Special topics Topic 3:

1. Special topicsTopic 3: Energy Balance and Body Composition Reference: understanding normal and clinical nutrition, 9th edition,2012, chapter8

2. Energy intakes cover people energy requirements' without too much excess. Excess energy is stored as fat, and stored fat is used for energy between meals. • The amount of body fat a person deposits in, or withdraws from, storage on any given day depends on the energy balance for that day. • For each 3500 kcalories eaten in excess, a pound of body fat is stored; similarly, a pound of fat is lost for each 3500 kcalories expended beyond those consumed. • The fat stores of even a healthy-weight adult represent a reserve of energy—50,000 to 200,000 kcalories.

4. Quick changes in body weight are not simple changes in fat stores. Weight gained or lost rapidly includes some fat, large amounts of fluid, and some lean tissues such as muscle proteins and bone minerals. • Even over the long term, the composition of weight gained or lost is normally about 75 percent fat and 25 percent lean. • During starvation, losses of fat and lean are about equal.

5. Energy In: The kCaloriesFoods Provide • Direct calorimetry, which measures the amount of heat released. • Indirect calorimetry, which measures the amount of oxygen consumed. • 1 g carbohydrate = 4 kcal • 1 g fat = 9 kcal • 1 g protein = 4 kcal

6. A bomb calorimeter • When the 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.

8. Food Intake • Hunger: • In the body, hunger is the physiological response to a need for food triggered 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 preceding meal, customary eating patterns, climate (heat reduces food intake; cold increases it), exercise, hormones, and physical and mental illnesses.

9. 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 people typically eat meals at roughly four-hour intervals. Most people do not feel like eating again until the stomach is either empty or almost so. 2. 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.

10. 3. Physiological influences • Empty stomach • Gastric contractions • Absence of nutrients in small intestine • GI hormones • Endorphins (the brain’s pleasure chemicals) are triggered by the smell, sight, or taste of foods, enhancing the desire for them 4. Sensory influences • Thought, sight, smell, sound, taste of food

11. 5. Mental influences • Presence of others, social stimulation • Perception of hunger, awareness of fullness • Favorite foods, foods with special meanings • Time of day • Availability of food

12. 2. Fullness (Satiation): During the course of a meal, as food enters the GI tract and hunger diminishes, satiationdevelops. As receptors in the stomach stretch and hormones such as cholecystokinin become active, the person begins to feel full. The response: satiation occurs and the person stops eating. 3. Satiety After a meal, the feeling of satiety continues to suppress hunger and allows a person to not eat again for a while. Whereas fullnesstells us to “stop eating,” satiety reminds us to “not start eating again

13. Post-ingestive influences (after food enters the digestive tract) • Food in stomach triggers stretch receptors • Nutrients in small intestine elicit hormones (for example which slows gastric emptying). • Post-absorptive influences (after nutrients enter the blood) • Nutrients in the blood signal the brain (via nerves and hormones) about their availability, use, and storage • As nutrients decrease, satiety diminishes and Hunger develops

14. 4. Overriding Hunger and fullness: eating can be triggered by signals 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. • Many people respond to external factors 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 stuffed”). • Environmental influences such as large portion sizes, favoritefoods • Eating can also be suppressed by signals other than satisfy, even when a person is hungry. People with the eating disorder anorexia for example

15. The greatest challenge now is to sort out the many actions of these brain chemicals. For example, one of these chemicals, neuropeptide Y, causes carbohydrate cravings, initiates eating, decreases energy using , and increases fat storage—all factors favoring a positive energy balance and weight gain.

17. Energy Out: The kCaloriesthe Body Expends Thermogenesis : the generation of heat; used in physiology and nutrition studies as an index of how much energy the body is expending. The total energy a body expends reflects three main categories of thermogenesis: Energy expended for basal metabolism Energy expended for physical activity Energy expended for food consumption

18. Basal Metabolism About two-thirds of the energy the average person expends in a day supports the body’s basal metabolism. Metabolic activities maintain the body temperature, keep the lungs inhaling and exhaling air, the bone marrow making new red blood cells, the heart beating, and the kidneys filtering wastes—in short, they support all the basic processes of life.

19. The basal metabolic rate (BMR) is the rate at which the body expends energy 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 hour) fast.

