Human Growth and Development Discussions

537

15 Learning Outcomes

After reading this chapter, you will be able to:

15.1 Explain why weight management is important to health and well-being.

15.2 Define the terms appetite, hunger, and satiety, and describe the physiological factors involved in regulating food intake.

15.3 Describe the role of hyperplasia and hypertrophy of adipocytes in the development of obesity.

15.4 Discuss the role of genetics and the environment in the development of underweight, overweight, and obesity.

15.5 Describe the role of diet and exercise in achieving a reasonable rate of weight loss.

15.6 Design a food and exercise plan to maintain a healthy weight.

15.7 Describe the role of diet and exercise in achieving a healthy weight gain.

15.8 Describe the role of weight-loss drugs and surgery for reducing obesity.

True or False?

1. Healthy weight loss occurs only with at least 2 hours of daily exercise. T/F

2. The body stops synthesizing fat cells after adolescence. T/F

3. Grazing throughout the day helps curb appetite and control body weight. T/F

4. Losing even 10 pounds can improve health. T/F

5. Genetics and the environment both affect body weight. T/F

6. Eating more vegetables and fruits can help an individual lose weight. T/F

7. Obesity is the result of consuming more energy than is expended. T/F

8. The nutrient that has the most effect on satiety is fat. T/F

9. You don’t need to diet and exercise if you are taking a weight-loss drug. T/F

10. Bariatric surgery results in weight loss without restricting food intake. T/F See page 572–573 for the answers.

Weight Management

538 Chapter 15 | Weight Management

Why Is Weight Management Important?

LO 15.1 Explain why weight management is important to health and well-being.

The term weight management means maintaining body weight within a healthy range. Achieving a healthy body weight is essential for physical and emotional well-being. It helps you feel good about yourself, provides the energy you need to enjoy life, and lowers the risk of chronic disease. In addition, weight management reduces costs to society. The costs for treating obese individuals are several thousand dollars higher than for their lean counterparts. It has been estimated that each additional pound of extra body weight above healthy body weight could add up to $13 a year per pound in added medical costs for men and up to $45 for women.6

Being Overweight or Obese Increases Health Risks

As you learned in Chapter 14, a healthy weight is a body weight that doesn’t increase the risk of developing any weight-related health problems or diseases.7 In contrast, over- weight—and especially obesity—is associated with numerous health problems. In fact, in 2013, the American Medical Association declared obesity a disease in itself—specifically a multi-metabolic and hormonal disease state.8 This new classification of obesity as a disease helps focus attention and resources on the problem, opening the door for the 90 million obese Americans to receive treatment for their obesity. It may also be changing the way physi- cians approach obesity management, increasing the use of drug therapies and surgery. Alternatively, the obesity-as-a-disease message suggests that body weight is uncontrollable, and—if it discourages patients—might hinder weight management efforts that focus on healthy eating and exercise.

weight management Maintaining a healthy

body weight; defined as having a BMI of

18.5–24.9.

Weight management is such a hot topic in

the United States that the mainstream media

frequently covers it.

I n the last two decades, rates of overweight and obesity have exploded in the United States. In the

early 1960s, fewer than 32 percent of Americans were overweight.1 Today, that number has risen

to an alarming 67 percent of Americans classified as overweight, and more than 33 percent of adults

(about 72 million people) and 17 percent of children are obese.2 Not surprisingly, as more and more

individuals cross the threshold from a healthy body weight to being overweight, the topic has garnered

much interest in popular culture. In fact, people often turn to social media sites such as Facebook,

Pinterest, and Twitter to talk about weight management and locate helpful tools to help manage their

body weight.3

Despite its prevalence, people do not enjoy being overweight, and regularly spend large amounts of

money in search of a “cure.” In fact, Americans annually spend over $60 billion4 on everything from

over-the-counter diet pills to books, magazines, online support groups, and commercial dieting centers to

help shed their excess weight. It has been estimated that 21 percent of the total U.S. health care budget is

spent to treat the medical complications associated with being overweight.5

If you are currently struggling with your weight or know someone who is, don’t despair. Weight

loss takes work, but it is achievable. This chapter emphasizes the key components of how to achieve and

sustain a healthy body weight.

Why Is Weight Management Important? 539

People who are overweight or obese have an increased risk for cardiovascular disease— including hypertension, heart disease, and stroke—and the risk increases as BMI increases.9 This increased risk may be due in part to the fact that overweight people tend to have high blood levels of both triglycerides and LDL cholesterol and low levels of HDL cholesterol. 10

Overweight and obesity are also strongly linked to type 2 diabetes. Excessive adipose tissue contributes to insulin resistance, which forces the pancreas to work harder to pro- duce more insulin. Eventually, the pancreas can stop producing insulin altogether, caus- ing diabetes. Nearly 85 percent of people with type 2 diabetes are overweight or obese.11

A higher BMI can also increase the risk of gallbladder disease, joint stress, sleep apnea, reproductive problems, and some cancers, including endometrial, breast, and colon cancer. Central obesity is especially harmful: It is one of the five risk factors that comprise metabolic syndrome, a condition that in turn increases the risk for cardiovascular disease and type 2 diabetes. Obesity also increases the risk for osteoarthritis, a condition in which the tissue that protects the joints of the knees, hips, and lower back wears away.

Carrying extra body weight is so detrimental to health that for overweight individuals, losing as little as five to ten percent of body weight can be lifesaving.12 For example, if you currently weigh 200 pounds, a weight loss of 10–20 pounds can reduce your risk of type 2 diabetes and other chronic diseases.

Being Underweight Also Increases Health Risks

As with being overweight, being underweight can lead to numerous diseases and condi- tions. These include anemia, heart irregularities, and amenorrhea (loss of menstruation in women). Underweight older adults are at risk for low body protein and fat stores and a depressed immune system, which makes it more difficult to fight infections. Injuries, wounds, and illnesses that would normally improve in healthy individuals can result in serious complications in individuals with a depressed immune system.

Individuals who are underweight are more likely to lack vital nutrients, such as cal- cium, which is important to maintain strong, dense bones. Being underweight increases the risk for osteoporosis and bone fractures later in life.13 Sustaining a normal, healthy body weight can reduce this risk.

Certain diseases, such as cancer, inflammatory bowel disease, and celiac disease, can cause malabsorption and result in significant weight loss. Other inadvertent causes of underweight include certain medications—such as some antidepressant, osteoporosis, and blood pressure drugs—all of which can decrease appetite. Smoking and substance abuse can also lead to unhealthy weight loss.

Overweight and Underweight Have Social

and  Psychological Risks

Beyond the physical effects of carrying too much body weight, obese and overweight individuals are often at a social, educational, and economic disadvantage. Overweight people suffer more discrimination and are more likely to be denied job promotions and raises than normal-weight individuals.14 Obese females are less likely to be accepted into college, especially higher-ranked schools.15 Social situations, such as attending movies or sporting events, and travel on buses and airplanes may be limited for obese individuals due to restrictive seat sizes.16 These prejudices and limitations can result in lower self-esteem.17

Popular perceptions of overweight individuals as being lazy or weak-willed can fur- ther affect their feelings of self-confidence and self-worth.18 Images of slender models as the ideal in advertising and other media help perpetuate the notion that overweight individuals are less desirable. Living in an antagonistic environment may compromise

540 Chapter 15 | Weight Management

attempts at achieving a healthy body weight. For example, obese and overweight people are less likely to exercise because they are embarrassed to change in the locker room or work out at a gym.19 Obese people have higher rates of suicide than healthy-weight people20 and are more likely to use alcohol and drugs when compared with their normal-weight peers.21

The psychological consequences of being underweight can be just as debilitating. Research has suggested that people who are underweight are at greater risk for irritability, anger, and depression.22 For example, underweight males are reported to have a 12 percent increased risk of committing suicide compared with healthy- weight males.23 People who are underweight can be more socially withdrawn compared with those with a healthy body weight.24

LO 15.1: THE TAKE-HOME MESSAGE Weight management means maintaining a healthy weight to reduce the risk of specific health problems. Classifying obe-

sity as a disease may improve treatment options but may also raise health care

costs, increase drug and surgical procedures, and hamper lifestyle changes to

lose weight. The physical risks of overweight and obesity include an increased

risk for cardiovascular disease, type 2 diabetes, certain cancers, and other dis-

orders, whereas underweight increases the risk for anemia, heart irregularities,

amenorrhea, and osteoporosis. The social and psychological effects of obesity

and underweight include discrimination, low self-esteem, depression, suicide,

and alcohol and drug problems.

How Is Food Intake Regulated?

LO 15.2 Define the terms appetite, hunger, and satiety, and describe the physiological factors involved in regulating food intake.

Why do you feel hungry or full? A variety of factors influence not only how much we eat, but also the type of food we choose to eat. These factors include strong physiological and psychological influences that go beyond the need for energy.

Appetite Often Triggers Eating for Unnecessary Reasons

Distinguishing between true hunger and appetite, or the desire to eat based on sig- nals other than hunger, can be difficult. Have you ever groaned after a huge meal, “I’m so full!” only to turn around and eat a thick slice of apple pie with ice cream? Appetite is often stimulated even when we are satiated. This desire to eat the apple pie may be triggered by the smell, taste, texture, or color of the food, or by external cues such as time of day, social occasions, or other people. Appetite can also be triggered by learned behavior and by emotions such as stress, fear, and depression. Identifying the triggers that affect your desire to eat is one of the key strategies in maintaining a healthy body weight.

appetite Desire to eat food whether or not

there is hunger; a taste for particular foods and

cravings in reaction to cues such as the sight,

smell, or thought of food.

Overweight and obese people are often embarrassed to exercise in a gym or change

clothes in a locker room because of their body weight.

How Is Food Intake Regulated? 541

Hunger and Satiation Affect the Desire to Eat

and Stop Eating

Two strong physiological factors, hunger and satiety, affect the amounts of food individu- als consume. Hunger is the physical sensation associated with the need or intense desire for food. Physiological signals such as low blood sugar or an empty stomach trigger hunger and searching for food. Once eating begins, hunger subsides as the feeling of fullness, or satiation, sets in and you stop eating. Satiety describes how you feel after a meal and before hunger is triggered again.

Satiety and hunger are both controlled by hormones produced in the brain and the gastrointestinal tract. In the brain, two regions of the hypothalamus control the trig- ger mechanisms that stimulate hunger and satiety: the ventromedial nucleus and the lateral hypothalamus. These regions receive signals from both inside and outside the brain. Focus Figure 15.1 explains the signals that control hunger and satiation.

Regulation of Satiety Satiety is triggered in the ventromedial nucleus in response to a variety of physiological cues. After a meal, the stomach becomes distended, sending signals from stretch recep- tors in the lining of the stomach to the brain to suppress hunger. As protein, fatty acids, and monosaccharides reach the small intestine, two hormones, cholecystokinin (CCK) and peptide YY (PYY), are released, sending feedback to the hypothalamus to increase satiety and decrease hunger.25 Once these nutrients are absorbed, the hormone insulin is released, which also results in a decrease in hunger.26

Other hormones, including leptin, produced in adipose tissue, influence satiety. The production of leptin is controlled by the obese gene (ob) and increases in amount as the fat stores increase. Leptin is a satiety signal. It acts on receptors found in the hypothalamus to decrease hunger and food intake, probably by inhibiting neuropeptide Y, a hormone that stimulates hunger. At the same time, leptin creates a negative energy balance by rais- ing the body temperature, which in turn increases energy expenditure and stimulates the oxidation of fatty acids in the liver and muscles. Thus, leptin regulates the amount of fat stored in the adipose tissue.27

In addition to the influence of hormones, certain macronutrients, especially protein, influence satiety and reduce the intake of food. Researchers have reported that protein intake ranging from 15 to 30 percent of total kilocalorie intake significantly reduces food intake.28

Regulation of Hunger Whereas the ventromedial nucleus affects satiety, the lateral hypothalamus controls hun- ger. The hormone ghrelin, produced in the gastric cells of the stomach, stimulates the lateral hypothalamus. Thus ghrelin has the opposite effect of leptin—it stimulates hunger. Ghrelin concentrations rise in the blood before a meal. Ghrelin travels through the blood to the hypothalamus, where it activates neuropeptide Y to stimulate hunger.

The production of ghrelin changes throughout the day. More ghrelin is produced between meals, during sleep, or when you fast. This increase in ghrelin production sig- nals the hypothalamus that the body needs energy. Ghrelin levels drop following a meal, especially one that contains high amounts of carbohydrate and/or kilocalories. This drop in ghrelin levels signals satiety and decreases the urge to eat.

Lean individuals tend to have higher levels of ghrelin than individuals with more body fat, especially in the morning hours. Ghrelin levels increase when an individual is on a low-kilocalorie diet, a fact that might help explain why people on weight-reduction diets continually feel hungry and find it difficult to lose weight.29

Leptin may also be partly responsible for hunger. When adipocytes shrink during weight loss, leptin levels drop. This reduction in leptin stimulates hunger and may drive the body to eat more to reestablish fat stores.

hunger Strong sensation indicating a

physiological need for food.

satiation State of being satisfactorily full

during a meal, which inhibits the ability to eat

more food.

satiety Feeling of satiation or “fullness” after a

meal before hunger sets in again.

Hunger is stimulated by circulating hormones

and signals from your intestinal tract.

542 Chapter 15 | Weight Management

Head to Mastering Nutrition and watch a narrated video tour of this figure by author Joan Salge Blake.

Figure 15.1 The Brain Controls Hunger and SatiationFOCUS

Neuropeptide Y (NPY) is

produced in the hypothalamus

and stimulates hunger.

NEUROPEPTIDE Y

Ghrelin is secreted from the

stomach when the stomach is

empty to stimulate hunger.

GHRELIN

INSULIN

Two regions of the brain—the ventromedial nucleus and the lateral hypothalamus—control eating behaviors in response to hormones released from the stomach, pancreas, small intestine, adipocytes, and the hypothalamus. The ventromedial nucleus responds to hormones to stimulate satiety. Hunger is triggered by hormones that stimulate the lateral hypothalamus.

Insulin is released from

the pancreas following

carbohydrate ingestion.

LEPTIN

Leptin produced in the

adipocytes is

released into the

blood to stimulate

satiety.

PEPTIDE YY

Peptied YY (PYY) is

released from the small

intestine when kilocalories

have been consumed.

CHOLECYSTOKININ

Cholecystokinin (CCK) is

released from the small

intestine when chyme enters

the duodenum.

HORMONES THAT

STIMULATE SATIETY

HORMONES THAT

STIMULATE HUNGER

GHRELIN

NPY

INSULIN

PYY

CCK

LEPTIN

The

ventromedial

nucleus

The

lateral

hypothalamus

How Do Fat Cells Form and Expand? 543

Certain vitamins and minerals have been shown to lower leptin concentrations and affect hunger levels. For example, zinc supplements have been reported to lower leptin in obese individuals and may be responsible for overeating.30 On the other hand, ingesting too little vitamin A and C also appears to inhibit leptin secretion.31 The mechanism of how vitamin and mineral intake affects the hormone leptin and hunger is still unclear.

