Fitness feature of- fers perspective on the contribution of physical activity to weight management, and Table 9-5 lists the energy costs of some activities.

The Built Environment Experts urge people to “take the stairs instead of the elevator” or “walk or bike to work.” Th ese are good suggestions: climbing stairs pro- vides an impromptu workout, and people who walk or ride a bicycle for transporta- tion most often meet their needs for physical activity.84 For many, though, such healthy lifestyle choices are challenging.

Some aspects of the built environment, including buildings, sidewalks, and transportation opportunities, can discourage physical activity. For example, most stairwells of modern buildings are inconvenient, stuff y, isolated, and unsafe. Road- ways often lack sidewalks, crosswalks, or lanes marked for bicycles. Th e air on road- ways can be dangerously high in carbon monoxide gas and other pollutants from gasoline engine emissions.‡‡ Hot and cold weather also pose hazards for outdoor

think fitness Activity for a Healthy Body Weight

Some people believe that physical activity must be long and arduous to obtain benefits, such as im- proved body composition. Not so. A brisk, 30-minute walk at a pace of about 100 steps per minute each day can help significantly (a pe- dometer can help count steps).76 To achieve an “active lifestyle” requires walking for an hour a day. Even in increments of 10 minutes throughout the day, exercising can measurably improve fitness.77 In one study, as little as 72 minutes of physical activity a week measur- ably reduced waist circumference in overweight and obese women, even in the absence of weight loss.78 Weight loss brought greater

reductions in waist circumference, however.

According to the American College of Sports Medicine’s 2009 position paper:

A negative energy balance in-• curred through physical activity will result in weight loss, and the larger the negative energy balance, the greater the weight loss.

Preventing weight gain and aug-• menting loss occurs with at least 2 hours and 30 minutes (150 minutes) a week of at least moderate inten- sity physical activity.

Episodes of physical activity of • at least 10 minutes duration count toward exercise goals.

Both aerobic (endurance) and • muscle-strengthening (resistance) physical activities are beneficial, but calorie restriction must accom- pany resistance training to achieve weight loss.79

A useful strategy is to incorporate bits of physical activity into your daily schedule in many simple, small-scale ways. Work in the gar- den; work your abdominal muscles while you stand in line; stand up straight; walk up stairs; fidget while sitting down; tighten your buttocks each time you get up from your chair. Small energy expenditures can add up to significant contribu- tions. Chapter 10 provides many more details.

START NOW

Ready to make a change? Consult the online behavior-change planner to commit to obtaining enough physical activity to help build lean tissue and improve fi tness while managing body fatness at www.cengage.com/sso.

Physical activity for weight loss or • maintenance:

Choose moderate or vigorous activities.1.

Move large muscle groups.2.

Invest longer times in physical activity.3.

Adopt informal strategies to be more 4. active.

Physical activity for building lean body • mass:

Choose strength-building exercises.1.

Use a balanced exercise routine.2.

Perform exercises with increasing 3. intensity.

Adopt informal strategies to be more 4. active.

‡‡Carbon monoxide (CO) avidly binds to hemoglobin in the blood, reducing blood oxygen content: CO in air surrounding roadways can reach levels suffi cient to impair driving ability.

built environment the buildings, roads, utilities, homes, fi xtures, parks, and all other man-made entities that form the physical characteristics of a community.

food deserts urban and rural low-income areas with limited access to affordable and nutritious foods. Also defi ned in Chapter 15.

http://www.cengage.com/sso

341H o w t h e B o d y L o s e s a n d G a i n s W e i g h t

commuters. In contrast, those with access to health-promoting built environments more easily make healthy choices. Safe, attractive, aff ordable biking and walking areas and public exercise facilities help maintain health and body leanness and so does access to nutritious foods.85

Food Access Th e kinds of foods recommended for weight management—fresh fruits, vegetables, lean meats, and other lower-calorie foods—are not equally avail- able across the United States. Residents of low-income urban and rural areas called food deserts may lack access to even a single supermarket but fi nd convenience stores and fast-food restaurants in abundance.86 Often overweight and without transportation, such people lack access to distant supermarkets that off er nutritious fresh foods.87 Th ey base their diets on refi ned packaged sweets and starches and fatty canned meats, or they eat mostly fast food, inviting malnutrition.88 A correla- tion exists between eating fast food and being obese, but this does not prove that eating fast food causes obesity.89 It may, but fast foods may simply coexist with a number of other factors that make obesity likely. After all, many lean people also eat fast food in moderation.

End of Story? Anyone involved in a good mystery wants to know how it ends. In the case of the causes of obesity, no one yet knows which of the suspects are the real culprits, and until evidence proves otherwise, any or all may be guilty as charged. In real life, the best way for most people to attain a healthy body composition boils down to control in three areas: diet, physical activity, and behavior change. Later sections focus on these areas, while the next section delves into the details of how, exactly, the body loses and gains weight.

