Energy Balance and Body Composition PDF

8 Learning gPS 8-1 energy Balance 236 Energy Balanc...

8 Learning gPS 8-1 energy Balance 236 Energy Balance and Learn iT Describe energy balance and the consequences of not being in balance. 8-2 energy in: The kCalories Foods Provide 236 Body Composition Learn iT Discuss some of the physical, emotional, and environmental influences on food intake. Food Composition 236 Food intake 237 8-3 energy Out: The kCalories the Body expends 240 Learn iT List the components of energy Nutrition in Your Life expenditure and factors that might influence each. Components of energy expenditure 240 It’s simple: energy balance occurs when energy in = energy out. The reality, of estimating energy requirements 244 course, is much more complex. One day you may devour a dozen doughnuts at 8-4 Body Weight and Body midnight and sleep through your morning workout—tipping the scales toward weight gain. Another day you may snack on veggies and train for this weekend’s Composition 245 Learn iT Distinguish between body weight 10K race—shifting the balance toward weight loss. Your body weight—especially and body composition, including methods to as it relates to your body fat—and your level of fitness have consequences for assess each. your health. So, how are you doing? In the Nutrition Portfolio at the end of Defining Healthy Body Weight 246 this chapter, you can see how your “energy in” and “energy out” balance and Body Fat and its Distribution 248 whether your body weight and fat measures are consistent with good health. 8-5 Health risks associated with Body Weight and Body Fat 251 Learn iT Identify relationships between body weight and chronic diseases. Health risks of Underweight 252 As Chapter 7 explains, the body’s remarkable metabolism can cope with varia- Health risks of Overweight 252 tions in the diet. When the diet delivers too little energy, carbohydrate, or pro- Fit and Fat versus Sedentary and Slim 253 tein, the body uses its fat to meet energy needs and degrades its lean tissue Highlight 8 Eating Disorders 256 Learn iT Compare the diagnoses, characteristics, to meet glucose and protein needs. When the diet delivers too much energy— and treatments of the different eating disorders. whether from excess carbohydrate, excess protein, or excess fat—the body stores fat. Both excessive and deficient body fat result from an energy imbalance. The simple picture is as follows. People who consume more food energy than they expend store the surplus as body fat. To reduce body fat, they need to expend more energy than they take in from food. In contrast, people who consume too little food energy to support their bodies’ activities must rely on their bod- ies’ fat stores and possibly some of their lean tissues as well. To gain weight, these people need to take in more food energy than they expend. As you will see, though, the details of energy balance and weight regulation are quite complex.1 This chapter describes energy balance and body composition and ex- amines the health problems associated with having too much or too little body fat. The next chapter presents strategies toward resolving these problems. 235 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  ENERGY 8-1 energy Balance ❯ LEARN IT Describe energy balance and the consequences of not being in balance. People expend energy continuously and eat periodically to refuel. Ideally, their energy intakes cover their energy expenditures with little, or no, excess. Excess en- ergy is stored as fat, and stored fat is used for energy between meals. The fat stores of even a healthy-weight adult represent an ample reserve of energy—50,000 to 200,000 kcalories. The amount of body fat a person deposits in, or withdraws from, storage on any IN OUT given day depends on the energy balance for that day—the amount consumed (energy in) versus the amount expended (energy out). When a person is maintain- ing weight, energy in equals energy out. When the balance shifts, weight changes. When energy in balances with energy out, a A classic rule states that for each 3500 kcalories eaten in excess, a pound of person’s body weight is stable. body fat is stored; similarly, a pound of fat is lost for each 3500 kcalories expended beyond those consumed.* To that end, many diet plans recommend lowering en- ergy intake by 500 kcalories a day to incur a weight loss of 1 pound per week. This “3500 kcalorie rule” has been used for more than 50 years, but it has several limi- tations.2 For one, as a person loses weight, the deficit in energy needed to continue losing weight shifts; in general, the kcalorie deficit is relatively low and weight loss is relatively rapid in the early phase but then it is followed by a markedly slower weight loss that plateaus as the kcalorie deficit needed to continue losing weight gradually increases. For another, body composition differs dramatically for men and women and for obese and lean people; in general, the kcalorie deficit needed FigUre 8-1 Bomb Calorimeter for weight loss is relatively larger for women than for men and for obese than for When food is burned, energy is released in the form lean people. Understanding the dynamic nature of weight loss may help people of heat. Heat energy is measured in kcalories. adopt more realistic expectations than a fixed 3500-kcalorie rule provides. Insulated Quick changes in body weight are not simple changes in fat stores. Weight container gained or lost rapidly includes some fat, large amounts of fluid, and some lean Thermometer measures keeps tissues such as muscle proteins and bone minerals. Because water constitutes temperature changes heat from escaping about 60 percent of an adult’s body weight, retention or loss of water can greatly inf luence body weight. Even over the long term, the composition of weight gained or lost is normally about 75 percent fat and 25 percent lean. During star- Motorized stirrer vation, losses of fat and lean are about equal. (Recall from Chapter 7 that without adequate carbohydrate, protein-rich lean tissues break down to provide glucose.) Invariably, though, fat gains and losses are gradual. The next two sections exam- ine the two sides of the energy-balance equation—energy in and energy out. As Reaction chamber you read, keep in mind that this simple equation falls short of fully explaining (bomb) the many metabolic changes that cause obesity.3 Food is ❯ REVIEW IT Describe energy balance and the consequences of not being Heating burned element in balance. When