Personal Health Assesment. I will provide my weight and other personal things to make it fit to me

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Nutrition From Science to You

Joan Salge Blake Boston University

Kathy D. Munoz Humboldt State University

Stella Volpe University of Pennsylvania

Benjamin Cummings San Francisco Boston New York

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Copyright © 2010 Pearson Education, Inc., publishing as Pearson Benjamin Cummings, 1301 Sansome St., San Francisco, CA 94111. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s) to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, 1900 E. Lake Ave., Glenview, IL 60025. For information regarding permissions, call (847) 486-2635.

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Library of Congress Cataloging-in-Publication Data Blake, Joan Salge.

Nutrition: from science to you / Joan Salge Blake, Kathy D. Munoz, Stella Volpe. p. cm.

Includes bibliographical references and index. ISBN 10: 0-321-51319-3; ISBN 13: 978-0-321-51319-9 (Student edition) ISBN 10: 0-321-59235-2; ISBN 13: 978-0-321-59235-4 (Professional copy)

1. Nutrition/—Textbooks./Munoz, Kathy D., 1951– II. Volpe, Stella, 1963– III. Title.

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About the Authors

Joan Salge Blake, MS, RD, LDN Boston University

Joan Salge Blake is a Clinical Associate Professor and Dietetics Internship Director at Boston University’s Sargent College of Health and Rehabilitation Sciences. She teaches both graduate and undergraduate nutrition courses. She received her MS from Boston University.

Joan is a member of the American Dietetic Association and the Massachusetts Dietetic Association (MDA). She has been a presenter and Presiding Officer at both the ADA Annual Meeting and the MDA Annual Convention and is a guest lecturer at the Boston University Goldman School of Dental Medicine. She was previously named MDA’s “Young Dietitian of the Year” and is the past Director of Education and Nominating Committee Chairperson for the MDA. She currently serves on the MDA board. Joan has received the Whitney Powers Excellence in Teaching award from Boston University and the Annie Galbraith Outstanding Dietitian award from the Massachusetts Dietetic Association.

In addition to teaching and writing, Joan has a private practice specializing in weight management and lifestyle changes. Joan is often asked to translate complex nutri- tional issues in popular terms. As an ADA National Spokesperson she conducts over 100 media interviews annually, and is a nutrition contributor of articles to a variety of magazines.

Kathy D. Munoz, EdD, RD Humboldt State University

Kathy D. Munoz is a professor of nutrition and Chair of the Department of Kinesiol- ogy and Recreation Administration at Humboldt State University. She teaches under- graduate introductory nutrition, exercise nutrition and weight management courses, and graduate exercise nutrition. She received her EdD from the University of South- ern California in curriculum design and an MS in Foods and Nutrition with a minor in exercise physiology from Oregon State University. Kathy has published research in the areas of nutrition and exercise, weight management, and body composition.

Kathy is a member of the American Dietetic Association and the California Dietetic Association. She has published articles in Research Quarterly for Exercise and Sport, Children’s Health Care, the Journal of Nutrition Education, and the International Jour- nal of Sport Nutrition and Exercise, and has co-authored a series of curriculum guides for elementary teachers. Kathy has also been recognized for her research in, and de- velopment of, asynchronous learning.

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iv About the Authors

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Stella L. Volpe, PhD, RD, LDN University of Pennsylvania

Stella Volpe is the Miriam Stirl Term Associate Professor of Nutrition in the School of Nursing at University of Pennsylvania. She is a nutritionist and exercise physiolo- gist whose research is on obesity prevention, body composition, bone mineral den- sity, and mineral metabolism and exercise. Stella’s current research revolves around the effects of the environment on obesity. Stella teaches introductory courses on nutrition and on nutrition, exercise, and fitness. She received her PhD from Virginia Tech.

Stella is a Core Member of the Biobehavioral Research Center, an Associated Faculty Member of the Center for Health Disparities in the School of Nursing, an Associate Scholar in the Center for Clinical Epidemiology and Biostatistics, an Associate Fac- ulty Member in the Graduate Program in Public Health, a co-Director in Excellence in Partnerships for Community Outreach, Research on Health Disparities, and Training (EXPORT), and a Member of the Penn Diabetes Center, all in the School of Medicine.

Among her professional memberships, Stella is a Fellow of the American College of Sports Medicine and a member of the American College of Nutrition, the American Society for Nutritional Sciences, the American Society of Clinical Nutrition, the American Dietetic Association, Community-Campus Partnerships for Health, and Sigma Xi.

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We wrote Nutrition: From Science to You to provide you with a solid foundation about nutrition and how it affects you and your nutritional needs, concerns, and questions.

Between the three of us, we have more than 40 years of teaching college-level nutrition. We’ve conducted and published research, studied the literature, and lis- tened to and watched our students learn this science. We’ve made copious notes re- garding students’ questions, interests, concerns, and misunderstandings, both in and outside the classroom. These years of experience have culminated in a textbook that we believe translates the latest nutrition science into a readable format to provide you with information that you can easily incorporate into your life and the lives of others. As a college student, you are exposed to a steady stream of nutrition and health information from the media, your family and friends, and the Internet. Al- though you may think Google has the answer to your nutrition questions, we have seen students frequently fall victim to misinformation found via a quick Web search and a few glitzy websites. We designed Nutrition: From Science to You to be as user friendly as possible, and packed exclusively with sound nutrition information. The text goes beyond basic nutrition science and provides realistic advice and strategies to help you apply what you learn in your own life. The text is written to meet your nutritional concerns and answer your questions.

As you read Nutrition: From Science to You, we want you to feel as though you are sitting in our class being engaged in the latest science of nutrition. For this rea- son, the text is written in a conversational tone designed to visually communicate complex nutrition science and topics in an easy-to-understand way.

The information in each chapter is presented using a “What,” “Why,” and “How” format in which we explain:

“What” the nutrition concept is and the science that supports it “Why” it is important and what role it plays in the body “How” to easily adjust and improve your diet based on what you just learned

“What” Is the Nutrition Concept? Each chapter begins with a Campus Corner, a short scenario involving a college stu- dent who is experiencing a common nutrition-related situation pertinent to the chapter topic. Don’t be surprised if the student reminds you of yourself, your room- mate, or a relative! We want you to be able to immediately relate to the character in the scenario and his or her nutrition problem. As you read, you will learn how to apply the information in the chapter to this person’s life situation (and yours) in a practical way and you will see the person revisited at several points throughout the chapter as you learn more.

The popular Myths and Misconceptions Pretest is the chapter-opening quiz that will help you recognize misperceptions that you may have about the chapter topic. The answers to these pretest questions are woven throughout the chapter and a complete explanation is given at the end of the chapter.

Our vision in writing this textbook was to present the science of nutrition and supporting chemistry and physiology in an easy-to-understand format surrounded

Why We Wrote Nutrition: From Science to You

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by colorful and visually appealing photos and illustrations that make the informa- tion memorable. The Visual Summary Tables have been specifically chosen and de- signed to help you understand and remember nutrition concepts and the important roles that featured nutrients play in your body and diet. You will find these sum- maries at the end of each macronutrient chapter (Carbohydrates, Lipids, Proteins, and Water). In the micronutrients chapters (Fat-Soluble Vitamins, Water-Soluble Vitamins, Major Minerals, and Trace Minerals), they comprise the bulk of each chapter. Each micronutrient is presented in a consistent, easily studied format that covers what the micronutrient is, its functions, daily needs, food sources, and the consequences of too much or too little in the diet.

The Feature boxes woven throughout the text present more in-depth informa- tion on up-to-date topics of interest, including protein bars, enhanced beverages, bottled water, and food allergies. The necessary calculations that you will use in your professional life are highlighted in Calculation Corner boxes, and you’ll find a review of key chemistry concepts in the Chemistry Boost boxes. Because we are passionate about our profession as Registered Dietitians (RD) and health care pro- fessionals, we’ve included a feature entitled Careers in Nutrition to provide you with an insight into this growing profession. These interviews with a wide variety of pro- fessionals in the field of nutrition are described briefly in the text and can be found in full on this book’s companion website. You’ll also note in selected places in the text a Health Focus icon. Whereas nutrition affects health in innumerable ways, we have highlighted four areas (heart disease, cancer, hypertension, and diabetes) in which the effects of diet are especially pronounced.

“Why” Is the Nutrition Concept Important to You? Chapters contain Self-Assessments that will help you determine whether your cur- rent diet and lifestyle habits need a little fine-tuning. The self-assessments were de- veloped to help you reflect upon your current diet and consider changes to implement. The Top Ten Points to Remember at the end of each chapter boils down the most important concepts of the entire chapter. Lastly, the Putting It All Together section at the end of each chapter builds upon all the chapters before it and shows you how the material learned in the current chapter fits in with the material learned in previous chapters.

“How” to Easily Adjust Your Lifestyle This book is filled with tools and tips to help you make positive diet and lifestyle changes. The Food Source Diagrams visually provide you with the most robust food sources of each nutrient and are based on the MyPyramid design. For additional in- formation on the nutritional values of common foods, The Food Composition Table is available to complement this text. The Table Tips are short, snappy lists of practi- cal changes that will help you achieve lasting improvements in your diet and lifestyle.

The what, why, and how of nutrition research is presented in the Focus on Re- search feature. These research summaries will help you develop critical thinking skills related to reading and interpreting current research.

Finally, the Two Points of View feature at the end of each chapter contains ques- tions and answers from two experts representing their viewpoints on a timely topic. This feature will encourage you to think critically about pro and con arguments on a given issue and decide for yourself which side you agree with. You will be applying

HEALTH FOCUS

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the critical thinking skills that you learned in the chapter as you read each expert’s point of view.

Remember, nutrition matters to you! What you eat today and tomorrow will af- fect you and your body for years to come. Just as important, what you learn about nutrition today will enable you to make a positive effect on the lives of others from now on.

Joan Salge Blake, MS, RD, LDN Boston University

Kathy D. Munoz, EdD, RD Humboldt State University

Stella L. Volpe, PhD, RD, LDN University of Pennsylvania

Acknowledgments It takes a village, and then some, when it comes to writing a dynamic textbook. Nutrition: From Science to You is no exception. We personally want to extend our gratitude to all of those who passionately shared their expertise and support to make Nutrition: From Science to You better than we could have envisioned.

Beginning with the energetic staff at Benjamin Cummings, we would like to thank Sandy Lindelof, who helped make our vision for this textbook into a reality. Cheryl Cechvala’s on-the-mark developmental editing improved Nutrition: From Science to You and made it enjoyable to read. It takes a project manager to make sure the village runs on a schedule, and Susan Malloy and Katie Cook kept us on track, es- pecially when the FedEx packages were arriving daily. A textbook needs cracker-jack supplements and assistant editor Emily Portwood worked diligently to obtain the best for Nutrition: From Science to You. Thanks also to assistant editor Shannon Cutt and editorial assistants Jacob Evans and Brianna Paulson for all of their work, espe- cially in commissioning reviewers during the developmental stages of this book.

A very special thanks to Caroline Ayres, production supervisor extraordinaire, and Chris Schabow, production coordinator at The Left Coast Group, for all of their hard work shepherding this book through to publication. Our humble appreciation also goes to Kelly Murphy, art development editor, for turning our rudimentary stick figures into true pieces of art; to Kristin Piljay for obtaining the most vivid and unique photos available; to Marilyn Perry, whose design made the text, art, and pho- tos all came alive; and to Yvo Riezebos, whose efforts we must thank for the book’s beautiful cover.

Marketing takes energy, and that’s exactly what marketing manager Neena Bali and her energetic team seem to generate nonstop. Our thoughtful thanks to Brooke Suchomel for coordinating the focus groups, market research, and enlisting the class

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Reviewers Janet Anderson Utah State University

Sandra Baker University of Delaware

Gita Bangera Bellevue Community College

Lisa Blackman Tarrant County College Northwest

Jeanne Boone Palm Beach Community College

John Capeheart University of Houston - Downtown

Susan Chou American River College

Nicole Clark Indiana University of Pennsylvania

Susan Cooper Montana State University Great Falls College of Technology

Jessica Coppola Sacramento City College

Lynn Monahan Couch West Chester University of Pennsylvania

Wendy Cunningham California State University Sacramento

testers. The many instructors who reviewed and class-tested early versions of this book are listed on the following pages; we are grateful to all of them for helping in the development of Nutrition: From Science to You. The village also included loyal contributors who lent their expertise to specific chapters. They are: Tara Smith at East Carolina University for solidifying the nutrition and fitness chapter; Elizabeth Quintana at West Virginia University School of Medicine for penning two of the “lifecycle” chapters; and Jennifer Koslo for writing the older adults lifecycle chapter, as well as the hunger and food safety chapters. We also thank Julie Lyons for her work on the “Two Points of View” interviews.

Lastly, an endless thanks to our colleagues, friends, and especially our families. Joan would like to “thank my family, Adam, Brendan, and Craig for their love and support when I was working more than I should have been.” Kathy sends a special thanks to “my husband Rich and our children Heather, Wes, and Ryan for keeping me sane and grounded, and my Mom, Dad, and sister Vicki for their steadfast sup- port.” Stella would like to acknowledge “my husband, Gary Snyder, for his constant support; and our wonderful dogs, Asko and Cenna, for always reminding me to stop and smell the roses! And to my Mom and Dad, who both instilled in me a wonderful relationship with food, especially home grown and homemade food.”

Susan Gaumont Chandler-Gilbert Community College

Jill Golden Orange Coast College

Gloria Gonzalez Pensacola Junior College

Donna Handley University of Rhode Island

William Helferich University of Illinois, Urbana

Catherine Howard Texarkana College

Karen Israel Anne Arundel Community College

Seema Jejurikar Bellevue Community College

Jayanthi Kandiah Ball State University

Vicki Kloosterhouse Oakland Community College

Allen Knehans University of Oklahoma

Kathy Knight University of Mississippi

Jeannette Davidson Bradley University

Holly Dieken University of Texas

Johanna Donnenfield Maricopa Community College

Roberta Durschlag Boston University

Brenda Eissenstat Pennsylvania State University

Sheryl L. Fuller-Espie Cabrini College

Eugene Fenster Monroe Community College - Longview

Alyce D. Fly Indiana University

Sara Folta Tufts University

Betty Forbes West Virginia University

Sue Fredstrom Minnesota State University

Teresa Fung Simmons College

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Shui-Ming Kuo University at Buffalo

Robert D. Lee Central Michigan University

Sharon Lemons Tarrant County College Northwest

Darlene Levinson Oakland Community College

Rose Martin Iowa State University

Mary Martinez Central New Mexico Community College

George F. McNeil Fort Hays State University

Monica Meadows University of Texas

Kathleen Melanson University of Rhode Island

Mithia Mukutmoni Sierra College

Pat Munn Longview College

Megan Murphy Southwest Tennessee Community College

Class Testers Janet Anderson Utah State University

Jeanne Boone Palm Beach Community College

Jessica Coppola Sacramento City College

Robert Cullen Illinois State University

Gloria Gonzales Pensacola Junior College

Jill Goode-Englett University of Northern Alabama

Debra Head University of Central Arkansas

Lenka Humenikova-Shriver Oklahoma State University

Allen Knehans University of Oklahoma

Janet Levin Pensacola Junior College

Darlene Levinson Oakland Community College

Anna Miller DeAnza College

Vijaya Narayanan Florida International University - University Park

Anna Page Johnson County Community College

Nancy Parkinson Miami University, Ohio

Renee Romig Western Iowa Technical Community College

Janet Sass Northern Virginia Community College - Annandale

Susan Swadener California Polytechnic State University, San Luis Obispo

Janelle Walter Baylor University

Suzy Weems Baylor University

Jennifer Zimmerman Tallahassee Community College

Dan Neisner Walla Walla Community College

Corin Nishimura Leeward Community College

Anna Page Johnson County Community College

Jill Patterson Pennsylvania State University

Janet Peterson Linfield College

Gwendolyn Pla Howard University

Roseanne Poole Tallahassee Community College

Linda Pope Southwest Tennessee Community College

Elizabeth Quintana West Virginia University

Denise Russo Cabrillo College

Kevin Schalinske Iowa State University

Diana Spillman Miami University, Ohio

Sherry Stewart Navarro College

Leeann Sticker Northwestern State University

Susan Swadener California Polytechnic State University, San Luis Obispo

Janelle Walter Baylor University

Sandy Walz West Chester University of Pennsylvania

Daryl Wane Pasco-Hernando College

Garrison Wilkes University of Massachusetts at Boston

Jessie Yearwood El Centro College

Gloria Young Virginia State University

Maureen Zimmerman Mesa Community College

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1 What Is Nutrition? 2 2 Tools for Healthy Eating 38 3 Digestion, Absorption, and Transport 80 4 Carbohydrates 116 5 Fats, Oils, and Other Lipids 172 6 Proteins and Amino Acids 222 7 Alcohol 268 8 Your Body’s Metabolism 300 9 Fat-Soluble Vitamins 336 10 Water-Soluble Vitamins 380 11 Water 422 12 Major Minerals 452 13 Trace Minerals 488 14 Energy Balance and Body Composition 522 15 Weight Management and Disordered Eating 548 16 Nutrition and Fitness 592 17 Life Cycle Nutrition: Pregnancy Through Infancy 632 18 Life Cycle Nutrition: Toddlers Through Adolescence 680 19 Life Cycle Nutrition: Older Adults 708 20 Food Safety and Technology 740 21 Hunger at Home and Abroad 794 A Metabolism Pathways and Biochemical Structures A-3

B Nutrition and Physical Activity Recommendations for Canadians B-1

C The Traditional Mediterranean Diet C-1

D Calculations and Conversions D-1

E U.S. Exchange Lists for Meal Planning E-1

F Organizations and Resources F-1

Brief Contents

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1 What Is Nutrition? 2 What Drives Our Food Choices? 4

Taste and Enjoyment 4 Culture and Environment 5 Social Reasons and Trends 5 Weight Concerns, Body Image, and Health Benefits 6 Advertising 6 Time, Convenience, and Cost 6 Habits and Emotions 7

What Is Nutrition? 9

What Are Nutrients? 9 Most Nutrients Are Organic 10 Most Nutrients Are Essential 11 Some Nutrients Provide Energy 11

What Are the Primary Roles of the Individual Nutrients? 13

Carbohydrates Are the Primary Energy Source 14 Lipids Also Provide Energy 14 Proteins Provide the Building Blocks for Tissue

Synthesis 14 Vitamins and Minerals Play Vital Roles in Metabolism 15 Water Is Critical for Numerous Functions 15

What Is Credible Nutrition Research? 16 Sound Nutrition Research Begins with the Scientific

Method 18 Research Studies and Experiments Confirm

Hypotheses 19

What Is Nutritional Genomics? 21

What Is Nutrition Assessment and What Does It Involve? 22

Nutrition Assessment Includes Examining a Patient’s Health and Diet History 23

Anthropometric Data Is Used to Help Assess Nutritional Status 26

Conduct a Physical Examination 26 Collect Laboratory Data 26

How Do We Assess the Nutritional Status of a Population Group? 27

Conduct or Review National Surveys 27

What Is Healthy People 2010? 28

How Does the American Diet Stack Up? 29

The Quality of the American Diet 29

Rates of Overweight and Obesity in Americans 30

What’s the Best Dietary Strategy for Health? 30

The Best Way to Meet Nutrient Needs Is with a Well-Balanced Diet 30

Some Nutrient Needs Can Be Met with a Supplement 31

2 Tools for Healthy Eating 38 What Is Healthy Eating? 40

Healthy Eating Means Adequate Intake of Nutrients 40 Healthy Eating Involves Balance between Food

Groups 40 Healthy Eating Means Consuming a Variety of Foods 41 Healthy Eating Means Moderate Intake of All Foods 41 Healthy Eating Involves Nutrient-Dense Foods 42 Healthy Eating Involves Low-Energy-Dense Foods 43 Resources for Planning a Healthy Diet 46

What Are the Dietary Reference Intakes? 47 The DRIs Suggest an Intake Level for Each Nutrient 48 The DRIs Encompass Several Reference Values 48 The DRIs Can Be Used to Plan a Quality Diet 51

What Are the Dietary Guidelines for Americans? 52

What Is MyPyramid? 54 MyPyramid Emphasizes Key Concepts for Planning a

Healthy Diet 54 How to Use MyPyramid 55

What Information Is on the Food Label? 62 Food Labels Are Strictly Regulated by the FDA 62 The Nutrition Facts Panel Indicates Nutrient Values 63 The Daily Values Help Compare Packaged Foods 64 Label Claims Can Reveal Potential Health Benefits 65

What Is the Exchange System? 70

Contents

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3 Digestion, Absorption, and Transport 80 What Are Digestion, Absorption, and Transport? 82

What Are the Organs of the GI Tract and Why Are They Important? 83

Digestion Begins in the Mouth 84 The Stomach Stores, Mixes, and

Prepares Food for Digestion 85 Most Digestion Occurs in the Small Intestine 86 The Large Intestine Absorbs Water and Some

Nutrients 87 The Accessory Organs Provide Digestive Juices 89

How Is Food Propelled through the GI Tract? 89 Peristalsis Squeezes Food Forward 90 Segmentation Shifts Food along the Intestinal Wall 90

How Is Food Chemically Digested? 91 Enzymes Drive the Process of Digestion 91 Other Chemicals Are Also Essential for Digestion 94

How Are Digested Nutrients Absorbed? 96 Nutrients Are Absorbed through the Small Intestinal

Lining 96 Fluid Absorption Occurs in the Large Intestine 97

How Do Hormones Affect Digestion? 98

How Does the Nervous System Affect Digestion? 98

How Are Nutrients Transported Throughout the Body? 99

The Circulatory System Distributes Nutrients through Blood 99

The Lymphatic System Distributes Some Nutrients through the Lymph 100

What Are Some Common Digestive Disorders? 100

Esophageal Problems: Heartburn and GERD 101 Disorders of the Stomach 101 Gallbladder Disease 102 Disorders of the Intestines 102 More Serious Intestinal Disorders 105

4 Carbohydrates: Sugars, Starches, and Fiber 116 What Are Carbohydrates and Why Are They Important? 118

How Do We Classify Carbohydrates? 120 Monosaccharides Are Single Sugar Units 120

Disaccharides Consist of Two Sugar Units 121

The Polysaccharides Consist of Many Sugar Units 122

Oligosaccharides 125

How Do We Digest and Absorb Carbohydrates? 126 Digestion of Carbohydrates 126 Absorption of Carbohydrates 128

What Is Lactose Intolerance? 129

What Functions Do Carbohydrates Perform in the Body? 130

Carbohydrates Provide Energy and Maintain Blood Glucose Levels 130

Carbohydrates Spare Protein 130 Carbohydrates Prevent Ketosis 131

How Do We Maintain Blood Glucose Levels? 131 Insulin Regulates Glucose in the Blood 131 Glucagon Regulates Liver Glycogenolysis 132 Epinephrine, Norepinephrine, Cortisol, and Growth

Hormone Regulate Glucose Metabolism 132

What Are Glycemic Index and Glycemic Load? 133

Why Is Dietary Fiber So Important? 134 Fiber Helps Prevent Constipation and Diverticulosis 135 Fiber Helps Prevent Heart Disease, Diabetes, and

Cancer 135 Fiber Helps Prevent Obesity 136

What Is the Recommended Intake for Carbohydrates? 136

What Are the Best Food Sources of Carbohydrates? 137

Choose Whole Grains to Meet Starch and Fiber Needs 137

Low-fat and Fat-free Dairy Products Provide Some Simple Sugars 140

Fruits and Vegetables Provide Simple Sugars, Starch, and Fiber 140

Legumes, Nuts, and Seeds Are Excellent Sources of Starch and Fiber 141

Packaged Foods Can Be Good Sources of Carbohydrates 142

What Is Diabetes? 143 There Are Several Forms of Diabetes 144 Diabetes Can Result in Long-Term Damage 145 Control Is Key 146 Preventing Type 2 Diabetes 146 Polycystic Ovary Syndrome May Increase

Risk for Diabetes 147

What Is Hypoglycemia? 147

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What Is the Difference Between Natural and Added Sugars? 149

Foods with Natural Sugars Generally Provide More Nutrients for Fewer Kilocalories 149

Added Sugars Are Used during Food Processing 150 Finding the Added Sugars in Foods 150

Health Effects of Too Much Sugar: Fact vs Fiction 154

Fact: Sugar Can Cause Dental Caries 154 Fiction: Sugar Causes Diabetes Mellitus 154 Fact: Too Much Sugar Can Hinder Weight Loss 154 Fiction: Sugar Is Addictive 155 Fiction: Sugar Causes Hyperactivity in Children 155

What Are Sugar Substitutes? 155 Polyols Are Sugar Alcohols 157 Saccharin Is the Oldest Sugar Substitute 157 Aspartame Is Derived from Amino Acids 159 Acesulfame-K Contains Potassium 160 Sucralose Is Made from Sucrose 160 Neotame Is Also Derived from Amino Acids 160 VISUAL SUMMARY TABLE Carbohydrates 162

5 Fats, Oils, and Other Lipids 172 What Are Lipids and Why Are They Important? 174

What Are Fatty Acids? 175 Fatty Acids Vary in Length 175 Fatty Acids Vary in Saturation 175 Fatty Acids Differ in the Location of the Double

Bond 177 Fatty Acids Vary in Their Shape 177 Fatty Acids and Rancidity 178

What Are Triglycerides? 179

What Are Phospholipids? 181

What Are Sterols? 183

What Happens to the Lipids You Eat? 183 Very Little Fat Digestion Occurs in the Mouth or the

Stomach 184 Most Fat Is Digested and Absorbed in the Small

Intestine 185 Chylomicrons Facilitate Lipid Absorption 186 Lipoproteins Transport Fat Through the Lymph

and Blood 187

How Does the Body Use Fat and Cholesterol? 188 Fat Is Used as Energy 189 Fat Helps Absorb Lipid Compounds 190 Fat Helps Insulate the Body and Protect Vital Organs 190 Essential Fatty Acids Manufacture Eicosanoids and

Maintain Cell Membranes 190

Cholesterol Is Used to Make Bile, Hormones, and Vitamin D 191

How Much Fat Do We Need Each Day? 191 Percentage of Daily Kilocalories from Fat 192 Specific Recommendations for Essential Fatty Acids 193 Dietary Cholesterol Is Not Essential 196

What Are the Best Food Sources of Fat? 196

What Foods Contain Trans Fat and Cholesterol? 198 Trans Fats Are Found in Many Foods 199 Trans Fats Must Be Listed on Food Labels 199 Replacing Trans Fats in Foods 199 Food Sources of Cholesterol and Plant Sterols 200

What Are Fat Substitutes? 200 Fat Substitutes Can Be Carbohydrate, Protein, or Fat

Based 201 Consuming Reduced-Fat Products May Not Reduce Total

Kilocalorie Intake 202

What Is Heart Disease and What Factors Increase Risk? 203

Heart Disease Begins with Atherosclerosis 203 Risk Factors for Heart Disease 204

How Can High Blood Cholesterol Levels Be Lowered? 206

Consume Less Saturated and Trans Fat and Moderate Cholesterol Intake 206

Eat More Fish and Plant Foods 208

Consume Antioxidants and Phytochemicals 208

Get Plenty of Exercise and Manage Your Weight 210

A Word About the Protective Effects of Red Wine and Alcohol 211

VISUAL SUMMARY TABLE

Lipids 212

6 Proteins and Amino Acids 222 What Are Proteins? 224

Proteins Differ Structurally from Carbohydrates and Lipids 224

The Building Blocks of Proteins Are Amino Acids 225 The Organization and Shape of Proteins Affect Their

Function 227 Denaturation of Proteins Changes Their Shape 227

What Happens to the Protein You Eat? 229 Protein Digestion Begins in the Stomach 229 Digestion Continues in the Small Intestine 230 Amino Acids Are Absorbed in the Small Intestine 230 Amino Acids Are Metabolized in the Liver 230

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How Does the Body Use Protein? 234 Proteins Provide Structural Support and Enable

Movement 234 Proteins Act as Catalysts 234 Proteins Act as Chemical Messengers 234 Proteins Regulate Fluid Balance 235 Proteins Help Regulate Acid-Base Balance 235 Proteins Transport Substances Throughout the Body 235 Proteins Contribute to a Healthy Immune System 236 Proteins Can Provide Energy 236 Protein Improves Satiety and Appetite Control 237

How Much Protein Do You Need? 238 Healthy Adults Should Be in Nitrogen Balance 238 Not All Protein Is Created Equal 239 Complementary and Complete Proteins Reflect

Quality 241 You Can Determine Your Own Protein Needs 242

What Are the Best Food Sources of Protein? 244

Eggs, Meat, Soy, and Dairy Contain Significant Amounts of Protein 244

You Don’t Need Protein Supplements 245

What Happens if You Eat Too Much or Too Little Protein? 248

Eating Too Much Protein Can Mean Too Much Fat and Weaker Bones 248

Eating Too Little Protein Can Lead to Protein-Energy Malnutrition 250

What Is a Vegetarian Diet? 251 Vegetarian Diets Carry Potential Benefits and Risks 252 Planning a Healthy Vegetarian Diet 253 VISUAL SUMMARY TABLE Protein 260

7 Alcohol 268 What Is Alcohol and How Is It Made? 270

Why Do People Drink Alcohol? 272

What Happens to Alcohol in the Body? 272 Alcohol Is Absorbed in the Stomach and Small

Intestine 274 The Liver Metabolizes Alcohol 276 Alcohol Circulates in the Blood 277 Alcohol Affects the Brain 277

What Is Moderate Drinking? 279

How Can Alcohol Be Harmful? 280 Overconsumption of Alcohol Can Have Numerous

Short-Term Consequences 280 Chronic Alcohol Abuse May Lead to Serious Health

Consequences 282

What Are Alcohol Abuse and Alcoholism? 291 Binge Drinking, Drinking and Driving, and Underage

Drinking Are Forms of Alcohol Abuse 291 Alcoholism Is a Disease 292

8 Your Body’s Metabolism 300 What Is Metabolism? 302

Metabolism Takes Place Within Cells 303 The Liver Plays a Central Role in Metabolism 303 Metabolism Follows Individual Metabolic Pathways 304 Enzymes and Hormones Regulate Metabolism 305

How Does the Body Fuel Metabolism? 308 The Importance of Adenosine Triphosphate 308 Creating ATP from ADP and Creatine Phosphate 308

How Do Carbohydrates Provide Energy? 310 Step 1: Glycolysis—From Glucose to Pyruvate 310 Step 2: The Intermediate Reaction—Pyruvate to

Acetyl CoA 310 Pyruvate to Lactate 312

How Does Fat Provide Energy? 313 Triglycerides Are Broken Down into Fatty Acids and

Glycerol 313 The Relationship of Triglycerides to Glucose 315

How Does Protein Provide Energy? 315 Amino Acids to Acetyl CoA 315 Amino Acids to Glucose 316

Where Do the Macronutrients Come Together? 317 Step 3: The Tricarboxylic Acid (TCA) Cycle 316 The TCA Cycle Provides Precursors for

Transamination 318 Step 4: The Electron Transport Chain 318

What Happens if You Eat Too Much? 321 Carbohydrate Is Stored as Glycogen 322 Fatty Acid Synthesis 322

What Happens if You Don’t Eat Enough? 323 Ketogenesis Generates Energy during Periods of

Fasting 323

How Does the Body Metabolize Alcohol? 325 The Enzymes That Metabolize Ethanol 325 Excess Alcohol Is Stored as Fat 326

What Are Inborn Errors of Metabolism? 328

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9 Fat-Soluble Vitamins 336 What Are Vitamins? 338

History of Vitamins 338 The Criteria for Vitamins 339 All Vitamins Are Organic, but Differ in

Structure and Function 339 Vitamins Differ in Absorption and

Storage 340 Vitamins Differ

in Bioavailability 341 Vitamins Can Be Destroyed during

Cooking or Storage 341 Overconsumption of Some Vitamins

Can Be Toxic 342 Provitamins Can Be Converted to

Vitamins by the Body 342

What Are Antioxidants? 343

What’s the Best Source of Vitamins? 350

What Are the Fat-Soluble Vitamins? 354

VISUAL SUMMARY TABLE Vitamin A 356 VISUAL SUMMARY TABLE Vitamin D 362 VISUAL SUMMARY TABLE Vitamin E 368 VISUAL SUMMARY TABLE Vitamin K 370

10 Water-Soluble Vitamins 380 What Are Water-Soluble Vitamins? 382

What Are the Primary Functions of Water-Soluble Vitamins? 383

The B Vitamins Act as Coenzymes in Many Metabolic Functions 384

Water-Soluble Vitamins in Noncoenzymatic Roles 384 VISUAL SUMMARY TABLE Thiamin (B1) 388 VISUAL SUMMARY TABLE Riboflavin (B2) 390 VISUAL SUMMARY TABLE Niacin (B3) 393 VISUAL SUMMARY TABLE Pantothenic Acid 396 VISUAL SUMMARY TABLE Biotin 397 VISUAL SUMMARY TABLE Vitamin B6 400 VISUAL SUMMARY TABLE Folate 402

Other Vitamin-Like Compounds 405 Choline Helps Protect the Liver 405 Carnitine, Lipoic Acid, and Inositol Are Vitamin-Like

Substances 405 VISUAL SUMMARY TABLE Vitamin B12 408 VISUAL SUMMARY TABLE Vitamin C 411

11 Water 422 Why Is Water So Important? 424

What Are the Functions of Water in the Body? 425 Water Is the Universal Solvent and Transport Medium 425 Water Helps Maintain Body Temperature 426 Water Is a Lubricant and a Protective Cushion, and

Provides Structure to Muscle Cells 426 Water Participates in Hydrolysis and Condensation

Reactions 427

How Is Water Balance Maintained? 428 Sources of Body Water Include Beverages and Food 428 Water Is Excreted through the Kidneys, Large Intestine,

Lungs, and Skin 429 Water Is Balanced between Fluid Compartments 429 Electrolytes Participate in Fluid Balance 429

How Do Water and Sodium Affect Blood Pressure? 432

ADH Helps Stimulate Fluid Intake and Reduce Urine Output 432

Renin Helps the Body Reabsorb Water and Salts 432 Aldosterone Helps Stimulate Sodium Reabsorption 432

How Much Water Do You Need and What Are the Best Sources? 434

Do Diuretics Like Caffeine and Alcohol Affect Water Balance? 438

Caffeine Does Not Cause Significant Loss of Body Water 438

Alcohol Can Be Dehydrating 438 Diuretic Medications Can Help Treat Hypertension 438

What Are the Effects of Too Much or Too Little Water? 439

Consuming Too Much Water Can Cause Hyponatremia 439

Consuming Too Little Water Is a Common Problem 439 Monitor Water Intake to Avoid Overhydration and

Dehydration 442 VISUAL SUMMARY TABLE Water 444

12 Major Minerals: What Are They and Why Do You Need Them 452 What Are Minerals? 454

Minerals Are Inorganic Elements Needed by the Body 454

Minerals Vary in Their Bioavailability 455 Minerals Serve Numerous Functions 456 Minerals Can Be Toxic 457 VISUAL SUMMARY TABLE Sodium and Chloride 460 VISUAL SUMMARY TABLE Potassium 468

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VISUAL SUMMARY TABLE Calcium 470 VISUAL SUMMARY TABLE Phosphorus 478 VISUAL SUMMARY TABLE Magnesium 480 VISUAL SUMMARY TABLE Sulfate 481

13 Trace Minerals 488 What Are Trace Minerals and Why Do You Need Them? 490

VISUAL SUMMARY TABLE Iron 492 VISUAL SUMMARY TABLE Copper 498 VISUAL SUMMARY TABLE Zinc 500 VISUAL SUMMARY TABLE Selenium 504 VISUAL SUMMARY TABLE Fluoride? 506 VISUAL SUMMARY TABLE Chromium 508 VISUAL SUMMARY TABLE Iodine 510 VISUAL SUMMARY TABLE Molybdenum 511 VISUAL SUMMARY TABLE Manganese 512

Other Minerals: Arsenic, Boron, Nickel, Silicon, and Vanadium 513

14 Energy Balance and Body Composition 522 What Is Energy Balance and Why Is It Important? 524

An Energy Imbalance Results in Weight Gain or Loss 524

Food and Beverages Provide Energy In 525 Body Processes and Physical Activity Result in

Energy Out 526

How Do We Measure Energy Expenditure? 530 Direct and Indirect Calorimetry 530 Simple Calculations to Estimate Energy

Expenditure 530

What Is Body Composition? 532 Most Body Fat Is Stored in Adipose Tissue 532 Body Fat Distribution Affects Health 533 Body Fat Levels for Optimal Health 533

How Do We Estimate a Healthy Body Weight? 534 Height and Weight Tables Can Provide a Healthy

Weight Range 534 Body Mass Index Is a Useful Indicator of Healthy Weight for

Most People 535

How Do We Assess Body Composition? 537 Several Methods Can Be Used to Determine Percent Body

Fat 537 Waist Circumference Will Indicate Abdominal Fat 539

What Are the Health Risks Associated with Body Weight and Body Composition? 539

Being Underweight Increases Health Risks 540 Being Overweight Increases Health Risks 540

15 Weight Management and Disordered Eating 548 What Is the Status of Obesity in America? 550

What Is Weight Management and Why Is It Important? 550

How Do Fat Cells Form and Expand? 552

How Is Food Intake Regulated? 554 Hunger and Satiety Affect the Desire to Eat and Stop

Eating 554 Appetite Often Triggers Eating for Unnecessary

Reasons 554 The Brain and Hormones Control Feeding 554

How Do Genetics and Environment Influence Obesity and Weight Management? 556

Genetics Can Make the Body More Susceptible to Weight Gain or Weight Loss 556

Environmental Factors Can Increase Appetite and Decrease Physical Activity 557

How Can You Lose Weight Healthfully? 559 Strive for a Reasonable Rate of Weight Loss 564 Remember that Kilocalories Count 564 Eat More Vegetables, Fruit, and Fiber 565 Add Some Protein and Fat to Meals 566 Use MyPyramid as a Weight-Loss Guide 567 Increase Physical Activity to Lose Weight 568 Break Bad Habits 569

How Can Weight Loss Be Maintained? 572

What Is the Healthiest Way to Gain Weight? 576

What Is Disordered Eating and What Are the Warning Signs? 577

Anorexia Nervosa Results from Severe Kilocalorie Restriction 579

Bulimia Nervosa Involves Cycles of Binge Eating and Purging 579

Binge Eating Disorder Involves Compulsive Overeating 580

Night Eating Syndrome Is a Type of Eating, Sleeping, and Mood Disorder 580

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There Are Some Common Signs of Disordered Eating 581

How Are Eating Disorders Treated? 583

16 Nutrition and Fitness 592 What Is Physical Fitness and Why Is It Important? 594

There Are Five Basic Components of Physical Fitness 594

Physical Fitness Provides Numerous Health Benefits 595

What Does a Successful Physical Fitness Program Look Like? 597

Cardiorespiratory Exercise Can Improve Cardiorespiratory Endurance and Body Composition 597

Strength Training Can Improve Muscle Strength, Muscle Endurance, and Body Composition 598

Stretching Can Improve Flexibility 598 The FITT Principle Can Be Used to Design a Fitness

Program 598 The Progressive Overload Principle Can Help Improve

Fitness Over Time 600

How Are Carbohydrate, Fat, and Protein Used During Exercise? 601

Carbohydrate Is the Primary Energy Source During High-Intensity Exercise 602

Fat Is the Primary Energy Source During Low- to Moderate- Intensity Exercise 605

Protein Is Primarily Needed to Build and Repair Muscle 609

Timing of Meals Affects Fitness and Athletic Performance 610

What Vitamins and Minerals Are Important for Fitness? 613

Antioxidants Can Help Protect Cells from Damage Caused by Exercise 613

Some Minerals Can Be of Concern in Highly Active People 613

Vitamin and Mineral Supplements Are Generally Not Necessary 615

How Does Fluid Intake Affect Fitness? 615 Fluid and Electrolyte Balance and Body Temperature

Are Affected by Exercise 616 Fluids Are Needed Before, During, and After

Exercise 616 Some Beverages Are Better than Others 617 Consuming Too Little or Too Much Fluid Can Be

Harmful 618

Can Dietary Supplements Contribute to Fitness? 620

Dietary Supplements and Ergogenic Aids May Improve Performance, but Can Have Side Effects 621

Sports Bars and Shakes May Provide Benefits 624

17 Life Cycle Nutrition: Pregnancy Through Infancy 632 Why Is Good Nutrition Essential for a Healthy Pregnancy? 634

What Are the Stages of Pregnancy and Why Is the Placenta Important? 634

Critical Periods Impact Fetal Development 636

What Nutrients and Behaviors Are Most Important for a Healthy Pregnancy? 638

Before Conception, Fathers-to-Be Need to Eat Well for Healthy Sperm 638

Before Conception, Mothers Need to Adopt a Healthy Lifestyle 638

In the First Trimester: Women Need to Eat When Food May Not Be Appetizing, Avoid Botanicals, and Practice Food Safety 642

In the Second Trimester: Healthy Weight Gain and Kilocalorie Intake Are Important 648

In the Third Trimester: Eating Frequent Small Meals and a High-Fiber Diet Can Help with Heartburn and Constipation 651

What Special Concerns Might Younger or Older Mothers-to- Be Face? 651

What Is Food Assistance? 653

What Is Breast-Feeding and Why Is It Beneficial? 653

Breast-Feeding Provides Physical, Emotional, and Financial Benefits for Mothers 654

Breast-Feeding Provides Nutritional and Health Benefits for Infants 655

What Are the Nutrient Needs and Best Lifestyle Habits for a Breast-Feeding Mother? 658

When Is Formula a Healthy Alternative to Breast Milk? 659

Some Woman May Not Be Able to Breast-Feed 659 Formula Can Be a Healthy Alternative to

Breast-Feeding 660

What Are the Nutrient Needs of an Infant and Why Are They So High? 661

Infants Grow at an Accelerated Rate 661

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Infants Have Specific Kilocalorie, Iron, and Other Nutrient Needs 662

When Are Solid Foods Safe? 664 Solid Foods May Be Introduced Once Certain Milestones

Are Met 664 Solid Foods Should Be Introduced Gradually 664 Some Foods Are Dangerous and Should Be

Avoided 665

18 Life Cycle Nutrition: Toddlers Through Adolescence 680 What Are the Nutritional Needs and Issues for Toddlers and Preschoolers? 682

Young Children Need to Eat Frequent, Small Meals and Nutrient-Dense Foods 683

Young Children Need Adequate Carbohydrate, Protein, and Fat 684

Young Children Need to Consume Enough Calcium and Iron 685

Young Children Need to Consume Enough Vitamin D 685

Young Children Need Nutrient-Dense Beverages 686 Picky Eating and “Food Jags” Are Common in Small

Children 686 Young Children and Vegetarianism 687

What Are the Nutritional Needs and Issues of School-Aged Children? 688

School-Aged Children Are Experiencing Higher Rates of Obesity 688

Increased Rates of Childhood Obesity May Lead to Increased Rates of Type 2 Diabetes 692

School-Aged Children Should Practice Good Dental Hygiene 693

MyPyramid For Kids Can Help Guide Food Choices 693

What Are the Nutritional Needs and Issues of Adolescents? 697

Adolescents Need Calcium and Iron for Growth and Development 698

Adolescents Are Sometimes at Risk for Disordered Eating 699

19 Life Cycle Nutrition: Older Adults 708 What Is Aging? 710

What Are the Demographics of Aging in America, and Why Are Americans Living Longer? 711

America’s Population Is Getting Older 711

Improved Health Care and Disease Prevention Are Lengthening the Life Span 712

Smoking, Poor Diet, and Physical Inactivity Still Contribute to Leading Causes of Death 712

What Changes Occur as Part of the Aging Process? 713

Physiological Factors Affect Aging 713

What Are the Nutrient Needs of Older Adults? 718 Older Adults Need Fewer Kilocalories, Not Less

Nutrition 719 Older Adults Need Adequate Protein 721 Older Adults Should Consume More Complex

Carbohydrate 721 Older Adults Should Continue to Moderate Fat

Intake 721 Older Adults Need to Watch Intake of Vitamins A, D,

and B12 721 Older Adults Need to Be Sure to Get Enough Iron, Zinc,

and Calcium 722 Older Adults Need to Stay Hydrated 723

What Additional Challenges May Older Adults Face? 727

Eating Right for Good Health and Disease Prevention 727

Staying Physically Active in Spite of Physical and Mental Challenges 729

Living with Alzheimer’s Disease 729 Economic Conditions Can Affect Nutritional Health 730 Psychological and Emotional Conditions Can Affect

Nutritional Health 731

20 Food Safety and Technology 740 What Is Food Safety and Why Is It Important? 742

What Causes Foodborne Illness? 742 Foodborne Illnesses Are Often Caused by

Pathogens 743 Some People Are at Higher Risk for Foodborne

Illness 749

What Are the Best Strategies to Prevent Foodborne Illness? 751

Clean Hands and Produce 752 Combat Cross-Contamination 753 Cook Foods Thoroughly 753 Chill Foods at a Low Enough Temperature 754

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What Mechanisms Are in Place to Protect the Food Supply? 758

Several Government Agencies and Programs Protect the Food Supply 758

Food Manufacturers Use Preservation Techniques to Destroy Contaminants 760

Product Dating Can Help Determine Peak Quality 763 The Safety of the Water Supply Is Regulated 764

What Are Food Additives and How Are They Used? 764

Preservatives Prevent Spoilage and Increase Shelf Life 764

Some Additives Enhance Texture and Consistency 765 Some Additives Improve Nutrient Content 765 Color Enhancers Improve the Visual Appeal of

Foods 765 MSG Is a Common Flavor Enhancer 766 Food Additives Are Closely Regulated by the FDA 767 Some Chemicals Are Used Intentionally to Enhance the

Food Supply 767 Some Food Additives Are Unintentional 768

What Are Toxins and Chemical Agents? 769 Some Toxins Occur Naturally 769 Chemicals Are Sometimes Due to Pollution 771 Pesticides Are Widely Used in Agriculture 772 The Risks of Pesticides 773 EPA, USDA, and FDA Regulate Pesticides 773 Alternatives to Pesticides 775 Minimizing Pesticides in the Diet 776

What Are Organic Foods and How Are They Labeled? 777

What Is Biotechnology and Why Is It Used? 780 Genetic Engineering Is the Latest Form of

Biotechnology 780 Genetic Engineering Can Produce More and Better

Foods 781 Some Consumers Have Concerns about GE Foods 782

GE Foods Are Highly Regulated in the United States 782

What Is Bioterrorism and How Can You Protect Yourself? 784

21 Hunger at Home and Abroad 794 What Is Hunger and How Prevalent Is It? 796

What Causes Hunger? 799 Domestic Food Insecurity Is Caused by Poverty, Illness, or

Lack of Opportunity 799

Disease, Disability, or Illness 802 Global Hunger Is Often Caused by Inequality, Political

Conflict, Crop Failure, or Overpopulation 803

What Are the Effects of Hunger? 806 Some Populations Are at Higher Risk 806 Impaired Growth and Development 808 Impaired Immunity and Disease 809 Increased Rates of Infant and Child Mortality 810

How Can We Eradicate Hunger? 811 Biotechnology, Better Land Management, Water Usage,

and Proper Sanitation 812 Fortification of Foods Can Ensure Adequate Intake of Some

Nutrients 814 Education Is Key 814

Appendices Appendix A Metabolism Pathways and Biochemical Structures A-3

Appendix B Nutrition and Physical Activity Recommendations for Canadians B-1

Appendix C The Traditional Mediterranean Diet C-1

Appendix D Calculations and Conversions D-1

Appendix E U.S. Exchange Lists for Meal Planning E-1

Appendix F Organizations and Resources F-1

Glossary G-1

Index I-1

Credits CR-1

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Feature Boxes Evaluating Media Headlines with a Critical Eye 17

Obtaining Nutrition Advice: Who Are the Experts? Who Are the Quacks? 24

Portion Distortion 44

Time of Day and Eating: Does It Impact Your Health? 60

Celiac Disease: An Issue of Absorption 106

Grains, Glorious Whole Grains 138

Is High-Fructose Corn Syrup Causing the Obesity Epidemic? 152

Facts and Myths About Fats, Oils, and Cholesterol 194

Mercury and Fish 209

Protein Bars: Are They a Health Bargain? 246

The Joy of Soy 256

Alcohol and Advertising 273

Does Moderate Alcohol Consumption Provide Health Benefits? 288

Can Energy Drinks Alter Your Metabolism? 306

Nutrition and Cancer Prevention 346

Fortified Foods and Supplements: Are They Necessary? 352

B Vitamins for Heart Health 385

Preventing and Treating the Common Cold 406

Tap Water or Bottled Water: Is Bottled Better? 436

Enhanced Water: What Are We Really Drinking? 441

Controlling Hypertension 464

Building a Stronger Bone 474

Preventing Iron-Deficiency Anemia 497

Fad Diets Are the Latest Fad 560

Extreme Measures for Extreme Obesity 573

Carbohydrate Loading 606

The Truth About the Fat-Burning Zone 608

What Is the Female Athlete Triad? 622

Breast-Feeding at Work Can Work 656

A Taste Could Be Dangerous: Food Allergies 666

Does Sugar Cause ADHD? 690

Drug, Food, and Drug-Herb Interactions 716

Does Kilocalorie Restriction Extend Life? 720

The Lowdown on Listeria 750

Mad Cow Disease 774

Farmer’s Markets 778

A Look at the Numbers: The State of Hunger Around the World 799

Food Assistance Programs in the United States 812

Hunger Among Us (and How You Can Help!) 815

Boxes

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Self-Assessments How Healthy Is Your Family Tree? 21

Are You at Risk for Type 2 Diabetes? 145

How Much Fat Is in Your Diet? 193

Red Flags for Alcohol Abuse 293

Are You Getting Enough Fat-Soluble Vitamins in Your Diet? 355

Are You Getting Enough Water-Soluble Vitamins in Your Diet? 384

Estimating Your Calcium Intake 473

Does Your Environment Impact Your Energy Balance? 557

Are You at Risk for an Eating Disorder? 582

Are You Meeting Your Fitness Recommendations and Eating for Exercise? 625

Are You Nutritionally Ready for a Healthy Pregnancy? 642

Are You at Nutritional Risk? 731

How Do Your Food Safety Habits Stack Up? 757

Are You at Risk for Hunger? 800

Two Points of View Food Advertisements: Help or Hindrance? 32

Does Your Diet Have Proportionality? 41

Are Supersized Portions a Super Problem for Americans? 74

Probiotics: Do They Improve Digestion? 110

Can Soft Drinks Be Part of a Healthy Diet? 165

Farmed Salmon vs Wild Salmon: Is One Healthier Than the Other? 216

Do You Need to Eat Meat to Compete? 263

Should the Drinking Age Be Lowered? 294

Can Genetics Be Used to Improve Nutritional Health? 330

Can Some Sun Exposure Be a Good Thing? 373

Is Folic Acid Fortification Good for Everyone? 415

How Much Water Do We Need? 446

Shaking the Habit 482

Does Drinking Unfluoridated Water Affect Dental Health? 515

Is Obesity a Disease? 542

Weighing the Pros and Cons of Gastric Bypass Surgery 584

Are Personal Trainers Reliable Sources of Credible Nutrition Information? 626

Choosing Among Baby Foods 670

Are Schools Out to Lunch? 701

Protein: DRI Recommendations for Older Adults 734

Can Organic Go Large Scale? 786

Why Does Hunger Exist in the United States? 817

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I am nothing without my ABCs.

Thanks.

—Joan Salge Blake

I dedicate this book to my family

for their love and support that sustained me through

the development of this book.

And to my students, both present and past,

for whom this book was written.

—Kathy D. Munoz

I would like to dedicate this book to

my Mom, Felicetta Volpe (in memory)

and my Dad, Antonio Volpe.

—Stella Lucia Volpe

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What Is Nutrition?

1

1. Food choices are driven primarily by flavor. T/F

2. Cancer is the leading cause of death in the United States. T/F

3. Eliminating all fat from the diet will improve health. T/F

4. Alcohol is a nutrient. T/F

5. The energy in foods is measured in kilocalories. T/F

6. Protein contains more energy per gram than fat. T/F

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? 7. The most effective method of nutritional assessment is to ask a client to write down what he’s eaten in the last 24 hours. T/F

8. You can get good nutrition advice from anyone who calls himself a nutritionist. T/F

9. The number of obese Americans is lower today than it was five years ago. T/F

10. As long as you take a vitamin pill, you don’t have to worry about eating healthy food. T/F

See page 36 for answers.

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4 Chapter 1 . What Is Nutrition?

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Chapter Objectives After reading this chapter, you will be able to:

1. Discuss the factors that influence food choice.

2. Define the term nutrition.

3. Describe how nutrition affects health.

4. Name and explain the six classifi- cations of nutrients found in food and in the body.

5. Compare and contrast organic and inorganic nutrients.

6. Differentiate between the three energy nutrients.

7. Calculate the kilocalorie content of a food based on the grams of carbohydrate, protein, and lipids.

8. Discuss how to assess the nutri- ent status of individuals and pop- ulation groups.

9. Identify sources of accurate nutri- tion information.

10. Discuss the current nutritional state of the American diet.

Would you be surprised to learn that Elizabeth did not do very well on her exam? Do you, like Elizabeth, sometimes eat snacks or other foods because you’re stressed, rather than hungry? What other factors influence your food choices?

In addition to exploring the factors that can affect food choice, this chapter will introduce you to the study of nutrition and why it is so important to your health. By the end of the chapter, you’ll be able to identify sources of credible nutrition information. Let’s start with the basic concepts of why you choose the foods you eat.

I t’s the night before her final biology exam, and Elizabeth, a junior, is in the midst of a down-to-the-wire cram ses-

sion. She hasn’t opened her textbook for weeks, so she is in high-stress mode. Elizabeth pours herself a tall glass of caf- feinated cola, opens up a family-size bag of potato chips, and nervously plows through the bag and the book. She snacks and studies until the early hours of the morning, and after a jittery 3 hours of sleep, Elizabeth heads to her 8 a.m. exam feeling tired, groggy, and still un- comfortably stuffed from her potato chip- and-soda cram session.

What Drives Our Food Choices? During the course of the day, we make over 200 decisions about food, from when to eat, how much to eat, and what to eat, to how the food is prepared, and even what plate to use.1 Have you ever considered what drives your food choices? Or are you on autopilot as you stand in line at the sub shop and squint at yet another menu board? What you choose to eat is both personal and complex and not solely driven by the need for sustenance. A multitude of interrelated factors affect your food choices, be- ginning with your personal preferences.

Taste and Enjoyment Research confirms that when it comes to making food choices, taste is the most im- portant consideration.2 This shouldn’t be too much of a surprise, considering there are more than 10,000 taste buds in the mouth, mostly on the tongue. Most people prefer the taste of salty or sweet foods but the degree to which we enjoy these foods varies, partly because of genetics.3 Our enjoyment of sweet foods also changes as we age; infants and children prefer extremely sweet flavors, while adults tend to enjoy more subtle sweet flavors.4 Breast-fed babies whose mothers eat a wide range of foods are more likely to embrace new foods as adults, and formula-fed infants re- main more tolerant of bitter and sour tastes at age 4 or 5.5

Our taste for fat may also be genetically linked, although a gene has not been found that supports this theory.6 When fat is combined with sugar, such as in a sugar-laden doughnut, our taste for that food is even stronger.7

Texture also affects our likelihood of enjoying foods. We enjoy a flaky pie crust but dislike one that is tough; we prefer crunchy apples to mealy ones, and creamy rather than lumpy soups. Almost 30 percent of adults dislike slippery foods, such as oysters and okra.8 Researchers have suggested that these preferences for sweetness, high fat, and specific textures may have begun early in life and this makes them re- sistant to change.9

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What Drives Our Food Choices? 5

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Culture and Environment Enjoying food is not just a physiological sensation. Other fac- tors, such as our culture and the environment, also play a role in which foods we enjoy eating.10 What you choose to put on your plate is often influenced by your culture. If you were a student in Mexico, you may regularly enjoy corn tortillas and tamales, as corn is a staple of Mexican cuisines. In India, meals commonly include lentils and other legumes with rice and vegetables, whereas Native Americans often enjoy stews of mutton (sheep), corn, vegetables, and berries. In China, rice likely would be front and center on your plate.

A culture’s cuisine is greatly influenced by the environment in which its people live. Foods that are available and accessible are more likely to be regularly consumed than foods that are scarce. For example, individuals who live near coastal waters are much more likely to consume large amounts of fresh seafood in their diets than those who live in landlocked areas.

Our food environment—the variety of food choices available, the size and shape of plates and glassware, the packaging of foods, and the types and amounts of food visible—also has a strong influence on what and how much we consume. We eat more food when the serving plates are larger, or drink less when beverages are served in taller glassware. Environmental cues also affect eating patterns. You are more likely to linger over a meal when the light is dimmed, or quickly finish your meal when others at the table stop eating.11

Social Reasons and Trends Eating is an important way to bond with others. For example, the social interaction between family and friends at holiday meals, such as Thanksgiving, is one reason a person is likely to eat more on Thanksgiving than on any other Thursday of the year. Eating dinner with others has been shown to increase the size of the meal by over 40 percent, and the more people present, the more you’ll eat.12 Choosing to eat a quick meal in the campus cafeteria may not be the best choice for healthy food op- tions, but it will allow you to socialize with classmates.

For many people, activities such as watching a football game with fellow fans or going to a movie with friends often involve particular foods. More pizzas are sold on Super Bowl Sunday than any other day of the year.13 Movie theater owners bank on their patrons buying popcorn, candy, and beverages at the concession stand before heading in to watch the film, and moviegoers are more likely to buy these snacks if they’re with a group of friends.14

Food choices are also affected by popular trends. For instance, home cooks in the 1950s bought bags of “newfangled” frozen vegetables in order to provide healthy meals in less time. A few decades later, vegeta- bles went upscale and consumers bought them as part of ready-to-heat stir-fry mixes. Today, shoppers pay a premium for bags of fresh veggies, like carrots, that have been prewashed and peeled, sliced, or diced, and they pay even more of a premium if the food is labeled “organic.” In 2005 alone, Americans spent more than $51 billion on organic or natu- ral foods.15 Consumers also ate more plant-based products, especially from locally grown farmer’s markets, and ate more foods with added benefits, such as eggs with more omega-3 fatty acids or calcium-fortified orange juice.16

Environmental factors including lighting at a meal, the size of a package, and the shape of a glass can influence the type and amount of food you eat.

One in four Americans is of Hispanic, Native American, Asian, or African descent. Cultural food preferences often influence food choices.

Eating junk food while watching sports sometimes seems like an American way of life.

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Weight Concerns, Body Image, and Health Benefits While the French take pleasure in cheese, bread, and high-fat desserts, Americans worry about fried eggs causing heart disease and butter-laden pastries leading to obesity. Hence, individuals may choose certain foods because they perceive them as being healthy, or avoid other foods that are associated with weight gain or loss. Your percep- tion of foods can be influenced by your current state of health. For example, if you are overweight, you are more likely to be aware of the kilocalorie content of foods and avoid foods that are high in fat and sugar.17 This can have a positive effect on health as long as body image concerns don’t become extreme and/or cause disordered eating patterns.

The more aware you are of the effects of food choices on health, the more likely you will make an effort to improve your eating habits.18 The fact that Americans are eating less saturated and trans fats is directly related to the perception that these foods damage health. The net effect of this has been positive, as more people have re- duced their consumption of red meat, packaged snacks, and processed foods, and in- creased their intake of whole grains and whole fruits and vegetables.19

Americans have also been consuming functional foods to improve their health since the late 1920s, when iodine was first added to salt. Today’s functional foods include whole foods such as oatmeal, genetically modified foods that are de- veloped to have a higher nutrient content, and foods that have been fortified with phytochemicals or added nutrients, such as calcium-fortified orange juice. These foods look, smell, and taste the same as regular foods but have added health bene- fits beyond their nutritional content. Although functional foods can be beneficial, consumers should not rely on them to replace other nutritious whole foods in their diet.

Advertising Manufacturers spend $10 billion to $15 billion annually on food advertising, with over $700 million each year spent to market breakfast cereals, candy, and gum. An- other $500 million is spent to advertise carbonated soft drinks.20 You probably saw at least a few food ads as you surfed online, watched TV, or drove to campus today. In comparison, when was the last time you saw an advertisement for broccoli? Have you ever seen an ad for broccoli?

Food companies spend these large sums on advertising for one reason: they work, especially on young people.21 American children view up to 40,000 televi- sion commercials annually. On Saturday morning, more than half of the between- cartoon ads are for foods. Of these, over 40 percent are for items such as candy, soft drinks, chips, and sugary breakfast cereals.22

In contrast, commercials for fruits and vegetables are rare, which is unfortunate, because healthy foods can be successfully marketed. When the dairy industry noted a decline in milk consumption among Americans in 1994, it launched the Got Milk? ad campaign, which featured celebrities wearing milk mustaches. This campaign strove to make drinking milk sexy and it worked. Milk sales increased by nearly 1.5 billion pounds, which is the equivalent of about 45 pounds of milk being sold for each ad- vertising dollar spent.23

Time, Convenience, and Cost When it comes to putting together a meal, time is often at a premium, and Ameri- cans, especially working women with families, want to spend less than 15 minutes

The USDA certifies that organic foods are grown without the use of pesticides, herbicides, or chemical fertilizers.

phytochemicals Nonnutritive plant compounds, found in fruits and vegeta-

bles, that may play a role in fighting

chronic diseases.

functional foods Foods that may pro- vide additional health benefits beyond the

basic nutrient value.

Rates of milk consumption increased after the Got Milk? advertising campaign.

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What Drives Our Food Choices? 7

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preparing a meal.24 Consequently, supermarkets are offering more prepared and par- tially prepared foods. If chicken is on the menu tonight, you can buy it uncooked at the meat counter in the supermarket, or you can go to the deli and buy it hot off the rotis- serie, cooked and stuffed with bread crumbs, or grilled with teriyaki sauce. The rice or pasta side dishes and cooked vegetables are also available to complete the meal.

Convenience has also become more of a factor in food selection. Decades ago, the most convenient way to get a hot cup of coffee was to brew it at home. Today, Americans are more likely to get their latte or half-caff from one of the 17,000 coffee shops, carts, and kiosks across the United States (more than 7,000 of which are Starbucks outlets).25, 26

For reasons related to both time and convenience, people are eating out more often today than they did a few decades ago. In the 1970s, Americans spent about 25 percent of their household food budget on eating out, compared with almost 45 percent today.27 Because cost is often an issue when considering where to eat out, most meals consumed away from home are fast food, which is often cheaper and quicker than more nutritious meals. Though cheap fast food may be easy on the pocketbook, it is taking its toll on the health of Americans. Epidemiological research suggests that low-cost, high-kilocalorie diets, such as those that incorporate lots of burgers, fries, tacos, and soft drinks, increase the risk of obesity, especially among those at lower socioeconomic levels.28 The long-term cost of the additional weight gain adds an estimated 36 percent to the annual cost of health care.29

The good news is that cheaper food doesn’t have to always mean fast food, and when healthy foods are offered at lower prices, people do buy them. Researchers found that lowering the cost of fresh fruits, vegetables, and lower fat snacks improves the consumption of these nutritious foods.30 The study demonstrates that price re- ductions are an effective strategy to increase the purchase of more healthful foods. Results were consistent across various food types and populations.

Habits and Emotions Your daily routine and habits often affect both when you eat and what you eat. For example, if you routinely start your day with a bowl of cereal and a glass of orange juice, you’re not alone. Ready-to-eat cereals are the number-one breakfast food choice among Americans, and citrus juice is their top juice in the morning.31 Many individuals regularly snack when watching television or sitting at the computer.32

For some individuals, emotions can sometimes drive food choice, and feeling happy or sad can trigger eating. In some cases, eating is suppressed during periods of sadness or depression. For many, food is used as an emotional crutch during times of stress, depression, or joy. Recall that Elizabeth ate her way through a large bag of chips before her exam. Her stress likely impaired her awareness of how much she was eating.

The Take-Home Message Taste and enjoyment are the primary rea- sons people prefer certain foods. Food availability affects its becoming part of a culture, and many foods can be regularly eaten out of habit. Advertising, food trends, limited time, convenience, emotions, and the perception that foods are healthy or unhealthy also influence food choices.

Which of the factors you just learned about had the strongestinfluence on Elizabeth’s food choices before her exam? Do you think her food choices had an impact on her test perfor- mance? Why or why not?

Although brown rice is a healthy whole-grain addition to any meal, it takes close to an hour to cook. For time-strapped consumers, food manufacturers have developed instant brown rice that cooks in 10 minutes, and a precooked, microwavable variety that reheats in less than 2 minutes.

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made each day for meals, snacks, and beverages. An example of the questions the researchers asked included: “There are many ‘when’ decisions you make with food. You decide when to eat, when to start cooking, when it is done cooking, when to start serving, when to stop eat- ing, and so on. Please try and estimate how many of these ‘when’ decisions you make in the following situations.”

Researchers also collected demo- graphic data, including age, gender, height, and weight, and used it to calcu- late the body mass index (BMI) of each participant. Normal weight was classified as a BMI of less than 25 kilograms per square meter; a BMI of greater than 25 kilograms per square meter was clas- sified as overweight; and a BMI of greater than 30 kilograms per square meter was classified as obese.

In Study 2, 379 volunteers were grouped into different, exaggerated con- ditions in which their consumption behav- ior was observed. These conditions in- cluded larger package, serving bowl, and plate sizes. Subjects were then asked two questions: “How much did you eat

compared to what is typi- cal for you?” and “In this study, you were in a group that was given [a larger bowl]. Those peo- ple in your group ate an average of 20 to 50 per- cent more than those who were instead given [a smaller bowl]. Why do you think you might have eaten more?”

Results

The results for Study 1 showed that initially most participants made 14.4 food-and-beverage decisions per day. When

asked more detailed questions related to food consumption decisions, the number rose to an average of 226.7 decisions per day. The food decisions made by individ- uals of various body weights indicated a U-shaped relationship, with obese individ- uals making significantly more food- related decisions per day (more than 100 additional decisions) compared with overweight subjects but similar to normal- weight people in the study (see figure).

In Study 2, those participants who were given an exaggerated amount of food ate 31 percent more than the control group. However, only 8 percent of these subjects felt that they ate more than they usually do. When these 8 percent were told they overate, 21 percent claimed they did not overeat. Of those subjects who accepted they overate, 69 percent said it was because they were hungry, while only 4 percent attributed it to the larger bowl or plate size.

Conclusions

The results from this research indicate that subjects drastically underestimate the number of food decisions they make each day, and may be participating in mindless eating. Normal-weight individu- als make a similar number of food deci- sions as obese individuals but appear to make more “no”-related food-and- beverage decisions. Tangible evidence was presented that people are either un- aware of how food decisions are being influenced by environmental cues, or are unwilling to accept that these cues play a role in their decisions.

QUESTIONS

1. Were the measurements appropriate to answer the research questions?

2. How do the results of this study an- swer the research questions?

3. Are there other factors not measured in this study that could have influenced the results?

4. Do you agree with the authors’ con- clusions?

Background

Most people are unaware of the amount of food they consume throughout the day. Their food consumption patterns are often influenced by what they perceive to be “normal,” which can be further af- fected by the package or plate size, the variety of food available, and the influence of other people. Being unaware of the im- pact of our environment as it affects food intake can have implications on nutrition education and food behavior research.

Research Question

There were two parts to the study. The first part investigated how many food- related decisions normal-weight, over- weight, and obese people make during a typical 24-hour period. The second part looked into whether subjects were aware that they overeat, and whether they were influenced by environmental cues.

Study Design

Study 1 asked 154 college students and adults to answer questions related to the number of food decisions they make. Subjects were asked, “How many total food-and-beverage decisions do you make in one day?” This was followed by a series of 15 questions that related to the number of when, what, how much, where, and who with decisions they

Wansink, B. and J. Sobal. 2007. Mindless Eating: The 200 Daily Food Decisions We

Overlook. Environment and Behavior 39:106–123.

FOCUS ON RESEARCH

0

50

100

150

200

250

300

350

400

Normal weight

Total decisions (calculated) Beverage-related decisions Meal-related decisions Snack-related decisions Initial estimate of decisions made

Weight of respondent

N u m

b e r

o f d

e c is

io n s

Overweight Obese

Calculated Number of Daily Food- and Beverage-Related Decisions

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What Are Nutrients? 9

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nutrition The science that studies how nutrients and compounds in foods nour-

ish the body and affect body functions and

overall health.

What Is Nutrition? The science of nutrition is the study of food and the nutrients we need to sustain life and reproduce. It also explores the way food nourishes the body and affects health.

The study of the relationship between food and health began as early as the 1600s. The term limey was coined after one of the earliest reported nutrition discoveries: that lime juice prevented scurvy (a disease caused by the lack of vitamin C) in sailors. During the 1700s, scientists recognized the value of what we ate in treating disease so that by the early 1900s the concept of essential nutrients had been widely accepted. By the late nine- teenth century, nutrition was becoming more quantitative, addressing the question of how much of each nutrient is required as well as accepting that individuals vary in their nutrient requirements. Nutritional epidemiology had been developed by the end of the twentieth century, and the advent of dietary surveys conducted by the government was used to further the science. The biochemistry of nutrition has exploded since the Human Genome Project in 2000. What began with British sailors in the 1600s today in- volves nutrition professionals, the government, and the food industry as they strive to develop new functional foods and nutraceuticals, and design diets for longevity.

Since its inception, the science of nutrition has explored how food is digested, ab- sorbed, transported, metabolized, and used or stored in the body. Nutritional scientists study how much we need of each nutrient, the factors that influence our needs, and what happens if we don’t consume enough. A chronic deficiency of even one nutrient will impact the body’s ability to function in the short term, and over time, chronic de- ficiencies, excesses, and imbalances will affect long-term health.

Good nutrition reduces the risk of four of the top ten leading causes of death in the United States, including the top three—heart disease, cancer, and stroke—as well as diabetes (Table 1.1). Nutrition also plays an important role in preventing other diseases and conditions that can impede one’s lifestyle. A healthy diet, for example, can keep bones strong and reduce the risk of developing osteoporosis. Eating well will also improve body weight, which in turn will reduce the risk of developing obe- sity, diabetes mellitus, and high blood pressure.

As with any science, nutrition is not stagnant. The more we discover about the relationship between nutrition and well-being, the greater the impact will be on long-term health.

The Take-Home Message Nutrition is the scientific study of how the nutrients and compounds in foods nourish the body. It has evolved over the past 400 years from a study of how nutrients relate to disease into a science that promotes health and longevity through a healthy diet. Good nutrition re- duces the risk of many chronic diseases, including heart disease, cancer, stroke, and diabetes.

What Are Nutrients? The body is one large organism made up of millions of cells that grow, age, repro- duce, and die, all without your noticing. You slough off millions of skin cells when you towel off after a shower, yet your skin isn’t noticeably thinner today than it was last week. Your body replaces skin cells at a rate fast enough to keep you covered, and it manufactures new cells using the same nutrients found in a variety of foods. As cells die, nutrients from food provide the building blocks to replace them. Nutrients

Table 1.1

Leading Causes of Death in the United States

Disease/ Cause of Death

Nutrition Related

† 1. Heart Disease X

2. Cancer X

3. Stroke X

4. Respiratory Diseases

5. Accidents

6. Diabetes X

7. Influenza/Pneumonia

8. Alzheimer’s Disease

9. Kidney Disease

10. Blood Poisoning

Source: Centers for Disease Control: 2008. “National Vital Statistics Report.” www.cdc.gov/nchs/data/nvsr/ nvsr56/nvsr56_10.pdf.

nutrients Compounds in foods that sus- tain body processes. There are six classes of

nutrients: carbohydrates, fats (lipids), pro-

teins, vitamins, minerals, and water.

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also provide the energy we need to perform all body functions and processes, from maintaining heart beat to playing tennis.

There are six categories of nutrients found in foods and in the body: carbohy- drates, lipids (fats), protein, vitamins, minerals, and water. Foods also often contain nonnutrient compounds, such as the phytochemicals mentioned earlier, non- digestible fiber, and other chemicals added by food manufacturers to enhance color, flavor, or texture, or extend shelf life.

About 10 percent of plant foods are made up of carbohydrates, fats, protein, vi- tamins, and minerals (Figure 1.1). The rest is typically water, and plant foods contain more water (90 percent) than do animal foods (60 percent). The other 40 percent of animal foods consist of protein, lipids, vitamins, and minerals. One unique quality of animal foods is that they do not contain any carbohydrates by the time we con- sume them.

In comparison with plant and animal products, a healthy human body is 60 per- cent water. The other 40 percent is made up of protein and fat, as well as a small amount of stored carbohydrates, minerals in the bone, and small amounts of vita- mins. Thus, the old saying is true: we are what we eat, from the carbohydrates in broccoli to the proteins in meat; the six biochemical ingredients needed to sustain life are all provided by the foods in our diets.

Most Nutrients Are Organic Carbohydrates, proteins, lipids, and vitamins are the most complex of the six classes of nutrients. These nutrients are organic because their chemical structures contain carbon. Organic nutrients also contain the elements hydrogen and oxygen, and in the case of proteins and some vitamins, nitrogen is also part of the molecule (Figure 1.2).

Minerals are the least complex of the nutrients and are inorganic because their chemical structure does not include carbon. Each mineral is an individual element, and its atoms are exactly the same whether found in food or in the body. For in- stance, the structure of zinc found in lean meats and nuts is the same as that found in a cell membrane or a hair follicle. Water, a three-atom molecule comprised of hydro- gen and oxygen, is also inorganic.

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20%

Human body

60%

15%

Broccoli (raw)

89%

7%

Chicken breast

67%

30%

Water

Fats

Vitamins

Minerals

Carbohydrates

Protein

Fiber

Figure 1.1 Nutrients in Foods and in the Body Water is the most abundant nutrient found in foods and in the body. Carbohydrates, fats, proteins, vitamins, and minerals make up the rest. Note that foods also contain nonnutritive compounds, such as phytochemicals and fiber.

inorganic Compounds that do not con- tain carbon, such as minerals, water, and

salts.

organic Compounds that contain carbon or carbon–carbon bonds.

Carbon

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

In o rg

a n ic

O rg

a n ic

Hydrogen Oxygen Nitrogen Single elements

Some vitamins contain nitrogen

Carbohydrates

Lipids

Proteins

Vitamins

Minerals

Water

Figure 1.2 The Chemical Composition of the Six Classifications of Nutrients in Food Each nutrient contains a unique combination of chemical elements.

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What Are Nutrients? 11

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Most Nutrients Are Essential In general, nutrients are essential and must come from foods, because either they cannot be made in the body, or they cannot be made in sufficient amounts to meet the body’s needs. A few nonessential nutrients can be made in sufficient quantities in the body. An example of this is vitamin D, which is synthesized in the skin upon exposure to sunlight. Under some circumstances, nonessential nutrients can become essential. In the case of vitamin D, if you are not exposed to enough sunlight, you will not be able to synthesize an adequate amount of the vitamin. You must then obtain vitamin D from foods.

Some Nutrients Provide Energy All creatures need energy in order to function, and humans are no exception. Energy is defined as the capacity to do work, and also provides a source of heat. The body derives energy from certain nutrients in foods, which store energy in their chemical bonds. During digestion and metabolism, the bonds are broken, and the energy is re- leased. Carbohydrates, lipids (fats), and proteins are defined as the energy-yielding nutrients because they contribute energy to the body. Whereas alcohol also provides energy, it is not considered a nutrient because it doesn’t serve a known function and it interferes with the repair and maintenance of the body.

Energy Is Measured in Kilocalories Kilocalorie is the term used by scientists to refer to the amount of energy found in a food. The term kilocalorie (kilo � 1,000) is defined as the amount of energy needed to raise the temperature of one kilogram of water 1 degree Celsius. A kilocalorie is not the same as a calorie (with a lowercase “c”), which is a much smaller unit of mea- surement. (In fact, a “calorie” is so small that one slice of bread contains about 63,000 calories.) One kilocalorie is equal to 1,000 calories.