LO 15.2: THE TAKE-HOME MESSAGE Food intake is controlled by hunger, satia- tion and satiety, and appetite. Appetite is a desire for food prompted by fac-

tors other than hunger. Hunger is a strong physiological need for food. Satiety

is the physiological response to food intake, resulting in satisfaction. Hunger,

satiation, and satiety are controlled by the hypothalamus and regulated by neu-

ropeptides, hormones, and neural signals from the gastrointestinal tract and

adipocytes. The hormones leptin and ghrelin play key roles in triggering hunger

and satiety, with ghrelin triggering hunger and leptin triggering satiation.

How Do Fat Cells Form and Expand?

LO 15.3 Describe the role of hyperplasia and hypertrophy of adipocytes in the development of obesity.

The increase in the stores of body fat occurs in two ways: (1) Adipocytes, like muscle cells and many other body cells, can grow in size. This process is known as hypertrophy. In adipocytes, hypertrophy is caused by increased storage of fat. (2) Once an adipocyte fills to capacity, the production of more adipocytes is stimulated. The stimulation of exces- sive cell division—which occurs in tumor formation and other physiological processes, is known as hyperplasia. Adipocyte hyperplasia causes a buildup of excess fat tissue, which is stored throughout the body (Figure 15.2).

The Number of Fat Cells in the Body Never Decreases

The average nonobese adult’s body contains approximately 30 billion to 50 billion adipo- cytes, each of which holds between 0.4 and 0.5 micrograms of fat. Overweight or obese adults most likely have the same number of adipocytes as healthy-weight adults but their fat cells are much larger, holding between 0.6 and 1.2 micrograms of fat. Thus, when a healthy-weight adult gains weight, it is likely due to hypertrophy.

When an overweight or obese adult loses weight, the size of the fat cell shrinks, but the number of cells does not. After weight loss, the smaller fat cells remain and can easily be filled up again when energy intake is greater than energy output.

hypertrophy Increase in size; in adipocytes,

hypertrophy refers to the increase in size of the

cells.

hyperplasia Increase in the number of cells

due to cell division.

▲ Figure 15.2 The Formation of Adipocytes

Preadipocytes are immature

cells formed from stem cells.

a Once the preadipocyte

begins to store fat, it becomes

a mature adipocyte.

b Hypertrophy results in

an increase in the size of

adipocytes, which happens

during weight gain.

d During hyperplasia the

number of adipocytes

increases.

c

Preadipocyte

Fat Fat droplet

Cutaway view of

mature adipocyte

Nucleus Cell membrane Hypertrophy

544 Chapter 15 | Weight Management

Although hyperplasia appears to slow with age,32 the growth and production of fat cells may continue throughout life, especially in obese individuals. Every year about 10 percent of fat cells die and are replaced by new ones. The number of fat cells you create as a child remains with you for life.33

Fat Cells Can Grow and Shrink

The size of fat cells is regulated by the enzyme lipoprotein lipase (LPL), which is made in the adipose tissue and lies on the surface of the adipocyte. As you learned in Chapter 5, LPL increases lipogenesis, or the accumulation of fat in the adipocyte. Another enzyme, called hormone-sensitive lipase (HSL), plays the opposite role in fat metabolism. HSL stimu- lates lipolysis, or the hydrolysis of triglycerides inside the adipocyte, and frees the fatty acids, which are then released into the bloodstream. The balance between lipogenesis and lipolysis affects the size of the adipocyte. This is similar to a savings account—as you save money, the balance grows until you take it out and the balance shrinks.

The activity of LPL and HSL differs in overweight and lean individuals.34 Heavier people have much more LPL activity, especially after eating (Figure 15.3). This makes it much easier to store energy from the meal. The activity of LPL increases following weight loss, which makes it much easier to regain lost weight.

Differences in LPL activity are also noted between genders.35 In men, LPL is more active in the visceral, abdominal fat cells than in females, but females have higher LPL activ- ity rates in the hips and thighs than do males. This is probably the reason women deposit more fat in the lower body and why adipose tissue in these areas is more stable and takes lon- ger to lose. Overall, women oxidize more fat for fuel during exercise than men do and a male’s LPL activity is higher following exercise than a female’s. The reason for this remains unclear.

LO 15.3: THE TAKE-HOME MESSAGE The average adult body contains 30 billion to 50 billion adipocytes. Once adipocytes are formed, they can increase or

decrease in size as fat storage needs change, but they can never decrease in

number. Every year 10 percent of fat cells die and are replaced. The enzymes

lipoprotein lipase and hormone-sensitive lipase influence the balance between

lipolysis and lipogenesis, and thus the growing or shrinking of fat cells.

▲ Figure 15.3 Lipoprotein Lipase

Activity in Lean, Obese, and

Post-Weight-Loss Adults

LPL increases lipogenesis, or the

accumulation of fat in the adipocyte.

Source: J. English. 2013. Reversing Altered Metabolic

Functions to Enhance Long-Term Weight Control.

Available at http://nutritionreview.org/2013/04/

reversing-altered-metabolic-functions-enhance-

longterm-weight-control/. Accessed April 2017.

8

10

6

4

2

0

Lean

L P

L a

c ti v it y

Obese Post

weight-loss

How Do Genetics and Environment Influence Obesity and Weight Management?

LO 15.4 Discuss the role of genetics and the environment in the development of underweight, overweight, and obesity.

The relationship of genes to obesity was first demonstrated in studies on separated identi- cal twins raised in different home environments who have similar weight gain and body fat distribution.36 On the other hand, our genetic code has not changed since the obesity epidemic began. Therefore the environment in which we work and live must also influ- ence body weight. Indeed, most health professionals now agree that obesity arises from a gene–environment interaction.37 The question is, which is stronger, nature or nurture?

Nutrigenomics and Epigenetics May Influence Weight Control

Two new areas of study introduced in Chapter 1, nutritional genomics and epigenetics, may help answer this question. The science of nutrigenomics has identified specific genes that are involved in the body’s response to certain nutrients, such as how we absorb,

gene–environment interaction Interaction

of genetics and environmental factors that

increases the risk of obesity in susceptible

individuals.

How Do Genetics and Environment Influence Obesity and Weight Management? 545

store, or break down dietary fat, and can pinpoint the variation in the gene that may be responsible for the body’s response. However, even with identical twins that have the same genetic makeup, the response to overeating or restricting kilocalories varies.

Researchers are still unclear what mechanism causes genes and nutrients to interact. This is where epigenetics comes into play. Recall that epigenetics studies changes in gene activity and gene expression that occur without changing the DNA sequence itself. The DNA in the body is wrapped around proteins called histones, much as thread is wrapped around a spool. Both the DNA and the histones are covered with chemical tags that can react to signals within the body, such as diet, stress, toxins, and physical activity. These chemical tags are collectively called the epigenome (Figure 15.4). The epigenome can cause the DNA-histone structure to tightly wrap, hiding genes. These genes are not accessible to the cell and therefore are not translated into proteins. However, the epigenome can also cause the DNA-histones to partially unwind, exposing the genes that were hidden and allowing them to be used to assemble proteins.

Food is one epigenetic factor that can cause the DNA-histones to partially unwind and expose inactive genes. For example, the B vitamins thiamin, ribof lavin, and vitamin B12 donate methyl groups during metabolic reactions. These methyl groups tag the DNA-histones and thereby influence the expression of certain genes. These genes may, for example, trigger or inhibit fat synthesis, although how the mechanism might work is still unknown.38 In other words, while we can’t alter the genetic makeup we are born with, we may eventually be able to control the factors that turn obesity genes on or off.

People who share genes often have similar

body weights.

▲ Figure 15.4 The Epigenome

The epigenome consists of chemical tags that influence the use of genes to assemble

proteins. The epigenome can cause the genome to wind more tightly, thereby hiding genes,

or unwind, making genes accessible for expression as proteins.

DNA alpha-helixa

DNA wraps around

proteins called histones.

This DNA-histone structure

is covered with chemical

tags (the epigenome),

some of which are derived

from foods.

b

The epigenome can

cause the genome to

wrap tightly and hide

genes or to unfold and

reveal genes.

c

546 Chapter 15 | Weight Management

Genetic Variants Can Influence Body Weight

Scientists currently associate more than 40 genetic variants with obesity.39 Some of these gene variants influence your levels of hunger-satiety hormones. Others affect eating behavior, insulin response, thermogenesis, and other factors.40 But how do these gene variants occur?

Recall that even small changes in a gene can affect its ability to code for protein assembly. Among the most common of these small changes are single-nucleotide polymor- phisms, referred to as SNPs, or “snips.” Unlike epigenetic factors, which don’t change the structure of the DNA itself, SNPs are copy errors that occur during DNA replication and do change the building blocks—the nucleotide bases—of DNA. For example, in a gene with an SNP, a length of DNA might have the nucleotide thymine (T) in place of the nucleotide cytosine (C). This shift in a single nucleotide changes the way the gene behaves. This is similar to dialing a telephone number with one wrong digit. Most SNPs have no direct effect whatsoever on body weight, but some play an important role in how individuals respond to food intake.

SNPs of certain genes can influence the level or the functioning of some hormones that influence hunger, satiety, and appetite.41 Earlier in the chapter, you learned that the hypothalamus regulates hunger and satiety by responding to signals from the adipocytes, the pancreas, the stomach, and the small intestine. These signals are conveyed to the brain by the hormones leptin, insulin, CCK, peptide YY, and ghrelin. The hypothalamus then instructs you to eat more or eat less. Multiple gene variants can influence the way the body receives and responds to these signals. For example, an SNP of the ghrelin gene may cause high levels of ghrelin secretion, which could cause some people to overeat and become obese.42 Individuals who are genetically prone to a leptin deficiency (remember, leptin suppresses hunger) become massively obese, yet when they are given leptin, their hunger decreases and their weight falls to within a healthy range.43 Ironically, many obese people have adequate amounts of leptin, but the brain has developed a resistance to it, rendering its hunger control ineffective.44 For these individuals, other mechanisms prevent leptin from functioning as a regulator of hunger.

The adipocytes also secrete another hormone called adiponectin, which improves the body’s response to insulin, reduces fat accumulation in the liver and muscle, and enhances energy expenditure.45 The levels of this hormone are higher in lean people but are low in people who are obese and those with type 2 diabetes. This difference may be explained by SNPs involving the adiponectin gene and may explain why obesity increases the risk for diabetes.

Genetics may also affect thermogenesis, which in turn affects energy expenditure. Gene variants may cause different rates of thermogenesis in brown adipose tissue and in nonexercise activity thermogenesis (NEAT). When some individuals overeat, they burn rather than store excess kilocalories and are thus better able to manage their energy bal- ance.46 Many overweight individuals don’t appear to have this compensatory mechanism.

Gene Theories May Help Explain Weight Variations

Some researchers have described a genetic “set point” that determines body weight. This theory holds that the body fights to remain at a specific body weight and opposes attempts at either weight loss or weight gain. In other words, a person’s weight remains fairly constant because the body “has a mind of its own.” Given that the average weight of Americans has increased dramatically over the last few decades relative to previous decades, this theory either isn’t true or the set point can be overridden.47

Other researchers have observed that, when excessive amounts of food are available, some people store more fat than others, and in environments where food is scarce, they lose less fat than others.48 Research comparing the Pima Indians in Arizona with their

adiponectin Hormone produced in the

adipocytes that controls the body’s response

to insulin and may be involved in reducing the

risk of obesity and type 2 diabetes.

set point Weight-control theory proposing

that each individual has a genetically

established body weight and that significant

deviation from this point stimulates changes

in body metabolism to reestablish the normal

weight.

How Do Genetics and Environment Influence Obesity and Weight Management? 547

ancestors in Mexico reveals that the environment can encourage weight gain in genetically susceptible populations; that is, populations with so-called thrifty genes.49 The Arizona Pima Indians are descended from the Pima Indians of northwestern Mexico. The original population of Mexican Pima Indians passed their genetic heritage on to their Arizona descendants, but not their lifestyle. This genetic inheritance is theorized to have included genes that have helped the Pimas expend less energy during times of famine and store more energy in times of plenty. However, as compared to the Arizona Pimas, the traditional Mexican Pimas engage in more physical activity and consume a diet higher in complex carbohydrates and lower in animal fats. Mexican Pimas have, on average, a BMI of about 25, compared with Arizona Pimas who have, on average, a BMI of over 33.50 Because they have a healthier lifestyle, the traditional Pimas have lower rates of obesity than the Arizona Pimas. This suggests that even if you have a genetic predisposition to being overweight, it’s not a done deal. If you are determined to make healthy dietary choices and engage in regular physical activity, you can overcome your genetic predisposition.

Environmental Factors Can Increase Appetite and Decrease

Physical Activity

As we saw with the Mexican and Arizona Pimas, the environment around us has changed in ways that have made it easier for people to gain weight. To explain how genetics and environment interact to produce obesity, researchers have used the analogy that genes load the gun but an obesity-promoting environment pulls the trigger.51 Environmental factors that seem particularly important include lack of time, an abundant food supply coupled with portion distortion, and lack of physical activity. Take the Self-Assessment: Does Your Environment Affect Your Energy Balance? to consider how your environment influences the lifestyle decisions you make throughout the day.

Self-Assessment

How Much Does Your Environment Affect Your Energy Balance? 1. Do you eat out at least once a day?

Yes □ No □

2. Do you often buy snacks at convenience stores or vending machines?

Yes □ No □

3. Do you buy the supersized portions of fast foods or snacks?

Yes □ No □

4. When you order pizza, do you have it delivered?

Yes □ No □

5. Do you drive around the parking lot to get the closest parking space to the

entrance?

Yes □ No □

6. Do you get off at the subway or bus stop that is nearest to your destination?

Yes □ No □

7. Do you take the elevator when stairs are available in a building?

Yes □ No □

Answer

All of the above habits contribute to an obesity-promoting environment. If you answered

“yes” to three or more, you should think about how you can improve your lifestyle habits.

548 Chapter 15 | Weight Management

Lack of Time Research shows that adults spend more time traveling to work and devote more of their daily hours to work than in previous decades.52 This longer workday means there is less time to devote to everyday activities, such as food preparation. Today, almost a third of Americans’ daily kilocalories come from ready-to-eat foods that are not pre- pared at home.53 Between 1972 and 1995, the prevalence of eating out in the United States increased by almost 90 percent, a trend that is expected to increase steadily to the year 2020.54 To accommodate this demand, the number of food service establish- ments in the United States has almost doubled—to nearly 900,000—during the last three decades.55

Dining out frequently is associated with a higher BMI.56 An Economic Research Service study found an average increase in kilocalorie intake for adults of 134 kilocalories for every meal eaten away from home.57 Eating out also reduces fruit and vegetable intake and adds more fat, sugar, and alcohol.58 The top foods selected when eating out, especially among college-age diners, are energy-dense French fries and hamburgers.59 Dining out also tends to displace nutrient-dense vegetables and fruits.