energy consumed equals energy expended, a person is in energy balance and body weight Water in which temperature is stable. If more energy is taken in than is expended, a person gains weight. If more energy is increase from burning food expended than is taken in, a person loses weight. is measured 8-2 energy in: The kCalories Foods Provide ❯ LEARN IT Discuss some of the physical, emotional, and environmental influences on food intake. Foods and beverages provide the “energy in” part of the energy-balance equation. energy balance: the energy (kcalories) consumed from foods How much energy a person receives depends on the composition of the foods and beverages compared with the energy expended through metabolic processes and physical activities. and beverages and on the amount the person eats and drinks. bomb calorimeter (KAL-oh-RIM-eh-ter): an instrument that measures the heat energy released when foods are Food Composition To find out how many kcalories a food provides, a burned, thus providing an estimate of the potential energy scientist can burn the food in a bomb calorimeter (see Figure 8-1). When the of the foods. calor 5 heat *Body fat, or adipose tissue, is composed of a mixture of mostly fat, some protein, and water. A pound of body fat metron 5 measure (454 g) is approximately 87 percent fat, or (454 3 0.87) 395 g, and 395 g 3 9 kcal/g 5 3555 kcal. 236 Chapter 8 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 food burns, energy is released in the form of heat. The amount of heat given off provides a direct measure of the food’s energy value (remember that kcalories are units of heat energy).* In addition to releasing heat, these reactions generate carbon dioxide and water—just as the body’s cells do when they metabolize the energy-yielding nutrients from foods. Details of the chemical reactions in a calo- rimeter and in the body differ, but the overall process is similar: when the food burns and the chemical bonds break, the carbons (C) and hydrogens (H) combine with oxygens (O) to form carbon dioxide (CO2) and water (H2O). The amount of oxygen consumed gives an indirect measure of the amount of energy released. A bomb calorimeter measures the available energy in foods but overstates the physiological fuel value—the amount of energy that the human body derives from foods. The body is less efficient than a calorimeter and cannot metabolize all of the energy-yielding nutrients in a food completely. Researchers can correct for this dis- crepancy mathematically to create useful tables of the energy values of foods (such as Appendix H). These values provide reasonable estimates, but they do not reflect the precise amount of energy a person will derive from the foods consumed. The energy values of foods can also be computed from the amounts of carbo- hydrate, fat, and protein (and alcohol, if present) in the foods.** For example, a food containing 12 grams of carbohydrate, 5 grams of fat, and 8 grams of protein will provide 48 carbohydrate kcalories, 45 fat kcalories, and 32 protein kcalories, for a total of 125 kcalories. (To review how to calculate the energy foods provide, turn to How To 1-2 on p. 10.) Food intake To achieve energy balance, the body must meet its needs without taking in too much or too little energy. Appetite prompts a person to eat—or not to eat. Somehow the body decides how much and how often to eat—when to start eating and when to stop. As you will see, many signals—from both the environment and genetics—initiate or delay eating.4 Hunger People eat for a variety of reasons, most obviously (although not neces- sarily most commonly) because they are hungry. Most people recognize hunger as an irritating feeling that prompts thoughts of food and motivates them to start eating. In the body, hunger is the physiological response to a need for food trig- gered by nerve signals and chemical messengers originating and acting in the brain, primarily in the hypothalamus. Hunger can be influenced by the presence or absence of nutrients in the bloodstream, the size and composition of the pre- ceding meal, customary eating patterns, climate (heat reduces food intake; cold increases it), physical activity, hormones, and illnesses. Hunger determines what to eat, when to eat, and how much to eat. The stomach is ideally designed to handle periodic batches of food, and peo- ple typically eat meals at roughly 4-hour intervals. Four hours after a meal, most, if not all, of the food has left the stomach. Most people do not feel like eating again until the stomach is either empty or almost so. Even then, a person may not feel hungry for quite a while. physiological fuel value: the number of kcalories that Satiation During the course of a meal, as food enters the GI tract and hun- the body derives from a food, in contrast to the number of kcalories determined by calorimetry. ger diminishes, satiation occurs. As receptors in the stomach stretch and hor- appetite: the integrated response to the sight, smell, mones such as cholecystokinin become active, the person begins to feel full. The thought, or taste of food that initiates or delays eating. response: satiation, which prompts the person to stop eating. hunger: the painful sensation caused by a lack of food that initiates food-seeking behavior. Satiety After a meal, the feeling of satiety continues to suppress hunger and allows hypothalamus (high-po-THAL-ah-mus): a brain center a person to not eat again for a while. Whereas satiation tells us to “stop eating,” that controls activities such as maintenance of water balance, satiety reminds us to “not start eating again.” Figure 8-2 (p. 238) summarizes the regulation of body temperature, and control of appetite. relationships among hunger, satiation, and satiety. Of course, people can override satiation (say-she-AY-shun): the feeling of satisfaction and these signals, especially when presented with stressful situations or favorite foods. fullness that occurs during a meal and halts eating. Satiation determines how much food is consumed during a meal. *As Chapter 1 mentions, many scientists measure food energy in kilojoules (a measure of work energy). Conversion satiety (sah-TIE-eh-tee): the feeling of fullness and factors for these and other measures can be found in Appendix K. satisfaction that occurs after a meal and inhibits eating until **Some of the food energy values in the table of food composition in Appendix H were derived by bomb calorim- the next meal. Satiety determines how much time passes