To add to the confusion, the term Calorie (with an uppercase “C”) is used on nutrition labels to express the energy content of foods and is often used in science textbooks to reflect kilocalories. This textbook will refer to the units of energy found in foods as kilocalories, abbreviated kcalories or kcals.

Calculating the Energy in Foods Each energy-yielding nutrient provides a set number of kilocalories per gram, thus the number of kilocalories in one serving of a given food can be determined based on the amount (weight, in grams) of carbohydrates, protein, and fat in the food. For example, carbohydrates and protein provide 4 kilocalories per gram, so a food that contains 5 grams of carbohydrate and 3 grams of protein would have 32 kilocalories ([5 � 4] � [3 � 4] � 32). Fats yield 9 kilocalories per gram, or more than twice the number of kilocalories in either carbohydrates or protein. Alcohol contains 7 kilo- calories per gram, which must be taken into account when calculating the energy of alcohol-containing foods and beverages (Figure 1.3).

Use the Calculation Corner box on the next page to determine the number of kilocalories in Elizabeth’s potato-chip-and-cola snack.

nonessential nutrients Nutrients that can be made in sufficient quantities in the

body to meet the body’s requirements and

support health.

essential [nutrients] Nutrients that must be consumed from foods because

they cannot be made in the body in suffi-

cient quantities to meet its needs and sup-

port health.

Most nutrients consist of carbon, hydro- gen, and oxygen. These elements com- bine to form compounds through chemical reactions. An atom of each ele- ment can form a set number of bonds with other elements. For example, carbon can form bonds with four elements, hy- drogen can form one bond, and oxygen can form two bonds, as illustrated below. When two atoms bond together to form a compound, they are called molecules. Molecules tend to be more stable than atoms, and, like atoms, can carry a posi- tive or negative charge. Charged atoms or molecules are called ions.

H

H—C—H H—O—H

H

— —

Chemistry Boost

energy The capacity to do work.

kilocalorie The amount of energy required to raise the temperature of 1 kilogram of

water 1 degree centigrade; used to express the

measurement of energy in foods; 1 kilocalorie

is equal to 1,000 calories.

energy-yielding nutrients The three nutrients that provide energy to the body

to fuel physiological functions: carbohy-

drates, lipids, and protein.

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Elizabeth ate an entire bag of potato chips and drank a 16-ounce cola while she studied for her exam. Together these two items contain 144 grams of carbohydrate (in the cola and chips), 12 grams of pro- tein (from the chips), and 60 grams of fat (also in the chips). How many kilocalories did she consume?

(a) To calculate the total kilocalories in Elizabeth’s snack, multiply the total grams of each energy nutrient times the number of kilocalories per gram of that nutrient. Remember, a gram of carbohy- drate and protein each contain 4 kilocalories and a gram of fat contains 9 kilocalories.

(144 g � 4 kcals/g) � (12 g � 4 kcals/g) � (60 g � 9 kcals/g) � 1,164 kcals

576 kcals � 48 kcals � 540 kcals � 1,164 kcals

In one sitting, Elizabeth consumed more than 1,100 kilocalories, or more than half of the amount she likely needs to meet her daily energy requirement. As you’ll learn in later chapters, if behaviors like this become habits, they can quickly result in weight gain.

(b) Another useful measure for assessing the nutritional quality of Elizabeth’s snack is the percent- age of fat, protein, and/or carbohydrate found in the food (you will learn in later chapters that there are ranges for each nutrient that are considered part of a healthy diet). For example, what percent of kilocalories in the chips and soda is from fat? To answer this question, divide the fat kilocalories by the total kilocalories in the food and multiply by 100:

(540 kcals � 1,164 kcals) � 100 � 46% fat

Almost half of the kilocalories in Elizabeth’s snack are from fat. Do you think this is likely to be a de- sirable proportion?

For practice, complete the same calculations for carbohydrate and protein.

C A L C U L AT I O N C O R N E R

Energy in the Body Energy in foods and in the body is trapped within the bonds that keep the molecules together. When the bonds are broken, such as during the process of metabolism, a significant amount of energy, including some heat, is released. The energy can then

Figure 1.3 Nutrients and Alcohol Provide Kilocalories to Fuel the Body Carbohydrates, fats, protein, and alcohol provide energy, or kilocalories.

Carbohydrates 4 kcal/g

Alcohol 7 kcal/g

Fats 9 kcal/g

Protein 4 kcal/g

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What Are the Primary Roles of the Individual Nutrients? 13

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be used to digest and absorb the meal, contract muscles, fuel the heart, and synthe- size new cells, as well as other functions.

People’s energy needs vary according to their age, gender, and activity level. Males generally need more energy because they weigh more, and have more muscle mass (which requires more kilocalories to function) and less body fat. A younger per- son requires more energy than an older adult because he is still growing and is there- fore synthesizing more new tissue. Physically active individuals require more energy than sedentary people to fuel their activities and meet their body’s basic energy needs.

Energy that is not used to fuel the body will be rearranged into storage forms for later use, predominantly as fat. If you regularly consume more kilocalories than you expend, you will accumulate stored fat in adipose tissue and gain weight. The oppo- site is also true. Eating fewer kilocalories than the body needs will result in the break- down of stored energy and weight loss.

The Take-Home Message The nutrients found in foods are used by the body to manufacture and replace cells. Carbohydrates, lipids, proteins, and vitamins are organic nutrients composed of the chemical elements car- bon, hydrogen, oxygen, and sometimes nitrogen. Minerals and water are inorganic. Minerals are comprised of single atoms and water is made up of hy- drogen and oxygen. Energy in foods is measured in kilocalories. The energy- yielding nutrients, carbohydrates (4 kilocalories per gram), lipids (9 kilocalories per gram), and proteins (4 kilocalories per gram), provide fuel to be used by the body or stored for future use. Alcohol (7 kilocalories per gram) is not a nu- trient but does provide energy.

What Are the Primary Roles of the Individual Nutrients? Individual nutrients serve unique roles in the body. They supply energy, regulate metab- olism, and provide structure (Table 1.2). Some nutrients, including carbohydrates, lipids, proteins, and water, are called macronutrients (macro � large) because they are needed in much larger amounts to support normal functioning. Vitamins and minerals,

Table 1.2

Functions of the Major Nutrients by Type

Nutrient Provides Energy

Participates in Growth, Maintenance, Support, or Structure

Regulates Body Processes

Macronutrients Carbohydrates Yes No No

Protein Yes Yes Yes

Fats Yes Yes Yes

Water No Yes Yes

Micronutrients Vitamins No Yes Yes

Minerals No Yes Yes

macronutrients Organic nutrients, in- cluding the energy-containing carbohy-

drates, lipids, proteins, and water that the

body needs in large amounts.

Converting Pounds to Kilograms

Some of the calculations used in nutrition re- quire conversion of body weight from pounds to kilograms (kg). For example, one common cal- culation for the recommended intake for protein uses kilograms (although there are also formu- las using pounds).

To determine how many kilograms Elizabeth weighs, use her weight in pounds (125 pounds) and divide by the conversion factor 2.2:

125 lb � 2.2 � 56.8 kg

Using your own body weight in pounds, calcu- late your weight in kilograms.

C A L C U L AT I O N C O R N E R

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though equally important to health, are considered micronutrients (micro � small) be- cause they are required in smaller amounts to perform their key roles.

Each of the six classifications of nutrients will briefly be introduced in this chap- ter, and then discussed in much greater detail later in the textbook.

Carbohydrates Are the Primary Energy Source Carbohydrates are the body’s main source of energy. All forms of carbohydrates are composed of carbon (carbo-), hydrogen, and oxygen (hydrate � water). Carbohy- drates supply the simple sugar, glucose, which is the primary source of energy for several body cell types, including red blood cells and brain cells. Carbohydrates are found in most foods. Breads, cereals, legumes, nuts, fruits, vegetables, and dairy products are all rich in carbohydrates. The only foods that do not provide significant amounts of carbohydrates are animal products other than dairy, such as eggs, meat, poultry, and fish. Carbohydrates will be covered in detail in Chapter 4.

Lipids Also Provide Energy The term lipid refers to a diverse group of organic compounds including fats (also called triglycerides), oils, phospholipids, and sterols that are insoluble in water. These nutrients contain the same chemical elements as carbohydrates, including carbon, hydrogen, and oxygen. The difference is that lipids are much more concentrated than carbohydrates and contain less oxygen and water.

Lipids in the form of triglycerides are an important energy source for the body, especially during rest and sleep. This is also the form in which the body stores excess energy. The stored energy makes up the adipose tissue beneath the skin and around several organs.

Triglycerides make up the majority of the lipids we eat and are found in margarine, butter, oils, and animal products. Chapter 5 will present more information on lipids.

Proteins Provide the Building Blocks for Tissue Synthesis Proteins can be used for energy but are usually not the primary energy source. Proteins are similar in composition to carbohy- drates and lipids in that they contain carbon, hydrogen, and oxy- gen. But they are unique in that all proteins contain the element nitrogen, and some also contain sulfur.

Proteins contribute the basic building blocks, known as amino acids, to synthesize, grow, and maintain tissues in the body. The tissues in muscles, bones, and skin are primarily made up of protein. Proteins also participate as neurotransmitters in

the complex communication network between the brain and the rest of the body, and play a role in the immune system and as enzymes in chemical reactions.

Protein is found in a variety of foods, including meats, dairy products, and legumes such as soy, nuts, and seeds. Whole grains, vegetables, and some fruits con- tain smaller amounts of protein. Chapter 6 covers protein in detail.

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Carbohydrates are found in a variety of foods, including breads, grains, and pasta.

enzymes Proteins in living cells that act as catalysts and control chemical reactions.

Meats and dairy products are excellent sources of protein. Plant products, such as nuts, seeds, and legumes, also provide protein to the diet.

micronutrients Essential nutrients the body needs in smaller amounts: vitamins

and minerals.

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Vitamins and Minerals Play Vital Roles in Metabolism Vitamins and minerals do not provide energy, but they are involved in numerous key functions in the body. They are essential to help regulate metabolism, for example, and without them we would be unable to use carbohydrates, fats, and proteins for energy, or to sustain numerous chemical reactions. A deficiency of vitamins and minerals can cause a cascade of ill health effects ranging from fatigue to stunted growth, weak bones, and organ damage. The metabolic fate of carbohydrates, pro- tein, and fats in the body is dependent upon consuming enough vitamins and min- erals in the daily diet.

Many vitamins function as coenzymes, that is, they help enzymes catalyze reac- tions in the body. For example, the B vitamin thiamin attaches to and assists an en- zyme involved in carbohydrate metabolism. Vitamins also activate enzymes that participate in building bone and muscle, energy production, fighting infections, and maintaining healthy nerves and vision.

There are 13 known vitamins, and each has a unique chemical structure. They are grouped into two classifications according to their solubility, which affects how they are absorbed, stored, and excreted. Water-soluble vitamins, which include vitamin C and the eight B-complex vitamins, are easily absorbed and excreted by the body, and need to be consumed daily. The fat-soluble vitamins, A, D, E, and K, are stored in the liver and other organs and thus don’t need to be consumed on a daily basis. Vitamins are described in Chapters 9 and 10.

Minerals are inorganic substances that assist in body processes and are essential to the structure of hard tissues, such as bone, and soft tissues, including the red blood cells. Minerals such as calcium and phosphorus work with protein-containing hormones and enzymes to maintain and strengthen teeth and bones. A deficiency of any of the minerals can cause disease symptoms. Falling short of daily iron needs, for example, can cause fatigue and interfere with the ability to function.

Minerals are classified by the amount needed in the diet and total content found in the body. Major minerals are needed in amounts of at least 100 milligrams per day, and are found in amounts of at least 5 grams in the body. Calcium and magne- sium are two examples of major minerals. In addition to the structure of bones and teeth, some major minerals help maintain fluid balance, participate in energy pro- duction, and participate in muscle contractions. Details on each individual major mineral will be discussed in Chapter 12.

Trace minerals are needed in amounts of less than 100 milligrams per day and are found in amounts of less than 5 grams in the body. Iron and zinc are two exam- ples of trace minerals. Among other functions, trace minerals transport oxygen and carbon dioxide, participate in cell growth and development, control the metabolic rate, and play a role as an antioxidant. Chapter 13 will provide more specific detail on the role of these trace minerals.

Water Is Critical for Numerous Functions Some of the essential roles of water in the body probably seem obvious, as it makes up the majority of all body fluids, including digestive secretions, blood, urine, and perspiration. However, less obvious is the fact that water is part of every cell in the body, from muscle and bone cells to brain and nerve cells. Water is also vital to several key body functions. It is essential during metabolism, for

A wide variety of fruits and vegetables are abundant sources of water-soluble vitamins.

fat-soluble vitamins Vitamins that dis- solve in fat and can be stored in the body.

water-soluble vitamins Vitamins that dissolve in water; generally cannot be

stored in the body and must be consumed

daily.

solubility The ability to dissolve into an- other substance.

coenzymes Substances, such as vita- mins or minerals, that facilitate the activ-

ity of enzymes.

major minerals Minerals needed by the body in amounts greater than 5 grams;

also referred to as macrominerals.

trace minerals Minerals needed by the body in amounts less than 5 grams; also

referred to as microminerals.

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example, because it provides the medium in which metabolic reactions take place. Water functions in digestion and absorption, and as a transport medium that de- livers nutrients and oxygen to the cells and excretes waste products through the urine. Water helps maintain body temperature and acts as a lubricant for the joints, eyes, mouth, and intestinal tract. It surrounds vital organs and cushions them from injury. Because the body can’t store water, it must be replenished every day to maintain hydration.

The role of water in the body is discussed in detail in Chapter 11.

The Take-Home Message There are six classes of essential nutri- ents: carbohydrates, lipids (fats), protein, vitamins, minerals, and water, that are needed in specific amounts for good health. Individual nutrients have specific roles in the body. Carbohydrates, fats, and protein provide energy, while vitamins, minerals, and water are needed to use the energy-producing nutrients and for various body processes.

What Is Credible Nutrition Research?

Anyone who has attempted to lose weight can probably tell you how hard it is to keep up with the latest diet advice—because it seems to keep changing. In the 1970s, waist watchers were told that carbohy- drates were the bane of their existence and that a protein-rich, low- carbohydrate diet was the name of the game when it came to shrinking their waistline. A decade later, avoiding fat was the key to winning the battle of the bulge. By 2000, carbohydrates were being ousted again, and protein-rich diets were back in vogue. But recently protein-heavy diets seem to be less popular and high-carbohydrate diets are once again becoming the way to fight weight gain. So . . . are you frustrated yet?

Whereas diet trends and popular wisdom seem to change fre- quently, basic scientific knowledge about nutrition actually does not. Results from individual studies are often deemed newsworthy and publicized in the media, but the results of one report do not radically change expert opinion. Only when multiple affirming re- search studies have been conducted is a consensus reached about nutrition advice. News of the results of one study is just that: news. In contrast, advice from an authoritative health organization or

committee, such as the American Heart Association or the Dietary Guidelines Com- mittee, which is based on a consensus of research information, is sound information that can be trusted for the long term. (See the feature box “Evaluating Media Head- lines with a Critical Eye” for tips on how to critically evaluate media headlines.)

What nutrients would you expect to find in Elizabeth’s potato-chip-and-cola snack? What nutrients do you think are likely missing from these foods? What would be some healthier food choices during her next study session?

consensus Agreed-upon conclusion of a group of experts based on a collection of

information.

Nutrition-related stories often lead in newspapers and magazines and on websites.

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Did this headline grab your attention? Are you likely to change your diet habits ac- cording to what you read here? If so, you may be doing a disservice to your health. Dramatic headlines are designed to grab your attention, but they can often be mis- leading. Whether they’re delivered via a magazine, newspaper, TV, or online, sen- sational headlines should always be con- sidered with a critical eye.

Why do such headlines appear so regularly in our popular press? The media is routinely bombarded by press releases sent from medical journals, food compa- nies, organizations, and universities about research being conducted and/or confer- ences being sponsored by these institu- tions. These releases are sent for one reason: to gain publicity. Rather than re- peat them indiscriminately, reputable news organizations that report on these findings will seek out independent ex- perts in the field to weigh in on the re- search and, just as importantly, explain how these findings relate to the public. Even with this added context, there’s often much detail that’s left out of the story. Here are some questions to con- sider when hearing or reading about a new study, finding, or claim in the main- stream media:

1. Was the Research Finding Published in a Peer-Reviewed Journal?

You can be confident that studies pub- lished in a peer-reviewed journal have

been thoroughly reviewed by experts in this area of research. In most cases, if there are flaws in the study, the study does not get published. If the research isn’t published in a peer-reviewed journal, you have no way of knowing if the study was conducted in an appropriate manner and whether the findings are accurate. The headlines in a newspaper about the potential of diet soda to increase the risk of heart disease have less credibility than an article published in the New England Journal of Medicine.

2. Was the Study Done Using Animals or Humans?

Experiments with animals are often used to study how a particular substance af- fects a health outcome. But if the study is conducted in rats, it doesn’t necessarily mean that the substance will have the same effect if consumed by humans. This doesn’t mean that animal studies are friv- olous. They are important stepping stones to designing and conducting simi- lar experiments involving humans.

3. Do the Study Participants Resemble Me?

When you read or hear about studies in- volving humans, you always want to find out more information about the individu- als who took part in the research. For ex- ample, were the people in the diet soda study college-aged subjects or older indi- viduals with heart disease and high blood

pressure? If older adults were studied, then would these findings be of any ben- efit to young adults who don’t have high blood pressure or heart disease?

4. Is This the First Time I’ve Heard About This?

A single study in a specific area of research is a lonely entity in the scientific world. Is this the first study regarding the relationship between diet soda and cardiovascular risk? If the media article doesn’t confirm that other studies have also supported these findings, this initial study may be the only study of its kind. Wait until you hear that these research findings are confirmed by a reputable health organization, such as the American Heart Association, before con- sidering making any changes in your diet. These organizations will only change their advice based on a consensus of research findings.

In your lifetime, you are going to read thousands of newspaper and website headlines, as well as watch and listen to countless television and radio reports. Your critical thinking skill in evaluating the sources and information presented will be your best friend when it comes to deciding which blurbs to believe. This skill may also save you considerable money by helping you avoid nutrition gimmicks. When it comes to assessing nutrition information in the media, it’s worth your time and effort to find out where it came from and why (or if) you should care.

Evaluating Media Headlines with a Critical Eye

February 12, 2008

Diet soda raises cardiovascular risks The New York Times

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hypothesis An idea or explanation pro- posed by scientists based on observations

or known facts.

scientific method A process used by scientists to gather and test information

for the sake of generating sound research

findings.

Sound Nutrition Research Begins with the Scientific Method Sound research studies begin with a process called the scientific method. Scientists observe something in the natural world, ask questions, and propose an explanation (or hypothesis) based on their observations. They then test their hypothesis to de- termine if their idea is correct. There are many steps in the scientific method and many adjustments made along the way before a scientist has gained enough infor- mation to draw a conclusion about his or her hypothesis. In fact, the entire process can takes years to complete.

Let’s walk through a nutrition-related study in which scientists used the scien- tific method to study rickets (Figure 1.4). Rickets is a disease in children in which the leg bones are so weakened that they cannot hold up the child’s body weight. The legs bow as a result. In the early 1800s, parents often used cod-liver oil to treat rickets be- cause it seemed to provide a miraculous cure.

Scientists noticed the cod-liver oil curing phenomenon and asked themselves why it cured rickets. In making note of the fact that cod-liver oil had an effect on rickets, and in asking why this was the case, these scientists were using the first step in the scientific method: observing and asking questions.

The second step of the scientific method is to formulate a hypothesis. Because cod-liver oil is very rich in vitamin A, scientists initially thought that this vitamin must be the curative factor. To confirm this, scientists proceeded to the third step, which was to conduct an experiment.

Observe and ask a question Why does cod liver oil cure rickets?

Hypothesis supported Rats were not cured.

Hypothesis not supported Rats were cured.

Revise or formulate a new hypothesis

Conduct an experiment Feed rats with rickets cod liver oil that contains no vitamin A.

Formulate a hypothesis The vitamin A in cod liver oil is the curative factor.

Figure 1.4 Steps of the Scientific Method The scientific method is used to conduct credible research in nutrition and other scientific fields.

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The scientists altered the cod-liver oil to destroy its vitamin A. The altered oil was given to rats that had been fed a diet that caused rickets. Surprisingly, the rats were still cured of rickets. This disproved the scientists’ original hypothesis that vita- min A was the curative factor. They then needed to modify their hypothesis, as it was obvious that there was something else in the cod-liver oil that cured rickets. They next hypothesized that it was the vitamin D that cured the rats, and conducted an- other experiment to confirm this hypothesis, which it did.

What good would it be to make such an important discovery if other scientists couldn’t find out about it? Fortunately, scientists today share their findings by sum- marizing and submitting their research to a peer-reviewed journal (Figure 1.5). Other scientists (peers) then look at the researchers’ findings to make sure that they are sound. If so, the research study is published in the journal. After that, it may be picked up by the popular press and relayed to the rest of the population. If the rela- tionship between vitamin D and rickets was discovered today, it would probably be the lead story on CNN.

As more and more studies confirmed that vitamin D could cure and prevent rickets, a theory developed. By the 1920s, researchers knew with great certainty that vitamin D prevents rickets, and that a deficiency of vitamin D can cause deformed bones in children. Because of this, there is a consensus among health professionals as to the importance of vitamin D in the diets of children.

Research Studies and Experiments Confirm Hypotheses Scientists can use different types of experiments to test a hypothesis. A laboratory experiment is done within the confines of a lab setting, such as the rickets experi- ments with rats. Research conducted with humans is usually observational or experimental.

Observational research involves exploring factors in two or more groups of sub- jects to see if there is a relationship to a certain disease or other health outcome. One type of observational research is epidemiological research, which looks at popula- tions of people. For example, scientists may look at people who live in Norway and notice that there is a higher incidence of rickets among children there than in Aus- tralia. Through their observations, they may find a relationship between the lack of sun exposure in Norway and the high incidence of rickets there compared with sunny Australia. However, the scientists can’t rule out that the difference in the inci- dence of rickets in these two populations may also be due to other factors in the sub- jects’ diet or lifestyle. This type of research does not answer the question of whether one factor directly caused the other.

Experimental research involves at least two groups of subjects. One group, the experimental group, is given a treatment, and another group, the control group, isn’t. When scientists hypothesized that vitamin D cured rickets, they would have ran- domly assigned children with rickets to two groups (Figure 1.6 on page 20). The sci- entist would have given the experimental group a vitamin D supplement but would have given the control group a placebo, which looked just like the vitamin D supple- ment but contained only sugar. If neither of the two groups of subjects knew which pill they received, then the subjects were “blind” to the treatment. If the scientist who gave the placebo and the vitamin D supplement also didn’t know which group re- ceived which treatment, this would be called a double-blind placebo-controlled study. The scientists would also have to make sure that the variables were the same or controlled for both groups during the experiment. For example, they couldn’t let the control group go outside in the sunshine, since sunlight is known to allow humans to

Hypothesis supported

Publish findings

Develop theory

Establish consensus

Figure 1.5 A Hypothesis Can Lead to a Scientific Consensus When a hypothesis is supported by research, the results are published in peer-reviewed journals. Once a theory has been developed and supported by subsequent experiments, a consensus is reached in the scientific community.

peer-reviewed journal A journal in which scientists publish research findings,

after the findings have gone through a rig-

orous review process by other scientists.

observational [research] Research that involves systematically observing sub-

jects to see if there is a relationship to cer-

tain outcomes.

laboratory experiment A scientific ex- periment conducted in a laboratory. Some

laboratory experiments involve animals.

experimental [research] Research in- volving at least two groups of subjects.

double-blind placebo-controlled study An experimental study in which neither the researchers nor the subjects in

the study are aware who is receiving the

treatment or the placebo.

placebo An inactive substance, such as a sugar pill, administered to a control group

during an experiment.

control group In experimental research, the group that does not receive the treat-

ment but may be given a placebo instead;

used as a standard for comparison.

experimental group In experimental research, the group of participants given a

specific treatment, such as a drug, as part

of the study.

epidemiological research Research that studies the variables that influence health in a

population; it is often observational.

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synthesize vitamin D, and at the same time keep the experimental group of subjects inside. The exposure to the sunshine would change the outcome of the experiment.

A double-blind placebo-controlled study is considered the “gold standard” of research because all of the variables are the same and controlled for the groups of subjects, and neither the subjects nor the researcher are biased toward one group.

In any scientific research, sample sizes must be large enough to ensure that dif- ferences found in the study are due to the treatment rather than to chance. Studying an entire population is usually impossible, because the population is too large, the study would be too expensive or time-consuming, or all members of the population do not want to participate. This was the case with the vitamin D and rickets study mentioned earlier. It would be virtually impossible to measure all children with rick- ets. Instead, a sample of the children with rickets was used and a statistical compari- son was done to estimate the effects on the population. Generally, the larger the sample size, the more confident the researchers are that the data reflects reliable dif- ferences that would most likely be seen in the population.

The beauty of science is that one discovery builds on another. Though this may seem frustrating when the findings of one research study dispute the results of an- other from just a few months before, conflicting findings actually help scientists for- mulate new questions. Though many hypotheses fail along the way, a great many discoveries are also made.

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Select a large number of subjects with rickets.

Randomly divide subjects into two groups.

Neither the subjects nor scientists know which group receives what treatment to prevent bias.

Compare results.

Did the vitamin D cure rickets in the experimental group and did the control group remain unchanged?

Experimental group receives vitamin D supplement.

Control group receives placebo.

Vitamin D cures rickets

Yes No

Revise hypothesis

1

2

3

4

Figure 1.6 Controlled Scientific Experiments Scientists use experimental research to test hypotheses.

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The Take-Home Message Sound nutrition advice is based on years of research using the scientific method. Several methods can be used to conduct nutrition research, including laboratory experiments (on animals), experimental research (on humans), and observational research. Double- blind placebo-controlled studies mean that neither the subjects nor the researchers are aware of who is receiving treatment, and such studies are therefore considered the gold standard of research. Findings from observa- tional and epidemiological research are only considered valid if the study was conducted with an adequate sample size of subjects.

What Is Nutritional Genomics? An area of nutrition research that may have far-reaching effects on health and disease is nutritional genomics. This is a science that studies the relationship between gene ex- pression, nutrition, and health. Until this new science emerged, nutrition research and the study of genetics contributed separately to the body of knowledge of chronic disease. Studied together, these two fields help us understand the interaction between genes and nutrients, and whether the genes are responding to the nutrients we eat (nutrigenetics), or whether the nutrients themselves influence genetic expression (nutrigenomics).

Recent advances in nutritional genomics have already yielded potential clinical ap- plications. For example, research has shown a relationship between chronic inflamma- tion and certain bioactive compounds found in food, including resveratrol in the skin of red grapes, theaflavins in tea, and lactones in chicory (a coffee substitute).33 Adding foods to the diet that contain these compounds may regulate the genes that cause the inflammation.

Nutritional genomics may have tremendous potential to provide personalized dietary recommendations based on an individual’s genetic makeup. Ultimately, fu- ture registered dietitians may be able to use this information to recommend diet modifications that are specific to a patient’s DNA.

The Take-Home Message Nutritional genomics is an evolving sci- entific field that studies how diet may modify the way genes work, and how genetic makeup affects nutrient requirements.

Self-Assessment

How Healthy Is Your Family Tree? You inherited your DNA from your parents, so the extent to which DNA affects health is largely hereditary. Does your family have a history of heart disease, diabetes, or obesity? What about other chronic diseases or conditions? Before you learn about the role that healthy eating plays in preventing chronic diseases, ask your parents and grandparents about your family’s health history. If there are certain diseases or condi- tions that run in your family, you’ll want to pay particular attention to these as you learn more throughout this book.

An easy way to gather information about your family’s health history is by visiting My Family Health Portrait at http://familyhistory.hhs.gov. The site generates a family tree report according to the medical history you enter. Save a copy of the report for future reference.

gene expression The processing of genetic information to create a specific

protein.

nutritional genomics A field of study of the relationship between genes, gene

expression, and nutrition.

The study of nutritional genomics may one day allow individuals to tailor their diets based on their DNA.

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What Is Nutrition Assessment and What Does It Involve? If an individual suspects that he may not be meeting all of his nutrient needs, or that she is suffering from a nutrition-related disease or condition, he or she may turn to a nutrition professional, such as a Registered Dietitian (RD), to determine current nutrition status (see the feature box “Obtaining Nutrition Advice: Who Are the Experts? Who Are the Quacks?” on page 24). An RD will then conduct an as- sessment to find out if a client is getting too much, too little, or the right amount of a nutrient. The methods used for the assessment depend on the type of informa- tion the nutrition professional has available to assess, and the validity and reliabil- ity of the tools he or she uses.

The first step in assessing nutrition status is to provide the basis for making any dietary recommendations. A person’s state of nutrition is usually described as either healthy or malnourished. Someone who lacks a specific nutrient, or isn’t consuming enough energy, is undernourished. which means that person is at risk of losing too much weight or developing a disease related to a nutrient deficiency. In contrast, an individual who overconsumes a particular nutrient, or eats too many kilocalories, is described as being overnourished. This person runs the risk of becoming over- weight, developing diseases such as diabetes or heart disease, and potentially accu- mulating toxic amounts of a specific nutrient in the body.

A variety of methods are used to assess both under- and overnutrition of indi- viduals. No one measurement is sufficient to determine malnutrition, and thus a combination of tools is used (see the ABCDs in Table 1.3).

overnourished The overconsumption of energy or nutrients.

undernourished A condition in which the individual lacks sufficient energy or is

deficient in quality or quantity of essential

nutrients.

malnourished A condition that results when the body does not receive the right

amount of essential nutrients to maintain

health; overnourished and undernourished

are forms of malnutrition.

Registered Dietitian (RD) A health professional who is a food and nutrition

expert; RDs obtain a college degree in nu-

trition from an American Dietetic Associa-

tion (ADA) accredited program, and pass

an exam to become a Registered Dietitian.

Table 1.3

The ABCDs of Nutrition Assessment Types of Assessment Measurements What They Are Used For

Anthropometric Height Weight Body mass index Waist-to-hip ratio Waist circumference

Monitors growth, obesity, changes in weight loss, and risk of developing chronic disease such as diabetes and heart disease

Biochemical Blood, urine, and feces Protein, mineral, and vitamin status and disease

Clinical Observe hair, fingernails, skin, lips, mouth, muscle, joints, overall appearance

Signs of deficiencies and ex- cesses of nutrients

Dietary Intake Diet history Diet record Food frequency questionnaire 24-hour dietary recall

Usual nutrient intake, and deficiencies or excesses of various nutrients

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Nutrition Assessment Includes Examining a Patient’s Health and Diet History Part of evaluating a person’s current nutrition status is to take a look at that person’s health history, including any experiences with acute or chronic illness, and diagnos- tic procedures, therapies, or treatments that may increase nutrient needs or induce malabsorption. Does the patient have a family history of diabetes or heart disease? Has the patient been overweight or underweight in the past?

Questioning an individual about his or her dietary intake and diet history is an important aspect of a nutrition assessment. A detailed diet history is conducted by a skilled researcher who knows just what types of questions to ask to help a patient re- member not only current food intake but food intake in the past.

Two tools used to collect dietary intake data are interviews and questionnaires. A nutrition interview can reveal data about lifestyle habits, such as how many meals are eaten daily, where they are eaten, and who prepares them. Food frequency ques- tionnaires (FFQs) can be used to gather information about how often a specific food or category of food is eaten.

Food Frequency Questionnaire One of the easiest ways to determine an individual’s intake of nutrients is to use the FFQ. This form of assessment provides evidence of consumption patterns over time. For example, if you wanted to determine the usual calcium intake over time of an older woman with osteoporosis, an FFQ could be used to indicate the number of servings “per day, per week, and per month,” as well as whether she “seldom” or “never” consumes milk, cheese, or yogurt. The FFQ is a reasonably reliable, accurate, and inexpensive method to assess usual intake.34

This assessment tool is not as helpful in assessing the actual grams consumed of a nutrient, nor does it always accurately reveal usual intake. For that information, a food record or 24-hour dietary recall usually provides a better picture.

Food Record A food record is simply a diary of what foods and beverages are eaten, how much, and when they are eaten over a defined period of time. Food records are often kept for three to seven days and are considered by some to be one of the best methods for collecting diet information. There are drawbacks to this method. The accuracy de- pends on the individual’s skill and commitment to keeping a valid record. Many people start out strong and then lose interest or simply forget to record the food. Or, they might alter their usual food intake to avoid feeling embarrassed about what they eat.

Food records can be kept in written form, such as a journal, or with an elec- tronic diet analysis program. There are also new handheld devices being tested that may help improve the accuracy, ease, and evaluation of recording dietary intake.35

The FFQ or a diet record should be selected based on the specific information the assessor needs to know, such as iron intake over time and how much iron the in- dividual eats daily, as well as the assessor’s ability to complete the instrument accu- rately.36 The information obtained from these tools is then compared with current dietary standards, which we will discuss in the next chapter.

malabsorption A problem associated with the lack of absorption of nutrients

through the intestinal tract.

chronic A symptom or condition that lasts over a long period of time.

acute A sudden onset of symptoms or disease.

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If you need legal advice, you seek the ex- pertise of an attorney. If you need knee surgery, you go to an orthopedic sur- geon. For nutrition advice, to whom should you turn?

The Nutrition Experts

Who is a credible expert with training in the field of nutrition? Different health pro- fessionals have varying levels of nutrition training, but by far, the professional with the most nutrition training is the Regis- tered Dietitian (RD). An RD has com- pleted at least a bachelor’s degree from a university or college accredited by the American Dietetic Association (ADA) and

has passed an ADA-administered na- tional exam. The ADA is the largest pro- fessional organization in the United States, with a membership of almost 67,000 nutrition experts. RDs must main- tain registration with the national organi- zation and participate in continuing professional education to remain current in the fast-changing world of nutrition, medicine, and health.

RDs are trained to administer medical nutrition therapy and work with patients to make dietary changes that can help prevent diseases such as heart disease, diabetes, stroke, and obesity. Patients are often referred to RDs for nutrition advice and guidance by their physicians. RDs work in hospi- tals and other health care facilities, pri- vate practice, universities, medical schools, professional athletic teams, food companies, and other nutrition- related businesses.

Some individuals other than RDs, in- cluding those with advanced degrees in nutrition, can also provide credible nutri- tion information. Some physicians have taken a nutrition course in medical school and gone on to get a master of science in public health (MPH), which in- volves some nutrition courses, or an MS in nutrition at an accredited university or college.

Some public health nutritionists may have an undergraduate degree in nutrition but didn’t complete a supervised prac- tice, so are not eligible to take the ADA exam. These individuals can work in the government organizing community out- reach nutrition programs, such as pro- grams for the elderly.

In order to protect the health of the public, over 40 states currently license nutrition professionals. A person who meets these qualifications is a licensed

dietitian (LD) and so will have the letters “LD” after his or her name. Because RDs have completed the rigorous standards set forth by the ADA, they automatically meet the criteria for LD and often will have both “RD” and “LD” after their names.

Be careful when taking nutrition advice from a trainer at the gym or the person who works at the local health food store. Whereas some of these people may be credible, many are not, and thus, less likely to give you information based on solid scientific evidence. Anyone who calls himself or herself a nutritionist may have taken few or no accredited courses in nutrition.

Be a Quackwatcher

Whereas credible nutrition experts can provide highly useful nutrition guidance, people of questionable credentials often dole out misinformation, usually for the sake of turning a profit. These skilled salespeople specialize in health quackery, or fraud, introducing health fears and then trying to sell services and products to allay these newly created fears. Part of their sales pitch is to make unrealistic promises and guarantees.

In order to help people avoid falling for profit-motivated schemes, Dr. Stephen Barrett has developed a list of common deceptive statements made by health quacks.1,2 Be leery of infomercials, maga- zine ads, and websites that try to con- vince you that: ■ Most Americans are not adequately

nourished. ■ Everyone should take vitamin

supplements. ■ You need supplements to relieve stress

or give you energy. ■ You can lose a lot of weight in a short

amount of time. ■ Their products can produce amazing

results and cure whatever ails you. ■ Your behavior is caused by your diet. ■ Herbs are safe because they are natural. ■ Sugar will poison you.

Obtaining Nutrition Advice: Who Are the Experts? Who Are the Quacks?

quackery The promotion and selling of health products and services of question-

able validity. A quack is a person who pro-

motes these products and services in order

to make money.

nutritionist A generic term with no rec- ognized legal or professional meaning.

Some people may call themselves a nutri-

tionist without having any credible train-

ing in nutrition.

licensed dietitian (LD) An individual who has met specified educational and expe-

rience criteria deemed by a state licensing

board necessary to be considered an expert in

the field of nutrition. An RD would meet all

the qualifications to be an LD.

public health nutritionists Individuals who may have an undergraduate degree

in nutrition but who are not Registered

Dietitians.

medical nutrition therapy The inte- gration of nutrition counseling and di-

etary changes, based on individual medical

and health needs, to treat a patient’s med-

ical condition.

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■ A hair sample can identify nutrient deficiencies.

■ Your MD or RD is a quack to whom you should not listen.

■ There is no risk, as there is a money- back guarantee. Good luck getting your money back!

You Can Obtain Accurate Nutrition Information on the Internet

Many people turn to various websites when they have a question about health or nutrition. In fact, over 70 percent of Ameri- can adult Internet users, or 117 million people, have surfed more than 3 million websites looking for health and medical information.3 The good news is that you can find credible nutrition information on- line; you just need to evaluate every site with a critical eye. Remember that anyone with computer skills can put up a slick website, and there are many that promote misleading or false information.

To help evaluate the validity of web- sites, the National Institutes of Health (NIH) has developed ten questions to consider:4

1. Who Runs the Site? Credible websites are willing to show their credentials. For example, the National Center for Complementary and Alternative Medicine (www.nccam.nih.gov) provides information about its association with the NIH and its extensive ongoing research and educational programs.

2. Who Pays for the Site? Running a website is expensive, and finding out who’s paying for a particular site will tell you something about the reliability of its content. Websites sponsored by the government (with URLs ending in .gov), a nonprofit organization (ending in .org), or an academic institution (.edu) are more reliable than many commercial websites (.com or .net). Some commercial websites, such as WebMD, carry articles that can be reliable if they are written by credible health professionals, but other websites may be promoting information to suit a company’s own purposes. For example, if the funding source for the

website is a vitamin and mineral supplement company, are all the articles geared toward supporting the use of supplements? Does the website have advertisers and do their products influence the content of the website?

3. What Is the Purpose of the Site? After you answer the first two questions, look for the “About This Site” link. This will help you understand the website’s purpose. For example, at www .nutrition.gov, the purpose is to “provide easy access to the best food and nutrition information across the federal government.” This website doesn’t exist to sell anything, but to help you find reliable information.

4. Where Does the Information Come From? You should always know who wrote what you are reading. Is the author a qualified nutrition expert or did she or he interview qualified individuals? If the site obtained information from another source, was that source cited?

5. What Is the Basis for the Information? Is the article’s information based on medical facts and figures that have references? For example, any medical news items released on the American Heart Association website (www.americanheart.org) will include the medical journal from which the information came.

6. How Is the Information Selected? Check to see if the website has an editorial board of medical and health experts and if qualified individuals review or write the content before it is released.

7. How Current Is the Information? Once a website is on the Internet, it will stay there until someone removes it. Consequently, the health information that you read may not be the most up-to-date. Check the date; if it is over a year old, check to see if it has been updated.

8. How Does the Site Choose Links to Other Sites? Some medical sites don’t like to link to other sites as they don’t have control over other sites’ credibility and content. Others do link, if they are confident that these sites meet their criteria. Don’t assume that the link is credible.

9. What Information Is Collected About the Viewer and Why? Websites track the pages consumers visit to analyze popular topics. Sometimes they elicit personal information such as gender, age, and health concerns, which can then be sold to interested companies. Credible sites should state their privacy policy and if they will or will not give or sell this informa- tion to other sources.

10. How Does the Site Manage Interactions with Visitors? Contact information of the website’s owners should be listed in case readers have any concerns or questions that they want answered. If the site has a chat room or ongoing discussion group, how is it moderated? Read the discussion group dialogue before you jump in.

When obtaining information from the Internet, carefully peruse the site to make sure that it is credible and contains up-to- date information, and that its content isn’t influenced by those who fund and sup- port the website.

References 1. Barrett, S. and V. Herbert. 2004. Twenty-

Five Ways to Spot Quacks and Vitamin Pushers. Accessed June 2008. Available at www.quackwatch.org.

2. Barrett, S. 2006. How to Spot a ‘Quacky’ Web Site. Accessed June 2008. Available at www.quackwatch.org.

3. Krane, D. 2005. Number of “Cyberchondriacs”—U.S. Adults Who Go Online for Health Information— Increases to Estimated 117 Million. Available at www.harrisinteractive.com. Accessed January 2008.

4. National Center for Complementary and Alternative Medicine. 10 Things to Know About Evaluating Medical Resources on the Web. Available at www.nccam.nih .gov. Accessed January 2008.

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body mass index (BMI) A measure- ment calculated as height divided by

weight squared; used to determine

whether an individual is underweight, at a

healthy weight, or overweight or obese.

Twenty-Four-Hour Dietary Recall The twenty-four-hour dietary recall method is a quick assessment conducted by a trained interviewer who asks a patient to recall all the food and drink, including snacks, eaten the previous day. This tool relies on the skills of the interviewer and the individual’s ability to remember what he ate and drank the day before. Because di- etary intake varies from one day to the next, one 24-hour period may not provide an accurate estimate of typical intake.

Anthropometric Data Is Used to Help Assess Nutritional Status Anthropometric data measures body size or body composition. In adults, this usu- ally means measuring height, weight, body mass index (BMI), waist-to-hip ratios, and waist circumference. For children, growth charts have been developed that com- pare height to weight, as well as how a child’s height and weight compare with others of the same age. All of these measurements are easily obtained with a scale and tape measure.

The BMI is a measure of weight relative to height, and waist circumference measures abdominal fat. Body composition measurements can provide data on an individual’s lean body tissue and the percent body fat, depending on the tool used. These measurements can be assessed with more specialized equipment, such as skin calipers, or more expensive equipment, such as the Bod Pod. We will discuss these measurements in greater detail in Chapter 14.

Data collected from anthropometric measurements is then compared with ref- erence standards. Patterns and trends become evident when more than one measure- ment is taken over time and compared with the initial values. By combining the results of the BMI and waist circumference with other information gathered during the nutrition assessment, an individual’s risk of developing diseases associated with obesity, such as diabetes and heart disease, can be determined.

Conduct a Physical Examination A person who is malnourished will exhibit physical symptoms as the body adjusts to the lack or over accumulation of nutrients. Therefore, several parts of the body can be inspected for evidence of poor nutrition. Observing the hair, skin, eyes, finger- nails, tongue, and lips of an individual can provide clues that point to under- or overnutrition. For example, cracks at the corners of the mouth can be evidence of B vitamin deficiencies, while small pinpoint hemorrhages on the skin may reflect a deficiency of vitamin C. Observations of physical symptoms should be followed up by more direct measurements, including laboratory assessments.

Collect Laboratory Data Laboratory tests based on body fluids, including blood and urine, can be important indicators of nutritional status, but they are also influenced by nonnutritional fac- tors. Biochemical tests assess nutritional status by measuring the nutrient levels in body fluids, how fast a nutrient is excreted through the urine, and the metabolic by- products of various nutrients found in urine. For example, low levels of albumin (a blood protein) in the serum reflect protein deficiency; low hemoglobin levels in the blood indicate iron-deficiency anemia; and a high fasting blood sugar level may sug- gest diabetes.

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How Do We Assess the Nutritional Status of a Population Group? 27

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The Take-Home Message Nutrition assessment is conducted by gathering information from health history, dietary record, anthropometric, clinical, and biochemical (laboratory) data. When the information from sev- eral tools is viewed together, a comprehensive picture of the individual’s nu- tritional status can be determined.

How Do We Assess the Nutritional Status of a Population Group? Assessing the nutritional status of an individual in a clinical setting is one thing, but how do we determine the nutritional status of a population? What percentage of Americans is meeting the dietary recommendations for healthy eating? To find out, we collect dietary intake information on a large scale. Such information allows researchers to determine the adequacy of the current recommendations for different population groups, to evaluate and develop food assistance programs, and to assess risk.

Assessing groups of people involves gathering the same type of information used to evaluate individuals, usually through the use of surveys.

Conduct or Review National Surveys Numerous national surveys have been developed by a variety of federal agencies to assess the health and nutritional status of Americans. These surveys, including the National Health and Nutrition Examination Survey (NHANES), the Behavioral Risk Factor Surveillance System (BRFSS), and the Framingham Heart Study, have col- lected and published reliable data that has been used to develop the current dietary recommendations.

The National Health and Nutrition Examination Survey (NHANES) The National Health and Nutrition Examination Survey (NHANES) is a series of sur- veys conducted by the National Center for Health Statistics (NCHS) and the Centers for Disease Control and Prevention. These surveys, which began in 1960, were established to determine the nutritional status of Americans of all ages and to monitor the risk be- haviors over time. The intake of carbohydrates, lipids, protein, vitamins, minerals, and fiber has been collected using a 24-hour recall method and reported in the document What We Eat In America. For more information about the data collected during the eight NHANES surveys, visit the CDC website at www.cdc.gov/nchs/nhanes/htm.

The Behavioral Risk Factor Surveillance System (BRFSS) The CDC began tracking the health behaviors of Americans in 1984 through the world’s largest telephone survey. With financial support from the CDC, the 50 state health departments develop surveys to assess the prevalence of specific health condi- tions including chronic disease, injury, and infectious diseases. These surveys track health behaviors such as sedentary lifestyles, obesity, not using a seatbelt, smoking, alcohol abuse, and lack of medical care that relate to the leading causes of death, in- cluding cardiovascular disease, cancer, stroke, diabetes, and injury.

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The data collected by each state is used to allocate state resources to plan and evaluate the health programs.

The Framingham Heart Study The term “risk factors” was first coined by the researchers of the 1948 Framingham Heart Study conducted in Framingham, Massachusetts. Fifty years later, these re- search pioneers had collected longitudinal data on two generations and more than 10,000 participants to establish the current recommendations for cardiovascular disease.

This study, supported by the National Heart, Lung, and Blood Institute, initially monitored participants as an epidemiological study. In the 1970s, advances in tech- nology resulted in better testing methods, such as the echocardiograms, exercise stress tests, and carotid artery ultrasounds. The current phase of the study, which began in the 1980s, is exploring the genetic connections to cardiovascular disease in a third generation of Framingham citizens.

The Framingham Heart Study had a major impact on the dietary intake of Americans. For instance, once the connection between blood cholesterol levels and heart disease was revealed, the common bacon-and-eggs breakfast eaten by most Americans in 1948 was replaced with whole grains and low-fat dairy.

The Take-Home Message National surveys are used to determine the nutritional status of a large population. Two surveys conducted by the U.S. federal government are the National Health and Nutrition Examination Survey (NHANES) and the Behavioral Risk Factor Surveillance System (BRFSS), both supported by the Centers for Disease Control. The Framingham Heart Study, which is a project of the National Heart, Lung, and Blood Institute, has pro- vided the foundation for the current dietary recommendations for heart health.

What Is Healthy People 2010? The U.S. Surgeon General has issued calls for a nationwide health improvement pro- gram since 1979. The latest edition of this report is Healthy People 2010, which con- tains a set of health objectives for the nation to achieve over the first decade of the twenty-first century.

Healthy People 2010 focuses on two broad goals: (1) to help all Americans in- crease their life expectancy and improve their quality of life and (2) to eliminate health disparities among different segments of the population. Under these two main goals are 28 areas of focus, ranging from adequate access to medical care to im- provements in diets and physical activity. Objectives have been developed within each focus area.

One focus area, “Nutrition and Overweight,” has been set to promote good health and reduce the chronic diseases associated with poor diet and excess weight. Individual objectives within this focus area (listed in Table 1.4) can help Americans improve their diet and maintain a healthy weight.

As you can see from the table, though the first objective is for 60 percent of Amer- icans to be at a healthy weight by 2010, only 42 percent of Americans met this objective in 2000, the starting year of Healthy People 2010.37 Current research indicates that Americans’ body weights are not decreasing.38 When it comes to eating adequate amounts of fruits, vegetables, and whole grains, which are all beneficial to managing

Healthy People 2010 A set of disease prevention and health promotion objec-

tives for Americans to meet during the

first decade of the new millennium.

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How Does the American Diet Stack Up? 29

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one’s weight, Americans also have plenty of room for improvement. The Healthy People 2020 goals are currently being developed and are planned for release in January 2010.

The Take-Home Message Healthy People 2010 is a set of health ob- jectives for Americans for the first decade of the new millennium. The goals of Healthy People 2010 are to help all Americans increase their life ex- pectancy and improve their quality of life, and to eliminate health disparities among different segments of the population. Nutrition and overweight is one focus area of Healthy People 2010.

How Does the American Diet Stack Up? The food supply in the United States provides an array of nutritious choices to meet the dietary needs of Americans. Fresh fruits and vegetables, whole grains, and lean meats, fish, and poultry are easily accessible and affordable through local grocery stores and farmer’s markets. With such an abundance of healthy foods to choose from, are Americans adopting healthy diets?

The Quality of the American Diet In general, Americans eat too much protein, sugar, sodium, and saturated fat, and too little fiber and some vitamins and minerals. Our low fiber intake is partly due to inadequate consumption of fruits and vegetables and overconsumption of refined grains. Only about 40 percent of Americans eat the minimum of five fruits and veg- etables per day. While dietary fiber intakes are low, sugar accounts for almost 30 per- cent of carbohydrate intake. This is largely due to Americans’ love of soft drinks and other sugary beverages.

The fat intake of most Americans ranges at the high end of the recommendation, at about 33 percent. The American diet contains too much saturated fat but most Americans don’t exceed the dietary cholesterol intake of 300 milligrams per day.

Table 1.4

Healthy People 2010 Nutrition and Overweight Objectives

Objectives Target for

Americans (%) Status of

Americans (%)

Increase the proportion of adults who are at a healthy weight 60 42

Reduce the proportion of adults who are obese 15 23

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

75 28

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 deep yellow vegetables

50 3

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

50 7

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overweight For adults, having a BMI greater than 25.

obesity For adults, having a BMI greater than 30.

Prevalence of obesity

25%

15%–19%

10%–14%

<10%

No data

20%–24%

1990

1998

2006

Figure 1.7 Obesity Trends Among U.S. Adults Over the last two decades, rates of overweight and obesity have risen significantly in the United States.

Source: Centers for Disease Control. 2006. “Overweight and Obesity: Obesity Trends.” www.cdc .gov/nccdphp/dnpa/obesity/trend/maps/index.htm.

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American men meet their recommendations for most vitamins and minerals but women fall short of many nutrients—iron, for example. Americans in general eat too much sodium, but not enough vitamin A, vitamin E, and calcium. In an at- tempt to balance our lack of healthy food choices, 40 percent of Americans take at least one vitamin or mineral supplement per day.39

The lack of a healthy diet may be due to where we eat. Today, 90 percent of Americans eat their meals away from home. Many of us eat in the car, or, as men- tioned earlier, buy prepared foods from the supermarket or take-out meals. When we eat at home, it’s often in front of the television. Research reports that meals eaten while watching television are usually lower in fruits and vegetables and higher in fat and soft drinks. Only one-third of Americans eat family meals at least twice a week and almost 50 percent report never eating together as a family.

One positive habit is that almost 85 percent of Americans eat breakfast. Break- fast provides almost 18 percent of the fiber and energy, and 25 percent of the vita- mins A and C, folate, calcium, and iron, that we consume each day.

Rates of Overweight and Obesity in Americans As people take in more kilocalories than they burn, usually due to sedentary lifestyles, they create a recipe for poor health. This is reflected in the high rates of overweight and obesity in the United States (see Figure 1.7). Along with the weight gain have come higher rates of type 2 diabetes, particularly among children, and increased rates of heart disease, cancer, and stroke. Over 65 percent of American adults and 15 percent of children aged 6 to 19 are currently overweight and 34 percent of adults over the age of 20 are obese.40 Whereas the latest statistics indicate that the epidemic of obesity may be slowing, rates are still too high, and reducing them is a top priority.41

The Take-Home Message The American diet is too high in kilocalo- ries, sodium, added sugar, and saturated fat, and too low in dietary fiber, vita- mins A and E, calcium, and iron. Rates of overweight and obesity among Americans have begun to level off, but are still too high.

What’s the Best Dietary Strategy for Health? There is no question that the body requires all six classes of nutrients to function properly. But is there an advantage to consuming them through food rather than taking them as supplements? Is there more to a healthy diet than just meeting the basic nutrient needs?

The Best Way to Meet Nutrient Needs Is with a Well-Balanced Diet Most credible nutrition experts will tell you that the best way to maintain nutritional health is to eat a variety of whole foods. There are a few reasons for this, one of which is that many foods provide a variety of nutrients. For example, low-fat milk is high in

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carbohydrates and protein, and provides a small amount of fat. Milk is also a good source of the vitamins A, D, and riboflavin, as well as the minerals potassium and calcium, and is approximately 90 percent water by weight.

Whole foods and a well-balanced diet will also provide other dietary com- pounds, such as phytochemicals and fiber, which have been shown to help fight many diseases. At least 900 different phytochemicals have been identified in foods and more are likely to be discovered. The disease-fighting properties of phytochemi- cals may be due to more than the compounds themselves, and instead result from the interactions between phytochemicals and fiber, nutrients, or unknown sub- stances in foods. Thus, these compounds cannot be extracted from foods, put in a pill, and still produce the same positive health effect. Further, whole foods almost al- ways contain more than one beneficial compound. Some foods, such as whole grains, fruits, and vegetables that are high in fiber, are also phytochemical power- houses. Studies have shown that diets rich in these foods fight disease.

That said, some individuals may need a supplement if they cannot meet their nutrient requirements through whole foods alone.

Some Nutrient Needs Can Be Met with a Supplement Individuals with diet restrictions or higher nutrient needs may benefit from taking a supplement in addition to consuming a healthy diet. For example, someone who is lactose intolerant (has difficulty digesting milk products) has to meet his or her cal- cium needs from sources other than dairy products. A calcium-fortified food, such as orange juice, or a calcium supplement would be an option for such an individual. Pregnant women should take an iron supplement because their increased need for this mineral is unlikely to be met through the diet alone. Note that a well-balanced diet and dietary supplements aren’t mutually exclusive. In some situations, the use of enriched and fortified foods can be partnered with dietary supplements as the best nutritional strategy for good health.

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Do you think Elizabeth should take a dietary supplement to im-prove her nutrient intake? Why or why not?

The Take-Home Message A well-balanced diet is the best way to meet all nutrient needs and also provide a variety of compounds that may help prevent chronic diseases. People who cannot meet their nutrient needs through food alone may benefit from taking a supplement.

CAREERS IN NUTRITION Dietetic Student

Joseph Barker is a dietetic student completing his dietetic internship at The Christ Hospital in Cincinnati,

Ohio. Read an interview with Joe about why he wants to become a Registered Dietitian and his advice for others considering a career in nutrition, online at www.aw-bc.com/blake.

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Two Points of View Food Advertisements: Help or Hindrance?

Radley Balko POLICY ANALYST, COLUMNIST

Radley Balko is a senior editor for Reason magazine. He was previously a policy analyst for the Cato Institute, a nonprofit public policy research founda- tion headquartered in Washington, DC, where he specialized in consumer

choice issues, including alcohol and tobacco control, drug prohibition, obesity, and civil liberties. He is a columnist for FoxNews.com and has been published in TIME magazine, the Washington Post, the Los Angeles Times, the Chicago Sun Times, Canada’s National Post, and several other publi- cations. Balko has also appeared on CNN, CNBC, Fox News Channel, NPR, and MSNBC.

Q: Is the consumer pressured by food companies to buy more heavily advertised foods, such as sweetened beverages, cookies, candies, and snack items? Why or why not?

A: I doubt it. Advertising’s two main purposes are to foster brand loyalty and to bump customers up to a higher (read: more expensive) line of product. Most people are smart enough to know that fruits and vegetables are bet- ter for them than cookies and chips. If you’ve made the conscious decision to eat healthy, television commercials aren’t going to bring you back to pizza and doughnuts. If more Americans are skipping the produce section for the snack aisle, that’s of course their prerogative. I don’t blame the food companies for what ultimately is an exer- cise in personal choice.

Q: Is there research to support your point of view? A: My point of view is driven primarily by philosophy—what

we put into our mouths ought to be our own business, not the business of nutrition activists, government bu- reaucrats, or politicians. I don’t think we need much re- search to prove the point that most of us know that produce is better for our health than ice cream. One thing that often gets lost in these debates is just how healthy America really is. Life expectancy continues to reach all- time highs in America. Deaths from heart disease, can- cer, and stroke—the country’s three biggest killers—have been in decline for 15 years. Our waistlines may be get- ting thicker, but it isn’t clear that that poses any large- scale threat to our overall health.

Dr. Margo G. Wootan, DSc DIRECTOR OF NUTRITION POLICY, CENTER FOR SCIENCE IN THE PUBLIC INTEREST

Dr. Margo Wootan, DSc, is the director of nutrition policy at the Center for Sci- ence in the Public Interest (CSPI), a health advocacy organization that spe- cializes in nutrition and obesity. Dr.

Wootan received her BS in nutrition from Cornell University and her doctorate in nutrition from Harvard University’s School of Public Health. Dr. Wootan cofounded the National Alliance for Nutrition and Activity (NANA).

Q: Is the consumer pressured by food companies to buy more heavily advertised foods, such as sweetened beverages, cookies, candies, and snack items? Why or why not?

A: Yes, company practices have a big effect on people’s food preferences and choices. While some experts are still scratching their heads and wondering why obesity rates have been skyrocketing in adults and children, all you have to do is look around to see why: The existing food environment is not supportive of healthy choices. There are many powerful forces—and powerful companies—working against Americans’ efforts to eat well and maintain a healthy weight. They include advertis- ing and marketing, large portion sizes, eating out, food everywhere, too many sugary soft drinks, and junk food in schools.

Q: Is there research to support your point of view? A: There’s no disputing the fact that the goal of food mar-

keting is to influence children’s food choices. Companies clearly believe that marketing works—or they wouldn’t spend billions of dollars each year marketing to children. Also, studies demonstrate that food advertising gets chil- dren’s attention and affects their food choices, food pur- chases, and what they ask their parents to purchase. A comprehensive study by the National Academies’ Insti- tute of Medicine strongly concluded that marketing works—it affects children’s diets and health. Any parent can tell you that ads and cartoon characters on food packages affect not only which foods their children ask them to purchase, but which foods their kids are willing to eat.

With so much money being spent on the advertising of foods, is it easy for the consumer to eat a healthy diet? Two experts share their point of view.

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Q: How can the food industry help consumers purchase and eat more fruits and vegetables?

A: Companies should market fruits and vegetables using television, print, and other ads, cartoon characters on packages or stickers on fruits and vegetables, Internet marketing, and other marketing techniques now used mostly to market foods of poor nutritional quality. Market- ing healthy foods can work. Sales of Darling clementines increased 25 percent after they put Nickelodeon’s Dora the Explorer and SpongeBob SquarePants on the packs.

Food manufacturers and restaurants also should de- velop new products and reformulate existing products to add more fruits and vegetables. It is great that McDonald’s has Apple Dippers, Fruit ’n Yogurt Parfaits, and salads, but that doesn’t give people enough choices to find some- thing that they really like. There are hundreds of other fruits and vegetables that could be added to the menu.

Q: What responsibility do food companies have to help Americans eat healthfully?

A: Of course, it is up to individuals to decide what they will eat. But, we need to recognize that it’s not easy to exer- cise personal responsibility in our junk-food culture. While obesity rates have increased over the last 20 years, there’s no evidence to show that over that time period willpower has declined or that parents love their children any less.

The Center for Science in the Public Interest (CSPI) is working to change policies and the “food environment” to make healthy eating easier. [Its efforts] include getting soda and junk food out of schools, stopping junk-food marketing to kids, and providing calorie labeling on fast- food menus. Such policies support personal responsibil- ity, parental authority, and parents’ ability to feed their children a healthy diet. For example, it is parents’ respon- sibility to keep their children from playing in traffic, but that doesn’t mean we don’t need laws that prohibit peo- ple from recklessly driving 80 miles per hour through resi- dential neighborhoods. Similarly, we need policies that make it possible for children—and adults—to eat well and achieve a healthy weight.

Dr. Margo G. Wootan, DSc, continued Radley Balko, continued

Q: How can the food industry help consumers purchase and eat more fruits and vegetables?

A: It isn’t so much what the food industry can do as what the government can do—or should stop doing. I do agree with the nutrition activists that government should stop subsidizing corn, and should lift its tariffs on sugar. These policies create unnatural distortions in the food market. Another suggestion: Access seems to be the main problem when it comes to produce and low-income people. Big-box stores such as Wal-Mart have figured out how to get inexpensive, high-quality produce to low- income consumers. We should be applauding when big- box grocers open stores in urban areas, not chasing them out of town.

Q: What responsibility do food companies have to help Americans eat healthfully?

A: Individual Americans are responsible for their own diets, not food companies. A company’s only real responsibility is to (1) make profits for its shareholders, and (2) be hon- est and forthright about what it’s putting on the market. If a food company is misleading or untruthful about its product, then yes, it should be held accountable. But to offer one example, Baskin-Robbins makes ice cream. It has always made ice cream. I see no reason why a com- pany that has always made a product meant to be con- sumed as an indulgence has any “responsibility” to help Americans “eat healthfully.” If Americans truly want to eat healthy, companies that produce healthy foods will flour- ish. But I see no reason why a fast-food company, for ex- ample, should take a loss or go out of business pushing health food no one wants to buy.

Food Advertisements: Help or Hindrance? continued

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The Top Ten Points to Remember

1. Food choices are influenced by personal taste, culture, environment, social life, trends, weight concerns, body image, advertising, time, convenience, cost, and health beliefs. People often eat out of habit, in response to emotions, and, of course, because food is delicious.

2. Nutrition is the science that studies the nutrient com- ponents and health effects of food, as well as how food is digested, absorbed, and metabolized by the body. Nutritional genomics is the study of how foods in the diet may affect gene expression.

3. Nutrition plays an important role in preventing many of the leading causes of death in the United States, including heart disease, cancer, stroke, and type 2 diabetes.

4. There are six categories of nutrients: carbohydrates, lipids, proteins, vitamins, minerals, and water. The body needs a combination of these nutrients in spe- cific amounts to stay healthy. Carbohydrates, lipids, proteins, and vitamins are organic because their chem- ical composition includes the element carbon. They also contain the elements hydrogen and oxygen, and protein contains nitrogen. Minerals are inorganic be- cause they do not contain carbon; minerals are single elements that are not changed in the body. Water is also inorganic and comprised of hydrogen and oxygen.

5. Carbohydrates, fats, and proteins provide energy in the form of kilocalories. Carbohydrates are the body’s pre- ferred source of energy. Fats also provide energy, and serve other roles, including insulating the body and cushioning internal organs. The primary role of di- etary protein is to build and maintain body tissues, in- cluding muscles and organs. Vitamins and minerals do not provide energy but are necessary to properly me- tabolize carbohydrates, fats, and protein. Many vita- mins aid enzymes in the body. Water is vital for many functions: It bathes the inside and outside of the cells, helps maintain body temperature, and acts as a lubri- cant and protective cushion.

6. Carbohydrates and proteins each contain 4 kilocalories per gram, while fats contain 9 kilocalories per gram. Alcohol, though not a nutrient, also contains energy at 7 kilocalories per gram.

7. Sound nutrition information is the result of numerous scientific studies, based on the scientific method, that are reviewed by the medical and scientific community. Reliable nutrition information can be obtained from

Registered Dietitians, licensed nutritionists, or profes- sionals with advanced degrees in nutrition.

8. Nutrient assessment methods include assessing health history, collecting anthropometric and laboratory data, clinical observation, and dietary intake surveys. Malnutrition occurs when too many or too few nutri- ents and/or kilocalories are consumed. Eating too few kilocalories or nutrients will result in being under- nourished; consuming too many kilocalories or nutri- ents results in being overnourished. The nutritional status of population groups is determined by national surveys, including the National Health and Nutrition Examination Survey (NHANES), the Behavioral Risk Factor Surveillance System (BRFSS), and the Framing- ham Heart Study. Healthy People 2010 is a set of na- tional health objectives designed to increase the quality and years of life and eliminate the disparities in the health of Americans.

9. Most Americans are not meeting all their nutrient needs without exceeding their kilocalorie require- ments. The average American diet is high in sodium, saturated fat, and kilocalories, but low in vitamin E, calcium, and fiber.

10. Eating a well-balanced diet is the best way to meet nu- trient and health needs. Vitamin and mineral supple- ments can help complete a healthy diet but should not replace foods.

Test Your Knowledge 1. Which of the following influences food choice?

a. ethnic background b. time constraints c. emotions d. all of the above

2. Nutrition is a. the study of genes, how they function in the body, and

the environment. b. the study of how the body functions. c. the scientific study of nutrients and compounds in

foods that nourish and affect body functions and health.

d. the study of hormones and how they function in the body.

3. The energy in foods is measured in a. grams. b. carbohydrates. c. micrograms. d. kilocalories.

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4. Minerals are considered an organic nutrient because they contain the element carbon. a. true b. false

5. Which of the following functions do nutrients perform in the body? a. providing energy b. providing structure for bone, muscle, and other tissues c. facilitating metabolism d. all of the above

6. A slice of whole-wheat bread contains 1 gram of fat, 18 grams of carbohydrate, and 4 grams of protein. How many kilocalories does it contain? a. 65 kilocalories b. 72 kilocalories c. 89 kilocalories d. 97 kilocalories

7. You want to lose weight and decide to seek the help of a professional to have your diet assessed. Which of the following individuals would be the most credible source of information? a. an employee at the local health food store b. a personal trainer at the gym c. a Registered Dietitian d. your aunt e. your roommate, who runs for the campus track team

8. The two broad goals of Healthy People 2010 are a. to help Americans increase their life expectancy and

improve their quality of life. b. to increase the hours Americans sleep each night. c. to eliminate health disparities among different

segments of the population. d. a and c only.

9. The first step in the scientific method is to a. make observations and ask questions. b. form a hypothesis. c. do an experiment. d. develop a theory.

10. When exploring a website that provides nutrition and health information, which of the following should you consider to assess its content? a. who wrote it b. when it was written c. when it was last updated d. all of the above

Answers 1. (d) Food choices are influenced by many factors, includ-

ing ethnic background, the limited time for food prepa- ration and/or shopping, and emotions.

2. (c) Nutrition is the science related to how nutrients are used in the body and how they affect health. The study of genes is called genomics. Physiology is the study of how the body functions. The study of hormones is called endocrinology.

3. (d) The energy content of food is measured in kilocalo- ries. Grams and micrograms are used to measure amounts of food and vitamins and minerals. Carbohy- drates are nutrients, not a unit of measure.

4. (False) Minerals are actually inorganic nutrients because they do not contain carbon. Nutrients that do contain carbon, including protein, carbohydrates, lipids, and vi- tamins, are classified as organic.

5. (d) Nutrients help perform numerous vital body func- tions. Carbohydrates, protein, and fats provide energy in the form of kilocalories; protein and some minerals help build body tissues; and several vitamins and minerals are essential during metabolic processes.

6. (d) A slice of bread contains 97 kilocalories. Use this cal- culation (18 g � 4) � (4 g � 4) � (1 g � 9).

7. (c) Unless the health food store employee, personal trainer, your aunt, and your roommate are Registered Dietitians, they are not qualified to provide nutrition counseling.

8. (d) The two broad goals are increasing life expectancy and the quality of life, as well as reducing health dispari- ties among Americans. Increasing the amount of hours Americans sleep isn’t a goal of Healthy People 2010.

9. (a) The scientific method begins with scientists observ- ing and asking questions. From this step, a hypothesis follows. The scientists will then test their hypothesis using an experiment. After many experiments confirm their hypothesis, a theory will be developed.

10. (d) When reading nutrition and health information on the Internet, it is very important to make sure the source is qualified to provide the information. Because you also need to assess if the information is current, you should find out when it was written and if it has been or needs to be updated.

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Answers to Myths and Misconceptions

1. True. Taste is the strongest motivating factor for choosing foods. However, numerous other factors, including cul- ture, social setting, health, advertising, habit, emotion, time, cost, and convenience, also play a role in food choice.

2. False. Heart disease is the leading cause of death among Americans. The good news is that your diet can play an important role in preventing it.

3. False. Dietary fat is essential for several body functions, including its role in providing energy.

4. False. Whereas alcohol does provide kilocalories, elimi- nating it from the diet would not result in malnutrition. Therefore, alcohol is not a nutrient.

5. True. Kilocalories are the measure of energy in foods. 6. False. Like carbohydrate, protein provides 4 kilocalories

per gram, while fat provides 9 kilocalories per gram. There- fore, fat provides more energy per gram than protein.

7. False. The 24-hour food record is one tool for gathering information about the quality of an individual’s diet, but it doesn’t reveal a complete picture. Long-term food records, interviews, and anthropometric data are addi- tional tools that can help a dietitian assess an individual’s eating habits.

8. False. There is no standard or legal definition of the word “nutritionist,” so it does not convey expert status. In fact, anyone can call himself or herself a nutritionist.

9. False. Although the obesity rate in American adults has remained the same over the past five years, 34 percent of adult Americans are still considered obese.

10. False. There is no replacement for whole foods in a healthy diet. A supplement can augment a healthy diet, but it can’t replace it.

Web Support Examples of reliable nutrition and health websites include: ■ Agricultural Research Service: www.nal.usda.gov/fnic/

foodcomp ■ American Cancer Society: www.cancer.org ■ American College of Sports Medicine: www.acsm.org ■ American Dietetic Association: www.eatright.org ■ American Medical Association: www.ama.assn.org ■ Center for Science in the Public Interest: www.cspinet.org ■ Centers for Disease Control: www.cdc.gov ■ Food and Drug Administration: www.fda.gov ■ Food and Nutrition Information Center: www.nal.usda

.gov/fnic

■ National Institutes of Health: www.nih.gov ■ Shape Up America!: www.shapeup.org ■ Tufts University Health and Nutrition Newsletter:

www.healthletter.tufts.edu ■ U.S. Department of Agriculture: www.nutrition.gov ■ Vegetarian Resource Group: www.vrg.org

References 1. Wansink, B. and J. Sobal. 2007. Mindless Eating: The 200 Daily Food

Decisions We Overlook. Environment and Behavior 39:106–123. 2. Glanz, K., M. Basil, E. Maibach, J. Goldberg, and D. Snyder. 1998. Why

Americans Eat What They Do: Taste, Nutrition, Cost, Convenience, and Weight Control Concerns as Influences on Food Consumption. Journal of the American Dietetic Association 98:1118–1126.

3. Keskitalo, K., A. Knaapila, M. Kallela, A. Palotie, M. Wessman, S. Sam- malisto, L. Peltonen, H. Tuorila, and M. Perola. 2007. Sweet Taste Pref- erences Are Partly Genetically Determined: Identification of a Trait Locus on Chromosome 16. American Journal of Clinical Nutrition 86:55–63.

4. Cooke, L. J. and J. Wardle. 2005. Age and Gender Differences in Children’s Food Preferences. British Journal of Nutrition 93:741–746.

5. Mennella, J. A. 2007. Flavor Programming During Breast Feeding. In Breast-feeding: Early Influences on Later Health. Hingham, MA: Kluwer Academic Press/Plenum.

6. Keskitalo, K. et al. 2007. American Journal of Clinical Nutrition. 7. Drewnowski, A. and M. R. Greenwood. 1983. Cream and Sugar: Human

Preferences for High-Fat Foods. Physiology & Behavior 30:629–633. 8. Drewnowski, A. 1997. Taste Preferences and Food Intake. Annual Review

of Nutrition 17:237–253. 9. Mennella, J. A. 2007. Sweet Taste and Development. In Handbook of the

Senses: Olfaction and Taste. G. Smith, D. S. Firestein, and S. Firestein, eds. San Diego: Elsevier.

10. Sneijder, P. and H. F. Te Molder. 2005. Disputing Taste: Foods Pleasure as an Achievement in Interaction. Appetite 45:51–61.

11. Wansink, B. 2004. Environmental Factors That Increase The Food Intake and Consumption Volume of Unknowing Consumers. Annual Review of Nutrition 24:455–470.

12. Freeland-Graves, J. and S. Nitzke. 2002. Total Diet Approach to Commu- nicating Food and Nutrition Information. Journal of the American Dietetic Association 102:100–108.

13. Horovitz, B. 2004. Pizza People Prepare Super Bowl Blitz. USA Today. Accessed June 2008. Available at www.usa.com.

14. Mintel International Group. 2005. Cinemas and Movie Theaters—United States, Mintel Reports-USA., Leisure-USA. Accessed June 2008. Available at www.reports.mintel.com.

15. Laux, M. 2006. Organic Food Trends Profile. Agriculture Marketing Resource Center. Accessed June 2008. Available at www.agmrc.org/agmrc/ markets/Food/organicfoodtrendsprofile.htm.

16. Food Consumption Trends. 2008. Accessed June 2008. Available at www.agmrc.org.

17. Carels, R. A., K. Konrada, and J. Harper. 2007. Individual Differences in Food Perceptions and Calorie Estimation: An Examination of Dieting Status, Weight, and Gender. Appetite 49:450–458.

18. Kolodinsky, J., J. R. Harvey-Berino, L. Berlin, R. K. Johnson, and T. W. Reynolds. 2007. Knowledge of Current Dietary Guidelines and Food Choice by College Students: Better Eaters Have Higher Knowledge of Dietary Guidance. Journal of the American Dietetic Association 107:1409–1413.

19. Mintel International Group. 2005. 20. Gallo, A. 1999. Food Advertising in the United States. In America’s Eating

Habits: Changes and Consequences. Edited by Economic Research Service. Accessed June 2008. Available at www.ers.usda.gov.

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Mediated by Food and Beverage Consumption during Viewing Time or Reduced Leisure-Time Physical Activity? American Journal of Clinical Nutrition 87:1148–1155.

33. Afman, L. and M. Muller. 2007. Nutrigenomics: From Molecular Nutrition to Prevention of Disease. Journal of the American Dietetic Asso- ciation 106:569–576.

34. Osowski, J. M., T. Beare, and B. Specker. 2007. Validation of a Food Frequency Questionnaire for Assessment of Calcium and Bone-Related Nutrient Intake in Rural Populations. Journal of the American Dietetic Association 107:1349–1355.

35. Wang, D., M. Kogashiwa, and S. Kira. 2006. Development of a New Instrument for Evaluating Individuals’ Dietary Intakes. Journal of the American Dietetic Association 106:1588–1593.

36. Briefel, R. R. 2007. Dietary Methodology: Advancements in the Develop- ment of Short Instruments to Assess Dietary Fat. Journal of the American Dietetic Association 107:744–749.

37. Healthy People 2010. Health Finder: Nutrition and Overweight. 2000. Accessed June 2008. Available at www.healthypeople.gov.

38. Centers for Disease Control. 2005. Overweight and Obesity: Obesity Trends. Accessed June 2008. Available at www.cdc.gov.

39. Abbot, J. M. and C. Byrd-Bredbenner. 2007. The State of the American Diet: How Can We Cope? Topics in Clinical Nutrition 22(3): 202–233.

40. Centers for Disease Control. 2005. Overweight and Obesity: Obesity Trends. Accessed June 2008. Available at www.cdc.gov.