An Abundant Food Supply and Portion Distortion In the United States food is plentiful, there’s a lot to choose from, and portion sizes are generous. All of these factors are associated with consuming too many kilocalories.60

Years ago, people went to a bookstore for the sole purpose of buying a book. Now they go to a bookstore to sip a vanilla latte and nibble on biscotti while they ponder which book to buy. Americans can grab breakfast at a fast-food drive-through, lunch at a museum, a sub sandwich at many gas stations, and a three-course meal of nachos, pizza, and ice cream at a movie theater.

This access to a variety of foods is problematic for weight-conscious individuals. The appeal of a food diminishes as it continues to be eaten (that is, the first bite tastes the best and each subsequent bite loses some of that initial pleasure), but having a variety of foods available allows the eater to move on to another food once boredom sets in.61 The more good-tasting foods that are available, the more a person eats. For example, during that three-course meal at the movie theater, once you’re tired of the nachos, you can move on to the pizza, and when that loses its appeal, you can dig into the ice cream. If the pizza and ice cream weren’t available, you would have stopped after the nachos and consumed fewer kilocalories.

As you learned from Chapter 2, the portion sizes of many foods, such as French fries and sodas, have doubled, if not tripled, compared with the portions listed on food labels. Consumers perceive “supersized” portions as bargains because they often cost only slightly more than the regular size. Research shows that people tend to eat more of a food, and thus more kilocalories, when larger portions are served.62 In other words, when served a supersized soft drink, a person consumes more, if not all, of it even though a smaller drink would have provided the same level of satisfaction.

At home, the size of the serving bowl or package of food influences the amount that ends up on the plate. Serving from a large bowl or package has been shown to increase the serving size by more than 20 percent.63 This means that you are more likely to scoop out (and eat) a bigger serving of ice cream from a half-gallon container than from a pint container. To make matters worse, most people don’t compensate for these extra kilocalo- ries by reducing the portions at the next meal.64

You have probably heard competing claims about the superiority of diets high in either protein or carbohydrate for promoting weight loss. Does the macronutrient compo- sition of the diet really influence body weight? To find out, see Examining the Evidence: Do Diets Rich in Carbohydrates Make Us Fat?

Research has shown that women who dine

out five or more times weekly consume close

to 300 kilocalories more on dining-out days

than do women who eat at home.

Do Diets Rich in Carbohydrates Make Us Fat? 549

E X A M I N I N G T H E

EVIDENCE

I n recent years, there has been a

renewed interest in altering the nutri-

ent composition of diets to achieve

weight loss. The recommended AMDR

(Acceptable Macronutrient Distribution

Range) is for 45–65 percent of daily

kilocalories to come from carbohydrates,

20–35 percent of daily kilocalories to

come from fat, and 10–35 percent of

daily kilocalories to come from pro-

teins. Some nutrition experts believe

that people who wish to lose weight

should increase their protein consump-

tion to as much as 45 percent of total

kilocalories, at the same time reducing

carbohydrates to 25 percent.1 They cite

studies reporting that high-protein diets

produce greater weight loss when com-

pared with high-carbohydrate diets of the

same kilocalorie content.2 A diet lower in

carbohydrate and higher in protein also

was reported to prevent weight regain

after weight loss had been achieved.3

Epidemiological evidence also suggests

that carbohydrates may be contributing

to America’s weight gain: According to a

2013 meta-analysis, our increased intake

in carbohydrate-rich, sugar-sweetened

beverages correlates with the weight

gain observed in both children and adults

in recent decades.4 This would suggest

that as dietary intake of carbohydrates

increases, so do our waistlines.

One big challenge is pinpointing the

mechanism that might be responsible for

weight gain with a higher  carbohydrate

intake. Some researchers argue that the

culprit is insulin, while others suggest

high-glycemic foods and beverages,

such as sugary drinks, are the cause. A

third theory is that carbohydrates alter

appetite- suppressing hormones, causing

hunger after a carbohydrate meal. Let’s

take a closer look at the evidence.

The Insulin Connection

As you learned in Chapter 4, the body

requires insulin to facilitate the trans-

port of glucose into body cells. But

that’s not the only function of insulin.

This pancreatic hormone also pro-

motes the synthesis of fatty acids, or

lipogenesis, in the liver. Excess glucose

not converted to glycogen in the liver,

or used for energy, is converted to

fatty acids and stored as fat. In theory,

the more carbohydrate ingested, the

more insulin the pancreas releases, the

greater the potential for glucose to be

stored as fatty acids in the adipocytes.

Insulin also prevents beta-oxidation

of fatty acids by inhibiting lipolysis of

stored fat in the adipose tissue, trap-

ping fatty acids in the adipocytes.5

Thus, the effects of insulin on lipid

metabolism tend toward conservation

of fat. To avoid elevated insulin levels, a

diet lower in carbohydrates would be a

logical strategy.

Hunger Control and Carbohydrate Intake

The composition of the diet may influ-

ence the release of hunger-suppressing

hormones. Recall that hunger is stimu-

lated when ghrelin levels increase or is

reduced when leptin levels increase.

In one study, total ghrelin levels were

shown to decrease significantly when

protein was consumed, compared with

carbohydrates or lipids.6 The research-

ers also noted that after 3 hours,

ghrelin levels rebounded following

carbohydrate intake but not following

protein intake, supporting the theory

that protein suppresses hunger for lon-

ger than does carbohydrate.

Ghrelin levels may be regulated by

insulin, at least initially. In one study,

a higher carbohydrate intake, which

increased the amount of insulin released,

led in turn to a reduction in the amount

of ghrelin in the blood.7 Researchers

suggest that this may be due to the

impact of insulin on circulating ghrelin

levels. Or insulin may be affected by

whether the carbohydrates ingested

were simple or complex carbohydrates.8

The theory is that the release of insulin

following a meal regulates the reduction

of ghrelin, thus influencing satiety.

Carbohydrate and protein may also

affect the satiety hormone peptide

YY. PYY levels have been shown to

increase gradually without declining

after consumption of a high-protein

meal, whereas PYY levels peak and

then begin to decline after consump-

tion of a high-carbohydrate meal.9

Researchers suggest that the increase

in PYY following a high-protein/low-

carbohydrate meal leads to more sus-

tained feelings of satiety and may play

a role in promoting a reduction in over-

all food intake and weight loss.

Glycemic Index and Weight Loss

The typical Western diet, based on

high-glycemic-index staples such as

potatoes, bread, and rice, may affect

hunger and ultimately body weight.

Foods with a high glycemic index are

digested quickly, and in turn quickly

raise blood glucose, thereby increas-

ing insulin secretion to a greater extent

compared with lower-glycemic foods.

Consumption of high-glycemic foods

has also been shown to be followed

by hunger earlier than consumption of

low-glycemic foods.10 The increase in

satiety with low-glycemic, high-fiber

foods also results in lower kilocalorie

intakes and potential weight loss.

Consuming a low-glycemic-index diet

may also be effective in reducing total

body fat. As noted above, increased

levels of insulin may increase lipogenesis

Do Diets Rich in Carbohydrates Make Us Fat?

550 Chapter 15 | Weight Management

6. Vancleef, L., T. Van Den Broeck, T. Thijs, S. Steensels, L. Briand, J. Tack, and I. Depoortere. 2015. Chemosensory signalling pathways involved in sensing of amino acids by the ghrelin cell. Scientific Reports 5:15725. doi: 10.1038/srep15725.

7. Steensels, S., L. Vancleef, and I. Depoortere. 2016. The Sweetener-Sensing Mechanisms of the Ghrelin Cell. Nutrients 8(12):795. doi: 10.3390/nu8120795.

8. Penaforte, F. R., C. C. Japur, L. P. Pigatto, P. G. Chiarello, and R. W. Diez-Garcia. 2013. Short-Term Impact of Sugar Consumption on Hunger and Ad Libitum Food Intake in Young Women. Nutrition Research and Practice 7(2):77–81.

9. Sedlackova, D., J. Kopeckova, H. Pape- zova, V. Hainer, H. Kvasnickova, M. Hill, and J. Nedvidkova. 2012. Comparison of a High-Carbohydrate and High-Protein Breakfast Effect on Plasma Ghrelin, Obestatin, NPY and PYY Levels in Women with Anorexia and Bulimia Nervosa. Nutrition and Metabolism 9:52. doi: 10.1186/1743-7075-9-52.

10. S. Wang, L. Yang, J. Lu, and Y. Mu. 2014. High Protein Breakfast Promotes Weight Loss by Suppressing Subsequent Food Intake and Regulating Appetite Hormones in Obese Chinese Adolescents. Hormonal Research in Paediatrics. doi: 10.1159/000362168.

11. A. M. Goss, L. L. Goree, A. C. Ellis, P. C. Chandler-Laney, K. Casazza, M. E. Lockart, and B. A. Gower. 2013. Effects of Diet Mac- ronutrient Composition and Fat Distribution During Weight Maintenance and Weight Loss. Obesity 21(6):1139–1142.

12. J. Halkjaer, T. I. Sorensen, A. Tjonneland, et al. 2004. Food and Drinking Patterns as Pre- dictors of 6-year BMI-Adjusted Changes in Waist Circumference. British Journal of Nutri- tion 92:735–748.

13. Naude, C. E., A. Schoonees, M. Senekal, T. Young, P. Garner, and J. Volmink. 2014. Low Carbohydrate versus Isoenergetic Balanced Diets for Reducing Weight and Cardiovas- cular Risk: A Systematic Review and Meta- Analysis. PLoS ONE 9(7):e100652. doi: 10.1371/journal.pone.0100652.

14. Astrup, A., and J. Brand-Miller. 2014. Obesity: Have New Guidelines Overlooked the Role of Diet Composition? Natural Review of Endocrinolog y 10(3):132–133.

with a smaller waist circumference.12 The

results of these studies suggest that con-

suming low-glycemic foods reduces the

impact of insulin on lipid metabolism and

may enhance fat loss.

The evidence supporting the prem-

ise that a high-carbohydrate diet may

promote weight gain is promising;

however, when researchers compare

the effects of isocaloric diets that are

low in carbohydrate (less than 45 per-

cent carbohydrate) versus moderate in

carbohydrate (45–65 percent carbohy-

drate), the weight loss is similar.13 Until

more conclusive evidence is presented,

a healthy weight-loss diet should

include lean meats, low-fat dairy, whole

grains, legumes and other vegetables,

and fresh fruits and limit high-glycemic

refined carbohydrates.14

References

1. Astrup, A., A. Raben, and N. Geiker. 2015. The Role of Higher Protein Diets in Weight Control and Obesity-Related Comorbidities. International Journal of Obesity 39(5):721–726. doi: 10.1038/ijo.2014.216.

2. Bray, G. A., D. H. Ryan, W. Johnson, et al. 2017. Markers of Dietary Protein Intake Are Associated with Successful Weight Loss in the POUNDS Lost Trial. Clinical Obesity. doi: 10.1111/cob.12188.

3. M. P. Lejeune, E. M. Kovacs, and M. S. Westerterp-Plantenga. 2005. Additional Protein Intake Limits Weight Regain After Weight Loss in Humans. British Journal of Nutrition 93:281–289.

4. V. S. Malik, A. Pan, W. C. Willett, and F. B. Hu. 2013. Sugar-Sweetened Beverages and Weight Gain in Children and Adults: A Sys- tematic Review and Meta-Analysis. American Journal of Clinical Nutrition 98(4):1084 –1102.

5. DiPilato, L. M., F. Ahmad, M. Harms, P. Seale, V. Manganiello, and M. J. Birnbaum. 2015. The Role of PDE3B Phosphorylation in the Inhibition of Lipolysis by Insulin. Molecular and Cellular Biolog y 35(16):2752– 2760. doi: 10.1128/MCB.00422-15

and decrease lipolysis, thereby preserv-

ing body fat. A 2013 study measured the

impact of a low-glycemic diet (average

49 on the glycemic index) compared with

a high-glycemic diet (average 60 on the

glycemic index) for 16 weeks. Results

showed that at the end of the 16-week

study, the low-glycemic group had

dropped 4.4 percent more intra-abdom-

inal fat compared with the high-glycemic

group (Figure 1).11 Another study reported

that a low- glycemic diet is associated

▲ Figure1

The Effects of a High versus Low Glyce-

mic Diet on Fat Loss A low-glycemic diet

resulted in a greater loss of abdominal fat

compared to a high-glycemic diet.

Source: A. M. Goss, L. L. Goree, A. C. Ellis, P. C.

Chandler-Laney, K. Casazza, M. E. Lockart, and B. A.

Gower. 2013. Effects of Diet Macronutrient Composition

and Fat Distribution during Weight Maintenance and

Weight Loss. Obesity 21(6):1139–1142.

-0.5

0

-3.5

-3

-2.5

-2

-1.5

-1

-4

-4.5

Low-GL

diet

T o ta

l fa

t lo

s s ( k g )

High-GL

diet

Lack of Physical Activity Since 1985, Americans have been consuming about 300 more kilocalories daily while also expending less energy during their entire day.65 The increase in “kilocalories in” and decrease in “kilocalories out” is a recipe for a positive energy imbalance and weight gain. Compared with years past, Americans expend less energy both at work and in the little leisure time that they have.

When your great-grandparents went to work in the morning in the 1940s, chances are good they headed out to the fields or into factories. Your parents, though, are more likely to head to an office and sit in front of a computer, and you will probably sit at a desk for much of your workday. This shift in work from jobs that required manual labor to jobs that are sedentary has contributed to the rising rates of overweight and obesity in

How Can You Lose Weight Healthfully? 551

How Can You Lose Weight Healthfully?

LO 15.5 Describe the role of diet and exercise in achieving a reasonable rate of weight loss.

The easiest way to avoid having to lose weight is to not gain weight in the first place. But for people who do need to shed pounds, following the principles discussed here can help.

America.66 One study found that men who sit for more than 6 hours during their workday are at higher risk of being overweight than those who sit for less than an hour daily.67

Technology in the workplace now allows us to communicate with everyone without having to leave our desks. This means that people no longer have to get up and walk to see the colleague down the hall or the client down the street. Researchers estimate that a 145-pound person expends 3.9 kilocalories for each minute of walking, compared with 1.8 kilocalories per minute sitting. Thus, walking 10 minutes during each workday to com- municate in person with coworkers would expend 10,000 kilocalories annually, yet only about 5,000 kilocalories would be expended if the person sat in the office sending e-mails or calling colleagues on the phone. Over the course of a year, these extra 5,000 kilocalories not expended could add up to over a pound of body weight. After 5 years in the workforce, there would be around seven extra pounds of body weight sitting in the chair.