etry, and many were calculated from their energy-yielding nutrient contents. between meals. energy Balance and Body Composition 237 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  FigUre 8-2 Hunger, Satiation, and Satiety 1 Physiological influences Empty stomach Gastric contractions 2 Sensory influences Absence of nutrients in small intestine Thought, sight, smell, GI hormones sound, taste of food Endorphins (the brain’s pleasure chemicals) are triggered by the smell, sight, or taste of foods, enhancing the desire for them Banana Stock, Ltd./Getty Images 1 Hunger Creatas/Getty images 5 Postabsorptive influences (after nutrients enter the blood) Nutrients in the blood signal the brain (via 2 Seek food nerves and hormones) about their availability, and start meal use, and storage As nutrients dwindle, satiety diminishes Hunger develops Andresr/Shutterstock.com 5 Satiety: Several hours later 3 Keep eating 4 Satiation: End meal 3 Cognitive influences Presence of others, social stimulation 4 Postingestive influences Perception of hunger, Rawpixel.com/Shutterstock.com (after food enters the digestive tract) awareness of fullness Food in stomach triggers Favorite foods, foods stretch receptors with special meanings Nutrients in small intestine Time of day elicit hormones (for example, fat Abundance of elicits cholecystokinin, which slows available food gastric emptying) Overriding Hunger and Satiety Not surprisingly, eating can be triggered by sig- nals other than hunger, even when the body does not need food. Some people experience food cravings when they are bored or anxious. In fact, they may eat in response to any kind of stress, negative or positive. (“What do I do when I’m grieving? Eat. What do I do when I’m celebrating? Eat!”) Not too surprisingly, repeatedly eating to relieve chronic stress can lead to overeating and weight gain. Many people respond to external cues such as the time of day (“It’s time to eat”) or the availability, sight, and taste of food (“I’d love a piece of chocolate even though I’m full”). Environmental influences such as large portion sizes, favorite foods, or an abundance or variety of foods stimulate eating and increase energy intake (see Photo 8-1). Cognitive influences—such as perceptions, memories, intellect, and social interactions—can easily lead to weight gain. Those who are overweight or obese may be especially susceptible to external cues that trigger hunger and the desire to eat.5 Eating can also be suppressed by signals other than satiety, even when a per- son is hungry. People with the eating disorder anorexia nervosa, for example, use tremendous discipline to ignore the pangs of hunger. Some people simply cannot eat during times of stress, negative or positive. (“I’m too sad to eat.” “I’m too ex- cited to eat!”) Why some people overeat in response to stress and others cannot eat at all remains a bit of a mystery, although researchers are beginning to un- derstand the connections between stress hormones, brain activity, and “comfort foods.” Factors that appear to be involved include how the person perceives the stress and whether usual eating behaviors are restrained. (Highlight 8 features anorexia nervosa and other eating disorders.) Sustaining Satiation and Satiety The extent to which foods produce satiation and sustain satiety depends in part on the nutrient composition of a meal. Of the 238 Chapter 8 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  Jupiterimages/Getty Images PHOTO 8-1 Regardless of hunger, people typically overeat when offered the abundance and variety of a buffet. To limit unhealthy weight gains, listen to hunger and satiety signals. three energy-yielding nutrients, protein is considered the most satiating. In fact, too little protein in the diet can leave a person feeling hungry. Including some protein—such as drinking milk—provides satiety and decreases energy intake at the next meal.6 In contrast, fructose in a sugary fruit drink seems to stimulate ap- petite and increase food intake. Chapter 1 explains that energy density is a measure of the energy a food pro- vides relative to the amount of food (kcalories per gram). Foods with a high energy density provide more kcalories, and those with low energy density pro- vide fewer kcalories, for the same amount of food. Foods low in energy density are also more satiating. High-fiber foods effectively provide satiation by filling the stomach and delaying the absorption of nutrients. For this reason, eating a large salad as a first course helps a person eat less during the meal. In contrast, fat has a weak effect on satiation; consequently, eating high-fat foods may lead to passive overconsumption. High-fat foods are flavorful, which stimulates the appetite and entices people to eat more. High-fat foods are also energy dense; consequently, they deliver more kcalories per bite. (Chapter 9 describes how con- sidering a food’s energy density can help with weight management.) Although fat provides little satiation during a meal, it produces strong satiety signals once it enters the intestine. Fat in the intestine triggers the release of cholecystokinin— a hormone that signals satiety and inhibits food intake. Eating high-fat foods while trying to limit energy intake requires small portion sizes, which can leave a person feeling unsatisfied. Portion size correlates directly with a food’s satiety. Instead of eating small portions of high-fat foods and feeling deprived, a person can feel satisfied by eating large portions of low-fat, high-fiber, and low- energy-density foods. Figure 8-3 (p. 240) illustrates how fat influences portion size. Message Central—The Hypothalamus As you can see, eating is a complex behav- ior controlled by a variety of genetic, psychological, social, metabolic, and physi- ological factors.7 The hypothalamus appears to be the control center, integrating messages about energy intake, expenditure, and storage from other parts of the brain and from the mouth, GI tract, and liver.8 Some of these messages influence satiation, which helps control the size of a meal; others influence satiety, which helps determine the frequency of meals.