41. National Center for Health Statistics. 2007. New CDC Study Finds No Increase in Obesity Among Adults, but Levels Still High. Edited by the National Center for Health Statistics. Accessed June 2008. Available at www.cdc.gov.

21. Linn, S. and C. L. Novosat. 2008. Calories for Sale: Food Marketing to Children in the Twenty-First Century. Annals of the American Academy of Political and Social Science 615:133–155.

22. Story, M. and S. French. 2004. Food Advertising and Marketing Directed at Children and Adolescents in the U.S. International Journal of Behav- ioral Nutrition and Physical Activity 1:1–17.

23. Blisard, N. 1999. Advertising and How We Eat: The Case of Dairy Products. In America’s Eating Habits: Changes and Consequences. Edited by Economic Research Service.

24. National Turkey Federation. 2006. Accessed June 2008. Turkey Facts and Trivia. Available at www.eatturkey.com/consumer/history/history.html.

25. Retail in the USA 2004–2007. Available at www.scaa.org. 26. Starbuck’s Company Fact Sheet. 2008. Accessed June 2008. www

.starbucks.com/aboutus/Company_Factsheet.pdf. 27. U.S. Department of Agriculture. 2005. Table 12 in Food CPI, Prices and

Expenditure Tables: Food Expenditure Table. Accessed June 2008. Available at www.ers.usda.gov/Briefing/CPIFoodAndExpenditures/Data/ table12.htm.

28. Drewnowski, A. and N. Darmon. 2005. The Economics of Obesity: Dietary Energy Density and Energy Cost. American Journal of Clinical Nutrition 82:265S–273S.

29. Sturm, R. 2002. The Effects of Obesity, Smoking, and Drinking on Medical Problems and Costs. Health Affairs 21:245–253.

30. French, S. A. 2003. Pricing Effects on Food Choices. Journal of Nutrition 133:841S–843S.

31. Mintel International Group. 2006. Breakfast Foods: The Consumer—US. Accessed June 2008. Available at www.marketresearch.com.

32. Cleland, V. J., M. D. Schmidt, T. Dwyer, and A. J. Venn. 2008. Television Viewing and Abdominal Obesity in Young Adults: Is the Association

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2

1. Having a balanced diet means eating the same number of servings from each food group. T/F

2. Nutrient density refers to foods that are lower in weight relative to volume. T/F

3. The current Dietary Reference Intakes for vitamins and minerals are set at the amount you should consume daily to maintain good health. T/F

4. The Recommended Dietary Allowance of a nutrient is based on an estimated average requirement, or EAR. T/F

5. According to the USDA, there are five basic food groups. T/F

6. If you follow the advice in the Dietary Guidelines for Americans you can reduce your risk of dying from chronic diseases such as heart disease, high blood pressure, and diabetes mellitus. T/F

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7. Americans typically have a good sense of portion sizes. T/F

8. All packaged foods must contain a food label. T/F

9. A nutrient claim on the food label boasts that the food contains a significant source of a specific nutrient. T/F

10. Exchange lists are similar to MyPyramid except the foods are based on the carbohydrate, protein, fat, and kilocalorie contents. T/F

See page 78 for answers.

Tools for Healthy Eating

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Chapter Objectives After reading this chapter, you will be able to:

1. Describe the four components of a healthy diet.

2. Define the terms nutrient and energy density.

3. Discuss the differences between the EAR, AI, RDA, UL, and AMDR.

4. Describe the principles in the 2005 Dietary Guidelines for Americans.

5. Explain the evolution of the tools developed to improve Americans’ eating habits.

6. Define the food groups, number of servings or portion sizes, and typical foods represented in the MyPyramid food guide.

7. Identify the required components of a food label.

8. Determine the nutritional ade- quacy of a food based on the food label and Nutrition Facts panel.

9. Describe the three types of nutrient claims that are regulated by law.

10. Plan a balanced diet using the ex- change list system or MyPyramid as a guide.

Do you think Emma needs to change her eating habits to return to feeling ener- getic and healthy? Are there guidelines she can follow to ensure that her diet pro- vides enough essential nutrients? Where can she go for reliable advice about how to plan her diet? We’ll answer all of these questions as we explore the numerous resources for diet planning in this chapter.

B y the end of her freshman year of college, Emma, a 19-year-old mathematics major, is anxious to

return home to relax and enjoy her mother’s healthy cooking. For the first time in her life, she feels like she isn’t eat- ing regular meals, sits for too many hours in front of her computer, snacks on too much junk food, and hardly ever exer- cises. She often feels tired and sluggish, and wonders if she’s getting enough nu- trients in her diet.

balance A diet that provides the correct proportion of nutrients to maintain health

and prevent disease.

adequate A diet that provides all the es- sential nutrients, fiber, and energy neces-

sary to maintain health and prevent

disease.

What Is Healthy Eating? Healthy eating involves the key principles of adequacy, balance, variety, and moderation. As a student, you are probably familiar with these principles from other areas of your life. You balance your time between work, school, and family and friends. You engage in a vari- ety of activities to avoid being bored, and enjoy each in moderation, as spending too much time on one activity (like working) will disrupt the amount of time you can spend on oth- ers (like studying or socializing). A chronic imbalance of any one of these activities will af- fect the others. If you regularly forgo sleep in order to work extra hours at a job, sleep deprivation will affect your ability to stay awake in class, which will hamper your studies. Your unbalanced life would soon become unhealthy and unhappy. Likewise, your diet must be adequate, balanced, varied, and moderate in order to be healthy.

Healthy Eating Means Adequate Intake of Nutrients Eating healthy means consuming a diet adequate in energy, dietary fiber, and all the essential nutrients the body needs to prevent disease. A diet that is inadequate can cause undernutrition. A diet that consists of only bread and rice, for example, and few or no milk products and vegetables would lack several essential nutrients, and would be considered inadequate. If the diet lacks a particular nutrient, such as cal- cium, over time the body suffers from malnutrition and begins to show symptoms of the deficiency, such as muscle cramping, muscle spasms, twitching, and, eventu- ally, reduced bone mass. Consuming adequate amounts of all essential nutrients is key to avoiding nutrient deficiencies, and, in many cases, chronic disease.

Healthy Eating Involves Balance between Food Groups Having a balanced diet means not eating too much of any one type of food. A meal that contains foods from the grain, vegetable, fruit, meat, and dairy groups, such as a turkey-and-cheese sandwich plus an apple at lunch, provides the proper proportion of foods from each of the food groups. This balancing act prevents overnutrition of a specific nutrient, such as fat,1 or too many kilocalories, which can lead to over- weight and obesity. Use the Self-Assessment to determine if your diet is balanced.

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Healthy Eating Means Consuming a Variety of Foods Choosing a variety of foods will improve the quality of the diet because the more varied the food choices, the better the chance of consuming adequate amounts of all the essential nutrients.2 Even within one food group, the nutrient composition of foods can vary dramatically. For example, while broccoli is a good source of folate, it has less than half the vitamin A of a carrot. Similarly, if the only fruit you eat is ba- nanas, your diet would include an excellent source of potassium, but little vitamin C. Because no single food or food group contains everything you need to be healthy, you should choose a variety of foods from each food group and among food groups each day to achieve a healthy diet. This is the basic principle of the Fruits and Vegeta- bles, More Matters campaign developed by the Produce for Better Health Foundation and the Centers for Disease Control and Prevention.3 This campaign promotes eat- ing a variety of colorful fruits and vegetables, which are rich in vitamins, minerals, fiber, and phytochemicals, each day to help reduce the risk of cancer and heart dis- ease, and slow the effects of aging.

Healthy Eating Means Moderate Intake of All Foods According to many registered dietitions, “there are no good or bad foods, just good or bad habits.” What they mean is that all foods—even less nutritious foods—can be part of a healthy diet, as long as they are consumed in moderation. Foods such as sweets and fried or packaged snack foods should be eaten only in small amounts to avoid consuming too much sugar and fat. Eating too much of these foods can also mean taking in more energy than you need, potentially resulting in weight gain. Fi- nally, these foods can displace more nutrient-rich choices, resulting in a diet that lacks essential nutrients. Even some healthy foods, such as nutrient-dense nuts, can be high in kilocalories and should be consumed in moderation. Healthy eating doesn’t

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Self-Assessment

Does Your Diet Have Proportionality? Answer “yes” or “no” to the following questions:

1. Are grains the main food choice at all your meals? Yes � No �

2. Do you often forget to eat vegetables? Yes � No �

3. Do you typically eat fewer than three pieces of fruit daily? Yes � No �

4. Do you often have fewer than three cups of milk daily? Yes � No �

5. Is the portion of meat, chicken, or fish the largest item on your dinner plate? Yes � No �

Answer If you answered “yes” to three or more of these questions, it is very likely that your diet lacks propor- tionality. You can use the information in this chapter to help improve the proportionality of your diet.

A meal that contains foods from every food group is part of a balanced, healthy diet.

overnutrition Consuming excess nutri- ents or energy.

variety A diet that contains a mixture of different food groups and foods within

each group.

moderation A diet that provides reason- able but not excessive amounts of foods

and nutrients.

malnutrition The long-term outcome of consuming a diet that is either lacking in the

essential nutrients or contains excess energy;

an imbalance of nutrients in the diet.

undernutrition A state of inadequate nu- trition whereby a person’s nutrient and/or

energy needs aren’t met through the diet.

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mean you can’t enjoy your favorite foods. It simply means eating those foods in moderation by limiting the portion size and number of servings you eat.

Many people overestimate the appropriate portion sizes of foods. An entire body of research is devoted to studying factors that affect how much we put on our plates (see the feature box, “Portion Distortion,” on page 44 for more on this topic), but the important point is that, in general, we consume two or more por- tions of a given food at a given meal. Fortunately, one easy way to tell if you are helping yourself to too much of a food is to use a visual that represents a standard portion of the food, such as a cup of vegetables, three ounces of meat, or 1 table- spoon of salad dressing. See Figure 2.1 for examples of visuals you can use to esti- mate portion sizes.

Healthy Eating Involves Nutrient-Dense Foods Healthy eating includes not only choosing foods based on these key principles of ad- equacy, balance, moderation, and variety, but also choosing foods that are nutrient dense. Nutrient dense means that foods are high in nutrients, such as vitamins and minerals, but low in energy (kilocalories). Nutrient-dense foods provide more nutri- ents per kilocalorie (and in each bite) than less nutrient-dense foods.4 Fresh fruits and vegetables, for example, are nutrient dense because they are high in B vitamins, vitamin C, minerals such as calcium and magnesium, and fiber, while usually pro- viding fewer than 60 kilocalories per serving.

Nutrient-dense foods are also low in fat and added sugars. To illustrate this concept, compare the nutrient density of two versions of the same food: a baked

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a

b

c

d

A woman’s palm is approximately 3 ounces of cooked meat, chicken, or fish

A woman’s fist is about 1 cup of pasta or vegetables (a man’s fist is the size of about 2 cups)

About 1 tablespoon of vegetable oil

The tip of the finger is about 1 teaspoon of margarine

Figure 2.1 What’s a Portion Size? Eat with Your Hands! Your hands can help you estimate the appropriate portion size of foods.

nutrient dense A measurement of the nutrients in a food compared with the kilo-

calorie content; nutrient-dense foods are high

in nutrients and low in kilocalories.

Choosing nutrient-dense foods you enjoy is a key ingredient for eating a healthy diet.

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potato and potato chips (Figure 2.2). Although a medium baked potato and one ounce of potato chips have about the same number of kilocalories, the baked po- tato provides much higher amounts of vitamins and minerals than the deep-fried chips.

Though many foods, such as broccoli and carrots, are clearly nutrient dense, and other foods, such as potato chips and doughnuts, are clearly not, not all foods fit neatly into these two categories. Items such as dried fruits, nuts, peanut butter, and avocados are high in kilocalories, but they are also excellent sources of important nutrients, including polyunsaturated fatty acids, calcium, and iron. Other foods, such as whole milk or yogurt, contain the same nutrients, but higher amounts of fat and kilocalories than their nonfat or low-fat counterparts. These higher fat versions still provide significant amounts of calcium, riboflavin, vitamins A and D, and pro- tein. Some foods, such as fruit-flavored yogurt and some fortified cereals, contain added sugars in addition to several essential nutrients. Do you think these foods can be considered nutrient dense?

In all of these scenarios, the answer is yes. Whereas nutrient dense usually means high in nutrients and low in energy, foods that are high in nutrients and high in en- ergy can also be considered nutrient dense. The key is to be aware of the extra kilo- calories and make up for them elsewhere in the diet. If you don’t like skim milk and won’t drink it, but do enjoy the taste of whole milk, then drinking whole milk is preferable to drinking non-calcium-containing beverages, such as soda. Just remem- ber that unless you compensate for the extra kilocalories (by cutting that night-time cookie, for example), you may gain weight.

Healthy Eating Involves Low-Energy-Dense Foods In contrast to nutrient density, energy density refers to foods that are high in en- ergy but low in weight or volume, such as that potato chip. A serving of deep- fried chips weighs much less than a plain baked potato, but is considerably higher in fat and kilocalories. Therefore, the chip contains more energy per gram. A big, leafy green salad, on the other hand, is large in volume but low in energy density, due to its high water content.

Most high-fat foods are considered energy dense.5 This is because fat has 9 kilo- calories per gram and is thus 2.25 times more energy dense than either carbohydrates or protein at 4 kilocalories per gram. Individuals who choose low-energy-dense foods will generally have diets that are lower in fat and higher in nutrient content.

Eating a low-energy-dense diet can sometimes be the key to weight loss. Recent studies have found that leaner individuals ate more low-energy-dense foods and fewer kilocalories, while consuming a greater volume of food, compared with their obese counterparts.6 Eating low-density foods means larger portions for the same number of kilocalories.

Even modest changes in dietary intake may promote and help maintain weight loss7 over time.8 One reason for this may be improved satiety and appetite control.9

Eating a larger volume of low-energy foods improves satiety and decreases hunger. In other words, low-energy foods will “fill you up before they fill you out.”

What Is Healthy Eating? 43

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100

0

20

40

60

80

P e rc

e n t D

R I*

Potato chips, 1 oz

Baked potato, medium

Vitamin CPotassiumFolate

Figure 2.2 Which Is the Healthier Way to Enjoy Potatoes? Whereas one ounce of potato chips and one medium baked potato have similar amounts of kilocalories, their nutrient content is worlds apart. A baked potato contains more folate, potassium, and vitamin C, and fewer kilocalories, than its fried counterpart. The baked potato is therefore more nutrient dense than potato chips. *Note: Based on the percentage of the DRI for 19-to-50-year-old males. All these percentages apply to females in the same age range, except for vitamin C. Females have lower vitamin C needs than males so a baked potato provides over 20 percent of the DRI of this vitamin for women.

Potatoes are naturally low in fat, unless they are fried, which increases the number of kilocalories. More kilocalories for fewer nutrients means a lower nutrient density, and a higher energy density.

energy density A measurement of the kilocalories in a food compared with the

weight (grams) of the food.

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44 Chapter 2 . Tools for Healthy Eating

Portion vs Serving Size: What’s the Difference?

The USDA defines a portion as the amount of food eaten at one sitting rather than a standard size of the food. In con- trast, a serving size (a term that’s only used on nutrient labels) is a standard amount of food for which the nutrient composition is presented. We can illus- trate the difference with a food that peo- ple often pile on their plates, such as spaghetti. A generous helping of cooked spaghetti that spills over the edge of a plate is probably equal to about 3 cups. According to MyPyramid, a standard serving size of pasta is 1/2 cup. A portion of 3 cups of cooked pasta is therefore six servings, which contains more than 600 kilocalories!

Unfortunately, many of us frequently underestimate the portion sizes we put on our plates, and therefore overcon- sume foods during snack and meal times.1 The table below illustrates several foods that people commonly consume in oversized portions.

How Have Portion Sizes Changed?

If your great-grandmother treated her- self to a Hershey’s chocolate bar when it was first introduced, at the beginning of the last century, she would have paid a small amount of money for about 0.6 ounce of chocolate. Today the same milk chocolate bar is sold in 1.6-, 2.6-, 4.0-, 7.0-, and 8.0-ounce weights. When McDonalds first introduced french fries in 1954, the standard serving weighed 2.4 ounces. Although a small 2.4-ounce size is still on the menu, you can also choose the medium french fries weighing 5.3 ounces or the large at 6.3 ounces. Twenty years ago, a cup of coffee was 8 ounces and just 45 kilocalories with

added milk and sugar. Today, consumers enjoy 16-ounce lattes on their way to work, to the tune of 350 kilocalories.2

The restaurant industry has appealed to Americans’ interest in getting more food for less money with larger portion sizes at relatively low costs.3 Americans eat out more often than they did in the past, and are offered a wide variety of in- expensive choices sold in larger than nor- mal portion sizes that often exceed the standards defined by the federal govern-

ment.4 And most people are un- aware of the changes in their

portion sizes.5 Though get- ting more food for the

money may be beneficial on the wallet, the health costs may be higher than Americans realize.

Portion Distortion

The typical portion of pasta (left) is often much larger than the recommended serving size (right).

Comparison of Portion Sizes of Common Foods

Food Typical Portion MyPyramid Serving Size FDA Label

Cooked pasta 2.9 cups 0.5 cup 1.0 cup

French fries 5.3 oz 10 fries 2.5 oz

Bagel 4.4 oz 2.0 oz 2.0 oz

Muffin 6.5 oz 1.5 oz 2.0 oz

Cookie, chocolate chip 4.0 oz 0.5 oz 1.1 oz

Beer 15.4 fluid oz 12.0 fluid oz 8.0 fluid oz

Soda 23.0 fluid oz 12.0 fluid oz 8.0 fluid oz

Source: Adapted from Young, L. R. and M. Nestle. 2003. Expanding Portion Sizes in the U. S. Marketplace: Implications for Nutrition Counseling. Journal of the American Dietetic Association 103:231–234.

serving size A recommended portion of food that is used as a standard reference

on food labels.

portion The quantity of a food usually eaten at one sitting.

Hershey’s milk chocolate bars now come in several sizes, including 1.6-, 2.6-, 4.0-, 7.0-, and 8.0-ounce versions.

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Portion Distortion 45

In addition to restaurant and packaged foods, home-cooked meals have also bulked up over the past few decades. If you were to measure your grandmother’s favorite dinner plates, they would likely be much smaller, about 9 inches in diameter, than the plates in your cupboard, which probably measure closer to 11.5 inches across. The bigger the plate, the more food you are likely to add to it. Further, the larger portions you put on your plate influence your perception of what is nor- mal. Thus, a large plate covered with pasta appears to be normal, whereas the 1⁄2 cup of pasta suggested by the MyPyramid guide seems small.

Another adverse result of oversized portions is that the larger the portion, the less we are able to estimate kilocalorie in- take. For example, eating potato chips di- rectly from the bag, rather than taking a handful out of the bag and only eating that portion, will likely mean consuming significantly more kilocalories.

Health Effects of Increased Portion Size

Research has shown that even slight changes in the portion sizes of typical foods can lead to increased energy intake and weight gain.6 As body weight in- creases, the risk of developing cardiovas- cular disease, diabetes, joint problems, and some cancers also increases.7

Tips for Controlling Portion Size

According to recent studies, young adults have distorted views of what a correct portion size should be.8 To reduce over- consumption of fat and kilocalories, and therefore the likelihood for an unhealthy body weight, consumers need to recog- nize healthy portion sizes, which are based on serving sizes. Steps that can help reduce oversized portions include buying smaller or single-portion packages of foods, or dividing larger packages into individual portion sizes. In restaurants, order one meal to share with your com- panion, or split the food in half and take the other half home. In your cupboard, replace larger glasses and plates with smaller versions.

References 1. National Institute of Health. 2007. Portion

Distortion. Available at http://hp2010. nhlbihin.net/portion/index.htm.

2. Smicikilas-Wright, H., D. C. Mitchell, S. Mickle, J. Goldman, and A. Cook. 2003. Foods Commonly Eaten in the United States, 1989–1991 and 1994–1996: Are Portion Sizes Changing? Journal of the American Dietetic Association 103:41–47.

3. Young, L. R. and M. Nestle. 2003. Expanding Portion Sizes in the U. S. Marketplace: Implications for Nutrition Counseling. Journal of the American Dietetic Association 103:231–234.

4. Diliberti, N., P. L. Bordi, M. T. Conklin, and B. J. Rolls. 2004. Increased Portion Size Leads to Increased Energy Intake in a Restaurant Meal. Obesity Research 12:562–568.

5. Nielsen, S. J. and B. M. Popkin. 2003. Patterns and Trends in Food Portion Sizes, 1977–1998. Journal of the American Medical Association 289:450–453.

6. Rolls, B., L. S. Roe, and J. S. Meengs. 2006. Larger Portion Sizes Lead to a Sustained Increase in Energy Intake Over 2 Days. Journal of the American Dietetic Association 106:543–549.

7. Centers for Disease Control. 2005. Overweight and Obesity: Obesity Trends. Available at www.cdc.gov.

8. Schwartz, J. and C. Byrd-Bredbenner. 2006. Portion Distortion: Typical Portion Sizes Selected by Young Adults. Journal of the American Dietetic Association 106:1412–1418.

Controlling Portion Size

Where You Eat What to Do

At Home ■ Measure your food until you develop an “eye” for correct portion sizes

■ Use smaller plates so portions appear larger

■ Plate your food at the counter before sitting down at the table or in front of the television

■ Store leftover foods in portion-controlled containers

■ Don’t eat snacks directly from the box or bag; measure a portion first, then eat only that amount

■ Cook smaller quantities of food so you don’t pick at the leftovers

■ Keep tempting foods, such as high-sugar or -kilocalorie foods, out of sight

Eating Out ■ Ask for half orders when available

■ Order an appetizer as your main entree

■ Don’t be compelled to “clean your plate”; stop eating when you’re full and take the rest home

Buying Groceries

■ Divide a package of snacks into individual portion sizes and consume only that amount at any one sitting

■ Be aware of the number of servings in a package; read the labels

■ Buy foods that are already divided into portion sizes such as 1 oz sliced cheese or lunch meat

■ Avoid “mini” sizes of crackers, cookies, etc.; just because they’re small doesn’t mean you can eat the whole box!

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If you are trying to maintain your current weight, or lose weight, you are proba- bly on a limited energy budget and need to choose foods that are nutrient dense and low in kilocalories. Use the guide in Table 2.1 to help stretch your energy budget while consuming the most nutrient-dense foods.

Resources for Planning a Healthy Diet Do you think all this advice for planning a healthy diet is hard to keep straight? If so, you’re not alone. Luckily, there are several resources available to help guide you. Two of these are the Dietary Reference Intakes (DRIs) and the Dietary Guidelines for Americans.

The DRIs were developed to improve Americans’ intake of individual nutrients (see Figure 2.3).10 They form the basis of the Dietary Guidelines for Americans, which provide broad dietary and lifestyle advice.

Two more resources, the MyPyramid food guidance system and the Daily Values (DVs), help implement the DRI recommendations for the purpose of se- lecting and comparing specific foods. MyPyramid reflects recommendations from the DRIs, the advice in the Dietary Guidelines, and the Finding Your Way to a Healthier You brochure. Finally, the Daily Values were created from previous Rec- ommended Dietary Allowances and the Dietary Guidelines and appear only on food labels. Their purpose is to help consumers decide which foods to buy. To- gether, these reference values, guidelines, and tools can help plan a varied, moder- ate, and balanced diet.

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Table 2.1

Bargain Shopping on an Energy Budget Use the following guidelines when choosing energy-dense foods.

Foods Energy Density Are They an Energy Bargain?

Soups Fruits Vegetables

0.0 to 0.6 kcal/g Great Bargain: Eat as much of these low-energy-density foods as you want on a low-energy budget; however, take care that soups don’t contain too much sodium, and are broth rather than cream based.

Starchy fruits and vegetables Lean meats Beans and legumes

0.6 to 1.5 kcal/g Good Bargain: Consume healthy portions of these foods on a low-energy budget.

Cheese Salad dressings Snack foods Desserts

1.5 to 4.0 kcal/g More Expensive Choices: These foods should be chosen carefully and consumed in moderation.

Chocolates Deep-fat fried foods Nuts Chips Candy

4.0 to 9.0 kcal/g Very Expensive Choices: Eat less of these foods and be aware of the portion size to avoid over- consuming kilocalories.

Source: Adapted from Rolls, B. and R. A. Barnett. 2000. Volumetrics: Feel Full on Fewer Calories. New York: HarperCollins.

Dietary Guidelines for Americans Guidelines published by the Department of

Health and Human Services and the United

States Department of Agriculture in 2005

that provide dietary and lifestyle advice to

healthy individuals age 2 and older to main-

tain good health and prevent chronic dis-

eases. They are the basis for the federal food

and nutrition education programs.

Dietary Reference Intakes (DRIs) Reference values for nutrients developed

by the Food and Nutrition Board of the

Institute of Medicine, used to plan and

evaluate the diets of healthy people in the

United States and Canada. It includes the

Estimated Average Requirement (EAR),

the Recommended Dietary Allowance

(RDA), the Adequate Intake (AI), and the

Tolerable Upper Intake Level (UL).

MyPyramid A food guidance system that il- lustrates the recommendations in the Dietary

Guidelines for Americans 2005 and the Dietary

Reference Intakes (DRIs) nutrient goals.

Daily Values (DVs) Reference values de- veloped by the Food and Drug Adminis-

tration and used on nutrition labels to

describe the amount of a nutrient pro-

vided in one serving of the food.

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The Take-Home Message Healthy eating emphasizes consuming the right amount of food from a variety of food groups to provide an adequate in- take of nutrients and a moderate level of energy. Choosing nutrient-dense and low-energy-dense foods ensures a diet high in nutrient content and low enough in energy to prevent weight gain. Reference values, guidelines, and tools have been developed to help individuals make healthy choices.

What Are the Dietary Reference Intakes? The DRIs are specific reference values issued by the Food and Nutrition Board (FNB) of the National Academy of Sciences’ Institute of Medicine for each nutrient. Unlike dietary advice of the past century, which focused on the minimum need with a safety factor built in for each nutrient, the DRIs reflect a new approach to diet plan- ning. The main focus is to maintain good health and reduce the risk of developing chronic diseases such as osteoporosis and cardiovascular disease,11 while avoiding unhealthy excesses. The Institute of Medicine periodically organizes committees of U.S. and Canadian scientists and health experts to update these recommendations based on the latest scientific research.

What Are the Dietary Reference Intakes? 47

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The Report of the Dietary Guidelines Advisory Committee on

Dietary Guidelines for Americans, 2005

Figure 2.3 Dietary Recommendations and Implementation Tools The Dietary Guidelines for Americans serve as the basis for several tools that guide Americans in choosing healthy diets.

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The DRIs Suggest an Intake Level for Each Nutrient Individuals have different nutrient requirements during different life stages, such as during pregnancy or older age, and men and women vary in some of their nutrient requirements due to the physiological differences of their bodies.12 The FNB reviews the research for different age groups and genders, and presents recommendations on how much of each nutrient a particular group needs. Because the recommendations are based on data from population groups and not individuals, this amount may be higher or lower than you need. However, you can be confident that if you follow the recommendations for your age and gender, you will consume sufficient nutrients to remain healthy and reduce the risk of developing a chronic disease or eating toxic amounts of any nutrient.

The DRIs Encompass Several Reference Values The DRIs can be thought of as an umbrella term that covers five reference values: the Estimated Average Requirement (EAR), the Recommended Dietary Allowance (RDA), the Adequate Intake (AI), the Tolerable Upper Intake Level (UL), and the Ac- ceptable Macronutrient Distribution Range (AMDR) (Figure 2.4). Each of these val- ues is unique, and serves a different need in planning a healthy diet. But only three of these values, the RDA or AI (not both), the AMDR, and the UL, are used to assess the quality of meals.

The EAR is the starting point in the process of determining the other values. Let’s look at how the values are determined.

Estimated Average Requirements The Estimated Average Requirement (EAR) is the amount of a nutrient projected to meet the needs of 50 percent of healthy Americans by age and gender.13 If you con- sume the EAR for iron, for example, you would be eating an amount that half of the people in your age and gender group need to consume to meet their needs. In other words, you would have a 50:50 chance that this amount would be sufficient for you to maintain a healthy iron status.

Let’s use Figure 2.5 to locate the EAR for Nutrient X. As you can see from the figure, the EAR for Nutrient X is about 40 units. If the recommended reference value for Nutrient X was set at 40 units, then half of the individuals would either meet or exceed their needs while the other half would not.

An EAR for each nutrient is established based on a measurement that indicates whether the individual is at risk of a deficiency. For example, the EAR for iron for a 19-year-old female uses hemoglobin concentrations in the blood to determine if iron intake is adequate. The measurement differs from nutrient to nutrient. For vitamin A, dark adaptation is used to determine the EAR, while researchers use enzyme activ- ity to recommend thiamin requirements.14 If there aren’t enough studies or collected data to develop an appropriate measurement for a nutrient, an EAR or requirement for that nutrient is not established.

Once the EAR has been set for each nutrient, the Recommended Dietary Al- lowances (RDAs) can be calculated.

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nutrient requirements The amounts of specific nutrients needed to prevent

malnutrition or deficiency; reflected in the

DRIs.

Die tary R

eference Intakes

EAR RDA AI UL

AM DR

Figure 2.4 The Dietary Reference Intakes Of the reference values that comprise the DRIs, the RDAs or AIs and the AMDR are most useful for diet planning. Individuals should avoid consuming the UL of any nutrient.

Estimated Average Requirement (EAR) The average daily amount of a nutrient needed by 50 percent of the

individuals in a similar age and gender

group.

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Recommended Dietary Allowances The Recommended Dietary Allowance (RDA) is the recommendation for each nu- trient that should meet the needs of nearly all (97 to 98 percent) of the individuals in a specific gender and age group. We can again use iron to illustrate the relationship between the EAR and the RDA. After careful review of the latest research on iron me- tabolism, the EAR for iron was set at 6 milligrams per day for both men and women over all age groups.15 The amount is increased to an RDA of 18 milligrams per day to cover the needs of 97 to 98 percent of females aged 19 to 30. For 19-to-30-year-old males, the RDA for iron is 8 milligrams daily. The RDA for each nutrient according to age and gender is presented in the front of the textbook.

Although the RDA is a valuable reference for healthy eating, researchers have not established RDAs for all nutrients. If there is insufficient evidence to determine an EAR for a nutrient, the RDA can’t be calculated. For nutrients for which no RDA has been established (such as calcium), the AI can provide an alternative guideline.

Adequate Intakes Adequate Intake (AI) is a formal reference value (and hence different from the prin- ciple of adequacy we discussed earlier in the chapter) that is estimated based on the judgment of the members of the FNB, according to the latest research. The AI is the next best scientific estimate of the amount of a nutrient that groups of similar indi- viduals should consume to maintain good health. One difference to note between the RDAs and the AIs is that the RDAs are based on EARs, whereas the AIs are set without having established a requirement. In other words, if a nutrient has an AI, then more research must be done to accurately set an RDA. Also, the RDAs should cover the needs of 97 to 98 percent of the population, but the AIs do not estimate how many people will be covered because the EAR is not available. However, if you consume an amount equal to the AIs you will likely exceed the EARs or RDAs.16 Fi- nally, for infants, AIs are the only estimations for nutrients to evaluate dietary ade- quacy. This is because conducting the types of studies necessary to determine more specific information would be unethical.

The nutrients with AIs are noted in the DRI tables in the front of your textbook and include some vitamins and minerals, such as biotin, pantothenic acid, and vita- mins D and K, and the minerals calcium and potassium.

What Are the Dietary Reference Intakes? 49

101166 C P BC A Bl k P N 49 C/M/Y/K DESIGN SERVICES OF

Amount of nutrient (in units) daily

N u m

b e r

o f in

d iv

id u a ls

in a

sp e c ifi

c a

g e a

n d

g e n d

e r

g ro

u p

1800 40 80 120 1601401006020

a Estimated Average Requirement (EAR)

c Tolerable Upper Intake Level (UL)

Recommended Dietary Allowance (RDA)

b

Number of individuals whose health needs are met by nutrient

Increased risk of toxicity

Figure 2.5 The DRIs in Action (a) The EAR is the average amount of a nutrient that is likely to meet the daily needs of half of the healthy individuals in a specific age and gender group. (b) The RDA, which is higher than the EAR, will meet the needs of approximately 97 to 98 percent of healthy individuals in a specific group. Consuming more than the RDA but less than the UL is safe for individuals. (c) The UL is the highest amount of a nutrient that is unlikely to pose any risk of adverse health effects even if consumed daily. As the intake of a nutrient increases above the UL, the risk of toxicity increases.

Recommended Dietary Allowance (RDA) The recommended daily amount of a nutrient that meets the needs of

nearly all individuals (97 to 98 percent) in

a similar age and gender group. The RDA

is set higher than the EAR.

Adequate Intake (AI) The approximate daily amount of a nutrient that is suffi-

cient to meet the needs of similar individ-

uals within a population group. The Food

and Nutrition Board uses AIs for nutrients

that do not have enough scientific evi-

dence to calculate an RDA.

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Tolerable Upper Intake Level Because consuming too much of some nutrients can lead to harmful side effects, the FNB developed the Tolerable Upper Intake Level (UL), which refers to the highest amount of a nutrient that is unlikely to cause harm if consumed daily. The higher the consumption above the UL, the higher the risk of toxicity. These reference values became necessary because of individuals’ increased interest in consuming dietary supplements and fortified foods in pursuit of supposed health benefits. Unfortu- nately, many individuals are unaware that consuming too much of some nutrients can have a deleterious effect.

Not all nutrients have UL values. This doesn’t mean that high intakes of those nutrients are safe, however. Because there aren’t any known benefits for a healthy adult to consume a higher amount than the UL, people should aim to consume less than the UL and avoid the risk of health problems.

Estimated Energy Requirements Although dietary recommendations have been established for carbohydrate, fat, protein, vitamins, and minerals that meet the optimal intake of nutrients, no DRI has been established for energy (kilocalorie) intake.17 The method used to deter- mine the amount of energy you need, or your Estimated Energy Requirement (EER), uses a different approach than the RDAs or AIs. The EER is calculated based on age, gender, height, weight, and activity level, and indicates the amount of energy needed to maintain energy balance. Individuals who consume more energy than they need will gain weight. Equations have been designed for males and fe- males to provide a general estimate of energy needs. You can find the approximate amount of energy you require daily in Table 2.2. We will cover this in greater detail in Chapter 14.

Acceptable Macronutrient Distribution Ranges To ensure that intake of the energy nutrients is adequate and proportionate to physi- ological needs, recommended ranges of carbohydrates, fats, and proteins have been

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Table 2.2

How Many Kilocalories Do You Need Daily? The amount of kilocalories needed daily to maintain a healthy weight is based upon age, gender, and activity level.*

Males Females

Moderately Moderately Age Sedentary* Active Active Age Sedentary Active Active

16–18 2,400 2,800 3,200 18 1,800 2,000 2,400 19–20 2,600 2,800 3,000 19–20 2,000 2,200 2,400 21–25 2,400 2,800 3,000 21–25 2,000 2,200 2,400 26–30 2,400 2,600 3,000 26–30 1,800 2,000 2,400 31–35 2,400 2,600 3,000 31–35 1,800 2,000 2,200 36–40 2,400 2,600 2,800 36–40 1,800 2,000 2,200 41–45 2,200 2,600 2,800 41–45 1,800 2,000 2,200 46–50 2,200 2,400 2,800 46–50 1,800 2,000 2,200

*These kilocalorie levels are based on the Institute of Medicine’s Estimated Energy Requirements from the Dietary Reference Intakes: Macronutrients Report, 2002. Sedentary: Partaking in less than 30 minutes a day of moderate physical activity in addition to daily activities. Moderately Active: Partaking in at least 30 minutes and up to 60 minutes a day of moderate physical activity in addition to daily activities. Active: Partaking in 60 or more minutes a day of moderate physical activity in addition to daily activities.

Source: U.S. Department of Agriculture. MyPyramid. Available at www.mypyramid.gov/professionals/pdf_calorie_levels.html.

Tolerable Upper Intake Level (UL) The maximum daily amount of a nutrient

considered safe in a group of similar

individuals.

toxicity The level of nutrient intake at which exposure to a substance becomes

harmful.

Estimated Energy Requirement (EER) The amount of daily energy to maintain a healthy body weight and meet

energy needs based on age, gender, height,

weight, and activity level.

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Use the following scenario to calculate Emma’s AMDR for carbohydrate and fat:

Emma needs 2,150 kcal per day to maintain her current healthy weight.

The AMDR for carbohydrate is 45 to 65 percent of total daily kilocalories. To determine the number of kilocalories Emma needs to obtain daily from carbohydrate, we run the following equations:

Thus, of the 2,150 kcal Emma eats each day, 968 to 1,398 kcal should be from carbohydrates.

The AMDR for fat is 20 to 35 percent of daily kilocalories. Therefore:

Of the 2,150 kcal Emma eats each day, 430 to 753 kcal should be from fat.

Can you calculate the AMDR for your daily intake of kilocalories?

2,150 kcal � 35 percent fats � 2,150 � 0.35 � 753 kcal

2,150 kcal � 20 percent fats � 2,150 � 0.20 � 430 kcal

2,150 kcal � 65 percent carbohydrates � 2,150 � 0.65 � 1,398 kcal 2,150 kcal � 45 percent carbohydrates � 2,150 � 0.45 � 968 kcal

C A L C U L AT I O N C O R N E R

Table 2.3

The Do’s and Don’ts of the DRIs Reference Value When Planning Your Diet

Estimated Average Requirement (EAR) Don’t use this amount.

Recommended Dietary Allowance (RDA) Do aim for this amount!

Adequate Intake (AI) Do aim for this amount if an RDA isn’t available.

Tolerable Upper Intake Level (UL) Don’t exceed this amount on a daily basis.

Acceptable Macronutrient Distribution Do follow these guidelines regarding Range (AMDR) the percentage of carbohydrates, protein,

and fat in the diet.

Source: Institute of Medicine. 2003. Dietary Reference Intakes: Applications in Dietary Planning. Washington, DC: The National Academies Press.

Acceptable Macronutrient Distribu- tion Ranges (AMDRs) A healthy range of intakes for the energy-containing nutrients—

carbohydrates, proteins, and fats—expressed

as a percentage of total daily energy. The

AMDRs for adults are 45 to 65 percent carbo-

hydrates, 10 to 35 percent protein, and 20 to

35 percent fat.

developed and are called the Acceptable Macronutrient Distribution Ranges (AMDRs). The AMDRs are as follows:

■ Carbohydrates should comprise 45 to 65 percent of your daily kilocalories ■ Fat should comprise 20 to 35 percent of your daily kilocalories ■ Proteins should comprise 10 to 35 percent of your daily kilocalories

Consuming these nutrients in these ranges will ensure that kilocalorie and nutrient needs are met, while the risk of developing chronic diseases such as heart disease and obesity is reduced.18

The DRIs Can Be Used to Plan a Quality Diet To meet your needs, your goal should be to achieve the RDA or the AI of all nutri- ents, but not exceed the UL. Table 2.3 summarizes the DRIs. You will also find the DRIs for all nutrients on the inside cover of this textbook.

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Each chapter in this textbook will further explain what each nutrient is, why it is important, how much (based on the DRIs) you need to consume, and how to get enough, without consuming too much, in your diet.

The Take-Home Message The Dietary Reference Intakes (DRIs) are specific reference values that help individuals determine daily nutrient needs to maintain good health, prevent chronic diseases, and avoid unhealthy ex- cesses. The reference values include the EAR, RDA, AI, UL, and AMDR. The EER can help determine the appropriate amount of energy needed to main- tain a healthy body weight given one’s age, gender, height, weight, and activ- ity levels. You should try to meet your RDA or AI and consume below the UL for each nutrient daily while maintaining sufficient energy intake.

What Are the Dietary Guidelines for Americans? By the 1970s, research had shown that Americans’ overconsumption of foods rich in fat, saturated fat, cholesterol, and sodium was increasing their risk for chronic dis- eases such as heart disease and stroke.19 In 1977, the U.S. government released the Dietary Goals for Americans, which were designed to improve the nutritional quality of Americans’ diets and to try to reduce the incidence of overnutrition and its associ- ated health problems.20

Amid controversy over the scientific validity of the goals, the government asked scientists to lend credence to the goals and provide dietary guidance. Their work cul- minated in the 1980 Dietary Guidelines for Americans, which emphasized eating a va- riety of foods to obtain a nutritionally well-balanced daily diet. Since 1990, the U.S. Department of Agriculture (USDA) and the Department of Health and Human Ser- vices (DHHS) have been mandated by law to update the guidelines every five years. The guidelines serve as one governmental voice to shape all federally funded nutri- tion programs in areas such as research and labeling, and to educate and guide con- sumers about healthy diet and lifestyle choices.21

The Dietary Guidelines for Americans 2005 reflect the most current nutrition and physical activity recommendations for good health. They are designed to help individuals aged 2 and over improve the quality of their diet in order to lower their risk of chronic diseases and unhealthy conditions, such as high blood pressure, high blood cholesterol levels, diabetes mellitus, heart disease, certain cancers, osteoporo- sis, and being overweight or obese. Following these guidelines could reduce Ameri- cans’ risk of dying of these conditions by as much as 9 to 16 percent.22

The Dietary Guidelines are divided into nine closely related, and often inter- twined, categories that address various health concerns. Because of the vast amount of information in these guidelines, only a short overview of each category and some supporting diet and lifestyle recommendations are presented in Table 2.4. Each chapter in this book elaborates on at least one of these guidelines and discusses how to easily make additional diet and lifestyle changes to improve health. The com- plete guidelines and more information are available online at www.healthierus.gov/ dietaryguidelines.

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The Dietary Guidelines encourage consumption of a variety of fruits and vegetables.

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Table 2.4

The Dietary Guidelines for Americans at a Glance

The Health Concern in a Nutshell It’s Recommended That You

Adequate nutrients within calorie needs

Many Americans consume more kilocalories than they need, yet still fall short of some im- portant nutrients.

Consume a variety of nutrient-dense foods and beverages within and among the basic food groups but be careful not to exceed the amount of daily kilocalories needed to maintain a healthy weight.

Weight management

Over 65 percent of Americans are overweight, and so are at an increased risk of heart dis- ease, cancer, stroke, and diabetes mellitus— some of the major causes of death in the United States.

Maintain a balance between the amount of kilocalories con- sumed daily and the amount needed to maintain a healthy weight. Daily physical activity will help, as it allows you to eat some additional kilocalories while maintaining a healthy weight. Individuals who need to lose weight should take in fewer kilo- calories and increase their physical activity level.

Physical activity

Even though being physically active reduces the risk of many chronic diseases, over half of American adults don’t exercise enough to gain this protective effect. In fact, 25 percent of Americans are considered “couch potatoes” because they don’t move at all during their leisure time.

Try to be physically active every day. Spend at least 30 minutes a day in moderately intense physical activity, such as brisk walking, Rollerblading, or aerobic dancing. More vigorous activities, such as jogging or a step aerobics class, will yield even more health benefits. Individuals seeking to lose weight should increase daily exercise to at least 60 minutes of a moderate-intensity activity throughout the day.

Food groups to encourage

Americans fall short of the recommended amounts of whole grains, fat-free and low-fat dairy products, whole fruits, and vegetables.

Eat more from these food groups on a daily basis. Remember this phrase: “Give three two me, please.” Have at least three servings of whole grains and three servings of fat-free or low-fat dairy products daily. Enjoy at least two cups of a variety of fruit and at least two-and-a-half cups of colorful vegetables through- out the day.

Fats Although some fat is essential, too much saturated and trans fat, as well as dietary cholesterol, is unhealthy for the heart.

Keep dietary fat intake to between 20 and 35 percent of daily kilo- calories and get mostly heart-healthy, unsaturated fats such as those found in vegetable oils, nuts, and fish. Consume less than 10 percent of kilocalories from saturated fat by choosing only lean meats, skinless poultry, and low-fat dairy foods. Eat fewer commer- cially made baked goods that are made with trans fats. Consume less than 300 milligrams of dietary cholesterol daily.

Carbohydrates Although carbohydrate-rich foods such as whole grains, lean dairy foods, whole fruits, and vegetables are excellent sources of nu- trients, foods high in sugary carbohydrates also tend to be high in kilocalories. These less healthy carbohydrate sources may also displace more nutritious foods in the diet.

Choose lean dairy products, whole grains, fruits, and vegetables more often than sugary soft drinks, candy, bakery items, and fruit drinks.

Sodium and potassium

Most Americans will develop high blood pressure sometime in their life. A continually high blood pressure increases the risk of heart disease and stroke. Generally, as in- take of salt goes up, so does blood pres- sure. Whereas potassium can help lower blood pressure, most individuals don’t eat enough potassium-rich fruits and vegetables for this to be effective.

Keep sodium intake to less than 2,300 milligrams (approximately 1 teaspoon) of salt daily. Avoid salting foods during cooking and at the table, and limit intake of processed foods. Consume plenty of fruits and vegetables daily.

Alcoholic beverages

Though alcohol in moderation may be heart- healthy for some individuals, it can be harmful to others depending upon their age, medical history, and lifestyle.

Avoid alcohol if you are a woman of childbearing age who may become pregnant, a pregnant or lactating woman, under the age of 21, taking medications that can interact with alcohol, have a specific medical condition for which doctors advise against alco- hol consumption, an alcoholic, or driving or operating machinery.

Food safety Each year, over 70 million Americans suffer from foodborne illnesses, also known as food poi- soning, from consuming foods that have been contaminated with bacteria, parasites, and viruses.

Properly clean, prepare, and store foods.

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The Take-Home Message The Dietary Guidelines consist of nine categories of general diet and lifestyle advice designed to help Americans lead a healthy lifestyle. They are updated every five years.

What Is MyPyramid? Illustrated graphics called food guidance systems are often used to summarize guidelines for healthy eating. MyPyramid is the most recent food guidance system developed by the USDA for Americans (Figure 2.6). Released in 2005, MyPyramid visually depicts the recommendations in the Dietary Guidelines for Americans 2005, and its online component provides a personalized diet plan based on the latest nutri- tion and health recommendations from the Dietary Guidelines Advisory Committee Report and the DRIs.

MyPyramid Emphasizes Key Concepts for Planning a Healthy Diet MyPyramid illustrates the diet and lifestyle themes of physical activity, proportional- ity, moderation, variety, personalization, and gradual improvement. The silhouette climbing the pyramid reminds you to engage in physical activity. Being physically

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Grains Vegetables Milk Meat & Beans

Fruits

O il s

Physical activity. Physical activity is important on a daily basis.

Proportionality. While all food groups are important, some groups, depicted by their wider bands in the pyramid, should be consumed in larger proportions in your diet than others.

Personalization. There are several MyPyramids available online that provide a personalized eating plan based on your needs.

Gradual improvement. The pyramid slogan reinforces that small, gradual changes in both your diet and lifestyle can be beneficial.

Variety. The pyramid contains numerous colorful bands to encourage a diet that contains a variety of food groups.

Moderation. The wide base of the pyramid is a visual reminder that your diet should contain predominantly nutrient-rich foods with little added sugars and unhealthy fats. The narrowing of the bands on the top of the pyramid reinforces that sugary food and solid fats should be consumed in moderation.

a

c

e

b

d

f

Figure 2.6 Anatomy of MyPyramid Individual elements of MyPyramid reinforce important concepts for planning a healthy diet.

Source: U.S. Department of Agriculture. 2005. The New Look and Messages of USDA’s MyPyramid, Background. Available at www.mypyramid.gov/global_nav/media_backgrounder.html. Accessed April 16, 2008.

food guidance systems Visual dia- grams that provide a variety of food rec-

ommendations to help a person create a

well-balanced diet.

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active helps you to stay fit and reduces the risk of chronic diseases such as heart dis- ease and cancer.

Each colored band represents the food groups: grains, vegetables, fruits, milk, and meat and beans. A sixth, yellow band represents oils. (Note that oils are not a food group.) The widths of the bands reinforce proportionality, or how much of the total diet should be eaten from each food group. The narrowing of the pyramid from a wide base to a thin tip tells you to choose mostly nutrient-dense foods from each food group (Figure 2.7); the multicolored bands remind you to eat a variety of foods (see Figure 2.8 on page 56).

Remember, “Rome wasn’t built in a day.” Adopting a healthier diet and lifestyle, and changing long-term eating habits, takes time. The slogan “Steps to a Healthier You” and the steps on the side of MyPyramid reinforce the need for grad- ual improvement.

How to Use MyPyramid You now know to eat a variety of nutrient-dense foods to be healthy, and that MyPyramid helps you select a diverse group of foods, but you may be wondering how much from each food group you, personally, should be eating. The MyPyramid inter- active website at www.mypyramid.gov will give you the exact quantities to eat from each food group based on your daily kilocalorie needs. If you cannot go to the web- site, you can obtain similar information by using Tables 2.2 and 2.5 in this chapter.

Once you create your personalized MyPyramid and know the number of kilo- calories you need daily, Table 2.6 on page 57 will tell you the quantity from each food group you should consume to healthfully obtain those kilocalories.

For a moderately active female who needs 2,000 kilocalories daily, a healthy daily diet would consist of the following:

■ At least 3 ounces of whole-grain breads, pasta, crackers, rice, and cereals ■ 21⁄2 cups of dark green, orange, starchy, and other vegetables, and some legumes ■ 2 cups of fruits ■ 3 cups of fat-free or low-fat milk and yogurt ■ 51⁄2 ounces of lean meat, poultry, and fish, or the equivalent in meat alternatives

such as beans ■ 6 teaspoons of vegetable oils

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Eat less of these

Eat more of these

Grains Vegetables Fruits Milk Meat and BeansOils Foods with high amounts of added sugars and heart- unhealthy fats. These are less nutrient dense.

Foods that are more nutrient dense.

Buttered popcorn, cake, cookies, donuts, pastries

French fries, potato chips

Fruit canned in syrup, fruit drinks, sweetened dried fruit

Butter, hydrogenated oils

Full-fat cheeses, fried mozzarella sticks, high-fat ice cream

Fatty cuts of meat and luncheon meats, fried chicken or fish, poultry with skin

Brown rice, bulgur, couscous, oats, pasta, popcorn, rice, whole-grain cereals, bread, crackers

Fresh, frozen, and canned vegetables; dried beans and peas

Dried beans and peas, eggs, fish, lean meat, nuts, skinless poultry, seeds

Vegetable oils Low-fat or nonfat cheese, milk or yogurt, low-fat ice cream or frozen yogurt

Dried fruit, whole fruit, 100% fruit juice

Figure 2.7 My Nutrient-Dense Pyramid Choose nutrient-dense foods more often to build a well-balanced diet.

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If all food selections are low in fat and added sugar, this menu will provide a total of about 1,740 kilocalories. This means that, after meeting all nutrient requirements, this individual will have about 260 of her 2,000 kilocalories left. This is her discretionary kilocalorie allowance (see Figure 2.9). She can “spend” these kilocalo- ries on extra servings of foods such as grains, fruits, and/or vegetables, or on occasion as an added fat, sweet, or dessert. Note that if you pour whole milk (high in fat) over your sweetened cereal (added sugar) instead of using skim milk (fat free) to drench your shredded wheat (no added sugar), the extra fat and sugar have used up some of your discretionary kilocalories. As you can see from Table 2.7 on page 58, these dis- cretionary kilocalories can be used up quickly depending on the foods you choose.

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Focus on fruits. Eat a variety of fruits— whether fresh, frozen, canned, or dried— rather than fruit juice for most of your fruit choices. For a 2,000 calorie diet, you will need 2 cups of fruit each day (for example, 1 small banana, 1 large orange, and 1/4 cup of dried apricots or peaches).

Know the limits on fats, salt, and sugars. Read the Nutrition Facts label on foods. Look for foods low in saturated fats and trans fats. Choose and prepare foods and beverages with little salt (sodium) and/or added sugars (caloric sweeteners).

Vary your veggies. Eat more dark green veggies, such as broccoli, kale, and other dark leafy greens; orange veggies, such as carrots, sweet potatoes, pumpkin, and winter squash; and beans and peas, such as pinto beans, kidney beans, black beans, garbanzo beans, split peas, and lentils.

Get your calcium-rich foods. Get 3 cups of low-fat or fat-free milk—or an equivalent amount of low-fat yogurt and/or low-fat cheese (11/2 ounces of cheese equals 1 cup of milk)—every day. For kids aged 2 to 8, it’s 2 cups of milk. If you don’t or can’t consume milk, choose lactose-free milk products and/or calcium-fortified foods and beverages.

Go lean with protein. Choose lean meats and poultry. Bake it, broil it, or grill it. And vary your protein choices—with more fish, beans, peas, nuts, and seeds.

Make half your grains whole. Eat at least 3 ounces of whole-grain cereals, breads, crackers, rice, or pasta every day. One ounce is about 1 slice of bread, 1 cup of breakfast cereal, or 1/2 cup of cooked rice or pasta. Look to see that grains such as wheat, rice, oats, or corn are referred to as “whole” in the list of ingredients.

Figure 2.8 Mix Up Your Choices Within Each Food Group

Source: USDA Consumer Brochure. Finding Your Way to a Healthier You. Based on the Dietary Guidelines for Americans. Available at www.health. gov/DIETARYGUIDELINES/dga2005/document/ html/brochure.htm. Accessed March 2008.

1,740 kilocalories (lean foods without added sugars)

260 kilocalories (discretionary calories)

2,000 total daily kilocalories

Figure 2.9 How Discretionary Calories Fit into a Balanced Diet If you select mostly nutrient-dense, lean foods that don’t contain added sugar, you may have leftover calories to “spend” on extra helpings or a sweet dessert.

discretionary kilocalorie allowance The balance of kilocalories remaining in

one’s energy allowance once all nutrient

needs have been met.

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Table 2.5

What Is Moderate and Vigorous Activity? Moderate Activities (Expend 3.5 to 7 Kilocalories per Minute):

Vigorous Activities (Expend More Than 7 Kilocalories per Minute):

Brisk walking Jogging or running

Bicycling 5 to 9 mph Bicycling more than 10 mph

Shooting hoops Playing competitive sports like basketball, soccer, or lacrosse

Using free weights Rowing on a machine vigorously

Yoga Karate, judo, or tae kwon do

Walking a dog Jumping rope

Adapted from The Centers for Disease Control and Prevention. 1999 General Physical Activities Defined by Level of Intensity. Available at www.cdc.gov. Accessed March 2008.

Table 2.6

How Much Should You Eat from Each Food Group? The following are suggested amounts to consume daily from each of the basic food groups and the oils based on daily kilocalorie needs. Remember that most food choices should be fat free or low fat and contain little added sugar.

Kilocalorie Grains Vegetables Fruits Oils Milk Meat and Beans Level (oz eq) (cups) (cups) (tsp) (cups) (oz eq)

1,400 5 1.5 1.5 4 2 4

1,600 5 2 1.5 5 3 5

1,800 6 2.5 1.5 5 3 5

2,000 6 2.5 2 6 3 5.5

2,200 7 3 2 6 3 6

2,400 8 3 2 7 3 6.5

2,600 9 3.5 2 8 3 6.5

2,800 10 3.5 2.5 8 3 7

Grains: Includes all foods made with wheat, rice, oats, cornmeal, or barley, such as bread, pasta, oatmeal, breakfast cereals, tor- tillas, and grits. In general, 1 slice of bread, 1 cup of ready-to-eat cereal, or 1⁄2 cup of cooked rice, pasta, or cooked cereal is consid- ered 1 ounce equivalent (oz eq) from the grains group. At least half of all grains consumed should be whole grains such as whole-wheat bread, oats, or brown rice.

Vegetables: Includes all fresh, frozen, canned, and dried vegetables, and vegetable juices. In general, 1 cup of raw or cooked veg- etables or vegetable juice, or 2 cups of raw leafy greens, is considered 1 cup from the vegetable group.

Fruits: Includes all fresh, frozen, canned, and dried fruits, and fruit juices. In general, 1 cup of fruit or 100% fruit juice, or 1⁄2 cup of dried fruit, is considered 1 cup from the fruit group.

Oils: Includes vegetable oils such as canola, corn, olive, soybean, and sunflower oil, fatty fish, nuts, avocados, mayonnaise, salad dressings made with oils, and soft margarine.

Milk: Includes all fat-free and low-fat milk, yogurt, and cheese. In general, 1 cup of milk or yogurt, 11⁄2 ounces of natural cheese, or 2 ounces of processed cheese is considered 1 cup from the milk group.

Meat and Beans: In general, 1 ounce of lean meat, poultry, or fish, 1 egg, 1 tablespoon peanut butter, 1⁄4 cup cooked dry beans, or 1⁄2 ounce of nuts or seeds is considered 1 ounce equivalent (oz eq) from the meat and beans group.

Source: U.S. Department of Agriculture. www.MyPyramid.com.

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Figure 2.10 shows how servings from the various food groups can create well- balanced meals and snacks throughout the day.

Although this particular menu is balanced and the foods are nutrient dense, it is unlikely that every day will be this ideal. Fortunately, nutrient needs are aver- aged over time. If an individual eats insufficient servings of one food group or a specific nutrient one day, he or she can make up for it the next day. For example, if Emma did not eat enough fruit one day, but did eat an extra serving of grains, she could adjust her diet the next day by cutting back on her grain servings and adding an extra serving of fruit. Should Emma worry about when she eats? Read more about the time of day you should eat in the feature box, “Time of Day and Eating on page 60.”

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Table 2.7

Using Discretion with Discretionary Calories As you can see, discretionary calories can be used up quickly depending on food choices.

Choosing . . . Over . . . Will Cost You

Whole milk (1 cup) Fat-free milk (1 cup) 65 discretionary calories

Roasted chicken thigh with skin (3 oz) Roasted chicken breast, skinless (3 oz) 70 discretionary calories

Glazed donut, (three 3⁄4" diameter) English muffin (one muffin) 165 discretionary calories

French fries (one medium order) Baked potato (one medium) 299 discretionary calories

Regular soda (one can, 12 fl oz) Diet soda (one can, 12 fl oz) 150 discretionary calories

Source: U.S. Department of Agriculture. MyPyramid: How Do I Count the Discretionary Calories I Eat? Available at www.mypyramid.gov/pyramid/discretionary_calories_count.html.

Plan a day’s menu for Emma based on the MyPyramid recom-mendations. First, decide how many kilocalories Emma should consume if she is moderately active. Next, determine the number of servings from each food group that Emma should eat based on her kilocalorie needs. Finally, write a day’s menu that incorporates these food groups.

The Take-Home Message MyPyramid is the latest food guidance system developed by the USDA. It is a personalized educational tool that helps individuals choose a well-balanced diet from all the food groups to meet their nutrient needs. It emphasizes daily physical activity, a varied diet rich in fruits, vegetables, whole grains, and lean dairy products, and only a moderate amount of foods high in saturated and trans fats, sugar, salt, and alcohol. MyPyramid encourages gradual, small changes to improve the diet and lifestyle.

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GrainsBreakfast: Bowl of cereal

Lunch: Tuna salad sandwich

Dinner: Roasted chicken and potato

Vegetables Milk Meat & Beans

Fruits

O il s

Bran flakes, 1 cup

Whole-wheat English muffin, 1/2

Banana, 1 small

Orange juice, 1 cup

S o ft m

a rg

a ri

n e , 1 t sp

S o ft m

a rg

a ri

n e , 1 t sp

S u n flo

w e r

o il,

3 t sp

Grains Vegetables Milk Meat & Beans

Fruits

O il s

Whole-wheat bread, 2 slices

Diced celery, 1 tbs

Romaine lettuce, 1/2 cup

Tomatoes, 2 slices

Fat-free milk, 1 cup

Fat-free milk, 1/4 cup

Tuna (packed in water), 2.5 oz

Pear, 1 medium

M a yo

n n a is

e , 2 t sp

Snack: Apricots and yogurt Grains Vegetables Milk Meat & Beans

Fruits

O il s

Low-fat vanilla yogurt, 1 cup

Dried apricots, 1/4 cup

Grains Vegetables Milk Meat & Beans

Fruits

O il s

Dinner rolls, 2 1 oz each

Baked sweet potato, 1 large

Peas and onions, 1/2 cup

Leafy green salad, 1 cup

Roasted chicken breast (boneless and skinless), 3 oz

Figure 2.10 Using MyPyramid to Plan a Healthy Diet A variety of foods from each food group create a well-balanced diet.

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60 Chapter 2 . Tools for Healthy Eating

We are all creatures of habit. Some of these habits, such as the time of day we eat, can either enhance or detract from overall health. Do you typically eat break- fast? Do you often snack after dinner or late at night? Do you overload on high-fat or fried foods, or drink a lot of alcohol, when you go out on the weekends? The choice to skip breakfast, eat later in the day, or overeat on the weekend can im- pact your nutrient intake, appetite, and body weight.

Eating Breakfast Means More Energy and Fewer Kilocalories Throughout the Day

You probably know that grabbing a latte on the way to your morning class is not a healthy breakfast, but do you understand how such a habit impacts your overall nu- trient intake? For one thing, skipping breakfast may affect the total number of kilocalories you consume the rest of the day. Dr. John de Castro evaluated the timing of food intake in 867 subjects over a seven-day period and found that peo- ple who ate a larger proportion of food earlier in the day had a significantly lower intake of total kilocalories (Figure 1).1 In other words, if you eat breakfast, you are more likely to eat less by the end of the day than if you skip this important meal.

The reduction in total kilocalories when you eat breakfast may be due to the size of the meal and how satisfied you feel. Most of us eat smaller meals at breakfast and more food at lunch and dinner. We also appear to spend less time eating breakfast than other meals. In Dr. de Castro’s study, both of these factors affected satiety. Satiety ratios, or the time between meals based on the size of the previous meal, decreased over the day from breakfast through late-evening snacks.2 Thus, a more substantial breakfast is more satiating than the evening meal.

One reason breakfast may be more satiating involves the types of foods consumed. Holt and colleagues investi- gated the effects of a high-fat breakfast ver- sus a high-carbohydrate meal on the amount of snacking reported later in the

Time of Day and Eating: Does It Impact Your Health?

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10–14 14–18 18–22 22–24

Time of day (h)

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Figure 2 Satiety index of Different Foods Subjects were asked to rate their feelings of hunger every 15 minutes for 2 hours after eating 240 kilocalorie portions of specific foods. All foods were compared to white bread which scored a satiety index of 100. Adapted from Holt, S. H., J. C. Miller, P. Petocz, and E. Farmakalidis. 1995. A Satiety Index of Common Foods. European Journal of Clinical Nutrition 49:675–690.

day (Figure 2).3 If the breakfast included higher fiber foods, such as cereal, and a good protein source, the subjects ate less later in the day. Breakfast foods including potatoes, eggs, and high-fiber cereals ranked higher than doughnuts or white bread for satiety.

What if you skip breakfast? Not only will you eat more during the day, chances are you will choose less-nutrient-dense foods. Those who eat breakfast, lunch, and dinner tend to have higher calcium and iron intakes than individuals who skip breakfast.4,5

Eating breakfast may also be a good strategy for weight control. Several studies have reported higher BMIs and body weight in subjects who don’t consistently eat breakfast compared with their breakfast- eating counterparts.6 In addition, eating breakfast helps maintain weight loss.7

Figure 1 Satiety Ratios Based on Time Between Meals and Energy Content Satiety ratios were calculated during five 4-hour periods of the day reported in 7-day diet diaries and were calculated as the duration of the after meal interval divided by the meal size in kJ.* To be considered a meal, there had to be at least 15 minutes from the preceding or following meal. Meal (a) contained 15 minutes and 209 kJ; (b) 45 minutes and 209 kJ or (b) 45 minutes and 418 kJ; and (c) 45 minutes and 837 kJ and (c) 90 minutes and 209 kJ. Values are means, n � 867; pooled SEM � 0.00007. Means without a common letter differ; p � 0.05. *Note: The International System uses kilojoules (kJ) to define energy in foods. One kilocalorie equals 4.184 joules.

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Time of Day and Eating: Does It Impact Your Health? 61

Recommendations

Based on the current research on eating and time of day, it is recommended that you:

■ Start your day with a nutrient-dense breakfast as part of a healthy eating pattern. Many breakfast foods, such as dry whole-grain cereals, fresh fruit, or whole-grain toast or bagels with low- fat cream cheese, can be eaten on the go. You’ll have more energy and will most likely eat fewer total kilocalories by the end of the day.

■ Choose breakfast foods that are more satisfying to improve your appetite con- trol throughout the day. Enjoy foods such as whole-grain cereals and whole fruits, which are higher in fiber, protein, and water, and lower in fat and sugar.

■ Control kilocalorie intake on nights and weekends. Monitor your weekend eating habits to maintain a consistent balance of carbohydrates, fats, and proteins and reduce alcohol consumption.

References 1. de Castro, J. M. 2003. The Time of Day of

Food Intake Influences Overall Intake in Humans. Journal of Nutrition 134:104–111.

2. Ibid. 3. Holt, S. H., J. C. Miller, P. Petocz, and

E. Farmakalidis. 1995. A Satiety Index of Common Foods. European Journal of Clinical Nutrition 49:675–690.

4. Kerver, J. M., E. Yang, S. Obayashi, L. Bianchi, and W. Song. 2006. Meal and Snack Patterns Are Associated with Dietary Intake of Energy and Nutrients in U.S. Adults. Journal of the American Dietetic Association 106:46–54.

5. Stockman, N. K. A., T. C. Schenkel, J. N. Brown, and A. Duncan. 2005. Comparison of Energy and Nutrient Intakes among Meals and Snacks of Adolescent Males. Preventive Medicine 41:203–210.

6. Ibid. 7. Wyatt, H. R., G. K. Grunwald, C. L.

Mosca, M. L. Klem, R. R. Wing, and J. O. Hill. 2002. Long-Term Weight Loss and Breakfast in Subjects in the National Weight Control Registry. Obesity Research 10:78–82.

8. Striegel-Moore, R. H., D. L. Franko, D. Thompson, S. Affenito, and H. C. Kraemer. 2006. Night Eating: Prevalence and Demographic Correlates. Obesity 14:139–147.

9. Halberg, F. 1989. Some Aspects of the Chronobiology of Nutrition: More Work Is Needed on “When to Eat.” Journal of Nutrition 119:333–343.

10. Stockman, N. K. A., et al. 2005. Preventive Medicine.

11. Keim, N. L., M. D. Van Loan, W. F. Horn, T. F. Barbieri, and P. L. Mayclin. 1997. Weight Loss Is Greater with Consumption of Large Morning Meals and Fat-Free Mass Is Preserved with Large Evening Meals in Women on a Controlled Weight Reduction Program. Journal of Nutrition 127:75–82.

12. Haines, P. S., M. Y. Hama, D. K. Guilkey, and B. M. Popkin. 2003. Weekend Eating in the United States Is Linked with Greater Energy, Fat, and Alcohol Intake. Obesity Research 11:945–949.

Eating More during Evenings and Weekends can Lead to Overconsumption of Kilocalories

Do you eat after 7:00 p.m. in the evening? Most young adults do, espe- cially during the weekend.8 For most stu- dents, eating schedules are influenced by hunger, pressures from work and school, convenience, and social habits. Regard- less of why you eat at various times, the timing of your meals can affect body weight, the level of hormones in the blood, body temperature, and blood pressure.9 Because eating later is less satisfying, you are likely to eat more food, and hence consume more kilocalories, particularly from carbohydrates, fat and alcohol, in the evening hours.

Though there is no current evidence that eating later in the day increases BMI or the risk of obesity,10 timing of meals may impact changes in body composition during a weight-loss program. In a con- trolled metabolic ward study, overweight women who ate the bulk of their kilocalo- ries in the morning hours had a slightly greater weight loss than when the bulk of the kilocalories was consumed later in the day. However, when they ate more of their kilocalories later in the day, they retained more lean muscle mass.11 More research is needed before any strong conclusions can be drawn from these results.

Weekend eating patterns can also in- fluence overall dietary intake. Haines re- ports that subjects in their study ate an average of 82 kilocalories more per day on Friday, Saturday, and Sunday as com- pared to weekdays. These increases in kilocalories were mostly due to an in- crease in fat (approximately 0.7 percent) and alcohol (1.4 percent); carbohydrates decreased by 1.6 percent.12 Over time, this increase in kilocalorie intake may lead to weight gain.

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What Information Is on the Food Label? Although most people probably do not pay close attention to the food labels of items they purchase at the supermarket, the information on labels can be tremendously useful when it comes to planning a healthy diet.

Food Labels Are Strictly Regulated by the FDA To help consumers make informed food choices, the Food and Drug Administration (FDA) regulates the labeling of all packaged foods in the United States. Since the 1930s, the FDA has mandated that every packaged food be labeled with:

■ The name of the food ■ The net weight, which is the weight of the food in the package, excluding the

weight of the package or packing material ■ The name and address of the manufacturer or distributor ■ A list of ingredients in descending order by weight, with the heaviest item listed first

New labeling laws have been enacted to further benefit the consumer.23 In 1990, the Nutrition Labeling and Education Act (NLEA) began mandating that labels in- clude uniform nutrition information, serving sizes, and specific criteria for health claims. Additional requirements for food labels have since been passed to require that labels now also show:

■ Nutrition information, which lists total kilocalories, kilocalories from fat, total fat, saturated fat, trans fats, cholesterol, sodium, total carbohydrate, dietary fiber, sugars, vitamin A, vitamin C, calcium, and iron

■ Serving sizes that are uniform among similar products, which allows for easier comparison shopping

■ An indication of how a serving of the food fits into an overall daily diet ■ Uniform definitions for descriptive label terms such as “light” and “fat free” ■ Health claims that are accurate and science based, if made about the food or

one of its nutrients

Compare the two food labels in Figure 2.11. Note that the amount and type of nutri- tion information on the 1925 box of cereal is vague and less informative than the more recent version, which meets the FDA’s current labeling requirements.

Very few foods are exempt from carrying a Nutrition Facts panel on the label. Such foods include plain coffee and tea; some spices, flavorings, and other foods that don’t provide a significant amount of nutrients; deli items, bakery foods, and other ready-to-eat foods that are prepared and sold in retail establishments; restaurant meals; and foods produced by small businesses (companies that have total sales of less than $500,000).24

Whereas raw fruits and vegetables and fresh fish typically don’t have a label, these foods fall under the FDA’s voluntary, point-of-purchase nutrition information program. Under the guidelines of this program, at least 60 percent of a nationwide sample of grocery stores must post the nutrition information of the most commonly eaten fruits, vegetables, and fish near where the foods are sold. The FDA surveys a sample of nationwide grocery stores every two years. The latest findings show that over 70 percent of stores surveyed are in compliance with the program.25

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CAREERS IN NUTRITION Corporate Nutrition Manager

Jane Andrews, MS, RD, is the corporate nutrition manager for Wegmans Food Markets. Read an

online interview with her about being a nutritionist in a retail setting at www.aw-bc.com/blake.

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Although a similar voluntary program is in place for meat and poultry, the USDA (which regulates meat and poultry) is considering mandating labels on these foods. This is because less than 60 percent of meat and poultry retailers and manu- facturers have provided the information voluntarily.26, 27

The Nutrition Facts Panel Indicates Nutrient Values One area of the food label in particular, the Nutrition Facts panel, provides a nutri- tional snapshot of the food inside a package. As mentioned above, by law, the panel must list amounts of specific nutrients. If an additional nutrient such as vitamin E or vitamin B12 has been added, or if the product makes a claim about a nutrient, then that nutrient must also be listed. Other nutrients, such as additional vitamins and minerals, can be listed by the manufacturer on a voluntary basis. The majority of packaged foods contain this nutrition information.

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a

b

The name of the product must be displayed on the front label.

The net weight of the food in the box must be located at the bottom of the package.

The ingredients must be listed in descending order by weight. This format is missing in the old box.

The Nutrition Facts panel lists standardized serving sizes and specific nutrients, and shows how a serving of the food fits into a healthy diet by stating its contribution to the percentage of the Daily Value for each nutrient.

Figure 2.11 Cereal Boxes: Then and Now (a) A cereal box from the 1920s carried vague nutrition information. (b) Today, manufacturers must adhere to strict labeling requirements mandated by the FDA.

Nutrition Facts panel The area on the food label that provides a list of specific

nutrients obtained in one serving of the

food.

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Nutrition Facts Serving Size 1 cup (228g) Serving Per Container 2

Amount Per Serving

Calories 250 Calories from Fat 110

% Daily Value* Total Fat 12g 18%

Saturated Fat 3g 15%

Trans Fat 3g

Cholesterol 30g 10%

Sodium 470mg 20%

Potassium 700mg 20%

Total Carbohydrate 31g 10%

Dietary Fiber 0g 0%

Sugars 5g

Protein 5g

Vitamin A 4%

Vitamin C 2%

Calcium 20%

Iron 4%

Total Fat Sat Fat Cholesterol Sodium Total Carbohydrate Dietary Fiber

Calories: Less than Less than Less than Less than

2,000 65g 20g 300mg 2,400mg 300g 25g

2,500 80g 25g 300mg 2,400mg 375g 30g

* Percent Daily Values are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs:

Serving sizes are standardized, making comparison shopping easier.

Calories per serving are listed as well as the number of servings in the box.

This section contains nutrients that should be limited in your diet.

This section contains dietary components and nutrients most individuals need more of in their diets.

Daily Values (DV) are general reference values.

The footnotes provide a summary of the DV for 2,000 kilocalorie and 2,500 kilocalorie diets.

The % DV can tell you if a food is high or low in a nutrient or dietary substance.

a

c

e

g

b

d

f

We can use Figure 2.12 to walk through a sample Nutrition Facts panel. At the top of the panel is the serving size. By law, the serving size must be listed both by weight in grams (less useful to you) and in common household measures, such as cups and ounces (more useful to you). Because serving sizes are standardized among similar food products, consumers can compare one brand of macaroni and cheese with a different brand to assess which one better meets their needs.

The rest of the information on the panel is based on the listed serving size (in this case, one cup) of the food. For example, if you ate two servings (two cups) of this macaroni and cheese, which is the number of serv- ings in the entire box, you would double the nutrient information on the label to calculate the kilocalories as well as the fat and other nutrients. The servings per container are particularly useful for portion control.

Below the serving size is listed the kilocalories per serving. The kilocalories from fat listing gives you an idea of what proportion of the food’s kilocalories comes from fat. In this box of macaroni and cheese, 110 out of a total of 250 kilocalories—that is, nearly half—are from fat.

Next are the nutrients that should be limited or added to the diet. Americans typically eat too much fat, including saturated fat, trans fat, and cholesterol, and too much sodium. In contrast, they tend to fall short in dietary fiber, vitamins A and C, and iron. These are on the label to remind consumers to make sure to eat foods rich in these substances. The Nutrition Facts panel can be your best shopping guide when identify- ing and choosing foods that are low in the nutrients you want to limit (like saturated fat) and high in the nutrients that you need to eat in higher amounts (like fiber).

Are you wondering what determines if a food contains a “high” or “low” amount of a specific nutri- ent? That’s where the Daily Values come into play.

The Daily Values Help Compare Packaged Foods Unlike the DRIs, which are precise recommended amounts for each nutrient, the Daily Values (DVs),

listed on the Nutrition Facts panel, are general reference levels for the nutrients listed on the food label. The DVs give a general idea of how the nutrients in the food fit into the overall diet. The DVs are based on older reference levels and are not as current as the DRIs. For example, whereas the DRIs recommend an upper level of dietary sodium of no more than 2,300 milligrams daily, the DVs use less than 2,400 milligrams as the reference level.

There are no DVs listed on the label for trans fat, sugars, and protein. For trans fat and sugars there isn’t enough information available to set reference values for these nutrients. Although there are reference values for protein, consuming adequate

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Figure 2.12 The Anatomy of the Nutrition Facts Panel

Source: Center for Food Safety and Applied Nutrition. 2004. How to Understand and Use the Nutrition Facts Label. Available at www.cfsan.fda.gov/~acrobat/foodlab.pdf. Accessed March 2008.