Another form of technology, mechanized transportation, may negatively affect your weight-management goals. Research on urban sprawl has shown that the greater the dis- tance between home and school or work, the more people drive or use public transporta- tion and the less they engage in biking or walking. In addition, the more you drive, the more you weigh.68 For each hour you spend driving to work or school, the likelihood of obesity increases 6 percent, whereas for each half-mile walked per day, the likelihood of obesity is reduced by almost 5 percent.69 This may be one of the factors in the increase in obesity rates among children. In a recent study in Canada, only 25–30 percent of chil- dren and youth reported walking or bicycling to school.70 Changing these behaviors while providing a safe way for children to arrive at school requires creative solutions. One such solution is the “walking school bus.” A walking school bus is similar to a car pool except students walk to school with one or more adults. Children arrive at school safely and increase their daily physical activity.71

As technology continues to advance and allows for less energy expenditure during the day, planned physical activity at another time of day must make up the difference. Unfortunately, more than 20 percent of Americans report no daily leisure-time physical activity.72 Research shows that those age 2–18 years old spend over 5 hours daily, on aver- age, on a combination of “screen-time” activities. These include watching TV, playing video games, and non-work/school-related computer time—even though experts have suggested limiting screen time to 2 hours daily.73

Students who walk to school accompanied

by their parents demonstrate the concept of a

“walking school bus.”

Increased amounts of “screen time” are con-

tributing to decreased amounts of physical

activity.

LO 15.4: THE TAKE-HOME MESSAGE Many genetic influences play a role in obe- sity and weight management. Nutrigenomics has identified specific genes that

are involved in how we absorb, store, or break down dietary fat. Epigenetics—

changes in gene expression rather than DNA—may help to explain the effects

on body weight when certain foods are eaten. Gene variants, such as single-

nucleotide polymorphisms that affect hormone levels, can influence body

weight, as can so-called thrifty genes. Several environmental factors—which

include lack of time, easy access to a variety of energy-dense foods and large

portions, and lack of physical activity—also encourage obesity.

552 Chapter 15 | Weight Management

Avoid Fad Diets

The low-carbohydrate, high-protein, and high-fat diets of the 1970s (Dr. Atkins’ Diet Revolution) were replaced by the very high-carbohydrate and very low-fat diets of the 1980s and early 1990s (Pritikin and Dr. Ornish’s diets), which were in turn replaced by the carbohydrate-restricted, moderate-protein and -fat diets of the late 1990s (the Zone diet), only to flip back to the low-carbohydrate, high-protein and high-fat diets in the early 2000s (Dr. Atkins’ New Diet Revolution, South Beach). Fifteen years later, we’re back to lower-carbohydrate and higher-protein diets (Paleo and New Atkins diets).

Fad diets promise quick weight loss by means that are typically unproven and unhealthy. For example, the latest fad diets claim that consumption of pasta, breads, rice, and many fruits and vegetables should be limited, whereas fatty meats, butter, and cheeses should be on the menu often. A diet high in saturated fat and low in fiber and phytochemi- cals is a recipe for heart disease, cancer, constipation, and deficiencies in many vitamins and minerals, such as vitamins A, E, C and folate, calcium, iron, zinc, and potassium.

Whereas each of the fad diets just mentioned provides a different percentage of carbohydrates, protein, and fat, they all had one important thing in common: They all reduced energy intake. A very interesting point emerged from a recent study comparing several of these diets: People who were most diligent about adhering to the diet—no matter which one—experienced the most weight loss.74 However, more than 20 percent of the dieters quit just two months into the study, and more than 40 percent of them dropped out after 1 year. The highest dropout rates occurred among followers of the Atkins or Ornish diets. The researchers speculate that the rigidity of these extreme diets may have caused the higher dropout rates. Thus, the problem with many fad diets is that people give up on them long before they meet their weight-loss goals. A fad diet doesn’t fix anything in the long term. If it did, new (or recycled) fad diets wouldn’t continually be appearing on the market.

Strive for a Reasonable Rate of Weight Loss

The National Institutes of Health advises that overweight individuals aim to lose about 10 percent of their body weight over a 6-month period.75 This means that the goal for an overweight, 180-pound person would be to shed 18 pounds in half a year, which would be about 3 pounds a month or 3�4 pound weekly. Because a person must have an energy deficit of approximately 3,500 kilocalories to lose a pound of fat, a deficit of 250–500 kilocalories daily will result in a reasonable weight loss of about 1�2 to 1 pound weekly. Any diet that promises quicker weight-loss results is likely to restrict kilocalories to the point of falling short of nutrient needs. Practice calculating the amount of reasonable weight loss you can expect in the Calculation Corner.

fad diet Diet that promises rapid weight loss

via a method that is typically unproven and

unhealthy.

Calculation Corner

Calculating Percentage of Weight Loss If an overweight individual weighs 237 pounds at the beginning of a weight-loss program, what

would he or she weigh after 6 months if the recommendations for healthy weight loss were

followed?

Answer:

The individual’s initial weight minus

10 percent

237 lbs - (237 * 0.10) = 213.3 lbs

C

Go to Mastering Nutrition and complete a Math Video activity similar to the problem in this Calculation Corner.

How Can You Lose Weight Healthfully? 553

Though there is no single diet approach that has been universally embraced, many health experts agree that a person needs to modify three areas of life for successful, long- term weight loss. These three areas are diet, physical activity, and behavior. Let’s begin with the diet.

Remember That Kilocalories Count

When it comes to losing weight, two important words need to be remembered: kilocalories count—no matter where they come from. An energy imbalance of too many kilocalories in and too few kilocalories out causes weight gain, and reversing the imbalance causes the opposite: Taking in fewer kilocalories and burning off more results in weight loss. The dietary goal, then, is to reduce the number of kilocalories consumed in foods. This can be done in several ways: by choosing lower-kilocalorie foods, by eating less food overall, or by doing both.

However, cutting back too drastically on kilocalories is the culprit behind many failed weight-loss attempts. If a person skips meals or isn’t satiated at each meal because of skimpy portions, the person will experience hunger between meals and be more inclined to snack on energy-dense foods. Thus a key factor for success during the weight-loss pro- cess is for the person to eat a healthy, balanced diet that provides fewer kilocalories but is also satisfying. One strategy that many find helpful is to eat three small, nutritious meals throughout the day combined with a midmorning and a midafternoon snack. Eating more frequently keeps a person from getting too hungry and overeating at one sitting, while keeping meals small and nutrient dense ensures adequate nutrient intake without an over- consumption of kilocalories. Note that eating three small meals plus snacks is not the same thing as grazing. Grazing involves constant eating or nibbling throughout the day with- out allowing for feelings of hunger or satiation. This mindless eating behavior results in overconsumption of kilocalories and is considered a high-risk behavior for weight gain.76

Reducing the intake of kilocalories a little at a time can add up to healthy weight loss. A 180-pound, overweight person who consumes 2,800 kilocalories daily can reduce his or her intake to 2,400–2,600 kilocalories, incurring a kilocalorie deficit of 200–400 kilocalories daily. He or she will then lose 10 pounds in about 3 months. Small changes, like switching from full-fat to nonfat dairy products or replacing an afternoon soda with a glass of water, can contribute to this kilocalorie reduction.

Eat More Vegetables, Fruits, and Fiber

Research suggests that the volume (or bulk) of food consumed at a meal is very important. High-volume (high-bulk) meals and snacks have a high water and/or fiber content and are filling. Thus, consuming high-volume, low-energy-density vegetables and fruits at meals and snacks is associated with increased satiety and reduced feelings of hunger and kilocalorie intake—all helpful in weight management.77 In contrast, people tend to eat the same amount of food regardless of its energy density—that is, the number of kilocalories in the meal.78 In other words, energy-dense, low-volume foods can easily fill you out before they fill you up. Try calculating the energy density of foods in the Calculation Corner.

Calculation Corner

Calculating Energy Density Energy density of foods can be calculated and compared using the method described by Barbara

Rolls, PhD.1 Divide the kilocalories in a serving of food by the weight in grams of a serving of the

food. Try calculating the energy density of the following foods to determine which one is more

energy dense.

C

554 Chapter 15 | Weight Management

In fact, consuming a large, high-volume, low-energy-density salad at the beginning of a meal can reduce the kilocalories eaten at that meal by over 10 percent.79 Adding veg- etables to sandwiches and soups increases both the volume of food consumed and meal satisfaction and helps displace higher-kilocalorie items (Figure 15.5). Feeling full after eating a sandwich loaded with vegetables reduces the consumption of energy-dense potato chips. This is important because you don’t need to eliminate chips from your diet if you enjoy them. Any food—from chocolate to chips—can be modest in kilocalories if eaten in modest amounts. Again, to lose weight, limit your intake of energy-dense, low-bulk foods and choose more nutrient-dense, high-bulk foods. Table 15.1 provides examples of foods low, moderate, and high in energy density.

(1) Chocolate ice cream: 1�2@cup serving (111 grams); 340 kilocalories (2) Frozen broccoli florets: 1-cup serving (85 grams); 25 kilocalories

To calculate the energy density of each food, divide the kilocalories by the weight in grams.

Answer:

Ice cream: 340 kcals/111 g = 3.1 Frozen broccoli florets: 25 kcals/85 g = 0.3

Reference

1. Vernarelli, J., D. C. Mitchell, B. J. Rolls, and T. J. Hartman. 2013. Methods for Calculat- ing Dietary Energy Density in a Nationally Representative Sample. Procedia Food Science 2:68–74.

▲ Figure 15.5 Adding Volume to Meals

Adding high-volume, low-energy-dense foods like fruits and vegetables to sandwiches, soups, and meals can add to satiety and displace foods

higher in kilocalories, two factors that can improve weight management.

Low-energy-dense foods

2 slices whole-wheat bread: 138 calories

4 oz ham: 125 calories

2 oz American cheese: 213 calories

324

2 slices whole wheat-bread: 138 calories

2 oz ham: 63 calories

1 oz American cheese: 106 calories

2 slices tomato: 7 calories

2 leaves Romaine lettuce: 10 calories

total kilocalories

total kilocalories total kilocalories

total kilocalories

347 300347

3/4 cup chicken broth: 29 calories 1/2 cup chicken (white meat): 106 calories

1 cup noodles: 212 calories

3/4 cup chicken broth: 29 calories 1/2 cup chicken (white meat): 106 calories 1/2 cup noodles: 106 calories 1/2 cup mixed vegetables: 59 calories

High-energy-dense foods

476

Go to Mastering Nutrition and complete a Math Video activity similar to the problem in this Calculation Corner.

How Can You Lose Weight Healthfully? 555

We just noted that dietary fiber contributes to the bulk of vegetables and fruits and their ability to prolong satiety.80 Intriguingly, overweight individuals have been shown to consume less dietary fiber than normal-weight people.81 The Table Tips provide easy ways to add these foods to your diet.

The composition of the diet alters the composition of the GI flora. This in turn may influence body weight. Read Examining the Evidence: The Microbiome: Is There a Link to Obesity? on page 556 to find out more.

Add Some Protein and Fat to Meals

Protein has the most dramatic effect on satiety; therefore, high-protein diets tend to reduce hunger and support weight loss.82 Because fat slows the movement of food out of the stomach into the intestines, it can also prolong satiety. Therefore, adding some lean pro- tein and healthy fat at all meals and even with snacks can help reduce hunger. This is not to say that carbohydrates should be severely restricted or eliminated; rather, all macronu- trients are necessary in the correct proportions.

Keep in mind, however, that a diet high in saturated fat increases the risk for cardio- vascular disease. To boost protein, choose lean meat, skinless chicken, fish, legumes, and nuts and seeds, which are kinder to the waist and heart.

Meals that contain fruits, vegetables, and whole grains, as well as some lean protein and a modest amount of fat, are sensible for weight loss. These meals are also balanced, meeting daily nutrient needs.

Increase Physical Activity

Regular physical activity can not only add to the daily energy deficit needed for weight loss, but can also displace sedentary activity such as watching television, which often leads to mindless snacking on energy-dense foods.83 Going for a walk and expending kilocalories rather than watching a movie while snacking on a bag of tortilla chips provides kilocalorie benefits beyond the exercise alone.

TA B L E T I P S

Eat More to Weigh Less

Eat more whole fruit and drink less juice

at breakfast. The orange has more fiber

and bulk than the OJ.

Make the vegetable portions on your

dinner plate twice the size of the meat

portion.

Have a side salad with low-fat dressing

with a lunchtime sandwich instead of a

snack bag of chips.

Order your next pizza with less pep-

peroni and more peppers, onions, and

tomatoes. A veggie pizza can have

25 percent fewer kilocalories and about

50 percent less fat and saturated fat

than a meat pizza.

Cook up a whole-wheat-blend pasta

for your next Italian dinner. Ladle on

plenty of tomato sauce and don’t forget

the big tossed salad as the appetizer.

▲ Low These foods provide 0.7–1.5 kilocalories

per gram and are high in water and fiber.

Examples include most vegetables and

fruits—tomatoes, cantaloupe, strawberries,

broccoli, cauliflower, broth-based soups, fat-

free yogurt, and cottage cheese.

▲ Medium These foods have 1.5–4 kilocalories per

gram and contain less water. They include

bagels, hard-cooked eggs, dried fruits,

lean sirloin steak, hummus, whole-wheat

bread, and part-skim mozzarella cheese.

▲ Hight These foods provide 4–9 kilocalories per

gram, are low in moisture, and include

chips, cookies, crackers, cakes, pastries,

butter, oil, and bacon.

Source: Adapted from B. J. Rolls and R. A. Barnett, The Volumetrics Weight-Control Plan (New York: HarperCollins, 2000) and Centers for Disease Control and Prevention,

How to Use Fruits and Vegetables to Manage Your Weight, 2012. Available at www.cdc.gov/healthyweight/healthy_eating/fruits_vegetables.html. Accessed May 2014.

TABLE 15.1 The Energy Density of Foods

556 Chapter 15 | Weight Management

E X A M I N I N G T H E

EVIDENCE

T he term microbiome refers to the

billions of microscopic organ-

isms that live within an individual’s

body, including in the GI tract, on the

skin, and in the lungs. The majority of

these microbes are the GI flora living in

the large intestine. Recall from Chapter 3

that GI flora participate in digestion and

metabolism. For instance, they extract

energy from undigested foods; synthesize

vitamins, including vitamin K; regulate

fatty acid tissue composition; and control

peptides secreted from the GI tract.

More than 1,000 different types of

bacteria live in the GI tract, but the pre-

cise species and the size of their popu-

lations vary.1 Recently, scientists have

suggested that when specific intestinal

microbes are significantly high in the gut,

obesity may result.2 If this is true, could

we alter the composition of our GI flora

and eliminate the obesity epidemic?