* Dozens of gastrointestinal hormones influence appetite control and energy balance.9 By understanding the action of these hormones, researchers may one day be able to develop anti-obesity treatments. An added challenge is to sort out *Gastrointestinal hormones that regulate food intake include amylin, cholecystokinin (CCK), enterostatin, satiating: having the power to suppress hunger ghrelin, glucagon-like peptide-1 (GLP-1), oxyntomodulin, pancreatic polypeptide (PP), and peptide YY (PYY). and inhibit eating. energy Balance and Body Composition 239 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  FigurE 8-3 How Fat influences Portion Sizes 100 kcal 837 kcal 9 g fat 71 g fat 55 kcal 100 kcal Polara Studios, Inc. Polara Studios, Inc. 3 g fat 5 g fat For the same size portion, peanuts deliver more than 15 times the For the same number of kcalories, a person can have a few kcalories and 20 times the fat of popcorn. high-fat peanuts or almost 2 cups of high-fiber popcorn. (This comparison used oil-based popcorn; using air-popped popcorn would double the amount of popcorn in this example.) the many actions of related brain chemicals. For example, one brain chemical, neuropeptide Y, causes carbohydrate cravings, initiates eating, decreases energy expenditure, and increases fat storage—all factors favoring a positive energy bal- ance and weight gain. neuropeptide Y: a chemical produced in the brain that ❯ REVIEW IT Discuss some of the physical, emotional, and environmental stimulates appetite, diminishes energy expenditure, and increases fat storage. influences on food intake. thermogenesis: the generation of heat; used in physiology A mixture of signals governs a person’s eating behaviors. Hunger and appetite initiate eating, and nutrition studies as an index of how much energy the whereas satiation and satiety stop and delay eating, respectively. Each responds to messages body is expending. from the nervous and hormonal systems. Superimposed on these signals are complex factors basal metabolism: the energy needed to maintain life when a body is at complete digestive, physical, and emotional rest. involving emotions, habits, and other aspects of human behavior. 8-3 Energy Out: The kCalories the Body Expends FigurE 8-4 Components of Energy ❯ LEARN IT List the components of energy expenditure and factors that might Expenditure influence each. The amount of energy expended in voluntary Chapter 7 explains that heat is released whenever the body breaks down carbo- physical activities has the greatest variability, hydrate, fat, or protein for energy and again when that energy is used to do work. depending on a person’s activity patterns. For a sedentary person, physical activities may account The generation of heat, known as thermogenesis, can be measured to determine for less than half as much energy as basal the amount of energy expended. The total energy a body expends reflects three metabolism, whereas an extremely active person main categories of thermogenesis: may expend as much on physical activity as for basal metabolism. Energy expended for basal metabolism Energy expended for physical activity 30–50% Physical Energy expended for food consumption activities A fourth category is sometimes involved: 10% Thermic effect Energy expended for adaptation of food 50–65% Basal metabolism Components of Energy Expenditure People expend energy when they are physically active, of course, but they also expend energy when they are rest- ing quietly (see Photo 8-2). In fact, quiet metabolic activities account for the larg- est share of most people’s energy expenditures, as Figure 8-4 shows. The amount of energy expended in a day differs for each individual, but in general, basal Basal Metabolism About two-thirds of the energy the average person expends metabolism is the largest component of energy expenditure and thermic effect of food is the in a day supports the body’s basal metabolism. Metabolic activities include the smallest. lungs inhaling and exhaling air, the bone marrow making new red blood cells, 240 Chapter 8 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  Jack Hollingsworth/Photodisc/Getty Images PHOTO 8-2 It feels like work and it may make you tired, but studying requires only one or two kcalories per minute. the heart beating 100,000 times a day, and the kidneys filtering wastes—in short, they support all the basic processes of life. The basal metabolic rate (BMR) is the rate at which the body expends en- ergy for these life-sustaining activities. The rate may vary from person to person and may vary for the same individual with a change in circumstance or physical condition. The rate is slowest when a person is sleeping undisturbed, but it is usually measured in a room with a comfortable temperature when the person is awake, but lying still, after a restful sleep and an overnight (12 to 14 hours) fast. A similar measure of energy output—called the resting metabolic rate (RMR)— is slightly higher than the BMR because its criteria for recent food intake and physical activity are not as strict. When energy needs cannot be measured, equa- tions can provide reasonably accurate estimates (see Table 8-1). In general, the more a person weighs, the more total energy is expended on basal metabolism, but the amount of energy per pound of body weight may be lower. For example, an adult’s BMR might be 1500 kcalories per day and an infant’s only 500, but compared to body weight, the infant’s BMR is more than twice as fast. Similarly, a normal-weight adult may have a metabolic rate one and a half times that of an obese adult when compared to body weight because lean tissue is metabolically more active than body fat. Table 8-2 (p. 242) summarizes the factors that raise and lower the BMR. For the most part, the BMR is highest in people who are growing (children, adoles- cents, and pregnant women) and in those with considerable lean body mass TaBLe 8-1 estimating energy expended on Basal Metabolism BMr estimates BMr equations Men Slightly.1 kcal/min (1.1 to 1.3 kcal/min) (10 3 wt) 1 (6.25 3 ht) 2 (5 3 age) basal metabolic rate (BMr): the rate of energy use for 15 metabolism under specified conditions: after a 12-hour fast or and restful sleep, without any physical activity or emotional 24 kcal/kg/day excitement, and in a comfortable setting. It is usually expressed as kcalories per kilogram of body weight per hour. Women Slightly ,1 kcal/min (0.8 to 1.0 kcal/min) (10 3 wt) 1 (6.25 3 ht) 2 (5 3 age) resting metabolic rate (rMr): similar to the basal or 2 161 metabolic rate (BMR), a measure of energy use for a person at 23 kcal/kg/day rest in a comfortable setting, but with less stringent criteria for recent food intake and physical activity. Consequently, the Note For perspective, a burning candle or a Use actual weight in kilograms, height RMR is slightly higher than the BMR. 