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amounts of protein isn’t a health concern for most Americans over age 4, so listing the percent of the DV for this nutrient isn’t warranted on the label. The DV for pro- tein will only be listed if the product, such as a jar of baby food, is being marketed for children under the age of 4, or if a claim is made about the food, such as that it is “high in protein.” 28

The DVs on the food label are based on a 2,000-kilocalorie diet. Individuals who need more or fewer than 2,000 kilocalories daily may have DV values that are higher or lower than those listed on the Nutrition Facts panel.

If a serving provides 20 percent or more of the DV for a given nutrient, it is con- sidered high in that nutrient. A serving of the macaroni and cheese (refer again to Figure 2.12) is high in sodium and calcium. If a serving provides 5 percent or less of the DV for a nutrient, it is considered low in that nutrient. A serving of macaroni and cheese doesn’t provide much fiber, vitamin A, vitamin C, or iron.

Lastly, depending on the size of the food package, there may be a footnote at the bottom of the label. This provides a summary of the DVs for a 2,000-kilocalorie diet as well as a 2,500-kilocalorie diet. This area of the panel is something of a “cheat sheet” when you are shopping so that you don’t have to memorize the values. As you can see from the footnote, you should try to keep your sodium intake to less than 2,400 milligrams daily. Because you know that this macaroni and cheese is high in sodium, providing 470 milligrams, or 20 percent of the DV, you should try to keep the sodium in your remaining food choices during the day to under 2,000 milligrams.

The Nutrition Facts panel on the side or back of the package can help you make healthier food choices, and some foods carry claims on their front labels that may also influence your decision to buy.

Label Claims Can Reveal Potential Health Benefits In the 1980s, the Kellogg Company ran an ad campaign for its fiber-rich All Bran ce- real reminding the public of the National Cancer Institute’s recommendation to eat low-fat, high-fiber foods, fresh fruits, and vegetables to maintain a healthy weight. According to the FDA, sales of high-fiber cereals increased over 35 percent within a year.29 Manufacturers realized that putting nutrition and health claims on labels was effective in influencing consumer purchases. Supermarket shelves were soon crowded with products boasting various claims.

The FDA mandates that all claims on labels follow strict guidelines. Currently, the FDA allows the use of three types of claims on food products: (1) nutrient con- tent claims, (2) health claims, and (3) structure/function claims. All foods display- ing these claims on the label must meet specified criteria.

Nutrient Content Claims A food product can make a claim about the amount of a nutrient it contains (or doesn’t contain) by using descriptive terms such as free (fat-free yogurt), high (high- fiber crackers), low (low saturated fat cereal), reduced (reduced-sodium soup), and extra lean (extra lean ground beef ) as long as it meets the strict criteria designated by the FDA. These terms can help identify at a glance the food items that best meet your needs. For instance, if you are concerned about consuming too much sodium, you could look for low-sodium claims on labels to decrease or limit the amount of sodium in your diet.

Look at the labels of the canned soups in Figure 2.13 on the next page. Note that the “low-sodium” version of the chicken soup cannot contain more than 140 milligrams

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structure/function claims Claims on the label that describe the role of a nutri-

ent or dietary compound that is proposed

to influence the structure or function of

the human body. For example, “calcium

builds strong bones” is a structure/

function claim.

health claims Claims on food labels that describe a relationship between a

food, food component, dietary ingredient,

or dietary supplement and a disease or

health-related condition.

nutrient content claims Claims on the food label that describe the level or

amount of a nutrient in the food. Terms

such as free, high, reduced, or lite are exam-

ples of nutrient content claims.

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of sodium per serving. In contrast, the soup with the term “less sodium” on the label contains 450 milligrams of sodium per serving, which is at least 25 percent less sodium than the regular variety. The can of classic chicken soup contains almost 900 milligrams for a serving, which is likely the same or even more sodium than the average American consumes at dinner. Table 2.8 provides some of the most common nutrient claims on food labels, and the specific criteria that each claim must meet as mandated by the FDA.

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Because this can of chicken noodle soup displays the “low sodium” nutrient claim, it can’t provide more than 140 milligrams of sodium in a serving.

a This can of soup has more than 25 percent less sodium than the classic version, so the term “less” can be displayed on its label.

b The classic variety of chicken noodle soup has the most sodium per serving.

c

a b c

Figure 2.13 Soup’s On! Nutrient claims on the food label must conform to strict criteria.

Reading labels can help Emma achieve her goals of eatinghealthier foods and choosing more nutrient-dense snacks. What information should Emma look for on the food label to help her cut down on fat and kilocalories, while making sure she gets enough calcium?

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Health Claims Suppose you are sitting at your kitchen table eating a bowl of Cheerios in skim milk, and staring at the front of the cereal box. You notice a claim that states: “The soluble fiber in Cheerios, as part of a heart-healthy diet, can help lower your cholesterol.” Do you recognize this as a health claim that links Cheerios with better heart health?

A health claim must contain two important components: (1) a food or a dietary compound, such as fiber, and (2) a corresponding disease or health-related condi- tion that is associated with the claim.30 In the Cheerios example, the soluble fiber (the dietary compound) that naturally occurs in oats has been shown to lower blood

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Table 2.8

What Does That Labeling Term Mean? Nutrient Free Low Reduced/Less Light

Calories �5 kilocalories (kcal) per serving

�40 kcal per serving At least 25% fewer kcal per serving

If the food contains 50% or more of its kcal from fat, then the fat must be reduced

Fat �0.5 grams (g) per serving

�3 g per serving At least 25% less fat per serving

Same as above

Saturated fat �0.5 g per serving �1 g per serving At least 25% less saturated fat per serving

N/A

Cholesterol �2 milligrams (mg) per serving

�20 mg per serving At least 25% less cholesterol per serving

N/A

Sodium �5 mg per serving �140 mg per serving At least 25% less sodium per serving

If the sodium is reduced by at least 50% per serving

Sugars �0.5 g N/A As least 25% less sugar per serving

N/A

Other Labeling Terms Term Definition

“High,” “Rich in,” or “Excellent source of”

The food contains 20% or more of the DV of the nutrient in a serving. Can be used to describe protein, vitamins, miner- als, fiber, or potassium.

“Good source of” A serving of the food provides 10–19% of the DV of the nutrient. Can be used to describe protein, vitamins, minerals, fiber, or potassium.

“More,” “Added,” A serving of the food provides 10% of the DV. Can only be “Extra,” or “Plus” used to describe vitamins, minerals, protein, fiber, and potassium.

“Lean” Can be used on seafood and meat that contains less than 10 g of fat, 4.5 g or less of saturated fat, and less than 95 mg of cholesterol per serving.

“Extra lean” Can be used on seafood and meat that contains less than 5 g of fat, less than 2 g of saturated fat, and less than 95 mg of cholesterol per serving.

“Healthy” Low in fat and saturated fat; limited in cholesterol content; sodium content can’t exceed 360 mg for individual foods or 480 for meal-type foods; contains 10% of the DV of one or more of vitamins A and C, iron, calcium, protein, or fiber.

N/A � not applicable

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cholesterol levels (the corresponding health-related condi- tion), which can help reduce the risk of heart disease.

There are three types of health claims: (1) authorized health claims, (2) health claims based on authoritative state- ments, and (3) qualified health claims. The differences be- tween them lie in the amount of supporting research and agreement among scientists about the strength of the relation- ship between the food or dietary ingredient and the disease or condition. See Table 2.9 for a definition of these claims and ex- amples of each.

Structure/Function Claims The last type of label claim is the structure/function claim, which describes how a nutrient or dietary compound affects the structure or function of the human body (Figure 2.14).31

The claims “calcium (nutrient) builds strong bones (body structure)” and “fiber (dietary compound) maintains bowel regularity (body function)” are examples of structure/ func- tion claims. Structure/function claims cannot state that the nutrient or dietary compound can be used to treat a disease or a condition.32 These claims can be made on both foods and di- etary supplements. Unlike the other health claims, structure/ function claims don’t need to be preapproved by the FDA. They do need to be truthful and not misleading, but the manufacturer is responsible for making sure that the claim is accurate.

Structure/function claims can be a source of confusion. Shoppers can easily fall into the trap of assuming that one brand of a product with a structure/function claim on its label is superior to another product without the claim. For instance, a yogurt that says “calcium builds strong bones” on its label may be identical to another yogurt without the flashy label claim. The consumer has to recognize the difference between

claims that are supported by a significant amount of solid research and approved by the FDA, and structure/function claims that don’t need prior approval for use.

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Figure 2.14 A Structure/Function Label Claim A structure/function claim describes how a nutrient or substance, such as the antioxidants that have been added to this cereal, support a function in the body, such as the immune system.

Cheerios uses an authorized health claim stating that soluble fiber reduces the risk of heart disease.

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Table 2.9

Sorting Out the Label Claims Type of Claim Definition Examples

Authorized health claims (well established)

Claims are based on a well-established rela- tionship between the food or compound and the health benefit. Food manufacturers must submit a petition to the FDA and provide the scientific research that backs up the claim. If there is significant agreement in the supporting research and a consensus among numerous scientists and experts in the field that there is a relationship between the food or dietary ingre- dient and the disease or health condition, the FDA will allow an authorized health claim. Specified wording must be used.

The FDA has approved 12 authorized health claims.

1. Calcium and osteoporosis 2. Sodium and hypertension 3. Dietary fat and cancer 4. Dietary saturated fat and cholesterol and risk

of coronary heart disease 5. Fiber-containing grain products, fruits, and

vegetables and cancer 6. Fruits, vegetables, and grain products that

contain fiber, particularly soluble fiber, and the risk of coronary heart disease

7. Fruits and vegetables and cancer 8. Folate and neural tube defects 9. Dietary sugar, alcohol, and dental caries

10. Soluble fiber from certain foods and risk of coronary heart disease

11. Soy protein and risk of coronary heart disease 12. Plant sterol/stanol esters and risk of coronary

heart disease

Health claims based on authoritative statements (well established)

Claims based on statements made by a U.S. government agency, such as the Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH).

If the FDA approves a claim submitted by the manufacturer, the wording of the claim must in- clude “may,” as in “whole grains may help reduce the risk of heart disease,” to illustrate that other factors in addition to the food or dietary ingredi- ent may play a role in the disease or condition.

This type of health claim can only be used on food and cannot be used on dietary supplements.

■ Whole-grain foods and risk of heart disease and certain cancers

■ Potassium and the risk of high blood pressure

Qualified health claims (less well established)

Claims based on evidence that is still emerg- ing. However, the current evidence to support the claim is greater than the evidence suggest- ing that the claim isn’t valid.

These claims are allowed in order to expedite the communication of potential beneficial health information to the public. They must be accom- panied by the statement “the evidence to sup- port the claim is limited or not conclusive” or “some scientific evidence suggests. . . .”

Many experts, including the American Dietetic Association, don’t support this type of health claim, as it is based on emerging evidence.

Qualified health claims can be used on dietary supplements if approved by the FDA.

■ Selenium and cancer ■ Antioxidant vitamins and cancer ■ Nuts and heart disease ■ Omega-3 fatty acids and coronary heart

disease ■ B vitamins and vascular disease ■ Monounsaturated fatty acids from olive oil and

coronary heart disease

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Dietary supplements that use structure/function claims must display a dis- claimer on the label stating that the FDA did not evaluate the claim and that the di- etary supplement is not intended to “diagnose, treat, cure or prevent any disease.” Manufacturers of foods bearing structure/function claims do not have to display this disclaimer on the label.

Although keeping the types of health and structure/function claims straight can be challenging, here’s one way to remember them: Authorized health claims and health claims based on authoritative statements are the strongest, as they are based on years of accumulated research or an authoritative statement. Qualified health claims are made on potentially healthful foods or dietary ingredients but because the evidence is still emerging, the claim has to be “qualified” as such. All health claims provide information on how the food or dietary ingredient can help reduce your risk of a condition or a disease.

Structure/function claims are the weakest claims, as they are just statements or facts about the role the nutrient or dietary ingredient plays in the body. They can’t claim how the food or dietary ingredient lowers the risk of developing a chronic dis- ease such as heart disease or cancer. In general, label claims with less established sci- entific evidence behind them have the weakest wording.

The Take-Home Message The FDA regulates the labeling on all packaged foods. Every food label must contain the name of the food, its net weight, the name and address of the manufacturer or distributor, a list of in- gredients, and standardized nutrition information. The FDA allows and regu- lates the use of nutrient content claims, health claims, and structure/function claims on food labels. Any foods or dietary supplements displaying these label claims must meet specified criteria and the claims must be truthful.

What Is the Exchange System? The exchange lists for meal planning were designed in 1950 to give people with dia- betes a structured, balanced eating plan. The lists are still in use today. Unlike some of the other dietary guides, the exchange lists group foods according to their carbo- hydrate, protein, and fat composition and provide specific portion sizes for each food. This assures that each food in the group contributes a similar amount of kilo- calories per serving.

This system of exchanges is organized into six food groups: starch, fruit, milk, vegetable, meat, and fat. You might be surprised to find some foods located in un- expected places. For example, in MyPyramid, cheese is in the milk group because of its calcium content. In the exchange system, cheese is placed in the meat group be- cause it has less carbohydrate than milk or yogurt but contains levels of protein and fat similar to those found in chicken or meat. Potatoes are not found in the vegetable list, but in the starch list; bacon is considered a fat exchange because it contains more fat than protein; and peanut butter is found in both the high-fat meat list and the fat list because it is high in both protein and fat.

Using the exchange lists is a convenient method for designing a meal plan to lose weight. Because of the similarity of the foods within each group, foods can be

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exchange lists A diet planning tool that groups foods together based on their

carbohydrate, protein, and fat content.

One food on the list can be exchanged for

another food on the same list.

Table Tips

Tips for an Adequate, Balanced, Varied, and Moderate Diet

Keep healthy snacks such as whole-grain crackers in your dorm room and combine them with protein-rich peanut butter or low-fat yogurt.

Pop a snack-pack size of light microwave popcorn for a portion-controlled whole- grain snack while you study.

Adopt a multicolor code to guide your food choices. Add tomato slices and a low-fat cheese slice to your whole-grain sandwich and carrots to your tossed green salad to ensure that your choices are adequate and varied.

Pack your own snack-sized portions of dried fruit, trail mix, whole-wheat crackers, baby carrots, or salt-free pretzels to carry in your backpack. Snack-sized bags of nuts and seeds are a nutritious way to help you avoid the vending machine and eat smaller, more moderate portions.

Keep your sweets to no more than about 100 calories.

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exchanged or swapped with each other at meals and snacks. The flexible meal plan is a useful tool to control kilocalorie, carbohydrate, protein, and fat intakes. For ex- ample, let’s assume you’ve determined that 1,800 kilocalories would be an appropri- ate level to gradually reduce your body weight while still consuming a healthy, balanced diet. Looking at Table 2.10, 1,800 calories equals 10 starch, seven meat, three vegetable, three fruit, two milk, and three fat exchanges. As you can see from the table, milk and fruit exchanges are the same but the higher the kilocalorie in- take, the greater the number of starch, meat, and vegetable exchanges allowed. Check Appendix E for an expanded list of foods for each exchange list group.

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Table 2.10

Number of Exchanges per Day by Caloric Intake List 1,200 kcal 1,500 kcal 1,800 kcal 2,000 kcal 2,200 kcal

Starch 5 8 10 11 13 Meat 4 5 7 8 8 Vegetable 2 3 3 4 4 Fruit 3 3 3 3 3 Milk 2 2 2 2 2 Fat 3 3 3 4 5

Starches and Bread. Each exchange under starches and bread contains about 15 grams of carbohydrates, 3 grams of protein, and a trace of fat for a total of 80 kilo- calories. A general rule is that a half cup of cooked cereal, grain, or pasta equals one exchange and 1 ounce of a bread product is 1 serving.

Meat and Cheese. The exchange groups for meat and cheese are categorized by lean meat and low-fat substitutes, medium-fat meat and substitutes, and high-fat meat and substitutes. High-fat exchanges should be used no more than three times a week. Fat should be removed before cooking. Exchange sizes on the meat list are generally 1 ounce and based on cooked meats (3 ounces of cooked meat equals 4 ounces of raw meat).

Vegetables. Exchanges for vegetables are 1⁄2 cup cooked, 1 cup raw, and 1⁄2 cup juice. Each group contains 5 grams of carbohydrates, 2 grams of protein, and between 2 and 3 grams of fiber. Vegetables can be fresh or frozen; canned vegetables are less desirable because they are often high in sodium. They should be steamed or microwaved without added fat.

Fruits and Sugar. Sugars are now included within the total carbohydrate count in the exchange lists. Sugars still should not be more than 10 percent of daily carbohydrates. Each exchange contains about 15 grams of carbohydrates for a total of 60 kilocalories.

Milk and Substitutes. The milk and substitutes list is categorized by fat content, similar to the meat list. A milk exchange is usually 1 cup or 8 ounces. For those who are on weight-loss or low-cholesterol diets, the skim and very low-fat milk lists should be fol- lowed, and the whole-milk group avoided. Others should use the whole-milk list very sparingly. All people with diabetes should avoid artificially sweetened milks.

Fats. A fat exchange is usually 1 teaspoon, but it may vary. Avoid saturated and trans fatty acids and choose polyunsaturated or monounsaturated fats instead.

Adapted from www.umm.edu/patiented/articles/what_diabetic_exchange_lists_000042_6.htm.

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72 Chapter 2 . Tools for Healthy Eating

101166 C P BC A Bl k P N 2 C/M/Y/K DESIGN SERVICES OF

FOCUS ON RESEARCH Background

Portion distortion, or perceiving larger por- tions of food as appropriate sizes, may be contributing to obesity. Studies conducted in the 1980s assessed breakfast and lunch foods typically consumed by young adults. Today, portion sizes may be even larger than in the past. Little research has been reported to verify the size of portions selected by this age group.

Research Question

How do the typical portion sizes of foods selected by young adults compare with the reference portion sizes, and have these typical portions changed over time?

Study Design

At a major northeastern university, en- rolled students served themselves typical portions of eight different breakfast foods or six different foods at lunch or dinner. Their food selections were weighed and given a score based on whether or not the portion was smaller or larger than the reference portion as defined from the Nutrition Labeling and Education Act.

If the food was 25 percent larger or 25 percent smaller than the reference size portion, it was given a score of 1. All other portion sizes were given a score of 0. The total score for the meal was achieved by adding the points for each food together. Thus, each participant’s unit score could range from 0 to 8 at breakfast or 0 to 6 at lunch and dinner. Analysis of variance or t tests were used to determine whether typical and refer- ence portion sizes differed, and whether typical portion sizes changed over time.

Results

The results of this study suggested that young adults today eat significantly larger portion sizes than their counterparts did two decades ago. The mean scores for breakfast (45 percent) and lunch/dinner (32 percent) were within the 25 percent range of smaller or larger than the refer- ence portion sizes.

Conclusions

The results of this study suggest that young adults today are consuming larger portions of food, and therefore more kilo- calories, than the reference portion sizes recommend. These portions, which are viewed as typical, may contribute to weight gain. The findings of this study are limited, however, to a small sample size of young adults at one university and should not be generalized to the larger population.

QUESTIONS

1. Was the measurement of foods com- pared to the reference portions appro- priate to answer the objectives of this study?

2. How do the results of this study an- swer the research question?

3. Are there other factors that could have influenced the results?

4. Do you agree with the author’s conclusions?

Schwartz, J. and C. Byrd-Bredbenner. 2006. Portion Distortion: Typical Portion

Sizes Selected by Young Adults. Journal of the American Dietetic Association

106:1412–1418.

Temporal Comparison of Typical Portion Size Selected by Young Adultsa

1984 2003

Mean±SDb Mean±SD n (g) n (g)

Breakfast

Cornflakes 53 37.2±15* 63 43.7±23.0*

Milk on cereal 53 158±61* 63 201.9±99.1*

Sugar on cereal 28 8.3±5* 63 5.6±3.0*

Butter 46 7.2±4.3 63 6.5±3.8

Jelly 35 18.8±9.2 63 21.6±13.8

Milk to drink 15 254.7±110.4 63 222.7±101.6

Orange juice 53 189.6±59.4* 63 271.9±117.2*

Lunch and dinnerc

Tuna salad 96 91.3±30.4 114 85.2±65.0

Tossed salad 94 67.6±21.9* 114 59.0±20.4*

Salad dressing 83 20.1±9.8* 114 15.8±10.6*

Fruit salad 91 123.5±32* 114 164.3±97.4*

aIncludes only the foods reported in both the previous (12) and present study.

bSD � standard deviation. cLunch and dinner included the same foods and did not differ significantly in terms of typical serving size selected, thus findings from these two meals were combined for this analysis.

*Means in the same row are significantly different (p � 0.05).

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Putting It All Together 73

101166 C P BC A Bl k P N 3 C/M/Y/K DESIGN SERVICES OF

Table 2.11

Putting It All Together: Tools for Healthy Eating

DRIs Dietary Guidelines for Americans 2005 MyPyramid

Nutrition Facts Panel

Exchange Lists for Healthy Eating

What Are They? Specific refer- ence values for each nutrient by age and gender

Reflect the most current nutrition and physical activity recommenda- tions for good health

A food guidance system that visually depicts the recom- mendations of the Dietary Guidelines for Americans 2005

Contains important nutrition informa- tion to be used to compare food products

Exchange lists are organized into food groups by their car- bohydrate, protein, fat, and calorie contents.

How Do They Guide You in Healthy Eating?

DRIs provide recommenda- tions to prevent malnutrition and chronic diseases for each nutrient. The upper level is designed to prevent overnu- trition or toxicity.

The Dietary Guidelines emphasize healthy food choices, maintaining healthy weight, and physical activity. Guide- lines for types of foods, moderate alcohol intake, and food safety are also included.

MyPyramid illustrates the diet and lifestyle themes of physical activity, proportional- ity, moderation, vari- ety, personalization, and gradual improvement.

You can use the Nutrition Facts panel to compare the nutrient density of foods.

It’s easy to plan healthy menus with a variety of foods. The exchanges are based on specific food por- tion sizes plus various fat levels in foods.

What Are They Made Up Of?

EARs, RDAs, AIs, ULs, and AMDRs

Divided into nine categories:

1. Adequate Nutrients 2. Weight Management 3. Physical Activity 4. Food Groups 5. Fats 6. Carbohydrates 7. Sodium and

Potassium 8. Alcoholic Beverages 9. Food Safety

Recommendations are made for physical activity as well as five food groups, plus oils:

1. Grains 2. Vegetables 3. Fruits 4. Milk 5. Meat and beans 6. Oils

Information is pre- sented about:

■ Serving size ■ Servings per

package ■ Total kilocalo-

ries and kilo- calories from fat

■ Macronutrients ■ Vitamins and

minerals ■ % Daily Values

Exchange lists consist of six food groups:

1. Starch 2. Meat 3. Vegetable 4. Fruit 5. Milk 6. Fat

Putting It All Together Healthy eating involves the key principles of adequate intake, balance, variety, and moderation. Nutrient density, energy density, and portion size also need to be taken into account when making food choices. Though implementing this advice may seem difficult at first, scientifically sound reference values and tools have been devel- oped to make healthy eating much easier. These include the DRIs, the 2005 Dietary Guidelines for Americans, MyPyramid, the Nutrition Facts panels on food labels, and exchange lists for creating healthy menus with a variety of foods. Table 2.11 provides a comparison of these tools, showing some of the unique features of each.

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74 Chapter 2 . Tools for Healthy Eating

Two Points of View Are Super Size Portions a Super Problem for Americans?

Portions sizes of meals served in restaurants have been steadily increasing. Do these larger meals play a role in America’s expanding waistlines?

Sheila R. Cohn, RD, LD NATIONAL RESTAURANT ASSOCIATION

Sheila R. Cohn, RD, LD is the director of nutrition policy in the health and safety regulatory affairs department of the National Restaurant Association. Her department advises the association, senior industry executives, and mem-

bership on legislative and regulatory health and safety issues that affect the restaurant industry. Typical subjects include nu- trition labeling, obesity, dietary guidelines for Americans, food allergies, public health and sanitation, security, and energy management.

Q: Why and how much have restaurant portion sizes in- creased over the years?

A: The restaurant industry is an industry of choice. Numer- ous studies have shown that customers want choice and flexibility in the foods they eat. For this reason, restau- rants have always offered consumers a wide variety of venues, menu items, and portion sizes to accommodate any individual’s dietary needs, tastes, and preferences. Serving several portion sizes (including appetizers, half- portions, and regular portions) has become prevalent across all types of restaurants, from casual to fine dining.

Q: How does portion size affect a person’s consumption and appeal of a meal when dining at restaurants?

A: With approximately half of all table-service restaurateurs reporting that their customers are even more value- conscious today than they were just two years ago, it isn’t surprising that most operators want consumers to choose portions that will satisfy them. Approximately half of table-service restaurants with per-person dinner checks of less than $25 made a practice of encouraging customers to order the size portion that was appropriate for them, and four out of 10 offered half-size portions at a reduced price.

Q: Is it the patron’s or the restaurant’s responsibility to control their portions of foods when dining out?

A: The responsibility of portion control is one that is shared between restaurants and their guests. As I mentioned earlier, restaurants provide many options (appetizers, shared portions, half-portions, regular portions) for their guests so that they make choices based on their individ- ual needs and preferences. It is not, however, the re- sponsibility of the restaurant to monitor or critique what their guests order or consume. (How would you like it if

Barbara J. Rolls, PhD PENNSYLVANIA STATE UNIVERSITY

Barbara J. Rolls, PhD, is professor of nutritional sciences and occupant of the Guthrie Chair in Nutrition. She is past- president of the North American Associ- ation for the Study of Obesity and in 2003 was awarded Honorary Member-

ship in the American Dietetic Association. In 2006 she was elected a fellow of the American Association of the Advance- ment of Science. She is the author of five books, including The Volumetrics Weight-Control Plan: Feel Full on Fewer Calories.

Q: Why and how much have restaurant portion sizes in- creased over the years?

A: Portion sizes have increased as the restaurant industry has found that customers appreciate good value for their money, which translates into large portions at a low price. The cost of the food is only a small percentage of the overall costs of serving a meal at a restaurant. Therefore, from the restaurant’s standpoint, increasing the portion size doesn’t dramatically increase the overall cost of the meal, but it can increase the loyalty of the customer to that restaurant. Customers often frequent restaurants based on the perceived value.

While some portion sizes, such as sliced bread, haven’t change over the years, other’s have, especially those items that are energy or calorie dense. For exam- ple, muffins can weigh as much as a half a pound and pasta served in bowls in restaurants can hold more than 2 pounds. Hamburgers can be more than double the size they were years ago.

Q: How does portion size affect a person’s consumption and appeal of a meal when dining at restaurants?

A: We have learned from our research that when you give individuals larger portions of food, they eat more at that meal. In one study, when we gave participants a serving of macaroni and cheese that was 50 percent larger than a standard portion, their caloric intake increased by 19 percent, and when we increased the portion size by 100 percent, they ate 30 percent more calories. Con- sumers appear to base the amount they eat on the amount that they are served. More disturbingly, our stud- ies show that individuals don’t make adjustments for this increased consumption of calories at other meals, setting the stage for potential weight gain over time.

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The Top Ten Points to Remember

1. Healthy eating involves the key principles of ade- quate intake, balance, variety, and moderation. Foods should be nutrient dense to provide adequate nutrition, but low in energy density to prevent un- wanted weight gain. A diet that is inadequate can cause undernutrition, and result in malnutrition. Balancing foods prevents overnutrition of nutrients

that can become toxic at high intakes, while modera- tion prevents the overconsumption of kilocalories and/or any one nutrient.

2. The Dietary Reference Intakes (DRIs) are specific ref- erence values, based on age and gender, that express the quantities of the essential nutrients needed daily. The DRIs are designed to prevent nutrient deficien- cies, maintain good health, prevent chronic diseases, and avoid unhealthy excesses. The DRIs consist of the Estimated Average Requirement, Recommended Di- etary Allowance, Adequate Intake, Tolerable Upper Intake Level, and the Acceptable Macronutrient

The Top Ten Points to Remember 75

Are Super Size Portions a Super Problem for Americans? continued

Sheila R. Cohn, RD, LD, continued Barbara J. Rolls, PhD, continued

your server commented that you were eating too much? Or that based on the fit of your pants, you should proba- bly just have a salad today?)

Based on research conducted by the National Restaurant Association, nearly two-thirds of adults agreed that table-service restaurants make it easy for them to choose the portion size they want. In fact, 75 percent of restaurant operators indicate increased customization of menu items by their guests.

One popular way to meet the needs of consumers who have smaller appetites is to encourage them to choose an appetizer or several appetizers in lieu of an entrée. It is important to note that this relaxed attitude to- ward portion-size options is coupled with an increase over the past five years in the proportion of table-service menus offering appetizer selections.

Q: What changes can the restaurant industry make to help Americans enjoy their experience, but not overindulge, when dining out?

A: Our research also shows that 71 percent of adults agreed that there are enough portion sizes available at restaurants, so they can receive as much or as little as they want. Virtually all restaurants allow customers to customize their meals, whether it is food-preparation method or substitution of food items to meet their individ- ual needs. Ninety-five percent of restaurants provide take-away containers for consumers that want to turn “tonight’s dinner into tomorrow’s lunch.”

Americans eat out an average of four times a week, meaning there are approximately 17 other meals each week that comprise one’s diet—not to mention other lifestyle choices, such as whether an individual exercises, and how much.

Q: Is it the patron’s or the restaurant’s responsibility to control their portions of foods when dining out?

A: Unfortunately, we are not a species that has a lot of re- straint when it comes to pleasurable experiences such as eating. In the end it is the consumer’s responsibility, but since people are unaware of how much they are eating, customers should have more choices. They need help from the restaurant industry.

Q: What changes can the restaurant industry make to help Americans enjoy their experience, but not over indulge, when dining out?

A: I would like to see restaurants offering a variety of por- tions sizes so that individuals have the option to order smaller portions. Restaurants could also reduce the en- ergy or calorie density of the meal by using less fat and adding more vegetables, fruits, and whole grains. This will enable the portion size to remain ample but lower the calories at that meal. For example, a pizza could be made with whole-wheat flour and topped with less cheese and plenty of vegetables instead of fatty meats. We need cuisines with more creative flavors that please our palate but for fewer calories. The focus in restaurants should be on the quality of the food, not on the quantity.

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76 Chapter 2 . Tools for Healthy Eating

Distribution Ranges. The EER indicates how much energy an individual needs based on age, gender, and activity level.

3. The Dietary Guidelines for Americans 2005 give the current nutrition and physical activity recommenda- tions for healthy Americans aged 2 and older. These guidelines can help improve the diet and lower the risk of chronic diseases and conditions such as diabetes mellitus, heart disease, certain cancers, osteoporosis, obesity, high blood pressure, and high blood choles- terol levels.

4. Food guidance systems are visualizations of food groups that provide a variety of food choices for creat- ing a well-balanced diet. MyPyramid is the USDA’s lat- est food guidance system. It visually represents many of the recommendations in the Dietary Guidelines for Americans 2005 and helps plan a diet to meet the daily DRIs for the essential nutrients. MyPyramid recom- mends the number of servings an individual should eat every day from each food group based on personal kilocalorie needs. There are five food groups: grains, vegetables, fruits, milk, and meat and beans. Oils are also shown on MyPyramid but are not a food group. MyPyramid emphasizes daily physical activity, propor- tionality, variety, and moderation. It provides a per- sonalized eating plan and encourages gradual improvements in diet and lifestyle to improve health.

5. The FDA regulates all packaged foods to ensure that they are accurately labeled. The Nutrition Facts panel on the food label must list the serving size of the food. It must also show the corresponding amount of kilo- calories, fat, saturated fat, trans fat, cholesterol, sodium, sugars, protein, vitamins A and C, calcium, and iron that are contained in a serving of the food. Other nutrients can be listed by the manufacturer vol- untarily. If a food product makes a claim about a nu- trient, that nutrient must be listed in the Nutrition Facts panel.

6. The Daily Values are reference levels of intakes for the nutrients listed on the food label. Unlike the DRIs, they are not individualized recommended intakes, but rather reference points that help consumers assess how the nu- trients in the foods can fit into the overall diet.

7. A food product label can carry a nutrient content claim about the amount of a nutrient the food con- tains by using descriptive terms such as free, high, low, reduced, and extra lean, as long as it meets the strict criteria for each item designated by the FDA.

8. A health claim must contain a food compound or a di- etary ingredient and a corresponding disease or health-related condition that is associated with the claim. All health claims must be approved by the FDA. Structure/function claims describe how a food or di- etary compound affects the structure or function of the body. These claims must be truthful and accurate and do not need FDA approval before being used. They cannot be tied to a disease or health-related condition.

9. Exchange lists group foods according to their carbohy- drate, protein, fat, and kilocalorie content while pro- viding specific portion sizes. Using the exchange lists for meal planning is a convenient method for develop- ing flexible meal plans.

10. Portion size is the amount of a food consumed at one sitting. Americans typically have a distorted view of what a portion of food should be. Misunderstanding portion sizes can lead to overconsumption of kilocalo- ries, and therefore weight gain, as well as increased risk of cardiovascular disease, diabetes, and some cancers. Serving size is the standard amount used on a nutrient label.

Test Your Knowledge 1. The Dietary Guidelines for Americans 2005 recommend

a. consuming adequate nutrients within kilocalorie needs and being physically active daily.

b. stopping smoking and walking daily. c. sleeping eight hours a night and jogging every other

day. d. consuming adequate nutrients within kilocalorie needs

and drinking more alcohol. 2. Nutrient-dense foods

a. contain an equal balance of carbohydrates, proteins, and fats.

b. are high in nutrients and lower in kilocalories. c. have a nutrition label. d. have greater weight than volume.

3. The Dietary Reference Intakes (DRIs) are reference values for nutrients and are designed to a. only prevent a nutritional deficiency. b. provide a general range of nutrient needs. c. prevent nutritional deficiencies by meeting nutrient

needs and prevent the consumption of excessive and dangerous amounts of nutrients.

d. apply only to infants and children.

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4. The Estimated Average Requirement (EAR) is a. the estimated amount of a nutrient that should be

consumed daily to be healthy. b. the amount of a nutrient that meets the average needs

of 50 percent of individuals in a specific age and gender group.

c. the maximum safe amount of a nutrient that should be consumed daily.

d. the amount of a nutrient that meets the needs of 99 percent of the population.

5. MyPyramid is a food guidance system that can a. help implement the recommendations in the DRIs. b. help individuals use the advice in the Dietary

Guidelines for Americans. c. provide personalized food choices among a variety of

food groups to help create a balanced diet. d. do all of the above.

6. Which of the following are the food groups in MyPyramid? a. grains, vegetables, milk, sweets, and meat and beans b. grains, fruits, alcohol, sweets, and meat and beans c. grains, vegetables, fruits, milk, and meat and beans d. grains, vegetables, sweets, milk, and meat and beans

7. Which of the following foods is most nutrient dense? a. an orange ice pop b. an orange c. orange-flavored punch d. orange sherbet

8. By law, which of the following MUST be listed on the food label? a. kilocalories, fat, and potassium b. fat, saturated fat, and vitamin E c. kilocalories, fat, and saturated fat d. kilocalories, sodium, and vitamin D

9. Bran cereal that carries a “high-fiber” claim on its label is an example of a a. nutrient claim. b. structure/function claim. c. health claim. d. density claim.

10. A yogurt that states that a serving provides 30 percent of the Daily Value for calcium contains a ________ amount of calcium. a. high b. medium c. low d. negligible

Answers 1. (a) The Dietary Guidelines for Americans recommend a

balanced diet to meet nutrient needs without overcon- suming kilocalories, and that individuals be physically ac- tive daily. Walking or jogging are wonderful ways to be physically active. Though the Dietary Guidelines do not specifically address stopping smoking, this is a habit worth kicking. Sleeping eight hours a night isn’t men- tioned in the Dietary Guidelines but is another beneficial lifestyle habit. Many people should abstain from alcohol, and those who choose to drink should do so only in moderation.

2. (b) Nutrient-dense foods are high in nutrients, such as vi- tamins and minerals, but low in energy (kilocalories).

3. (c) The DRIs recommend the amount of nutrients needed to prevent deficiencies, maintain good health, and avoid toxicity.

4. (b) The EAR is the amount of a nutrient that would meet the needs of half of the individuals in a specific age and gender group. The EAR is used to obtain the Recom- mended Dietary Allowance (RDA), which is the amount of a nutrient that should be consumed daily to maintain good health. The Tolerable Upper Intake Level (UL) is the maximum amount of a nutrient that can be consumed on a regular basis that is unlikely to cause harm.

5. (d) MyPyramid is a food guidance tool that helps individ- uals create a balanced diet. It is designed to help meet the nutrient needs recommended in the DRIs and also imple- ment the advice in the Dietary Guidelines for Americans.

6. (c) Grains, vegetables, fruit, milk, and meat and beans are the five basic food groups in MyPyramid. Sweets and al- cohol are not food groups and should be limited in the diet. Although fats and oils are included on MyPyramid, they are not a food group.

7. (b) Though an orange ice pop or orange sherbet may be a refreshing treat on a hot day, the orange is by far the most nutrient-dense food among these choices. The orange- flavored punch is a sugary drink.

8. (c) The Nutrition Facts panel on the package must indi- cate the amounts of kilocalories, fat, and saturated fat per serving. Vitamins E and D do not have to be listed unless they have been added to the food and/or the product makes a claim about them on the label.

9. (a) This high-fiber cereal label boasts a nutrient claim.

Test Your Knowledge 77

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78 Chapter 2 . Tools for Healthy Eating

10. (a) A product with 20 percent or more of the Daily Value for a nutrient is considered “high” in that nutrient. If a food provides 5 percent or less of the Daily Value for a nutrient, it is considered “low” in that nutrient.

Answers to Myths and Misconceptions

1. False. Eating a balanced diet means not eating too much of any one food.

2. False. Nutrient density refers to foods that are high in nutrients but low in energy or kilocalories.

3. True. The Dietary Reference Intakes are specific reference values for each nutrient according to age, gender, and life stage. Their main focus is to maintain good health and re- duce the risk of developing chronic diseases and avoid unhealthy excesses.

4. True. If there is adequate scientific evidence to establish an Estimated Average Requirement (EAR) for a nutrient, then an RDA can be calculated. Some nutrients have not been sufficiently researched to provide an EAR and there- fore an Adequate Intake is recommended.

5. True. The five basic food groups are grains, vegetables, fruit, milk, and meat and beans.

6. True. These guidelines are the latest recommendations for nutrition and physical activity for healthy Americans over the age of 2.

7. False. Many people overconsume a food at any one sit- ting by piling two or more portions of it on their plate.

8. True. The FDA requires a food label on all packaged food items, and specific information must be included.

9. True. Specific descriptive terms approved by the FDA must be used.

10. True. Exchange lists allow you to swap foods within each food group while still controlling the amount of carbohy- drate, protein, fat, and kilocalories you ingest.

Web Support ■ For more tips and resources for MyPyramid, visit www

.MyPyramid.gov ■ For the USDA’s Recipes and Tips for Healthy, Thrifty

Meals, visit www.usda.gov/cnpp/Pubs/Cookbook/ thriftym.pdf

■ For a seasonal guide to healthy eating, visit www.fns.usda .gov/tn/Students/Food_Family/index.html

References 1. Simpson, K. M., E. R. Morris, and J. D. Cook. 1981. The Inhibitory Effect

of Bran on Iron Absorption in Man. American Journal of Clinical Nutri- tion 34:1469–1478.

2. Murphy, S., J. Foote, L. Wilkens, P. Basiotis, A. Carlson, K. White, and K. Yonemoriet. 2006. Simple Measures of Dietary Variety Are Associated with Improved Dietary Quality. Journal of the American Dietetic Associa- tion 106:425–429.

3. Produce for Better Health Foundation. 2007. Fruits and Vegetables, More Matters. Available at www.fruitsandveggiesmorematters.org Accessed June 2007.

4. Ledikwe, J. H., H. M. Blanck, L. K. Khan, M. K. Serdula, J. D. Seymour, B. C. Tohill, and B. J. Rolls. 2006. Low-Energy-Density Diets Are Associ- ated with High Diet Quality in Adults in the United States. Journal of the American Dietetic Association 106:1172–1180.

5. Bell, E. A. and B. J. Rolls. 2001. Energy Density of Foods Affects Energy Intake Across Multiple Levels of Fat Content in Lean and Obese Women. American Journal of Clinical Nutrition 73:1010–1018.

6. Ledikwe, J. H., H. M. Blanck, L. K. Khan, M. K. Serdula, J. D. Seymour, B. C. Tohill, and B. J. Rolls. 2006. Dietary Energy Density Is Associated with Energy Intake and Weight Status in U.S. Adults. American Journal of Clinical Nutrition 83:1362–1368.

7. Ledikwe, J. H., B. J. Rolls, H. Smiciklas-Wright, D. C. Mitchell, J. D. Ard, C. Champagne, N. Karanja, P. Lin, V. J. Stevens, and L. J. Appel. 2007. Re- ductions in Dietary Energy Density Are Associated with Weight Loss in Overweight and Obese Participants in the PREMIER Trial. American Journal of Clinical Nutrition. 85:1212–1221.

8. Greene, L., C. Z. Malpede, C. S. Henson, K. A. Hubbert, D. C. Heim- burger, and J. D. Ard. 2006. Weight Maintenance 2 Years After Participa- tion in a Weight Loss Program Promoting Low-Energy-Density Foods. Obesity 14:1795–1801.

9. Rolls, B. J., E. A. Bell, V. H. Castellanos, M. Chow, C. L. Pelkman, and M. L. Thorwart. 1999. Energy Density but not Fat Content of Foods Af- fected Energy Intake in Lean and Obese Women. American Journal of Clinical Nutrition 69: 863–871.

10. U. S. Department of Agriculture. 2005. MyPyramid: USDA’s New Food Guidance System. Available at www.mypyramid.gov/professionals/index .html. Accessed March 2007.

11. Institute of Medicine. 2003. Dietary Reference Intakes: Applications in Di- etary Planning. Washington, DC: The National Academies Press.

12. Barr, S. I., S. P. Murphy, T. D. Agurs-Collins, and M. I. Poose. 2003. Plan- ning Diets for Individuals Using the Dietary Reference Intakes. Nutrition Reviews 61:352–360.

13. Tarasuk, V. 2006. Use of Population-Weighted Estimated Average Re- quirements as a Basis for Daily Values on Food Labels. American Journal of Clinical Nutrition 83:1217S–1222S.

14. Institute of Medicine. 2001. Dietary Reference Intakes for Vitamin A, Vit- amin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: The National Academies Press.

15. Ibid. 16. Shils, M. E., M. Shike, A. C. Ross, B. Caballero, and R. J. Cousins. 2006.

Modern Nutrition in Health and Disease, 10th ed. Baltimore: Lippincott Williams & Wilkins.

17. Institute of Medicine. 2002. Dietary Reference Intakes for Energy, Carbohy- drate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Wash- ington, DC: The National Academies Press.

18. U. S. Department of Agriculture. 2005. 19. Davis, C. and E. Saltos. 1999. Dietary Recommendations and How They

Have Changed Over Time, in America’s Eating Habits: Changes and Con- sequences. E. Frazo, ed. Agriculture Information Bulletin No. AIB750.

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20. Lee, P. R. 1978. Nutrition Policy: From Neglect and Uncertainty to Debate and Action. Journal of the American Dietetic Association 72:581–588.

21. U. S. Department of Agriculture. 2005. The Report of the Dietary Guide- lines Advisory Committee on Dietary Guidelines for Americans, 2005. Available at www.hhs.gov. Accessed June 2008.

22. Ibid. 23. Center for Food Safety and Applied Nutrition. 1999. A Food Labeling

Guide. Available at www.cfsan.fda.gov/~dms/flg-toc.html. Accessed March 2008.

24. Food and Drug Administration. 2007. Food Labeling and Nutrition. Available at www.cfsan.fda.gov/label.html. Accessed March 2008.

25. Ibid. 26. United States Department of Agriculture. 2002. Food Labeling: Guide-

lines for Voluntary Nutrition Labeling of Raw Fruits, Vegetables, and Fish; Identification of the 20 Most Frequently Consumed Raw Fruits, Vegetables, and Fish. Federal Register 67:12918–12937.

27. Food Safety and Inspection Service. 2001. Nutrition Labeling Proposed for Raw Meat and Poultry Products. Available at www.fsis.usda.gov. Ac- cessed March 2008.

28. Center for Food Safety and Applied Nutrition. 2004. How to Understand and Use the Nutrition Facts Label. Available at www.cfsan.fda.gov/~acro- bat/foodlab.pdf. Accessed March 2008.

29. Kurtzweil, P. 1998. Staking a Claim to Good Health. FDA Consumer. Available at www.fda.gov/FDAC/features1998/698_labl.html.

30. Center for Food Safety and Applied Nutrition. 2003. Claims That Can Be Made for Conventional Foods and Dietary Supplements. Available at www.cfsan.fda.gov/~dms/hclaims.html. Accessed March 2008.

31. Hasler, C. M., et al. 2004. Position of the American Dietetic Association: Functional Foods. Journal of the American Dietetic Association. 104: 814–826.

32. Institute of Food Technologists. 2005. Expert Report on Functional Foods: Opportunities and Challenges, Executive Summary. Available at www.ift .org. Accessed March 2008.

References 79

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3 1. Saliva can alter the taste of food. T/F2. Without mucus, the stomach would digest itself. T/F 3. The major function of bile is to emulsify fats. T/F

4. Acid reflux is caused by gas in the stomach. T/F

5. The primary purpose of the large intestine is to absorb water. T/F

6. Feces contain a high amount of bacteria. T/F

7. The lymphatic system transports all nutrients through the body once they’ve been absorbed. T/F

8. Hormones play an important role in digestion. T/F

9. Diarrhea is always caused by bacterial infection. T/F

10. Irritable bowel syndrome is caused by an allergy to gluten. T/F

See page 114 for answers.

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Digestion, Absorption,

and Transport

How the Body Processes Food

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82 Chapter 3 . Digestion, Absorption, and Transport

Chapter Objectives After reading this chapter, students will be able to:

1. Define digestion, absorption, and transport.

2. Describe the organs involved in di- gestion and their primary functions.

3. Explain the roles of the gallbladder, liver, and pancreas in digestion.

4. Explain the function of peristalsis and segmentation in the move- ment of food through the GI tract.

5. Explain the role of enzymes in digestion.

6. List the main carbohydrate-, protein-, and fat-digesting enzymes and the tissues that secrete them.

7. Identify the hormones involved in digestion, including their primary action and their source of origin.

8. Describe the four mechanisms of absorption in the small intestine.

9. Explain how the circulatory and lymphatic systems transport ab- sorbed nutrients throughout the body.

10. Describe the symptoms and causes of the most common digestive disorders.

What Are Digestion, Absorption, and Transport? To absorb the nutrients in food, the bonds that link the nutrients together must be broken down in the gastrointestinal (GI) tract (digestive tract). Digestion is the process that breaks the bonds and reduces food into individual molecules. The parti- cles that result are small enough to pass through the cells of the small intestinal wall by absorption. Once the nutrients have been absorbed, they are transported through the circulatory system to the liver and various tissues throughout the body. Those nutrients that aren’t digested or absorbed are excreted as waste (feces) by elimination.

When digestion, absorption, and transport work properly, these complex processes go unnoticed. You consciously chew and swallow food, but you don’t feel the muscular contractions that propel it through the GI tract organs. Nor is it obvi- ous when the pancreas and small intestine release secretions, or when the single mol- ecules of nutrients are absorbed into the intestinal cell wall. In fact, unless you feel a few grumblings of borborygmus, which occurs when gas and air pockets form as stomach contents are pushed through the GI tract, the entire process goes unnoticed until about 48 hours after eating, when the body is ready to eliminate waste through the rectum.

The body accomplishes digestion chemically, by actions of digestive secretions such as enzymes (which we’ll discuss in detail later in the chapter), and mechanically, by the actions of the teeth and powerful muscular contractions of the GI tract. This chapter provides an overview of the processes of both chemical and mechanical digestion.

Have you had, or known someone who has had, symptoms similar to Emily’s? Can you guess the reason for Emily’s gastrointestinal distress? What advice might you give to help her relieve her symptoms?

In this chapter, we’ll find out more about Emily’s condition, as well as other common digestive disorders. We’ll ex- plore the processes of digestion, absorption, and transport, the organs involved, and the other biological mechanisms that regulate our bodies’ processing of food and nutrients.

T wenty-one-year-old Emily doesn’t eat breakfast before her 11 a.m. nutrition class because she knows

she’s likely to feel uncomfortably full and bloated after. Lately, Emily has had frequent bouts of abdominal pain that are only re- lieved by a bowel movement, followed by several loose, watery stools. Her symp- toms are worse when she eats a large meal, especially when the meal contains wheat, and right before a midterm exam or a paper is due. For a few weeks at the be- ginning of the semester, her symptoms had subsided. But lately, they’ve returned and appear to be getting worse.

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What Are the Organs of the GI Tract and Why Are They Important? 83

Digestion converts whole foods into individual nutrients that can be used by the body’s cells.

What Are the Organs of the GI Tract and Why Are They Important? The GI tract is a 23-foot-long muscular tube that extends from the mouth to the anus. Stretched vertically, the tube would be about as high as a two-story building. It provides a barrier between the food we eat (external) and the body cells (internal). This barrier regulates which nutrients enter the body and which nutrients pass through the GI tract unabsorbed based on the needs of the body.

The five organs that make up the digestive tract—the mouth, esophagus, stom- ach, small intestine, and large intestine—contain numerous specialized cells involved in the digestive process. Cells in the lining of the small intestine, for example, secrete enzymes involved in chemical digestion, while specialized muscles of the stomach mechanically digest and propel food through the tract. Various sphincters along the way allow food to pass from one organ to the next. These muscular rings act like one-way doors, allowing the mixture of food and digestive juices to flow into one organ but not back out.

Outside the GI tract are the accessory organs: the liver, pancreas, and gallblad- der, which aid in digestion by secreting digestive juices through ducts into the small intestine. Figure 3.1 on page 84 illustrates the organs involved in digestion and their roles in the digestion process.

Each organ has specific tasks designed to prepare food to be absorbed. The follow- ing discussion explores the structure and function of the individual GI tract organs.

gastrointestinal (GI) tract A long tube comprised of the organs of the digestive

tract. It extends from the mouth through

the esophagus, stomach, and small and

large intestines to the anus.

digestion A process that breaks down food into individual molecules small

enough to be absorbed through the intes-

tinal wall.

absorption The process of moving nutrients from the GI tract into the

bloodstream.

elimination Excretion of undigested and unabsorbed food through the feces.

transport The process of moving absorbed nutrients throughout the body through the

circulatory and lymph systems.

borborygmus Grumbling of the stom- ach caused by air pockets formed as food

is pushed through the GI tract.

enzymes Substances, mostly proteins, that increase the rate of chemical changes

or catalyze chemical reactions; also called

biological catalysts.

chemical digestion Breaking down food through enzymatic reactions.

mechanical digestion Breaking down food by chewing, grinding, squeezing, and

moving food through the GI tract by peri-

stalsis and segmentation.

accessory organs Organs that partici- pate in digestion but are not considered

part of the GI tract. They include the liver,

pancreas, and gallbladder.

sphincter A circular ring of muscle that opens and closes in response to nerve

input.

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84 Chapter 3 . Digestion, Absorption, and Transport

Digestion Begins in the Mouth Both chemical digestion and mechanical digestion begin in the mouth. During mastication, the teeth, powered by strong jaw muscles, mechanically cut and grind food into smaller pieces as the tongue mixes it with saliva (refer again to Figure 3.1). The salivary glands, located beneath the jaw and under and behind the tongue, pro- duce about 1 quart of saliva per day.1 Saliva dissolves small food particles, which al- lows them to react with the taste buds so we can savor food, and it moistens and binds food to lubricate it for comfortable swallowing and travel down the esophagus. Saliva also contains the enzyme amylase, which begins to break down carbohydrate. (You can taste this enzyme working when you each a starch-containing food; as the enzyme breaks down starch into smaller pieces, or sugars, the flavor will become sweeter. Remember this the next time you eat a cracker.) In adults, no other chemical digestion takes place in the mouth.

Once food has been adequately chewed and moistened, the tongue rolls it into a bolus, and thrusts it into the pharynx to be swallowed. The pharynx is the gateway

salivary glands Cluster of glands located underneath and behind the tongue

that release saliva in response to the sight,

smell, and taste of food.

bolus A soft mass of chewed food.

pharynx The area of the GI tract be- tween the mouth and the esophagus; also

called the throat.

Salivary glands

Pharynx

Epiglottis

Esophagus

Liver

Gallbladder

Stomach

Pancreas

Large intestine

Small intestine

Rectum

Anus

INGESTION

Mouth Mastication tears, shreds, and mixes food with saliva

Pharynx Food passes between the mouth to the esophagus

Epiglottis prevents the bolus from flowing into the trachea

DIGESTION AND ABSORPTION

Stomach mixes and churns food with acid, enzymes, and gastric fluid into a liquid called chyme

Small intestine secretes digestive enzymes and absorbs nutrients

Large intestine reabsorbs salts and water; compacts unwanted waste to be stored in the rectum

ACCESSORY ORGANS

Liver manufactures bile acids to digest fats

Gallbladder stores bile to be released into the small intestine

Pancreas secretes digestive enzymes and bicarbonate ions through the pancreatic duct into the small intestine

ELIMINATION

Rectum Warehouses waste before the release through the anus

Anus relaxes to release waste

Figure 3.1 A Journey through The GI Tract The journey through the GI tract begins in the mouth. As food travels through the GI organs, it is broken down into individual nutrients and eventually absorbed into the circulation. Undigested waste is eliminated through the rectum.

saliva Secretion from the salivary glands that softens and lubricates food, and

begins the chemical breakdown of starch.

mastication Chewing food.

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upper esophageal sphincter The muscular ring located at the top of the

esophagus.

What Are the Organs of the GI Tract and Why Are They Important? 85

Esophagus

Trachea (open)

Esophagus

Trachea (closed)

Bolus

Tongue

Epiglottis (up)

Bolus

Tongue

Epiglottis (down)

Figure 3.2 The Role of the Epiglottis The epiglottis prevents food from entering the trachea during swallowing.

The LES (lower esophageal sphincter) relaxes after swallowing to allow the bolus to enter the stomach.

1 The LES contracts to prevent stomach contents from returning to the esophagus.

2

Esophagus

Bolus LES relaxes

Stomach

Esophagus

LES contracts

Stomach

Figure 3.3 Sphincters at Work Sphincters control the passage of food by contracting or relaxing.

to the esophagus, as well as to the trachea (or windpipe, the tube that connects to the lungs). Normally, a flap of cartilage called the epiglottis closes off the trachea during swallowing, so that food doesn’t accidentally “go down the wrong pipe” (see Figure 3.2). When the epiglottis doesn’t work properly, food can get lodged in the trachea and potentially result in choking.

The esophagus has only one function—to transport food and fluids from the mouth to the stomach. As food passes through the pharynx, the upper esophageal sphincter opens, allowing the bolus to enter the esophagus. After swallowing, rhyth- mic muscular contractions, with the help of gravity, move the bolus toward the stomach. The esophagus narrows at the bottom (just above the stomach) and ends at the lower esophageal sphincter (LES) (Figure 3.3). Under normal conditions, when the bolus reaches the stomach, the LES relaxes and allows food to pass into the stom- ach. The stomach also relaxes to comfortably receive the bolus. After food enters the stomach, the LES closes to prevent the stomach contents from regurgitating back- ward into the esophagus.

The Stomach Stores, Mixes, and Prepares Food for Digestion The primary purpose of the stomach is to mix food with various gastric juices to chemically break it down into smaller and smaller pieces (see Figure 3.4 on page 86). The stomach lining includes four layers. The innermost layer contains goblet cells and gastric pits or ducts, which contain gastric glands that secrete a variety of criti- cal digestive juices. Various other cells in the stomach lining, among them parietal cells, chief cells, and mucus neck cells, secrete other gastric juices and mucus.

Mechanical digestion in the stomach occurs as the longitudinal, circular, and diagonal muscles that surround the organ forcefully push, churn, and mix the con- tents of the stomach with the gastric juices. These powerful muscles can also stretch to accommodate different volumes of food. Stomach capacity is a little less than a cup when it’s empty but it can expand to hold up to 1 gallon (4 liters).2 For several hours, food is continuously churned and mixed in the stomach.

By the time the mixture reaches the lower portion of the stomach it is a semi- liquid mass called chyme, which contains digestive secretions plus the original food.

epiglottis Cartilage at the back of the tongue that closes off the trachea during

swallowing.

esophagus Tube that connects the mouth to the stomach.

lower esophageal sphincter (LES) The muscular ring located between the

base of the esophagus and the stomach.

gastric pits Indentations or small pits in the stomach lining where the gastric

glands are located; gastric glands produce

gastric juices.

goblet cells Cells throughout the GI tract that secrete mucus.

stomach A J-shaped muscular organ that mixes and churns food with digestive

juices and acid to form chyme.

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As the chyme accumulates near the pyloric sphincter, the sphincter relaxes and the chyme gradually enters the small intestine. Because you eat much faster than you can digest and absorb food, the stomach also acts as a holding tank for chyme until it can be released into the small intestine. The numerous folds of the stomach lining, which stretch out after a large meal, make it an ideal site for temporarily storing chyme. Approximately 1 to 5 milliliters (1 teaspoon) of chyme is released into the small intestine every 30 seconds.3 The pyloric sphincter prevents chyme from exiting the stomach too soon, and blocks the intestinal contents from returning to the stomach.

Most Digestion Occurs in the Small Intestine As chyme passes through the pyloric sphincter, it enters the long, coiled chamber of the small intestine (Figure 3.5). This organ consists of three segments—the duode- num, jejunum, and ileum—and extends from the pyloric sphincter to the ileocecal valve at the beginning of the large intestine. The first segment, the duodenum, is ap- proximately 10 inches long. The second area, the jejunum, measures about 8 feet long, and the final region, the ileum, is about 12 feet long. The “small” in “small in- testine” refers to its diameter, not its extended length.

As in the stomach, both mechanical and chemical digestion occur in the small intestine. Muscular contractions allow the organ to squeeze chyme forward while digestive secretions from the pancreas, gallbladder, and intestinal lining chemically break down the nutrients. The small intestine is lined with numerous fingerlike projections, called villi, that help increase its surface area to maximize absorption. The villi extend about 1 millimeter into the interior (or lumen), creating a velvety appearance and are arranged into hundreds of overlapping, circular folds. Scattered along the villi are goblet cells whose sole function is to secrete lubricating mucus into the intestine.

Around the base of the villi lie glands called crypts that secrete intestinal juice. Within the crypts, stem cells continually divide, producing younger cells that travel up the villi to replace the mature cells when they die. A constant source of nutrients is needed to replace these cells and maintain a healthy absorptive surface. Without the proper nutrients, the villi deteriorate and flatten, resulting in malabsorption. In addition to providing increased surface area, the villi help mix the partially digested

glycocalyx Substance on the microvilli that contains protein- and carbohydrate-

digesting enzymes.

microvilli Tiny projections on the villi in the small intestine.

crypts Glands at the base of the villi; they contain stem cells that manufacture

young cells to replace the cells of the villi

when they die.

villi Small, fingerlike projections that line the interior of the small intestine.

small intestine The long coiled cham- ber that is the major site of digestion of

food and the absorption of nutrients.

86 Chapter 3 . Digestion, Absorption, and Transport

chief cells Specialized cells in the stomach that secrete an inactive protein-

digesting enzyme called pepsinogen.

chyme The semi-liquid, partially di- gested food mass that leaves the stomach

and enters the small intestine.

Longitudinal muscles

Stomach Cross section of inner stomach walls

Small intestine

Esophagus

Lower esophageal sphincter

Circular muscles

Diagonal muscles

Inner stomach walls

Chief cells

Gastric pits

Parietal cells

Submucosa

Gastric glands

Goblet cells

Figure 3.4 Anatomy of the Stomach The cross section of the stomach illustrates the gastric cells that secrete digestive juices.

parietal cells Specialized cells in the stomach that secrete the gastric juices

hydrochloric acid and intrinsic factor.

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large intestine The lowest portion of the GI tract, where water and electrolytes

are absorbed and waste is eliminated.

What Are the Organs of the GI Tract and Why Are They Important? 87

The multifolded arrangement and villi provide an immense surface area over which nutrients can be absorbed.

a Blood and lymph vessels pick up nutrients through the brush border and transport them throughout the body.

b Microvilli on the surface of intestinal cells further increase the surface area.

c

Small intestine Fingerlike structure of the villi

Villi Microvilli (brush border)

Nutrients

Cells of the intestinal lining

Goblet cell

Crypt

Figure 3.5 Anatomy of the Small Intestine The small intestine is a long, narrow, tightly coiled chamber in which most digestive absorption takes place.

chyme with intestinal secretions, and the circular folds cause chyme to spiral forward through the small intestine, further increasing its exposure to the villi.

Villi are in turn covered with smaller projections called microvilli that provide additional surface area and maximize nutrient absorption. The microvilli, also called the brush border, are covered with glycocalyx, which contains carbohydrate- and pro- tein-digesting enzymes. Once the final stages of digestion have been completed, the nutrients are trapped by the microvilli and absorbed into the cells to be transported throughout the body. Brush border cells also secrete several enzymes that digest spe- cific nutrients. We’ll discuss these secretions in more detail later in the chapter.

Depending on the amount and type of food eaten, the contact time in the small intestine is between 3 and 10 hours. Usually, by the time you sit down to dinner, your breakfast is just about reaching the end of the small intestine.

The Large Intestine Absorbs Water and Some Nutrients Chyme passes from the small intestine into the large intestine through the ileocecal valve. About 750 milliliters of unabsorbed residue enters the large intestine each day. The large intestine is about 5 feet long and 2.5 inches in diameter. Like the small intestine, the large intestine has three segments: the cecum, colon, and rectum (see Figure 3.6 on page 88). However, it looks and acts much differently than the small intestine in that it is much shorter, does not have villi or microvilli, does not produce digestive enzymes, and is not tightly coiled.

A closer look at the villi of the small intestine.

ileocecal valve The sphincter that separates the small intestine from the large

intestine.

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anus The opening of the rectum, or end of the GI tract.

rectum Final 8-inch portion of the large intestine.

stool Waste produced in the large intestine; also called feces.

ferment To metabolize sugar into carbon dioxide and other gases.

88 Chapter 3 . Digestion, Absorption, and Transport

The colon is the largest portion of the large intestine, and it is further sub- divided into the ascending, transverse, descending, and sigmoid regions. These re- gions are relatively long and straight. Note that though the terms “colon” and “large intestine” are often used interchangeably, technically they’re not the same thing.

By the time chyme enters the large intestine, the majority of the nutrients, except water and the electrolytes sodium, potassium, and chloride, have been absorbed. The cells of the large intestine absorb water and these electrolytes much more efficiently than the cells of the small intestine. The large intestine also produces mucus that protects the cells and acts as a lubricant for fecal matter.

Bacteria in the colon produce some vitamins, including vitamin K, thiamin, ri- boflavin, biotin, and vitamin B12. Only biotin and vitamin K can be absorbed, how- ever. Bacteria also ferment some of the undigested and unabsorbed dietary carbohydrates into simpler compounds, methane gas, carbon dioxide, and hydrogen. This fermentation process is the major source of intestinal gas. Similarly, some of the colon’s bacteria break down undigested fiber and produce various short-chain fatty acids. Amino acids that reach the colon are converted to hydrogen, sulfide, some fatty acids, and other chemical compounds.

About l liter of fluid material, consisting of water, undigested or unabsorbed food particles, indigestible residue, and electrolytes, passes into the colon each day. Gradu- ally, the material is reduced to about 200 grams of brown fecal matter (also called stool, or feces). Stool consists of the undigested food residue, as well as sloughed-off cells from the GI tract, and a large quantity of bacteria. The brown color is due to un- absorbed iron mixing with a yellowish-orange substance called bilirubin. The greater the iron content the darker the feces. The intestinal matter passes through the colon within 12 to 70 hours, depending on a person’s age, health, diet, and fiber intake.

Stool is propelled through the large intestine until it reaches the final 8-inch portion called the rectum. The anus is connected to the rectum and controlled by two sphincters: an internal and an external sphincter. Under normal conditions, the anal sphincters are closed. When stool distends the rectum, the action stimulates stretch receptors that in turn stimulate the internal anal sphincters to relax, allowing the stool to enter the anal canal. This causes nerve impulses of the rectum to com- municate with the rectum’s muscles, resulting in defecation. The final stage of defe- cation is under voluntary control and influenced by age, diet, prescription medicines, health, and abdominal muscle tone.

Rectum

Anal sphincter

Cecum

Appendix

Ileocecal valve

Ileum

Ascending colon

Transverse colon

Descending colon

Sigmoid colon

Figure 3.6 Anatomy of the Large Intestine By the time chyme reaches the large intestine, most of its nutrients have been absorbed. However, water and some electrolytes are absorbed in the colon. The final waste products of digestion pass out of the body through the anus.

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pancreas A large gland located near the stomach that releases digestive enzymes

after a meal. The pancreas also secretes the

hormones insulin and glucagon, which

control blood glucose.

gallbladder A pear-shaped organ lo- cated behind the liver. The gallbladder

stores bile produced by the liver and se-

cretes the bile through the common bile

duct into the small intestine.

liver The largest organ in the body, lo- cated in the upper abdomen. This organ

aids digestion by secreting bile.

How Is Food Propelled through the GI Tract? 89

The Accessory Organs Provide Digestive Juices There are three organs that food does not pass through during di- gestion, but that are still key to the digestive process (Figure 3.7). These organs, the liver, gallbladder, and pancreas, release digestive secretions such as bile and enzymes that help transport and break down nutrients.

Weighing in at about three pounds, the liver is the largest organ in the body. It is located just beneath the rib cage, and functions as a major player in the digestion, absorption, and transport of nutrients. The liver is the first accessory organ to re- ceive absorbed nutrients from the portal vein. The liver plays an essential role in carbohydrate metabolism, produces proteins, and manufactures bile salts used to digest fats. The bile produced by the liver is secreted into the gallbladder for storage. The liver is also the site for alcohol metabolism and removes and degrades toxins and excess hormones from the circulation.

The gallbladder is located beneath the right side of the liver. This pear-shaped organ receives bile from the liver through the common hepatic duct and secretes bile into the small intestine through the common bile duct.

The pancreas is a flat organ about 10 to 15 centimeters long that hides behind the stomach and snugly fits in the bend of the duodenum. The function of the pancreas is both endocrine (endo � inside) and exocrine (exo � outside). As an endocrine organ, the pancreas releases hormones to maintain blood glucose levels. As an exocrine organ, the pancreas pro- duces and secretes digestive enzymes into the small intestine.

The Take-Home Message Saliva mixes with and moistens food in the mouth, making it easier to swallow. Once a bolus of food mixes with gas- tric juices in the stomach, it becomes chyme. Maximum digestion and ab- sorption occur in the small intestine. Undigested residue enters the large intestine, where water is removed from the chyme as it is prepared for elimi- nation. Eventually, the remnants of digestion reach the anus and exit the body in the feces. The liver, gallbladder, and pancreas are important acces- sory organs. The liver produces bile and the gallbladder concentrates and stores it. The pancreas produces enzymes and hormones.

Duodenum

Liver

Gallbladder

Pancreas

Common hepatic duct

Figure 3.7 The Accessory Organs The liver, gallbladder, and pancreas produce digestive secretions that flow into the duodenum through various ducts.

How Is Food Propelled through the GI Tract? We’ve already noted that food is propelled through the GI tract by mechanical, syn- chronized contractions of the diagonal, circular, and longitudinal muscles that line the individual organs of the digestive system. But how do these contractions work? The two primary types of contractions, called peristalsis and segmentation, depend upon the coordination between the muscles, nerves, and hormones in the

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90 Chapter 3 . Digestion, Absorption, and Transport

Longitudinal, circular, and diagonal muscles constrict in wavelike motions to propel food through the GI tract.

1

Longitudinal and circular muscles in the small intestine mix and squeeze food back and forth along the intestinal wall.

2

Stomach

Small intestine Segmentation

Peristalsis

Longitudinal

Circular

Longitudinal

Circular

Diagonal

Figure 3.8 Peristalsis and Segmentation

digestive tract (Figure 3.8). As food moves down the GI tract, the muscles help me- chanically digest the food by mixing and pushing it at just the right pace through each organ.

Peristalsis Squeezes Food Forward The circular muscles that contract during peristalsis in the esophagus prevent food from moving backward. A second wave of contractions follows as the circular mus- cles relax and the longitudinal muscles push the food forward.

In the stomach, circular, longitudinal, and diagonal muscles move the food from the top of the stomach toward the pyloric sphincter at the base of the stomach. The waves of contractions in the stomach are slower than in other GI organs, as peristalsis mixes and churns the stomach contents with gastric juices until the food is liquefied.

Segmentation Shifts Food along the Intestinal Wall As the partially digested food leaves the stomach, the second form of mechanical di- gestion, called segmentation, helps break down the mass of food into smaller pieces while mixing it with the chemical secretions of the intestine. Segmentation differs from peristalsis in that food is shifted (rather than squeezed) back and forth along the intestinal walls to increase the time food is in contact with the surface of the small intestine. This shifting action moves food through the small intestine at a rate of 1 centimeter per minute4.

Segmentation contractions in the large intestine are much stronger and slower as the chyme moves through the colon, allowing for the maximum amount of water to be absorbed. Three or four times a day, these slow but powerful muscular contrac- tions force the waste products toward the rectum. These contractions often occur shortly after eating and are stronger when the diet contains more fiber.

peristalsis The forward, rhythmic mo- tion that moves food through the digestive

system. Peristalsis is a form of mechanical

digestion because it influences motion, but

it does not add chemical secretions.

segmentation Muscular contractions of the small intestine that move food back

and forth, breaking the mixture into

smaller and smaller pieces and combining

it with digestive juices.

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How Is Food Chemically Digested? 91

substrate A substance or compound that is altered by an enzyme.

hydrolysis A chemical reaction that breaks the bond between two molecules

with water. A hydroxyl group is added to

one molecule and a hydrogen ion is added

to the other molecule.

Enzyme

Substrate

Bond

H2O

The substrate binds to the active site of the enzyme.

1 The individual products are released and the enzyme is ready to take action again.

3 The bond is broken between the two molecules by hydrolysis.

2

Figure 3.9 An Enzyme in Action Enzymes increase the rate of digestion without altering their shape.

The Take-Home Message Food is propelled through the GI tract by strong muscular contractions. Peristalsis in the esophagus, stomach, and small intestine squeezes the food and propels it forward, while segmentation in the small and large intestines shifts food back and forth along the intes- tinal walls, moving it further down the intestinal tract.

How Is Food Chemically Digested? Thus far, we’ve discussed the path that food travels as it moves through the organs of the GI tract during digestion, but we haven’t specifically described the chemicals in- volved in breaking down food into nutrients, or the regulation of the process. Chem- ical digestion is accomplished with the aid of digestive enzymes and other substances, and is regulated by a series of hormones. The chemicals generally com- plete their activities by the time the food reaches the large intestine.

Enzymes Drive the Process of Digestion Enzymes are proteins that catalyze hydrolysis (hydro � water, lysis �break), the chemical reaction that uses water to split the bonds of all digestible foods, and pro- duces single molecules small enough to be absorbed by the intestines. During hy- drolysis, the hydroxyl (OH) group from water is added to one of the molecules, while the hydrogen ion (H) is incorporated into the other molecule. Enzymes aren’t changed in the reaction and can thus be used over and over again.

In order for enzymes to catalyze hydrolytic reactions, three conditions must be present. First, enzymes are compatible only with a specific compound or nutrient, referred to as a substrate. Each enzyme has a binding site that only fits certain sub- strates, much like a key fits a specific lock. When the substrate binds to the active site of the enzyme, the bond is hydrolyzed. This reaction is illustrated in Figure 3.9.

Enzymes are often named by the type of substrate they act upon, plus the suffix -ase. For example, sucrase hydrolyzes the sugar sucrose, and maltase hydrolyzes

maltose. Some enzymes, such as the protein enzyme pepsin, were named before this new nomenclature was developed and don’t follow these naming rules.

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14

pH of Common Substances

Basic

Acidic

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Concentrated lyeLow concentration of hydrogen ions

High concentration of hydrogen ions

Oven cleaner

Household ammonia

Baking soda

Toothpaste

Bile Pancreatic juice Blood WaterpH neutral

Saliva Urine

Coffee

Tomato juice

Lemon juice

Gastric juice

Orange juice Soda

Battery acid

92 Chapter 3 . Digestion, Absorption, and Transport

The pH is a measure of the concentration of hydrogen ions (H�) in a solution. When acidic compounds dissociate or break apart in water, they produce more H�. The more H� produced, the stronger the acid. For example, the acidic gastric juice hydrochloric acid breaks down into hydrogen and chloride ions:

HCl S H� � Cl�

Basic compounds dissociate in a solution and release hydroxide ions (OH�). The more OH� in the solution, the stronger the base. For example, sodium hydroxide breaks down into sodium and hydroxide ions:

NaOH S Na� � OH�

An acidic solution can be buffered by adding a base, such as NaOH, to the solution. When the NaOH breaks apart, the OH� reacts with the H� to form water and reduce the acidity or number of H� ions present. One of the main buffers in the blood is car- bonic acid (HCO3). This acid is formed when carbon dioxide dissolves in the blood:

H� � HCO3 Sd H2CO3 Sd H2O � CO2

Acidity level is expressed using a pH scale that measures the hydrogen ion concentra- tion. The range of a pH scale is 0 to 14, with 7 considered a neutral pH. A solution that has a pH lower than 7 is considered acidic (0 is the most acidic); one higher than 7 is basic (14 is the most basic).

Chemistry Boost

pH Scale A low pH corresponds to a high concentration of hydrogen ions and is considered acidic, whereas a low concentration of hydrogen ions has a higher number on the pH scale and means the substance is more basic.

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How Is Food Chemically Digested? 93

Table 3.1

Digestive Enzymes and Their Actions

Organ or Gland Nutrient

Enzyme or Digestive Juice Action

Mouth Carbohydrate Salivary amylase Begins the digestion of starch

Stomach Protein Hydrochloric acid Denatures protein

Activates pepsinogen S pepsin

Pepsin Begins the hydrolysis of polypeptides

Lipid Gastric lipase Begins digestion of lipids

Pancreas Carbohydrate Pancreatic amylase Digestion of starch

Protein Trypsinogen S Trypsin A protein enzyme activated in the small intestine that catalyzes the hydrolysis of proteins to form smaller polypeptide units

Chymotrypsinogen S Chymotrypsin

A protein enzyme activated in the small intestine that catalyzes the hydrolysis of proteins into polypeptides and amino acids

Procarboxypeptidase S Carboxypeptidase

A protein enzyme that hydrolyzes the carboxy end of a peptide, releasing the last amino acid in the peptide chain

Lipid Pancreatic lipase Digests triglycerides

Small Intestine Carbohydrate Sucrase Digests sucrose

Maltase Digests maltose

Lactase Digests lactose

Protein Dipeptidase Digests dipeptides

Tripeptidase Digests tripeptides

Lipid Lipase Digests monoglycerides

The second condition that must be met involves the pH of the surrounding en- vironment. Enzymes are the most active and efficient when the fluid environment falls within a certain range of acidity or alkalinity (see the Chemistry Boost box). When the pH falls outside of that range, the activity of the enzyme is decreased or even halted. For example, saliva has a pH of about 6.4, which is optimal for the starch-digesting enzymes in the mouth. When the bolus containing the salivary en- zymes reaches the stomach, where the pH is closer to 1, the salivary enzyme activity is stopped. However, another enzyme, pepsin, becomes activated in this acidic envi- ronment. As chyme continues to travel through the GI tract, various organs secrete digestive juices that produce the optimal range of pH for the enzymes to function.