Effect of Diet on Intestinal Bacteria

Different diets, whether followed briefly

or persistently, influence the types of

intestinal bacteria that live in the GI

tract and the types of genes expressed

by those bacteria.3 In fact, differences

in diet may explain up to 57 percent of

the differences in the type of intestinal

bacteria.6 The changes are thought

to occur because diet influences the

bacteria’s metabolism and your body’s

immune functions.

For example, breast-fed infants have

more Bifidobacterium and Ruminococ-

cus, with significantly less Escherichia

coli, Clostridium difficile, Bacteroides

fragilis, and Lactobacillus than infants

fed formula.4 As soon as infants begin

to eat solid food, the composition of the

GI flora changes again, resembling that

of an adult, with Firmicutes and Bacte-

roidetes becoming dominant.5 In addition,

a change from a low-fat, high-fiber diet

to a high-fat, high-sugar diet increases

the bacteria Firmicutes and decreases

Bacteroidetes.7 These changes can

occur within just 24 hours.8,9 In other

studies, people eating a vegetarian or

vegan diet had significantly lower levels

of Bacteroidetes, Bifidobacterium, E.

coli, Enterobacteriaceae, and Clostridium

bacteria than people eating a normal

mixed diet.10,11 What effect, if any, do these

variations in microbiome have on obesity?

Intestinal Bacteria and Obesity

The first clue that intestinal bacteria

could influence obesity was the dis-

covery that obese mice have a higher

proportion of Firmicutes and significantly

fewer Bacteroidetes than lean mice.12

Similarly, 12 obese human subjects

were found to have a larger proportion

of Firmicutes and very few Bacteroide-

tes compared with two lean subjects.13

Other studies report slightly different pat-

terns,14,15,16 but the question remains: Do

these differences in the type of intestinal

bacteria cause or contribute to obesity?

Just as the diet affects the different

forms of bacteria that live in the GI tract,

the presence of certain strains of intes-

tinal bacteria can also influence human

metabolism. Several theories have been

proposed for the role of the microbi-

ome in physiological mechanisms con-

tributing to obesity. Different species

of intestinal bacteria may control the

amount of energy produced from non-

digested food in the intestinal tract. For

instance, an increase in Firmicutes and

a drop in Bacteroidetes could increase

the amount of energy produced. The

Firmicutes bacteria are genetically prone

to increase the digestion of polysaccha-

rides, producing monosaccharides and

short-chain fatty acids. These short-

chain fatty acids attach to the entero-

cytes on the surface of the intestinal villi,

slowing intestinal motility and transit.

These short-chain fatty acids attach to

the epithelial cells that cover the villi lin-

ing the intestinal cells, slowing intestinal

motility and transit. Not only does the

intestinal tract have receptor sites for

ghrelin to stimulate hunger, but there are

also receptor sites on the intestinal cells

to which short-chain fatty acids attach

that may also stimulate hunger. Certain

bacteria may also cause inflammation

and alter human genes that stimulate fat

synthesis in the adipocyte.17

If we altered the diet of obese

people in order to change the composi-

tion of intestinal bacteria, would they

lose weight? Perhaps. One case study

involved a morbidly obese male whose

intestinal bacteria were 35 percent

Enterobacter. This form of intestinal

bacteria produces lipopolysaccharide

endotoxins that, if they leak through

the intestinal tract into the blood, can

cause inflammation and contribute to

obesity, at least in animal models. The

subject in this case study was placed

on a 9-week dietary regimen composed

of whole grains, prebiotics, and foods

promoted in traditional Chinese medi-

cine. After 9 weeks, the subject lost

66 pounds and reduced the Enterobac-

ter population to 1.8 percent.18 As the

level of Enterobacter decreased, the

inflammation and levels of lipopolysac-

charide endotoxins also dropped.

The majority of the research

reported thus far, however, has been in

animal models. Well-designed research

in humans is needed to unravel the

complex relationship between micro-

biome composition and obesity. At this

point, manipulating the GI flora is not a

realistic weight-management tool.

References

1. Komaroff, A. L. 2017. The Microbiome and Risk for Obesity and Diabetes. Journal of the American Medical Association 317(4):355–356. doi: 10.1001/jama.2016.20099.

2. Gérard, P. 2016. Gut Microbiota and Obesity. Cellular and Molecular Life Sciences 73(1):147– 162. doi: 10.1007/s00018-015-2061-5.

3. Ibid. 4. Stearns, J. C., M. A. Zulyniak, R. J. de Souza,

N. C. Campbell, M. Fontes, and M. Shaikh. 2017. Ethnic and Diet-Related Differences in the Healthy Infant Microbiome. Genome Medicine 9:32. doi: 10.1186/s13073-017-0421-5

5. F. Turroni, C. Peano, D. A. Pass, E. Foroni, M. Severgnini, M. J. Claesson, et al. 2012. Diversity of Bifidobacteria within the Infant Gut Microbiota. PLoS ONE 7:e36957. doi: 10.1371/journal.pone.0036957.

The Microbiome: Is There a Link to Obesity?

13. Ibid. 14. John, G. K., and G. E. Mullin. 2016. The Gut

Microbiome and Obesity. Current Oncolog y Report 18(7):45. doi: 10.1007/s11912-016-0528-7.

15. Ibid. 16. Blaut, M. 2015. Gut Microbiota and Energy

Balance: Role in Obesity. The Proceedings of the Nutrition Society 74(3):227-234. doi: 10.1017/ S0029665114001700.

17. Moreno-Indias, I., F. Cardona, and M. I. Queipo-Ortuño. 2014. Impact of the Gut Microbiota on the Development of Obesity and Type 2 Diabetes Mellitus. Frontiers in Microbiolog y 5:190–200.

18. Cani, P. D., J. Amar, M. A. Iglesias, M. Poggi, C. Knauf, D. Bastelica, et al. 2007. Metabolic Endotoxemia Initiates Obesity and Insulin Resistance. Diabetes 56:1761–1772.

Microbiota Revealed by a Comparative Study in Children from Europe and Rural Africa. Proceedings of the National Academy of Science

U.S.A. 107:14691–14696. 10. Glick-Bauer, M., M. C. Yeh. 2014. The

Health Advantage of a Vegan Diet: Explor- ing the Gut Microbiota Connection. Nutrients 6(11), 4822–4838. doi: 10.3390/nu6114822.

11. Zimmer, J., B. Lange, J. Frick, H. Sauer, K. Zimmermann, A. Schwiertz, et al. 2011. A Vegan or Vegetarian Diet Substantially Alters the Human Colonic Faecal Microbiota. Euro- pean Journal of Clinical Nutrition 66:53–60.

12. Brahe, L. K., A. Astrup, and L. H. Larsen. 2016. Can We Prevent Obesity-Related Metabolic Diseases by Dietary Modulation of the Gut Microbiota? Advances in Nutrition 7(1):90–101. doi: 10.3945/an.115.010587.

6. Cong, X., W. Xu, R. Romisher, S. Poveda, S. Forte, A. Starkweather, and W. A. Henderson. 2016. Gut Microbiome and Infant Health: Brain- Gut-Microbiota Axis and Host Genetic Factors. Yale Journal of Biolog y and Medicine 89(3):299–308.

7. Murphy, E. A., K. T. Velazquez, and K. M. Herbert. 2015. Inf luence of High-Fat-Diet on Gut Microbiota: A Driving Force for Chronic Disease Risk. Current Opinion in Clinical Nutrition and Metabolic Care 18(5):515–520. doi: 10.1097/MCO.0000000000000209

8. Wu, G. D., J. Chen, C. Hoffmann, K. Bit- tinger, Y. Y. Chen, S. A. Keilbaugh, et al. 2011. Linking Long-Term Dietary Patterns with Gut Microbial Enterotypes. Science 334:105–108.

9. De Filippo, C., D. Cavalieri, M. Di Paola, M. Ramazzotti, J. B. Poullet, S. Massart, et al. 2010. Impact of Diet in Shaping Gut

Individuals are advised to devote 60–90 minutes daily to moderate-intensity activities to aid in weight loss and prevent weight gain.84 Moderately intense physical activity would be the equivalent of walking 3.5 miles per hour (Table 15.2). The longer your exercise session, the more oxygen is consumed after the exercise ends, which contributes to a higher sustained metabolic rate and more kilocalories burned throughout the day, even at rest.85 Establishing an exercise program that incorporates cardiorespiratory and strength-training activities has even greater benefits, one of which is the increased metabolic rate that occurs with an increase in muscle mass. For more information on the influence of exercise on losing weight, see Examining the Evidence: Which Exercise Is Most Effective for Weight Loss? on page 558.

Research suggests that accumulating 10,000 steps daily, which generally is the equivalent of walking 5 miles, can help reduce the risk of becoming over- weight.86 Americans, on average, accumulate only 900–3,000 steps daily.87 To reach 10,000 steps, most people need to make a conscious effort to keep mov- ing. Using a pedometer can help you track the number of steps you take and let you know if you are hitting this target, or if you need to get up and move much more often. The Fitness Tips provide more suggestions on how to expend more energy during the day.

Wearing a pedometer, like the one shown here, can help you

track your steps. Remember to aim for 10,000 steps per day.

Moderate Physical

Activity

Approximate Kilo-

calories/Hour for a

154-lb Person*

Vigorous Physical

Activity

Approximate Kilo-

calories/Hour for

a 154-lb Person*

Hiking 370 Running/jogging

(5 mph)

590

Light gardening/yard

work

330 Bicycling

(7 10 mph) 590

Dancing 330 Swimming (slow

freestyle laps)

510

Golf (walking and

carrying clubs)

330 Aerobics 480

Bicycling (6 10 mph) 290 Walking (4.5 mph) 460 Walking (3.5 mph) 280 Heavy yard work

(chopping wood)

440

Weight lifting (gen-

eral light workout)

220 Weightlifting (vigor-

ous effort)

440

Stretching 180 Basketball (vigorous) 440

Note:* Calories burned per hour will be higher for persons who weigh more than 154 lbs (70 kg) and lower for

persons who weigh less.

Source: Adapted from 2015–2020 Dietary Guidelines for Americans. 2017. Available at https://health.gov/

dietaryguidelines/2015/. Accessed April 2017.

TABLE 15.2 Kilocalories Used during Activities

F I T N E S S T I P S

Get UP and MOVE

Skip the text messages and walk to

visit your friends on campus.

Don’t go to the closest coffee shop for

your morning latte; walk to the java joint

that is a few blocks farther away.

Take a 5-minute walk at least twice

a day. A little jolt of exercise can help

break the monotony of studying and

work off some stress.

Accomplish two goals at once by

cleaning your dorm room or apartment.

A 150-pound person burns about

4 kilocalories for every minute spent

cleaning. Scrub, sweep, or vacuum

for 30 minutes and you could work off

about 120 kilocalories.

Offer to walk your neighbor’s dog daily.

How Can You Lose Weight Healthfully? 557

558 Chapter 15 | Weight Management

E X A M I N I N G T H E

EVIDENCE

W eight loss occurs when the

amount of energy you expend

is greater than the amount of

energy you consume, creating an energy

deficit. Adding exercise to your daily rou-

tine can help create this energy deficit.

Exercise mobilizes energy stores, includ-

ing fat stored in adipocytes, to fuel the

exercise, ultimately reducing the size of

adipocytes, increasing the ratio of lean

body mass to fat mass, and reducing risk

factors correlated with obesity.1

The American College of Sports

Medicine recommends that most

adults engage in moderate-intensity

cardiorespiratory exercise for at least

225–300 minutes per week to maintain

a healthy body weight and prevent

weight gain.2 For weight loss, how-

ever, some researchers advocate more

intense exercise regimens. What are

the potential weight-loss benefits of dif-

ferent types and intensities of exercise?

Aerobic Exercise and Weight Loss

Even though aerobic exercise provides

numerous health benefits, including

blood glucose control, reduced blood

pressure, and an increase in high-

density lipoproteins for overweight or

obese subjects, clinical trials report

only modest weight-loss effects related

to the exercise itself.3 Aerobic exercise

is classified as exercise of low to mod-

erate intensity that utilizes the aerobic

reactions that produce ATP. Carbo-

hydrates, fats, and protein all provide

energy to perform aerobic-type exer-

cise, which includes brisk walking, jog-

ging, hiking, and cross-country skiing.

Recall from Chapter 8 that lipolysis,

or the breakdown of stored fatty acids

for energy production, occurs during

aerobic metabolism. However, in the first

few minutes of any moderate exercise,

carbohydrates, creatine phosphate,

and the 3–5 seconds’ worth of stored

ATP—not fat—provide most of the fuel.

As aerobic metabolism begins to fully

power up, lipolysis of stored fat and

beta-oxidation of fatty acids increases,

eventually exceeding carbohydrate as

the main fuel source. Does this mean

that moderate aerobic exercise is the

key to successful weight loss?

A classic 3-month study reported

the influence of diet and exercise on

body composition in obese women.

Ninety-one obese women were ran-

domly assigned to diet only, exercise

only, diet plus exercise, or control

group. Those in the exercise groups

were asked to complete 45 minutes

of moderate-intensity cardiorespira-

tory exercise per day, 5 days a week.

The results were surprising: those in

the diet-plus-exercise group lost the

same amount of weight as those who

only dieted.4 The aerobic exercise–only

group did not differ in weight loss

from the control group at the end of

the study. A more recent study found

similar results. Subjects who increased

the cardiorespiratory exercise to

50  minutes, 5 days a week without

dieting lost a similar amount of weight

to those who restricted kilocalories

without exercise.5 In another study

involving obese women, moderate-

intensity aerobic exercise without

dieting had the same effect as dieting

without exercise. Both groups lost an

average of 8 kilograms (about 17.5

pounds) over the course of 12 weeks.6

Over the course of a 1-year study,

subjects who performed aerobic

exercise without dieting for 60  minutes

a day, 6 days a week, lost only an

average of 3.5 pounds over the year.7

Unless the overall volume of accumu-

lated time devoted to aerobic exercise

is high, according to the experts,

significant weight loss is unlikely from

aerobic exercise alone.8 Moreover, as

you already learned in this chapter,

finding—or making—the time to exer-

cise is a barrier for most adults. Per-

haps the answer lies in short, intense

bouts of anaerobic exercise?

Anaerobic Exercise and Weight Loss

Anaerobic exercise is more intense

than aerobic, but it is also by necessity

shorter in duration because the body’s

glucose and glycogen stores are

rapidly depleted. For instance, heavy

weightlifting, sprinting, jumping rope,

and climbing stairs are all examples of

anaerobic, high-intensity exercise. The

higher the intensity of anaerobic exer-

cise, the less fat is oxidized and the

more glycogen and blood glucose are

used to produce energy.