20. 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, equations can provide accurate estimates. In general, the more a person weights, 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.

22. For the most part, the BMR is highest in people who are growing (children, adolescents, and pregnant women) and in those with considerable lean body mass (physically fit people and males). One way to increase the BMR then is to participate 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.

24. 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.

26. Thermic Effect of Food When a person eats, the GI tract muscles speed up their rhythmic contractions, the cells that manufacture and secrete digestive juices begin their tasks, and some nutrients are absorbed by active transport. This acceleration of activity requires energy and produces heat; it is known as the thermic effect of food (TEF).

27. 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 influenced 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 Thermic effect of foods: Carbohydrate: 5–10% Fat: 0–5% Protein: 20–30%

28. Adaptive Thermogenesis Some additional energy is spent when a person must adapt to dramatically changed circumstances. When the body has to adapt to physical conditioning, extreme cold, overfeeding, starvation, trauma, or other types of stress, it has extra work to do, building the tissues and producing the enzymes and hormones necessary to cope with the demand. In some circumstances, this energy makes a considerable difference in the total energy expended. Because this component of energy expenditure is so variable and specific to individuals, it is not included when calculating energy requirements.

29. Estimating Energy Requirements • Gender. In general, women have a lower BMR than men, in large part because men typically have more lean body mass. • Growth. The BMR is high in people who are growing. • Body composition and body size. The BMR is high in people who are tall and so have a large surface area. Similarly, the more a person weighs, the more energy is expended on basal metabolism • Physical activity

30. 5. 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 less, active with age. Physical activities tend to decline as well, bringing the average reduction in energy expenditure to about 5 percent per decade. The decline in BMR that occurs when a person becomes less active reflects the loss of lean body mass and may be minimized with ongoing physical activity.

31. Estimate Energy Requirements To determine your estimated energy requirement (EER), use the appropriate equation, inserting your age in years, weight (wt) in kilograms, height (ht) in meters, and physical activity (PA) factor from the accompanying table. (To convert pounds to kilograms, divide by 2.2; to convert inches to meters, divide by 39.37.) For men 19 years and older: EER = [662 − (9.53 × age)] + PA ×[(15.91 × wt) + (539.6 × ht)] For women 19 years and older: EER = [354 − (6.91 × age)] + PA ×[(9.36 × wt) + (726 × ht)]

32. Example Consider an active 30-year-old male who is 5 feet 11 inches tall and weighs 178 pounds. First, he converts his weight from pounds to kilograms and his height from inches to meters, if necessary: 178 lb ÷ 2.2 = 80.9 kg 71 in ÷ 39.37 = 1.8 m

33. EER = [662 − (9.53 × 30)] + 1.25 × [(15.91 × 80.9) + (539.6 × 1.8)] EER = 3199 The estimated energy requirement for an active 30-year-old male who is 5 feet 11 inches tall and weighs 178 pounds is about 3200 kcalories/day. His actual requirement probably falls within a range of 200 kcalories above and below this estimate.

34. Body Weight, Body Composition,and Health In metric terms, a person 1.78 meters tall who weighs 68 kilograms may carry only about 14 of those kilograms as fat. body composition: the proportions of muscle, bone, fat, and other tissue that make up a person’s total body weight. The rest is mostly water and lean tissues—muscles, organs such as the heart and liver, and the bones of the skeleton. Body weight = fat + lean tissue (including water)

36. Body Mass Index The body mass index (BMI) describes relative weight for height: BMI = weight (kg)/ height (m)2

37. Body Fat and Its Distribution Although weight measures are inexpensive, easy to take, and highly accurate, they fail to reveal two valuable pieces of information in assessing disease risk: How much of the weight is fat and where the fat is located. The ideal amount of body fat depends partly on the person. A normal-weight man may have from 13 to 21 percent body fat; a woman, because of her greater quantity of essential fat, 23 to 31 percent.

38. In general, health problems typically develop when body fat exceeds 22 percent in young men, 25 percent in men older than age 40, 32 percent in young women, and 35 percent in women older than age 40. Body fat may contribute as much as 70 percent in excessively obese adults. Some People Need Less Body Fat For many athletes, a lower percentage of body fat may be ideal—just enough fat to provide fuel, insulate and protect the body, assist in nerve impulse transmissions, and support normal hormone activity, but not so much as to burden the body with excess bulk.