The third and final condition is temperature. As temperature falls below optimal levels, enzyme activity slows. If the temperature becomes too high, the enzyme is in- activated. In the body, the optimal temperature for enzymatic activity is 98.6°F (35.7°C), which is also considered normal body temperature. Temperature also controls enzyme activity in foods. Cooling or freezing food in a refrigerator or freezer slows down enzymes, and cooking food completely inactivates any enzymes it contains.

Digestive enzymes are secreted all along the GI tract, but most are produced in the pancreas. The last of the digestive enzymes are released by the brush border of the small intestine. Table 3.1 summarizes the digestive enzymes, the organs that se- crete them, and their actions.

pH A scale of measurement that indicates the acidity or alkalinity of a solution.

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94 Chapter 3 . Digestion, Absorption, and Transport

Other Chemicals Are Also Essential for Digestion Enzymes and other essential chemicals are often contained in fluids that are secreted throughout the digestion process. These secretions, including saliva, the gastric juices, bile, and bicarbonate ions, provide optimal conditions for digestion to occur.

Saliva Saliva is 99 percent water and rich in mucus, electrolytes, salivary amylase, and anti- bacterial compounds. Saliva functions mostly as a lubricant, but it also helps protect teeth and sanitize the mouth. It contains an antiseptic enzyme called lysozyme, which destroys the cell membranes of oral bacteria. What’s more, saliva contains bicarbonate, which neutralizes acids in the food. This change in pH is essential for optimal enzyme activity of salivary amylase.

Gastric Juices The gastric juices secreted by the stomach are produced by the specialized parietal and chief cells introduced earlier in the chapter. When food enters the stomach, the parietal cells produce hydrochloric acid (HCl) and a protein called intrinsic factor (which is important for the absorption of vitamin B12 in the ileum).

Hydrochloric acid is unique in that it can destroy the activity of some proteins while activating others. It is essential for digestion because of its ability to change the acidity of digestive fluids to a pH close to 1.5. This acidic pH denatures proteins, which means it inactivates the protein by uncoiling the strands to allow proteases, or protein-digesting enzymes, to attack the bonds. Once the protein is denatured, the protease hydrolyzes the bonds into shorter chains. Denaturing applies to all proteins, including hormones, and bacteria found in food, which are destroyed before they can be absorbed intact. Hydrochloric acid can also activate proteins, such as pepsinogen, a protein-digesting enzyme secreted from the chief cells lining the gastric glands. In the presence of HCl, pepsinogen is converted to its active form, pepsin, which begins the digestion of protein. HCl also enhances the absorption of certain minerals, such as calcium. In addition to HCl, the chief cells produce gastric lipase, which begins to di- gest fats, although this enzyme is not a particularly active digestive enzyme in adults.

You might think that such a strong acid would “digest” the stomach itself, but mucus secreted by the goblet cells and neck cells acts as a barrier between the HCl and the stomach lining, protecting the lining from irritation or damage. This slip- pery secretion is also produced in the mucus membranes lining the esophagus to lu- bricate food as it passes down the GI tract.

Bile Bile, the yellowish-green substance synthesized in the liver, helps digest dietary fat. This dilute, alkaline liquid is stored in concentrated form—up to five times its origi- nal composition—in the gallbladder. It functions to emulsify fat, breaking down large fat globules into smaller globules, much like dishwashing detergent breaks up the grease in a frying pan. Emulsification increases the surface area of the fat globule. The increased surface raises the efficiency of fat digestion to more than 95 percent.

In addition to dietary fat, bile also increases the absorption of the fat-soluble vi- tamins A, D, E, and K. Because bile has an alkaline pH, it also helps neutralize excess HCl and exhibits antibacterial properties that destroy bacteria in food.

Unlike other digestive juices, bile can be reused. From the large intestine, bile is recycled back to the liver through enterohepatic (entero � intestine, hepatic � liver) circulation. This recycling allows each bile salt to be reused up to 20 times.

bile A secretion produced in the liver and stored in the gallbladder. It is released

through the common bile duct into the

duodenum to digest dietary fat.

emulsify To break large fat globules into smaller droplets.

hydrochloric acid (HCl) A strong acid produced in the stomach that aids in

digestion.

proteases A classification of enzymes that catalyze the hydrolysis of protein.

pepsinogen The inactive protease se- creted by the chief cells in the stomach;

this enzyme is converted to the active form

called pepsin in the presence of HCl.

pepsin The active protease that begins the digestion of proteins in the stomach.

enterohepatic circulation The process of recycling bile from the large

intestine back to the liver to be reused

during fat digestion.

mucus Secretion produced throughout the GI tract that moistens and lubricates

food and protects membranes.

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How Is Food Chemically Digested? 95

Bicarbonate Bicarbonate ions alter the pH of food at various points along the GI tract. The sali- vary glands produce enough bicarbonate to neutralize the food you eat and produce a favorable pH (between 6.5 and 7.5) for salivary enzymes to hydrolyze starch. The pancreas secretes bicarbonate ions that flow into the duodenum via the pancreatic duct. The bicarbonate helps neutralize chyme as it arrives in the small intestine. The alkaline pH (about 8) is critical to protect the cells lining the duodenum, which are not resistant to damage by HCl, and to provide a favorable pH for the pancreatic and brush border enzymes (sucrase, maltase, lactase).

Table 3.2 summarizes the important digestive chemicals and the organs that se- crete them.

bicarbonate A negatively charged alkali ion produced from bicarbonate salts;

during digestion, bicarbonate ions are

released from the pancreas to neutralize

HCl in the duodenum.

Table 3.2

Secretions of the GI Tract and Their Actions Organ Secretion Secreted From or Into Action(s)

Mouth Saliva Salivary glands in the mouth Moistens food, eases swallowing; contains the enzyme salivary amylase

Stomach Hydrochloric acid (HCl) Parietal cells Denatures protein; activates pepsinogen S pepsin

Intrinsic factor Needed for vitamin B12 absorption

Ghrelin Stimulates gastric motility; stimulates hunger

Pepsinogen Chief cells Hydrolyzes proteins

Mucus Gastric glands Lubrication and coating of the internal mucosa to protect it from chemical or mechanical damage

Gastrin Cells lining the stomach A hormone that stimulates parietal cells to release HCl

Small Intestine Intestinal juice Intestinal glands Enzymes that digest carbohydrate, protein, and lipid

Mucus Intestinal glands Protects the intestinal cell

Secretin Duodenum A hormone that stimulates the pancreas to release bicarbonate ions

Cholecystokinin (CCK) Intestinal wall A hormone that stimulates the gallbladder to secrete bile and the pancreas to secrete bicarbonate ions and enzymes

Gastric inhibitory peptide (GIP)

Duodenum A hormone that stimulates secretions from the intestines and pancreas; inhibits stomach motility

Peptide YY Ileum Slows stomach motility

Liver Bile Liver (stored in the gallbladder) Produces bile to be stored in the gallbladder

Gallbladder Bile Gallbladder through the bile duct into the small intestine

Emulsifies large globules of lipid into smaller droplets

Pancreas Bicarbonate ions Pancreas through the pancreatic duct into the small intestine

Raises pH and neutralizes stomach acid

Enzymes Pancreas through the pancreatic duct into the small intestine

Break down carbohydrate, protein, and fat into nutrients that can be absorbed

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passive diffusion The process of absorbing nutrients freely across the cell

membrane.

96 Chapter 3 . Digestion, Absorption, and Transport

The Take-Home Message Foods are chemically digested by hydrol- ysis, which is catalyzed by enzymes. The three conditions that govern enzyme action are specific substrates (nutrients), pH, and optimal temperature. Other secretions produced in the GI tract, such as saliva, gastric juices, bile, and bi- carbonate, contribute to the optimal environment for digestion to occur.

How Are Digested Nutrients Absorbed? Digestion is the key to breaking down food; absorption is the key to using food once it’s digested. Some absorption occurs in the stomach and large intestine, but most nutri- ents are absorbed by specially designed cells along the small intestinal wall. Nutrients that are digested by the time they reach the duodenum are absorbed quickly. Nutrients that need more time to be disassembled are absorbed lower in the GI tract. The body is remarkably efficient when it comes to absorbing nutrients. Under normal conditions, you digest and absorb 92 to 97 percent of the nutrients in food.

Nutrients Are Absorbed through the Small Intestinal Lining The remarkable surface area (enough to cover a tennis court) of the folds and crevices of the small intestine lining allows for continuous, efficient absorption of virtually all digested nutrients. The villi are covered with mature enterocytes that ab- sorb digested nutrients. These cells live only a few days before they are sloughed off into the lumen to be digested.

Nutrients move across cell membranes in the small intestine via one of four mechanisms: passive diffusion, facilitated diffusion, active transport, or endocytosis.

Passive Diffusion Passive diffusion is a process in which nutrients are absorbed due to a concentration gradient. When the concentration of a nutrient is greater in the GI tract than inside the enterocyte, the nutrient is forced across the cell membrane. Thus, the nutrient moves from a high concentration to a low concentration. This simple process re- quires neither energy nor a special carrier molecule. Water, small lipids, a few miner- als, and vitamin C are examples of nutrients absorbed via passive diffusion.

Facilitated Diffusion The lipid layer of the enterocyte is impermeable to most nutrients and requires an al- ternate route for absorption. In facilitated diffusion, these nutrients are helped across the membrane by specific carrier proteins. This form of absorption is similar to passive diffusion in that it does not require energy and transport is from a higher to a lower concentration. Fructose is an example of a nutrient that needs a carrier to move across a membrane.

Active Transport Active transport is the absorption of nutrients from a low to a high concentration that requires both a carrier molecule and energy to shuttle nutrients across the cell membrane. This transport mechanism allows foods that are in short supply in the

facilitated diffusion The process of ab- sorbing nutrients with the help of a carrier

molecule.

active transport The process of ab- sorbing nutrients with the help of a carrier

molecule and energy expenditure.

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How Are Digested Nutrients Absorbed? 97

diet to be absorbed because the concentration outside the absorptive cell is lower than inside the cell. Glucose and amino acids are examples of nutrients absorbed by active transport.

Endocytosis Endocytosis occurs when a cell forms a vesicle to surround and engulf a nutrient. Once inside the vesicle, the nutrient is dissolved in water (this is why endocytosis is often referred to as “cell drinking”). This type of absorption allows whole proteins, such as an immunoglobulin from breast milk, to be absorbed intact.

Figure 3.10 illustrates the four processes involved in the absorption of various nutrients.

Fluid Absorption Occurs in the Large Intestine By the time chyme enters the large intestine, the majority of the nutrients have been absorbed. However, the water and salts that remain in the chyme when it enters the large intestine are absorbed before it reaches the rectum for excretion. The same mechanisms used to absorb water and salts in the small intestine are also used in the large intestine. For example, water is absorbed via passive diffusion and sodium is absorbed via active transport.

The Take-Home Message The brush border of the small intestine is the major site of absorption for digested nutrients. Water and salts not absorbed in the small intestine are absorbed in the large intestine. Nutrients are absorbed by passive diffusion, facilitated diffusion, active transport, or endocytosis.

endocytosis A type of active transport in which the cell membrane forms an in-

dentation, engulfing the substance to be

absorbed.

Nutrient

High concentration

Low concentration

Low concentration

High concentration

Cell membrane

Carrier protein

Nutrient

Carrier protein

Nutrient

ATP

Nutrient

Passive diffusion: Nutrients pass through the cell membrane.

a Facilitated diffusion: Requires a specific carrier but no energy is needed to cross the membrane.

b Active transport: Requires both a carrier protein and energy to cross the cell membrane.

c Endocytosis: Whole molecules are engulfed by the cell membrane. d

Figure 3.10 Four Methods of Nutrient Absorption in the Small Intestine

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gastric inhibitory peptide (GIP) A hormone produced by the small intes-

tine that slows the release of chyme from

the stomach.

cholecystokinin (CCK) A hormone released by the duodenum that stimulates

the gallbladder to release bile.

secretin A hormone secreted from the duodenum that stimulates the stomach to

release pepsin, the liver to make bile, and

the pancreas to release digestive juices.

98 Chapter 3 . Digestion, Absorption, and Transport

How Do Hormones Affect Digestion? Hormones secreted throughout the GI tract regulate digestion by controlling the release of gastric and pancreatic secretions, peristalsis, and enzyme activity. Enterogastrones, for example, are produced and secreted by the cells lining the stomach and small intes- tine. These hormones, including gastrin, secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP), have a powerful influence on gastrointestinal motility, stom- ach emptying, gallbladder contraction, intestinal absorption, and even hunger.

The release of hormones is stimulated by the type of food passing through the di- gestive tract. For example, when a protein-containing bolus passes through the LES, the hormone gastrin is secreted in the stomach and small intestine. This hormone causes the release of gastric secretions that contain gastric lipase and stimulates the secretion of HCl. Gastrin also increases gastric motility and emptying, and the tone of the LES.

Secretin is released by the duodenum when the acidic chyme passes through the pyloric sphincter. The release of secretin in turn stimulates the pancreas to send bi- carbonate ions through the pancreatic duct to neutralize the acid.

At the same time that secretin is stimulating the release of bicarbonate ions, an- other intestinal hormone, cholecystokinin (CCK), is secreted as partially digested protein and fat enter the duodenum. This powerful hormone also stimulates the pancreas to release lipase and the gallbladder to contract and release bile, while it slows down gastric motility (which controls the pace of digestion) and contributes to meal satisfaction. Gastric inhibitory peptide (GIP) also inhibits gastric motility and stomach secretions to allow time for the digestive process to proceed in the duode- num before it receives more chyme.

This synchronized effort by the GI tract hormones ensures the efficiency of di- gestion and maintains homeostasis in the body. Refer again to Table 3.2 for a sum- mary of the individual hormones, the tissues that secrete them, and their actions.

The Take-Home Message The enterogastrones gastrin, secretin, cholecystokinin, and gastric inhibitory peptide regulate digestion by stimulat- ing or inhibiting the release of secretions from the stomach, small intestine, pancreas, and gallbladder. They also influence gastric motility, which con- trols the pace of digestion.

How Does the Nervous System Affect Digestion? The main role of the nervous system in digestion is to let you know when you need to eat and drink, and when to stop. The brain, with the help of hormones, has a cen- tral role in communicating and interpreting the message of hunger and encouraging you to seek food. Receptors within the walls of the GI tract organs respond to changes in the cells and communicate these changes to the brain.

Two types of nerves are involved in communicating and interpreting these changes: extrinsic and intrinsic nerves. The extrinsic nerves originate in the brain or the spinal cord; the intrinsic nerves are woven like a spider web into the linings of the esophagus, stomach, and the small and large intestines. These nerves communicate

Table Tips

Improve Your Digestion

Eat and drink slowly and thoroughly chew your food. This will reduce the amount of air taken in, and may reduce the need for belching later on.

Drink plenty of fluids and add more fiber to increase the bulk of feces and prevent constipation.

Include probiotic bacteria such as Lactobacillus acidophilus and Bifidobacterium bifidum, found in yogurt, kefir, kimchi, and sauerkraut, because they may help to maintain the health of the intestinal tract.

Practice mindful eating. Savor the flavor of food and enjoy every bite to reduce overeating and improve portion control.

Identify foods that cause irritation or sensitivities. Reduce or eliminate these foods if necessary to improve digestion.

enterogastrones A group of GI tract hormones, produced in the stomach and

small intestine, that controls gastric motil-

ity and secretions.

gastrin A hormone released from the stomach that stimulates the release of acid.

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How Are Nutrients Transported Throughout the Body? 99

changes in the GI tract, which, in turn, affect motility and the release or inhibition of digestive juices.

Imagine that you walk by a bakery and smell freshly baked bread. The extrinsic nerves signal to the GI tract what your senses just experienced, and the intrinsic nerves interpret this signal and respond by stimulating the release of digestive juices. If you haven’t eaten in the past few hours, the fact that your stomach is empty is communi- cated from the intrinsic nerves back to your brain. The result is a feeling of hunger.

Hormones, such as ghrelin and peptide YY, work together with these nerves to communicate these feelings. Ghrelin, which is referred to as the “hormone of hunger,” is released from the gastric cells when the stomach is empty. Peptide YY signals the brain when you have eaten or are full. After you eat that warm piece of fresh bread, the receptor cells lining the stomach stretch, and the hormone peptide YY is released. This hormone travels through the circulation to the brain and signals that you’ve eaten. In addition, the extrinsic nerves excite the muscles stimulating peristalsis, pushing the food and digestive juices through the GI tract. Once the stomach has emptied, the re- lease of hormones and digestive juices ceases and the process begins again.

peptide YY A hormone produced in the small intestine that reduces hunger.

ghrelin A hormone produced in the stomach that stimulates hunger.

Recall that Emily’s distressing symptoms are more severe whenshe is preparing for a midterm exam or trying to meet assign- ment deadlines. How is the nervous system involved in the develop- ment of her symptoms? Do you have any suggestions for Emily related to controlling stress?

Top part of body

Lungs

KidneysPortal vein

Lower part of body

Heart

IntestinesLiver

Lymph system

Circulatory system

Figure 3.11 The Circulatory and Lymphatic Systems Blood and lymph circulate throughout the body to distribute nutrients to cells. Blood also picks up waste products from cells and delivers them to the kidneys for excretion.

The Take-Home Message Extrinsic and intrinsic nerves communi- cate and interpret changes in the GI tract, which affects gastric motility, the release or inhibition of digestive juices, and hunger. Two hormones, ghrelin and peptide YY, communicate with the nervous system to help you decide when to eat and when to stop eating.

How Are Nutrients Transported Throughout the Body? Once the nutrients have been absorbed through the small intestinal mucosa, they are carried off either through the bloodstream or the lymphatic system to other parts of the body (Figure 3.11). These two transportation systems consist of varying levels of pathways that deliver nutrients to, and pick up waste products from, cells in a simple route that begins with the heart.

The Circulatory System Distributes Nutrients through Blood The blood is the body’s primary transport system, shuttling oxygen, nutrients, hor- mones, and waste products throughout the body. This closed system of vessels flows continuously as the heart pumps blood through the hands and feet, up to the head, and back to the heart.

The heart is divided into four chambers, two upper atria and two lower ventri- cles. The oxygen-poor blood the heart receives from the body flows into the right

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100 Chapter 3 . Digestion, Absorption, and Transport

atrium, through the right ventricle, and into the lungs, where it is replenished with valuable oxygen. The oxygen-rich blood flows from the lungs to the left atrium. The blood travels through the aorta and arteries to the capillaries, where it exchanges substances with the cells. These compounds are eventually returned via the veins as the blood completes its route. Carbon dioxide produced during metabolism is one example of a substance that is picked up from the cells and routed back to the lungs to be exchanged for oxygen, and eventually expelled.

During digestion the blood travels through the arteries to the capillaries lining the intestinal tract. Water-soluble nutrients, including carbohydrates, amino acids, and water-soluble vitamins, are picked up by the capillaries in the GI tract and trans- ported out of the intestine by way of the hepatic portal vein to the liver. The portal vein branches out into capillaries supplying all the liver cells with nutrient-rich blood. From the liver, blood continues on its journey through the hepatic vein and back to the heart. Thus, the liver plays a key role in nutrition—it is the first organ to process absorbed nutrients.

The Lymphatic System Distributes Some Nutrients through the Lymph The lymphatic system is a complex network of capillaries, small vessels, valves, nodes, and ducts that transport fat-soluble nutrients throughout the body. The lym- phatic system, which is connected to the villi of the small intestine, collects fat-soluble vitamins, long-chain fatty acids, and some proteins too large to be transported via the capillaries. Unlike the circulatory system, the lymph system does not contain ar- teries, but rather the cells of the lymph capillary overlap one another, allowing the contents of the lymph vessels to seep out under pressure and circulate between the cells. The fat-soluble nutrients are transported from the lymph capillaries through the lymphatic vessels and eventually arrive at the thoracic duct. At the junction of the thoracic duct is a valve that allows the lymph fluid to flow into the subclavian vein, but not back into the duct, where it mixes with the blood. The nutrients travel throughout the body to be picked up and used by cells.

The Take-Home Message The circulatory and lymph systems trans- port absorbed nutrients throughout the body and deliver them to cells. Water-soluble nutrients, including carbohydrate, proteins (amino acids), and the water-soluble vitamins, are transported via the circulatory system, and fat-soluble nutrients, including the fat-soluble vitamins and long-chain fatty acids, are transported via the lymph system.

What Are Some Common Digestive Disorders? Generally, the digestive tract doesn’t require tinkering or medications to be healthy. But sometimes the digestive tract gets “off track” and the resulting symptoms can quickly catch your attention. Some of the problems are minor, like occasional heart- burn or indigestion; other problems such as ulcers or colon cancer are very serious and require medical treatment.

lymphatic system A system of inter- connected spaces and vessels between the

tissues and organs that contains lymph

and circulates fat-soluble nutrients

throughout the body.

hepatic vein The vein that carries the blood received from the hepatic portal

vein away from the liver.

hepatic portal vein A large vein that connects the intestinal tract to the liver

and transports newly absorbed nutrients.

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What Are Some Common Digestive Disorders? 101

Esophageal Problems: Heartburn and GERD Several minor esophageal problems can lead to annoying symptoms such as belch- ing, hiccups, burning sensations, or uncomfortable feelings of fullness. More serious esophageal problems include cancer, obstruction from tumors, faulty nerve im- pulses, severe inflammation, abnormal sphincter function, and even death.5,6

One of the most common problems involving the esophagus is the burning sensa- tion in the middle of the chest known as heartburn (also called indigestion, or acid re- flux). About 7 percent of the population experiences daily heartburn; about 20 percent of adults report frequent heartburn; and 25 to 35 percent of adults have occasional symptoms. Collectively, this adds up to millions of people experiencing heartburn symptoms.7 Heartburn generally occurs when the lower esophageal sphincter (LES) doesn’t close properly, and HCl from the stomach flows back into the esophagus and irritates its lining. Chronic heartburn and the reflux of stomach acids are typical symp- toms of gastroesophageal reflux disease (GERD).8

Certain foods, including chocolate, fried or fatty foods, coffee, soda, onions, and garlic, seem to be associated with this condition.9 Lifestyle factors also play a role. For example, smoking cigarettes, drinking alcohol, wearing tight-fitting clothes, being over- weight or obese, eating large evening meals, and reclining after eating tend to cause or worsen the condition. If dietary changes and behavior modification are insufficient to relieve the heartburn, over-the-counter antacids or prescription drugs may help. In rare circumstances, surgical intervention is required to treat severe, unrelenting heartburn.

Esophageal cancer is another medical condition that has serious consequences. According to the National Cancer Institute, esophageal cancer is one of the most com- mon cancers of the digestive tract, and the seventh leading cause of cancer-related deaths worldwide. In the United States, this type of cancer is typically found among individuals older than 50 years, men, those who live in urban areas, long-term smok- ers, and heavy drinkers. Treatments include surgery, radiation, and chemotherapy.10

Disorders of the Stomach Stomach problems can range from the trivial, such as belching or an occasional stomachache, to life-threatening complications such as bleeding ulcers or stomach cancer. Common causes of stomachache include overeating, gastric bloating, or eat- ing too fast. Other possible causes include eating foods that are high in fat or fiber, lactose intolerance, or swallowing air while eating.

Belching Belching is usually caused by swallowing air. The air may distend the stomach, and then be expelled up through the esophagus and out through the mouth, to relieve abdominal discomfort. Swallowing large amounts of air (called aerophagia) is most often due to eat- ing or drinking too fast, consuming carbonated beverages, or anxiety. However, aeropha- gia can occur without any act of swallowing, such as during chewing gum or smoking.

Stomach Flu and Foodborne Illness A stomachache can be due to a number of causes, including stomach flu or food- borne illness. Despite its name, stomach flu, or gastroenteritis, is not caused by the influenza virus but rather by a variety of viruses (the most common being the ro- tavirus) that cause an inflammation of the stomach or intestines. Stomach flu symp- toms include nausea, vomiting, diarrhea, and abdominal cramping. Sometimes the problem requires medical intervention, but usually rest, oral rehydration therapy, and a soft-food diet will help with the symptoms of this type of illness.

gastroesophageal reflux disease (GERD) The backward flow of stomach contents into the esophagus due to im-

proper functioning of the LES, resulting in

heartburn.

gastroenteritis Inflammation of the lining of the stomach and intestines; also

known as stomach flu.

Being overweight and eating certain foods are two factors that can cause GERD.

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102 Chapter 3 . Digestion, Absorption, and Transport

Foodborne illnesses are usually contracted by eating food or drinking fluid that is contaminated with a pathogenic microbe such as the bacteria campylobacter, sal- monella, or E. coli, or a calicivirus (also known as the Norwalk and Norwalk-like viruses). Symptoms such as vomiting, abdominal cramps, diarrhea, and fever occur when enough of the pathogen has been ingested to trigger the body’s immune re- sponse. You will read more about specific foodborne illnesses in Chapter 20.

Ulcers An ulcer is a sore or erosion in the lining of the lower region of the stomach or the upper part of the duodenum.11 They are named according to the location of the ulcer, such as gastric ulcers, duodenal ulcers, and esophageal ulcers. Whereas spicy foods and stress were once thought to cause most ulcers, researchers have since discovered that a bacterium, Helicobacter pylori, is often involved. The use of anti- inflammatory drugs, such as aspirin, ibuprofen, naproxen, and ketoprofen, may also cause or aggravate ulcers. These pain relievers inhibit the hormonelike substances that protect the stomach lining from HCl, which results in bleeding and ulceration. Nicotine increases the production of HCl, which increases the risk of developing an ulcer and slows the healing process of ulcers that have already developed. Both excess consumption of alcohol and stress can contribute to ulcer formations, although these factors may not be directly involved.

Burning pain is the most common symptom of an ulcer, along with vomiting, fatigue, bleeding, and general weakness. Medical treatments may consist of prescrip- tion drugs and dietary recommendations, such as limiting alcohol and caffeine- containing beverages, and/or restricting spices and acidic foods. Surgery is necessary only when an ulcer does not respond to drug treatment. Left untreated, ulcers can re- sult in internal bleeding and perforation of the stomach or intestinal lining, causing peritonitis, or infection of the abdominal cavity. Scar tissue can also form in the GI tract, obstructing food and causing vomiting and weight loss. People who have ulcers caused by H. pylori have a greater risk of developing stomach cancer.

Gallbladder Disease The incidence of gallbladder disease is high in the United States, especially in women and older Americans. Obesity is one of the major risk factors, and this risk is even greater following rapid weight loss.12 One common problem of an unhealthy gall- bladder is the presence of gallstones. Most people with gallstones have abnormally thick bile, and the bile is high in cholesterol and low in bile acids. Over time, the high-cholesterol bile forms crystals, then sludge, and finally gallstones. Some indi- viduals with gallstones experience no pain or mild pain. Others have severe pain ac- companied by fever, nausea, vomiting, cramps, and obstruction of the bile duct.

Medical treatment for gallstones may involve surgery to remove the gallbladder, prescription medicine to dissolve the stones, shock-wave therapy (a type of ultra- sound treatment) to break them up, or a combination of therapies. If surgery is re- quired to remove the gallbladder, patients typically recover quickly. After gallbladder removal surgery, the anatomy of the biliary tract adapts. The liver continues to pro- duce the bile and secretes it directly into the duodenum.

Disorders of the Intestines Disorders of the intestines can occur anywhere along the length of the small and large intestines. Common, temporary problems can include gassiness or constipa- tion; more serious disorders include celiac disease and Crohn’s disease.

gallstones Stones formed from choles- terol in the gallbladder or bile duct.

ulcer A sore or erosion of the stomach or intestinal lining.

An ulcer is created when the mucosal lining of the GI tract erodes.

The size and composition of gallstones vary.

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What Are Some Common Digestive Disorders? 103

onions, artichokes, and green beans) containing foods will improve the symp- toms associated with fructose malab- sorption and irritable bowel syndrome.

Study Design

A dietary strategy was developed to reduce the symptoms associated with irritable bowel syn- drome and fructose mal- absorption. The diet ex- cluded foods that contain free fructose and short- chain fructans, limited the total dietary fructose load, incorporated foods that balance glucose and fructose levels, and in- cluded foods that con- tained free glucose to balance any excess free fructose.

Symptoms were recorded for 62 subjects with irritable bowel syn- drome and fructose mal- absorption. They were then instructed on the di- etary strategies to re- duce the symptoms. Patients were contacted by telephone two to

40 months later and asked about the ability to adhere to the diet and the diet’s effect on symptoms. A positive response to the diet was defined by an improve- ment of all symptoms by at least five points on a �10 to +10 point scale.

Results

Of the 62 subjects who began the study, 48 (77 percent) adhered to the diet al- ways or frequently. Forty-six (74 percent) of the subjects had a positive response to the diet, in all abdominal symptoms. As il- lustrated in the figure, a positive response was significantly better in those subjects who adhered to the diet compared to those who did not ( p < 0.01).

Conclusions

A diet which limits fructose and fructan intake correlated to a significant improve- ment in all of the symptoms associated with irritable bowel syndrome and fruc- tose malabsorption. Whether these re- sults were due to the reduction in fruc- tose and or fructan intake, to the placebo effect, or some other reason, is unknown.

QUESTIONS

1. Was this a well-designed study? Why or why not?

2. Do the results of this study support the hypothesis?

3. Are there other factors that could have influenced the results?

4. Do you agree with the authors conclusions?

Background

Patients with fructose malabsorption and irritable bowel syndrome report abdomi- nal symptoms when they consume di- etary fructose. Prior to this study, no studies had been published that report positive dietary management techniques to reduce the symptoms.

Hypothesis

Following a diet low in fructose and fruc- tan- (a fructooligosaccharide found in

Shepherd, S. J., and P. R. Gibson. 2007. Fructose Malabsorption and Symptoms of Irritable Bowel Syndrome: Guidelines for

Dietary Management. Journal of the American Dietetics Association

106:1631–1639.

FOCUS ON RESEARCH

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The proportion of subjects who showed an improvement in symptoms associated with a diet which limited fructose and fructan intake. A significant difference was noted between those subjects who were adherent and those who were not on every symptom ( p < 0.01).

Flatulence Flatulence is an uncomfortable and sometimes embarrassing (but normal) condi- tion that results from the formation of intestinal gas. Intestinal gas is produced for a variety of reasons, and most adults release it 10 to 20 times a day. Eating too fast, or drinking beverages with added air such as beer or carbonated beverages, can result in the intake of incidental air that makes its way through the digestive tract. Foods including beans, lentils, and other legumes can lead to gas production because they contain indigestible carbohydrates that are fermented by intestinal bacteria. The

flatulence Production of excessive gas in the stomach or the intestines.

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104 Chapter 3 . Digestion, Absorption, and Transport

bacteria produce the gas as a by-product. Lack of exercise and smoking have also been identified as culprits in flatulence.

The gas (or flatus) is a mixture of carbon dioxide, hydrogen, nitrogen, oxygen, and methane. The offending odor comes from the gases that contain sulfur, chiefly hydrogen sulfide and methylmercaptan. Foods high in fiber and starches tend to pro- duce more intestinal gas. Using products such as Beano or eating smaller meals will help reduce the amount of gas produced.

Diarrhea and Constipation Two of the most common intestinal disorders are diarrhea and constipation.13

Diarrhea is the passage of watery, loose stools more than three times a day. Acute di- arrhea lasts for up to two days and is usually the result of bacterial, viral, or parasitic infection. The infection results in the enterocytes becoming inflamed and secreting, rather than absorbing, fluid into the GI tract. The result is that food and fluids pass too quickly through the colon and out through the rectum.

Diarrhea can be potentially serious because of the loss of fluids and electrolytes. Whereas brief episodes of diarrhea may be a sign of infection or an adverse reaction to a specific food, medication, or other compound (such as the sugar substitute sor- bitol), chronic diarrhea may be a sign of irritable bowel syndrome (see below) or co- litis, two conditions that require medical treatment and need to be diagnosed by a health care provider.

Diarrhea is generally treated with fluid and electrolyte replacement. Diarrhea that lasts for an extended period of time can lead to malabsorption of additional nu- trients, which can in turn lead to malnutrition. Left untreated, diarrhea can lead to dehydration and potentially even death. The condition can be particularly dangerous for children and the elderly, who are more susceptible to dehydration.

Constipation is caused by excessively slow movements of the undigested residue through the colon, and is often due to insufficient fiber or water intake. Ignoring or putting off the need to defecate can also result in more absorption of water from fecal matter in the large intestine, leading to harder, drier stools. Stress, inactivity, cessation of smoking, or various illnesses can also lead to constipation.14,15 Because fiber attracts water, adds bulk to stool in the colon, and stimulates peristalsis, consti- pation is often treated with a high-fiber, high-liquid diet. Daily exercise, establishing eating and resting routines, and using over-the-counter stool softeners are usually recommended to treat this condition without the use of laxatives or enemas.

If constipation persists, laxatives can provide some relief, but should be used sparingly. A variety of laxatives can be purchased over the counter, including bulk- forming laxatives, stool softeners, and stimulants. Bulk-forming or stool-softening laxatives trigger peristalsis by drawing water into the GI tract, which increases the bulk of the feces and stretches the circular muscles in the intestine. Stimulant laxa- tives, such as Ex-lax or Senokot, are the harshest form of laxative and work by irritat- ing the lining of the GI tract to stimulate peristalsis. Because laxatives can cause dehydration, salt imbalances, and laxative dependency, they should not be used rou- tinely unless under the supervision of a physician.

One harmful and unnecessary practice is colonic cleansing (or using enemas), the use of drugs to draw water or other fluids into the large intestine through the anus and rectum. The practice can interfere with the absorption of fat-soluble vita- mins, and can be dangerous if the equipment isn’t sanitized, or if the bowel is perfo- rated when the rubber tube (used to administer the enema) is inserted. Other problems may result from electrolyte and water imbalance, and dependency.

diarrhea The abnormally frequent passage of watery stools.

constipation The infrequent passage of dry, hardened stools.

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What Are Some Common Digestive Disorders? 105

Hemorrhoids The term hemorrhoid refers to a condition in which pressure in the veins in the rec- tum and anus cause swelling and inflammation similar to varicose veins in the legs. Though the exact cause of hemorrhoids is not known, there are contributing factors that result in pressure buildup within the veins. These factors include straining to pass dry stools, pregnancy, constant constipation or diarrhea, and aging. Whatever the cause, the result is that the walls of the veins dilate, become thin, and bleed. As the pressure builds, the vessels protrude. The presence of hemorrhoids may not be noticed until they begin to bleed (following a bowel movement), itch, or become painful. The most common treatment for hemorrhoids is the same as for constipa- tion: increase dietary fiber and fluid intake. Other symptoms, including itching and pain, can be relieved with over-the-counter creams, ice packs to relieve swelling, and soaking in a warm bath. In severe cases of hemorrhoids, surgery may be necessary.

More Serious Intestinal Disorders Both diarrhea and constipation can be indicative of small and large intestine problems that involve nutrient malabsorption, which can cause severe health consequences. Celiac disease, gastroenteritis, duodenal ulcers, intestinal enzyme deficiencies, irrita- ble bowel syndrome, ulcerative colitis, and Crohn’s disease are examples of serious in- testinal disorders. The symptoms of these diseases vary, but they include abdominal pain, nausea, vomiting, bloating, loss of appetite, diarrhea, anxiety, weight loss, and fa- tigue. The prevalence of some of these disorders may be increasing16 or it could be that these disorders are now being more readily recognized and documented.

Irritable Bowel Syndrome (IBS), Ulcerative Colitis, and Crohn’s Disease Although irritable bowel syndrome (IBS) is a general term used to describe changes in colon rhythm, not an actual disease, it causes a great deal of discomfort for the es- timated 30 million North Americans who have it.17 People with IBS do not have tis- sue damage, inflammation, or immunologic involvement of the colon. They do, however, overrespond to colon stimuli. This results in alternating patterns of diar- rhea, constipation, and abdominal pain. The exact cause of IBS is unknown, but low- fiber diets, stress, consumption of irritating foods, and intestinal motility disorders are all suspected factors. Medical management includes increasing dietary fiber18, stress management, and occasional use of prescription drugs.

Ulcerative colitis is a chronic inflammation of the large intestine that results in ulcers in the lining of the colon. This disorder of the large intestine usually begins between the ages of 15 and 30, occurs in both men and women, and tends to run in families, especially in Caucasians and people of Jewish descent. Crohn’s disease is similar to ulcerative colitis except that the ulcers can occur throughout the gastro- intestinal tract, from the mouth to the anus, not just in the colon.

The cause of ulcerative colitis and Crohn’s disease is not known and there is no cure. Physical examinations, laboratory tests, and a colonoscopy are often used to distinguish between the two conditions. Treatment includes drug therapy and in severe cases, surgery may be required.

Celiac disease, also known as gluten-induced enteropathy, is a genetic disorder that causes damage to the small intestine when foods containing gluten are con- sumed. The boxed feature “Celiac Disease: An Issue of Absorption” explains this intestinal disorder in greater detail.

Crohn’s disease A form of ulcerative colitis in which ulcers form throughout

the GI tract and not just in the colon.

ulcerative colitis A chronic inflamma- tion of the colon or large intestine that

results in ulcers forming in the lining of

the colon.

irritable bowel syndrome (IBS) An intestinal disorder resulting in abdominal

discomfort, pain, diarrhea, constipation,

and bloating; the cause is unknown.

hemorrhoid Swelling in the veins of the rectum and anus.

celiac disease Genetic disease that causes damage to the small intestine when

gluten-containing foods are eaten.

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One of the more serious malabsorption conditions to occur in the small intestine is celiac disease. A healthy small intes- tine contains the numerous villi and mi- crovilli that efficiently and exhaustively absorb nutrients from food. With celiac disease, the lining of the small intestine flattens out, which reduces its ability to absorb nutrients. The flattening is due to an abnormal reaction to the protein gluten, found in wheat, rye, and barley.

Celiac disease is most common among people of European descent. Though the exact cause of celiac disease is unknown, it is believed to be genetic. The most recent estimates suggest that 1 in 133 people is affected by celiac dis- ease in the United States and in close family members, it is estimated to be as high as 4.5 percent.1 Because of this ge- netic link, celiac disease is classified as a lifelong disorder.

What Are the Symptoms of Celiac Disease?

Classic celiac symptoms include reoccur- ring abdominal bloating, cramping, diar- rhea, gas, fatty and foul-smelling stools, weight loss, anemia, fatigue, bone or joint pain, and even a painful skin rash called dermatitis herpetiformis. Some people develop the symptoms of celiac disease in infancy or childhood. Others develop it later in life, after being misdiagnosed with irritable bowel syndrome or various food intolerances.

How Serious Is Celiac Disease?

Depending on the length of time between symptom development and diagnosis, the complications from celiac disease can be serious. Celiac patients have an in- creased incidence of osteoporosis from poor calcium absorption, diminished growth because of nutrient malabsorp- tion, and even seizures due to inadequate folate absorption. Celiac disease also

increases the risk of developing certain types of cancer, including esophageal cancer and melanoma.2

How Is Celiac Disease Diagnosed?

In the past, diagnosing celiac disease was sometimes difficult because it resem- bles other similar malabsorption diseases. The contemporary method of diagnosis begins with a simple blood test.3 If the test proves positive, the next step is a tis- sue biopsy of the small intestine to con- firm the diagnosis2,4.

How Is Celiac Disease Treated?

The only treatment for celiac disease is a gluten-free diet.5 This should stop the symptoms from progressing, allow the in- testine to heal, and prevent further dam- age. The symptoms often improve within a few days after beginning the gluten-free diet. If the diet is followed faithfully, the absorption area of the intestinal tract often returns to normal status within three to six months.

Adhering to a gluten-free diet, which means avoiding all gluten-containing foods, can be challenging. All breads, pasta, cereals, and other wheat-containing foods must be eliminated. Gluten-free foods such as meat, milk, eggs, fruit, and vegetables are permissible. Rice, pota- toes, corn, and beans, as well as grains such as quinoa, amaranth, and millet do not contain gluten and are also accept- able. The accompanying table provides a brief list of foods that are allowed or are to be avoided. However, check with the American Dietetic Association for a more comprehensive list of foods allowed on a gluten-free diet.6

Until recently, oats had been consid- ered a forbidden food for celiac patients. Recent studies suggest that moderate amounts, up to about 1⁄4 cup of dry oats, may be safe for adults and children with celiac disease.7 Concerns about adding oats to the gluten-free diet are related to the possibility that oats may be contami- nated with “latent,” or hidden, sources of gluten. Such concerns can be allayed by purchasing oats from companies that ad- vertise gluten-free products and avoiding oats sold in bulk bins.

Be cautious of cross-contamination and additives from foods found in salad bars and buffets, medications and dietary supplements, and foods that contain vegetable gums or modified food starch. When you purchase any packaged food at the grocery store, be sure that you read the food labels carefully. Otherwise, you could be unpleasantly surprised by latent gluten content.

Celiac disease is a manageable condi- tion. Individuals with celiac disease can live normal lives by successfully imple- menting the guidelines for gluten-free diets, reading labels, and finding re- sources for gluten-free products. In the meantime, more research will be con- ducted to increase our understanding of the disease and lead to new treatments.8

Celiac Disease: An Issue of Absorption

Bread and other foods containing wheat, barley, and rye must be avoided on a gluten- free diet.

106 Chapter 3 . Digestion, Absorption, and Transport

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References 1. Fasano, A., I. Berti, T. Gerarduzzi, et al.

2003. Prevalence of Celiac Disease in At- Risk and Not-At-Risk Groups in the United States: A Large Multicenter Study. Archives of Internal Medicine 163:286–292.

2. Westerberg, D. P., J. M. Gill, B. Dave, M. J. DiPrinzio, A. Quisel, and A. Foy. 2006. New Strategies for Diagnosis and Management of Celiac Disease. The Journal of the American Osteopathic Association 106(3):145–151.

Gluten-Free Diets

Allowed Foods Foods to Avoid Processed Foods That May Contain Wheat, Barley, or Rye

Amaranth

Arrowroot

Buckwheat

Cassava

Corn

Flax

Indian rice grass

Job’s tears

Legumes

Millet

Nuts

Potatoes

Quinoa

Rice

Sago

Seeds

Soy

Sorghum

Tapioca

Wild rice

Yucca

Wheat, including:

Einkorn

Emmer

Spelt

Kamut

Wheat starch

Wheat bran

Wheat germ

Cracked wheat

Hydrolyzed wheat protein

Bromated flour

Durum flour

Semolina

White, wheat, graham flour

Barley

Rye

Triticale (a cross between wheat and rye)

Bouillon cubes

Brown rice syrup

Candy

Chips/potato chips

Cold cuts, hot dogs, salami, sausage

Communion wafer

French fries

Gravy

Imitation fish

Matzo

Rice mixes

Sauces

Seasoned tortilla chips

Self-basting turkey

Soups

Soy sauce

Vegetables in sauce

Adapted from T. Thompson. Celiac Disease Nutrition Guide, 2nd ed. (Chicago: American Dietetic Association, 2006), used with permission. For a complete copy of this guide, visit www.eatright.org.

Celiac Disease: An Issue of Absorption 107

3. Russo, P. A., L. J. Chartrand, and E. Seidman. 1999. Comparative Analysis of Serologic Screening Tests for the Initial Diagnosis of Celiac Disease. Pediatrics 104:75–78.

4. van Heel, D. A. and J. West. 2006. Recent Advances in Celiac Disease. Gut 55:1037–1046.

5. Lee, A. and J. Newman. 2003. Celiac Diet: Its Impact on Quality of Life. Journal of the American Dietetic Association 103:1533–1535.

6. American Dietetic Association. Available at www.eatright.org.

7. Thompson, T. 2003. Oats and the Gluten-Free Diet. Journal of the American Dietetic Association 103:376–379.

8. National Digestive Diseases Information Clearinghouse. Celiac Disease. June 2007. Available at www.digestive.niddk .nih.gov/ddiseases/pubs/celiac/index .htm#10.

Rice noodles are a good substitute for pasta.

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Polyp

108 Chapter 3 . Digestion, Absorption, and Transport

Colon Cancer Colon cancer is one of the leading forms of cancer and the third leading cause of cancer death.19 Fortunately, colon cancer is one of the most curable forms of cancer, if it is detected in the early stages.

Colon cancer often begins with polyps on the lining of the colon. They vary in size from that of a small pea to that of a mushroom or plum. The good news is that polyps are often small and benign, and they can be removed sur- gically. If the polyps are not removed, or if they develop into cancerous tu- mors, colon cancer can be difficult to cure.

Individuals diagnosed with colon cancer may require radiation ther- apy, chemotherapy, and surgery to remove part or all of the colon. After sur- gery, patients are given dietary advice regarding the foods that would be the most comfortable to eat. Survival rates vary depending on the individual’s age, health, treatment response, and stage of cancer diagnosis.

Table 3.3 summarizes these common digestive disorders.

Table 3.3

Common Digestive Disorders Site Disorder Symptoms Cause Treatment

Esophagus GERD Heartburn, nausea, and belching

Reflux of HCl into esophagus Lifestyle changes including diet, exercise, and smoking cessation

Stomach Gastroenteritis Flulike symptoms Virus or bacteria; irritation of the stomach lining

Soft-food diet and fluid

Peptic ulcer Abdominal pain, vomiting, bleeding, and general weakness

Drugs, alcohol, or H. pylori bacteria

Drug therapy and limiting alcohol, caffeine, and acidic foods

Gallbladder Gallstones Cramps, nausea, fever, vomiting

Bile high in cholesterol; obesity; rapid weight loss

Surgery and drug therapy

Small Intestine

Celiac disease

Malabsorption Error of gluten metabolism Gluten-free diet

Large Intestine

Diarrhea Frequent loose, watery stools

Contaminated water or food; stress; excessive fiber intake

Water and electrolyte replacement

Constipation Cramping, bloating Insufficient water and fiber intake; inactivity

High fiber, high fluid intake; exercise

Irritable bowel syndrome (IBS)

Diarrhea, constipation, and abdominal pain

Unknown cause(s); stress worsens the condition

Self-management with increased dietary fiber, stress relief, good sleep habits

Ulcerative colitis

Abdominal pain and bleeding

Unknown cause Drug therapy

Crohn’s disease

Abdominal pain and bleeding

Unknown cause Drug therapy

Colon cancer

Often none detectable

Multiple causes (genetics, various colon diseases, smoking, dietary carcinogens)

Surgery, radiation, and chemotherapy

Polyps on the lining of the colon can be one of the first signs of colon cancer.

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Putting It All Together 109

Emily’s symptoms include bouts of abdominal pain and constipa-tion followed by diarrhea. Based on her age, symptoms, and the impact of stress on her symptoms, which of the gastrointestinal disorders do you suspect Emily is suffering from? Are there any serious complications that Emily should be concerned about? What dietary recommendations would you suggest to relieve Emily’s condition?

The Take-Home Message Gastrointestinal diseases and digestive disorders include less serious conditions, like heartburn, GERD, and stomach flu, and more serious conditions, such as esophageal cancer and ulcers. Dis- orders of the small intestine can be the most dangerous, as they may result in malabsorption and/or malnutrition. Constipation, diarrhea, and irritable bowel syndrome are all disorders of the large intestine. Colon cancer typically be- gins with polyps on the intestinal lining.

Putting It All Together You may be familiar with the saying, “Food is food, until you swallow it; and then it becomes ‘nutrition.’ ” The digestive process prepares the food you eat to be absorbed out of the GI tract and into the circulation to be delivered to cells. Your body builds your health around the food choices you make.

The guidelines presented in Chapter 2, including the DRIs and MyPyramid, to make healthful food choices and ensure that you receive adequate amounts of the es- sential nutrients without taking in too many kilocalories. Food choice, however, is a multifaceted effort. What we should eat, actually eat, and prefer to eat are sometimes conflicting decisions. Hopefully, the more you learn, the more healthful your choices will be.

In the next few chapters, you will learn more about the metabolism of the ab- sorbed nutrients, the individual categories of nutrients that make up a healthy diet, and their functions in the body. As you read about carbohydrates, fat, proteins, vita- mins, minerals, and water, keep in mind that they are all digested in the GI tract, ab- sorbed in the intestines, distributed throughout the body by the blood and lymph, provide energy to individual cells, and regulate numerous critical processes.

CAREERS IN NUTRITION Independent Nutrition Consultant, Celiac Disease

Tricia Thompson, MS, RD, is an indepen- dent nutrition consultant who specializes in celiac disease. She’s also the

author of The Gluten Free-Nutrition Guide (McGraw-Hill, 2008) and coauthor of The Complete Idiot’s Guide to Gluten Free Eating (Penguin, 2007). Read an interview with Tricia about her work with celiac disease online at www.aw-bc.com/blake.

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Mary Ellen Sanders, MS, PhD DAIRY AND FOOD CULTURE TECHNOLOGIES

Mary Ellen Sanders, MS, PhD, has been a consultant in the area of probi- otic microbiology for 18 years, working with the food and supplement indus- tries, as well as trade organizations and scientific societies. She was the found-

ing president of the International Scientific Association for Pro- biotics and Prebiotics and is its current executive director. She serves on the NIH-NCCAM Product Quality Working Group, served on a committee to establish guidelines for probiotics for the World Gastroenterology Association, and has worked with the FAO/WHO in establishing guidelines for probiotics and prebiotics.

Q: Are probiotics necessary for health? A: No. Research has documented ways that microbes can

play an important role in our health and physiology. Con- trolled studies on probiotics show that external sources of viable microbes can also contribute to health for some people. Furthermore, modern diets are considerably defi- cient in microbes compared to our ancestors. However, we do not have sufficient information today to say that di- etary supplementation with probiotics is essential.

Q: What are some of the concerns associated with buy- ing products that contain probiotics?

A: One concern is uneven product quality that is not evident to consumers. It is difficult for consumers to know whether products in the marketplace contain what they claim or that the products have been subjected to con- trolled clinical evaluation. Another concern is knowing when their use is appropriate. Patients with short bowel syndrome, who are immunocompromised, recovering from surgery, or have compromised gut integrity are at el- evated risk and should take probiotics only under the ad- vice of a healthcare provider. Probiotics sold as foods and supplements must meet FDA safety standards for use in the generally healthy population. Although there are many research studies that have used probiotics for the treatment of disease and to manage symptoms of disease, no products have been approved for such use in the United States.

Miguel Freitas, MS, PhD SCIENTIFIC AFFAIRS, DIRECTOR THE DANNON COMPANY, INC.

Miguel Freitas, MS, PhD, is the direc- tor of scientific affairs/medical marketing for The Dannon Company. Dr. Freitas serves as a liaison between Dannon and the scientific community and is respon-

sible for ensuring the integrity of the Dannon product portfolio with respect to health. He also serves as a liaison between The Dannon Company and Danone Research, Carasso Re- search Centre in Palaiseau, France, the international research center of the Danone Group, Dannon’s parent company. In this capacity, Freitas designed and managed research proj- ects investigating human health and functional foods, particu- larly probiotics.

Q: Are probiotics necessary for health? A: Probiotics provide many positive benefits. They are

mainly found in cultured dairy foods and are important in helping maintain proper functioning of, for instance, the digestive and immune systems. Because of stress, im- proper diet, or the ingestion of antibiotics, the body’s di- gestive and immune functions can be affected. Regular consumption of certain probiotics helps maintain the nor- mal functioning of these systems.

Q: What are some of the concerns associated with buy- ing products that contain probiotics?

A: Every probiotic strain has a unique effect on the body. Therefore, it is important to know not only what strain of probiotics is in a product, but also what benefits that strain can confer. Only clinically tested strains and probi- otic products are guaranteed to provide a benefit.

Q: Do we know enough about probiotics to recommend them to the public?

A: Since the potential benefits of probiotics were discovered more than a century ago, clinical studies have continued to show that they are not only safe to consume in foods, but that they can have a positive effect on several func- tions of the body, including immune and digestive health. Between 2000 and 2008, more than 2,200 original stud- ies were published on the effects of certain probiotics.

Two experts discuss if probiotics improve digestion and the implications of including probiotics in food.

Two Points of View Probiotics: Do They Improve Digestion?

110 Chapter 3 . Digestion, Absorption, and Transport

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Q: Should the FDA be regulating probiotics in foods? A: Food products are well-regulated today. The FDA regula-

tions in place today require that food labeling and claims provide consumers with accurate and relevant informa- tion to make educated decisions about their diets.

Q: Do we know enough about probiotics to recommend them to the public?

A: It is tempting to think of probiotics as one entity, but not all probiotics are the same. Probiotic products are com- prised of a variety of genera, species, and strains; are de- livered via different vehicles (foods and supplements); and may be of variable quality. Some products are evaluated in well-controlled human studies, while others have no verification of efficacy. Since different strains of even the same species can function differently, the strongest rec- ommendations are based on clinical evaluations and meta-analyses documenting efficacy. For antibiotic-asso- ciated diarrhea, infectious diarrhea, some intestinal symptoms, and incidence of common infectious dis- eases, there is good evidence that some probiotic prod- ucts may help. For some other clinical targets, evidence is promising. Keep this in mind: the science on probiotics is emerging, so expect new findings in this area.

Q: Should the FDA be regulating probiotics in foods? A: The FDA does regulate probiotics in foods–but this is

done under the general regulations on foods and supple- ments; there are no “probiotic-specific” regulations. Products are required to be labeled in a truthful and not misleading fashion. Theycan only bear statements re- garding the impact of the probiotic on the normal struc- ture and function of the human body or an FDA-approved health claim linking the probiotic to reduc- ing the risk of a diet-related disease. Unfortunately, the FDA does not aggressively enforce their requirement for efficacy substantiation for structure/function claims, so there are many products on the market making claims of functionality that are unsubstantiated.

Probiotics: Do They Improve Digestion? continued

Miguel Freitas, MS, PhD, continued Mary Ellen Sanders, MS, PhD, continued

The Top Ten Points to Remember

1. Digestion is the process of breaking down whole food into absorbable nutrients. Digestion takes place in the GI tract, a long tube comprised of the mouth, esopha- gus, stomach, small intestine, and large intestine. Ac- cessory organs, including the liver, gallbladder, and pancreas, secrete bile, hormones, and enzymes that help regulate and facilitate digestion. Several sphinc- ters control entry and exit of food and chyme through the various organs of the GI tract.

2. Digestion begins in the mouth as chewing breaks down food and mixes it with saliva. The stomach mixes food with gastric juices before propelling it into the small intestine, where most digestion and absorp- tion occurs. The small intestine is the primary organ for the absorption of digested nutrients. The walls of the small intestine are covered with villi and microvilli that greatly increase its surface area and facilitate ab- sorption. Two ducts, the pancreatic duct and the bile duct, are passageways by which bile and pancreatic en- zymes enter the small intestine. The large intestine ab- sorbs water and electrolytes before pushing waste through the colon and out of the body via the rectum.

The Top Ten Points to Remember 111

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112 Chapter 3 . Digestion, Absorption, and Transport

3. The liver is a key organ in the digestion, absorption, and transport of nutrients. Bile produced in the liver helps digest fat. The liver is the first organ to receive, process, and store absorbed nutrients. The liver also plays an im- portant role in detoxifying alcohol. The pancreas and gallbladder are two other accessory organs that provide digestive fluids to the GI tract.

4. Chemical digestion involves mixing food with enzymes that break the bonds by adding water through hydroly- sis. HCl and bicarbonate ions alter the pH as food travels down the GI tract. HCl also denatures protein and acti- vates pepsinogen to initiate protein digestion. Bile from the gallbladder emulsifies large fat globules into smaller pieces to improve enzymatic action. Digestion is com- pleted by the brush border enzymes maltase, sucrase, and lactase, and the proteases aminopeptidase and dipeptidase, breaking nutrients down into single mole- cules that can be absorbed into the small intestine lining.

5. Nutrients pass through the small intestinal wall via passive diffusion, facilitated diffusion, active transport, or endocytosis.

6. Mechanical digestion includes mastication, peristalsis, and segmentation. Peristalsis moves food through the stomach and intestines by rhythmic contractions of longitudinal and circular muscles. Segmentation squeezes the mass of food into smaller pieces while mix- ing it with the chemical secretions of the intestine. Mus- cular contractions in the large intestine facilitate the absorption of water from the feces by compacting the mass and pushing it toward the rectum for excretion.

7. Hormones, including gastrin, secretin, cholecys- tokinin, and gastric inhibitory peptide, are chemical messengers that direct enzymes and the release of di- gestive secretions during digestion.

8. Body systems other than the digestive system are in- volved in the body’s digestion, absorption, and trans- port of nutrients. The nervous system communicates signals of hunger and thirst. The circulatory system distributes water-soluble nutrients throughout the body and carries carbon dioxide and other waste products to be excreted through the lungs and the kid- neys. The lymph system transports fat-soluble vita- mins from the GI tract through the lymph system and into the circulatory system.

9. Heartburn is the layman’s term for the uncomfortable sensation of stomach acid returning to the esophagus or throat; chronic heartburn can lead to GERD. Diar- rhea is frequent, watery stool and can be caused by in- fection, some compounds (such as medications), and sensitivity to foods. Constipation is a generally benign condition of sluggish colon movements commonly caused by a low-fiber, low-fluid diet. Hemorrhoids can form in the blood vessels of the rectum and anus from constipation, inactivity, pregnancy, obesity, and aging.

10. Peptic ulcers are sores or breaks in the lining of the stomach or the upper part of the small intestine. Colon cancer begins with polyps on the intestinal lin- ing and is very treatable if caught early. Those with ir- ritable bowel syndrome have difficulty establishing and sustaining a normal rhythm in their colon and often alternate between bouts of diarrhea and consti- pation. Ulcerative colitis and Crohn’s disease are two types of inflammatory bowel disorders that result in the ulceration of the lining of the intestinal tract. Celiac disease is a disorder of the small intestine that can be treated with a gluten-free diet.

Test Your Knowledge 1. Food is moved through the GI tract by rhythmic muscular

waves called a. segmentation. b. peristalsis. c. bowel movement. d. mastication.

2. The protective tissue that covers the trachea during swal- lowing is the a. esophagus. b. tongue. c. pharynx. d. epiglottis.

3. What is the function of hydrochloric acid in the digestive process? a. activates pepsinogen to pepsin b. slows peristalsis c. neutralizes the pH in the stomach d. begins the digestion of carbohydrates

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4. The sphincter that separates the stomach from the duode- num is the a. lower esophageal sphincter. b. ileocecal valve. c. pyloric sphincter. d. colon sphincter.

5. Which of the following is true regarding the small intestine? a. The small intestine is shorter than the large intestine. b. The small intestine is the major organ for digestion

and absorption. c. The small intestine has access to lymph tissue but not

to the bloodstream. d. The small intestine is composed of the ileum, duode-

num, and jejunum, in that order. 6. Chemical digestion does not involve

a. enzymes. b. segmentation. c. HCl. d. bile.

7. The emulsifying agent that is produced by the liver but stored in the gallbladder is called a. pepsin. b. gastrin. c. cholecystokinin. d. bile.

8. Glucose is absorbed by the process called a. passive diffusion. b. facilitated diffusion. c. active transport. d. osmosis.

9. What causes heartburn? a. rapid swallowing b. improper breathing and chest congestion c. a weak lower esophageal sphincter allowing acid to re-

flux back into the esophagus d. improper contraction of the lower esophageal sphinc-

ter preventing acid from leaving the esophagus 10. Celiac disease is caused by a reaction to gluten found in

which foods? a. citrus fruits b. wheat, barley, and rye c. legumes, nuts, and seeds d. milk, cheese, and yogurt

Answers 1. (b). Peristalsis is the process that moves food through the

stomach and small intestine. Segmentation is also a form of mechanical digestion but its function is to squeeze chyme back and forth along the intestinal walls to in- crease the time food is in contact with the small intestine lining. A bowel movement is achieved by peristalsis mov- ing feces through the large intestine toward the rectum. Mastication is the process of chewing food.

2. (d). Epiglottis. The esophagus is a tube that connects the mouth with the stomach. The tongue is a muscle that pushes food to the back of the mouth into the pharynx. The pharynx is a chamber that food passes through just before being swallowed.

3. (a). Hydrochloric acid is part of the gastric juices pro- duced in the stomach that activates pepsinogen to pepsin, breaks down connective tissue in meat, and destroys some ingested microorganisms. Cholecystokinin and gastric in- hibitory hormones are released from the small intestine and slow peristalsis. Bicarbonate ions neutralize the acid in the chyme that comes from the stomach into the small intestine. Amylase is an enzyme in the mouth that begins breaking down carbohydrates.

4. (c). The pyloric sphincter allows chyme to pass from the bottom of the stomach to the beginning of the duode- num, the first part of the small intestine. The lower esophageal sphincter connects the base of the esophagus to the stomach; it controls the entry of the bolus into the stomach and prevents reflux of stomach acid back into the esophagus. The ileocecal valve separates the ileum from the colon. The colon sphincter is also called the anal sphincter and it is the last part of the GI tract.

5. (b). The small intestine is critical to the process of diges- tion and absorption. With numerous villi and microvilli along its interior wall, the small intestine has a vast sur- face area, which enhances absorption. The small intestine allows nutrients to pass into both blood and lymph for transport throughout the body. The small intestine con- sists of the duodenum, then the jejunum, and finally the ileum. The small intestine is much longer than the large intestine.

6. (b). The chemicals involved in the chemical digestion of food include enzymes, HCl, and bile. Segmentation is a form of mechanical digestion that helps food move through the GI tract.

Test Your Knowledge 113

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7. (d). The liver makes bile in a dilute, liquid form that is concentrated and stored in the gallbladder. Pepsin is a protease secreted by the chief cells in the stomach. Gas- trin and cholecystokinin are GI tract hormones.

8. (c). Active transport and passive and facilitated diffusion are all mechanisms by which nutrients can pass through a cell membrane. Glucose and amino acids are absorbed by active transport. Osmosis is a form of diffusion in which water moves across a cell membrane from a low concen- tration to a high concentration.

9. (c). A weak lower esophageal sphincter allows acid to re- flux back into the esophagus, causing heartburn. This sphincter is designed to relax and allow the bolus to enter the stomach and then contract to keep the contents of the stomach from refluxing back into the esophagus.

10. (b). Wheat, barley, and rye contain gluten, which causes the symptoms associated with celiac disease. Fruits, veg- etables, dairy, meat, nuts, legumes, and seeds are free of gluten and are safe to eat on a gluten-free diet.

Answers to Myths and Misconceptions

1. True. The enzyme salivary amylase, found in saliva, be- gins digesting carbohydrate during chewing; hence, starchy foods will begin to taste sweet as they are broken down. All other nutrients stay intact until they reach the stomach.

2. True. The stomach secretes a powerful acid, HCl, that is critical to breaking down the bonds in foods during di- gestion. However, the acid is also strong enough to dam- age the cells of the stomach wall. A thick layer of mucus protects the stomach wall from HCl.

3. True. Bile emulsifies fat by breaking up the large globules into smaller fat droplets. This allows enzymes to access and break the bonds.

4. False. Acid reflux occurs when stomach contents pass back through the lower esophageal sphincter into the esophagus.

5. True. After food has been completely broken down and its nutrients absorbed in the small intestine, it passes into the large intestine, where water and electrolytes continue to be absorbed. Some vitamins are also made by bacteria in the large intestine.

6. True. Fecal matter consists of 50 percent bacteria, while the rest is undigested food, water, and sloughed intestinal cells.

7. False. Lymph only transports fat-soluble components such as fatty acids, fat-soluble vitamins, and cholesterol, to the liver and cells. Blood transports water-soluble ma- terials including glucose, amino acids, and water-soluble vitamins.

8. True. Several hormones, including gastrin, secretin, cholecystokinin (CCK), and gastric inhibitory peptide help regulate digestion.

9. False. Though foodborne illness can cause diarrhea, the condition can also result from an adverse reaction to cer- tain foods, medications, or other compounds, including sugar substitutes such as sorbitol.

10. False. The cause of irritable bowel syndrome is not known, but low-fiber diets, stress, consumption of irritat- ing foods, and intestinal motility disorders are all sus- pected factors.

Web Support ■ To learn more about the various conditions related to di-

gestion, absorption, and elimination, visit the Center for Digestive Health and Nutrition at www.gihealth.com

■ Visit the National Library of Medicine for an abundant Internet resource for health care professionals, the public, researchers, and librarians at www.nlm.nih.gov

■ Search the National Digestive Diseases Information Clear- inghouse site for more information about various diges- tive diseases: http://digestive.niddk.nih.gov

■ To locate sources of gluten-free foods, go to the Gluten Free Mall at www.gfmall.com

References 1. Pedersen, A. M., A. Bardow, S. Jensen, and B. Nauntofte. 2002. Saliva and

Gastrointestinal Functions of Taste, Mastication, Swallowing and Diges- tion. Oral Diseases 8:117–129.

2. Marieb, E. N. and K. Hoehn. 2007. Human Anatomy and Physiology. 7th ed. Benjamin Cummings: San Francisco.

3. Gropper, S. S., J. L. Smith, and J. L. Groff. 2005. Advanced Nutrition and Human Metabolism. 4th ed. Thomson Wadsworth: Belmont, CA.

4. Tortora, G. J. and N. P. Anagnostakos. 2008. Principles of Anatomy and Physiology. 12th ed. Harper & Row: New York.

114 Chapter 3 . Digestion, Absorption, and Transport

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References 115

5. Jansson, H., E. Lindholm, C. Lindh, L. Groop, and G. Bratthall. 2006. Type 2 Diabetes and Risk for Periodontal Disease: A Role for Dental Health Awareness. Journal of Clinical Periodontology 33:408–414.

6. Watt, E. and M. N. Whyte. 2003. The Experience of Dysphagia and Its Ef- fect on the Quality of Life of Patients with Oesophageal Cancer. European Journal of Cancer Care 12:183–193.

7. Wong, W. and R. Pass. 2004. Extraesophageal and Atypical Manifesta- tions of GERD. Journal of Gastroenterology and Hepatology 19:S33–S43.

8. Ibid. 9. Rantanen, T. K., E. I. T. Sihvo, J. V. Rasanen, and J. A. Salo. 2007. Gastroe-

sophageal Reflux Disease as a Cause of Death Is Increasing: Analysis of Fatal Cases after Medical and Surgical Treatment. American Journal of Gastroenterology 102:246–253.

10. Hungin, A. P., A. S. Raghunath, and I. Wiklund. 2005. Beyond Heartburn: A Systematic Review of the Extra-Oesophageal Spectrum of Reflux-In- duced Disease. Family Practice 22:591–603.

11. Tytgat, G. N. J. 2002. Review Article: Treatment of Mild and Severe Cases of GERD. Alimentary Pharmacology & Therapeutics 16:73–78.

12. Vega, K. J. and M. Mazen Jamal. 2000. Changing Pattern of Esophageal Cancer Incidence in New Mexico. The American Journal of Gastroenterol- ogy 95:2352–2356.

13. Yuan, Y., I. T. Padol, and R. H. Hunt. 2006. Peptic Ulcer Disease Today. Nature Clinical Practice Gastroenterology and Hepatology 3:80–90.

14. Fobi, M. 2002. Prophylactic Cholecystectomy with Gastric Bypass Opera- tion: Incidence of Gallbladder Disease. Obesity Surgery 12:350–353.

15. Wald, A. 2007. Chronic Constipation: Advances in Management. Neurog- astroenterology Motility 19:4–10.

16. Hajek, P., F. Gillison, and H. McRobbie. 2003. Stopping Smoking Can Cause Constipation. Addiction 98:1563–1567.

17. Dukas, L., W. C. Willett, and E. L. Giovannucci. 2003. Association Be- tween Physical Activity, Fiber Intake, and Other Lifestyle Variables and Constipation in a Study of Women. American Journal of Gastroenterology 98:1790–1796.

18. Saito, Y. A., P. Schoenfeld, and G. R. Locke. 2002. The Epidemiology of Ir- ritable Bowel Syndrome in North America: A Systematic Review. American Journal of Gastroenterology 97:1910–1915.

19. Rose, D. J., M. T. DeMeo, A. Kesharvarzian, and B. R. Hamaker. 2007. In- fluence of Dietary Fiber on Inflammatory Bowel Disease and Colon Can- cer: Importance of Fermentation Pattern. Nutrition Reviews 65: 51–62.

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4

1. Carbohydrates are the least important macronutrient. T/F

2. Most babies are born lactose intolerant. T/F

3. Carbohydrates are a main cause of obesity. T/F

4. Sugar causes hyperactivity in children. T/F

5. Whole grains are more nutrient dense than refined grains. T/F

6. Sugar causes tooth decay. T/F

Carbo

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o hydrates Sugars, Starches, and Fiber

7. Aspartame causes cancer in humans. T/F

8. Americans do not consume enough fiber. T/F

9. Soda and other sugar-sweetened beverages play a big role in Americans’ rising rate of obesity. T/F

10. Obese individuals are more likely to develop type 2 diabetes. T/F

See page 169 for answers.

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118 Chapter 4 . Carbohydrates

Chapter Objectives After reading this chapter, students will be able to:

1. Compare and contrast the monosaccharides, disaccha- rides, oligosaccharides, and polysaccharides.

2. List the functions of carbohy- drates in the body.

3. Describe the differences between insoluble and soluble fibers and their role in promoting health.

4. Explain the process of digest- ing and absorbing dietary carbohydrates.

5. Explain how the body regulates blood glucose levels, and the hor- mones involved in the process.

6. Describe the guidelines for car- bohydrate intake, including the AMDR for carbohydrates, the AI for fiber, and the recommendation for consuming simple sugars.

7. Identify good food sources for each type of carbohydrate.

8. Describe the potential health im- plications of consuming too much or too little dietary carbohydrate.

9. Define type 1 and type 2 diabetes and describe how diabetes differs from hypoglycemia.

10. List alternative sweeteners used as sugar substitutes.

What Are Carbohydrates and Why Are They Important? Carbohydrates originate in plants during a process called photosynthesis (Figure 4.1). During photosynthesis, plants use the chlorophyll in their leaves to absorb the energy in sunlight. The absorbed energy splits water in the plant into its component parts of hydrogen and oxygen. The hydrogen joins with carbon dioxide that the plant has taken in from the air to form the most abundant carbohydrate, glucose (ose � carbohydrate). Thus, carbohydrates are literally hydrated carbons. The oxygen is released as a waste product.

Plants use glucose directly for energy, or combine it with minerals from the soil to make other compounds, including protein and vitamins. Plants also link glucose units together and store them in the form of starch, and use glucose to form fiber. Plants can generate all the nutrients they need for their own health and maintenance from sunlight, water, and minerals. An estimated 140 billion tons of carbohydrate, or about 20 tons per person in the world, are synthesized in plants every year.1

When humans eat plant foods, they take in carbohydrates that can be converted into glucose in the body. Glucose is the preferred source of energy for the blood, brain, and nervous system. With such an important role in the body, it isn’t surpris- ing that foods high in carbohydrates are a big part of the diet, no matter what conti- nent you live on.

Carbohydrate-rich plant foods, including rice, beans, fruits, tubers and nuts, make up the foundation of diets the world over. In Asia, rice accounts for 80 percent of people’s daily kilocalories. In Latin America, carbohydrate-laden bananas, chilies,

Ironically, because of my diabetes, I probably eat better than anyone else on the team and have the most energy. I can outskate them all,” Adam says proudly.

Do you know what causes type 1 di- abetes? What advice do you think Adam’s campus dietitian might provide to help him maintain his blood glucose lev- els during games? In this chapter, you will learn more about diabetes, including the role carbohydrates play in regulating the condition. We will also discuss different types of carbohydrates, how they provide

fuel for the body, and the role that high-fiber foods can play in fighting obesity, heart disease, cancer, and diabetes. Finally, we will cover how to incorporate plenty of carbohydrates into your daily diet.

A dam is a star hockey center on his college team, and skates 2 to 4 hours a day during the height of

hockey season. When not on the ice, Adam is in the library maintaining a 3.7 GPA. Besides being a hockey genius, Adam has been an insulin-dependent, type 1 diabetic ever since he laced up his first pair of skates at age two.

Adjusting his daily diet and insulin injections to his rigorous exercise sched- ule is no small feat. “Once when I was in a hockey league in high school, I buck- led on the ice because I didn’t eat enough before the game. I was taken to the hospital in an am- bulance because my blood glucose dropped too low,” recalls Adam. “Now, I work with the team trainer and the campus di- etitian to make sure my pregame snack covers my ice time.

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What Are Carbohydrates and Why Are They Important? 119

beans, tubers, and nuts adorn most dinner plates. In the Mediterranean, grain-based pastas, breads, and couscous are plentiful, and here in the United States, many people consume the potato on a daily basis.2

The Take-Home Message Carbohydrates are found primarily in plant- based foods and are needed by the cells for energy. Glucose, produced in plants through photosynthesis, is the preferred source of energy in the body. Glucose is stored in plants in the form of starch, and fiber is part of plants’ cell walls. Numerous cultures around the world rely on carbohydrate-based foods as staples in their diets.

H

OH

O

OH

H

HO

H OH

CH2OH

C

C

C

C

CO2

CO2

CO2

CO2 CO2

CO2 O2

H2O H2OH2O

H2O H2O

H2O

O2

O2

O2

O2

O2

Carbon dioxide in air

Sunlight

Oxygen

Photosynthesis

Glucose

Water in soil

H C

Figure 4.1 Photosynthesis: How Glucose Is Made During photosynthesis, the leaves of green plants absorb energy from sunlight. The energy splits six molecules of water (H2O) into hydrogen and oxygen. The hydrogen joins with carbon dioxide in the plant to create glucose (C6H12O6). In this process, six molecules of oxygen are released into the air.

chlorophyll The green pigment in plants that absorbs energy from sunlight to begin

the process of photosynthesis.

glucose The most abundant carbohy- drate in nature and the primary energy

source for the body.

starch The storage form of glucose in plants.

photosynthesis A process by which plants create carbohydrates using the en-

ergy from sunlight.

fiber A nondigestible carbohydrate that provides structural support to the cell

walls in plants.

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120 Chapter 4 . Carbohydrates

How Do We Classify Carbohydrates? All carbohydrates consist of strings of sugar units bound together. We classify carbohydrates according to how many of these units are in the string. Simple carbohy- drates consist of either a single sugar unit called a monosaccharide (mono � one, saccharide � sugar) or two units bonded together as a disaccharide (di � two). Oligosaccharides (oligo � a few) are slightly longer and contain three to ten units. Complex carbohydrates in- clude more than ten and up to hundreds or thousands of connected units. Such polysaccharides (poly � many) include starch and fiber.

Monosaccharides Are Single Sugar Units There are three nutritionally important monosaccha-

rides: glucose, fructose, and galactose. Glucose is the most common, but fructose and galactose are also found naturally in foods. All three simple sugars share the same molecular formula of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms (C6H12O6), referred to as a hexose (hex � six, ose � sugar). The difference be- tween the three monosaccharides lies in how their atoms are arranged (see Figure 4.2). Glucose and galactose are six-sided ring structures that, at first glance, look identical to each other. If you examine both structures carefully, you notice that the hydroxyl group (OH) and the hydrogen (H) on the fourth carbon of galactose is shifted in a different direction from the hydroxyl group on glucose. This slight rearrangement of atoms makes a difference in the way the body metabolizes and uses these two monosaccharides.

Fructose contains the same number of carbon, hydrogen, and oxygen atoms as glucose and galactose but its molecular structure is arranged as a five-sided, rather than a six-sided, ring. However, fructose is still classified as a hexose because it con- tains six carbons (notice the location of all six carbons on the fructose molecule in Figure 4.2).

Because glucose is found as a monosaccharide, is part of every disaccharide, and is the only monosaccharide in starch, it is the most abundant monosaccharide in foods. Glucose is also the most abundant monosaccharide in the body. The brain in particular relies on glucose (also known as blood glucose or blood sugar in the body) as its main source of energy, as do the red blood cells.

Galactose is seldom found on its own in nature; it most commonly occurs as part of the disaccharide lactose found in milk and milk products. Several plant prod- ucts, including cereals, beans, nuts, seeds, and vegetables, contain slight amounts of galactose but it is in a form that is resistant to digestion.