Performing intermittent cycles of

high-intensity exercise, also known

as high-intensity intermittent exercise

(HIIE) or high-intensity interval train-

ing (HIIT), has been shown to result

Which Exercise Is the Most Effective for Weight Loss?

Which Exercise Is the Most Effective for Weight Loss? 559

group, a resistance-training group, or

a group that performed both aerobic

exercise and resistance training. The

aerobic-exercise group exercised the

equivalent of 12 miles per week either

on a treadmill or elliptical trainer. The

resistance-training group lifted weights

3 days per week, three sets per day,

with 8–12 repetitions per set. The aer-

obic-exercise plus resistance-training

group completed both protocols. After

10 weeks, the aerobic-exercise group

and the aerobic-plus-resistance-training

group lost more total body weight and

fat loss than the resistance-training

group.12 Interesting to note, however, is

that the subjects in the combined group

significantly reduced their waist circum-

ference compared with the aerobic-only

group or the resistance-training group.

Another study tested the hypothesis

that short-term aerobic activity com-

bined with anaerobic exercise might

improve weight loss compared with

aerobic activity alone. Sixteen obese

subjects performed one of two exer-

cise protocols for 4 weeks. Group one

performed an aerobic cycle workout for

30 minutes while group two completed

a 25-minute aerobic workout followed

by 5 minutes of anaerobic exercise.

Shifting 5 minutes to anaerobic exer-

cise achieved a significantly greater

reduction in body fat compared with

aerobic exercise alone.13 Total body

fat, visceral fat, and abdominal fat also

appear to be significantly reduced with

the addition of anaerobic resistance

training. The addition of anaerobic

resistance training may have produced

greater lipolysis of stored body fat.

Choosing the Right Exercise for You

Not all individuals respond to the same

type of exercise. Most research com-

pares the group mean response of

weight loss to exercise, not the individ-

ual variation. Just because one study

failed to show results for the group of

subjects doesn’t mean it may not work

for you. In other words, if you enjoy a

specific type of exercise and you find it

effective in weight loss or maintaining

a healthy weight—don’t stop! Any exer-

cise is better than not exercising at all.

finally, while the changes in lean muscle

mass were not significantly different

between groups, the high-intensity exer-

cise group gained lean muscle, while

the steady-state group lost lean muscle.

This is important for weight loss, as loss

of lean muscle reduces basal metabolic

rate, whereas an increase in active mus-

cle tissue continues to burn more fatty

acids even at rest.

One of the advantages of anaero-

bic exercise is that it burns more total

kilocalories per minute than moder-

ate aerobic exercise. For instance, a

150-pound female who jogged at a

pace of 12 minutes per mile would

burn approximately 220 kilocalories

in 30 minutes compared with running

a 7-minute-mile pace, which would

burn approximately 390 kilocalories

in 30 minutes. Even though less fat

is burned during anaerobic exercise,

anaerobic exercise increases resting

metabolic rate and lean muscle mass

that continues to burn kilocalories

(mostly fat kilocalories) after the exer-

cise is complete, for up to 14 hours.

Whether you enjoy anaerobic or

aerobic exercise, the key

is to exercise every day.

Gradually increase the

duration and intensity of

the exercises, and if you

are overweight or obese,

slow down or stop if you

experience chest pains,

joint pain, or nausea or

become dehydrated.11

Aerobic Exercise Combined with Resistance Training

If aerobic exercise

utilizes fatty acids for

energy but anaerobic

exercise increases lean

muscle mass and rest-

ing metabolic rate, why

not combine the two in

one exercise bout? In

a recent study at Duke

University, researchers

followed 234 overweight

and obese adults who

were randomly assigned

to an aerobic-exercise

in greater fat loss than aerobic exer-

cise in some studies.9 For example,

one 15-week study involved women

performing either three 20-minute

HIIE exercise sessions per week or a

steady-state exercise (SSE) at 60 per-

cent of their maximum heart rate for

40 minutes three times per week. The

HIIE group’s exercise sessions con-

sisted of 8 seconds of sprint cycling

followed by 12 seconds of slow cycling

repeated for 20 minutes. The HIIE sub-

jects lost 2.5 kilograms, or 5.5 pounds,

of subcutaneous body fat over the

15-week study, whereas women who

performed SSE aerobic exercise for the

15 weeks experienced no change in

body fat (Figure 1).10 Notice that fat loss

was achieved with 50 percent less time

exercising and a similar energy expen-

diture. Researchers suggested that

the significant loss of body fat in the

HIIE group might be due to the impact

of high-intensity exercise on reducing

hunger hormones and overall kilocalo-

rie intake. Another explanation may be

that high-intensity exercise enhances

lipolysis and fatty-acid oxidation. And

▲ Figure 1 The Effects of High-Intensity Intermittent

Exercise on Fat Loss

Source: E. G. Trapp, D. J. Chisholm, J. Freud, and S. H. Boutcher. 2008.

The Effects of High-Intensity Intermittent Exercise Training on Fat Loss and

Fasting Insulin Levels of Young Women. International Journal of Obesity

32:684–691.

0

1

2

–1

–2

–3

–4

*

High-intensity

intermittent

exercise

C h a n g e i n f a t

m a s s ( k g )

Steady state

exercise

Control

560 Chapter 15 | Weight Management

In addition, research is clear that

achieving healthy weight loss requires

not just exercise but dieting as well.14

In an 18-month study of 288 obese

men and women, the results reported

a significant drop in body fat and an

increase in lean muscle mass when

subjects participated in both exercise

and a weight-loss diet compared with

those who just exercised without diet-

ing.15 The bottom line? If you want to

lose weight, eat a healthy, lower-energy

diet and engage in a combination of

aerobic and anaerobic exercise.

References

1. Swift, D. L., N. M. Johannsen, C. J. Lavie, C. P. Earnest, and T. S. Church. 2014. The Role of Exercise and Physical Activity in Weight Loss and Maintenance. Progress in Cardiovascular Diseases 56(4):441–447.

2. Garber, C. E., B. Blissmer, M. R. Deschenes, B. A. Franklin, M. J. Lamonte, et al. 2011. American College of Sports Medicine Position Stand. Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Muscu- loskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise. Medicine and Science in Sports and Exercise 43(7):1334 –1359.

3. Kemmler, W., M. Scharf, M. Lee, C. Petrasek, and S. von Stengel. 2014. High versus Moderate Intensity Running Exercise to Impact Cardiometabolic Risk Factors: The Randomized Controlled RUSH- Study. BioMed Research International doi: 10.1155/2014/843095.

4. Utter, A. C., D. C. Nieman, E. M. Shannon- house, et al. 1998. Inf luence of Diet and/or Exercise on Body Composition and Cardio- respiratory Fitness in Obese Women. Interna- tional Journal of Sport Nutrition 8(3):213–222.

5. Redman, L. M., L. K. Helbronn, C. K. Mar- tin, A. Alfonso, S. R. Smith, and E. Ravus- sin. 2007. Effect of Calorie Restriction With or Without Exercise on Body Composition and Fat Distribution. Journal of Clinical Endo- crinolog y and Metabolism 92(3):865–872.

6. Hoppes, E., and G. Caimi. 2011. Exercise in Obesity Management. Journal of Sports Medicine and Physical Fitness 51(2):275–282.

7. McTiernan, A., B. Sorensen, M. L. Irwin, A. Morgan, Y. Yasui, R. E. Rudolph, et al. 2007. Exercise Effect on Weight and Body Fat in Men and Women. Obesity 15(6):1496–1512.

8. Swift, D. L., N. M. Johannsen, C. J. Lavie, C. P. Earnest, and T. S. Church. 2014. The Role of Exercise and Physical Activity in Weight Loss and Maintenance. Progress in Cardiovascular Diseases 56(4):441–447.

9. Heydari, M., J. Freund, and S. H. Boutcher. 2012. The Effect of High-Intensity Intermittent Exer- cise on Body Composition of Overweight Young Males. Journal of Obesity doi: 10.1155/2012/4804.

10. Trapp, E. G., D. J. Chisholm, J. Freud, and S. H. Boutcher. 2008. The Effects of High- Intensity Intermittent Exercise Training on Fat Loss and Fasting Insulin Levels of Young Women. International Journal of Obesity 32:684–691.

11. Willis, L. H., C. A. Slentz, L. A. Bateman, A. T. Shields, L. W. Piner, C. W. Bales, J. A. Houmard, W. E. Kraus. Effects of Aerobic and/or Resistance Training on Body Mass and Fat Mass in Over- weight or Obese Adults. Journal of Applied Physiolog y 113(12):1831. doi: 10.1152/ japplphysiol.01370.2011.

12. Ibid. 13. Salvadori, A., P. Fanari, P. Marzullo,

F.  Codecase, I. Tovaglieri, M. Cornacchia, et al. 2014. Short Bouts of Anaerobic Exercise Increase Non-Esterified Fatty Acids Release in Obesity. European Journal of Nutrition 53(1):243–249.

14. Fletcher, G., F. F. Eves, E. I. Glover, et al. 2017. Dietary Intake is Independently Asso- ciated with the Maximal Capacity for Fat Oxidation During Exercise. American Journal of Clinical Nutrition 105(4):864 –872. doi: 10.3945/ajcn.116.133520.

15. Beavers, K. M., D. P. Beavers, B. A. Nesbit, W. T. Ambrosium, A. P. Marsh, B. J. Niclas, and W. J. Rejeski. 2014. Effect of an 18-Month Physical Activity and Weight- Loss Intervention on Body Composition in Overweight and Obese Older Adults. Obesity 22(2):325–331.

Modify Your Eating Behaviors

Many incoming college freshmen worry more about gaining weight—the “freshman 15”—than about how they’ll manage their course load. The term freshman 15 was coined to describe a gain in weight that some college students experience during their first year away from home. However, little data supports the theory. As with adults, freshman weight gain can be prevented by establishing healthy eating and exercise behaviors that lead to a healthy weight.

Behavior modification focuses on changing the eating behaviors that contribute to weight gain or impede weight loss. Several behavior modification techniques can be used to identify and improve eating behaviors. These techniques include self-monitoring by keeping a food log, controlling environmental cues that trigger eating when not hun- gry, and learning how to better manage stress.88 Understanding the habits and emotions that drive your eating and exercise patterns is a key element of behavior modification. Once you have identified the less-than-healthy behaviors, you can replace them with new behaviors that promote weight loss and weight management.

A food log allows individuals to track the kinds of foods they eat during the day, when and where they eat them, their moods, and their hunger ratings. Based on this informa- tion, people can restructure their environment, how they respond to their environment, or both to improve the eating behaviors and manage their weight. A typical day’s log may be similar to the one in Figure 15.6.

You might have habits that work against your desire to maintain a healthy weight. These include skipping breakfast, which causes people to be very hungry in the late morn- ing and increases impulsive snacking on energy-dense, low-nutrition foods from vending machines. A study of overweight women who typically skipped breakfast showed that once

behavior modification Changing behaviors

to improve health outcomes. In the case of

weight management, it involves identifying

and altering eating patterns that contribute to

weight gain or impede weight loss.

How Can You Lose Weight Healthfully? 561

they started consuming cereal for breakfast, they indulged in less impulsive snacking.89 Eat- ing a bowl of high-fiber, whole-grain cereal with skim milk (approximately 200 kilocalories) can help you bypass an 11:00 a.m. vending machine snack of 270-kilocalorie cookies. This one behavior change would not only save you 70 kilocalories, but also reduce your intake of added sugars and boost your intake of essential nutrients and fiber. Additionally, adding a high-volume, low-energy salad to your sandwich at lunch could help increase your satiety and displace at least one of the energy-dense cookies that people often grab with a sandwich.

Stress-induced eating associated with studying can be modified by a change in envi- ronment—for example, by going to the campus library, where eating is prohibited. In fact, removing access to snacks altogether is an excellent environmental change—once snacks are “out of sight” they are more likely to be “out of mind.” Exercising before or after studying would be a healthier way to relieve stress than eating a bag of chips. The nearby Table Tips list some additional healthy behaviors that can easily be incorporated into your life.

Based on the information presented in the Nutrition in Practice on page 562, what recommendations would you have for Adam in his quest to lose weight?

◀ Figure 15.6 Food Log

Keeping track of when, where, and what

you eat, as well as why you ate it, can yield

some surprising information. Do you think

you sometimes eat out of boredom or stress,

rather than because you’re hungry?

† Moods:

Mood †

TA B L E T I P S

Adopt Some Healthy Habits

Don’t eat out of boredom or stress; go

for a jog instead.

Food-shop with a full stomach and a

grocery list. Walking around aimlessly

while hungry means you are more likely

to grab items on a whim.

The next time you pass a difficult

course or get that long-awaited raise,

celebrate without a plate. Replace

the traditional restaurant dinner with a

no-kilocalorie reward such as a new

music download or a weekend hike.

Declare a vending machine–free day at

least once a week, save money, and

stop the impulsive snacking. On that

day, pack two pieces of fruit as satisfy-

ing snacks.

LO 15.5: THE TAKE-HOME MESSAGE For successful, long-term weight loss, people can reduce their daily kilocalorie intake, increase their physical activity,

and improve their eating behaviors. Choosing low-energy-density, high-volume

vegetables and fruits, along with lean-protein foods, can help increase satiety

and reduce unplanned snacking. Incorporating approximately 60–90 minutes

of physical activity daily can facilitate weight loss. Establishing healthy eating

and exercise habits by restructuring the environment to minimize or eliminate

unhealthy eating behaviors can also help shed extra pounds.

562 Chapter 15 | Weight Management

NUTRITION in PRACTICE: Sports Medicine Specialist and PT

A dam is a 40-year-old Fine Arts

professor who has gained

20 pounds over the last year. He

blames his weight gain on the nagging

pain in his shoulder, which has caused

him to drop out of the faculty tennis

league. Adam used to play league tennis

games three to four times a week and

practice drills on the weekend. Unhappy

with his excess weight, Adam decided to

visit the campus health center. While he

was at the center, he saw a flyer advertis-

ing the new Sports Medicine Clinic on

campus, adjacent to the Health Center.

Adam made an appointment with the

sports medicine specialist, a physician

who specializes in sports medicine, for the

next day. The doctor diagnosed his shoul-

der soreness as impingement syndrome,

which is pain sometimes experienced by

tennis players when they lift and rotate

their arm. The doctor referred Adam to

the physical therapist (PT) at the clinic for

guidance for an exercise program that

would strengthen his shoulder muscles to

ease the pain. To help him lose his excess

weight, the doctor recommended that

Adam visit with the registered dietitian

nutritionist (RDN) at the clinic.

Adam’s Stats

❏ Age: 40

❏ Height: 6 feet

❏ Weight: 210 pounds

❏ BMI: 28.5

Critical Thinking Questions

1. Based on Adam’s food log, which

waist-friendly food groups are missing

from his diet?