75-watt light bulb releases about 1 kcal/min in centimeters, and age in years lean body mass: the body minus its fat. energy Balance and Body Composition 241 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  TaBLe 8-2 Factors That affect the BMr Factor effect on BMr Age Lean body mass diminishes with age, slowing the BMR.a Height In tall, thin people, the BMR is higher.b Growth In children, adolescents, and pregnant women, the BMR is higher. Body composition The more lean tissue, the higher the BMR (which is why males usually (gender) have a higher BMR than females). The more fat tissue, the lower the BMR. Fever Fever raises the BMR.c Stresses Stresses (including many diseases and certain drugs) raise the BMR. Environmental Both heat and cold raise the BMR. temperature Fasting/starvation Fasting/starvation lowers the BMR.d Malnutrition Malnutrition lowers the BMR. Hormones The thyroid hormone thyroxine, for example, can speed up or slow down the BMR.e Premenstrual hormones slightly raise the BMR. Smoking Nicotine increases energy expenditure. Caffeine Caffeine increases energy expenditure. Sleep BMR is lowest when sleeping. aThe BMR begins to decrease in early adulthood (after growth and development cease) at a rate of about 2 percent/ decade. A reduction in voluntary activity as well brings the total decline in energy expenditure to about 5 percent/decade. bIf two people weigh the same, the taller, thinner person will have the faster metabolic rate, reflecting the greater skin surface, through which heat is lost by radiation, in proportion to the body’s volume (see Figure 8-5, p. 244). c Fever raises the BMR by 7 percent for each degree Fahrenheit. dProlonged starvation reduces the total amount of metabolically active lean tissue in the body, although the decline occurs sooner and to a greater extent than body losses alone can explain. More likely, the neural and hormonal changes that accompany fasting are responsible for changes in the BMR. eThe thyroid gland releases hormones that travel to the cells and influence cellular metabolism. Thyroid hormone activity can speed up or slow down the rate of metabolism by as much as 50 percent. (physically fit people and males). One way to increase the BMR, then, is to par- ticipate in endurance and strength-training activities regularly to maximize lean body mass. The BMR is also high in people with fever or under stress and in people with highly active thyroid glands. The BMR slows down with a loss of lean body mass and during fasting and malnutrition. Physical activity The second component of a person’s energy output is physi- cal activity: voluntary movement of the skeletal muscles and support systems. Physical activity is the most variable—and the most changeable—component of energy expenditure. Consequently, its influence on both weight gain and weight loss can be significant. During physical activity, the muscles need extra energy to move, and the heart and lungs need extra energy to deliver nutrients and oxygen and dispose of wastes. The amount of energy needed for any activity, whether playing tennis or studying for an exam, depends on three factors: muscle mass, body weight, and activity. The larger the muscle mass and the heavier the weight of the body part being moved, the more energy is expended. Table 8-3 gives average energy expenditures for various activities. The activity’s duration, frequency, and inten- sity also influence energy expenditure: the longer, the more frequent, and the more intense the activity, the more kcalories expended. (An activity’s duration, frequency, and intensity also inf luence the body’s use of the energy-yielding nutrients.) thermic effect of food (TeF): an estimation of the energy required to process food (digest, absorb, transport, Thermic effect of Food When a person eats, the GI tract muscles speed up their metabolize, and store ingested nutrients); also called the rhythmic contractions, the cells that manufacture and secrete digestive juices be- specific dynamic effect (SDE) of food or the specific dynamic come active, and some nutrients require energy to be absorbed. This acceleration activity (SDA) of food. The sum of the TEF and any increase in the metabolic rate due to overeating is known as diet-induced of activity requires energy and produces heat; it is known as the thermic effect thermogenesis (DIT). of food (TEF). 242 Chapter 8 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 TaBLe 8-3 estimating energy expended on Physical activities The values listed in this table reflect both the energy expended in physical activity and the amount used for BMR. To calculate kcalories spent per minute of activity for your own body weight, multiply kcal/lb/min (or kcal/kg/min) by your exact weight and then multiply that number by the number of minutes spent in the activity. For example, if you weigh 142 pounds, and you want to know how many kcalories you spent doing 30 minutes of vigorous aerobic dance: 0.062 3 142 5 8.8 kcalories per minute; 8.8 3 30 minutes 5 264 total kcalories expended. kCal/lb kCal/kg kCal/lb kCal/kg kCal/lb kCal/kg activity min min activity min min activity min min Aerobic dance (vigorous).062.136 Handball.078.172 Table tennis (skilled).045.099 Basketball (vigorous, Horseback riding Tennis (beginner).032.070 full court).097.213 (trot).052.114 Vacuuming and other Bicycling Rowing (vigorous).097.213 household tasks.030.066 13 mph.045.099 Running Walking 15 mph.049.108 5 mph.061.134 3.5 mph.035.077 17 mph.057.125 6 mph.074.163 4.5 mph.048.106 19 mph.076.167 7.5 mph.094.207 Weight lifting 21 mph.090.198 9 mph.103.227 light-to-moderate.024.053 23 mph.109.240 10 mph.114.251 vigorous.048.106 25 mph.139.306 11 mph.131.288 Wheelchair basketball.084.185 Canoeing, flat water, Soccer (vigorous).097.213 Wheeling self in moderate pace.045.099 wheelchair.030.066 Studying.011.024 Cross-country skiing Wii games Swimming 8 mph.104.229 bowling.021.046 20 yd/min.032.070 Gardening.045.099 boxing.021.047 45 yd/min.058.128 Golf (carrying clubs).045.099 tennis.022.048 50 yd/min.070.154 The thermic effect of food is proportional to the food energy taken in and is usually estimated at 10 percent of energy intake. Thus a person who ingests 2000 kcalories probably expends about 200 kcalories on the thermic effect of food. The proportions vary for different foods, however, and are also inf lu- enced by factors such as meal size and frequency. In general, the thermic effect of food is greater for high-protein foods than for high-fat