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Nutrition facts.

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Nutrition facts.

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A key to healthy eating is to become familiar with the "Nutrition Facts" panel on food packages. Look for products with fewer than 30% of calories from fat.

are listed in descending order by weight. Figure 18.19 shows where nutritional information can be found on a food label. Clinical Application 18.4 discusses some ways that understanding nutrition can help athletic performance.

Malnutrition

Malnutrition (mal"nu-trish'un) is poor nutrition that results from a lack of essential nutrients or a failure to utilize them. It may result from undernutrition and produce the symptoms of deficiency diseases, or it may be due to overnutrition arising from excess nutrient intake.

The factors leading to malnutrition vary. For example, a deficiency condition may stem from lack of availability or poor quality of food. On the other hand, malnutrition may result from overeating or taking too many vitamin supplements. Malnutrition from diet alone is called primary malnutrition.

The Food and Drug Administration allows the following specific food and health claims:

Dietary calcium decreases risk of osteoporosis (a bone-thinning condition).

• A low-fat diet lowers risk of some cancers.

• A diet low in saturated fat and cholesterol lowers risk of coronary heart disease.

• Fiber, fruits and vegetables, and whole grains reduce the risk of some cancers and coronary heart disease.

• Lowering sodium intake lowers blood pressure.

• Folic acid lowers the risk of neural tube defects.

Take any other health claims with a grain of salt!

Nutrition and the Athlete

Can a marathoner, cross-country skier, weight lifter, or competitive swimmer eat to win? A diet of 60% or more carbohydrate, 18% protein, and 22% fat should be adequate to support frequent, strenuous activity.

Macronutrients

As the source of immediate energy, carbohydrates are the athlete's best friend. Athletes should get the bulk of their carbohydrates from vegetables and grains in frequent meals, because the muscles can store only 1,800 calories worth of glycogen.

Many people erroneously believe that an athlete needs protein or amino acid supplements. Excess dietary protein, however, can strain the kidneys in ridding the body of the excess nitrogen, dehydrating the athlete as more water is used in urine. The only evidence that clearly supports a benefit is that consuming amino acids soon after exercise stimulates muscle cells to take up amino acids, thereby perhaps accelerating manufacture of muscle proteins.

The American Dietetic Association suggests that athletes eat 1 gram of protein per kilogram of weight per day, compared to 0.8 grams for nonathletes. Athletes should not rely solely on meat for protein, because these foods can be high in fat. Supplements are necessary for only young athletes at the start of training, under a doctor's supervision. Too little protein in an athlete is linked to "sports anemia," in which hemoglobin levels decline and blood may appear in the urine.

The body stores 140,000 calories of fat, so it is clear why no one needs to replenish that constantly with fatty foods. Athletes should consume low-fat milk and meats.

water

A sedentary person loses a quart of water a day as sweat; an athlete may lose 2 to 4 quarts of water an hour! To stay hydrated, athletes should drink 3 cups of cold water two hours before an event, then 2 more cups fifteen minutes before the event, and small amounts every fifteen minutes during the event. They should drink afterward too. Another way to determine water needs is to weigh in before and after training. For each pound lost, athletes should drink a pint of water. They should also avoid sugary fluids, which slow water's trip through the digestive system, and alcohol, which increases fluid loss.

Vitamins and minerals

If an athlete eats an adequate, balanced diet, vitamin supplements are not needed. Supplements of sodium and potassium are usually not needed either, because the active body naturally conserves these nutrients. To be certain of enough sodium, athletes may want to salt their food; to get enough potassium, they can eat bananas, dates, apricots, oranges, or raisins.

A healthy pregame meal should be eaten two to five hours before the game, provide 500 to 1,500 calories, include 4 or 5 cups of fluid. The pregame meal should also be high in carbohydrates, which taste good, provide energy, and are easy to digest. ■

Secondary malnutrition occurs when an individual's characteristics make a normally adequate diet insufficient. For example, a person who secretes very little bile salts may develop a deficiency of fat-soluble vitamins because bile salts promote absorption of fats. Likewise, severe and prolonged emotional stress may lead to secondary malnutrition, because stress can change hormonal concentrations, and such changes may result in amino acid breakdown or excretion of nutrients.

Starvation

A healthy human can stay alive for fifty to seventy days without food. In prehistoric times, this margin allowed survival during seasonal famines. In some areas of

Africa today, famine is not a seasonal event but a constant condition, and millions of people have starved to death. Starvation is also seen in hunger strikers, in prisoners of concentration camps, and in sufferers of psychological eating disorders such as anorexia nervosa and bulimia.

Whatever the cause, the starving human body begins to digest itself. After only one day without eating, the body's reserves of sugar and starch are gone. Next, the body extracts energy from fat and then from muscle protein. By the third day, hunger ceases as the body uses energy from fat reserves. Gradually, metabolism slows to conserve energy, blood pressure drops, the pulse slows, and chills set in. Skin becomes dry and

Two types of starvation in the young. (a) This child, suffering from marasmus, did not have adequate nutrition as an infant. (b) These children suffer from kwashiorkor. Although they may have received adequate nourishment from breast milk early in life, they became malnourished when their diet switched to a watery, white extract from cassava that looks like milk but has very little protein. The lack of protein in the diet causes edema and the ascites that swells their bellies.