39. For some athletes, then, ideal body fat might be 5 to 10 percent for men and 15 to 20 percent for women. Some People Need More Body Fat For an Alaska fisherman, a higher percentage of body fat is probably beneficial because fat provides an insulating blanket to prevent excessive loss of body heat in cold climates. A woman starting a pregnancy needs sufficient body fat to support conception and fetal growth

40. Below a certain threshold for body fat, hormone synthesis falters, and individuals may become infertile, develop depression, experience abnormal hunger regulation, or become unable to keep warm. These thresholds differ for each function and for each individual; much remains to be learned about them. Visceral fat is most common in men and to a lesser extent in women past menopause. Even when total body fat is similar, men have more visceral fat than women.

41. Regardless of gender, the risks of cardiovascular disease, diabetes, and mortality are increased for those with excessive visceral fat. Interestingly, smokers tend to have more visceral fat than nonsmokers even though they typically have lower BMI. Subcutaneous fat around the hips and thighs, sometimes referred to as lower body fat, is most common in women during their reproductive years and seems relatively harmless.

42. Waist circumference is a better indicator of abdominal fat, but some researchers use the waist-to-hip ratio when studying disease risks. The ratio requires another step or two (measuring the hips and comparing that measure to the waist measure), but it does not provide any additional information. Therefore, waist circumference alone is the preferred method for assessing abdominal fat in a clinical setting Women: greater than 35 inches (88 centimeters) and men with a waist circumference of greater than 40 inches (102 centimeters) In fact, overweight people who have little visceral fat are less susceptible to health problems than overweight people with visceral fat.

43. Other Measures of Body Composition 1. Skin fold measures estimate body fat by using a caliper to gauge the thickness of a fold of skin on the back of the arm (over the triceps), below the shoulder blade (subscapular), and in other places (including lower-body sites), and then comparing these measurements with standards.

44. 2. Air displacement plethysmo-graphy estimates body composition by having a person sit inside a chamber while computerized sensors determine the amount of air displaced by the person’s body. 3. Dual energy X-ray absorptiometry (DEXA) uses two low-dose X-rays that differentiate among fat-free soft tissue (lean body mass), fat tissue, and bone tissue, providing a precise measurement of total fat and its distribution in all but extremely obese subjects.

45. 4. Bioelectrical impedance: measures body fat by using a low-intensity electrical current. Because electrolyte-containing fluids, which readily conduct an electrical current, are found primarily in lean body tissues, the leaner the person, the less resistance to the current. The measurement of electrical resistance is then used in a mathematical equation to estimate the percentage of body fat.

46. Health Risks Associated with Body Weight and Body Fat 1. Cardiovascular Disease The relationship between obesity and cardiovascular disease risk is strong, with links to both elevated blood cholesterol and hypertension. Central obesity may raise the risk of heart attack and stroke as much as the three leading risk factors (high LDL cholesterol, hypertension, and smoking) do. In addition to body fat and its distribution, weight gain also increases the risk of cardiovascular disease.

47. 2. Diabetes Most adults with type 2 diabetes are overweight or obese. Diabetes (type 2) is three times more likely to develop in an obese person than in a nonobese person. Furthermore, the person with type 2 diabetes often has central obesity. Central-body fat cells appear to be larger and more insulin-resistant than lower-body fat cells. The association between insulin resistance and obesity is strong. Both are major risk factors for the development of type 2 diabetes. resistance.

48. Diabetes appears to be influenced by weight gains as well as by body weight. A weight gain of more than 10 pounds (4.5 kilograms) after the age of 18 doubles the risk of developing diabetes, even in women of average weight. In contrast, weight loss is effective in improving glucose tolerance and insulin.

49. 3. Cancer: The risk of some cancers increases with both body weight and weight gain, but researchers do not fully understand the relationships. One possible explanation may be that obese people have elevated levels of hormones that could influence cancer development. For example, adipose tissue is the major site of estrogen synthesis in women, obese women have elevated levels of estrogen, and estrogen has been implicated in the development of cancers of the female reproductive system—cancers that account for half of all cancers in women.

50. 4. Metabolic syndrome is a cluster of at least three of the following risk factors: • High blood pressure • High blood glucose • High blood triglycerides • Low HDL cholesterol • High waist circumference