Fructose, the sweetest of the natural sugars, is found abundantly in fruits and is also known as fruit sugar. Fructose is part of high-fructose corn syrup, a sweetener

polysaccharides Many sugar units combined. Starch, glycogen, and fiber are

all polysaccharides.

disaccharides Simple sugars that con- sist of two sugar units combined. There

are three disaccharides: sucrose, lactose,

and maltose.

monosaccharides Simple sugars that consist of a single sugar unit. There are

three monosaccharides: glucose, fructose,

and galactose.

simple carbohydrates Carbohydrates that consist of one sugar unit (monosaccha-

rides) or two sugar units (disaccharides).

oligosaccharides Three to ten units of monosaccharides combined.

galactose A monosaccharide that links with glucose to create the sugar found in

dairy foods.

hexose A sugar that contains six car- bons; glucose, galactose, and fructose are

all hexoses.

complex carbohydrates A category of carbohydrates that contain many sugar

units combined. A polysaccharide is a

complex carbohydrate.

Hexose sugars (C6H12O6)

Glucose

C

OH

CH OH

CHO H

CH OH

CH OH

C

H

H OH

H

H

OH

O

OH

H

HO

H OH

CH2OH

C

C

C

C

C

Galactose

C

OH

CH OH

CHO H

CHO H

CH OH

C

H

H OH

H

OH

O

OH H

HO

H

H OH

CH2OH

C

C

C

C

C

Fructose

C

H

C O

H OH

CHO H

CH OH

CH OH

C

H

H OH

OH OH

O

H H

OH H

HOCH2 CH2OH

C

C C

C

Figure 4.2 The Structural Differences between Glucose, Galactose, and Fructose The three monosaccharides are shown in their linear form (as found in foods) and in the ring structure found in the body.

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How Do We Classify Carbohydrates? 121

commonly used by the food industry in soft drinks and fruit beverages. Some U.S. health professionals have expressed concern that overconsumption of high-fructose corn syrup may contribute to the obesity epidemic.3 (See the feature box on this topic on page 152.)

From the three monosaccharides, disaccharides and complex carbohydrates can be created.

Disaccharides Consist of Two Sugar Units The three disaccharides, sucrose, lactose, and maltose, all have a common characteris- tic: At least one of their two monosaccharides is glucose. The disaccharide sucrose consists of glucose and fructose; lactose is glucose and galactose; and maltose is two glucose units linked together.

Disaccharides are created through a process called condensation. This process chemically links monosaccharides with a glycosidic bond (Figure 4.3). Glycosidic bonds can be either alpha bonds or beta bonds and, though they don’t seem signifi- cantly different, the type of bond will affect the digestibility of the sugar. For in- stance, sucrose is formed with an alpha bond and is easily digested, whereas lactose is formed with a beta bond and is not easily digested by some individuals.

fructose The sweetest of all the mono- saccharides; also known as fruit sugar or

levulose.

glycosidic bond A bond that forms when two sugar molecules are joined

together during condensation.

condensation A chemical reaction in which two molecules combine to form a

larger molecule, and water is released.

H2O

a

b

c

H

H

OH

O

OH

H

HO

H OH

CH2OH

C

C

C

C

C H

H

OH

O

OH

H

HO

H OH

CH2OH

C

C

C

C

C

Glucose

Monosaccharides Disaccharides

Glucose

+ H

HO

OH

H

HO

H OH

CH2OH

C

C

C

C O

C H

H

OH

O

OH

H

H OH

CH2OH

C

C

C

C

C

Maltose

H2O

H

H

OH

O

OH

H

HO

H OH

CH2OH

C

C

C

C

C

Galactose Glucose

+ H

H

OH

O

OH

H

H OH

CH2OH

C

C

C

C

C

Lactose

H2O

H

H

OH

O

OH

H

HO

H OH

CH2OH

C

C

C

C

C

Glucose Fructose

+ H

HO

OH

H

HO

H OH

CH2OH

C

C

C

C O

C

Sucrose

OH OH

O

H H

OH H

HOCH2 CH2OH

C

C C

C

OH OH

O

H

OH H

HOCH2 CH2OH

C

C C

C

H

OH

O

OH H

HO

H

H OH

CH2OH

C

C

C

C

C H

O

OOH H

HO

H

H OH

CH2OH

C

C

C

C

C

Figure 4.3 Monosaccharides Link to Form Disaccharides Through the process of condensation, monosaccharides join together to form disaccharides. (a) Two glucose units join together to produce maltose. (b) The disaccharide sucrose is composed of a molecule of glucose linked to a molecule of fructose. (c) The disaccharide lactose is composed of glucose and galactose.

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resistant starch A type of starch that is not digested in the GI tract but has impor-

tant health benefits in the large intestine.

amylopectin A branched chain of poly- saccharides found in starch.

amylose A straight chain of polysaccha- rides found in starch.

glycogen The storage form of glucose in animals, including humans.

122 Chapter 4 . Carbohydrates

The white granulated sugar you add to coffee and the brown sugar you use to make cookie dough are examples of sucrose (brown sugar is made by adding mo- lasses to refined sugar and is about 90 percent sucrose.4) Sucrose is also found natu- rally in sugar cane and sugar beets and is the most commonly used natural sweetener.

Lactose, or milk sugar, is found in milk and dairy products. Lactose is a particu- larly important carbohydrate in the diets of newborn infants because it is the first and only carbohydrate they consume in breast milk.

Maltose, or malt sugar, is the least common of the disaccharides and is formed during the digestion of starch. Other food sources of maltose include corn syrup, which contains a small amount, and the malted barley used to brew beer.

In general, simple carbohydrates are sweeter than complex carbohydrates (which we’ll discuss next). Foods such as table sugar and fruit, which are high in sim- ple carbohydrates, are perceived as sweet compared with the carbohydrates found in starchy foods such as rice or bread. This perception is due to the structure of the molecule, which mixes with saliva and reacts with taste buds, signaling the brain that the food is sweet.

Some of us experience a stronger sense of sweetness than others do when we eat foods high in monosaccharides and disaccharides. For example, across all eth- nic groups, females seem to crave sweetness more than males.5,6 This ability to sense sweetness may be influenced by age or by health conditions or have a genetic component.7

The Polysaccharides Consist of Many Sugar Units Complex carbohydrates, or polysaccharides, consist of long chains and branches of sugars linked together. Some polysaccharides, such as starch and glycogen, serve as storage forms of carbohydrates in plants and animals, while dietary fiber provides structure in plant cells.

Starch Plants store glucose in chains of starch. These chains can be hundreds or even thou- sands of units long. Straight chains are referred to as amylose, and the branched chains are called amylopectin (Figure 4.4). Although plants contain both forms of these polysaccharides, about 60 percent of most starches is usually amylopectin, with the remainder (about 40 percent) in the form of amylose. When we eat plant foods such as corn, rice, and potatoes, we consume the stored starch.

Some starch is resistant to digestion. In beans, half of the starch is digestible and the remainder is in the form of resistant starch. The amylose in starch is more resist- ant to digestion than is the amylopectin. Linear chains of amylose are harder to break down during digestion because the molecules stack together into tight granules, which hinders the ability of enzymes to reach and break down the bonds. The branched-chain shape of amylopectin makes it impossible to compact and therefore allows for much easier digestion. Unripe bananas, cooked and chilled pasta, raw po- tatoes, baked beans, and plantains are examples of foods with high levels of resistant starch.8

Resistant starches that are found naturally in food are considered dietary fiber because they resist digestion. Resistant starches that are added to foods for health benefits are classified as functional fiber, and eating foods higher in resistant starch may have health benefits.9 Some researchers have reported that resistant starch may improve the health of the digestive tract by increasing bulk; improve glucose

sucrose A disaccharide composed of glucose and fructose; also known as table

sugar.

maltose A dissacharide composed of two glucose units joined together.

lactose A dissacharide composed of glu- cose and galactose; also known as milk

sugar.

A condensation reaction occurs when two smaller molecules join to form a larger molecule. When two monosaccha- rides join together, a hydroxyl group (—OH) from one sugar gains a hydrogen and forms a molecule of water. The OH group on the second sugar loses a hy- drogen and links to the other molecule where the OH group was removed.

Chemistry Boost

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insoluble fiber A type of fiber that isn’t dissolved in water or fermented by intes-

tinal bacteria.

soluble fiber A type of fiber that dis- solves in water and is fermented by intes-

tinal bacteria. Many soluble fibers are

viscous and have thickening properties.

lignin A noncarbohydrate form of di- etary fiber that binds to cellulose fibers to

harden and strengthen the cell walls of

plants.

cellulose A nondigestible polysaccha- ride found in plant cell walls.

How Do We Classify Carbohydrates? 123

Starch (amylopectin) Starch (amylose)

Glycogen

Starch: Two types of polysaccharides in starch are amylose (straight chain) and amylopectin (branched).

a

Glycogen: The storage form of glucose in animals, including humans. Glycogen is more branched that amylopectin. Each new glycogen needs a special protein to attach the glucose molecule.

b

Figure 4.4 The Comparison of Starch and Glycogen Molecules

Plantains contain a fair amount of resistant starch.

tolerance by lowering the glycemic impact on the blood and increasing insulin sensitivity10; and stimulate the growth of beneficial intestinal bacteria.11

Fiber Most forms of dietary fiber are nondigestible polysaccharides and occur naturally as a structural component called cellulose in the cell walls of plants. Cellulose looks simple—just a straight string of glucose units (never branched like amylopectin) linked with beta-glycosidic bonds (Figure 4.5). When several strands stack together, like a wall of bricks, it gives the plant cell its structure and shape, and contributes to the texture of fruits and vegetables. Lignin, which is also a type of dietary fiber, is not a carbohydrate but acts as an adhesive in cell walls.

Humans lack the digestive enzyme needed to break the beta form of the glyco- sidic bond, so for the most part, fiber cannot be digested, and passes through the in- testines intact. This means that fiber does not provide energy. However, it performs numerous key roles in the body and is an essential component of a healthy diet.

Dietary fiber is sometimes classified according to its affinity for water. Soluble fiber dissolves in water, while insoluble fiber does not. Viscous, soluble fibers in- clude pectins, beta-glucans, some gums, such as guar gum, and mucilages (for exam- ple, psyllium). Cellulose, lignin, and some hemicelluloses are considered insoluble, nonviscous fibers.12,13 Soluble fibers are more easily fermented by intestinal bacteria. Fruits and vegetables that are rich in pectin and hemicellulose can be hydrolyzed by these bacteria to form carbon dioxide, methane, and some fatty acids. Insoluble fibers, including cellulose found in grains, are not easily fermented.

Viscous, soluble fibers may have numerous health benefits. The gels formed by soluble fibers slow gastric emptying and may delay the absorption of some nutrients, which helps to reduce serum cholesterol, improve appetite control, and normalize

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functional fiber The nondigestible polysaccharides that are added to foods

because of a specific desired effect on

human health.

124 Chapter 4 . Carbohydrates

Pectin: soluble fiber

Cellulose: insoluble fiber

Figure 4.6 Most Plant Foods Contain Both Soluble and Insoluble Fibers The skin of an apple is high in cellulose and insoluble fiber, while the pulp is high in pectin, a soluble fiber.

Table 4.1

Forms of Dietary Fiber and Their Health Benefits Type Found in These Foods Reduces the Risk of

Insoluble Fiber

■ Cellulose ■ Hemicellulose ■ Lignins

Whole grains, whole-grain cereals, bran, oats, fruit, vegetables, legumes

Constipation, diverticulosis, certain cancers, heart disease, obesity

Soluble Fiber

■ Pectin ■ Beta-glucan ■ Gums ■ Psyllium

Citrus fruits, prunes, legumes, oats, barley, brussels sprouts, carrots

Constipation, heart disease, diabetes mellitus, obesity

blood glucose levels. The by-products produced by intestinal bacteria during fiber fer- mentation may also help protect against colon cancer. In comparison, less viscous, in- soluble fibers increase the bulk of the stool. The greater stool weight stimulates peristalsis, which speeds up the movement of the feces through the intestinal tract. This increase in movement, called transit time, relieves constipation and keeps the gas- trointestinal tract healthy. There are exceptions to this statement because not all soluble fibers reduce serum cholesterol, and constipation may be relieved by some soluble fiber. At the end of the day, the solubility is not as important as the overall dietary fiber intake, and the good news is that most plant foods contain both soluble and insoluble forms of dietary fiber (Figure 4.6). Animal products do not contain fiber.

Many compounds can be classified as both dietary fiber and functional fiber, de- pending on how they are used. Functional fiber is a type of fiber that has been ex- tracted or isolated from a plant or animal or manufactured by the food industry, and has been shown to have health benefits.14 For example, psyllium, used in products such as Metamucil, is isolated from psyllium seed husks. Psyllium is high in soluble fiber and has been reported to reduce total cholesterol and LDL cholesterol. Synthetic or manufactured forms of functional fiber also include some forms of resistant starch. Together, dietary fiber and functional fiber contribute to the total fiber in the diet.

Table 4.1 summarizes the various types of fiber and some of their health benefits.

H OH

O

OH HO

H OH

Plant cells

Glucose

Cell wall

CH2OH

C

C

C

C

C

Figure 4.5 Plants Contain Cellulose Found in the cell walls of plants, cellulose is a polysaccharide composed of numerous glucose units linked together.

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How Do We Classify Carbohydrates? 125

Glycogen Whereas starch is the storage form of glucose in plants, glycogen is the storage form in animals, including humans. Molecules of glycogen are long, branched chains, sim- ilar to amylopectin, and stored in muscle and in the liver. The branched structure en- ables the body to break it down quickly and easily because there are so many sites where enzymes can attach. When blood glucose levels decrease, the liver breaks down the glycogen branches, and glucose is released into the blood. Muscle glycogen can similarly be broken down for energy by the muscle. Because glycogen breaks down quickly after an animal dies, animal products do not contain this polysaccharide. In other words, eating meat or poultry will not provide glycogen.

Oligosaccharides One carbohydrate class falls in between the definitions of simple and complex carbo- hydrates—the oligosaccharides (Figure 4.7). They are short chains of three to ten monosaccharides that are similar in length to simple carbohydrates. But they are also similar to polysaccharides because they make up part of the cellulose found in plant cell walls, and, like fiber, most of the oligosaccharides we consume escape digestion.15

Two common oligosaccharides are raffinose and stachyose. Raffinose is a three- unit simple carbohydrate made up of galactose, glucose, and fructose (see Figure 4.7). Stachyose is similar to raffinose except it contains one extra galactose unit. Humans lack the enzyme necessary to break apart the bonds in oligosaccharides and they pass undigested into the large intestine, where the intestinal microflora digest and ferment them. This fermentation may result in bloating, discomfort, and flatulence (gas).

Adam indicated that he eats better than anyone on the hockeyteam and has the most energy. Do foods high in dietary fiber contribute to Adam’s higher energy level? Why or why not?

H

O

O

OH H

HO

H

H OH

CH2OH

Raffinose

Galactose

C

C

C

C

C

H

H

O

O

OH

H

HO

H OH

CH2

C

C

C

C

C

OH OH

O

H

OH H

HOCH2 CH2OH

C

C C

C

Sucrose

Figure 4.7 The Structure of an Oligosaccharide The oligosaccharide raffinose consists of galactose connected to sucrose.

Foods high in carbohydrates are staples in many of the world’s cultures.

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126 Chapter 4 . Carbohydrates

Beano helps reduce the production of gas in the large intestine.

Foods that contain high amounts of oligosaccharides include legumes, beans, cabbage, brussels sprouts, and broccoli. Taking a product such as Beano with a meal containing oligosaccharides can reduce the amount of flatulence produced.16 Beano contains enzymes that digest the oligosaccharides in the gastrointestinal tract, which increases the absorption of the available monosaccharides and reduces the amount that can be used by the intestinal bacteria.

Oligosaccharides are also present in breast milk. Even though these carbohy- drates aren’t digested, they may stimulate the immune system and increase the amount of healthy intestinal microflora in newborn infants.17

The Take-Home Message Simple carbohydrates include the monosac- charides and disaccharides, and complex carbohydrates include polysac- charides. The monosaccharides glucose, fructose, and galactose combine to form the disaccharides sucrose, lactose, and maltose. Starch, fiber, and glycogen are all polysaccharides. The total fiber in the diet is a combination of both soluble and insoluble dietary fiber and functional fiber added to foods. Viscous, soluble fiber has thickening properties, can be fermented by intestinal bacteria, and moves slowly through the intestinal tract. Insoluble fiber typically moves quickly through the digestive system, reducing consti- pation. Oligosaccharides contain three to ten units and are part of cellulose in cell walls.

How Do We Digest and Absorb Carbohydrates? Disaccharides and starch are digested into monosaccharides that can be easily ab- sorbed through the walls of the small intestine, whereas fiber generally passes through the GI tract undigested. Let’s follow the carbohydrates from a meal of pasta, milk, and cherries through the digestive process illustrated in Figure 4.8.

Digestion of Carbohydrates The digestion of carbohydrates begins in the mouth, where the teeth grind the food and mix it with saliva, which contains the enzyme salivary amylase (recall that ase � enzyme). The amylase begins breaking down some of the amylose and amylopectin in the pasta into the disaccharide maltose. The disaccharide lactose, found in the milk, and the sucrose and fiber in the cherries are not altered in the mouth.

This food mixture, which now contains starch and amylase, along with the malt- ose, lactose, sucrose, and fiber, travels down the esophagus to the stomach. The amy- lase continues to break down the starch until the hydrochloric acid in the stomach deactivates this enzyme. There are no carbohydrate-digesting enzymes in the stom- ach; thus, little to no carbohydrate digestion takes place there.

The arrival of carbohydrates in the small intestine signals the pancreas to release another enzyme called pancreatic amylase. The pancreatic amylase breaks down the remaining starch units from the pasta into maltose.

The disaccharides from maltose, lactose, and sucrose will need further disman- tling by the brush border enzymes, including maltase, lactase, and sucrase, housed in

salivary amylase A digestive enzyme that begins breaking down carbohydrate

(starch) in the mouth; other important en-

zymes during carbohydrate digestion in-

clude pancreatic amylase, maltase, sucrase,

and lactase.

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How Do We Digest and Absorb Carbohydrates? 127

Amylose Amylose

Salivary amylase

Smaller chains

Amylopectin

Amylose No further digestion of carbohydrates

No further digestion of carbohydrates Amylopectin

Amylopectin Salivary amylase

Smaller chains

Amylose

Pancreatic amylase

Short chains of carbohydrates

Maltose Amylopectin

Short chains of carbohydrates

Pancreatic amylase

Maltose

Amylose

Maltase

Maltose

Glucose

Amylopectin Maltose

Maltase

Glucose

Lactose

Lactase

Glucose

Galactose

Sucrose

Sucrase

Glucose

Fructose

d All disaccharides are broken down to the monosacchrides glucose, fructose, and galactose with the help of enzymes located in the lining of the digestive tract.

a In the mouth, salivary glands release salivary amylase which hydrolyzes amylose and amylopectin into smaller chains of carbohydrates.

The acidity of the stomach inactivates the salivary amylase; thus, very little digestion of carbohydrates occurs in the stomach.

b

The pancreas releases pancreatic amylase into the small intestine which hydrolyzes the amylose, amylopectin, and smaller chains of carbohydrates into maltose.

c

Figure 4.8 From Carbohydrates to Glucose in the Body

the microvilli of the small intestine. These enzymes break down the disaccharides into monosaccharides, specifically glucose, fructose, and galactose. The monosaccha- rides are now ready to be absorbed into the blood.

By the time the remnants of the pasta meal reach the large intestine, all starch and simple sugars have been broken down and absorbed, and only the indigestible fiber remains. The bacteria in the colon can metabolize some of the fiber, producing water, gas, and some short-chain fatty acids. The colon uses these short-chain fatty acids for energy. The majority of the fiber is eliminated from the body in the feces. Resistant starch can also be metabolized by intestinal bacteria or excreted in the feces.

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glycogenesis The process of assembling excess glucose into glycogen in the liver

and muscle cells.

128 Chapter 4 . Carbohydrates

Glucose and other monosacchrides transported to liver

b

Blood levels of glucose maintained for brain and other body cells

c

Glucose transported to muscle

d

Dietary carbohydrates from stomach delivered to small intestine

a

Small intestine

Liver

Glycogen

Glucose

Glucose

Glycogen +

Energy

Muscle

Figure 4.9 Glucose Is Stored in the Liver and Muscle Cells as Glycogen Surplus glucose is stored in the liver and muscle cells. The liver glycogen can be used to supply the blood with glucose when the diet is deficient in carbohydrates. Muscle glycogen provides energy to the muscle cell.

Absorption of Carbohydrates After carbohydrate digestion, the monosaccharides glucose and galactose are ab- sorbed into the intestinal cell mucosa by active transport, while fructose is absorbed by facilitated diffusion. Once glucose, galactose, and fructose are absorbed into the intestinal cell, they are transported through the portal vein to the liver. Some fructose may be converted to glucose in the intestinal cell before it enters the portal vein, but both glucose and galactose remain intact.

The fate of the monosaccharides once they’ve reached the liver depends on an individual’s metabolic needs. Galactose and fructose are used mostly by the liver for energy, or they can be converted into glucose before entering the blood to circulate throughout the body. Any surplus glucose that is not used immediately for energy is stored as glycogen. The process of converting excess glucose to glycogen is called glycogenesis and occurs mostly in the liver and muscle cells (see Figure 4.9). As you learned earlier in the chapter, this stored form of glucose can be used by the body when the diet lacks sufficient carbohydrate.

Once the glycogen stores are fully replenished and energy needs have been met, excess glucose will be converted into glycerol and fatty acids. These two are com- bined into a triglyceride and stored in the adipocytes (fat cells).

The Take-Home Message The digestion of carbohydrates begins in the mouth with the breakdown of starch by the enzyme salivary amylase. Most carbohydrate digestion occurs in the small intestine. Pancreatic and small intestinal enzymes break down the carbohydrates into disaccharides and then monosaccharides so that they can be absorbed. All the monosac- charides are converted to glucose in the liver to be used as energy, or stored as glycogen in the liver and muscle cells. Fiber travels to the colon un- digested and most of it is eliminated from the body.

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lactose intolerant When maldigestion of lactose results in symptoms such as

nausea, cramps, bloating, flatulence, and

diarrhea.

lactose maldigestion The inability to digest lactose due to low levels of the en-

zyme lactase.

What Is Lactose Intolerance? 129

What Is Lactose Intolerance? People with a deficiency of the brush border enzyme lactase cannot properly digest lactose, the principal carbohydrate found in dairy products. They may be diagnosed with lactose maldigestion, which can lead to distressing symptoms. For example, the undigested lactose can draw water into the digestive tract, causing diarrhea. Once the lactose reaches the colon, the bacteria in the colon ferment the sugar and pro- duce various gases. For some lactose-sensitive individuals, bloating, flatulence, and cramps can sometimes be an unpleasant reminder that they ate lactose-containing foods. Individuals who develop these symptoms within two hours after eating or drinking foods that contain lactose may be lactose intolerant.18

Lactose maldigestion is a natural part of the aging process. In fact, as soon as a child stops nursing, his body makes less lactase. An estimated 25 percent of Americans, and 75 percent of adults around the world, maldigest lactose. Individuals of some specific ethnic origins, such as those from northern Europe, central Africa, and the Middle East, aren’t as prone to developing lactose maldigestion. They appear to have a genetic predisposition to maintaining higher levels of lactase throughout their adult life.19,20

People with lactose maldigestion don’t necessarily need to eliminate dairy foods from the diet. In fact, many people continue to eat milk, yogurt, and cheese without any problems or unpleasant side effects.21,22 This is good news, as dairy products pro- vide over 70 percent of the calcium in the diet.23,24

However, people with lactose intolerance have varying thresholds for tolerating lactose-containing foods and beverages (Table 4.2). These thresholds can be raised depending upon how much of a lactose-containing food one eats at a time. Consum- ing smaller amounts of dairy foods throughout the day can be better tolerated than having a large amount at one time. Eating lactose-containing foods with a meal or snack, rather than by themselves, can also influence how much can be tolerated.25,26

People respond differently to various dairy foods.27,28 Whole milk tends to be tolerated better than skim milk. Cheese typically has less lactose than milk, espe- cially hard, aged cheeses, as the amount of lactose remaining after the aging process is negligible. Yogurts that contain active cultures are better tolerated than skim or low-fat milk.

Consuming dairy foods regularly may improve lactose tolerance. The continu- ous exposure to undigested lactose promotes an acidic environment created by the fermenting of lactose by the bacteria in the colon, which inhibits further fermenta- tion. Also, the constant presence of lactose in the colon perpetuates an increase in the growth of nongaseous bacteria and subsequent displacement of the gas-producing bacteria.29

For those who want to enjoy dairy foods without worrying about unpleasant side effects, there are lactose-reduced dairy products such as milk, cottage cheese, and ice cream in many supermarkets. Lactase pills or drops can also be used to break down lactose in foods before or while they are eaten. See the Table Tips on the next page for more ideas on improving your lactose tolerance.

Finally, note that lactose intolerance is not the same as having an allergy to milk. A milk allergy is a response by the immune system to one or more of the proteins in cow’s milk. This condition typically affects only about 1 to 3 percent of children, and rarely occurs in adults.30 Food allergies will be covered in Chapter 17.

Table 4.2

How Much Lactose Is in Your Foods?

Food Amount Lactose (grams)

Milk, whole, 1%, or skim 1 cup 11

Lactaid milk 1 cup �1

Soy milk 1 cup 0

Ice cream 1⁄2 cup 6

Yogurt, low fat 1 cup 5

Sherbet 1⁄2 cup 2

Cottage cheese 1⁄2 cup 2

Swiss, Blue, Cheddar, or Parmesan cheese 1 oz

1

Cream cheese 1 oz 1

Don’t Forget These Hidden Sources of Lactose

Baked goods

Baking mixes for pancakes, biscuits, and cookies

Bread

Breakfast drinks

Candies

Cereals, processed

Instant potatoes

Lunch meats (other than kosher meats)

Margarine

Salad dressings

Soups

Source: Adapted from the American Dietetic Associa- tion, Manual of Clinical Dietetics (2000); food manu- facturers; and the National Digestive Diseases Information Clearinghouse, “Lactose Intolerance,” National Institutes of Health Publication No. 02-2751 (2002).

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130 Chapter 4 . Carbohydrates

Table Tips

Improving Lactose Tolerance

To determine the amount of milk you can tolerate, start with less than one cup and gradually increase the serving size until symptoms develop.

Choose aged hard cheeses such as cheddar, Colby, and Parmesan over softer cheeses.

Drink one serving of milk with lunch and have an ounce of cheese as an afternoon snack, rather than having the milk and the cheese at the same time.

Drink that cup of milk along with a meal or snack, rather than by itself.

Try reduced-lactose yogurt or cottage cheese.

The Take-Home Message Lactose maldigestion is the inability to break down the milk sugar lactose due to a decreased amount of lactase in the brush border of the small intestine. Prolonged lactose maldigestion can re- sult in a diagnosis of lactose intolerance. There are several strategies that in- dividuals with lactose intolerance can use to consume some dairy foods.

What Functions Do Carbohydrates Perform in the Body? Carbohydrates—primarily glucose—are the most desirable source of energy for the body. A complete discussion of the metabolism of glucose will be found in Chapter 8. This section briefly describes the overall functions of carbohydrates and the variety of health benefits they provide.

Carbohydrates Provide Energy and Maintain Blood Glucose Levels Whether the carbohydrate is in the form of a monosaccharide, disaccharide, or poly- saccharide, if it is digested, it provides 4 kilocalories of energy per gram. Much of the energy we need to fuel our activities comes from a combination of glucose and fats.

Eating carbohydrate-rich foods helps maintain blood glucose levels. If you haven’t eaten for longer than four hours, the body will tap into its glycogen stores by initiating glycogenolysis (lysis � loosening) to hydrolyze liver glycogen and supply glucose to the blood (refer again to Figure 4.9). Once liver glycogen stores are de- pleted, the body turns to other sources, such as amino acids, to maintain blood glu- cose. Note that muscle glycogen cannot be used to raise blood glucose levels, because muscles lack the enzyme necessary to release glucose into the blood. Instead, muscle uses glycogen to fuel its own energy needs.

Carbohydrates Spare Protein Glucose is the body’s preferred fuel source, and as long as there is adequate glucose in the blood, protein can be spared for its myriad other essential functions. In times of carbohydrate deprivation, however, the body turns to noncarbohydrate sources, partic- ularly amino acids (the building blocks of protein, which we will discuss in Chapter 6), to generate glucose. The process of creating glucose from noncarbohydrate sources is called gluconeogenesis (gluco � sugar/sweet, neo � new, genesis � origin). Gluconeo- genesis primarily occurs in the liver, but can also take place in the kidneys, because these are the only organs that contain the enzymes needed for this process. The kidney is not an active site of gluconeogenesis except after long periods of fasting.

The body does not store extra protein for this situation, so protein must be bro- ken down from the muscles and organs. To preserve these tissues and lessen the de- mand for glucose, after a few days of fasting some parts of the brain begin to use ketone bodies as fuel. This reduces the need to generate glucose from internal pro- tein sources.

glycogenolysis The hydrolysis of glyco- gen to release glucose.

gluconeogenesis The creation of glu- cose from noncarbohydrate sources, pre-

dominantly protein.

ketone bodies The by-products of the incomplete breakdown of fat.

Many products are available to help those who are lactose intolerant enjoy dairy foods.

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How Do We Maintain Blood Glucose Levels? 131

Carbohydrates Prevent Ketosis After about 18 hours of fasting, the liver’s glycogen stores are depleted and the body continues to break down fat stores for fuel. However, some carbohydrate is needed to burn fat thoroughly. Without adequate amounts of glucose, ketone bodies spill out into the blood, reducing its pH. After about two days of fasting, the number of ke- tone bodies in the blood doubles, which results in a state of ketosis. Individuals who follow low-carbohydrate diets are often in ketosis.

The Take-Home Message Glucose is the body’s preferred source for energy, especially for the brain and red blood cells. Adequate carbohydrate in- take helps maintain normal blood glucose levels, spares protein to be used for important functions other than energy production, and prevents ketosis.

How Do We Maintain Blood Glucose Levels? Blood glucose levels are not constant—they rise and fall depending on the body’s en- ergy needs. Blood glucose levels also change following a carbohydrate-heavy meal. How does the body regulate blood glucose levels, given these changes in metabolic needs and dietary intake? The answer is: hormones. In fact, two hormones in partic- ular, insulin and glucagon, secreted from the pancreas, maintain blood glucose levels between 70 and 110 mg/dl. Other hormones, including epinephrine, norepi- nephrine, cortisol, and growth hormone, also assist in the process.

Insulin Regulates Glucose in the Blood After eating a carbohydrate-heavy meal, the blood is flooded with glucose, which cannot be used by the cells until it crosses the cell membrane. Insulin helps glucose enter cells by attaching to specific receptor sites on the cell membrane, which stimu- lates an increase in the number of glucose transporters found on the membrane sur- face. These transporters unlock the cell membrane and transport glucose inside the cell. As soon as glucose enters the cell, insulin stimulates the enzymes that will con- vert glucose to energy or store it for later use. This role of stimulating the uptake of glucose by the cells is what makes insulin so integral to blood glucose regulation. Note that liver, kidney, and brain cells can use glucose without the aid of insulin.

In addition to helping glucose enter cells, insulin also helps convert glucose to glycogen if the amount of glucose in the blood exceeds the body’s immediate energy needs. It does this by stimulating glycogenesis in both the liver and the muscle (see Figure 4.10 on page 132), and by inhibiting the enzymes involved in glycogenolysis and gluconeogenesis. The body will store excess glucose as glycogen until it reaches its limit.

When glycogen stores are full, excess glucose may be converted into fatty acids in a process called lipogenesis. Insulin promotes lipogenesis in the same way it pro- motes glycogenesis, by increasing the number of glucose receptors on the surface of the fat cell. Insulin also inhibits lipolysis (fat breakdown) by reducing the activity of the enzyme that hydrolyzes stored fat. The result of insulin’s actions is that more fat is formed and fewer fatty acids are found in the blood.

ketosis The condition of increased ke- tone bodies in the blood.

glucagon The hormone secreted from the alpha cells of the pancreas that stimu-

lates glycogenolysis and gluconeogenesis to

increase blood levels of glucose.

insulin The hormone secreted from the beta cells of the pancreas that stimulates

the uptake of glucose from the blood into

the cells.

lipogenesis The process that converts excess glucose into fat for storage.

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132 Chapter 4 . Carbohydrates

Glucagon Regulates Liver Glycogenolysis Glucagon has the opposite effect of insulin on blood glucose levels—it stimulates re- lease of glucose into the blood (Figure 4.10b). The alpha cells of the pancreas release glucagon into the circulation when blood glucose levels are low, following a protein- rich meal, or during a period of stress. The main target organ of glucagon is the liver, where it promotes glycogenolysis to provide a burst of glucose into the blood. Under the control of glucagon, liver glycogen stores will be depleted after 10 to 18 hours without sufficient dietary carbohydrate.

Glucagon stimulates glucose production by encouraging the uptake of amino acids by the liver. The carbon skeletons of the amino acids are then used to produce glucose through gluconeogenesis. Glucagon also promotes the conversion of lactic acid to glucose through the same process.

Epinephrine, Norepinephrine, Cortisol, and Growth Hormone Regulate Glucose Metabolism In addition to glucagon, other hormones can increase blood glucose levels. Epinephrine (also known as adrenaline) and norepinephrine, both secreted from the adrenal glands, act on the liver to stimulate glycogenolysis and gluconeogenesis

Insulin

Glucose

Glycogenesis Lipogenesis

Glycogen

Muscle Fat cells

Pancreas Pancreas

Liver

Blood

a High blood glucose levels

Glycogen

Fat

Glucagon Glucose

Glycogenolysis: Glycogen stores broken down

Gluconeogenesis: Glucose is created

Liver

Blood

Low blood glucose levelsb

Figure 4.10 Insulin and Glucagon Regulate Glucose Metabolism (a) When blood glucose levels increase following a high-carbohydrate meal, the pancreas releases the hormone insulin into the blood. Insulin alters cell membranes to allow the passage of glucose into the cells. Excess glucose will be stored in muscles and liver as glycogen and in fat cells as a triglyceride. (b) When blood glucose levels drop too low, the pancreas releases the hormone glucagon, which stimulates glycogenolysis, releasing glucose from stored liver glycogen into the blood.

norepinephrine A hormone produced by the adrenal glands that stimulates

glycogenolysis and gluconeogenesis.

epinephrine A hormone produced by the adrenal glands that signals the liver

cells to release glucose; also referred to as

the “fight-or-flight” hormone.

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What Are Glycemic Index and Glycemic Load? 133

to raise blood glucose. Epinephrine production can increase in the body during peri- ods of emotional and physical stress, such as fear, excitement, and bleeding. For ex- ample, if a ferocious dog was chasing you down the street, your body would be pumping out epinephrine to help provide the fuel you need to run. For this reason, epinephrine is also referred to as the “fight-or-flight” hormone.

A low blood glucose level can trigger the release of both epinephrine and norephinephrine. In fact, some of the symptoms that you may experience when your blood glucose level dips too low, such as anxiety, rapid heart beat, turning pale, and shakiness, are caused by the release of both of these hormones.

Two other hormones—cortisol and growth hormone—also regulate glucose metabolism. Cortisol, often referred to as the stress hormone, stimulates gluco- neogenesis and reduces the uptake of glucose by the muscle cells. Both of these actions increase blood glucose levels. Growth hormone has the opposite effect of insulin: It conserves glucose by stimulating fat breakdown for energy, reducing the uptake of glucose by the muscle cells, and increasing glucose production in the liver.

The Take-Home Message Blood glucose levels are maintained by two hormones, insulin and glucagon, both secreted from the pancreas. When blood glucose levels rise, insulin is released, to stimulate the uptake of glucose by the muscle and liver, lowering the levels back to normal. When blood glucose levels fall below normal, glucagon is released to stimulate glycogenolysis of liver glycogen, raising blood glucose levels. Epinephrine, norepinephrine, cortisol, and growth hormone also raise blood glucose by stimulating either glycogenolysis or gluconeogenesis.

What Are Glycemic Index and Glycemic Load? The glycemic index (GI) and glycemic load (GL) can be used to classify the effects of carbohydrate-containing foods on blood glucose and may be potentially helpful for those with diabetes. The GI refers to the measured upward rise, peak, and even- tual fall of blood glucose following the consumption of a high-carbohydrate food. Some foods cause a sharp spike and rapid fall in blood glucose levels; others cause less of a spike and a more gradual decline.31 The index ranks foods according to their effect on blood glucose levels compared with that of an equal amount of white bread or pure glucose (see Figure 4.11).

If a carbohydrate-rich food causes the blood glucose level to rise more than the standard white bread, the food is considered a high-GI food. A carbohydrate- containing food that produces a smaller rise in blood glucose than white bread would be considered a low-GI food. For example, 50 grams of white bread has a glycemic index of 100. A 50-gram portion of kidney beans has a GI of 42, whereas the same amount of puffed wheat cereal has a GI of 105. Consequently, the kidney beans are considered a low-GI food compared with the white bread, while puffed wheat is con- sidered a high-GI food. The problem with using the GI is that 50 grams of puffed wheat would be over 4 cups of cereal, an amount that is unlikely to be eaten in one sit- ting. The glycemic load (GL) adjusts the GI to take into account the amount of carbo- hydrate consumed in a typical serving of a food, and in the case of puffed wheat cereal, the normal portion size has a dramatically lower effect on blood glucose.

growth hormone A hormone that regu- lates glucose metabolism by increasing

glycogenolysis and lipolysis.

cortisol A hormone produced by the ad- renal cortex that stimulates gluconeogene-

sis and lipolysis.

glycemic load The amount of carbohy- drate in a food multiplied by the amount

of the glycemic index of that food.

glycemic index A rating scale of the likelihood of foods to increase the levels of

blood glucose and insulin.

Foods

Rice, low amylose

Potato, baked

Cornflakes

Jelly beans

Green peas

Cheerios

Puffed wheat

Bagel, plain

White bread

Angel food cake

Ice cream

Bran muffin

Rice, long grain†

Brown rice

Oatmeal

Popcorn

Corn

Banana, overripe

Chocolate

Baked beans

Sponge cake

Pear, canned in juice

Custard

Spaghetti

Rice, long grain‡

Apple

Pear

Banana, underripe

Kidney beans

Whole milk

Peanuts

*GI = Glycemic Index

†Boiled for 25 minutes.

‡Boiled for 5 minutes.

GI*

126

121

119

114

107

106

105

103

100

95

87

85

80

79

79

79

78

74

70

69

66

63

61

59

58

52

47

43

42

39

21

Figure 4.11 The Glycemic Index of Commonly Eaten Foods The glycemic index is a ranking of foods that indicates their potential to raise insulin and glucose levels in the blood.

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134 Chapter 4 . Carbohydrates

Other factors can also affect the GI of a food. Overripe fruits have more easily digested sugar, and therefore a higher GI, than underripe ones. Both cooking and food processing partially break down foods and make them more easily digested, increasing the GI compared with their raw, unprocessed equivalents. Larger chunks or bigger particle sizes of food contribute to slower digestion and lower GI than the same foods chopped into smaller pieces. Foods with viscous, soluble fiber tend to be absorbed more slowly, so will have a lower GI than refined carbo- hydrates. The combinations in which foods are eaten also affects GI, and eating carbohydrate-heavy foods with protein and/or fat can lower the GI.32,33 In general, whole grains, vegetables, whole fruit, and legumes tend to have a low GI, while re- fined grains and cereals, some starchy vegetables (such as potatoes), and bakery items all have higher GIs.34

The usefulness of the GI for disease prevention or weight management is a controversial topic. Research suggests that high-glycemic-index foods do not raise blood glucose levels as rapidly as once believed. In fact, blood glucose levels peak at about the same level regardless of the source of the carbohydrate.35 There are sev- eral reasons why the use of the glycemic index may not be practical. For example, individuals respond differently to foods and the response may differ in the same person from day to day. The ripeness of a food, how it’s cooked, and even the country in which it was grown can influence its glycemic level. Trying for a low glycemic index is probably not the best approach to healthy eating. Several foods with a low glycemic index, such as ice cream (glycemic index of 32) or a Snicker’s candy bar (55), are not nutrient-dense foods compared with some high-glycemic- index foods such as green peas (107). To complicate matters even more, we usually don’t eat single foods, but rather consume several foods in a meal. Adding a table- spoon of olive oil to a meal that contains high-glycemic-index foods will slow the blood glucose response.

Using the glycemic index is helpful in educating people about the carbohy- drate content of foods, correct portion sizes, and the number of servings to con- sume during the day. But it doesn’t appear to have the clear health advantages originally proposed.

The Take-Home Message The glycemic index ranks foods according to their effect on blood glucose levels compared with an equal amount of white bread or pure glucose. The glycemic load adjusts the glycemic index to take into account the amount of carbohydrate consumed in a typical serving of a food. Foods that contain high fiber, or that are eaten with protein or fat, gener- ally have a lower index than refined foods.

Why Is Dietary Fiber So Important? Even though fiber is a nondigestible substance, it can have many powerful health ef- fects in the body. As mentioned earlier, fiber has been shown to help lower the risk of bowel irregularity, as well as obesity, heart disease, cancer, and diabetes mellitus. Let’s look closely at how this works.

Colon

Diverticula

Stool

Figure 4.12 Diverticulosis Diverticulosis is a condition in which small pouches, or diverticula, bulge out along the colon. When stool gets trapped in these pouches, they can become inflamed, leading to diverticulitis.

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Why Is Dietary Fiber So Important? 135

Fiber Helps Prevent Constipation and Diverticulosis Over 4 million Americans complain about being constipated, with pregnant women, children, and adults 65 years of age and older experiencing it more often than others.36

Constipation is usually caused by sluggish muscle contractions in the colon that move stool along too slowly, which leads to too much water being reabsorbed along the way. This can create hard, dry stools that are more difficult and painful to expel.

A diet plentiful in insoluble fibers such as bran, whole grains, and many fruits and vegetables will reduce the transit time of food in the colon and decrease the like- lihood of constipation. (Note: Some soluble fibers, such as psyllium, can also assuage constipation; psyllium’s water-attracting capability allows the stool to increase in bulk and form a gel-like, soft texture, which makes it easier to pass.)

Chronic constipation can lead to a disorder called diverticulosis (osis � condi- tion), in which increased pressure in the colon causes weak spots along its wall to bulge out and form pouches called diverticula (see Figure 4.12). Infection of the di- verticula, a condition known as diverticulitis (itis � inflammation), can lead to stomach pain, fever, nausea, vomiting, cramping, and chills. Approximately 50 per- cent of Americans age 60 to 80 and the majority of individuals over 80 years of age have diverticulosis.37 The best way to prevent both diverticulosis and diverticulitis is to eat a diet that is adequate in fiber.

Fiber Helps Prevent Heart Disease, Diabetes, and Cancer Viscous, soluble fibers have been shown to help lower elevated blood cholesterol lev- els, which may decrease the risk of heart disease. Viscous fiber is believed to interfere with the reabsorption of bile acids in the intestines (Figure 4.13). Bile acids are high in cholesterol and are secreted into the intestine by the gallbladder to help with the digestion of fat. The bile acids are likely “grabbed” or sequestered by the fiber before they can be reabsorbed by the body. They end up being excreted along with the fiber in the feces. The liver then removes cholesterol from the blood to replace the bile acids that were lost. Blood cholesterol levels are lowered as a result.

Slow-moving, viscous, soluble fibers may also reduce the rate at which fat and carbohydrates are absorbed from meals. Delayed absorption can lower the surge of fat in the blood after a meal, and may help improve sensitivity to the hormone, insulin. Both high levels of fat in the blood and a decreased sensitivity to insulin are consid- ered risk factors for heart disease.

While soluble fibers may decrease the risk for heart disease, insoluble fiber may promote heart health. Several research studies have shown that ce- real and grains, which contain insoluble fiber, may help to lower the risk of heart disease.38,39 A study that explored the dietary habits of over 65,000 women for 10 years found that the risk of developing heart disease was over 30 percent lower in those consuming the highest amount of cereal fiber.40

Research studies involving both men and women have shown that a higher con- sumption of fiber from cereals helped reduce the risk for type 2 diabetes.41 Viscous, soluble fibers have also been shown to help individuals who already have diabetes mellitus manage the condition. Viscous fibers slow the release of food from the

diverticulitis Infection of the diverticula.

diverticula Small bulges at weak spots in the colon wall.

Blood

Liver

Bile

Fiber and bile

Feces

Cholesterol

Figure 4.13 Dietary Fiber Reduces Blood Cholesterol Levels Dietary fiber acts as a bile acid sequestrant as it binds the bile in the intestinal tract and carries it out in the feces.

Dried fruits and nuts are excellent sources of fiber, though nuts can also contribute significantly to fat intake, and should be eaten in moderation.

diverticulosis The existence of divertic- ula in the lining of the large intestine or

colon.

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136 Chapter 4 . Carbohydrates

stomach, and thus slow down the digestion and absorption of glucose. This could help avoid a large spike in blood glucose after eating and help individuals with dia- betes improve the long-term control of their blood glucose level.42,43

Fiber is thought to have many positive and protective effects in the fight against certain cancers. Fiber from cereals has been shown to help lower the risk of breast cancer.44,45 Research also suggests that as fiber consumption increases, the incidence of colorectal cancer is reduced.46 This may be due to the increase in the bulk of stools, which can dilute cancer-promoting substances in the colon. Fiber helps keep things moving through the digestive tract so that potential cancer-promoting sub- stances spend less time in contact with the intestinal lining. Fiber encourages the growth in the colon of friendly bacteria and their fermentation by-products, both of which may have cancer-fighting potential. Because an increased amount of bile acids in the colon is thought to be associated with colon and rectal cancer, fiber’s ability to reduce the concentration of these acids is viewed as a cancer deterrent.47

Fiber Helps Prevent Obesity High-fiber foods, such as whole grains, fruits, and vegetables, can help you feel fuller faster (recall the concept of satiety from Chapter 1), helping reduce overall caloric in- take. Research studies have shown that obese men and women tend to consume lower amounts of dietary fiber daily than their leaner counterparts. This lends cre- dence to the concept that fiber plays a role in weight management.48,49 Whereas some weight-loss diets restrict carbohydrates, these plans would work better if they increased high-fiber carbohydrates.

A twelve-year, longitudinal study of middle-aged women found that women who consume whole grains gained less weight over time than those who consumed higher amounts of refined grains. These results suggest that the intake of dietary fiber, especially whole grains, is a useful dietary tool to control body weight.50 Similar results have been observed in men.51

A word of caution: Initially, a high-fiber diet can have negative side effects. An intake of greater than 60 grams of dietary fiber per day may cause fluid imbalance or lead to mineral deficiencies by reducing the absorption and increasing the excretion of minerals such as iron and zinc, especially when the diet is low in these minerals or needs have temporarily increased, such as during pregnancy. Gradually increasing the dietary fiber in the diet, and increasing water intake, will allow the body to adjust to the increased amount of fiber and minimize the side effects. See the Table Tips for some easy ways to gradually introduce more fiber into your diet.

The Take-Home Message A diet high in fiber has been found to have numerous health benefits, including reduced risk for constipation, diverticulo- sis, heart disease, obesity, diabetes mellitus, and certain cancers.

What Is the Recommended Intake for Carbohydrates? The body needs a minimum amount of carbohydrate daily to support brain and nerve function and to efficiently meet its energy needs. The latest Dietary Reference Intakes (DRIs) for carbohydrates recommend that adults and children consume a

The abundant fiber found in beans and legumes will help provide bulk to stool and may help with weight management.

Table Tips

Increasing Daily Fiber Intake

Choose whole-grain breakfast cereals such as shredded wheat, bran flakes, raisin bran, and oatmeal.

Enjoy a lunchtime sandwich made with a whole-wheat pita or 100% whole-grain bread.

Have two pieces of whole fresh fruit daily.

Layer lettuce, tomatoes, or other vegetables on sandwiches.

Include plenty of root vegetables, such as carrots, turnips, and potatoes, at lunch and dinner.

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What Are the Best Food Sources of Carbohydrates? 137

minimum of 130 grams of carbohydrate daily. This is based on the estimated mini- mum amount of glucose the brain needs to function efficiently. Though this may seem high, 130 grams is less than the amount found in the recommended daily serv- ings for each food group in MyPyramid, that is, 6 servings from the grain group, 3 servings each from the vegetable and dairy groups, and 2 servings from the fruit group.

In the United States, most adults consume well over the minimum DRI. Adult males consume, on average, 220 grams to 330 grams of carbohydrates daily, whereas adult females eat 180 grams to 230 grams daily.

Recall from Chapter 2 that the AMDR for carbohydrates is 45 to 65 percent of total daily kilocalories. Adults in the United States consume at least 50 percent of their kilocalories from carbohydrate-rich foods, so they are easily within this opti- mal range.

For fiber, the current DRIs recommend 14 grams of fiber for every 1,000 kilo- calories consumed. The AI for fiber is 25 to 38 grams per day for adults based on the amount needed to protect them from developing cardiovascular disease (see Table 4.3). Adults in the United States fall short of these recommendations and cur- rently consume only about 12 to 18 grams per day. Thus, whereas most Americans consume an adequate amount of carbohydrate overall, they are getting less than the AI for dietary fiber, on average.

What Are the Best Food Sources of Carbohydrates? The DRIs indicate the minimum amount of carbohydrate that individuals should consume daily, but it’s important to note that all carbohydrates are not created equal, and some carbohydrate-rich foods are nutritionally better than others. For example, some high-carbohydrate foods contain considerably higher amounts of kilocalories than others, and excess kilocalories can lead to weight gain; eating high-sugar foods that don’t contain many other nutrients will provide kilocalories but not much else. If the high-carbohydrate foods are high in saturated fat, they can also be unhealthy for the heart. Therefore, the best food choices for meeting carbohydrate require- ments include a range of nutrient-dense, low-saturated-fat foods, with low to mod- erate amounts of simple carbohydrates and higher amounts of fiber and other complex carbohydrates.

Choose Whole Grains to Meet Starch and Fiber Needs Whole grains (but not refined grains) are abundant in complex carbohydrates, in- cluding starch and dietary fiber. Select whole-grain breads and cereals that have at least 2 to 3 grams of total fiber per serving, such as whole-wheat (or whole-grain) bread, bulgur, brown rice, quinoa, and whole-grain pasta. See the feature box “Grains, Glorious Whole Grains” on the next page for a closer look at the differ- ences between whole and refined grains.

C A L C U L AT I O N C O R N E R

(a) Daily, Adam needs to eat approximately 4,000 kilocalories (kcals) to maintain his current weight, given his age, gender, height, weight, and activity level. Calculate how many kcals of carbohydrate Adam should eat each day to meet the AMDR.

4,000 (kcals) � 0.45 � 1,800 (kcals)

4,000 (kcals) � 0.65 � 2,600 (kcals)

Answer: If Adam ate between 1,800 and 2,600 kilocalories of carbohydrate each day, he would meet the AMDR for carbohydrates.

(b) How many grams of carbohydrate should Adam eat to equal 45 to 65 percent of his total kilocalories?

1,800 kcals � 4 kcals/gram � 450 grams

2,600 kcals � 4 kcals/gram � 650 grams

Answer: Adam should eat between 450 and 650 grams of carbohydrate each day.

(c) Would this intake of carbohydrate meet the minimum suggested intake?

Answer: Yes; Adam needs a minimum of 130 grams of carbohydrate.

Table 4.3

What Are Your Fiber Needs?

Grams of Fiber Daily*

Males Females

14 through 18 years old 38 36

19 through 50 years old 38 25

51 through 70� years old 30 21

Pregnancy 28

Lactation 29

*Based on an Adequate Intake (AI) for fiber.

Source: Institute of Medicine, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cho- lesterol, Protein, and Amino Acids (Washington, DC: The National Academies Press, 2002).

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Whole grains are not only an important staple in the diet but are also associated with a reduced risk of several chronic dis- eases, including cardiovascular disease and diabetes.1 In view of these potential health benefits, one of the objectives of Healthy People 2010 is to increase the in- take of whole grains to three servings each day. Currently, Americans are con- suming less than one serving of grains per day, most of which are refined rather than whole grains.2

Before processing, a kernel of a grain, such as wheat or oats, includes three edi- ble parts: the bran, the endosperm, and the germ (see figure). The bran, or outer shell, of the kernel is rich in fiber, B vita- mins, phytochemicals such as lignins and phytosterols, and trace minerals like chromium and zinc. The germ, or seed, of the kernel is a nutritional powerhouse providing vitamin E, heart-healthy fats, phytochemicals, fiber, and plenty of B vi- tamins. The endosperm, or starchy com- ponent, of the grain contains protein, B vitamins, and some fiber, although not as much as the bran.

Whole-grain foods contain all three parts of the grain. In refined grains, such as wheat or white bread and white rice, the grain kernel goes through a milling process that strips out the bran and germ, leaving only the endosperm of the kernel in the end product. As a result, some, though not all, of the B vitamins, iron, phytochemicals, and dietary fiber are removed. Refining also improves the di- gestibility of the carbohydrate in the en- dosperm, resulting in a more rapid rise in blood glucose and an increased demand for insulin.3

To restore some of the nutrition lost from refined grains, enriched grains have folic acid, thiamin, niacin, riboflavin, and iron added back after the milling process. This improves their nutritional quality somewhat, but the fiber and the phyto- chemicals are lost.

Grains, Glorious Whole Grains

Bran • High fiber • B vitamins • Phytochemicals • Minerals

Endosperm • Starch • Protein • B vitamins

Germ • Vitamin E • Healthy unsaturated fats • Antioxidants • Phytochemicals • Minerals • B vitamins

Missing ingredients: • Enriched folic acid

Missing ingredients: • Bran (fiber) • Phytochemicals • Calcium • Vitamin E • Heart-healthy fats • Antioxidants

Missing ingredients: • Bran (fiber) • Phytochemicals • Calcium • Vitamin E • Heart-healthy fats • Antioxidants • Folic acid • Thiamin • Niacin • Riboflavin • Iron

a

b Whole kernel used c Only endosperm used

d Only endosperm used

Folic acid,thiamin, niacin,riboflavin, andiron added

A kernel of wheat

-

From Wheat Kernel to Flour (a) The wheat grain kernel has three parts: bran, germ, and endosperm. (b) Whole-wheat flour is made using the entire grain kernel. It is not enriched. (c) Enriched wheat flour doesn’t contain the bran and germ, so it is missing nutrients and phytochemicals. The nutrients, including folic acid, thiamin, niacin, riboflavin, and iron, are added back to the flour during an enrichment process. (d) Wheat flour that is not enriched lacks not only the bran and germ, but also many nutrients and phytochemicals.

138 Chapter 4 . Carbohydrates

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Whole grains are potential disease- fighting allies in the diet.4 Research has shown that as little as one serving of whole grains daily may help lower the risk of dying from heart disease5,6 or cancer,7

reduce the risk of stroke,8 improve intes- tinal health,9,10 and improve body weight.11 Several research studies have also shown that the fiber in whole grains may help reduce the risk of diabetes.12,13

Because whole grains are abundant in vi- tamins, minerals, fiber, and phytochemi- cals, it is uncertain which substances are the disease-fighting heroes or if some or all of them work in a complementary fashion to provide the protection.

References 1. Newby, P. K., J. Maras, P. Bakun,

D. Muller, L. Ferrucci, and K. L. Tucker. 2007. Intake of Whole Grains, Refined Grains, and Cereal Fiber Measured with 7-d Diet Records and Associations with Risk Factors for Chronic Disease.

American Journal of Clinical Nutrition 86:1745–1753.

2. Slavin, J., D. Jacobs, L. Marquart, and K. Wiemer. 2001. The Role of Whole Grains in Disease Prevention. Journal of the American Dietetic Association 101:780–785.

3. Liu, S., J. E. Manson, M. J. Stampfer, F. B. Hu, E. Giovannucci, G. A. Colditz, C. H. Hennekens, and W. C. Willett. 2000. A Prospective Study of Whole- Grain Intake and Risk of Type 2 Diabetes Mellitus in US Women. American Journal of Public Health 90:1409–1415.

4. Slavin, J., et al. 2001. Journal of the American Dietetic Association.

5. Jensen, M. K., P. Koh-Banerjee, F. B. Hu, M. Franz, L. Sampson, M. Gronbaek, and E. B. Rimm. 2004. Intakes of Whole Grains, Bran, and Germ and the Risk of Coronary Heart Disease in Men. American Journal of Clinical Nutrition 80:1492–1499.

6. Behall, K. M., D. J. Scholfield, and J. Hallfrisch. 2004. Lipids Significantly Reduced by Diets Containing Barley in Moderately Hypercholesterolemic Men. Journal of the American College of Nutrition 23:55–62.

7. Larsson, S. C., E. Giovannucci, L. Bergkvist, and A. Wolk. 2005. Whole Grain Consumption and Risk of Colorectal Cancer: A Population-Based Cohort of 60,000 Women. British Journal of Cancer 92:1803–1807.

8. de Munter, J. S. L., F. B. Hu, D. Spie- gelman, M. Franz, and R. M. van Dam. 2007. Whole Grain, Bran, and Germ Intake and Risk of Type 2 Diabetes: A Prospective Cohort Study and Systematic Review. PLoS Medicine 4:e261.

9. Farrell, R. J., J. J. Farrell, and M. M. Morrin. 2001. Diverticular Disease in the Elderly. Gastroenterology Clinics of North America 30:475–496.

10. National Digestive Diseases Information Clearinghouse. 2002. Diverticulosis and Diverticulitis. Available at http://digestive .niddk.nih.gov/ddiseases/pubs/ diverticulosis/index.htm. Accessed October 2007.

11. Newby, P. K., et al. 2007. American Journal of Clinical Nutrition.

12. Liu, S., et al. 2000. American Journal of Public Health.

13. de Munter, J. S. L., et al. 2007. PLoS Medicine.

enriched grains Refined grain foods that have folic acid, thiamin, niacin, ri-

boflavin, and iron added.

refined grains Grain foods that are made with only the endosperm of the ker-

nel. The bran and germ have been re-

moved during milling.

endosperm The starchy inner portion of a cereal grain.

germ The vitamin-rich embryo, or seed, of a grain.

bran The indigestible outer shell of the grain kernel.

whole grains Grain foods that are made with the entire edible grain kernel: the

bran, the endosperm, and the germ.

Grains, Glorious Whole Grains 139

Table Tips

Ways to Enjoy Whole Grains

Choose whole-grain cereal such as shredded wheat, bran flakes, raisin bran, and oatmeal in the morning.

Combine a 100% whole-wheat English muffin and low-fat cheddar cheese for a hearty breakfast cheese melt.

Enjoy your lunchtime sandwich made with a whole-wheat pita or 100% whole- grain bread.

Try instant brown rich for a quick whole grain at dinner.

Snack on popcorn or 100% whole-wheat crackers for a high-fiber filler in the afternoon.

Choosing whole-grain rather than refined grain products, such as whole-grain cereal, provides more nutrition, including fiber, per bite.

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140 Chapter 4 . Carbohydrates

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1

1 2

1 7

2 33 4

1 0 1 1

C or

n, c

oo ke

d, 1

c up

3 2

Pa st

a, c

oo ke

d, 1

/2 c

up

Figure 4.14 Food Sources of Carbohydrates Eating the minimum recommended servings from the grains, vegetables, fruits, and dairy groups will meet the need to consume 130 grams of carbohydrate daily.

Low-fat and Fat-free Dairy Products Provide Some Simple Sugars Milk and milk products, including cheese and yogurt, contain 12 grams of lactose per serving. Choose low-fat or fat-free dairy products whenever possible, for the sake of heart health. The lactose content is the same regardless of the fat content.

Fruits and Vegetables Provide Simple Sugars, Starch, and Fiber Fruit contains a combination of both simple and complex carbohydrates. The skins of many fruits contain the fiber cellulose, so eating an unpeeled fruit is preferable to eating a peeled fruit. Another type of fiber, pectin, is found in the flesh of fruit, and makes up about 15 to 30 percent of the fiber in fruit. Fruit overall contains about 2 grams of dietary fiber per serving. The flesh of fruit is also rich in simple sugars, in- cluding fructose and glucose.

When selecting fruit, fresh or frozen versions will provide more nutrients than canned versions, which lose some vitamins and minerals during processing. If canned fruit is the only option, be sure the product is packed in fruit juice rather than heavy syrup, to cut down on added sugar and kilocalories.

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What Are the Best Food Sources of Carbohydrates? 141

In general, starchy vegetables, such as corn and potatoes, contain more carbohy- drate per serving than nonstarchy vegetables like green beans or carrots (Figure 4.14). Overall, a serving of vegetables contains approximately 2 grams of soluble and insoluble fiber. As with fruit, many vegetable skins are an excellent source of fiber, so consuming edible skins whenever possible will also increase fiber intake.

Legumes, Nuts, and Seeds Are Excellent Sources of Starch and Fiber Legumes, such as black beans and peas, are a rich source of starch and dietary fiber (Figure 4.15). Legumes provide an average of 4 grams of fiber per serving, about half of which is in the form of hemicellulose.

Nuts and seeds contain very little starch but are good sources of fiber. Nuts con- tain approximately 6 grams of fiber per serving, in the form of pectin and cellulose. The size of a serving (1 ounce or 1⁄4 cup) of nuts will vary depending on the type of nut. For example, there are approximately 30 peanuts, 14 walnut halves, or 49 shelled pistachios in 1 ounce.

Grains

V e

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le s Fruits

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m s

( g

) o

f F

ib e

r

0 .5 1

2 2

2 .5 3

3 .5

7 .5

1 .5 2

3

4 4

2 .5

4 .5

3

Meat and Beans

B ea

ns , k

id ne

y, c

an ne

d, 1

/2 c

up

N ut

s, m

ix ed

, d ry

ro as

te d,

1 o

z

St ra

w be

rr ie

s, ra

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, 1 /2

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ad , w

ho le

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at , 1

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e

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at , c

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nr ic

he d,

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up

B re

ad , w

he at

/

w hi

te , 1

s lic

e

Figure 4.15 Food Sources of Fiber Adults need to consume about 20 to 38 grams of fiber daily.

Source: Position of the American Dietetic Association, “Health Implications of Dietary Fiber,” Journal of the American Dietetic Association 102 (2002): 993–1000; USDA National Nutrient Database for Standard Reference, www.nal.usda.gov/fnic.

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142 Chapter 4 . Carbohydrates

Packaged Foods Can Be Good Sources of Carbohydrates Packaged and processed foods, such as ready-to-eat cereals and baked crackers, can be good sources of starch and fiber, but can also contain high amounts of added sugar (which we’ll discuss in depth later in this chapter), fat, kilocalories, and salt, and should generally be consumed in moderation. When selecting packaged foods, choose products that contain at least two grams of dietary fiber per serving, and be aware of the amounts of added sugar, fat, and total kilocalories. If you’re buying snack items, aim for the baked, whole-grain crackers or low-fat pita bread rather than the box of cookies or doughnuts. The amount of total carbohydrates, including starch, dietary fiber, and sugars, in a packaged food is listed on the nutrition label (see Figure 4.16).

Nutrition Facts Serving Size 1 cup (30.0g)

Amount Per Serving

Calories 120 Calories from Fat 9

% Daily Value* Total Fat 1.0g 2%

Saturated Fat 0.2g 1%

Trans Fat 0.0g

Polyunsaturated Fat 0.2g

Monounsaturated Fat 0.5g

Cholesterol 0mg 0%

Sodium 190mg 8%

Total Carbohydrates 26.5g 9%

Dietary Fiber 1.2g 5%

Sugars 13.0g

Protein 1.0g

Vitamin A 0%

Vitamin C 10%

Calcium 10%

Iron 25% * Based on a 2,000 calorie diet.

a

Nutrition Facts Serving Size ½ cup (30g) Servings Per Container about 15

Amount Per Serving

Fiber One

Cereal

Calories Calories from Fat

60 10

with ½ cup

skim milk

100 10

% Daily Value* Total Fat 1g 1% 2%

Saturated Fat 0g 0% 0%

Trans Fat 0g

Polyunsaturated Fat 0g

Monounsaturated Fat 0g

Cholesterol 0mg 0% 1%

Sodium 105mg 4% 7%

Potassium 180mg 5% 11%

Total Carbohydrate 25g 8% 10%

Dietary Fiber 14g 57% 57%

Soluble Fiber 1g

Sugars 0g

Other Carbohydrates 11g

Protein 2g

Vitamin A 0% 4%

Vitamin C 10% 10%

Calcium 10% 25%

Iron 25% 25%

bFigure 4.16 Dietary Fiber Content of Breakfast Cereals Nutrition labels list total carbohydrates, dietary fiber, and sugars per serving. Compare the two breakfast cereal labels. Which cereal provides more than 50 percent of the DV for fiber in just one serving? Which cereal is higher in sugar content per serving?

What specific foods would you recommend that Adam eat toensure he meets his carbohydrate and energy needs? Would his diet need to be different if he wasn’t regularly exercising?

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What Is Diabetes? 143

The Take-Home Message Fresh fruits and vegetables, whole grains, legumes, and low-fat dairy products are the best food sources of carbohy- drates. Whole grains, fruits, vegetables, legumes, nuts, and seeds are excel- lent sources of fiber. Packaged foods can be a good source of starch and fiber, but nutrition labels should be read carefully to avoid consuming too much added sugar, fat, or kilocalories.

What Is Diabetes? Diabetes mellitus, or diabetes, is a condition related to an inadequate regulation of blood glucose, and it’s becoming so common in the United States that it would be rare if you didn’t know someone who has it. An estimated 20.8 million American adults—over 7 percent of the population—have diabetes. Another 6 million have the disease, but don’t know it yet. The incidence of adults being diagnosed with di- abetes in the United States grew by almost 50 percent from 1990 to 2000, and is ex- pected to continue to grow at this rapid rate in the decades to come. In fact, diabetes is expected to afflict about 9 percent of American adults in the year 2025. The number of people who have diabetes is not only strikingly high; it’s rising, particularly among children. Whereas the disease used to be common only in adults, in the last couple of decades there’s been a steady increase among those under age 20. Over 200,000 Americans die from diabetic complications annually, and diabetes is the sixth leading cause of death in the United States. Diabetes is not only a deadly disease, but also an extremely costly one. Disability insurance pay- ments, time lost from employment, and the medical costs associated with diabetes cost almost $100 billion annually in the United States.52,53 This is an epidemic that is spiraling out of control.54,55

There are different types of diabetes, but they all result from the inability of the body to make or properly use the hormone insulin. Insulin directs glucose into the cells to be used as immediate energy or stored for later use. Diabetes develops when individuals either produce an inadequate amount of insulin and/or develop insulin resistance, such that their cells do not respond to the insulin when it ar- rives. In either case, the bloodstream is flooded with glucose that can’t get into the cells. When this happens, the body shifts into fasting mode. The liver begins the process of breaking down its glycogen stores (glycogenolysis) and making glucose from noncarbohydrate sources (gluconeogenesis) in an attempt to provide glucose to the cells. This floods the blood with even more glucose. Eventually, the level of glucose builds up in the blood and some of it spills over into the urine.

At the same time, the body has called on its energy reserve—fat—to be used as fuel. The body needs glucose in order to thoroughly burn fat; otherwise, it makes ke- tone bodies. In poorly managed diabetes, when glucose is unable to get into the cells, acidic ketone bodies build up in the blood to dangerous levels, causing ketoacidosis. Diabetic ketoacidosis can cause nausea and confusion, and in some cases, if left un- treated, could result in coma or death. (Note: Ketoacidosis occurs when insulin is lacking in the body, and is different from the condition of ketosis, which can develop in individuals who are fasting or consuming a low-carbohydrate diet; unlike diabetic ketoacidosis, ketosis is not life-threatening.)

diabetes mellitus A medical condition whereby an individual either doesn’t have

enough insulin or is resistant to the insulin

available, resulting in a rise in blood glu-

cose levels. Diabetes mellitus is often

called diabetes.

insulin resistance The inability of the cells to respond to insulin.

ketoacidosis The buildup of ketone bodies in the blood to dangerous levels,

which can result in coma or death.

HEALTH FOCUS

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144 Chapter 4 . Carbohydrates

There Are Several Forms of Diabetes All forms of diabetes involve insulin and unregulated blood glucose levels. Some are due to insulin resistance, as just described, and others are due to a lack of insulin production. Still another version occurs only during pregnancy.

Type 1 and Type 2 Diabetes The most prevalent types of diabetes are type 1 and type 2. Type 1 diabetes is consid- ered an autoimmune disease and is the rarer of the two forms.56 Type 2 diabetes is more common and is seen in people who have become insulin resistant, often as the result of being overweight or obese.

Type 1 diabetes usually begins in childhood and the early adult years and is found in 5 to 10 percent of the individuals with diabetes in the United States.57

The immune system in people with type 1 diabetes actually destroys the insulin- producing cells in the pancreas. An obsessive, uncontrollable thirst (polydipsia), excessive urination (polyuria), and a strong desire to eat (polyphagia) are common symptoms associated with diabetes, due to the increased level of blood sugar. Other common symptoms are constant blurred vision, hunger, weight loss, and fatigue, as the glucose can’t get into the cells of the body. If not treated with insulin, the person is susceptible to the dangers of ketoacidosis. Individuals with type 1 diabetes must monitor their glucose levels and inject insulin every day in order to live a normal life.

Type 2 diabetes accounts for 90 to 95 percent of diagnoses of the disease and oc- curs frequently in individuals who are overweight.58 People with type 2 diabetes typ- ically produce insulin but have become insulin resistant. After several years of exhausting their insulin-producing cells in the pancreas, their production of insulin decreases to the point where they have to take medication and/or insulin to manage their blood glucose level.

One of the major problems with type 2 diabetes is that this condition can go un- diagnosed for some time. Some people may have symptoms such as increased thirst; others may not. Consequently, diabetes can damage a person’s vital organs without their being aware of it. Because of this, the American Diabetes Association (ADA) recommends that everyone 45 years of age and older undergo testing for diabetes. However, if a person is at a higher risk for developing diabetes (such as those who are overweight or obese, or who are genetically predisposed), he or she shouldn’t wait until age 45 to be tested. (See the Self-Assessment to determine whether you are at risk for type 2 diabetes.)

Because the hormone insulin is derived from the components of protein and is digestible by the GI tract, it can’t be taken orally. Therefore, most individuals have to inject insulin directly into their fat or muscle tissue with a syringe. Researchers are continually testing alternative, non-needle methods for those with diabetes to self- administer insulin. Insulin pens, insulin jet injectors, and insulin pumps are among the devices becoming available.

Prediabetes A simple blood test at a physician’s office can reveal if a person’s blood glucose is higher than normal and whether he or she has impaired glucose tolerance, or prediabetes. The blood is typically drawn first thing in the morning after fasting overnight for 8 to 12 hours. A fasting blood glucose level of under 100 milligrams per deciliter (mg/dl) is considered “negative,” and a fasting blood glucose of 126 mg/dl or higher is considered a “positive” test for diabetes (Table 4.4). A reading between 100 mg/dl and 126 mg/dl is classified as prediabetes. Individuals with prediabetes have a blood glucose level that is higher than it should be but not yet high enough to be classified as diabetic. About 16 million people over the age of 40 have prediabetes

polyphagia The symptom of an excessive desire to eat, common in diabetes mellitus.

polyuria The symptom of excessive uri- nation, common in diabetes mellitus.

polydipsia The symptom of excessive thirst, common in diabetes mellitus.

Individuals with diabetes must regularly monitor blood glucose levels.

impaired glucose tolerance A condi- tion whereby a fasting blood glucose level

is higher than normal, but not high

enough to be classified as having diabetes

mellitus. Also called prediabetes.

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and are at a higher risk of developing not only diabetes, but also heart disease.59

When a person is in this prediabetic state, damage may already be occurring to the heart and circulatory system.

Diabetes Can Result in Long-Term Damage Constant exposure to high blood glucose levels can damage vital organs over time. Diabetes, especially if it is poorly managed, increases the likelihood of a multitude of health effects such as nerve damage, leg and foot amputations, eye diseases, blind- ness, tooth loss, gum problems, kidney disease, and heart disease.60

Nerve damage occurs in an estimated 50 percent of individuals with diabetes, and the longer the person has diabetes, the greater the risk of damage. Numbness in the toes, feet, legs, and hands, as well as changes in bowel, bladder, and sexual func- tion are all signs of damage to nerves. This nerve damage can affect the ability to feel a change in temperature or pain in the legs and feet. A cut or sore on the foot could go unnoticed until it becomes infected. The poor blood circulation common in dia- betics can also make it harder for sores or infections to heal. The infection could in- filtrate the bone, causing the need for an amputation.

What Is Diabetes? 145

Self-Assessment

Are You at Risk for Type 2 Diabetes? Take the following quiz to assess if you are at risk for developing type 2 diabetes. Whereas this list contains the presently known risk factors for type 2 diabetes, there may be others. If you have questions or doubts, check with your doctor.

Table 4.4

Interpreting Blood Glucose Levels

If a Fasting Blood Glucose Level Is

It Means That the Level Is Considered

�100 mg/dl Normal

100 to 125 mg/dl Prediabetic

�126 mg/dl* Diabetic

*There must be two “positive” tests, done on sepa- rate days, for an official diagnosis of diabetes.

Source: American Diabetes Association, “Diagnosis and Classification of Diabetes Mellitus,” Diabetes Care 29 (2006): S43–S48.

Do you have a body mass index (BMI) of 25 or higher*? Yes � No �

If you answered “no,” you don’t need to continue. If you answered “yes,” continue.

1. Does your mom, dad, brother, or sister have diabetes? Yes � No �

2. Do you typically exercise for less than 30 minutes daily? Yes � No �

3. Are you of African-American, Alaska Native, Native Ameri- can, Asian-American, Hispanic-American, or Pacific Islander-American descent? Yes � No �

4. Have you ever delivered a baby that weighed more than 9 pounds at birth? Yes � No �

5. Have you ever had diabetes during pregnancy? Yes � No �

6. Do you have a blood pressure of 140/90 millimeters of mercury (mmHg) or higher? Yes � No �

7. Have you been told by your doctor that you have too much triglyceride (fat) in your blood (more than 250 mg/dl) or too little of the “good” HDL cholesterol (less than 35 mg/dl)? Yes � No �

8. Have you ever had blood glucose test results that were higher than normal? Yes � No �

9. Have you ever been told that you have vascular disease or problems with your blood vessels? Yes � No �

10. Do you have polycystic ovary syndrome**? Yes � No �

Answers If you are overweight and answered “yes” to any of the above 10 questions, you could benefit from speaking with your doctor.

*BMI is a measure of your weight in relationship to your height. See Chapter 14 for a chart to determine your BMI.

**Polycystic ovary syndrome is a disorder in women due to an abnormal level of hormones, including insulin. This disorder increases the risk of diabetes as well as of heart disease and high blood pressure.

Source: American Diabetes Association, “Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus,” Diabetes Care 26 (2003): S5–S20.

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146 Chapter 4 . Carbohydrates

Diabetes can also damage the tiny blood vessels in the retina of the eye, which can cause bleeding and cloudy vision, and eventually destroy the retina and cause blindness. A high blood glucose level can cause tooth and gum problems, including the loss of teeth, and damage to the kidneys. If the kidneys are damaged, protein can leak out into the urine and, at the same time, cause a backup of wastes in the blood. Kidney failure could result.

Diabetes is a risk factor for heart disease. The excess amount of fat often seen in the blood in poorly managed diabetes is likely an important factor in this increased risk. Fortunately, good nutrition habits play a key role in both the prevention and management of diabetes.