foods (see Table 8-4) and for a meal eaten all at once rather than spread out over a couple of hours. For most purposes, however, the thermic effect of food can be ignored when estimating energy expenditure because its contribution to total energy output is smaller than the probable errors involved in estimating overall energy in- take and output. adaptive Thermogenesis Additional energy is expended when circumstances in the body are dramatically changed. A body challenged to physical condition- ing, extreme cold, overfeeding, starvation, trauma, or other types of stress must adapt; it has extra work to do and uses extra energy to build the tissues and produce the enzymes and hormones necessary to cope with the demand. This energy is known as adaptive thermogenesis, and in some circumstances (for example, in burn victims), it makes a considerable difference in the total en- ergy expended. Because this component of energy expenditure is so variable and TaBLe 8-4 estimating energy expended on Thermic effect of Foods Food Component energy expended Carbohydrate 5–10% Fat 0–5% Protein 20–30% adaptive thermogenesis: adjustments in energy Alcohol 15–20% expenditure related to changes in environment such as NOTE: Percentages are calculated by dividing the energy expended during digestion and absorption (above basal) by the extreme cold and to physiological events such as overfeeding, energy content of the food. trauma, and changes in hormone status. energy Balance and Body Composition 243 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  FigUre 8-5 How Body Size influences BMr specific to individuals, it is not included when estimating energy requirements for most healthy people. estimating energy requirements In estimating energy requirements, the DRI Committee developed equations based on research measuring total daily energy expenditure. These equations consider how the following factors influence BMR and consequently energy expenditure: Gender. In general, women have a lower BMR than men, in large part because men typically have more lean body mass. Two sets of energy equations—one for men and one for women—were developed to accom- modate the influence of gender on energy expenditure (provided on the next page). Growth. The BMR is high in people who are growing. For this reason, preg- nant and lactating women, infants, children, and adolescents have their own sets of energy equations. Age. The BMR declines during adulthood as lean body mass diminishes. This change in body composition occurs, in part, because some hormones that influence appetite, body weight, and metabolism become more, or Each of these structures is made of eight blocks. less, active with age. Physical activities tend to decline as well, bringing They weigh the same, but they are arranged the average reduction in energy expenditure to about 5 percent per de- differently. The short, wide structure has 24 sides cade. The decline in BMR that occurs when a person becomes less active exposed and the tall, thin one has 34. Because the tall, thin structure has a greater surface area, it reflects the loss of lean body mass and may be minimized with ongoing will lose more heat (expend more energy) than the physical activity. Because age influences energy expenditure, it is also fac- short, wide one. Similarly, two people of different tored into the energy equations. heights might weigh the same, but the taller, thin one will have a higher BMR (expending more Physical activity. Using individual values for various physical activities energy) because of the greater skin surface. (as in Table 8-3 on p. 243) is time-consuming and impractical for es- timating the energ y needs of a population. Instead, various activities are clustered according to the typical intensity of a day’s efforts. Energy equations include a physical activity factor for various levels of intensity for each gender. Body composition and body size. The BMR is high in people who are tall and so have a large surface area, as illustrated in Figure 8-5. Similarly, the more a person weighs, the more energy is expended on basal metabo- lism. For these reasons, energy equations include a factor for both height and weight. As just e xplained, energ y needs var y between individuals depending on such factors as gender, growth, age, physical activity, and body size and composition. Even when two people are similarly matched, however, their energy needs still differ because of genetic differences. Perhaps one day genetic research will reveal how to estimate requirements for each individual. For now, How To 8-1 provides instructions on estimating energy requirements using the DRI equations and physical activity factors. Appendix F presents a table of estimated daily energy needs by age, gender, and activity level, based on the DRI equations using reference heights and weights. ❯ REVIEW IT List the components of energy expenditure and factors that might influence each. A person in energy balance takes in energy from food and expends much of it on basal me- tabolism, some of it on physical activities, and a little on the thermic effect of food. Energy requirements vary from person to person, depending on such factors as gender, age, weight, and height as well as the intensity and duration of physical activity. All of these factors must be considered when estimating energy requirements. 244 Chapter 8 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  8-1 How To estimate energy weighs 178 pounds. First, he converts his (Another reminder: Do calculations within the weight from pounds to kilograms and his brackets next.) requirements height from inches to meters, if necessary: EER 5 376 1 1.25 3 2258 To determine your estimated energy 178 lb 4 2.2 5 80.9 kg requirement (EER), use the appropriate equa- (One more reminder: Do multiplication before tion, inserting your age in years, weight (wt) 71 in 4 39.37 5 1.8 m addition.) in kilograms, height (ht) in meters, and physi- cal activity (PA) factor from the accompany- Next, he considers his level of daily physical EER 5 376 1 2823 ing table. (To convert pounds to kilograms, activity and selects the appropriate PA factor EER 5 3199 divide by 2.2; to convert inches to meters, from the accompanying table. (In this exam- divide by 39.37.) ple, 1.25 for an active male.) Then, he inserts The estimated energy requirement for an his age, PA factor, weight, and height into the active 30-year-old male who is 5 feet 11 For men 19 years and older: appropriate