KE Y POINT Studies of human behavior identify stimuli that lead to overeating. Too little physical activity, the built environment, and a lack of access to fresh foods are also linked with overfatness.

How the Body Loses and Gains Weight Th e causes of obesity may be complex, but the body’s energy balance is straightfor- ward. Th e balance between the energy you take in and the energy you spend deter- mines whether you will gain, lose, or maintain body fat. A change in body weight of a pound or two may not indicate a change in body fat—it can refl ect shifts in body fl uid content, in bone minerals, in lean tissues such as muscles, or in the contents of the bladder or digestive tract. A change often correlates with the time of day: people generally weigh the least before breakfast. One of the most important things for people concerned with weight control to realize is that quick, large changes in weight may not indicate fat loss.

Th e type of tissue lost or gained depends on how you go about losing or gain- ing it. To lose fl uid, for example, you can take a “water pill” (diuretic), causing the kidneys to siphon extra water from the blood into the urine; intense exercise while wearing heavy clothing in hot weather also causes abundant fl uid loss in sweat. (Both practices are dangerous and are not being recommended here.) To gain water weight, you can overconsume salt and water; for a few hours, your body will retain water until it manages to excrete the salt. (Th is, too, is not recommended.) Most quick weight-change schemes promote large changes in body fl uids that register dramatic, but temporary, changes on the scale and accomplish little weight change in the long run.

One other practice is hazardous and not recommended: smoking. Each year, many adolescents, particularly girls, take up smoking as a means to control weight.90 Nic- otine blunts feelings of hunger and smokers do tend to weigh less than nonsmokers.

To determine the calorie cost of an activity, multiply the number listed by your weight in pounds. Then multiply by the number of minutes spent performing the activity.

Example: Jessica (125 pounds) rode a bike at 17 mph for 25 minutes:

.057 � 125 � 7.125

7.125 � 25 � 178.125

(about 180 calories)

Activity Cal/lb Body Weight/min

Aerobic dance (vigorous) .062 Basketball (vigorous, full

court) .097

Bicycling 13 mph .045 15 mph .049 17 mph .057 19 mph .076 21 mph .090 23 mph .109 25 mph .139

Canoeing (fl at water, moderate pace) .045

Computer sports gamesa

bowling .021 boxing .021 tennis .022

Cross-country skiing 8 mph .104

Golf (carrying clubs) .045 Handball .078 Horseback riding (trot) .052 Rowing (vigorous) .097 Running

5 mph .061 6 mph .074 7.5 mph .094 9 mph .103 10 mph .114 11 mph .131

Soccer (vigorous) .097 Studying .011 Swimming

20 yd/min .032 45 yd/min .058 50 yd/min .070

Table tennis (skilled) .045 Tennis (beginner) .032 Walking (brisk pace)

3.5 mph .035 4.5 mph .048

Weight lifting light-to-moderate effort .024 vigorous effort .048

Wheelchair basketball .084 Wheeling self in wheelchair .030

aSuch as Wii™, by Nintendo.

Energy Spent

in Activities

table 9-5

34 2 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

Fear of weight gain prevents many people from quitting smoking, too. Th e best advice to those hoping to quit is to adjust eating and exercise habits to maintain weight during and after cessation. To the person fl irting with the idea of taking up smoking for weight control, don’t do it—many thousands of people who became addicted as teenagers die from tobacco-related illnesses each year.

Moderate Weight Loss Versus Rapid Weight Loss Being able to eat periodically, store fuel, and then use up that fuel between meals is a great advantage. Relieved of the need to constantly seek food, human beings are free to dance, study, converse, wonder, fall in love, and concentrate on endeavors other than eating. Th e between-meal interval is normally about 4 to 6 waking hours—about the length of time the body takes to use up most of the readily available fuel—or 12 to 18 hours at night, when body systems slow down and the need is less.

When you eat less food energy than you need, your body draws on its stored fuel to keep going. If a person exercises appropriately, moderately restricts calories, and consumes an otherwise balanced diet that meets protein and carbohydrate needs, the body is forced to use up its stored fat for energy. Gradual weight loss will occur. Th is is preferred to rapid weight loss because lean body mass is spared and fat is lost.

The Body’s Response to Fasting If a person doesn’t eat for, say, three whole days, then the body makes one adjustment after another. Less than a day into the fast, the liver’s glycogen is essentially exhausted. Where, then, can the body ob- tain glucose to keep its nervous system going? Not from the muscles’ glycogen be- cause that is reserved for the muscles’ own use. Not from the abundant fat stores most people carry because these are of no use to the nervous system. Fat cannot be converted to glucose—the body lacks enzymes for this conversion.§§ Th e muscles, heart, and other organs use fat as fuel, but at this stage the nervous system needs glucose. Th e body does, however, possess enzymes that can convert protein to glu- cose. Th erefore, the underfed body sacrifi ces the proteins in its lean tissue to supply raw materials from which to make glucose.