Control Is Key For years, people with diabetes have been advised to keep their blood glucose level under control. In the early 1990s, the research community finally gathered the evi- dence to back up that advice. The groundbreaking Diabetes Control and Complica- tions Trial (DCCT), conducted from 1983 to 1993, involved over 1,400 people with type 1 diabetes. It showed that controlling the level of blood glucose with an intense regimen of diet, insulin, and exercise, along with monitoring blood sugar levels and routinely visiting health care professionals, slowed the onset of some of the compli- cations of diabetes. In this study, reducing high blood glucose was shown to help lower the risk of eye disease by 76 percent, and the risk of kidney and nerve disease by at least 50 percent. However, because some individuals experienced bouts of hypoglycemia (low blood glucose levels, discussed in the next section), this type of intense regimen is not recommended for children under age 13, people with heart disease or advanced complications of heart disease, older people, and those prone to frequent severe hypoglycemia.61,62 For all others, diligent and conscientious manage- ment of their blood glucose can minimize the devastating complications of diabetes often seen later in life.

The nutrition and lifestyle goals for individuals with type 1 or type 2 diabetes are the same: to minimize the complications of diabetes by adopting a healthy, well- balanced diet and participating in regular physical activity that maintains blood glu- cose levels in a normal or close to normal range. The ADA recommends that individuals with diabetes consume a combination of predominantly high-fiber car- bohydrates from whole grains, fruits, and vegetables, along with low-fat milk, ade- quate amounts of lean protein; and unsaturated fats.63

Though sugar was once thought of as a “diabetic no-no” it can now be part of a diabetic’s diet. Research has found that eating sucrose doesn’t cause a greater rise in a person’s blood glucose level than starch does, so avoidance of sugar isn’t necessary. However, because weight management is often a concern, especially for those with type 2 diabetes, there’s little room for sweets and treats in a diabetic diet (or anyone’s diet, for that matter).

Preventing Type 2 Diabetes Recent research has suggested that shedding some excess weight, exercising regularly, and eating a balanced, high-fiber, healthy diet may be the best strategy to lower the risk of developing diabetes (Table 4.5). A landmark study by the Diabetes Prevention Program of over 3,000 individuals with prediabetes showed that those who made changes in their lifestyle, such as losing weight, exercising several hours a week, eat- ing a plant-based, heart-healthy diet, and meeting with a health professional for on- going support and education, were 58 percent less likely to develop type 2 diabetes

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What Is Hypoglycemia? 147

than those who did not undertake such intervention. When it comes to winning the battle against diabetes, a healthful diet and lifestyle is the best game plan.

Polycystic Ovary Syndrome May Increase Risk for Diabetes Another risk factor for diabetes is a condition called polycystic ovary syndrome (PCOS), a hormonal imbalance that affects more than 5 million American women of childbearing age. Women who have been diagnosed with PCOS have a higher inci- dence of insulin resistance and hyperinsulinemia, which increases their risk of devel- oping type 2 diabetes. Some estimates suggest that by the age of 40, as many as 40 percent of women with PCOS will have type 2 diabetes or impaired glucose tolerance.64 Treatment of PCOS focuses on managing the risks such as diabetes and includes eating a diet that is moderate to low in carbohydrates.65

The Take-Home Message Diabetes is a condition that involves inade- quate regulation of blood glucose levels. Individuals with type 1 diabetes pro- duce inadequate amounts of insulin. Those with type 2 diabetes have developed insulin resistance. Chronic high blood glucose levels can damage the vital organs of the body, including the heart. Individuals with diabetes need to take medications and/or insulin to manage their blood glucose. A high-fiber diet and routine exercise play important roles in managing and preventing diabetes. Polycystic ovary syndrome increases the risk of developing type 2 diabetes.

What Is Hypoglycemia? Whereas a consistently high level of glucose in the blood isn’t healthy, a blood glu- cose level that is too low (usually less than 70 mg/dl), or hypoglycemia, can be un- pleasant and downright dangerous for some with diabetes. Individuals who

Table 4.5

Red Flags for Type 2 Diabetes in Children and Adolescents

The following risk factors may increase the risk of childhood type 2 diabetes in children and adolescents:

Being overweight

AND any two of the following:

Having a parent or grandparent with type 2 diabetes

Being of American Indian, African-American, Hispanic-American, Asian- American, or Pacific Islander descent

Showing signs of being resistant to insulin or having conditions associated with insulin resistance such as high blood pressure or too much fat and/or choles- terol in the blood, and polycystic ovary syndrome

Source: American Diabetes Association, “Type 2 Diabetes in the Young: The Evolving Epidemic,” Diabetes Care 27 (2004): 1798–1811.

hypoglycemia A blood glucose level that drops to lower than 70 mg/dl.

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148 Chapter 4 . Carbohydrates

experience hypoglycemia may feel hungry, nervous, dizzy, light-headed, confused, weak, and shaky, and even begin to sweat. Eating or drinking carbohydrate-rich foods, such as hard candies, juice, or soda, can relieve these symptoms quickly and raise the blood glucose level to a normal range.

Those with diabetes who need to use insulin and/or blood glucose–lowering medications daily are at risk of hypoglycemia if they skip meals and snacks or if they don’t eat enough to cover the effects of the medication. If these individuals ignore their symptoms, their blood glucose level can drop so low that they could faint, or slip into a coma (see Figure 4.17).66 This is why individuals with diabetes need to eat regularly, so as to maintain blood glucose levels that coincide with their medication. A change in activity or exercise level can also lower blood glucose, so individuals with diabetes need to check their blood glucose level before they exercise to deter- mine if a snack is needed.

Though not common, people without diabetes may also experience bouts of reactive hypoglycemia within four hours after a meal. Reactive hypoglycemia can cause symptoms similar to hypoglycemia: shakiness, dizziness, hunger, and perspira- tion. A doctor can diagnose this condition by testing a person’s blood glucose level while they are having these symptoms. Though the cause of reactive hypoglycemia is not known, one theory is that it is hormone related. Some people may be overly sen- sitive to epinephrine, which is released when the blood glucose level begins to drop. The hormone glucagon may also play a role. Eating smaller, well-balanced meals throughout the day can help avoid hypoglycemia.

Another type of hypoglycemia, called fasting hypoglycemia, can occur in the morning, after overnight fasting. It can also occur during long stretches between meals or after exercise. Some medications, illnesses, certain tumors, hormone imbal- ances, or drinking too much alcohol may cause this type of hypoglycemia.

The Take-Home Message Symptoms of hypoglycemia, or low blood sugar, include feeling hungry, nervous, light-headed, shaky, and sweaty. Those who take medication and/or insulin to manage their diabetes but don’t eat properly are at a greater risk of experiencing hypoglycemia. Individuals without diabetes may experience reactive hypoglycemia several hours after a meal. Fasting hypoglycemia can occur in the morning upon awakening and can be caused by some medications, illnesses, hormone imbalances, or excessive consumption of alcohol.

Eat meal

B lo

o d

g lu

c o se

2 hours

Normal

Hypoglycemia

Time

Figure 4.17 Change in Blood Glucose After Eating a High-Carbohydrate Meal An individual with hypoglycemia experiences a more rapid decline in blood glucose after a carbohydrate-rich meal.

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What Is the Difference Between Natural and Added Sugars? 149

What Is the Difference Between Natural and Added Sugars? Your taste buds can’t distinguish between naturally occurring sugars, like the fruc- tose and lactose found in fruit and dairy products, and added sugars, which are added by manufacturers to foods such as soda or candy. From a nutritional stand- point, however, there is a big difference be- tween these sugar sources.

Foods with Natural Sugars Generally Provide More Nutrients for Fewer Kilocalories Foods that contain naturally occurring sugar tend to be nutrient dense and thus provide more nutrition per bite. In contrast, foods that contain a lot of added sugar tend to pro- vide high amounts of kilocalories but little else. In fact, the calories in sugar-laden foods are often called empty calories because they provide so little nutrition.

Many fruits are among the most naturally sweet foods available, and just one bite into a ripe peach or navel orange will confirm that fruit can contain more than 12 per- cent sugar by weight. There are many nutritional advantages of satisfying a sweet tooth with fruit, such as a whole orange, rather than sweets with added sugar, such as a pack- age of candy orange slices. Let’s compare these two snacks (Figure 4.18).

For the 65 kilocalories in six slices of a navel orange, you get more than 100 percent of the daily value for vitamin C, and 3.5 grams of fiber, which is more than 10 percent of the amount of fiber that many adults should consume daily. These juicy slices also pro- vide fluid. In fact, over 85 percent of the weight of the orange is water. The hefty amounts of fiber and water make the orange a sweet snack that provides bulk. This bulk can in- crease satiety and reduce the likelihood that you’ll need to eat a second or third orange to feel satisfied. Eating fruit not only meets the urge for something sweet but reduces the risk of overeating.

In contrast, for the 300 kilocalories found in six candy orange slices, you’ll get about 19 teaspoons of added sugar and little else. Although the candy is quite energy dense, it provides no fiber and only negligible amounts of water, and it contains a concentrated amount of kilocalories in relationship to the volume of food in the serving. You wouldn’t likely feel satiated after consuming six candy orange slices. To consume close to the 300 kilocalories found in the six pieces of candy, you would have to eat more than four oranges. It would be easier to overeat candy orange slices than fresh oranges.

naturally occurring sugars Sugars such as fructose and lactose that are found

naturally in foods.

added sugars Sugars that are added to processed foods and sweets.

empty calories Kilocalories that pro- vide little nutrition, such as those found

in candy.

Kilocalories

Vitamin C

Added sugar 0

Fiber

Kilocalories

Vitamin C

Added sugar

Fiber 01/2

65

130% DV

300

0% DV

Fresh orange Candy orange

= 1 gram of fiber

= 1 tsp of added sugar

Figure 4.18 Slices of an Orange versus Orange Slices A fresh orange provides more nutrients for fewer kilocalories, and without any added sugars, compared with candy orange slices.

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Ingredients: Granola (whole grain rolled oats, sugar, rice flour, whole grain rolled wheat, partially hydrogenated soybean and cottonseed oils* with TBHQ and citric acid added to preserve freshness and/or sunflower oil with natural tocopherol added to preserve freshness, whole wheat flour, molasses, sodium bicarbonate, soy lecithin, caramel color, barley malt, salt, nonfat dry milk), corn syrup, crisp rice (rice, sugar, salt, barley malt), semisweet chocolate chunks (sugar, chocolate liquor, cocoa butter, soy lecithin, vanillin [an artificial flavor]), sugar, corn syrup solids, glycerin,high fructose corn syrup, partially hydrogenated soybean and/or cottonseed oil*, sorbitol, fructose. calcium carbonate, natural and artificial flavors, salt, soy lecithin, molasses, water, BHT (a preservative), citric acid.

* Adds a dietarily insignificant amount of trans fat.

Nutrition Facts Serving Size 1 Bar (24g) Servings Per Container 10

Amount Per Serving

Calories 90 Calories from Fat 20

% Daily Value* Total Fat 2g 3%

Saturated Fat 0.5g 3%

Trans Fat 0g

Sodium 80mg 3%

Total Carbohydrate 19g 6%

Dietary Fiber 1g 3%

Sugars 7g

Protein 1g

Calcium 8% • Iron 4%

Total Fat Sat Fat Cholesterol Sodium Total Carbohydrate Dietary Fiber

Calories: Less than Less than Less than Less than

2,000 65g 20g 300mg 2,400mg 300g 25g

2,500 80g 25g 300mg 2,400mg 375g 30g

Not a significant source of Cholesterol, Vitamin A, Vitamin C

* Percent Daily Values are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs:

Corn sweetener Corn syrup

Fruit juice concentrate

High-fructose corn syrup

Brown sugarDextrose

Honey

Malt syrup Maltose

Molasses

Fructose Lactose

Sucrose

Invert sugar Raw sugar

Syrup

ba The many aliases of added sugar

Figure 4.19 Finding Added Sugars on the Label (a) A food is likely to contain a large amount of sugar if added sugars appear first or second on the ingredients list and/or if there are many varieties of added sugars listed. (b) You can also look on the Nutrition Facts panel to see the total grams of sugar.

150 Chapter 4 . Carbohydrates

Added Sugars Are Used during Food Processing Sugars are added to foods for many reasons. In baked goods, they can hold onto water, which helps keep the product moist, and they help turn pastries a golden brown color. Sugars function as preservatives and thickeners in foods such as sauces. Fermenting sugars in dough produce the carbon dioxide that makes yeast breads rise. And of course, sugars make foods taste sweet. In the last several decades, Ameri- cans’ increased consumption of processed foods has led to an increased consump- tion of added sugar. In fact, between 1980 and 2000, our yearly consumption of added sugars increased by more than 20 percent.67

Finding the Added Sugars in Foods Sugars can appear on the food label under numerous different names (see Figure 4.19). To find the amount and type of added sugars in the foods, read the in- gredients list. If added sugars appear first or second on the list, or if the product contains many varieties of added sugars, it is likely high in sugar. Note, for example, that the ingredient label from the box of low-fat chocolate chip granola bars lists ten different added sugars!

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What Is the Difference Between Natural and Added Sugars? 151

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The Nutrition Facts panel that is currently used on food labels doesn’t distin- guish between naturally occurring and added sugars. For example, the nutrition labels on a box of raisin bran and a carton of milk list 21 grams of sugars for raisin bran and 12 grams for low-fat milk. This can be misleading, as the grams of sugars listed for the raisin bran include both the amount of naturally occurring sugars from the raisins and the sugars added to sweeten the cereal. For the milk, the sugar listed on the Nutri- tion Facts panel is just the naturally occurring sugar, lactose. With the growing con- cern about the rising levels of added sugars in the diets of Americans, various health professionals and organizations have pressured the FDA to require that all added sug- ars be disclosed on the food label. A final decision by the FDA is pending.

Americans don’t eat the majority of the added sugars in their diets—they drink them (see Figure 4.20). The number-one source of added sugars in the United States is sweetened soft drinks. Fruitades and sugary fruit drinks are also major sources. This fact isn’t too surprising when you look at the size of the sweetened beverages that Americans consume (see Figure 4.21). A classic (and rare) 8-ounce bottle of cola pro- vides almost 7 teaspoons of added sugars. In today’s vending machine, you are more likely to find a 12-ounce can or a 20-ounce bottle. Because people typically consume the entire can or bottle, regardless of its size, they consume more sugar. See the Table Tips for ways to cut down on your consumption of added sugars.

Since the 1970s, high-fructose corn syrup (HFCS) has replaced sucrose in most sweetened beverages.68 This sweetener has been implicated in many health-related problems, including obesity. See the feature box, “Is High-Fructose Corn Syrup Causing the Obesity Epidemic?” on the next page to gain more information on the health concerns associated with HFCS.

The Take-Home Message Your taste buds can’t distinguish between naturally occurring and added sugars. Foods with naturally occurring sugars, such as whole fruit, tend to provide more nutrition and satiation than empty- calorie sweets such as candy. There are numerous names for sugar found on food labels, and soft drinks are the number-one contributor of added sugars to Americans’ diets.

Table Tips

Lowering Consumption of Added Sugars

Mix chocolate milk with an equal amount of regular low-fat milk.

Mix equal amounts of sweetened cereal with an unsweetened variety for a breakfast cereal with half the added sugar.

Drink water rather than soda or sweetened beverages throughout the day.

Buy sweets such as candy and cookies in individual serving size pouches rather than in large packages. The less you buy, the less you’ll eat.

Mix an ounce of 100% fruit juice with 10 ounces of sparkling water for a no-sugar-added “fruit” drink.

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When high-fructose corn syrup (HFCS) was first introduced in 1970, U.S. adults consumed approximately 85 pounds of sweeteners per year, most of which was refined sugar. Since 1970, the consump- tion of sweeteners has risen to more than 100 pounds per year, mostly due to the in- crease in HFCS (41.5 pounds per individ- ual per year in 2006).1 At the same time that our consumption of HFCS has in- creased, obesity rates among Americans have also skyrocketed.2 Is this a coinci- dence or is HFCS to blame?

What Is High-Fructose Corn Syrup?

HFCS is a sweetener produced from modified corn and composed of glucose and fructose. Because glucose and fructose are in a “free” state, the syrup is stable and easy to handle in food processing—a plus for manufacturers. HFCS is less expensive than sucrose, which is probably the reason HFCS has replaced sucrose as the most common sweetener in processed foods, including baked goods, sweets, and soft drinks. In baked products, HFCS gives cookies and snacks their chewy, soft texture, and makes bread brown better. HFCS inhibits the growth of microbes by reducing the availability of water and thus improves

freshness and extends the shelf life of many food products. It’s no wonder that HFCS is estimated to represent the high- est percentage—more than 40 percent— of added sugar in the food supply.3 The question is, has our increased consump- tion of this particular sweetener led to our expanded waistlines?

Does HFCS Consumption Lead to Weight Gain?

Two theories have been proposed to ex- plain the possible connection between weight gain and the increased consump- tion of HFCS. One theory suggests that HFCS is sweeter than sucrose, resulting in an increased consumption of kilocalories.4

A second theory posits that the increase in HFCS means an increase in fructose con- sumption, which may stimulate appetite and alter insulin metabolism.5 Research exploring both of these theories has yielded some interesting results.

HFCS Is Not Sweeter than Sugar

Monosaccharides and disaccharides vary in their level of sweetness. Fructose is the sweetest monosaccharide, and sucrose, because of its high fructose content, is the sweetest of the disaccharides.

Sucrose contains 50 percent glucose and 50 percent fructose—one molecule

of glucose for every molecule of fructose. HFCS comes in two different forms: HFCS-42 and HFCS- 55. HFCS-42 is 42 percent fructose and 58 percent glu- cose. This version is used in bakery prod- ucts, jams and jellies, canned fruit, and dairy products. HFCS-55 is 55 per- cent fructose and 45 percent glucose and is used to sweeten beverages, including soft drinks and sweetened teas.

Essentially, HFCS has the same composi- tion as sucrose. Thus, despite its name, HFCS is not dramatically higher in fruc- tose than sucrose and therefore is not any sweeter than sucrose.

HFCS May Impact Satiation

Some researchers have suggested that HFCS may change our appetite control mechanisms, resulting in less satiation and a greater intake of kilocalories. This theory is based on earlier studies con- ducted with pure crystalline fructose (not HFCS), which reported that fructose in- gestion resulted in a decrease in the hor- mones insulin and leptin. Both of these hormones increase satiety. Fructose does not increase insulin levels because it does not depend on insulin to enter the liver cell. Whereas glucose stimulates satiety, fructose does not.

This is significant in that insulin stimu- lates the release of leptin, a hormone that decreases appetite.6 These two hor- mones also suppress the release of ghre- lin, another hormone that stimulates our appetite. If insulin is reduced, then leptin is reduced and ghrelin is not suppressed, which leads to feeling hungry and eating more kilocalories. Thus, if pure fructose re- duces the release of appetite-suppressing hormones, then does high-fructose corn syrup increase appetite?

Based on research, the answer is no, because HFCS does not cause the same reaction as pure fructose does in the body. Remember, HFCS is approximately 50 percent fructose and 50 percent glu- cose. If HFCS did increase appetite, re- search subjects would report a decrease in satiety and an increase in kilocalorie in- take compared with otherwise sweetened drinks. A recent study showed no signifi- cant differences in hunger or satiety rat- ings, or in the amount of kilocalories eaten at a later meal when subjects drank a beverage sweetened with HFCS, low- fat milk, or orange juice.7 Nor did a bever- age with HFCS increase the amount of food eaten later in the day when com- pared with a beverage containing sucrose.8

Is High-Fructose Corn Syrup Causing the Obesity Epidemic?

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The Per Capita Consumption Patterns, in Pounds, of Sucrose and High-Fructose Corn Syrup

152 Chapter 4 . Carbohydrates

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Is High-Fructose Corn Syrup Causing the Obesity Epidemic? 153

How Does the Body Metabolize HFCS?

Because HFCS contains fructose and glucose, the metabolism of this sweetener is generally the same as the metabolism of each individual monosac- charide.

As soon as it is absorbed, fructose is transported through the portal vein and metabolized by the liver. During metabo- lism, fructose can be converted to inter- mediate substrates used by the liver for energy production or used as the starter molecules for lipogenesis or fat synthesis. If intake of fructose is high, there is a potential that the liver may accumulate higher than normal levels of stored triglyc- eride, reduce the sensitivity to insulin, and increase the formation of lipoproteins in the blood, leading to increased risk of cardiovascular disease.9 The lack of glu- cose makes the absorption of pure fruc- tose different from HFCS. Glucose appears to have a tempering effect on the metabolism of fructose.10

The current evidence suggests that HFCS and sucrose are metabolized in a similar way once the monosaccharides have been absorbed.11

Different Sweeteners and Insulin Production

Whether the sweetener is sucrose or HFCS, they both trigger an insulin re- sponse. Pure glucose stimulates the greatest release of insulin compared with pure fructose, which stimulates the least. Because HFCS and sucrose contain ap- proximately the same ratio of glucose to

fructose, they trigger a similar, intermedi- ate release of insulin. Fructose is generally eaten as part of a food, such as fruit, or as part of a sweetener, such as sucrose or HFCS. The composition of the entire meal, rather than just the type of mono- saccharide, also affects the release of in- sulin in the body.

The Bottom Line: Does HFCS Cause Obesity?

Currently, there is no evidence that HFCS consumption contributes more to obesity than do other sweeteners or energy sources.12 In fact, obesity has increased sharply in countries where beverage con- sumption is lower than in the United States and HFCS is not a common sweetener.13 One expert review of the re- search literature on the dietary role of HFCS found insufficient support for the theory that HFCS could play a role in obesity. The report states that there are many other “plausible explanations for ris- ing overweight and obesity rates” in the United States, including a reduction in smoking, a decrease in physical activity including physical education programs in schools, an increase in technology, which leads to more sedentary activities, and watching television, for the rise in obesity rates.14

Although HFCS may not be the main culprit in the dramatic rise in obesity, it likely does play a role in Americans’ over- all increased caloric intake, including from energy-dense sweets, snacks, and baked goods, which contain more kilocalories than nutrient-dense fruits and vegetables.

The DRI recommends reducing all refined sugars, regardless of whether the sweet- ener is fructose, sucrose, or HFCS.

References 1. United States Department of Agriculture.

2007. Table 52: High-Fructose Corn Syrup: Estimated Number of Per Capita Calories Consumed Daily, by Calendar Year. Sugar and Sweeteners Yearbook 2006. Economic Research Service.

2. Centers for Disease Control and Prevention. 2007. U.S. Obesity Trends 1985–2006. Available at www.cdc.gov/ nccdphp/dnpa/obesity/trend/maps. Accessed October 2007.

3. Bray, G. A., S. J. Nielsen, and B. M. Popkin. 2004. Consumption of High- Fructose Corn Syrup in Beverages May Play a Role in the Epidemic of Obesity. American Journal of Clinical Nutrition 79:537–543.

4. Ibid. 5. Forshee, R. A., M. L. Storey, D. B. Allison,

W. H. Glinsmann, G. L. Hein, D. R. Lineback, S. A. Miller, T. A. Nicklas, G. A. Weaver, and J. S. White. 2007. A Critical Examination of the Evidence Relating High-Fructose Corn Syrup and Weight Gain. Critical Reviews in Food Science and Nutrition 47:561–582.

6. Melanson, K. J., L. Zukley, J. Lowndes, V. Nguyen, T. J. Angelopoulos, and J. M. Rippe. 2007. Effects of High- Fructose Corn Syrup and Sucrose Consumption on Circulating Glucose, Insulin, Leptin, and Ghrelin and on Appetite in Normal-Weight Women. Nutrition 23:103–112.

7. Almiron-Roig, E. and A. Drewnowski. 2003. Hunger, Thirst, and Energy Intakes Following Consumption of Caloric Beverages. Physiology of Behavior 79:767–774.

8. Akhavan, T. and G. H. Anderson. 2007. Effects of Glucose-to-Fructose Ratios in Solutions on Subjective Satiety, Food Intake, and Satiety Hormones in Young Men. American Journal of Clinical Nutrition 86:1354–1363.

9. Bray, G. A., et al. 2004. American Journal of Clinical Nutrition.

10. Melanson, K. J., et al. 2007. Nutrition. 11. Schorin, M. 2005. High-Fructose Corn

Syrups Part 1: Composition, Consumption, Metabolism. Nutrition Today 40:248–252.

12. Monsivais, P., M. Perrigue, and A. Drewnowski. 2007. Sugars and Satiety: Does the Type of Sweetener Make a Difference? American Journal of Clinical Nutrition 86:116–123.

13. Ibid. 14. Forshee, R. A., et al. 2007. Critical

Reviews in Food Science and Nutrition.

The Monosaccharide Composition and Sweetness Levels of Sucrose and High-Fructose Corn Syrup

HFCS-42 Sucrose HFCS-55

Fructose 42% 50% 55%

Glucose 53% 50% 42%

Moisture 29% 5% 23%

Sweetness index 92 100 99

Adapted from G. L. Hein, M. L. Storey, and J. S. White, “The Highs and Lows of High-Fructose Corn Syrup: A Report from the Center for Food and Nutrition Policy and Its Ceres Workshop,” Nutrition Today 40(2005): 253–256.

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154 Chapter 4 . Carbohydrates

Health Effects of Too Much Sugar: Fact vs Fiction Scientists, dietitians, doctors, and especially diet book authors have a variety of opin- ions about including carbohydrates in the diet. Many popular publications have branded carbohydrates as dietary evils—the cause of obesity, hyperactivity, and in- creased risk of developing serious medical complications, including diabetes melli- tus. Are any of these allegations accurate?

Fact: Sugar Can Cause Dental Caries Carbohydrates do play a role in tooth decay. Sugars and starches contribute to dental caries because they provide an energy source for the bacteria in the mouth. As the bac- teria grow, they produce acids that erode the enamel of the teeth. The stickier the car- bohydrate, the longer it is in contact with the teeth and the more opportunity there is for the bacteria to produce their damaging acids. Hence hard candies that dissolve slowly in the mouth, or dried fruits that can adhere to the teeth, are potentially more harmful than foods that are quickly swallowed, such as whole fruits and vegetables. To avoid increased risk of dental caries, sugary snacks should be kept to a minimum, and whole fruits and raw vegetables should be chosen over candies or pastries as snacks.

Some foods may actually help reduce the risk of acid attacks on teeth. The tex- ture of cheese, for example, stimulates the release of cleansing saliva. Cheese is also rich in protein, calcium, and phosphorus, all of which help buffer the acids in the mouth following a meal or snack. The calcium can also assist in remineralization of the teeth. Chewing sugarless gum encourages the production of saliva and provides a postmeal bath for your teeth.

Fiction: Sugar Causes Diabetes Mellitus Contrary to popular belief, sugar does not cause diabetes mellitus. However, too much sugar in the diet can increase the blood level of triglycerides (the primary form of fat in the body, discussed in Chapter 5) and lower the “good” HDL cholesterol, which may increase risk for heart disease.69 Luckily, a reduction in the amount of sugar coupled with an increase in dietary fiber can typically alleviate this problem.

Fact: Too Much Sugar Can Hinder Weight Loss Sugar itself does not lead to or impede weight loss. However, it is easy to overeat energy-dense, sugary foods and quickly add excess kilocalories to the diet. If the increased consumption of kilocalories is not offset by increased exercise or physical activity, weight gain can occur.

Individuals on low-carbohydrate diets sometimes report initial success with weight loss. However, this loss is usually due to the reduced consumption of overall kilocalories, and is often short term. Once normal eating habits resume, the weight is regained. Research hasn’t yet concluded what the long-term effects of eating few or no

remineralization Replacing the lost minerals in a decayed lesion or dental carie

on a tooth.

dental caries Tooth decay.

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What Are Sugar Substitutes? 155

sugar substitutes Alternatives to table sugar that sweeten foods for fewer

kilocalories.

carbohydrates are. A diet that is low in carbohydrates can be high in heart-unhealthy fats or too high in protein.

Fiction: Sugar Is Addictive Some people claim that sugar is addicting, but most experts agree that this is not the case. To be classified as an addiction, a substance must meet several requirements: It has to make you feel good, change the chemicals in the brain, trigger a physical de- pendence and irrepressible cravings, and, when removed from consumption, result in severe physical and psychological reactions.

Fiction: Sugar Causes Hyperactivity in Children Adults often point to sugary foods as the culprit behind the overly excited behavior of children at parties and holidays; however, research does not support the theory that sugar makes kids hyperactive.70 The behavior in the kids is more likely due to the excitement and festivities of the day than the sweets being consumed.

The Take-Home Message Sugar can contribute to dental caries, an elevated level of fat in the blood, and a lowering of the “good” HDL choles- terol. Sugar does not increase the risk of diabetes, nor cause hyperactivity in children. Sugar is not considered an addictive substance.

What Are Sugar Substitutes? Because most people perceive eating too much sugar as un- healthy, food manufacturers often use artificially created sugar substitutes to provide the sweet taste of sugar for fewer kilo- calories, and Americans’ consumption of these products has increased steadily over the last two decades (see Figure 4.22). All sugar substitutes must be approved by the FDA and deemed safe for consumption before they are allowed in food products sold in the United States.71

There are several sugar substitutes presently available to con- sumers, including polyols, saccharin, aspartame, acesulfame-K, sucralose, and neotame. Alitame and cyclamate are two other sugar substitutes that are not yet approved for use in the United States but are on the horizon. Polyols don’t promote dental caries and cause a slower rise in blood glucose than sugar. Sac- charin, aspartame, acesulfame-K, sucralose, and neotame also won’t promote dental caries and have the added advantage of not affecting blood glucose levels at all. These sugar substitutes are a plus for people with diabetes, who have a more challenging time managing their blood glucose levels. Additionally, all sugar substitutes are either reduced in calories or are calorie free. See Table 4.6 for a comparison of available sweeteners.

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Figure 4.22 Growing Interest in Sugar-Free Foods and Beverages The use of sugar-free products has more than doubled since 1986.

Source: Calorie Control Council, Trends and Statistics. 2007. www.caloriecontrol.org.

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156 Chapter 4 . Carbohydrates

Table 4.6

Oh So Sweet!

Sweetener Calories/Gram Trade Names Sweetening Power The Facts

Sucrose 4 Table sugar — Sweetens food, enhances flavor, tenderizes, and contributes browning properties to baked goods

Reduced-Calorie Sweeteners Polyols (Sugar Alcohols)

Sorbitol 2.6 Sorbitol 50% to 70% as sweet as sucrose

Found in foods such as sugarless chewing gum, jams, baked goods, and candy

Mannitol 1.6 Mannitol 50% to 70% as sweet as sucrose

Found in foods such as chewing gum, jams, and as a bulking agent in powdered foods. May cause diarrhea.

Xylitol 2.4 Xylitol Equally sweet as sucrose

Found in foods such as chewing gum, candies; also in pharmaceuticals and hygiene products

Hydrogenated starch hydrolysates

3.0 HSH 50% to 70% as sweet as sucrose

Found in confections and can be used as a bulking agent

Calorie-Free Sweeteners

Saccharin 0 Sweet ‘N Low 200% to 700% sweeter than sucrose

Retains its sweetening power at high temperatures such as baking

Aspartame 4* Nutrasweet, Equal

Approximately 200% sweeter than sucrose

Sweetening power is reduced at high temperatures such as baking. Can be added at end stages of recipes such as cooked puddings if removed from heat source. Individuals with PKU need to monitor all dietary sources of phenylala- nine, including aspartame.

Acesulfame-K 0 Sunette 200% sweeter than sucrose

Retains its sweetening power at high temperatures

Sucralose 0 Splenda 600% sweeter than sucrose

Retains its sweetening power at high temperatures

Neotame 0 Neotame 7,000% to 13,000% sweeter than sucrose

Retains its sweetening power at high temperatures

*Because so little aspartame is needed to sweeten foods, it provides negligible calories.

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What Are Sugar Substitutes? 157

Polyols Are Sugar Alcohols Polyols are often called sugar alcohols because they have the chemical structure of sugar, with an alcohol component added. Whereas polyols such as sorbitol, mannitol, and xyl- itol are found naturally in plants, they are also produced synthetically and are used as sweeteners in foods such as chewing gum and candies. They can be used tablespoon for tablespoon to substitute for sucrose. Sorbitol and mannitol are less likely to promote dental caries because the bacteria on the teeth metabolize them so slowly. (Humans lack the enzyme needed to ferment xylitol.) Their slower absorption means that they do not produce a spike in blood glucose, which is a benefit for those with diabetes.

Chewing gums and candies that contain sugar alcohols can be labeled “sugar free” and claim that they don’t promote tooth decay. Keep in mind, however, that though these products are sugar free, they are not necessarily calorie free. Even more important, because polyols are incompletely absorbed in the digestive tract, they can cause diarrhea. For this reason, they should be used in moderation.

Another type of polyol is hydrogenated starch hydrolysate (HSH), which is made by partially breaking down corn, wheat, or potato starch and adding hydrogen. The end product is a wide range of polyols, including those that can be strung to- gether and used commercially. HSH adds sweetness, texture, and bulk to many sug- arless products such as baked goods and candies.72

Saccharin Is the Oldest Sugar Substitute Consumers today often associate saccharin with the pink packets found on restau- rant tables, but it’s been in use for more than a century. Saccharin was first discov- ered in 1879, and was used as a sugar substitute in the United States and Europe during the sugar-rationing periods of the mid-twentieth century. It is used in more than 100 countries in foods, beverages, vitamins, and pharmaceuticals. Because sac- charin is not metabolized by the body, it doesn’t provide any kilocalories.

In 1977, the FDA banned saccharin due to reports from the research commu- nity that it could cause bladder cancer in rats. Congress immediately implemented an 18-month moratorium on this ban through the Saccharin Study and Labeling Act. This allowed the continued commercial use of saccharin, but required that any saccharin-containing products bear a warning label stating that saccharin was poten- tially hazardous to health as it caused cancer in laboratory animals.

In 2000, the National Toxicology Program (NTP) removed saccharin from the list of substances that could potentially cause cancer. After extensive review, the NTP determined that the observed bladder tumors in rats were actually from a mechanism that wasn’t relevant to humans.73 The lesson learned from this is that though you can safely consume saccharin in moderation, you shouldn’t feed it to your pet rat.

A variety of sugar substitutes are available to consumers.

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158 Chapter 4 . Carbohydrates

FOCUS ON RESEARCH Monsivais, P., M. M. Perrigue, and

A. Drewnowski. 2007. Sugars and Satiety: Does the Type of Sweetener Make a

Difference? American Journal of Clinical Nutrition 86:116–123.

Background

The substitution of sucrose with high- fructose corn syrup in beverages oc- curred at approximately the same time as the sharp rise in obesity in Americans. The rise in obesity was also observed in countries where soft-drink consumption and the use of high-fructose corn syrup is much lower. One of the arguments pre- sented in support of high-fructose corn syrup and sweetened beverages causing obesity is that these sweeteners are less satiating that protein and fat. Beverages and foods that are less satiating may re- sult in an increase kilocalorie intake and obesity.

Hypothesis

The researchers hypothesize that carbon- ated soft drinks sweetened with high- fructose corn syrup will stimulate satiety less than either the soft drink sweetened with sucrose or low-fat milk.

Study Design

Thirty-seven subjects, 19 males and 18 females ages 20–29 years old, drank

three different cola beverages sweetened with either sucrose (50 percent sucrose), HFCS 42 (42 percent fructose), or HFCS 55 (55 percent fructose). Each beverage contained 215 kilocalories. A control group drank either a diet cola sweetened with aspartame (2 kilocalories), 1%-fat milk (215 kilocalories), or no beverage at all. The beverages were consumed 2 hours after eating breakfast. Subjects were asked to rate their hunger, thirst, and satiety before drinking the beverage and every 20 minutes after consuming the drink. A lunch was provided 2 hours and 20 minutes after the first beverage was consumed and the amount of kilo- calories eaten were recorded.

Results

The results reported no differences in hunger, satiety, or the amount of food consumed at lunch. Those subjects who consumed the diet beverage or no bever- age at all, had higher kilocalorie intakes at lunch compared to those beverages with kilocalories.

Conclusions

The research suggests that there is no difference between beverages sweetened with high-fructose corn syrup and su- crose on hunger, satiety, or energy in- takes in the short term.

QUESTIONS

1. Was this study well designed? Why or why not?

2. How do the results of this study prove or disprove the hypothesis?

3. Are there other factors that could have influenced the results?

4. Do you agree with the authors’ conclusions?

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Figure 1 The hunger ratings following the consumption of a diet beverage sweetened with aspartame, low-fat milk, two beverages sweetened with high-fructose corn syrup, and a sucrose sweetened beverage. The no-beverage control had significantly higher ( p < .005) hunger ratings than any of the beverages. All five beverages had lower hunger ratings and there was no significant difference between the beverages on hunger or satiety.

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What Are Sugar Substitutes? 159

Aspartame Is Derived from Amino Acids In 1965, a scientist named James Schlatter was conducting research on amino acids in his quest to find a treatment for ulcers. To pick up a piece of paper in his laboratory, he licked his finger and stumbled upon a sweet-tasting compound.74 It was the “lick” that was soon to be “tasted” around the world. Schlatter had just discovered aspartame, a substance that has become one of the most-used sugar substitutes in the world.

Aspartame is composed of two amino acids: a modified aspartic acid and phenylalanine. Enzymes in the digestive tract break down aspartame into its compo- nents, and the amino acids are absorbed, providing 4 kilocalories per gram. Conse- quently, aspartame has the potential to provide kilocalories to foods as an added sweetener. However, as aspartame is 200 times sweeter than sucrose, only a small amount is needed to sweeten a food.

In 1981, the FDA approved aspartame for use in tabletop sweeteners such as Equal and Nutrasweet, and for various other uses, such as to sweeten breakfast cereals, chew- ing gums, and carbonated beverages. The majority of the aspartame that is consumed in the United States is in soft drinks. In 1996, the FDA gave the food industry carte blanche to use aspartame in all types of foods and beverages. It is currently used as a sweetener in over 100 countries, and can now be found in over 6,000 foods, as well as pharmaceuticals and personal care products, sold in the United States.

Aspartame has undergone continual, vigorous reviews to ensure that it is safe for human consumption. The FDA considers it one of the most thoroughly studied and tested food additives approved by the agency. The FDA has reevaluated the safety of aspartame more than 25 times since it first came on the market and each time has concluded that it is safe to consume.75

Despite its intense evaluation, aspartame has been, and still is, blamed for ail- ments ranging from headaches to Gulf War Syndrome. Major health organizations such as the American Dietetic Association, the American Medical Association, and the American Diabetes Association all support aspartame’s use by healthy adults, children, and pregnant women in moderation as part of a well-balanced diet.76 The FDA has set an acceptable daily intake (ADI) for aspartame at 50 milligrams per kilogram (mg/kg) of body weight. To exceed this ADI, a 150-pound person would need to consume almost sixteen 12-ounce cans of a “diet” (aspartame-containing) soda daily for a lifetime. Currently, the general public consumes an estimated 4 to 7 percent of the ADI, or 2 to 3.5 milligrams per kilogram of body weight daily.

Individuals with a rare, inherited disorder known as phenylketonuria (PKU) are unable to metabolize one of the amino acids in aspartame, phenylalanine, and must adhere to a special diet. PKU affects about 1 out of every 15,000 infants in the United States. It is usually the result of a deficiency of phenylalanine hydroxylase, an enzyme needed to properly metabolize phenylalanine.77

Foods and beverages that contain aspartame must carry a label warning that phenylalanine is present.

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160 Chapter 4 . Carbohydrates

Because of the seriousness of this disorder, the FDA mandates that all food products that contain phenylalanine carry a label declaring its content. People with PKU need to control all dietary sources of this amino acid, including aspartame as well as protein-rich foods such as meat, milk, eggs, and nuts. These individuals do not necessarily have to avoid aspartame, but they need to monitor it as an additional source of phenylalanine in their diet.

Acesulfame-K Contains Potassium Although its name is less than sweet sounding, acesulfame-K (the K refers to the potassium component) is about 200 times sweeter than sucrose. It is available as a tabletop sweetener, called Sunette, and is currently used in chewing gum, candy, desserts, yogurt, and alcoholic beverages. The body does not metabolize acesulfame- K and it’s excreted intact in the urine.78

Sucralose Is Made from Sucrose Sucralose was developed in 1976 by slightly changing the structure of the sucrose molecule. Unlike sucrose, sucralose isn’t digested or absorbed by the body—it passes through the GI tract and is excreted. In 1998, sucralose was approved as a tabletop sweetener, and it’s available commercially as Splenda. Sucralose can be used in bak- ing because it doesn’t break down when it reaches high cooking temperatures.

Neotame Is Also Derived from Amino Acids The newest addition to the world of sugar substitutes is neotame, which was ap- proved by the FDA in 2002. Neotame comprises the same two amino acids—aspartic acid and phenylalanine—as aspartame, but they are joined together in such a way that the body cannot break them apart. So, individuals with PKU can use neotame without concern. Neotame is completely eliminated in either the urine or stool. It has been approved as a sweetener and for a variety of uses such as chewing gum, frostings, frozen desserts, puddings, fruit juices, and syrups.79

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Putting It All Together 161

The Take-Home Message Millions of Americans consume reduced- calorie or calorie-free sugar substitutes. The FDA has approved polyols, sac- charin, aspartame, acesulfame-K, sucralose, and neotame to be used in a variety of foods. These sugar substitutes do not promote dental caries and can benefit those with diabetes who need to carefully manage their blood glucose.

Putting It All Together Carbohydrates are an important part of a healthy diet. Whole grains, fruits, vegeta- bles, and lean dairy products provide carbohydrates along with vitamins and miner- als and should be the predominant source of carbohydrates in the diet. Whole grains, fruits, and vegetables are also good sources of fiber and phytochemicals. A diet that contains adequate amounts of these foods can help prevent many chronic diseases. Sugary foods also provide carbohydrates but often contain fewer nutrients, so should be used in moderation.

Based on what you’ve learned in this chapter, do you thinkAdam should avoid refined sugars? Should he include sugar substitutes in his diet? Why or why not?

CAREERS IN NUTRITION Certified Diabetes Educator

In addition to her private practice, Alison Kaplanes, MS, RD, CDE, is a certified diabetes educator with

the Joslin Clinic at Beth Israel Hospital– Needham. Read an online interview with Alison about her work with diabetes patients at www.aw-bc.com/blake.

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What Are Carbohydrates?

Carbohydrates are essential nutrients composed of carbon, hydrogen, and oxy- gen that are predominant in plant-based foods. The main role of carbohydrates is to supply fuel, primarily in the form of

glucose (ose = sugar), the predomi- nant sugar in carbohydrate-rich foods, to the cells. Plants form glucose in a process called photosynthesis.

Simple and Complex Carbohydrates

Carbohydrates are divided into two cate- gories based on the number of sugar units that are joined together. Simple carbohydrates, or sugars, include monosaccharides and disaccharides, and complex carbohydrates include polysaccharides (see figures). Oligo- saccharides contain 3 to 10 mono- saccharides.

There are hundreds of monosaccha- rides found in nature but only three that are nutritionally important to the body: glucose, fructose, and galactose. Each monosaccharide has the same six- carbon molecular composition (C6H12O6), called a hexose. Fructose, a five-ring

structure, is the sweetest of the simple sugars and is found abundantly in fruit. Galactose is found in dairy foods. From these three sugars, disaccharides and complex carbohydrates can be formed. The process of condensation allows simple sugars to join together to form disaccharides and polysaccharides.

Monosaccharides are linked into disaccharides by glycosidic bonds. When two glucose units join together, the disac- charide maltose is created. Maltose is the sugar found in grains. When glucose and fructose combine, the disaccharide sucrose, or table sugar, is formed. Galactose is linked with glucose to form lactose, or milk sugar, found in dairy foods.

Polysaccharides contain the most sugars so it makes sense that they are called complex carbohydrates. Starch, including amylose and amylopectin, fiber, and glycogen are all polysaccharides.

Carbohydrates Are Digested and Absorbed in the Mouth and Small Intestine

The digestion of carbohydrates begins in the mouth with salivary amylase. In the small intestine, pancreatic amylase con- tinues the digestion of starch, while the disaccharides sucrose, maltose, and lac- tose are digested by enzymes produced

Carbohydrates

162 Chapter 4 . Carbohydrates

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Functions of Carbohydrates

The body uses carbohydrates, specifically glucose, for energy. Hormones maintain the amount of glucose in the blood at 70 to 110 mg/dl. To lower blood glucose when levels are high, the pancreas releases the hormone insulin into the blood. Surplus glucose is linked into long

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Fiber Has Many Health Benefits

Fiber has been shown to help lower the risk of developing constipation, diverticu- losis, obesity, heart disease, cancer, and diabetes mellitus.

Meals high in fiber are typically digested more slowly, which allows the absorption of the nutrients to be extended over a longer period of time. Foods high in fiber, such as whole

grains, fruits, and vegetables, can add to satiation so that fewer

kilocalories need to be eaten to feel full.

Viscous, soluble fibers have been shown to help

lower elevated blood choles- terol levels. Insoluble fibers in- crease the bulk of the feces and reduce the risk of constipa-

tion and diverticulosis.

Daily Needs

The latest Dietary Reference Intakes (DRIs) for carbohydrates recommend that adults and chil-

Carbohydrates 163

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dren consume a minimum of 130 grams daily. This is based on the estimated mini- mum amount of glucose the brain and red blood cells need to function efficiently. A quick look at MyPyramid shows that 130 grams is less than the amount consumed by eating the minimum recommended daily servings from the grain group (6 servings), vegetable group (3 servings), fruit group (2 servings), and dairy group (3 servings).

U.S. adult males consume, on aver- age, 220 grams to 330 grams of carbo- hydrates daily, whereas adult females eat 180 grams to 230 grams daily, well over the minimum DRI.

The DRI for fiber is 14 grams per 1,000 kilocalories per day. A range of 20 to 38 grams per day is considered adequate to reduce the risk of cardiovas- cular disease in adults. No UL is set for dietary fiber.

According to the latest DRIs, 45 to 65 percent of total daily calories should come from carbohydrates. Adults in the United States consume about half of their

chains of glycogen by the process of glycogenesis, and then stored in the liver and muscle.

The pancreas releases another hor- mone, glucagon, when the body needs to direct the release of glucose from the stored glycogen in the liver to raise blood glucose levels. This breakdown of glyco- gen is called glycogenolysis.

Carbohydrates spare protein from being used for energy and prevent the rapid break- down of triglycerides, or lipolysis.

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164 Chapter 4 . Carbohydrates

calories from carbohydrate-laden foods, so they are easily meeting this optimal range.

Food Sources

In general, the diet should contain low to moderate amounts of simple carbohy- drates and be high in fiber and other complex carbohydrates. This is the best strategy for long-term health.

Simple carbohydrates are found natu- rally in fruits, vegetables, and dairy foods. Though processed foods and sweets also contain simple sugars, the higher kilocalorie and lower nutri- ent levels in these foods make them a less healthy option.

Complex carbohy- drates, including starch and fiber, are found abun- dantly in grains, whole fruits, and vegetables. Starch is the primary complex carbohydrate found in grains and potatoes, while fiber is found in whole grains, whole fruits, vegetables, legumes, nuts, and seeds. Whole grains contain more fiber and are more nutrient dense than refined grains.

Too Much or Too Little?

Adding too many carbohydrates to the diet can displace other essential nutrients. Excess fiber can cause bloating and intes- tinal gas, and may bind vitamins and min-

erals, reducing their absorption. Eating too many added sugars may increase tooth decay. Consuming insufficient carbohy- drates can create a diet that falls short of many vitamins, minerals, fiber, and phyto- chemicals. Individuals with diabetes need to monitor their carbohydrate intake to maintain a healthy blood glucose level. Chronic, poor regulation of blood glucose levels can damage the body.

What Is Diabetes?

Individuals develop diabetes because they aren’t producing enough

insulin (type 1 diabetes) and/or they have developed insulin resistance, such that

their cells do not respond to the insulin

when it arrives (type 2 dia- betes). Type 1 diabetes is considered an autoimmune

disease and is the rarer of the two forms. Type 2 is the more

common form and is seen in people who have become insulin resistant.

One of the major problems with type 2 diabetes is that this condition can go un- diagnosed for some time. While some people may have symptoms such as in- creased thirst, others may not. Conse- quently, diabetes can damage a person’s vital organs without their being aware of it. Because of this, the American Diabetes Asso- ciation recommends that everyone 45 years of age and older undergo testing for dia- betes. However, if a person is at a higher risk for developing diabetes, (such as those who are overweight or obese, or who are genetically predisposed) he or she shouldn’t wait until age 45 to be tested.

Poorly managed diabetes increases the likelihood of nerve damage, leg and

foot amputations, eye diseases, tooth loss, gum problems, kidney disease, and heart disease. Diabetes can also damage the retina of the eye, which can cause bleeding and cloudy vision, and eventu- ally blindness.

Good nutrition habits play a key role in both the prevention and management of diabetes. The ADA (American Diabetes Association) recommends that individuals with diabetes consume a diet that includes a combination of predominantly high-fiber carbohydrates from whole grains, fruits, and vegetables, along with low-fat milk, adequate amounts of lean protein sources, and unsaturated fats. Adequate physical activity is also impor- tant to manage diabetes.

Carbohydrates continued

Terms to Know glucose ■ photosynthesis ■ simple carbohydrates ■ monosaccharides ■ disaccharides ■ complex carbohydrates ■ polysaccharides ■ oligosaccharides ■ glucose ■ fructose ■ galactose ■ hexose ■ maltose ■ sucrose ■ lactose ■ starch ■ fiber ■ glycogen ■ insulin ■ glycogenesis ■ glucagon ■ glycogenolysis ■ lipolysis ■ diabetes ■ insulin resistance

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Two Points of View 165

Barry M. Popkin, PhD PROFESSOR, DEPARTMENT OF NUTRITION; DIRECTOR, INTERDISCIPLINARY OBESITY CENTER UNIVERSITY OF NORTH CAROLINA, CHAPEL HILL

Dr. Barry M. Popkin PhD has a doctor- ate in economics and is a professor of nutrition at the University of North Car- olina, Chapel Hill (UNC-CH), where he

heads the Division of Nutrition Epidemiology in the School of Public Health. He also directs the UNC-CH’s Interdisciplinary Obesity Center. He initiated the Beverage Guidance Panel, a group of prominent scholars that offers guidance on the ben- efits and risks of various beverage choices. Popkin conducts a wide range of U.S. and international research on diet, health, and obesity solutions.

Q: Has Americans’ soft drink consumption changed over time? If so, how has it changed and why?

A: Today, the average American gets about 21 percent of his or her calories from beverages. Most age and gender groups are consuming about 150 to 300 more calories than they did, and about half of that increase comes from soft drinks and fruit drinks. From the 1970s to the pres- ent, per capita intake of soft drinks and fruit drinks went up. The number of times per day that people consumed caloric, sweetened beverages went up. The portion size went up. In the late 1970s, we used to get just under 3 percent of our daily calories from soft drinks. By the late 1990s, that figure went up to 7 percent.

A principal driver behind this change is how drink manufacturers are working to make us drink more and more of their products. And that’s not just soft drinks. We are getting more of our calories from fruit drinks com- pared to the late 1970s, and more from alcohol.

Q: How has the change in soft drink consumption af- fected the health of Americans?

A: The evidence isn’t perfect that soft drinks will increase your weight or lead to obesity or diabetes or tooth decay, but it’s pretty likely. Soft drinks and fruit drinks are clearly a bigger culprit than any other beverage for 10- to 35-year-olds. But other beverages have contributed too. Some groups of adults have tripled their daily alcohol in- take. Others have started having a smoothie a day.

People need to remember that beverages are less satiating than solid foods. When you consume calories from beverages, you don’t compensate by eating less

Two Points of View Can Soft Drinks Be Part of a Healthy Diet?

From sodas to fruit drinks and sports drinks, two experts weigh in on Americans’ soft drink consumption and its ramifications for public health.

Robert Earl, MPH, RD SENIOR DIRECTOR, NUTRITION POLICY, FOOD PRODUCTS ASSOCIATION

Robert Earl MPH, RD, directs nutrition and health policy activities for the Food Products Association, the principal sci- entific and technical trade association representing the food products industry.

Earl provides food industry leadership and technical assis- tance for the Washington, DC-based group, focusing on di- etary and food guidance, food and nutrition programs, nutrition requirements, and nutrition and health claims in food labeling. A registered dietitian, Earl holds a master’s degree in public health nutrition from the University of North Carolina at Chapel Hill.

Q: Has Americans’ soft drink consumption changed over time? If so, how has it changed and why?

A: Just looking at traditional soft drinks such as sodas—not newer products such as fruit drinks or sports drinks— consumption had been going up. But that has changed in the last couple of years. Consumption now appears to be leveling off or dropping.

Why is this the case? The variety of caloric and non- caloric beverages has changed, so there are more choices. It is becoming clearer that Americans under- stand the “calories count” message. They are under- standing that to manage weight or lose weight, they need to think about overall calorie consumption and their level of physical activity. That is factoring into their bever- age choices. People understand that beverages are a part of their calorie intake.

Q: How has the change in soft drink consumption af- fected the health of Americans?

A: That depends on what individuals consume, their overall diet, and their level of physical activity. One has to look at whether a consumer is drinking caloric soft drinks or calorie-free soft drinks. And those choices have to be factored into total dietary patterns and physical activity patterns.

Q: How can soft drinks be part of a healthy diet? A: Any individual has room to consume soft drinks, particu-

larly non-caloric soft drinks, as part of a healthful diet. Beverages that have no calories are useful in fulfilling an individual’s hydration needs. While many beverages—

continued continued

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166 Chapter 4 . Carbohydrates

food later on. Liquid calories don’t register with our ap- petite controls.

Q: How can soft drinks be part of a healthy diet? A: I don’t see a way soft drinks can be part of a healthy diet

unless you are an athlete or very physically active. Other- wise, they lead to weight gain. Non-diet soft drinks have zero benefits and major costs. If you have a 12-ounce serving of soft drinks or fruit drinks, you’ve got to com- pensate for the 160 calories you get from it.

I am also very cautious about saying that you can consume a lot of diet drinks. Some studies suggest that these beverages condition children and adults to have a high preference for sweetness. That may drive up overall consumption of sweet or sweetened foods, which also leads to weight gain. Our (beverage) panel is monitoring some of this new research closely.

Q: What can the soft drink industry do (or what is it doing) to help improve public health?

A: They could promote water and unsweetened, unflavored low-fat or skim milk. They could also change their mes- sages about how we need to be drinking beverages all the time to stay hydrated. That messaging is really bad— people already know how to follow their thirst and con- sume enough liquids. The messages only serve to drive up consumption.

milk, juice, soft drinks—can come with a contribution of calories, if someone is active and eats a wide variety of foods, a caloric soft drink could fit within their caloric needs. It’s all about balance, variety, and moderation. One has to look at one’s food and beverage choices, and factor in physical activity to get the total picture.

Q: What can the soft drink industry do (or what is it doing) to help improve public health?

A: The soft drink and beverage industry has introduced a wide variety of options for the consumer. Those options aren’t limited to the range of regular, mid-calorie, and calorie-free versions of soft drinks now available. There are so many other beverage alternatives from these com- panies, and one benefit to the public is this incredible va- riety. Most large traditional soft drink companies now also sell sports drinks, calorie-free beverages, juice, and water. Some even have dairy-based products. And look at water. While this isn’t a benefit exclusively driven by soft drink companies, never before has water been so available to consumers in portable form.

The soft drink industry is also being very active in promoting responsible beverage consumption to chil- dren, adolescents, and adults. The industry is working with schools, promoting both nutrition and hydration, as well as providing support for improved physical activity. They are working to expand the range of options in vend- ing machines and cafeterias in schools and in work- places. Nutrition education and physical activity programs are also being funded.

Robert Earl, MPH, RD, continued Barry M. Popkin, PhD, continued

Can Soft Drinks Be Part of a Healthy Diet? continued

The Top Ten Points to Remember

1. There are three nutritionally important monosaccha- rides found in nature: glucose, fructose, and galactose. Glucose is the most abundant monosaccharide and the preferred fuel for the human nervous system, including the brain, and red blood cells. Disaccharides consist of two joined monosaccharides. The best-known disaccha- ride, sucrose (table sugar), is made of fructose and glu- cose. Lactose, or milk sugar, is made up of glucose and galactose. Maltose is two glucose units joined together. Oligosaccharides consist of 3 to 10 sugar units, and poly- saccharides consist of 10 or more. The polysaccharide

starch is the storage form of glucose in plants. Glycogen is the storage form of glucose in animals, and is found in the liver and muscle cells. Fiber is a nondigestible poly- saccharide found in the cell walls of plants.

2. Carbohydrate digestion begins in the mouth, where the enzyme salivary amylase begins to break down starch. The enzyme is deactivated in the stomach, and most carbohydrate digestion and absorption occurs in the small intestine. Fiber is nondigestible and generally passes through the GI tract, adding bulk to the stool.

3. Blood glucose levels are maintained in a healthy range with the help of the hormones insulin and glucagon. When blood glucose is too high, insulin directs glucose into cells. When blood glucose levels drop too low, the glucagon stimulates the breakdown of liver glycogen

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Test Your Knowledge 167

to provide glucose to the blood. When the diet is defi- cient in carbohydrates, the body cannot break down fat completely. Ketone bodies are created.

4. A minimum of 130 grams of dietary carbohydrates is needed daily, and 45 to 65 percent of daily calories should come from carbohydrates. Adults should con- sume approximately 20 to 35 grams of fiber daily, de- pending on their age and gender. A high-fiber diet can help avoid constipation and lower the risk of divertic- ulosis, heart disease, obesity, diabetes, and certain can- cers.

5. Diabetes mellitus is a condition characterized by hyper- glycemia due to the body’s inability to regulate insulin secretion, insulin action, or both. Type 2 diabetes is be- coming more prevalent in the United States, especially among children. Those with diabetes should consume a well-balanced diet and exercise regularly to help main- tain a blood glucose level within a healthy range. Med- ication and/or insulin as well as regular blood tests may also be needed to manage blood glucose. Those with dia- betes can include a modest amount of added sugar in their diets as long as their weight is being managed. Pre- vention will be key to halting the rising incidence of dia- betes in the United States.

6. Hypoglycemia, or low blood sugar, can occur in indi- viduals with diabetes, especially if they are taking medication and/or insulin and are not eating properly. Individuals without diabetes can also experience hy- poglycemia, but the incidence is less common.

7. Human taste buds can’t distinguish between naturally occurring and added sugar. Foods with naturally oc- curring sugars tend to be more nutritious than foods with a lot of added sugar, which are usually manufac- tured or processed. A diet too high in added sugar may increase the level of fat and decrease the level of the “good” cholesterol in the blood. Sugary foods contain calories but little else and can crowd out more nutri- tious food choices in the diet. The major source of di- etary added sugar is soft drinks.

8. Frequently exposing teeth to starch and sugary foods, especially sticky foods, can increase the risk of dental caries. Chewing sugarless gum and eating low-fat cheese may help reduce the risk of dental caries. Car- bohydrates themselves don’t cause weight gain. Con- suming excess calories from any source on a regular basis is the culprit behind gaining weight. Meals con- taining whole grains, fruits, and vegetables tend to be higher in bulk and are processed more slowly in the

body than low-fiber meals, and may improve satiety and result in eating less.

9. Polyols, saccharin, aspartame, acesulfame-K, sucralose, and neotame are sugar substitutes currently deemed safe by the FDA. Because aspartame contains the amino acid phenylalanine, individuals with phenylke- tonuria, a rare disorder, must limit all dietary sources of this amino acid.

10. Whole grains contain vitamins, minerals, fiber, and phytochemicals. Whereas refined grains can be “enriched” with some of the vitamins and minerals lost during processing, the fiber and phytochemicals are not added back. At least half of your daily servings of grains should be whole grains. High-fructose corn syrup is a sweetener produced from modified corn and composed of glucose and fructose. It likely plays a role in Americans’ overall increased caloric intake, including from energy-dense sweets, snacks, and baked goods, which contain more kilocalories than nutrient-dense fruits and vegetables; HFCS does not contribute more to obesity than do other sweeteners.

Test Your Knowledge 1. Sucrose is a

a. monosaccharide. b. disaccharide. c. oligosaccharide. d. polysaccharide.

2. _______ is the storage form of glucose in animals, includ- ing humans. a. Glucagon b. Glycogen c. Gluconeogenesis d. Glucose

3. Three brush border enzymes that hydrolyze carbohydrates in the small intestine are a. insulin, glucagon, and cortisone. b. salivary amylase, salivary lipase, and gastric lipase. c. maltase, lactase, and sucrase. d. fiber, starch, and glycogen.

4. The hormone that directs the breakdown of glycogen is a. galactose. b. glucagon. c. insulin. d. none of the above

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5. The minimum amount of carbohydrates needed daily is a. 75 grams. b. 100 grams. c. 120 grams. d. 130 grams. e. 150 grams.

6. Which of the following can help someone who is lactose intolerant enjoy dairy products? a. drinking Lactaid milk b. pouring milk over a cup of bran cereal c. enjoying cheese a little at a time, and building up to

larger servings d. all of the above e. none of the above

7. Reducing consumption of which item would have the biggest impact on decreasing the amount of added sugars that Americans consume? a. watermelon b. candy c. soft drinks d. apples

8. Your blood cholesterol level is too high, so you would like to eat additional viscous, soluble high-fiber foods to help lower it. A good choice would be a. low-fat milk. b. chocolate chip cookies. c. bananas. d. oatmeal.

9. Which of the following can help reduce your risk of type 2 diabetes? a. avoiding sugar b. eating a high-fiber, plant-based diet c. exercising regularly d. all of the above e. b and c only

10. An individual who has PKU should not consume which of the following sugar substitutes? a. sucralose b. acesulfame-k c. aspartame d. neotame

Answers 1. (b). Sucrose contains the two monosaccharides glucose

and fructose, and is therefore a disaccharide. Oligosaccha- rides and polysaccharides contain more than two sugar units.

2. (b). Glycogen is stored in the liver and muscles and pro- vides a ready-to-use form of glucose for the body. Glucagon is the hormone that directs the release of glu- cose from the stored glycogen. Gluconeogenesis is the creation of glucose from noncarbohydrate sources.

3. (c). The enzymes maltase, lactase, and sucrase are located in the brush border of the small intestine and hydrolyze the disaccharides maltose, lactose, and sucrose, respec- tively. Insulin, glucagon, and cortisone are hormones, not enzymes. Salivary amylase is an enzyme in the saliva that begins digesting starch, a form of complex carbohydrate.

4. (b). When the blood glucose level drops too low, glucagon is released from the pancreas to direct the breakdown of glycogen in the liver, which provides glucose to the blood. Insulin is a hormone that directs the uptake of glucose by cells. Galactose is a monosaccharide found in dairy foods.

5. (d). The DRI for carbohydrate is to consume at least 130 grams daily. This is the minimum amount needed to supply the glucose that the body, particularly the brain, must have to function effectively.

6. (d). All of these can help improve lactose absorption. The Lactaid milk is pretreated to facilitate the breakdown of the lactose in the milk. Consuming lactose-containing foods with a meal or snack will improve the digestion of lactose. Gradually adding dairy foods to the diet will lessen the symptoms of lactose intolerance.

7. (c). Soft drinks are the number-one source of added sug- ars in the American diet, so reducing the intake of these sugary beverages would go a long way in reducing the amount of added sugars that Americans consume. Reduc- ing the amount of candy would also help reduce the added sugars in the diet but not as much as soft drinks. Watermelon and apples contain only naturally occurring sugars.

8. (d). Oatmeal is rich in beta-glucan, a viscous fiber that can help lower cholesterol when eaten as part of a heart- healthy diet. Though nutrient dense, the bananas and milk do not contain fiber. Cookies won’t help lower cho- lesterol.

9. (e). Eating a high-fiber, plant-based diet and getting regu- lar exercise, both of which will help you maintain a healthy weight, is the best approach, at present, to help re- duce the risk of developing type 2 diabetes. Eating sugar doesn’t cause diabetes.

10. (c). Individuals diagnosed with PKU, or phenylketonuria, should not consume aspartame because it contains the amino acid phenylalanine.

168 Chapter 4 . Carbohydrates

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References 169

Answers to Myths and Misconceptions

1. False. All macronutrients are essential for health, includ- ing carbohydrate, which is vital for numerous body func- tions.

2. False. In fact, infants have higher amounts of lactase, the enzyme necessary for lactose digestion, due to their initial diet of breast milk. As people get older, however, their bodies produce less of this enzyme, which can result in the condition of lactose intolerance.

3. False. Kilocalories, not carbohydrates, are the main cul- prit behind most weight gain. In fact, some high-fiber carbohydrates can actually help people lose weight.

4. False. There is insufficient evidence to suggest that eating sugar causes hyperactivity or other behavioral problems in children.

5. True. Whole grains contain more fiber and nutrients than refined grains, which have had much of the grain kernel removed during processing.

6. True. Simple carbohydrates, especially added sugars, en- courage the growth of acid-producing bacteria in the mouth, which in turn promote dental caries.

7. False. There is no scientific evidence to support claims that aspartame causes cancer or other health problems in humans.

8. True. The average American consumes about half the amount of fiber that’s recommended daily.

9. True. Much of the added sugars and excess kilocalories in the American diet come from sodas and other sugary beverages. Consuming more kilocalories than are neces- sary to meet energy needs causes weight gain.

10. True. Being overweight or obese can increase one’s chances of developing type 2 diabetes.

Web Support ■ For more on fiber, visit the American Heart Association at

www.americanheart.org ■ For more on diabetes, visit the FDA’s Diabetes Information

site at www.fda.gov/diabetes/ or the American Diabetes Association website at www.diabetes.org

■ For more on lactose intolerance, visit the National Institute of Diabetes and Digestive and Kidney Disease (NIDDK) at http://digestive.niddk.nih.gov/ddiseases/ pubs/lactoseintolerance

References 1. Johnson, M. 2008. Human Biology: Concepts and Current Issues. 4th ed.

San Francisco: Benjamin Cummings. 2. Painter, J., J. Rah, and Y. Lee. 2002. Comparison of International Food

Guide Pictorial Representations. Journal of the American Dietetic Associa- tion 102:483–489.

3. Bray, G. A., S. J. Nielsen, and B. M. Popkin. 2004. Consumption of High- Fructose Corn Syrup in Beverages May Play a Role in the Epidemic of Obesity. The American Journal of Clinical Nutrition 79:537–543.

4. Riegel’s Handbook of Industrial Chemistry. 2003. 10th ed. P. James and A. Kent, eds. New York: Kluwer Academic/Plenum Publishers.

5. Laeng, B., K. C. Berridge, and C. M. Butter. 1993. Pleasantness of a Sweet Taste During Hunger and Satiety: Effects of Gender and “Sweet Tooth.” Appetite S21:247–254.

6. Zellner, D. A., A. Garriga-Trillo, E. Rohm, S. Centeno, and S. Parker. 1999. Food Liking and Craving: A Cross-Cultural Approach. Appetite 33:61–70.

7. Bretz, W. A., P. M. Corby, M. R. Melo, M. Q. Coelho, S. M. Costa, M. Robinson, N. J. Schork, A. Drewnowski, and T. C. Hart. 2006. Heri- tability Estimates for Dental Caries and Sucrose Sweetness Preference. Archives of Oral Biology 51:1156–1160.

8. Higgins, J. A., D. R. Higbee, W. T. Donahoo, I. L. Brown, M. L. Bell, and D. H. Bessesen. 2004. Resistant Starch Consumption Promotes Lipid Oxidation. Nutrition and Metabolism. Available at www. nutritionand metabolism.com/content/pdf/1743-7075-1-8.pdf. Accessed March 2008.

9. Ibid. 10. Robertson, M. D., A. S. Bickerton, A. L. Dennis, H. Vidal, and K. N. Frayn.

2005. Insulin-Sensitizing Effects of Dietary Resistant Starch and Effects on Skeletal Muscle and Adipose Tissue Metabolism. American Journal of Clinical Nutrition 82:559–567.

11. Topping, D. L., M. Fukushima, and A. R. Bird. 2003. Resistant Starch as a Prebiotic and a Synbiotic: State of the Art. Proceedings for the Nutrition Society 62:171–176.

12. Zellner, D. A., et al. 1999. Appetite. 13. Bretz, W. A., et al. 2006. Archives of Oral Biology. 14. Institute of Medicine. 2006. Dietary Reference Intakes: The Essential Guide

to Nutrient Requirements. Washington, DC: The National Academies Press.

15. Osborn, H. and T. Kahn. 2000. Oligosaccharides: Their Synthesis and Bio- logical Role. Oxford Chemistry Masters: Oxford University Press.

16. Queiroz, K. S., A. C. de Oliveira, E. Helbig, S. M. Reis, and F. Carraro. 2002. Soaking the Common Bean in a Domestic Preparation Reduced the Contents of Raffinose-Type Oligosaccharides but Did Not Interfere with Nutritive Value. Journal of Nutritional Science and Vitaminology 48:283–289.

17. Boehm, G. and B. Stahl. 2007. Oligosaccharides from Milk. Journal of Nu- trition 137:847S–849S.

18. National Digestive Diseases Information Clearinghouse. 2002. Lactose In- tolerance. National Institutes of Health Publication No. 02-2751.

19. McBean, L. and G. Miller. 1998. Allaying Fears and Fallacies About Lac- tose Intolerance. Journal of the American Dietetic Association 98:671–676.

20. Johnson, A., J. Semenya, M. Buchowski, C. Enwonwu, and N. Scrimshaw. 1993. Correlation of Lactose Maldigestion, Lactose Intolerance, and Milk Intolerance. American Journal of Clinical Nutrition 57:399–401.

21. Ibid. 22. Suarez, F., D. Savaiano, and M. Levitt. 1995. A Comparison of Symptoms

After the Consumption of Milk or Lactose-Hydrolyzed Milk by People with Self-Reported Severe Lactose Intolerance. New England Journal of Medicine 333:1–4.

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170 Chapter 4 . Carbohydrates

23. McBean, L. and G. Miller. 1998. Journal of the American Dietetic Associa- tion.

24. Putnam, J., J. Allshouse, and L. Kantor. 2002. U.S. Per Capita Food Supply Trends: More Calories, Refined Carbohydrates, and Fats. Economic Re- search Service, Food Review 25:2–15.

25. Suarez, F., D. Savaiano, P. Arbisi, and M. Levitt. 1997. Tolerance to the Daily Ingestion of Two Cups of Milk by Individuals Claiming Lactose In- tolerance. American Journal of Clinical Nutrition 65:1502–1506.

26. Dehkordi, N., D. Rao, A. Warren, and C. Chawan. 1995. Lactose Malab- sorption as Influenced by Chocolate Milk, Skim Milk, Sucrose, Whole Milk, and Lactic Cultures. Journal of the American Dietetic Association 95:484–486.

27. Hertzler, S., B. Huynh, and D. Savaiano. 1996. How Much Lactose Is Low Lactose? Journal of the American Dietetic Association 96:243–246.

28. Lee, C. and C. Hardy. 1989. Cocoa Feeding and Human Lactose Intoler- ance. American Journal of Clinical Nutrition 49:840–844.

29. Johnson, A., J. Semenya, M. Buchowski, C. Enwonwu, and N. Scrimshaw. 1993. Adaptation of Lactose Maldigesters to Continued Milk Intakes. American Journal of Clinical Nutrition 58:879–881.

30. McBean, L. and G. Miller. 1998. Journal of the American Dietetic Associa- tion.

31. Sheard, N., N. Clark, J. Brand-Miller, M. Franz, F. Pi-Sunyer, E. Mayer- Davis, K. Kulkarni, and P. Geil. 2004. Dietary Carbohydrate (Amount and Type) in the Prevention and Management of Diabetes. Diabetes Care 27:2266–2271.

32. Foster-Powell, K. and J. Brand-Miller. 1995. International Tables of Glycemic Index. American Journal of Clinical Nutrition 62:871S–898S.

33. Roberts, S. 2000. High-Glycemic Index Foods, Hunger, and Obesity: Is There a Connection? Nutrition Reviews 58:163–169.

34. Ludwig, D. 2002. The Glycemic Index: Physiological Mechanisms Relat- ing to Obesity, Diabetes, and Cardiovascular Disease. Journal of the Amer- ican Medical Association 287:2414–2423.

35. Ibid. 36. National Digestive Diseases Information Clearinghouse. 2000.

Constipation. Available at http://digestive.niddk.nih.gov/ddiseases/pubs/ constipation. Accessed October 2007.

37. National Digestive Diseases Information Clearinghouse. 2002. Diverticu- losis and Diverticulitis. Available at http://digestive.niddk.nih.gov/ ddiseases/pubs/diverticulosis/index.htm. Accessed October 2007.

38. Rimm, E., A. Ascherio, E. Giovannucci, D. Spiegelman, M. Stampfer, and W. Willett. 1996. Vegetable, Fruit, and Cereal Fiber Intake and Risk of Coronary Heart Disease Among Men. Journal of the American Medical As- sociation 275:447–451.

39. Pietinen, P., E. Rimm, P. Korhonen, A. Hartman, W. Willet, D. Albanes, and J. Virtamo. 1996. Intake of Dietary Fiber and Risk of Coronary Heart Disease in a Cohort of Finnish Men: The Alpha-Tocopherol, Beta- Carotene Cancer Prevention Study. Circulation 94:2720–2727.

40. Wolk, A., J. Manson, M. Stampfer, G. Colditz, F. Hu, F. Speizer, C. Hen- nekens, and W. Willett. 1999. Long-Term Intake of Dietary Fiber and Decreased Risk of Coronary Heart Disease among Women. Journal of the American Medical Association 281:1998–2004.

41. Marlett, J., M. McBurney, and J. Slavin. 2002. Position of the American Dietetic Association: Health Implications of Dietary Fiber. Journal of the American Dietetic Association 102:993–1000.

42. Chandalia, M., A. Garg, D. Lutjohann, K. von Bergmann, S. Grundy, and L. Brinkley. 2000. Beneficial Effects of High Fiber Intake in Patients with Type 2 Diabetes Mellitus. New England Journal of Medicine 342:1392–1398.

43. Anderson, J., L. Allgood, J. Turner, P. Oeltgen, and B. Daggy. 1999. Effects of Psyllium on Glucose and Serum Lipid Responses in Men with Type 2 Diabetes and Hypercholesterolemia. American Journal of Clinical Nutri- tion 70:466–473.

44. Institute of Medicine. 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements.

45. Institute of Medicine. 2005. Dietary Reference Intakes for Energy, Carbohy- drate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Wash- ington, DC: The National Academies Press.

46. Terry, P., E. Giovannucci, K. B. Michels, L. Bergkvist, H. Hansen, L. Holm- berg, and A. Wolk. 2001. Fruit, Vegetables, Dietary Fiber, and Risk of Col- orectal Cancer. Journal of the National Cancer Institute 93:525–533.

47. National Cancer Institute. 2007. Prevention of Colorectal Cancer. Avail- able at www.cancer.gov. Accessed October 2007.

48. Miller, W., M. Niederpruem, J. Wallace, and A. Lindeman. 1994. Dietary Fat, Sugar, and Fiber Predict Body Fat Content. Journal of the American Dietetic Association 94:612–615.

49. Appley, P., M. Thorogood, J. Mann, and T. Key. 1998. Low Body Mass Index in Non-Meat Eaters: The Possible Roles of Animal Fat, Dietary Fibre and Alcohol. International Journal of Obesity-Related Metabolic Dis- orders 22:454–460.

50. Liu, S., W. Willett, J. Manson, F. Hu, B. Rosner, B. Rosner, and G. Colditz. 2003. Relation between Changes in Intakes of Dietary Fiber and Grain Products and Changes in Weight and Development of Obesity among Middle-Aged Women. American Journal of Clinical Nutrition 78:920–927.

51. Bazzano, L., Y. Song, V. Bubes, C. Good, J. Manson, and S. Liu. 2005. Di- etary Intake of Whole and Refined Grain Breakfast Cereals and Weight Gain in Men. Obesity Research 13:1952–1960.