2. Why do you think Adam is snacking

between meals, even when he isn’t

very hungry?

3. What beverage recommendations

would you make based on Adam’s

food log?

PT’s Observation and Plan for Adam

❏ Explain that impingement syndrome

occurs when the tissues in the shoul-

der are pitched or compressed due to

poor mechanics.

❏ Provide Adam with a strengthening pro-

gram for shoulder stabilizing muscles.

RDN’s Observation and Plan

for Adam

❏ Discuss the lack of adequate amounts

of whole fruits and vegetables in his

diet and the role these high-fiber, high-

volume, lower-energy-dense foods

play in weight reduction. Explain the

concept that these foods displace

other higher-kilocalorie foods in the diet

and “fill you up before they fill you out.”

❏ Discuss the issue of routinely snack-

ing when not hungry. Consider alter-

natives to eating when bored.

❏ Replace the bowl of energy-dense

granola cereal with lower-kilocalorie

shredded wheat cereal with a sprin-

kling of granola as a topping.

❏ Substitute skim milk for whole milk on

his cereal and the cream in his coffee.

❏ Decrease the size of the sandwich at

lunch. Instead of a large sub, order a small

sub and a side salad with light dressing.

Two weeks later, Adam returns for

a follow-up visit with the RDN and PT.

While he has only lost a pound, he is

feeling better about this diet and the

strengthening program that the PT

designed for him, although his overhead

tennis serve is still somewhat painful. He

has added more fruits and vegetables

to his diet and, surprisingly, doesn’t feel

hungry. The RDN works with Adam to

choose leaner sources of protein at lunch

and dinner. Adam agrees to try a smaller

turkey sandwich at lunch and grilled

salmon or chicken for dinner more often.

He made another appointment to see the

RDN in a month. The PT tweaks Adam’s

strengthening program and continues to

work with him through the month.

Adam

ADAM’S FOOD LOG

Food/Beverage Time

Consumed

Hunger

Rating* Location Granola with whole milk, orange juice, coffee with cream

7:00 A.M. 3 Kitchen

Coffee with cream, donut 10:30 A.M. 2 Campus coffee shop Ham and cheese sub 1:30 P.M. 5 Sub shop on campus Cookies

4:00 P.M. 1 Vending machine in faculty lounge

Steak, rice, and corn 6:30 P.M. 3 Kitchen Peanuts

9:00 P.M. 1 Watching TV *Hunger Rating (1–5): 1 = not hungry; 5 = super hungry.

How Can Weight Loss Be Maintained? 563

How Can Weight Loss Be Maintained?

LO 15.6 Design a food and exercise plan to maintain a healthy weight.

Losing weight can be difficult, but not regaining the lost weight over time can be just as challenging. You or someone you know may be familiar with the typical weight-loss experience: the triumphant rush associated with dropping 10 pounds of weight, the dis- appointment that sets in when 15 pounds are regained, then a new round of hope when 10 of them are re-shed.

But don’t be discouraged! Weight loss can be maintained when the right strategies are used. The National Weight Control Registry (NWCR) was developed to follow those individuals who have not only succeeded at weight loss but kept it off. In a recent study of 3,000 individuals who had lost at least 30 pounds, researchers reported that 87 percent of the subjects who lost at least 10 percent of their body weight had maintained the weight loss when measured at 5 and 10 years.90 The researchers reported that low-fat diets, avoid- ing overeating, being physically active, and daily self-weighing were successful strategies in maintaining the subjects’ weight loss.

Diet and Exercise Can Aid in Maintaining Weight Loss

Consuming a healthy diet is as essential to weight-loss maintenance as it was to the weight loss. Individuals who lose weight often experience an energy gap. After weight loss, a person will have lower overall energy needs, as there is less body weight to main- tain. The energy gap is the difference in daily kilocalories that are needed for weight maintenance before and after weight loss.91 Researchers have estimated that the energy gap is about 8 kilocalories per pound of lost weight.92 For example, someone who lost 30 pounds would need approximately 240 fewer kilocalories a day to maintain the new, lower body weight.

One problem with maintaining weight loss is that once the weight has been lost, individuals revert to the unhealthy eating habits that caused the excess weight in the first place. To adapt your eating pat- terns to the new body weight, limit the intake of fatty foods, monitor your kilocalorie intake, and follow a pattern of eating three small meals and two snacks a day. For many people, eating more frequent, smaller meals allows them to avoid becoming ravenous and overeating at the next meal. If weight loss continues even though you’ve reached your goal weight, gradu- ally add about 200 kilocalories of healthy, low-fat, high-fiber foods to your daily intake until weight balance is achieved.

Another way to close the energy gap and help the body adjust to its new lower weight is to increase exercise. Because the environment we live in seems to encourage eating more than discourage it, researchers believe that increasing daily physical activity is likely the easier way to close the energy gap.93 Adding something (physi- cal activity) to one’s lifestyle is often easier than removing something (kilocalories). Thus, the rec- ommendation is to engage in 60 –90 minutes of moderate physical activity daily in order to main- tain weight loss.94

energy gap Difference between the numbers

of kilocalories needed to maintain weight

before and after weight loss.

Daily self-weighing may help maintain a healthy body weight.

564 Chapter 15 | Weight Management

Self-Weighing Is a Positive Strategy to Maintain Weight Loss

Daily or weekly self-weighing has often been discouraged to prevent increasing the risk of disordered eating, negative body image, mood disorders, or binge eating. Recent research refutes these claims and reports that daily self-weighing improved body satisfaction95 and helped maintain weight loss.96

LO 15.6: THE TAKE-HOME MESSAGE People who lose weight are most likely to keep it off if they maintain the positive diet and lifestyle habits that helped them

lose the weight. Exercise improves muscle mass, prevents a decline in basal

metabolism, and helps overcome plateaus often associated with weight loss.

Eating less and/or exercising more helps close the energy gap that occurs

after weight loss.

What Is the Healthiest Way to Gain Weight?

LO 15.7 Describe the role of diet and exercise in achieving a healthy weight gain.

For people who are underweight, trying to gain weight can be as challenging and frustrat- ing as trying to lose weight is for an overweight individual. The major difference is that the thin person rarely gets sympathy from others.

Like overweight individuals, those who are underweight experience an energy imbalance. In their case, however, they consume fewer kilocalories than they expend each day. Because those who wish to gain weight generally want to add muscle mass, rather than large amounts of fat, the challenge is to eat sufficient energy to meet their basal metabolic needs plus provide fuel for the exercise needed to stimulate muscle synthesis.

People who want to gain weight need to do the opposite of those who are trying to lose weight—they need to make each bite more energy dense. Adding at least 500 kilocalories to their daily energy intake will enable them to add about a pound of extra body weight weekly.

Of course, someone who wants to gain weight should not just load up on high-fat, high-kilocalorie foods. The quality of the extra kilocalories is very important. Snacking on an extra 500 kilocalories of jellybeans adds 500 kilocalories of sugar and little nutri- ent value. Instead, these individuals should make energy-dense, nutritious choices from a variety of foods within each food group. For example, instead of eating a slice of toast in the morning, they should choose a whole-grain waffle. In a salad bar lunch, adding coleslaw provides 10 times the kilocalories of plain cabbage. Figure 15.7 contrasts more- and less-energy-dense foods within each food group. Eating larger portion sizes at meals and energy-dense snacks during the day also adds kilocalories. The Table Tips provide easy and portable snack ideas.

Regular exercise and resistance training stimulate muscle growth and help avoid excess fat storage. Remember that it takes time to gain weight and build sufficient muscle mass. Be patient and continue to choose healthy foods until you reach your goal weight.

TA B L E T I P S

Healthy Snacks for Healthy Weight Gain

Stash an 8-ounce container of

100 percent fruit juice (about 100

kilocalories) in your bag, plus one of the

150- kilocalorie snacks listed below for

a quick 250-kilocalorie snack (food and

juice combined) between meals.

Graham crackers, 5 crackers

(2 1�2″ square)

Mixed nuts, 1 oz

Fig bars, 2-oz package

Pudding, individual serving sizes, 4 oz

Peanut butter on whole-wheat crackers

(1 Tbsp peanut butter on six crackers)

LO 15.7: THE TAKE-HOME MESSAGE People who want to gain weight need to consume additional kilocalories through energy-dense foods so that they

take in more energy than they expend. Adding nutrient-dense snacks between

meals and increasing portion sizes during meals are easy ways to increase

the number of kilocalories consumed. Add resistance exercise to build muscle

mass and avoid excess fat storage.

What Are the Medical Interventions for Severe Obesity? 565

◀ Figure 15.7 More- and Less-Energy-

Dense Food Choices, by Food Group

Choosing more energy-dense, but still nutri-

tious, foods can help those who are under-

weight gain weight.

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HEALTHCONNECTION

disease and stroke, and even of dying, that medications and/or surgery may be necessary.

Weight-Loss

Medications May

Improve Weight Loss

but Have Side Effects

Some prescription medications can help a person lose weight by either suppressing hunger or inhibiting the absorption of fat in the GI tract. These drugs typically have potentially dangerous side effects; because of this, they are almost always available

only by prescription and must be taken under the care of a health care provider.

One hunger suppressant is the drug sibutramine (trade name Meridia), which also increases thermogenesis and thereby increases energy expenditure. However, the drug can also increase a person’s heart rate and blood pressure, and therefore may not be appropriate for those who have hyperten- sion, which is common in obese individuals.

The fat-absorption-inhibitor orlistat (trade name Xenical) is a prescription medi- cation that inhibits an intestinal enzyme needed to break down fat. If fat isn’t bro- ken down, the body doesn’t absorb the fat

What Are the Medical Interventions for Severe Obesity?

LO 15.8 Describe the role of weight- loss drugs and surgery for reducing obesity.

For most people, the best path to a healthy body weight is to commit to improving their diet and exercising more. However, those who are severely obese are at such a high risk for conditions such as heart

566 Chapter 15 | Weight Management

HEALTHCONNECTION (CONTINUED)

gastric bypass surgery Type of bariatric

surgery that reduces the functional volume of

the stomach to minimize the amount of food

eaten. Such surgeries are sometimes used to

treat extreme obesity.

been shown to cause chest pains, palpita- tions, hypertension, and an accelerated heart rate and has been linked to numer- ous deaths.102

Bariatric Surgery

Restricts Food Intake

Bariatric surgery has been shown to be an effective means of weight loss for mod- erately to severely obese people compared with low-kilocalorie diets and medica- tion.103 A variety of bariatric surgery proce- dures either reduce the absorption of food or restrict food intake.

The most common form of bariat- ric surgery is gastric bypass surgery. This surgical technique was developed in the middle of the twentieth century and quickly grew in popularity. The first gastric bypass surgery was performed in 1967 by Dr.  Edward Mason, a surgeon at the University of Iowa.104 By 1998, approximately 13,000 obese patients each year underwent gastric bypass. Ten years later that number had increased to over 190,000.105 During gastric bypass surgery, the stomach is reduced in size by making a small pouch at the top of the stomach with surgical staples (Figure 15.8). The pouch is

bariatric surgery Surgical procedure that

promotes weight loss by limiting the amount

of food that can be eaten or absorbed.

using Xenical and Alli, both of these drugs must now carry warnings on their labels.98

The latest weight loss drug to be approved by the FDA is called liraglutide (trade name Saxenda). This injectable drug stimulates the release from the GI tract of GLP-1, a hormone that stimulates satiety and may therefore contribute to weight loss.99 A 2017 study showed benefits of liraglutide using a randomized, double- blind study of 2,254 adults with predia- betes and a body mass index of at least 30 kg/m2. Either liraglutide or a placebo was given over 3 years. The results showed that after 3 years, subjects receiving liraglu- tide lost more weight and improved glucose control compared to the placebo group.100 Unfortunately, this drug may cause serious side effects, including severely low blood glucose leading to extreme weakness, con- fusion, tremors, fast heart rate, trouble speaking, nausea and vomiting, rapid breathing, fainting, and seizures.101

The side effects of certain weight-loss supplements are so serious that the FDA has required the supplement be withdrawn from the market. For instance, the FDA has prohibited the sale of supplements that contain ephedra (also called Ma huang), the plant source for ephedrine. Ephedrine has

(and kilocalories). In patients using orlistat, up to about a third of the dietary fat in a meal is blocked and expelled in the stool. Orlistat needs to be taken at each meal and should be used with a diet that provides no more than about 30 percent of its kilocalo- ries from fat. Because fat is lost in the stool, the drug can cause oily and more frequent stools, f latulence, and oily discharge.97 Ironically, these side effects may help an individual adhere to a low-fat diet, as these effects are more pronounced if a high-fat meal is consumed.

A reduced-strength version of orlistat (brand named Alli) is approved as an over- the-counter medication for overweight adults 18 years and older. Alli, combined with a low-kilocalorie, low-fat diet and reg- ular exercise, aids in modest weight loss. Because of the recent reports of rare, but serious, cases of liver damage in individuals

Alli promotes weight loss by reducing the

digestion and absorption of fat.

▲ Figure 15.8 Gastric Bypass Surgery

In gastric bypass surgery, much of the stomach is closed off and a small

pouch is left that can hold about 1�4 cup of food at a time. The pouch is

reattached to the jejunum, bypassing the duodenum.

In gastric bypass, most

of the stomach is closed

off and a small pouch is

left that can hold about 1/4

cup of food at a time.

a Path of food

Small intestineUnused portion

of small intestine

Staples

Bypassed

stomach

HEALTHCONNECTION (CONTINUED)

Vitamin B12 injections or supplements as well as calcium and iron supplements, plus vitamin C, are prescribed to help maintain a healthy balance.

Although weight loss varies from one individual to the next, the average weight loss with gastric bypass surgery is approxi- mately 5–15 pounds per week for the first 2 or 3 months.107 The weight loss gradually tapers off to about 1–2 pounds per week after the first 6 months. Other benefits of gastric bypass include a reduction in dia- betes in 76.8 percent of patients, improved lipid profiles in more than 70 percent of patients, and the elimination of hyperten- sion (in 61.7 percent) and sleep apnea (in 85.7 percent).108

Although dramatic amounts of weight loss can occur with gastric bypass, there are also risks involved. About 10 percent of those undergoing gastric bypass surgery experience complications such as gall- stones, ulcers, and bleeding in the stomach and intestines. Approximately 1–2 percent die from complications relating to the surgery.109 After surgery, individuals need to be monitored long term by their physi- cian and nutrition professionals to ensure that they remain healthy and meet their nutritional needs.

released, which results in less iron available for absorption. Iron and calcium are also typically absorbed in the upper part of the small intestine, which is now bypassed.

then connected to the jejunum, bypassing the rest of the stomach and the duodenum (the upper small intestine). This reduces the size of the stomach so that it holds less than 1�4 cup of food and also reduces the small intestine’s ability to absorb food. After the surgery, individuals need to consume fre- quent, small meals because the stomach pouch can only expand to a maximum of about 5 ounces, the size of a woman’s fist. Bypass patients not only eat less because of their smaller stomachs, but also have higher levels of satiety and lower levels of hunger after the surgery. This loss of appetite is thought to be due to lower levels of ghrelin associated with the loss of stomach area.106

Because food is rerouted past the majority of the stomach and the duodenum, individuals can experience deficiencies of vitamin B12, iron, and calcium. Recall from Chapter 10 that vitamin B12 needs to be separated from the protein in food before it can be absorbed. Also, intrinsic factor (IF) secreted from the gastric cells is needed for vitamin B12 to be absorbed. Levels of IF are significantly reduced after surgery. To be absorbed, iron must be converted from fer- ric iron to ferrous iron by hydrochloric acid secreted in the stomach. Bariatric surgery reduces the amount of hydrochloric acid

LO 15.8: THE TAKE-HOME MESSAGE Pharmacological or surgical weight loss approaches may be necessary for

obese individuals. The current weight-loss drugs suppress appetite, reduce

fat absorption, or increase satiety; however, they have serious side effects.