equation: inches tall and weighs 178 pounds is about EER 5 [662 2 (9.53 3 age)] 1 PA 3 3200 kcalories/day. His actual requirement [(15.91 3 wt) 1 (539.6 3 ht)] EER 5 [662 2 (9.53 3 30)] 1 1.25 3 probably falls within a range of 200 kcalories For women 19 years and older: [(15.91 3 80.9) 1 (539.6 3 1.8)] above and below this estimate. EER 5 [354 2 (6.91 3 age)] 1 PA 3 (A reminder: Do calculations within the NOTE: Appendix F provides estimates of energy needs based on EER [(9.36 3 wt) 1 (726 3 ht)] equations, using reference heights and weights for each age-gender parentheses first.) He calculates: group. For example, consider an active 30-year- old male who is 5 feet 11 inches tall and EER 5 [662 2 286] 1 1.25 3 [1287 1 971] Physical activity (Pa) Factors for eer equations Men Women Physical activity Sedentary 1.0 1.0 Typical daily living activities Low active 1.11 1.12 plus 30–60 min moderate activity Active 1.25 1.27 plus $ 60 min moderate activity Very active 1.48 1.45 plus $ 60 min moderate activity and 60 min vigorous or 120 min moderate activity NOTE: Moderate activity is equivalent to walking at 3 to 4½ mph. ❯ TrY iT Estimate your energy requirement based on your current age, weight, height, and activity level. 8-4 Body Weight and Body Composition ❯LEARN IT Distinguish between body weight and body composition, including methods to assess each. A person 5 feet 10 inches tall who weighs 150 pounds may carry only about 30 of those pounds as fat.* The rest is mostly water and lean tissues—muscles, organs such as the heart and liver, and the bones of the skeleton. Direct measures of body composition are impossible in living human beings; instead, researchers assess body composition indirectly based on the following assumption: Body weight 5 fat 1 lean tissue (including water). Weight gains and losses tell us nothing about how the body’s composition may have changed, yet weight is the measure most people use to judge their “fat- ness.” For many people, overweight is overfat, but this is not always the case. Athletes with dense bones and well-developed muscles may be overweight by some standards but have little body fat. Conversely, inactive people may seem to have acceptable weights, when, in fact, they may have too much body fat. body composition: the proportions of muscle, bone, fat, and *In metric terms, a person 1.78 meters tall who weights 68 kilograms may carry only about 14 of those kilograms as fat. other tissue that make up a person’s total body weight. energy Balance and Body Composition 245 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203  Defining Healthy Body Weight How much should a person weigh? How can a person know if her weight is appropriate for her height? How can a person know if his weight is jeopardizing his health? Such questions seem so simple, yet the answers can be complex—and quite different depending on whom you ask. The Criterion of Fashion In asking what is ideal, people often mistakenly turn to friends and fashion for the answer and judge body weight by appearances. No doubt our society sets unrealistic ideals for body weight, especially for women. Magazines, movies, and television all convey the message that to be thin is to be beautiful and happy. As a result, the media have a great influence on the weight concerns and dieting patterns of people of all ages, but most tragically on young, impressionable children and adolescents. Importantly, perceived body image may have little to do with actual body weight or size. People of all shapes, sizes, and ages—including extremely thin fash- ion models with anorexia nervosa and fitness instructors with ideal body composition—have learned to be unhappy with their “overweight” bodies. Such dissatisfaction can lead to dam- aging behaviors, such as starvation diets, diet pill abuse, and health-care avoidance. The first step toward making healthy changes may be self-acceptance. Keep in mind that fashion is fickle; the body shapes valued by our society change with time. Furthermore, body shapes valued by one society differ from those of other societies. The standards defining “ideal” are sub- jective and may have little in common with health. Table 8-5 offers some tips for adopting health as an ideal. The Criterion of Health Even if our society were to accept fat as beautiful, obesity is still a major risk factor for several life-threat- ening diseases, including heart disease, type 2 diabetes, and some cancers. For this reason, the most important criterion for determining how much a person should weigh and how much Randy M.Ury/Corbis body fat a person needs is not appearance but good health and longevity. Ideally, a person has enough fat to meet basic needs but not so much as to incur health risks (see Photo 8-3). This range of healthy body weights has been identified using a com- PHOTO 8-3 A healthy body contains enough lean tissue to mon measure of weight and height—the body mass index. support health and the right amount of fat to meet body needs. Body Mass index The body mass index (BMI) describes relative weight for height: body mass index (BMi): a measure of a person’s weight weight (kg) weight (lb) relative to height; determined by dividing the weight (in BMI = or × 703 kilograms) by the square of the height (in meters). height (m)2 height (in.)2 underweight: body weight lower than the weight range that Weight classifications based on BMI are presented in Table 8-6. Notice that is considered healthy; BMI less than 18.5. healthy weight falls between a BMI of 18.5 and 24.9, with underweight below overweight: body weight greater than the weight range that is considered healthy; BMI 25 to 29.9. 18.5, overweight above 25, and obese above 30. Figure 8-6 shows examples of obese: too much body fat with adverse health effects; BMI body shapes with different BMI. More than two-thirds of adults in the United 30 or more. States have a BMI greater than 25, as Figure 8-7 shows.10 TaBLe 8-5 Tips for accepting a Healthy Body Weight Value yourself and others for human attributes other than body Follow the USDA Food Patterns. Never restrict food intake below weight. Realize that prejudging people by weight is as harmful as the minimum levels that meet nutrient needs. prejudging them by race, religion, or gender. Become physically active, not because it will help you get thin but Use positive, nonjudgmental descriptions of your body. because it will make you feel good and improve your health. Accept positive comments from others. Seek support from loved ones. Tell them of your plan for a healthy Focus on your whole self, including your intelligence, social grace, and life in the body you have been given. professional and scholastic achievements. Seek professional counseling from someone who can help you Accept that no magic diet exists. make gains in self-esteem without weight as the primary focus. Stop dieting to lose weight. Adopt a lifestyle of healthy eating and Appreciate body weight for its influence on health, not physical activity permanently. appearance. 