If the body were to continue to consume its lean tissue unchecked, death would ensue within about ten days. After all, in addition to skeletal muscle, the blood pro- teins, liver, digestive tract linings, heart muscle, and lung tissue—all vital tissues— are being burned as fuel. (Fasting or starving people remain alive only until their stores of fat are gone or until half their lean tissue is gone, whichever comes fi rst.) To prevent this, the body plays its last ace: it converts fat into compounds that the nervous system can adapt for use and so forestalls the end. Th is process is ketosis, an adaptation to prolonged fasting or carbohydrate deprivation.

Ketosis In ketosis, instead of breaking down fat molecules all the way to carbon dioxide and water, the body takes partially broken-down fat fragments and combines them to make ketone bodies, compounds that are normally kept to low levels in the blood. It converts some amino acids—those that cannot be used to make glucose—to ketone bodies, too. Th ese ketone bodies circulate in the bloodstream and help to feed the brain; about half of the brain’s cells can make the enzymes needed to use ketone bodies for energy. Under normal conditions, the brain and nervous system devour glu- cose—about 400 to 600 calories’ worth each day. After about ten days of fasting, the brain and nervous system can meet most of their energy needs using ketone bodies.

Th us, indirectly, the nervous system begins to feed on the body’s fat stores. Keto- sis reduces the nervous system’s need for glucose, spares the muscle and other lean tissue from being quickly devoured, and prolongs the starving person’s life. Th anks to ketosis, a healthy person starting with average body fat content can live totally deprived of food for as long as six to eight weeks. Figure 9-10 reviews how energy is used during both feasting and fasting.

Fasting Respected, wise people in many cultures have practiced fasting as a peri- odic discipline. Th e body tolerates short-term fasting, and at least in animal studies,

CONCEPT LINK 9-8 Chapter 8 discussed the body’s water and electrolyte balancing systems, pages 286–287.

Smoking may keep some people’s weight • down, but at what cost?

Cancer.•

Chronic lung diseases.•

Heart disease.•

Low-birthweight babies.•

Miscarriage.•

Osteoporosis.•

Shortened life span.•

Sudden infant death.•

Many others.•

In early food deprivation:•

The nervous system cannot use fat as fuel; •

it can only use glucose.

Body fat cannot be converted to glucose.•

Body protein can be converted to glucose.•

In later food deprivation:•

Ketone bodies help feed the nervous sys-•

tem and so help spare tissue protein.

§§Glycerol, which makes up 5 percent of fat, can yield glucose but is a negligible source.

CONCEPT LINK 9-9 Chapter 4 discussed ketosis and some of its drawbacks (page 126).

ketone bodies acidic compounds derived from fat and certain amino acids. Nor- mally rare in the blood, they help to feed the brain during times when too little carbohydrate is available. Also defi ned in Chapter 4.

343H o w t h e B o d y L o s e s a n d G a i n s W e i g h t

short-term fasting seems to benefi t the body in some ways, although there is no evidence that the body becomes internally “cleansed,” as some believe. Fasting may harm the body, however, when ketosis upsets the acid-base balance of the blood or when fasting promotes excessive mineral losses in the urine. In as little as 24 hours of fasting, the intestinal lining begins to lose its integrity.

When a person overeats (feasting):

Food component: a

Is broken down in the body to: And then ends up as:

When a person draws on stores (fasting):

Glucose

Energy

Liver and muscle glycogen stores

Body fat stores

Nitrogen lost in urine

Carbohydrate

Fat Fatty acids

Fatty acids

Protein

Liver and muscle glycogen stores

Amino acids (first used to replace body proteins)

Glucose

Nitrogen and some ketone bodies lost in urine

Ketone bodies

Storage component: Is broken down in the body to: And then used for:

If the fast continues beyond glycogen depletion:

Body component: Is broken down in the body to: And then converted to:

Body fat stores

Body fat

Body protein Amino acids

Feasting and Fasting figure 9-10

aAlcohol is not included because it is a toxin and not a nutrient, but it does contribute energy to the body. After detoxifying the alcohol, the body uses the remaining two- carbon fragments to build fatty acids and stores them as fat.

34 4 chapter 9 E n e r g y B a l a n c e a n d H e a l t h y B o d y W e i g h t

Food deprivation also leads to a tendency to overeat or even binge when food be- comes available. Th e eff ect seems to last beyond the point when weight is restored to normal, sometimes for years; people with eating disorders often report that fasting or a severely restricted diet heralded the beginning of their loss of control over eat- ing.91 Th is indictment applies to extreme dieting and fasting, but not to the moder- ate weight-management strategies described later in this chapter.