52. National Digestive Diseases Information Clearinghouse. 2005. Diabetes Overview. Available at www.niddk.nih.gov. Accessed October 2007.

53. Centers for Disease Control and Prevention. 2007. Diabetes: Disabling Disease to Double by 2050. Available at www.cdc.gov. Accessed October 2007.

54. National Digestive Diseases Information Clearinghouse. 2005. Diabetes Overview.

55. American Diabetes Association. 2006. Diagnosis and Classification of Di- abetes Mellitus. Diabetes Care 29:S43–S48.

56. National Digestive Diseases Information Clearinghouse. 2005. Diabetes Overview.

57. Ibid. 58. Centers for Disease Control and Prevention. 2007. Diabetes: Disabling

Disease to Double by 2050. 59. American Diabetes Association. 2003. Tests of Glycemia in Diabetes.

Diabetes Care 26:S106–S108. 60. National Diabetes Information Clearinghouse. 2001. Diabetes Control

and Complications Trial (DCCT). Available at www.diabetes.niddk.nih .gov. Accessed October 2007.

61. American Diabetes Association. 2002. Evidence-Based Nutrition Princi- ples and Recommendations for the Treatment and Prevention of Diabetes and Related Complications. Diabetes Care 25:202–212.

62. Diabetes Prevention Program Research Group. 2002. Reduction in the In- cidence of Type 2 Diabetes with Lifestyle Intervention or Metformin. New England Journal of Medicine 346:393–403.

63. Ibid. 64. Mavropoulos, J., W. Yancy, J. Hepburn, and E. Westman. 2005. The Effects

of a Low-Carbohydrate, Ketogenic Diet on the Polycystic Ovary Syn- drome: A Pilot Study. Nutrition & Metabolism 2:35.

65. Azziz, R., K. S. Woods, R. Reyna, T. J. Key, E. S. Knochenhauer, and O. B. Yildiz. 2004. The Prevalence and Features of the Polycystic Ovary Syndrome in an Unselected Population. Journal of Clinical Endocrinology & Metabolism 89:2745–2749.

66. National Digestive Diseases Information Clearinghouse. 2003. Hypo- glycemia. National Institutes of Health Publication No. 03–3926.

67. Putnam, J., J. Allshouse, and L. Kantor. 2002. U.S. Per Capita Food Supply Trends: More Calories, Refined Carbohydrates, and Fats. Economic Re- search Service, Food Review 25:2–15.

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References 171

68. Schorin, M. 2005. High Fructose Corn Syrups Part 1: Composition, Con- sumption, Metabolism. Nutrition Today 40:248–252.

69. Howard, B. and J. Wylie-Rosett. 2002. Sugar and Cardiovascular Disease: A Statement for Healthcare Professionals from the Committee on Nutri- tion of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association. Circulation 106:523–527.

70. American Dietetic Association. 1998. Position of the American Dietetic Association: Use of Nutritive and Nonnutritive Sweeteners. Journal of the American Dietetic Association 98:580–587.

71. Ibid. 72. Calorie Control Council. 2006. Reduced Calorie Sweeteners: Hydro-

genated Starch Hydrolysates. Available at www.caloriecontrol.org. Ac- cessed November 2007.

73. Report on Carcinogens. 9th ed. 2000. U.S. Department of Health and Human Services. Public Health Service, National Toxicology Program.

74. Ajinomoto USA, Inc. 2006. The History of Aspartame. Available at www .aspartame.net/media/history.html. Accessed November 2007.

75. Council on Scientific Affairs. 1985. Aspartame: Review of Safety Issues. Journal of the American Medical Association 254:400–402.

76. American Diabetes Association. 2003. Evidence-Based Nutrition Princi- ples and Recommendations for the Treatment and Prevention of Diabetes and Related Complications. Diabetes Care 26:S51–S61.

77. National Institutes of Health. 2000. Report of the NIH Consensus Devel- opment Conference on Phenylketonuria (PKU): Screening and Manage- ment. Available at www.nichd.nih.gov. Accessed November 2007.

78. Mayer, D. G. and F. H. Kemper. 1991. Acesulfame-K. Boca Raton, FL: CRC Press.

79. The Nutra Sweet Company. 2002. Neotame: A Scientific Overview. Avail- able at www.neotame.com. Accessed November 2007.

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Fats, Oils, and Other Lipids

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1. Cholesterol should be consumed daily to meet the body’s needs. T/F

2. A healthy diet is fat free. T/F

3. Only commercially made fried foods and snack items contain trans fats. T/F

4. Saturated fat is a major dietary factor for elevated blood cholesterol. T/F

5. You can eat as many fat-free cookies as you want without gaining weight. T/F

6. A high level of HDL cholesterol in the blood is considered heart healthy. T/F

7. Butter is a healthier choice than margarine. T/F

8. Nuts are high in cholesterol. T/F

9. Taking fish oil supplements is the best way to consume adequate omega-3 fatty acids. T/F

10. Dietary LDL cholesterol is unhealthy for the heart. T/F

See page 219 for answers.

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174 Chapter 5 . Fats, Oils, and Other Lipids

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What Are Lipids and Why Are They Important? When you think of the word lipid, you may think it’s a synonym for fat. That’s not entirely correct. Whereas “lipo” means fatty, lipids actually refer to a category of compounds that includes triglycerides (fats and oils), sterols, and phospholipids. These compounds all contain carbon, oxygen, and hydrogen and they are all hydrophobic (hydro = water, phobic = fearing). In other words, they don’t dissolve in water. If you were to drop lipids like butter or olive oil into a glass of water, you would see these substances rise to the top and sit on the water’s surface. This re- pelling of water allows lipids to play a unique role in foods and in the body.

Whereas the popular press often portrays lipids as bad or unhealthy, the reality is that lipids serve several basic functions for maintaining health. In the body, lipids store and provide energy, provide insulation, help manufacture steroids and bile salts, and play a key role in transporting fat-soluble nutrients in the blood. They are also used to manufacture the major sex hormones, and one type of lipid is key to the structure of cell membranes.

We’ll begin the discussion of lipids by introducing the chemical structure of the various forms, starting with fatty acids.

The Take-Home Message Lipids are hydrophobic compounds made up of carbon, hydrogen, and oxygen. The three types of lipids are triglycerides, phospholipids, and sterols. Lipids provide and store energy for the body, trans- port fat-soluble nutrients, provide insulation, and are used to synthesize bile salts, sex hormones, and cell membranes.

I t’s October and Heather just returned to school after spending a long week- end at home with her parents. She had

gone home to visit her 52-year-old mother Patricia, who hadn’t been feeling very well lately. Patricia, who owns her own business, also takes care of her eld- erly mother, is in the late stages of menopause, and is a worrywart when it comes to her family, especially with her daughter being away from home. The stress in her life and change in hormones is starting to take its toll on Patricia. The past few weeks she has experienced difficulty breathing, ex- treme fatigue, and nausea. She wonders if these symptoms are just part of menopause, or whether they could indicate some- thing more serious.

Heather is worried her mother might be developing coronary heart disease, but Patricia thinks Heather is overreacting. After all, she doesn’t have any chest pain and there isn’t a family

history of heart disease. Patricia thinks she’s experiencing these symptoms because she works long hours, gets little exercise, and is 15 pounds overweight. She is not concerned about her serum cholesterol level of 260 mg/dl nor the fact that that she loves to eat high-fat animal products such as cheese and high-fat meats.

Do you think Heather is right to be concerned about her mother’s potential heart disease? What else might be caus- ing Patricia’s fatigue? Are there certain

foods or nutrients that Patricia should limit or add to her diet to reduce her risk of cardiovascular disease?

In this chapter, we will discuss the structure and functions of the different types of lipids, how they are handled in the body, and the amounts of each that should be consumed in a healthy diet. We will also explore the role of high-fat foods on the devel- opment of cardiovascular disease and other health conditions.

Chapter Objectives After reading this chapter, you will be able to:

1. Describe the three classifications of lipids.

2. Explain the differences in the structure of triglycerides, phos- pholipids, and cholesterol.

3. Describe how lipids are digested and absorbed in the body.

4. Explain how lipids are transported in the blood.

5. Describe the functions of lipids in the body.

6. Define the dietary recommenda- tions for total fat, the essential fatty acids, cholesterol, and trans fat.

7. Identify the major food sources of the different types of fats, includ- ing the essential fatty acids, satu- rated fats, and trans fats.

8. Compare the different fat substi- tutes currently used in food products.

9. Describe the development of ath- erosclerosis, including its role in the risk of heart disease.

10. Explain how lifestyle factors can affect the risk for cardiovascular disease.

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fatty acid The most basic unit of triglyc- erides and phospholipids; fatty acids con-

sist of even numbers of carbon chains

ranging from two to 80 carbons in length.

What Are Fatty Acids? 175

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What Are Fatty Acids? Triglycerides and phospholipids are built from a basic unit called a fatty acid. All fatty acids (Figure 5.1) are organic compounds that consist of chains of carbon and hydrogen atoms, with an acid group (called a car- boxyl group, abbreviated as COOH) at one end (the alpha end) and a methyl group (CH3) on the other end (the omega end). The ratio of car- bon and hydrogen to oxygen accounts for the higher number of kilocalo- ries in fat (9 kilocalories per gram) than in carbohydrates and proteins (4 kilocalories per gram).

There are over 20 different fatty acids. They vary in structure by the length of the carbon chain, degree of saturation, and shape.

Fatty Acids Vary in Length The carbon chains of most naturally occurring dietary fatty acids contain two to 80 carbons (usually in even numbers), with the most common fatty acids containing 12 to 24 carbons. If the fatty acid is two to four carbons long, it is a short-chain fatty acid. The shortest fatty acid, acetic acid, contains two carbons and is illustrated in Figure 5.2a. Fatty acids with six to 10 carbons are called medium-chain fatty acids, and those with 12 or more carbons are called long-chain fatty acids. Long-chain fatty acids are the most common type of fatty acid found in foods.

Long-chain fatty acids are strongly attracted to one another so they are able to pack tightly together; foods that contain predominantly long-chain fatty acids thus tend to be solid at room temperature. Shorter saturated fatty acids have a weaker at- traction to one another so do not pack tightly together. Because of this, foods that contain them are liquid at room temperature. Whole milk is an example of a food that contains medium- and short-chain fatty acids.

Fatty Acids Vary in Saturation Every carbon molecule has four bonds, and if there are not enough hydrogens to complete or saturate) those bonds, then the carbons will form a double bond with each other. When all of the carbons on a fatty acid are bound with hydrogen, a saturated fatty acid is formed. In contrast, if a fatty acid has carbons that are not bound to hydrogen, but rather to each other so that one or more double bonds are created, the structure is called an unsaturated fatty acid.

Palmitic acid (Figure 5.2b) is an example of a saturated fatty acid, because all of its 14 carbons are bound with hydrogen and none are double bound to each other. In contrast, two of the 18 carbons in oleic acid (Figure 5.2c) are paired with each other rather than hydrogen, forming one double bond. This lone double bond makes oleic acid a monounsaturated fatty acid (MUFA) (mono = one). A polyunsaturated fatty acid (PUFA) (poly = many) contains two or more double bonds, and is less saturated with hydrogen. Linoleic acid, shown in Figure 5.2d, is an example of a polyunsatu- rated fatty acid.

Double bonds cause a kink in the chain of the fatty acid, which inhibits fatty acids from packing together tightly. Thus, unsaturated fatty acids are liquid at room temperature. (Fats that are liquid at room temperature are called oils). The mono- unsaturated fatty acid oleic acid is found in olive oil, and the polyunsaturated fatty acids, linoleic acid and alpha-linolenic acid, are found in soybean oil.

hydrophobic “Water fearing.” In nutri- tion, the term refers to compounds that

are not soluble in water.

phospholipids A category of lipids that consist of two fatty acids and a phospho-

rus group attached to a glycerol backbone.

Lecithin is an example of a phospholipid

found in food and in the body.

sterols A category of lipids that contains four connecting rings of carbon and

hydrogen. Cholesterol is the most common

sterol.

triglycerides A type of lipid commonly found in foods and the body; also known

as fat. Triglycerides consist of three fatty

acids attached to a glycerol backbone.

lipid A category of carbon, hydrogen, and oxygen compounds that are insoluble in

water.

Chain of carbons of various lengths

C

H

H C

H

H

C

C

H

H

H

H C

H

H

C

H

H C

H

H

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H C

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H

C

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H C H

H

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a Carboxylic acid group

b A methyl group (CH3) c

Figure 5.1 Chemical Structure of a Fatty Acid The basic chemical structure of a fatty acid is composed of three different parts.

short-chain fatty acid A fatty acid with a chain of two to four carbons.

medium-chain fatty acids Fatty acids with a chain of six to 10 carbons.

long-chain fatty acids Fatty acids with a chain of 12 carbons or more.

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oils Fats that are liquid at room temperature.

polyunsaturated fatty acid (PUFA) A fatty acid with two or more double bonds.

176 Chapter 5 . Fats, Oils, and Other Lipids

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c

C

H

H C

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HO

C

b Palmitic acid, a saturated fatty acid (C14 : 0)

C

H

H C

H

H

C

H

H C

H

H

C

H

H C

H

H

C

H

H C

H

H

C

H

H C

H

H

C

H

H C

H

H

C

H

H

C

H

C

H

H

C H

H

H

C

H

H

C

C

H

H

C H

H C

H

H C

H

H C

H

H C

H

H H

O

C C

H

H

Oleic acid, a monounsaturated fatty acid (C18 : 1)

a Acetic acid (C2 : 0)

Double bond in carbon chain creates a bend

C

H

H C

H

H

C

H

H C

H

H

C

H

H C

H

H

C

H

C

H

H

O

C C

H

H

Linoleic acid, a polyunsaturated fatty acid (C18 : 2)

2 double bonds create 2 bends

HO

C

H

H

C

C

H

H

C H

H C

H

H

C H

C H

H C HH

H

C

H

H C

H

H

C

H

H C

H

H

C

H

H C

H

H

C

H

C

H

H

O

C C

H

H

3 double bonds create 3 bends

d

Alpha-linolenic acid, a polyunsaturated, omega-3 fatty acid (C18 : 3)e

Figure 5.2 Fatty Acids Vary by Length, Degree of Saturation, and Shape Fatty acids differ by the number of carbons in the chain, whether or not the chain contains any double bonds (the saturation of the fatty acid), and the shape of the carbon chains on either side of the double bonds.

monounsaturated fatty acid (MUFA) A fatty acid that has one double bond.

unsaturated fatty acid A fatty acid in which there are one or more double bonds

between carbons.

saturated fatty acid A fatty acid in which all of the carbons are bound with

hydrogen.

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essential fatty acids The two polyun- saturated fatty acids that the body cannot

make and therefore must be eaten in

foods: linoleic acid and alpha-linolenic

acid.

alpha-linolenic acid A polyunsatu- rated essential fatty acid; part of the

omega-3 fatty acid family.

linoleic acid A polyunsaturated essen- tial fatty acid; part of the omega-6 fatty

acid family.

omega-6 fatty acid A family of polyunsaturated fatty acids with the first

double bond located at the sixth carbon

from the omega end.

omega-3 fatty acid A family of polyunsaturated fatty acids with the first

double bond located at the third carbon

from the omega end.

a Saturated fatty acids

Unsaturated fatty acidsb

Figure 5.3 Saturated and Unsaturated Fatty Acids Help Shape Foods The straight chains of saturated fatty acids pack tightly together and are solid at room temperature. The double bonds in unsaturated fatty acids cause kinks in their shape and prevent them from packing tightly together, so they tend to be liquid at room temperature.

The length of the fatty acid chain and the presence of double bonds between carbons will also determine the melting point of a fat, or the temperature at which it changes from a solid to liquid (Figure 5.3). In general, straight, long-chain saturated fatty acids have higher melting points than do unsaturated fatty acids. This is be- cause the saturated fatty acids can stack closer together and interact with one an- other. This results in higher melting points. The more bends in the chain due to double bonds reduces the interaction between the molecules and produces a fatty acid with a lower melting point. The lower melting points of shorter chain and un- saturated fatty acids mean they tend to be liquid at room temperature. For example, the triglycerides found in cocoa butter are made up of short-chain fatty acids and melt at body temperature. This is why solid milk chocolate melts in the mouth.

Fatty Acids Differ in the Location of the Double Bond The location of the first double bond from the methyl (or omega) end of the fatty acid chain also affects the properties of a fatty acid (Figure 5.4). If the first double bond in a polyunsaturated fat is located between the third and fourth carbon from the omega end, it is referred to as an omega-3 fatty acid. If the first double bond is between car- bons six and seven from the omega end, it is called an omega-6 fatty acid.

Linoleic acid is an omega-6 fatty acid. It has 18 carbons with two double bonds, the first of which is located on the sixth carbon from the omega end. Alpha- linolenic acid is an omega-3 fatty acid, and is the same length as the omega-6 (18 carbons) but has three double bonds, with the first double bond on carbon three from the omega end. These two fatty acids are called essential fatty acids because they must be obtained from foods.

Fatty Acids Vary in Their Shape Unsaturated fatty acids form two different shapes based on the position of the car- bon chains around the double bond. If the carbon chains are on the same side of

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Methyl end (ω)

Alpha-linolenic acid Acid end

3

Methyl end (ω)

Linoleic acid Acid end

6

H

C CH

H

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C O

O

H

C

H

H

C

H H

C

H

C

H

C

H

C CH

H

H

H H

C

H

H

C

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C O

O

H

C

H

H

C

H

H H

C

H

C

H

C

Figure 5.4 The Omega Fatty Acids Omega-3 and omega-6 fatty acids are named for the position of the first double bond from the omega (ω) end of the fatty acid.

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H

H

C

C C

C

O

C

H H

CC CC

C

Cis form

C CC

C H C C

C C

H

H

C

C C

O

C COH

OH

H

H

CC CC

C

Trans form

C

CC

C H C C

C C

cis Hydrogens are on the same side of the double bond

trans Hydrogens are on opposite sides of the double bond

Figure 5.5 The Cis and Trans Configurations of Unsaturated Fatty Acids

hydrogenation Adding hydrogen to an unsaturated fatty acid to make it more sat-

urated and solid at room temperature.

rancidity The spoiling of fats through oxidation.

trans The configuration of a fatty acid in which the carbon chains are on opposite

sides of the double bond.

cis The configuration of a fatty acid in which the carbon chains on each side of

the double bond are on the same side.

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the double bond, or both appear “up” or “down” as illustrated in Figure 5.5, the fatty acid has a cis configuration. If the fatty acid is twisted with one side of the car- bon chain on the opposite side of the double bond, it is a trans configuration.

Fatty Acids and Rancidity Foods that contain unsaturated fatty acids can develop a bitter, pungent smell or taste when exposed to oxygen. This rancidity results when fatty acids are oxidized, as the hydrogen next to the double bond is unstable and easily re- moved (Figure 5.6). The carbon becomes available to bond with oxygen, forming new compounds that cause the rancid smell and flavors.

Because double bonds are less stable than single bonds, foods that contain unsaturated fatty acids become rancid faster than foods with saturated fatty acids. Similarly, polyunsaturated fatty acids are more susceptible to rancidity than monounsaturated fatty acids because they have more double bonds. Flax oil, which is rich in polyunsaturated fatty acids, is more susceptible to oxida- tion than corn oil, which contains more saturated and monounsaturated fatty acids. Saturated fatty acids have no double bonds, and are thus much less sus- ceptible to oxidation.

Enhancing the Stability of Fatty Acids Food manufacturers have tested various ways to reduce rancidity, including adding an- tioxidants to hinder the oxidation process. Antioxidants bond with available hydro- gens, thereby preventing oxygen from attacking the bonds. Vitamins such as C and E are natural antioxidants but lack the shelf life of synthetic antioxidants such as buty- lated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Chapter 20 dis- cusses the use of antioxidants in further detail.

Rancidity can also be reduced by limiting the food’s exposure to oxygen, heat, and light. Storing oils and fats in airtight containers, in a cool, dry, and dark location will lessen the formation of free radicals, which contribute to the rancidity of foods. Another method used to stabilize unsaturated fatty acids is a process called hydrogenation. Hydrogenation involves heating oil and exposing it to hydrogen gas, which adds hydrogen to the carbons in the double bonds, making the fatty acids

H

C CCOOH

H

H

C

H

H

HC

H

H

H

C

H

C

H

C

H

C CCOOH

H

C

H

H

H H++C

H

H

H

C

H

C

H

C

Figure 5.6 Rancidity Reaction of a Fatty Acid When fatty acids become oxidized, the chemical structure is altered, creating the off smell and flavors characteristic of rancid food.

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more saturated. This process gives crackers and snack foods a longer shelf life, im- proves the texture of pastries, and makes french fries crisper. Hydrogenation makes liquid oils become more solid at room temperature. It is less expensive and provides a “mouthfeel” like butter. We will discuss the use of hydrogenation in more detail later in the chapter.

The Take-Home Message Fatty acids, which consist of a carbon and hydrogen chain, a carboxylic acid, and a methyl group, are the basic struc- tural units of triglycerides and phospholipids. Fatty acids differ in chain length, degree of saturation, and shape. Fatty acids with no double bonds are saturated fatty acids, while those with one or more double bonds are ei- ther mono- or polyunsaturated fatty acids. Omega-3 and omega-6 fatty acids are polyunsaturated fatty acids with their first double bond on the third and sixth carbon, respectively, from the methyl end. The two essential fatty acids, linoleic and alpha-linolenic acid, cannot be made in the body and must be consumed in foods. Fatty acids can become spoiled from oxidation, so food manufacturers may hydrogenate them to be more saturated, or add antioxi- dants to make them less susceptible to rancidity.

What Are Triglycerides? The most common lipid in both foods and the body is the triglyceride (commonly called fat), which makes up about 95 percent of the lipids found in food. A triglyc- eride molecule consists of three fatty acids connected to a glycerol (glyc = sweet,

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Fatty acids are frequently represented by two different methods of notation. The first method, the delta (Δ) system, is often used by chemists (see figure below). In this form, the first number indicates the number of carbons in the chain. The second number, after the colon, notes how many double bonds are in the molecule. The two super- script numbers indicate the location of the two double bonds from the carboxyl end of the fatty acid.

The second method, called the omega (ω) system, is similar to the delta system. This system uses either the symbol ω or the letter n after the number of double bonds. This symbol notes the position of the first double bond from the omega (methyl) end of the fatty acid. In polyunsaturated fatty acids, double bonds are usually separated by three carbons. Using this notation makes it easy to locate the rest of the double bonds in a fatty acid molecule. With linoleic acid, the first double bond is located on carbon 6, followed by the second double bond on carbon 9.

Delta system describing linoleic acid:

18:2 �9,12

Omega system describing linoleic acid:

C18:2, n–6

18 carbons 2 double omega-6 long bonds

Chemistry Boost

glycerol The three-carbon backbone of a triglyceride.

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C

H

H OH

C + + 3 H=H OH C

H

H OH

C

H

H O

CH O

C

H

H O

Three fatty acids

A fat (triglyceride)

Palmitic acid (16 : 0)

Palmitic acid

Oleic acid

Stearic acid

Glycerol backbone

C

H

H

C

H

H

C

O Water

H

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C H

H

H

C

O

Oleic acid (18 : 1)

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

O

Stearic acid (18 : 0)

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C H

H

H

C

O

H

Figure 5.7 Structure of a Triglyceride A triglyceride is formed when three fatty acids attach to a glycerol backbone with a condensation reaction. Adapted from J. L. Smith, S. S, Gropper, and J. L. Groff. 2005. Advanced Nutrition and Human Metabolism. 4th ed. Thomson Wadsworth.

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ol = alcohol) backbone, which contains three alcohol (OH) groups. Through a condensation reaction, a hydrogen from the glycerol bonds with the hydroxyl group (OH) of the fatty acid, attaching the fatty acid to the glycerol (Figure 5.7). A molecule of water is released in the process. A variety of fatty acids can bond with the same glycerol backbone, so a triglyceride usually contains a mixture of fatty acids. Thus, canola oil is not just composed of polyunsaturated fatty acids; there are also small amounts of saturated and monounsaturated fats present.

Triglycerides perform a variety of functions in food, including adding flaky tex- ture to pie crusts and other baked goods, and making meat tender. Triglycerides are also important in food processing, particularly when it comes to preserving fresh- ness. In the body, triglycerides are carried through the blood and stored in the adi- pose tissue to provide a major source of available energy. Higher levels of triglycerides in the blood are a risk factor associated with heart disease. This topic will be covered later in the chapter.

The Take-Home Message Triglycerides, or fats, consist of three fatty acids attached to a glycerol backbone by condensation reactions. Triglyc- erides are found in blood, stored in the adipose tissue, and are a major source of energy to the body.

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What Are Phospholipids? Like fats, phospholipids contain a glycerol backbone, but instead of three fatty acids, the glycerol is linked to two fatty acids, a phosphorus group, and different nitrogen- containing compounds such as choline (Figure 5.8). The glycerol backbone and phosphorus group form a polar head, which means it attracts charged particles, such as water. The fatty acid–containing tail is nonpolar, and therefore soluble with other nonpolar molecules, such as fats. In other words, one end of the phospholipid is hy- drophilic (philic = loving) and the other end is hydrophobic.

Phospholipids make up the phospholipid bilayer in cell membranes. Their hy- drophilic heads are attracted to the watery fluids both outside and inside of the cells, and their hydrophobic tails line up with each other in the center, creating a phospholipid barrier that surrounds the cell (Figure 5.9 on the next page). The cell membrane allows certain substances, such as water, to enter the cell but keeps oth- ers, like protein, from leaking out. Visualize this phospholipid layer as similar to a picket fence, protecting the cells as a gated fence would surround and protect a piece of property.

The major phospholipid in cell membranes is lecithin. As shown in Figure 5.8, lecithin, also called phosphatidylcholine, contains a choline group attached to the phosphate on the third carbon of the glycerol backbone. The fatty acids, phosphate and choline, give the phospholipid both fat-soluble and water-soluble properties, which allow it to shuttle other lipids across the cell membranes.

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+

+

=

Two fatty acids

Fatty acid 1

Fatty acid 2

Phosphate group

Glycerol

Choline

Nonpolar tail (hydrophobic = repels water)

Phospholipid Choline

Polar head (hydrophilic = attracts water)

N + 3

H3C

CH3

CH3

CH2 HC

2

CH2

C

H

H

1 OC

H

H

P

C

O

O C

O

C

H

H

C

H

C

H

C

H

H

C

H

C

H

C

H

H

H

C

H

H

C

H

C

H

C

H

H

C

H

C

H

C

H

H

H

Figure 5.8 Phospholipids Phospholipids, such as the lecithin shown here, are similar in structure to triglycerides, but they have only two fatty acids and a phosphate group connected to the glycerol backbone. This configuration allows phospholipids to be attracted to both water and fat.

choline A member of the B vitamin family that is a component of the

phospholipid lecithin.

lecithin A phospholipid made in the body that is integral in the structure

of cell membranes; also known as

phosphatidylcholine.

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Cell membrane

Outside of cell (watery extracellular fluid)

Cell

Inside of cell (watery cytoplasm)

Phospholipid head

Protein

Phospholipid head

Cholesterol

Phospholipid tails

Phospholipid tails

Figure 5.9 Phospholipids’ Role in Cell Membranes Because the phosphorus-containing head is polar, it attracts charged particles, such as water, which is the main component of fluids outside and inside the cells. The phospholipid’s fatty acid–containing tail is nonpolar, so it lines up with other nonpolar molecules, such as the fatty acid–containing ends of other phospholipids. This creates a two-layer membrane that surrounds the cell and acts as a barrier, allowing certain substances to enter the cell but keeping others from leaving.

Water

Emulsifier (lecithin, a phospholipid)

Fat droplet

Figure 5.10 Keeping a Salad Dressing Blended Emulsifiers are often added to salad dressing to keep the oil part of the dressing blended in the watery solution. When a salad dressing does separate, it is usually because it doesn’t contain an emulsifier.

emulsifier A compound that keeps two incompatible substances, such as oil and

water, mixed together.

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Even though lecithin plays an important role in the body, it does not need to be consumed in foods or in supplements, because the liver is able to synthesize all phos- pholipids, including lecithin. In fact, dietary lecithin is digested in the GI tract, which means it does not reach the cell membranes intact. Despite their frequent mention in the popular press, lecithin supplements, which are often marketed as a miracle solu- tion for weight loss, fat metabolism, cardiovascular health, exercise performance, and arthritis relief, have not been scientifically proven to be effective in weight loss or im- proving health. In addition, the fatty acids present in dietary phospholipids (which, like all lipids, contain 9 kilocalories per gram) can add unwanted kilocalories.

Because of its unique water- and fat-loving attributes, lecithin is used in many foods as an emulsifier, which helps keep incompatible substances, such as water and oil, mixed together. An emulsifier is sometimes added to commercially made salad dressings to prevent the fat from separating and rising to the top of the dressing (Figure 5.10). The emulsifier’s nonpolar, fat-attracting tail surrounds the droplets of fat, which orients the polar, water-attracting head toward the watery solution of the dressing. This keeps the fat droplet suspended and allows the water and the oil to stay blended together.

The Take-Home Message Phospholipids are made of two fatty acids and a phosphate group attached to a glycerol backbone. Phospholipids are an important part of the structure of cell membranes. The phospholipid lecithin plays important roles in cell membranes and as an emulsifier in foods.

cholesterol A common sterol found in animal products and made in the liver

from saturated fatty acids; cholesterol is

found in cell membranes and is used to

make a variety of hormones.

phytosterols Naturally occurring sterols found in plants.

lipases A group of lipid-digesting enzymes.

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What Are Sterols? Sterols are a much more complex molecule than phospholipids or triglycerides. They do not contain glycerol or fatty acids, but rather are composed mainly of four con- necting rings of carbon and hydrogen (Figure 5.11). Unlike the other lipids, sterols do not provide energy.

The best known sterol, cholesterol, is found in every cell in the body. It plays an important role as a structural component in cell membranes and is the precursor of some very important compounds. In cell membranes, cholesterol is interwoven with phospholipids to provide integrity to the cells (refer again to Figure 5.9). The unique shape of cholesterol makes the outer surface less soluble to very small molecules that could pass too easily across the cell membrane. Without cholesterol, the membrane would be too fluid and lack firmness; the cells in the body would need a cell wall sim- ilar to plants to maintain their shape. Cholesterol also helps keep phospholipids sep- arate from each other so that the tails or fatty acid chains of the phospholipid don’t crystallize. In this way, cholesterol improves cell fluidity.

Another key role of cholesterol is to serve as the starting material in the synthe- sis of steroid hormones, including the sex hormones estrogen and testosterone, and the adrenal corticoids such as cortisol and aldosterone. Cholesterol is used by the liver to manufacture bile, and a type of cholesterol in the skin is converted to a pre- vitamin D by the ultraviolet rays of the sun.

The majority of sterols found in plants are phytosterols, which are similar in structure to cholesterol. While there are over 40 different types of sterols found in plants, the most common are sistanol, campesterol, and stigmasterol. Plants also con- tain the stanols sitostanol and campestanol, which are more saturated than sterols.

Figure 5.12 summarizes the three types of lipids.

The Take-Home Message Unlike triglycerides and phospholipids, sterols do not contain fatty acids; they are made up of four connected rings of carbon and hydrogen. Sterols do not provide energy. The most well known sterol, cholesterol, is made in the liver and is found in the cell membranes; it is used as a precursor for bile, sex hormones, adrenal hormones, and vitamin D. Plant sterols are similar in structure to cholesterol.

What Happens to the Lipids You Eat? The lipids found in food are primarily in the form of fat and, to a lesser extent, phospholipids and sterols. During the diges- tion of fat, the fatty acids are removed from the glycerol back- bone by hydrolysis to form a combination of free fatty acids, glycerol, and monoglycerides. This action is accomplished by a group of enzymes called lipases (-ase = enzyme), which act on a specific site along the glycerol backbone.

CH2

HO

CH3 CH

CH3

CH2

CH2 CH3

CH3

CH

H3C

Cholesterol

CH2

HO

CH3 CH

CH

CH3

CH2

CH2 CH3

CH3

CH

CH3

H3C

Sistanol

Figure 5.11 Structure of a Sterol Sterols have a carbon ring configuration with hydrogens and an oxygen attached. Cholesterol is the best-known sterol found in animal products. Sistanol is a common sterol found in plants.

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Lipid

Triglycerides Saturated fat

Unsaturated fat

Trans fat

Fatty acids

Structure Examples

Glycerol

Phospholipids Lecithin

Fatty acids

Polar head

Sterols Cholesterol

HO

Sistanol

HO

Figure 5.12 Three Types of Lipids The three types of lipids vary in structure. Triglycerides and phospholipids are built from fatty acids, while sterols are composed of carbon rings.

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In the mouth, mastication begins the mechanical digestion of food. Solid fat melts with the warmth of the body. Lingual lipase in the saliva begins the chemical digestion of fats.

a

By-products of lipid digestion are absorbed into the small intestinal cells where they are repackaged into triglycerides.

d

In the stomach, peristalsis mixes and churns the fat-containing food with gastric juices. In infants, lingual lipase continues to hydrolyze fats, creating diglycerides and one free fatty acid. Gastric lipase has a small role in fat digestion.

b

In the small intestine, bile acids secreted from the gallbladder through the common bile duct into the duodenum emulsify fat into smaller globules. The pancreas secretes pancreatic lipase through the pancreatic duct into the small intestine to hydrolyze the triglycerides into monoglycerides, glycerol, and free fatty acids.

c

Blood vessel

Lymph vessel

Esophagus

Liver

Gallbladder

Stomach

Hepatic duct

Common bile duct

Pancreatic duct

Pancreas

Small intestine

Intestinal cells

Inside of small intestine

Micelles (free fatty acids and bile salts)

Chylomicrons

Figure 5.13 Digesting and Absorbing Fat

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Very Little Fat Digestion Occurs in the Mouth or the Stomach The digestion of fat begins in the mouth as the warmth of the body begins to melt fats. As chewing continues and food mixes with saliva, lingual lipase (secreted from the glands located at the base of the tongue) begins to hydrolyze the medium-chain fatty acids (Figure 5.13a). Lingual lipase is structurally different from the other li- pases found in the body, and it can hydrolyze fatty acids from any of the three carbons of the glycerol molecule. Lingual lipase can also function in the acid environment of the stomach before being inactivated. Because adults produce sufficient pancreatic li- pase, lingual lipase is probably not significant in fat digestion in adults.

diglyceride A remnant of fat digestion that consists of a glycerol with two at-

tached fatty acids; also the form of fat used

as an emulsifier in food production.

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Once the food enters the stomach, the hormone gastrin is released from the G cells in the gastric pits lining the stomach. Gastrin in turn stimulates the release of gastric juices, rich in gastric lipase, from the chief cells. Fat mixes with the gastric lipase, and the enzyme hydrolyzes one fatty acid from the triglyceride, which produces a free fatty acid and a diglyceride (Figure 5.13b).

Most Fat Is Digested and Absorbed in the Small Intestine The majority of fat digestion occurs in the small intestine (Figure 5.13c). Just as oil can’t disperse in water without the help of an emulsifier, the fat globules in chyme tend to cluster together rather than disperse in the watery digestive juices. The emulsifier that helps fats mix with the digestive juices in the small intestine is bile, the greenish liquid made in the liver and stored in the gallbladder. When the fat in chyme enters the duodenum, the hormone chole- cystokinin (CCK) is secreted, which in turn stimulates the gallbladder to release bile through the bile duct into the duodenum. The hydrophobic portions of the bile acids combine with the fat while the hydrophilic portion attracts the water in the digestive juices (Figure 5.14). This action reduces the fat globules to smaller droplets that are packaged in phospholipid carriers called micelles, which are easily dispersed throughout the fluids. Reducing the size of the fat globules also provides more surface area so that an- other enzyme, pancreatic lipase, can more easily hy- drolyze the fat.

Micelles also help transport the triglyceride rem- nants to the intestinal walls for absorption into the bloodstream. As pancreatic lipase continues to hy- drolyze the triglyceride into two free fatty acids and a monoglyceride, these components are added to the micelle and transported inside the intestinal cell.

Phospholipids and sterols are also emulsified by bile during digestion. Phospho- lipids are hydrolyzed by a group of enzymes called phospholipases. They dismantle the phospholipids, producing two free fatty acids and the phospholipid remnant, which are then packaged as micelles and transported through the intestinal wall. Sterols are not digested and are absorbed intact through the intestinal wall.

If lipids are not digested and prepared for absorption in the small intestine, the un- digested lipids bind to fiber and move into the large intestine, where they are eliminated in the feces. The large intestine does not have the enzymes necessary to digest lipids.

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Intestinal cell

Two fatty acids

Monoglycerides

Fat globule

Bile

Pancreatic lipase

Large fat globules are emulsified by bile salts into smaller fat droplets.

Emulsified fat droplets repel each other as they are suspended in water.

b

c Pancreatic lipase hydrolyzes the triglyce- rides into two fatty acids and monoglycerides.

d Monoglycerides and fatty acids are absorbed into the intestinal cell as micelles interact with the intestinal cell membranes.

a

Figure 5.14 Role of Bile in Emulsifying Fat As fat globules enter the small intestine, bile salts break them apart into smaller globules called micelles.

micelles Transport carriers in the small intestine that enable fatty acids and other

compounds to be absorbed.

monoglyceride A remnant of fat digestion that consists of a glycerol with

only one fatty acid attached to one of the

three carbons.

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Chylomicrons Facilitate Lipid Absorption Micelles are the carriers that transport digested fats and phospholipids from the GI tract into the intestinal cell. Once inside the intestinal cell, the different lipids are ab- sorbed based on their structure and the circulatory system. Glycerol and short- to medium-chain fatty acids can be absorbed into the bloodstream directly through the mucosa of the small intestine. They then enter the portal vein and go directly to the liver. Long-chain fatty acids must first be reassembled before being absorbed.

Once inside the intestinal cell, free long-chain fatty acids reattach to the glycerol molecule to reform a triglyceride. These fats, together with the other dietary lipids including phospholipids and cholesterol, are combined into a protein-containing transport carrier (or lipoprotein) called a chylomicron (Figure 5.15) and released into the lymph fluid (Figure 5.16).

lymph fluid Fluid that circulates through the body in lymph vessels and eventually

enters the bloodstream.

chylomicron A type of lipoprotein that carries digested fat and other lipids

through the lymph system into the blood.

Blood vessel

Albumin

Portal circulation

Direct absorption of medium- and short- chain fatty acids

Micelle

Phospho- lipids Free

fatty acids

Monogly- cerides

Glycerol Cholesterol

Chylomicron

Interior of small intestine

Intestinal cell

Chylomicron

Endoplasmic reticulum

Triglycerides

Proteins

Lacteal Lymph system

To bloodstream

To liver

Figure 5.16 Absorption of Dietary Lipids Short- and medium-chain fatty acids are absorbed from the intestinal cells directly into the bloodstream. Longer chain fatty acids, cholesterol, phospholipids, and other remnants are reassembled into chylomicrons and enter lymph before being routed into the bloodstream.

lipoprotein Capsule-shaped transport carrier that enables fat and cholesterol to

travel through the lymph and blood.

Cholesterol

Fat droplet (triglycerides)

Phospholipid

Protein

Figure 5.15 Structure of a Chylomicron A chylomicron contains a core of triglycerides and dietary lipids, surrounded by a coat of protein, phospholipids, and cholesterol.

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Chylomicrons are too large to be absorbed directly into the bloodstream, so they travel through the lymph system before entering the main circulation. They ulti- mately enter the bloodstream when the lymph fluid joins the blood through the tho- racic duct located next to the heart. As the chylomicrons travel through the blood en route to the liver, they interact with the enzyme lipoprotein lipase located in the walls of the capillaries. This enzyme hydrolyzes the fatty acids from the glycerol backbone so they can be stored in the cells.

Fatty acids are used by the heart and muscles as energy, or stored as an energy reserve in the fat cells. After the fat is removed from the chylomicrons, the remnants of these lipoproteins travel to the liver to be dismantled.

Lipoproteins Transport Fat Through the Lymph and Blood Chylomicrons are one form of lipoprotein, but there are three others important to the transport of fat in the body: very low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs). These lipoproteins are globular molecules comprised of a lipid center surrounded by a plasma membrane (refer again to the similarly shaped chylomicron in Figure 5.15). The density of each lipoprotein determines how it functions. Density is determined by the amount of lipid and protein each lipoprotein contains (Figure 5.17). The more protein in the lipoprotein, the higher its density. For example, VLDLs are composed mostly of triglycerides and contain the least amount of protein. The opposite is true for HDLs. These lipoproteins are smaller and contain more protein, which makes them more dense.

The role of the VLDLs is to transport triglycerides and cholesterol away from the liver to the cells, where they interact with lipoprotein lipase (Figure 5.18a on the next page). This enzyme resides on the surface of the cells and hydrolyzes the fatty acids and glycerol from the core of the lipoprotein. As fat is deposited in cells and tissues, the ratio of protein to lipid increases. What began as a VLDL becomes an LDL, which continues to transport triglycerides to the cells. The LDLs are often referred to as the “bad” cholesterol carriers because they deposit cholesterol in the walls of the arteries, which can lead to heart disease (Figure 5.18b). To help remember this, think of the “L” in LDL as being “Lousy.”

The primary role of the HDLs is to pick up cholesterol from the body cells and re- turn it to the liver to be used to make bile, which is then either reabsorbed or excreted through the feces. In fact, approximately 25 percent of the cholesterol in blood is car- ried by HDLs back to the liver (Figure 5.18c). Because of this function, HDLs are often referred to as the “good” cholesterol. An easy way to remember this is to think of the “H” in HDL as referring to “Healthy.” HDLs begin as high-density molecules but as they pick up cholesterol from the cells, the percentage of lipid to protein changes and the density decreases. Thus, lipoproteins are constantly changing as they transport lipids throughout the body.

The level of LDL cholesterol relative to HDL cholesterol in the blood can be useful in determining the health of arteries. Essentially, the more HDL carriers in the blood, the harder the body is working to remove cholesterol from arterial cells and excrete it from the body. Higher levels of LDL carriers in the blood indicate that more fatty acids are being delivered to cells and deposited in the arterial walls and may contribute to blockage.

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Triglycerides 60%

Triglycerides 90%

5%

10%

5%

Triglycerides

Cholesterol 12%

Cholesterol 50%

20%

Cholesterol

Cholesterol

Phospholipids

Phospholipids

Phospholipids

Phospholipids 3%

Protein 10%

Protein 25%

Protein 50%

Protein 2%

HDL

LDL

VLDL

Chylomicron

Triglycerides

18%

15%

25%

Figure 5.17 Lipoproteins The ratio of protein to lipid determines the density of the lipoprotein (as well as its name). Chylomicrons are the largest of the lipoproteins and contain the least amount of protein.

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The Take-Home Message Most fat is digested in the small intestine with the help of emulsifying bile acids and pancreatic lipase. Short- and medium-chain fatty acids are absorbed directly into the bloodstream through the intestinal lining. Longer chain fatty acids and other remnants of fat diges- tion must first be packaged as part of a chylomicron lipoprotein carrier, and travel in the lymph before entering the bloodstream. Lipoproteins are globular- shaped transport carriers that have an outer shell high in protein and phospho- lipids and an inner core that carries the insoluble fat, as well as cholesterol and other lipids, through the lymph and bloodstream. The VLDLs and HDLs are synthesized in the liver. The VLDLs eventually become LDL cholesterol carriers after they have deposited some of the fatty acids they carry in the body’s cells. LDL cholesterol carriers deposit cholesterol in the cells and the arterial walls. HDL cholesterol carriers remove cholesterol from the arteries and deliver it to the liver to be used in the synthesis of bile or excreted in the feces.

How Does the Body Use Fat and Cholesterol? Once they are delivered to the tissues by lipoproteins, lipids serve several critical roles in the body. They are used as a source of energy, to form body structures (including cell membranes), regulate metabolism, enhance the absorption of fat-soluble vita- mins, provide a layer of insulation to help regulate body temperature, and help cush- ion the major organs.

high-density lipoproteins (HDLs) Lipoproteins that remove cholesterol from

the tissues and deliver it to the liver to be

used as part of bile and/or to be excreted

from the body. Because of this, HDL is

known as the “good” cholesterol.

low-density lipoproteins (LDLs) Lipoproteins that deposit cholesterol in

the walls of the arteries. Because this can

lead to heart disease, LDL is referred to as

the “bad” cholesterol.

very low-density lipoproteins (VLDLs) Lipoproteins that deliver fat made in the liver to the tissues. VLDL

remnants are converted into LDLs.

Figure 5.18 Roles of VLDL, LDL, and HDL Lipoproteins The VLDL, LDL, and HDL lipoproteins transport fat and cholesterol to and from the liver.

VLDL

LDL

HDL

Liver

Body cells

Fatty acids

Body cells (including arteries)

HDLs transport cholesterol from the body cells and deliver it to the liver for disposal.

VLDLs deliver fatty acid made in the liver to the cells.

a

c

LDLs transport cholesterol to the cells, in some cases into the arterial lining.

b

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FOCUS ON RESEARCH Wooten, J. S., K. D. Biggerstaff, and

C. Anderson. 2008. Response of Lipid, Lipoprotein-cholesterol, and

Electrophoretic Characteristics of Lipoproteins Following a Single Bout of Aerobic Exercise in Women. European

Journal of Applied Physiology 104:19–27.

Background

Physical activity and exercise have been shown to reduce triglyceride and increase HDL-cholesterol levels in the blood. The observed changes may be due to a reduction in the particle size. In men who have high cholesterol and triglyceride levels, exercise has also improved HDL- cholesterol and triglyceride levels up to 48 hours post exercise. Similar responses have not been measured in women at the same level of exercise and over a 48 hour period.

Objectives

The objective of this study was to report the effects of a single bout of moderate intensity aerobic exercise (65 percent VO2max that expended approximately

500 kcal) on serum lipid and lipoprotein- cholesterol concentrations including LDL and HDL particles in premenopausal women.

Study Design

Eleven premenopausal, non-smoking, sedentary women were recruited for the study. Participants fasted for at least 10 hours prior to each blood collection session. Participants walked on a tread- mill at 3.5 mph at a grade that elicited an

exercise intensity of 65 percent VO2max. Blood was collected immediately before the exercise and 24 hours and 48 hours post exercise and analyzed for triglyc- erides, total cholesterol, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), and the particle sub-fractions of HDL-C.

Results

Significant changes were observed for triglycerides and high density lipoprotein cholesterol over time (see table). Triglycerides were significantly reduced 25 percent at 48 hours post-exercise compared to baseline. HDL-C concentra- tions were reduced by 10.9 percent at 48 hours post-exercise compared to baseline. Total cholesterol and LDL-C did not significantly change over time.

Conclusion

The authors concluded that a single ses- sion of aerobic exercise that expended 500 kcal did not affect LDL and total cho- lesterol levels in premenopausal women but it did significantly reduce triglyceride and HDL-C levels.

QUESTIONS

1. What type of study design did the re- searchers use?

2. What factors other than exercise might have influenced the results?

3. Do you agree with the author’s conclusions?

4. What suggestions would you make to further this line of research?

Lipid and Lipoprotein-Cholesterol Concentrations Before and After Exercise

Pre-Exercise +24 Hr +48 Hr

TG mg/dl�1 103.2 ± 61.5 83.0 ± 41.5 77.4 ± 45.8†*

TC mg/dl�1 167.3 ± 25.3 164.5 ± 35.3 154.1 ± 33.8

LDL-C mg/dl�1 95.4 ± 24.7 98.3 ± 36.7 93.0 ± 27.6

HDL-C mg/dl�1 51.3 ± 9.4 49.6 ± 8.8 45.7 ± 12.9†*

Data are mean ± standard deviation.

TG, triglyceride; TC, total cholesterol; LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; IPre, immediately prior to exercise session; +24 h, 24 h after exercise session; +48 h, 48 h after exercise session

†Significant effect (p < 0.05)

*Significant (p < 0.05) different than IPre I

Fat Is Used as Energy Fat is a powerful source of fuel because it provides a concentrated source of kilocalo- ries, is easily stored, and is readily available when the body needs energy. At 9 kilocalo- ries per gram, fat provides more than twice the energy of either carbohydrates or protein. In fact, fat is the body’s main source of energy throughout the day. The body has an unlimited ability to store excess energy as fat in adipocytes (see Figure 5.19 on page 190). Fat cells have the capacity to enlarge as much as 1,000 times their original size, and if they fill to capacity, the body makes more. Though some fat is also stored in the muscle, and a small amount is found in blood plasma, the majority of it is in

How Does the Body Use Fat and Cholesterol? 189

adipocytes Cells in adipose tissue that store fat; also known as fat cells.

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Fatty acid and glycerol

Chylomicron

Adipocytes

Triglyceride

Figure 5.19 Adipocytes Excess triglycerides are stored in the adipocytes for later use. When the body needs energy, the enzyme lipoprotein lipase, located on the outside of the adipocyte, breaks off the fatty acids from the chylomicron or VLDL.

lipoprotein lipase (LPL) An enzyme that hydrolyzes triglycerides in lipopro-

teins into three fatty acids and glycerol.

arachidonic acid An omega-6 fatty acid formed from linoleic acid; it is used to

synthesize the eicosanoids including

leukotrienes, prostaglandins, and

thromboxanes.

adipose tissue. The body stores more than 60 times the energy reserves in adipo- cytes as it does as both liver and muscle glycogen combined.

Fat is deposited into adipose (and some muscle) cells from the chylomicrons and VLDLs that carry it through the blood. An enzyme located on the outside of adipocytes and muscle cells, called lipoprotein lipase (LPL), reacts with the

lipoprotein carriers and cleaves the fatty acids from the triglyceride. This allows the fatty acid to move into the cells to be stored for later use.

Remember from Chapter 4 that when blood glucose levels begin to de- cline, the hormone glucagon promotes the release of glucose from the liver and fat from adipocytes to provide additional energy for the body. The heart, liver,

and resting muscles prefer fat as their fuel source, which spares glucose to be used by the central nervous system and red blood cells. The fat stored in the

adipocytes provides a backup source of energy between meals. In a famine situation, some individuals could last months without eating,

depending upon the extent of their fat stores and the availability of adequate fluids. However, people can still die from starvation before their fat stores

are depleted if they do not consume some glu- cose. Fat stores alone cannot sustain life because glucose cannot be made from fatty acids or ketone bodies. Glycerol is the only part of the stored triglycerides that can be used for gluconeogenesis.

Fat Helps Absorb Lipid Compounds Several essential nutrients, including the fat-soluble vitamins A, D, E, and K, as well as carotenoids, cholesterol, phospholipids, and other lipid compounds, require dietary fat in order to be absorbed. Twenty grams of dietary fat is needed daily to stimulate the for- mation of the chylomicrons that transport the fat-soluble vitamins. Consuming less than this amount may impede fat-soluble vitamin absorption.

Fat Helps Insulate the Body and Protect Vital Organs The fat that is located in the subcutaneous tissue, just under the skin, helps to insu- late the body and maintain body temperature, especially during cold temperatures. However, excess body fat may actually hinder temperature regulation in hot weather, as the excess layer of fat prevents heat from flowing to the skin for release.

Fat also acts as a protective cushion against trauma for the bones and vital or- gans including the brain, liver, kidneys, and spinal cord. Stored fat in the abdomen acts like a fatty apron protecting the liver and stomach from injury. However, too much stored fat eliminates the protective benefits because of the accompanying in- creased risk of heart disease, hypertension, and diabetes.

Essential Fatty Acids Manufacture Eicosanoids and Maintain Cell Membranes The essential fatty acids mentioned earlier in the chapter, linoleic acid and alpha- linolenic acid, are needed as precursors to form other compounds in the body. For instance, linoleic acid can be elongated and converted to arachidonic acid, a

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20-carbon, four-double-bond polyunsaturated fatty acid. Alpha-linolenic acid is con- verted to eicosapentaenoic acid (EPA) and then elongated to docosahexaenoic acid (DHA). Once these compounds are formed, EPA and arachidonic acid are used to manufacture eicosanoids, which are hormonelike substances such as prostaglandins, thromboxanes, and leukotrienes. These compounds regulate the immune system, blood clotting, inflammation, and blood pressure.

Alpha-linolenic acid is also needed for the structure of healthy cell membranes, particularly in nerve tissues and the retina. A lack of this essential fatty acid in the diet can result in scaly skin.

Cholesterol Is Used to Make Bile, Hormones, and Vitamin D When dietary cholesterol is consumed, it is absorbed along with other lipids and can perform the essential functions of cholesterol in the body. The body needs cholesterol both as a structural part of cell membranes and as the precursor for vitamin D and bile acids. Cholesterol is also the precursor for sex hormones such as estrogen and testosterone, which help to determine sexual characteristics.

Many people are confused about the merits of cholesterol. Though dietary cho- lesterol has been proclaimed as unhealthy, the cholesterol in the blood can be either “good” or “bad” cholesterol. How can one substance be both Dr. Jekyll and Mr. Hyde? Later in this chapter, we will look at the health effects of cholesterol, and un- ravel this confusion. During the discussion keep in mind that dietary cholesterol isn’t the only factor that determines the levels of cholesterol in the blood.

The Take-Home Message Fat is an energy-dense source of fuel for the body. Fat cushions and protects bones, organs, and nerves, and helps maintain body temperature. Fat also provides essential fatty acids and is needed for the absorption of fat-soluble vitamins and carotenoids. Essential fatty acids are precursors to EPA and DHA, which manufacture prostaglandins, thrombox- anes, and leukotrienes, substances that regulate the immune system, blood clotting, inflammation, and blood pressure. Cholesterol performs several es- sential functions in the body. It is part of cell membranes and is needed to make vitamin D, bile acids, and sex hormones.

How Much Fat Do We Need Each Day? Americans’ fat consumption has gone up and down over the last century. The latest re- search indicates that our dietary fat intake is at an all-time low of about 33 percent of total kilocalories.1 However, using fat consumption as a percentage of total kilocalo- ries, without including the absolute grams of fat, can be misleading. The latest patterns of food intake by Americans indicate that not only have the total grams of fat we con- sume daily increased about 4 percent since the early 1990s, but the amount of total kilocalories has also increased, about 10 percent.2 In other words, Americans are eating more of both kilocalories and grams of fat, and the reason that the percentage of di- etary fat has declined is because the number of kilocalories has increased.

Clearly, the overall consumption of fat in the United States is higher than it should be. But dietary fat is still essential for health. So, how much should you consume?

eicosanoids Hormonelike substances in the body. Prostaglandins, thromboxanes,

and leukotrienes are all eicosanoids.

eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) EPA (C20:5n–3) and DHA (C22:6n–3) are

omega-3 fatty acids that are synthesized in

the body and may be beneficial in reducing

heart disease.

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Percentage of Daily Kilocalories from Fat The current AMDR (Acceptable Macronutrient Distribution Range) recommenda- tion is that 20 to 35 percent of daily kilocalories should come from all fats. For some individuals, especially those who are sedentary and/or overweight, a very low-fat diet (providing less than 20 percent of daily kilocalories from fat) that is consequently high in carbohydrates may increase LDL cholesterol and triglyceride levels in the blood and lower HDL cholesterol—which is not a healthy combination for the heart. For others, consuming more than 35 percent of total daily kilocalories from fat could perpetuate obesity, which is a risk factor for heart disease.

The overconsumption of dietary fat doesn’t increase overall body weight unless it’s coupled with too many kilocalories. However, because dietary fat is more concen- trated in kilocalories than either carbohydrates or protein, a diet high in fat is likely to result in eating too many kilocalories, and could make for a weight management problem. Numerous research studies have shown that reducing dietary fat also can reduce dietary kilocalories, which can result in weight loss.3 Consequently, control- ling fat intake may help control body weight.

For heart health, the recommendation is to consume no more than 10 percent of total kilocalories from saturated fats and to limit trans fats to less than 1 percent.4 Indi- viduals are encouraged to use more monounsaturated and polyunsaturated fats to re- place saturated fats. For example, if a person consumes 30 percent of his total kilocalories as fat, about 6 percent should be derived from saturated fats, 1 percent or less from trans fat, about 10 percent from polyunsaturated fats, and 13 percent from monounsaturated fats. This is because monounsaturated fats are the best at lowering LDL cholesterol and either maintaining or slightly increasing HDL cholesterol.

When it comes to keeping track of fat intake, counting grams of fat in foods is a good strategy. Table 5.1 provides a healthy range of recommended fat intake based

Table 5.1

Capping Your Fat Intake Daily Energy Needs (Kilocalories)

Maximum Recommended Amount of Daily Dietary Fat Intake

Fat (g) (20% to 35% of Total Kilocalories)

Saturated Fat and Trans Fat (g) (<10% of Total Kilocalories)

1,600 36–62 18 1,700 38–66 19 1,800 40–70 20 1,900 42–74 21 2,000 44–78 22 2,100 47–82 23 2,200 49–86 24 2,300 51–89 26 2,400 53–93 27 2,500 56–97 28 2,600 58–101 29 2,700 60–105 30 2,800 62–109 31

Sedentary women consume approximately 1,600 kilocalories daily. Teenage girls, active women, and many sedentary men need approximately 2,200 kilocalories daily. Teenage boys, many active men, and some very active women need about 2,800 kilocalories daily.

Approximately how many grams of total fat does an individual with a 2,000-kilocalorie energy requirement need to consume to meet the recommendations?

The AMDR recommends that 20 to 35 percent of daily kilocalories (kcal) come from fat, so the range for an individual who needs 2,000 kilo- calories per day would be:

2,000 kcal � 0.20 (20%) � 400 kcal � 9 kcal/g = 44 g

2,000 kcal � 0.35 (35%) � 700 kcal � 9 kcal/g � 78 g

Answer: This person’s range of fat intake should be 44 to 78 grams daily.

To find the maximum grams of saturated and trans fats that this person should consume daily, calculate 10 percent of total kcals:

2,000 kcal � 0.10 (10%) � 200 kcal � 9 kcal/g � 22 g

Answers: The total amount of saturated fat and trans fat should be no more than 22 grams daily.

C A L C U L AT I O N C O R N E R

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Self-Assessment

How Much Fat Is in Your Diet?

Food Log

Meal Food/Drink Total Fat (g) Saturated Fat (g) Trans Fat (g)

Breakfast

Snack

Lunch

Snack

Dinner

Snack

Total

on daily kilocalorie needs. (To figure out your approximate daily kilocalorie needs, see Chapter 2.) Use the Self-Assessment to estimate how much total fat you currently consume daily.

Patricia’s activity levels put her in the sedentary category. Basedon Table 5.1, approximately how many grams of total fat and total saturated fat plus trans fat would you suggest she consume each day?

Specific Recommendations for Essential Fatty Acids The only necessary dietary fats are the two essential fatty acids: linoleic acid and alpha-linolenic acid. The Adequate Intake (AI) of alpha-linolenic acid per day for men and women is 1.6 and 1.1 grams, respectively. The AI for linoleic acid is set much higher, at 17 grams per day for adult men and 12 grams per day for adult women.5

Americans currently consume only about 0.1 to 0.2 grams of EPA and DHA daily. The AMDR for linoleic acid is set at 5 to 10 percent of the total kilocalories, while

alpha-linolenic acid should make up 0.6 percent to 1.2 percent of the total kilocalories. These recommended amounts are based on the estimated daily kilocalorie needs ac- cording to gender and age.

Based on randomized trials, the American Heart Association recommends that people diagnosed with heart disease consume about 1 gram of essential fatty acids each day. For those who have been diagnosed with hypertriglyceridemia (elevated blood triglycerides) a supplement of 2 to 4 grams per day of EPA and DHA supple- ments may lower blood triglycerides.6 Individuals who consume supplements of over 3 grams of EPA and DHA should be under the care of a health care provider, as excessive amounts can causing bleeding (see the feature box, “Facts and Myths About Fats, Oils, and Cholesterol,” on the next page for more about fish oil supplements).7

hypertriglyceridemia The presence of high levels of triglycerides in the blood.

Defined as triglyceride levels between

400 and 1,000 milligrams per deciliter.

Are you consuming too much fat, saturated fat, and/or trans fat? Use a diet analysis program, the food tables in the appendix, or food labels to track your fat consumption for a day and fill out the food log below. How does your actual intake compare to the amount recommended for you in Table 5.1?

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Many people are confused about whether to embrace or avoid fat, which types they should aim to eat, and how much they need. Below, we address six common consumer (mis)perceptions about dietary fat with research-based answers.

Fact or Myth?

The amount of fat you eat is more important than the type of fat.

Myth. The type of fat matters more than the amount consumed when it comes to impacting the risk of certain diseases, in- cluding heart disease and cancer. Data from the Women’s Health Initiative Dietary Modification Trial, which followed 50,000 women between ages 50 and 79 for eight years, showed that women who con- sumed a low-fat diet did not have a signifi- cant reduction in breast cancer compared with those who ate high-fat diets,1 nor did low fat intake reduce the risk of develop- ing colon cancer,2 stroke, or cardiovascu- lar disease.3 However, intake of trans fats and saturated fats correlated to an in- creased risk for cardiovascular disease, stroke, and cancer. Substituting or replac- ing hydrogenated fats, which are rich in trans fats, and saturated fats with mono- unsaturated and polyunsaturated fatty acids can lower the risk of developing heart disease and cancer, regardless of the amount consumed. (Remember though, that kilocalories count, and con- suming more fat means consuming more kilocalories, thereby potentially resulting in weight gain.)

Fact or Myth?

Fat free means kilocalorie free.

Myth. To be considered fat free, a prod- uct must contain less than 0.5 gram of fat per serving, while the definition of kilo- calorie free requires less than 5 kilocalo- ries per serving. This means that a product that is low in fat or even fat free isn’t necessarily lower in total kilocalories. Some fat-free foods, especially baked goods, may have reduced fat content, but have added carbohydrates to make up for the lost flavor, which adds back some kilocalories. For example, two fat- free fig cookies contain 90 kilocalories, which is not much different from the 110 kilocalories found in two regular fig cookies4 (see table).

Consumers should be careful not to assume that fat-free foods are healthy, because they often aren’t. Jelly beans are fat free, but they don’t provide the vita- mins and minerals found in, for example, naturally fat-free green beans. And while snacking on 4 ounces of fat-free chips will provide half of the 600 kilocalories found in the same amount of regular chips, the real problem is that the fat-free chips are displacing 300 calories of more nutritious foods, such as fruits, vegetables, and whole grains, elsewhere in the diet.

Fact or Myth?

Olive oil is the healthiest oil.

Myth. While it’s true that olive oil has beneficial health effects because of its high content of monounsaturated fatty

acids (especially oleic acid) and antioxi- dants (including phenols and vitamin E) and a low content of saturated fatty acids, that doesn’t mean that other veg- etable oils are less healthy. All plant oils contain the same number of fat grams and kilocalories per tablespoon. The dif- ference lies in the type of fat they contain (see graph). Canola oil is less saturated than olive oil and contains more polyun- saturated fatty acids. Olive oil is higher in monounsaturated fatty acids. Sunflower, safflower, and corn oil are also lower in saturated fat and higher in polyunsatu- rated fatty acids than olive oil. Thus, olive oil is not the only healthy oil available to consumers; all these oils are considered healthy choices.

The American Heart Association rec- ommends vegetable oils that contain no more than 2 grams of saturated fat per tablespoon.5 Canola, corn, olive, saf- flower, sesame, soybean, and sunflower oils all fit the heart-healthy recommenda- tions. Tropical oils such as coconut and palm oils should be used less often, as they contain higher levels of saturated fat.

Fact or Myth?

Eggs should be avoided in a heart- healthy diet.

Myth. Eggs have long been considered a villain in the fight against heart disease because of their cholesterol-containing yolks. However, this threat has largely been overstated. The reality is that dietary cholesterol does not have as big an

Facts and Myths About Fats, Oils, and Cholesterol

Fat Free Doesn’t Equal Kilocalorie Free

Serving Size (g) Kilocalories

Fat (g)

Carbohydrates (g)

Kilocalories Saved

Fig Newtons (Nabisco) 2 (31 g) 110 2 22 Fat-Free Fig Newtons (Nabisco) 2 (29 g) 90 0 22 20

Oatmeal Raisin Cookies (Archway) 1 (28 g) 120 3.5 20 Fat-Free Oatmeal Raisin Cookies (Archway) 1 (31 g) 110 0 25 10

Fudgsicle Pop (Popsicle) 1 (1.65 fl oz) 60 1.5 12 Fat-Free Fudgsicle Bar (Popsicle) 1 (1.75 fl oz) 60 0 13 0

Source: Food manufacturers.

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included in a low-cholesterol diet. But though shrimp is high in cholesterol, it contains less than 0.25 gram of saturated fat and 0.4 gram, or 15 percent, of the omega-3 recommendation. Researchers have shown that eating shellfish, including shrimp, reduced the risk of dying from a heart attack by 20 percent.9

References 1. Prentice, R. L., B. Caan, R. T. Chlebowski,

R. Patternson, L. H. Kuller, J. K. Ockene, K. L. Margolis, et al. 2006. Low-Fat Dietary Pattern and Risk of Invasive Breast Cancer: The Women’s Health Initiative Randomized Controlled Dietary Modification Trial. Journal of the American Medical Association 295:629–642.

2. Beresford, S. A. A., K. C. Johnson, C. Ritenbaugh, N. L. Lasser, L. G. Snetselaar, G. Linda, H. R. Black, et al. 2006. Low-Fat Dietary Pattern and Risk of Colorectal Cancer: The Women’s Health Initiative Randomized Controlled Dietary Modification Trial. Journal of the American Medical Association 295:643–654.

3. Howard, B.V., L. Van Horn, J. Hsia, J. E. Manson, M. L. Stefanick, S. Wassertheil-Smoller, L. H. Kuller, et al. 2006. Low-Fat Dietary Pattern and Risk of Cardiovascular Disease: The Women’s Health Initiative Randomized Controlled Dietary Modification Trial. Journal of the American Medical Association 295:655–666.

4. United States Department of Agriculture. 2002. Fat-Free vs Regular Calorie Com- parison. FDA Consumer. Available at www.cfsan.fda.gov/~dms/fdweigh4.html. Accessed June 2008.

5. American Heart Association. 2008. Fats and Oils. Available at www .americanheart.org. Accessed June 2008.

6. Hu, F. B., E. B. Rimm, M. J. Stampfer, A. Ascherio, D. Spiegelman, and W. C. Willett. 1999. A Prospective Study of Egg Consumption and Risk of Cardiovascular Disease in Men and Women. Journal of the American Medical Association 281:1387–1394.

7. Ibid. 8. Elvevoll, E. O., H. Barstad, E. S. Breimo,

J. Brox, K. E. Eilertsen, T. Lund, J. O. Olsen, and B. Osterud. 2006. Enhanced Incorporation of ω-3 Fatty Acids from Fish Compared with Fish Oils. Lipids 41:1109–1114.

9. Yuan, J., R. K. Ross, G. Yu-Tang, and M. C. Yu. 2001. Fish and Shellfish Consumption in Relation to Death from Myocardial Infarction among Men in Shanghai, China. American Journal of Epidemiology 154:809–816.

impact on heart disease as blood cholesterol levels, which are affected more by saturated and trans fat intake than cholesterol intake. In a study of over 80,000 nurses, researchers found that increasing dietary cholesterol by about 200 milligrams per 1,000 kilocalories (about the amount in a large egg), didn’t raise blood cholesterol levels.6

However, that’s not to say that people should aim to eat more cholesterol- containing foods. High cholesterol intake is associated with an increased risk for heart disease. Because egg yolks tend to be a significant source of cholesterol in Americans’ diets, the National Institutes of Health (NIH) recommends consuming no more than four egg yolks per week to help prevent heart disease. Given that eggs are also a source of many healthy nutrients, including protein, numerous B vitamins, and vitamins A, D, and E, some health professionals have sug- gested lifting the weekly cap on egg yolks for healthy individuals and focusing on keeping dietary cholesterol to no more 300 milligrams daily, regardless of the source.7 Hence, egg yolks can be eaten more often if other sources of dietary cholesterol are low.

Fact or Myth?

Fish oil supplements are essential for health.

Myth. A daily dose of >1 gram of both EPA and DHA is needed to achieve heart- healthy benefits. But though consuming some omega-3 fatty acids is good, more

may not be better, and too much can produce harmful side effects. Taking fish oil supplements increases the chance of consuming high doses of DHA and EPA, which can interfere with blood clotting. Consuming more than 3 grams, which typically only happens by taking supple- ments, could raise both blood glucose and LDL cholesterol levels, increase the risk of excessive bleeding, and cause other related side effects, including nau- sea and GI distress. Consuming large amounts of fish oil supplements can also leave a less-than-appealing fishy after- taste in the mouth. Because of these po- tential adverse side effects, omega-3 fatty acid supplements (fish oil supplements) should only be consumed with the advice and guidance of a doctor.

Norwegian researchers report that omega-3 fatty acids are better absorbed from food than from fish oil supplements.8

For healthy individuals who have not been diagnosed with coronary artery disease, increasing intake of omega-3 fatty acids through food is the preferred method.

Fact or Myth?

Shellfish is high in cholesterol.

It depends on the shellfish. A 3-ounce serving of scallops contains 34 milligrams of cholesterol, but the same size portion of shrimp contains 5 times more choles- terol (165 milligrams), half the recom- mended daily intake. Shrimp is also higher in cholesterol than three ounces of beef (80 milligrams). At first glance, it would seem that shellfish should not be

Coconut oil Butter

Beef tallow Palm oil

Lard Olive oil

Canola oil Peanut oil

Safflower oil Flaxseed oil

Walnut oil Sunflower oil

Corn oil

Saturated Monounsaturated Polyunsaturated

Composition of Various Oils Oils used for cooking and in food preparation vary in their saturation.

Facts and Myths About Fats, Oils, and Cholesterol 195

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Dietary Cholesterol Is Not Essential Cholesterol does not need to be consumed in the diet, as the liver synthesizes all that the body needs. The liver manufactures about 900 milligrams of cholesterol per day. This is three times greater than the 300 milligrams the average American consumes daily. However, if cholesterol is consumed, the body adjusts the amount it synthe- sizes. Normally, the total amount of cholesterol remains constant because the rate of cholesterol synthesis in the liver is under feedback control. When the dietary intake is high, liver synthesis is low; when intake is low, synthesis increases.

As mentioned earlier, dietary cholesterol should be limited to reduce the risk of developing cardiovascular disease. Healthy individuals over the age of 2 are advised to limit their dietary cholesterol to under 300 milligrams (mg) daily, on average.8

Adult males in the United States currently consume about 330 milligrams daily, whereas adult females take in slightly more than 210 milligrams of cholesterol daily, on average. Table 5.2 lists a variety of foods and their cholesterol content.

The Take-Home Message Dietary lipids, particularly the essential fatty acids, are key for a healthy diet, but intake of saturated fats, trans fats, and cholesterol should be limited. Dietary fat intake should range from 20 to 35 percent of total kilocalories. To meet essential fatty acid needs, 5 to 10 per- cent of total kilocalories should come from linoleic acid and 0.6 to 1.2 percent of total daily kilocalories should come from alpha-linolenic acid. Dietary intake of saturated fat should be limited to no more than 10 percent of total fat con- sumption, and less than 1 percent of fat consumption should be from trans fats. Dietary cholesterol should be limited to less than 300 milligrams per day.

What Are the Best Food Sources of Fat? Eating foods that contain unsaturated fats (which also contain essential fatty acids) are better for health than eating foods high in saturated fat, cholesterol, and/ or trans fat. So, which foods contain the healthier fats?

Unsaturated fats are abundant in vegetable oils, such as soybean, corn, and canola oils, as well as soybeans, walnuts, flaxseeds, and wheat germ. These foods are also all good sources of linoleic acid. Walnuts, flaxseeds, and canola oil also contain alpha-linolenic acid. Figure 5.20 lists examples of foods that are excellent sources of unsaturated fats and essential fatty acids.

Fish are generally good sources of omega-3 fatty acids, and all fish contain EPA and DHA, with fatty fish being especially rich sources (Figure 5.21). Cod-liver oil is abundant in EPA and DHA. Eating fish, rather than taking cod-liver oil, is a safer way to obtain EPA and DHA, and has been shown to improve heart health.9

Individuals are sometimes hesitant to consume fish due to a concern about mer- cury levels. Although all fish and shellfish contain a trace of mercury, the levels of mercury are not considered a health risk for most people. More information is pro- vided on this topic in the feature box, “Mercury and Fish” on page 209.

Foods high in saturated fat should be limited in the diet. Most saturated fat comes from animal foods, such as fatty cuts of meat, whole-milk dairy products (in- cluding cheese, butter, and ice cream), and the skin on poultry. Certain vegetable oils, such as coconut, palm, and palm kernel oils, are also very high in saturated fat.

Table 5.2

How Much Cholesterol Is in Foods?

Cholesterol (mg)

Liver, 3 oz 324

Breakfast biscuit with egg and sausage, 1

302

Egg, 1 large 212

Shrimp, 3 oz, canned 147

Fast-food hamburger, large, double patty

122

Ice cream, soft serve, vanilla, 1⁄2 cup

78

Beef, ground, cooked, 3 oz

77

Salmon, cooked, 3 oz 74

Chicken or turkey, breast, cooked, 3 oz

72

Lobster, cooked, 3 oz 61

Turkey, light meat, cooked, 3 oz

59

Egg noodles, 1 cup 53

Butter, 1 tbs 31

Cheddar cheese, 1 oz 30

Frankfurter, beef, 1 24

Milk, whole, 1 cup 24

Cheddar cheese, low fat, 1 oz

6

Milk, skim, 1 cup 4

Source: USDA National Nutrient Database for Standard Reference, Release 16. Available at www.ars.usda.gov. Accessed March 2008.

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Figure 5.20 Food Sources of the Essential Fatty Acids Many oils and nuts are good sources of the two essential fatty acids.

These tropical oils are sometimes found in candies, commercially made baked goods, and gourmet ice cream. Checking the ingredi- ent label on food packages is the best way to check for these oils.

While it’s important to limit saturated fat in the diet, it’s im- possible to eliminate it entirely. All fats and oils contain a variety of fatty acids, some of which are bound to be saturated. Avoiding all fat-containing foods, or eliminating all oils during cooking, could lead to the unnecessary exclusion of healthy foods, such as soybean and canola oils, lean meats, fish, poultry, and low-fat dairy foods. The result may be an inadequate intake of important nutrients such as essential fatty acids, protein, and calcium. A better strategy

Patricia loves to cook, and uses a lot of cheese and Italianmeats, including sausage, in her favorite dishes. Would you classify these foods as high in fat? What types of lipids do they contain? What changes or substitutions could Patricia make to improve the nutritional quality of her cooking?

Figure 5.21 Food Sources of Omega-3 Fatty Acids Several types of fish, particularly fatty fish, are high in the heart- healthy omega-3 fatty acids.

What Are the Best Food Sources of Fat? 197

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is to consume lower fat versions of these foods, so you obtain the healthy nutrients while avoiding unnecessary, unhealthy fats. Figure 5.22 helps compare high-fat and lower fat versions of several commonly eaten foods.

The Take-Home Message Lean meat and poultry, fish, low-fat or non- fat dairy products, and limited amounts of nuts and cheese are the best food sources to obtain the essential fatty acids while limiting intake of saturated and trans fats. Commercially prepared baked goods and snack items, which tend to be high in kilocalories as well as in saturated and trans fats, should be con- sumed rarely, and vegetable oils should be used in place of butter.

What Foods Contain Trans Fat and Cholesterol? At one time, saturated fats from animal sources, like lard, and highly saturated tropi- cal plant oils, like coconut and palm oils, were staples in home cooking and commer- cial food preparation. These saturated fats worked well in commercial products because they provided a rich, flaky texture to baked goods and were more resistant to rancidity than the unsaturated fats found in oils. Later, the technique of hydrogena- tion of oils and the use of trans fat performed a similar function without adding cho- lesterol to the diet.

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