246 Chapter 8 Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-200-203 TaBLe 8-6 Body Mass index (BMi) Under- weight Healthy Weight Overweight Obese (,18.5) (18.5–24.9) (25–29.9) ($30) 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 Height Body weight (pounds) 4’10” 86 91 96 100 105 110 115 119 124 129 134 138 143 148 153 158 162 167 172 177 181 186 191 4’11” 89 94 99 104 109 114 119 124 128 133 138 143 148 153 158 163 168 173 178 183 188 193 198 5’0” 92 97 102 107 112 118 123 128 133 138 143 148 153 158 163 168 174 179 184 189 194 199 204 5’1” 95 100 106 111 116 122 127 132 137 143 148 153 158 164 169 174 180 185 190 195 201 206 211 5’2” 98 104 109 115 120 126 131 136 142 147 153 158 164 169 175 180 186 191 196 202 207 213 218 5’3” 102 107 113 118 124 130 135 141 146 152 158 163 169 175 180 186 191 197 203 208 214 220 225 5’4” 105 110 116 122 128 134 140 145 151 157 163 169 174 180 186 192 197 204 209 215 221 227 232 5’5” 108 114 120 126 132 138 144 150 156 162 168 174 180 186 192 198 204 210 216 222 228 234 240 5’6” 112 118 124 130 136 142 148 155 161 167 173 179 186 192 198 204 210 216 223 229 235 241 247 5’7” 115 121 127 134 140 146 153 159 166 172 178 185 191 198 204 211 217 223 230 236 242 249 255 5’8” 118 125 131 138 144 151 158 164 171 177 184 190 197 203 210 216 223 230 236 243 249 256 262 5’9” 122 128 135 142 149 155 162 169 176 182 189 196 203 209 216 223 230 236 243 250 257 263 270 5’10” 126 132 139 146 153 160 167 174 181 188 195 202 209 216 222 229 236 243 250 257 264 271 278 5’11” 129 136 143 150 157 165 172 179 186 193 200 208 215 222 229 236 243 250 257 265 272 279 286 6’0” 132 140 147 154 162 169 177 184 191 199 206 213 221 228 235 242 250 258 265 272 279 287 294 6’1” 136 144 151 159 166 174 182 189 197 204 212 219 227 235 242 250 257 265 272 280 288 295 302 6’2” 141 148 155 163 171 179 186 194 202 210 218 225 233 241 249 256 264 272 280 287 295 303 311 6’3” 144 152 160 168 176 184 192 200 208 216 224 232 240 248 256 264 272 279 287 295 303 311 319 6’4” 148 156 164 172 180 189 197 205 213 221 230 238 246 254 263 271 279 287 295 304 312 320 328 6’5” 151 160 168 176 185 193 202 210 218 227 235 244 252 261 269 277 286 294 303 311 319 328 336 6’6” 155 164 172 181 190 198 207 216 224 233 241 250 259 267 276 284 293 302 310 319 328 336 345 Obesity-related diseases become evident beyond a BMI of 25. For this reason, a BMI of 25 for adults represents a healthy goal for overweight people and an up- per limit for others. The lower end of the healthy range may be a reasonable target for severely underweight people. BMI values slightly below the healthy range may FigUre 8-6 BMi and Body Shapes FigUre 8-7 Distribution of Body Weights Standard silhouette figures such as those shown below are commonly used in research studies in US adults (without the BMI numbers) to determine how accurately people perceive their body size. Overweight Healthy weight (BMI 25 – 29.9) (BMI 18.5 – 24.9) Obesity Underweight (BMI 30 – 39.9) (BMI FigUre 8-10 Common Methods Used to assess Body Fat Skinfold measures estimate Air-displacement body fat by using a caliper to plethysmography (commonly gauge the thickness of a fold of called the bod pod) estimates skin on the back of the arm body composition by having a (over the triceps), below the person sit inside a chamber Photo courtesy of Life Measurement, Inc. shoulder blade (subscapular), while computerized sensors © Fitness & Wellness, Boise, Idaho and in other places (including determine the amount of air lower-body sites), and then displaced by the person’s comparing these measure- body. ments with standards. Hydrodensitometry measures Dual-energy X-ray body density by weighing the absorptiometry (DEXA) uses person first on land and then two low-dose X-rays that again while submerged in differentiate among fat-free water. The difference between soft tissue (lean body mass), the person’s actual weight and fat tissue, and bone tissue, Amelie-Benoist/BSIP/Age Fotostock underwater weight provides a providing a precise mea- measure of the body’s volume. surement of total fat and its A mathematical equation using distribution in all but extremely the two measurements (volume Yoav Levy/Phototake obese subjects. and actual weight) determines body density, from which the percentage of body fat can be estimated. Bioelectrical impedance Waist circumference measures body fat by using a measures central obesity by low-intensity electrical current. placing a nonstretchable Because electrolyte-containing measuring tape around the fluids, which readily conduct an waist just above the bony electrical current, are found crest of the hip. The tape runs primarily in lean body tissues, parallel to the floor and is Adam Gault/SPL/Getty Images the leaner the person, the less snug, but does not compress © Geri Engberg Photography resistance to the current. The the skin. measurement of electrical resistance is then used in a mathematical equation to estimate the percentage of body fat. FigUre 8-11 BMi and Mortality 8-5 Health risks associated with Body This J-shaped curve describes the relationship between body mass index (BMI) and mortality and Weight and Body Fat shows that both underweight and overweight present risks of a premature death. ❯ LEARN IT Identify relationships between body weight and chronic diseases. Risk increases Body weight and body fat correlate with disease risks and life expectancy. The as BMI rises Risk increases as correlation suggests a greater likelihood of developing chronic diseases and short- ening life expectancy for those with a higher BMI and waist circumference.17 Not BMI declines all overweight and underweight people will get sick and die before their time nor will all normal-weight people live long healthy lives. Correlations are not causes. For the most part though, people with a BMI between 18.5 and 24.9 have relatively Mortality few weight-related health risks; risks increase as BMI falls below or rises above this range, indicating that both t