If you want to lose weight, fasting is not the best way. While the body’s lean tis- sues continue to be degraded, tissues are deprived of nutrients they need to assemble new enzymes, red and white blood cells, and other vital components. Th e body also slows its metabolism to conserve energy—the wrong eff ect for weight loss. A diet that moderately restricts calories promotes a faster rate of fat loss and the retention of more lean tissue than a severely restricted fast or very-low-calorie diet.92 Addi- tionally, moderate diets are sustainable—they provide the best chance at long-term weight management.

The Body’s Response to a Low-Carbohydrate Diet Any diet too low in carbo- hydrate brings about responses that are similar to fasting. As carbohydrate runs out, the body breaks down fat and protein for energy and forms ketone bodies to feed the brain. To prevent these eff ects, the DRI committee sets a minimum intake for carbohydrate at 130 grams per day but recommends far more for health—between 45 and 65 percent of total calories from carbohydrate, an amount associated with low chronic disease risks.

Low-carbohydrate, high-protein diets have been heavily promoted for weight loss, and they take many guises, each enjoying a new surge of popularity that sub- sequently fades away. Over decades, these and other fad diets continue to sell, how- ever, and the Consumer Corner provides a look at some of them.

KE Y POINT When energy balance is negative, glycogen returns glucose to the blood. When glycogen runs out, body protein is called upon for glucose. Fat also supplies fuel as fatty acids. If glucose runs out, fat supplies fuel as ketone bodies, but ketosis can be dangerous. Both prolonged fasts and low-carbohydrate diets are ill-advised.

Weight Gain What happens inside the body when a person does not use up all of the food energy taken in? Previous chapters have already provided the answer—the energy-yielding nutrients contribute the excess to body stores as follows:

Protein is broken down to amino acids for absorption. Inside the body, these •

may be used to replace lost body protein and, in a person who is exercising or

growing, to build new muscle and other lean tissue.

Excess amino acids have their nitrogen removed and are used for energy or are •

converted to glucose or fat. Th e nitrogen is excreted in the urine.

Fat is broken down to glycerol and fatty acids for absorption. Inside the body, •

the fatty acids can be broken down for energy or stored as body fat with great

effi ciency. Th e glycerol enters a pathway similar to carbohydrate.

Carbohydrate (other than fi ber) is broken down to sugars for absorption. In the •

body tissues, excesses of these may be built up to glycogen and stored, used for

energy, or converted to fat and stored.

Alcohol is absorbed and, once detoxifi ed, used for fuel or converted into body fat •

for storage.

Four sources of energy—the three energy-yielding nutrients and alcohol—may en- ter the body, but they become only two kinds of energy stores: glycogen and fat. Glycogen stores amount to about three-fourths of a pound; fat stores can amount to

Did You Know? Names of some low-carbohydrate, high-protein diets: Atkins New Diet Revolution, Calories Don’t Count Diet, Protein-Power Diet, the Carbohydrate Addict’s Diet, the Lo-Carbo Diet, and the Zone Diet. New ones keep coming out, but they are essentially the same diet.

People who have healthy body weight con- sume more, not less, carbohydrate-rich whole foods.

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weight loss while physical activity helps to maintain it. Singling out protein, car- bohydrate, or fat for elimination from the diet does not enhance long-term weight loss or help to maintain it.3

ARE THEY SAFE? Although many diets are tolerated by most people, exceptions exist. For example, a rare but life-threatening form of severe blood acid imbalance has been associ- ated with a low-carbohdrate diet.4 In addi- tion, recent evidence suggests that such a diet may produce unfavorable effects on both blood lipids and artery linings associ- ated with heart disease.5 More evidence comes from a documented case of heart disease and other health problems in a previously healthy man who had begun following the Atkins low-carbohydrate diet; his problems resolved after he gave up the

Weight-loss books and products are a $33 billion-a-year business—so many fad diets exist that they could fi ll a bookstore. Some restrict fats or carbohydrates, some disallow certain foods, some advocate certain food combinations, some claim that a person’s genetic type or blood type determines the best diet, and so forth.

Unfortunately, many of these diets are more fi ction than science. The writers may skillfully weave in bits of authen- tic nutrition knowledge and include impressive-sounding terms, such as eicosanoids or adipokines, to make their ideas sound credible. Table 9-6 presents some fad diet fantasies along with the scientifi c truths. What is it about these diets that consumers fi nd so irresistible?

ARE THE DIETS EFFECTIVE? If fad diets were entirely ineffective, con- sumers would eventually stop buying into them. If they were especially effective, the obesity problem would have been solved. In reality, most fad diets succeed in limiting calorie intakes and so produce weight loss (at least in the short