Gastric bypass surgery is the most common form of bariatric (weight-loss)

surgery. It reduces the size of the stomach and bypasses the duodenum,

thereby restricting both food intake and absorption of food. Patients typically

experience not only weight loss, but reduction in chronic disease risks.

Al Roker, a weatherman on NBC’s Today

Show, lost approximately 140 pounds after

gastric bypass surgery.

What Are the Medical Interventions for Severe Obesity? 567

568 Chapter 15 | Weight Management

Visual Chapter Summary

LO 15.1 Weight Management Is Important for Physical and Emotional

Well-Being Weight management means maintain- ing a healthy weight to reduce the risk of specific health problems. Classifying obesity as a disease may improve treat- ment options but may also raise health care costs, increase drug and surgical procedures, and reduce emphasis on lifestyle changes to lose weight. Physical problems associated with obesity include an increased risk for cardiovascular dis- ease, type 2 diabetes, certain cancers, and many other disorders. Both obesity and underweight significantly increase the risk of premature death. Social and psy- chological misperceptions and prejudices toward people who are obese or under- weight may contribute to discrimination, low self-esteem, depression, suicide, and alcohol and drug problems.

LO 15.2 Food Intake Is Regulated by the

Hypothalamus Food intake is regulated by the physiological responses known as hunger and satiety. Hunger prompts the body to eat and subsides soon after eating begins. Satiety deter- mines the length of time between meals or snacks. Appetite is psychological, not physiological, and can be affected by the sight, smell, taste, and thought of food, as well as emotions, environment, and social settings.

Hunger is controlled by the lateral hypothalamus and satiety is con- trolled by the ventromedial nucleus of the hypothalamus. Both areas of the brain respond to hormonal and neural signals from the GI tract. Certain hormones, including neuropeptide Y from the hypothalamus and ghrelin from the stomach, stimulate hunger. Other hormones, including cholecystokinin and peptide YY from the small intestine, insulin from the pancreas, and leptin from adipose tissue, increase satiety.

GHRELIN

NPY

INSULIN

PYY

CCK

LEPTIN

Visual Chapter Summary 569

LO 15.3 Fat Cells Form, Expand, and Shrink Fat cells can increase in size to store additional fat (hypertrophy) and new fat cells can be produced (hyperplasia) to replace old cells and to create additional cells once existing ones fill to capacity. During weight loss, fat cells shrink but are not destroyed.

The enzyme lipoprotein lipase (LPL) stimulates lipogenesis and the enzyme hormone-sensitive lipase stimulates lipolysis. LPL activity is greater in obese individuals; in males, LPL is more active in the abdominal fat cells than in females, but females have higher LPL activity rates in the hips and thighs.

LO 15.4 Genetics and  Environment

Both Influence Body Weight Obesity is explained as a gene–environment interaction in which genetically prone individuals have easy access to a variety of large portions of food and an environment that encourages a seden- tary lifestyle. Nutrigenomics has identified specific genes that influence how we absorb, store, or break down foods. Epigenetic factors, including components of the foods we eat, can turn gene expression on or off, thereby influencing many physiological fac- tors that affect body weight. Single-nucleotide polymorphisms result in variant genes, some of which influence the secretion of hormones such as ghrelin and leptin that affect hunger and sati- ety. Populations with “thrifty genes” may experience increased fat storage and reduced energy expenditure as compared to other populations. Environmental factors such as lack of time, an abundant food supply and portion distortion, and lack of physi- cal activity due to the advances in technology increase the risk of obesity.

Preadipocyte

Fat Fat droplet

Cutaway view of

mature adipocyte

Nucleus Cell membrane Hypertrophy

570 Chapter 15 | Weight Management

LO 15.5 Losing Weight Healthfully Involves Eating Less

and Exercising More A healthy, reasonable rate of weight loss is losing 10 percent of body weight over a 6-month period. Losing weight rapidly can cause a per- son to fall short of meeting nutrient needs. Many fad diets promise quick results but can be unhealthy for the long term.

Expending more kilocalories than consumed is the key to weight loss. Eating more low-energy-density, high-volume (high in water and fiber) foods, such as vegetables and fruits, improves satiation, which results in fewer kilocalories consumed. Protein has the most dra- matic effect on satiety. Eating high-protein foods such as lean meats, chicken, and fish at meals can help reduce hunger between meals. Because fat slows the movement of food out of the stomach into the intestines, it can also prolong satiety.

Routine physical activity and exercise can add to the daily energy deficit needed for weight loss. To support weight loss, overweight individuals should engage in 60–90 minutes of moderate-intensity exercise daily.

Individuals who wish to lose weight must change the eating behaviors that contributed to weight gain or impeded weight loss. Keeping a food record, controlling environmental cues that trigger eating when not hungry, and learning how to better manage stress are all behavior modification techniques that can be used by individuals who eat “out of habit” and in response to their environment.

LO 15.6 Behavior Modification Helps

Maintain a Healthy Weight To maintain weight loss, individuals must modify their food intake to reflect their smaller body’s reduced energy requirements. After weight loss, there is an energy gap between the original body weight and the new healthy weight, which may be as high as 8 kilo- calories per pound of lost body weight. The energy gap can also be reduced with an increase in exercise of about 60–90 minutes per day. Self-weighing each day can improve body satisfaction and help maintain weight loss.

LO 15.7 Increase Kilocalories

and Exercise to Gain Weight

Healthfully Individuals who wish to gain weight must increase kilocal- orie intake and engage in strength training to build muscle mass. Consuming larger portions of nutrient-dense foods at mealtimes and snacking on nutritious foods between meals can help with weight gain.

Gastric bypass

Path of food

Small intestineUnused portion

of small intestine

Staples

Bypassed

stomach

Check Your Understanding 571

LO 15.8 Medications or Surgery May Be

Necessary to Treat Severe Obesity For severely obese individuals who have tried diet and exercise and failed to achieve a healthy body weight, pharmacological or surgical treatments may be necessary. The current weight-loss drugs approved by the FDA suppress appetite, reduce fat absorption, or increase satiety. However, they have serious side effects and their use must be monitored by the patient’s physician. Bariatric (weight-loss) surgery reduces the consumption and absorption of food. Gastric bypass surgery, the most common procedure, involves reducing the size of the stomach to a small pouch and connecting it to the jejunum, in order to bypass the duodenum. Gastric bypass is effective in helping patients lose significant body weight and reduce their risk for chronic disease.

Terms to Know ■ weight management

■ appetite

■ hunger

■ satiation

■ satiety

■ hypertrophy

■ hyperplasia

■ gene–environment interaction

■ adiponectin

■ set point

■ fad diet

■ behavior modification

■ energy gap

■ bariatric surgery

■ gastric bypass surgery

Mastering Nutrition Visit the Study Area in Mastering Nutrition to hear an MP3 chapter summary.

Check Your

Understanding

LO 15.1 1. A healthy body weight can be defined as a body weight that a. does not increase the risk of

developing weight-related health problems or diseases

b. enhances an individual’s physical attributes

c. is generally acceptable in society

d. is the easiest to maintain by all individuals of a given height and age

LO 15.2 2. Which region of the brain responds to hormones by stim- ulating satiety? a. Lateral hypothalamus b. Ventromedial nucleus c. Hippocampus d. Pineal gland

LO 15.3 3. When an individual loses body fat a. there is a decrease in the

number of adipocytes due to hyperplasia.

b. there is a decrease in the size of the fat cells due to hypertrophy.

c. subcutaneous fat, not visceral fat, is lost.

d. the adipocytes shrink but their number stays the same.

LO 15.4 4. Which of the following is a factor that increases the risk of obesity? a. Increased time b. Increased physical activity c. Low consumption of fruits

and vegetables. d. Small portion sizes

LO 15.5 5. Which of the following can increase the risk of becoming obese? a. Having a parent who is obese b. Consuming more meals at

home than dining out c. Reducing the amounts of

“screen time” during the day d. Decreasing the size of your

food portions at meals

572 Chapter 15 | Weight Management

LO 15.5 6. What is the best dietary approach to losing weight? a. Eliminate all sweets from

the diet b. Reduce kilocalorie intake by

reducing portion sizes c. Consume foods high in

carbohydrate to stimulate satiety

d. Limit fat intake to less than 5 grams per day

LO 15.6 7. Mary Ellen was obese and lost 30 pounds during the last year by eating a well-balanced, kilocalorie-reduced diet and being physically active daily. To maintain her weight loss, she should continue to eat a healthy diet, monitor her eating behav- iors, and a. accumulate 30 minutes of

physical activity three times a week.

b. accumulate 45 minutes of physical activity three times a week.

c. accumulate at least 60 min- utes of physical activity daily.

d. accumulate more than 2 hours of physical activity daily.

LO 15.7 8. After recovering from a lengthy illness, Simon has been trying to regain the weight he lost while he was sick. It seems easy enough to load up on doughnuts and French fries, but Simon would prefer to return to his normal weight in a healthy way. Which of the following strategies would help Simon reach his goal? a. Decreasing his portions at

meals b. Eliminating all exercise c. Eating salads without salad

dressing d. Drinking 100% fruit juice

with a nutrient-dense snack between meals

LO 15.8 9. Which of the following weight-loss medications may stimulate thermogenesis? a. Meridia b. Xenical c. Alli d. Saxenda

LO 15.8 10. Which of the follow- ing occurs in the majority of patients who undergo gastric bypass surgery? a. Iron toxicity b. Gallstones c. Elimination of hypertension d. All of these are correct.

Answers

1. (a) A healthy body weight can be defined as a body weight that does not increase the risk of developing weight-related health problems or diseases.

2. (b) The ventromedial nucleus responds to certain hormonal sig- nals by inducing satiety. The lateral hypothalamus controls hunger, the hippocampus is a structure involved in memory consolidation, and the pituitary gland, located beneath the hypothalamus, secretes many hor- mones important to homeostasis; it is not technically part of the brain.

3. (d) When the body loses fat, adipo- cytes shrink in size, but their number remains constant. Adipocytes are the specialized cells that make up all adi- pose tissue, including both subcuta- neous and visceral fat. Hyperplasia is an increase, not a decrease, in num- ber of cells, and hypertrophy is an increase, not a decrease, in cell size.

4. (a) Low consumption of fruits and vegetables increases the risk of becoming obese. Having more time, increasing physical activity, and eat- ing smaller portions will all decrease your risk of obesity.

5. (a) Having a parent who is obese increases the probability that you have a genetic predisposition to obe- sity. Increasing your regular physical activity by reducing screen time, eat- ing more meals at home, and reduc- ing food portions are methods that reduce your risk.

6. (b) The best healthy dietary approach to losing weight is to reduce kilo- calorie intake by eating smaller por- tion sizes. Eliminating all sweets would be unnecessarily restrictive, as would reducing fat intake to less than 5 grams per day, which would also be unhealthful. Foods high in

carbohydrate are less satiating than foods high in protein and fat.

7. (c) If Mary Ellen wants to continue to maintain the weight she has lost, she should try to accumulate 60–90 minutes of exercise daily.

8. (d) To gain weight, Simon should drink 100% fruit juice with a nutrient-dense snack, such as nuts, between meals. Decreasing his por- tions at meals and eating salads with- out salad dressing would cause him to lose more weight rather than gain weight. Eliminating all exercise is unhealthful.

9. (a) Meridia (or sibutramine) increases thermogenesis and energy expendi- ture. Xenical, also known as orlistat, and Alli, the less potent over-the- counter weight-loss medication, inhibit fat absorption. Liraglutide, sold as Saxenda, increases satiety.

10. (c) The majority of people who undergo gastric bypass surgery experience an elimination of hyper- tension. A minority of patients expe- rience gallstones. Iron deficiency, not toxicity, is a concern following gastric bypass surgery.

Answers to True

or False?

1. False. While the recommendation for weight loss is to accumulate at least 60–90 minutes of daily physical activity, the bottom line is that for weight loss to occur, more energy must be expended than is consumed. This can be accomplished by con- suming less, exercising more, or a combination of both.

2. False. While the overall number of fat cells generally doesn’t increase in adulthood, fat cell synthesis contin- ues to replace old cells. Ten percent of fat cells are replaced with new cells every 10 years.

3. False. Grazing is considered a high- risk behavior for weight management because the foods that are typically chosen are low in protein and not satiating. Individuals may also con- sume higher amounts of kilocalories by eating mindlessly rather than con- suming planned, smaller meals.

References 573

4. True. Weight loss of as little as 10 pounds can improve health if an individual is overweight.

5. True. Nature and nurture both play a role in regulating body weight. Nature (genes) often sets the stage, while nurture (environment and personal behavior) directly affects weight management.

6. True. Increasing the volume of food and the fiber content of meals by eating more vegetables and fruits can improve appetite control, reducing kilocalorie intake and thus helping attain weight loss.

7. True. At its most basic, weight gain occurs because of a positive energy balance. However, genetics and the environment play strong roles.

8. False. Of all the nutrients, protein has the most powerful effect on satiety.

9. False. Most weight-loss supplement labels indicate that you need to eat a healthy diet and exercise regularly if you want to shed the pounds.

10. False. Bariatric surgery alters the gastrointestinal tract and requires permanent changes to eating habits.

Web Resources

■ For more on overweight and obesity, visit the Centers for Disease Control and Prevention at www.cdc.gov/nccd- php/dnpa/obesity/index.htm

■ For more information on weight control and physical activity, visit the Weight-control Information Network (WIN) at http://win.niddk.nih.gov/ index.htm

■ For more weight-loss shopping tips, recipes, and menu makeovers, visit the USDA’s Nutrition and Weight Man- agement website at www.nutrition.gov

■ For more information on gastric bypass surgery, visit the American Society for Metabolic and Bariatric Surgery at www.asbs.org

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