Figure

Two types of starvation in the young. (a) This child, suffering from marasmus, did not have adequate nutrition as an infant. (b) These children suffer from kwashiorkor. Although they may have received adequate nourishment from breast milk early in life, they became malnourished when their diet switched to a watery, white extract from cassava that looks like milk but has very little protein. The lack of protein in the diet causes edema and the ascites that swells their bellies.

hair falls out as the proteins in these structures are broken down to release amino acids that are used for the more vital functioning of the brain, heart, and lungs. When the immune system's antibody proteins are dismantled for their amino acids, protection against infection declines. Mouth sores and anemia develop, the heart beats irregularly, and bone begins to degenerate. After several weeks without food, coordination is gradually lost. Near the end, the starving human is blind, deaf, and emaciated.

Marasmus and Kwashiorkor

Lack of nutrients is called marasmus, and it causes people to resemble living skeletons (fig. 18.20). Children under the age of two with marasmus often die of measles or other infections, their immune systems too weakened to fight off normally mild viral illnesses.

Some starving children do not look skeletal but have protruding bellies. These youngsters suffer from a form of protein starvation called kwashiorkor, which in the language of Ghana means "the evil spirit which infects the first child when the second child is born." Kwashiorkor typically appears in a child who has recently been weaned from the breast, usually because of the birth of a sibling. The switch from protein-rich breast milk to the protein-poor gruel that is the staple of many developing nations is the source of this protein deficiency. The children's bellies swell with fluid, which is filtered from capillaries in greater than normal quantities due to a lack of plasma proteins. This condition is called ascites. Their skin may develop lesions. Infections over whelm the body as the immune system becomes depleted of its protective antibodies.

Anorexia Nervosa

Anorexia nervosa is self-imposed starvation. The condition is reported to affect 1 out of 250 adolescents, and 95% of them are female, although the true number among males is not known and may be higher than has been thought. The sufferer, typically a well-behaved adolescent girl from an affluent family, perceives herself to be overweight and eats barely enough to survive. She is terrified of gaining weight and usually loses 25% of her original body weight. In addition to eating only small amounts of low-calorie foods, she further loses weight by vomiting, by taking laxatives and diuretics, or by exercising intensely. Her eating behavior is often ritualized. She may meticulously arrange her meager meal on her plate or consume only a few foods. She develops low blood pressure, a slowed or irregular heartbeat, constipation, and constant chilliness. She stops menstruating as her body fat level plunges. Like any starving person, the hair becomes brittle and the skin dries out. She may develop soft, pale, fine body hair called lanugo, normally seen only on a developing fetus, to conserve body heat.

When the person with anorexia reaches an obviously emaciated state, her parents usually have her hospitalized, where she is fed intravenously so that she does not starve to death or die suddenly of heart failure due to a mineral imbalance. She also receives psychotherapy and nutritional counseling. Despite these efforts, 15% to 21% of people with anorexia die.

Anorexia nervosa has no known physical cause. One hypothesis is that the person is rebelling against approaching womanhood. Indeed, her body is astonishingly childlike, and she has often ceased to menstruate. She typically has low self-esteem and believes that others, particularly her parents, are controlling her life. Her weight is something that she can control. Anorexia can be a one-time, short-term experience or a lifelong obsession.

Bulimia

A person suffering from bulimia is often of normal weight. She eats whatever she wants, often in huge amounts, but she then rids her body of the thousands of extra calories by vomiting, taking laxatives, or exercising frantically. For an estimated one in five college students, the majority of them female, "bingeing and purging" appears to be a way of coping with stress.

Sometimes a bulimic's dentist is the first to spot her problem by observing teeth decayed from frequent vomiting. The backs of her hands may bear telltale scratches from efforts to induce vomiting. Her throat is raw and her esophageal lining ulcerated from the stomach acid forced forward by vomiting. The binge and purge cycle is very hard to break, even with psychotherapy and nutritional counseling.

A person with bulimia tends to eat soft foods that can be consumed in large amounts quickly with minimal chewing. Reveals one athletic young woman, "For me a binge consists of a pound of cottage cheese, a head of lettuce, a steak, a loaf of Italian bread, a 10-ounce serving of broccoli, spinach or a head of cabbage, a cake, an 18-ounce pie, with a quart or half gallon of ice cream. When my disease is at its worst, I eat raw oatmeal with butter, laden with mounds of sugar, or a loaf of white bread with butter and syrup poured over it." She follows her "typical" 20,000-calorie binge with hours of bicycle riding, running, and swimming.

Life-span Changes

Dietary requirements remain generally the same throughout life, but the ability to acquire those nutrients may change drastically. Changing nutrition with age often reflects effects of medical conditions and social and economic circumstances. Medications can dampen appetite directly through side effects such as nausea or altered taste perception or alter a person's mood in a way that prevents eating. Poverty may take a greater nutritional toll on older people who either cannot get out to obtain food or who give whatever is available to younger people.

Medical conditions that affect the ability to obtain adequate nutrition include depression, tooth decay and periodontal disease, diabetes mellitus, lactose intolerance, and alcoholism. These conditions may lead to deficiencies that are not immediately obvious. Vitamin A deficiency, for example, may take months or years to become noticeable because the liver stores this fat-soluble vitamin. Calcium depletion may not produce symptoms, even as the mineral is taken from bones. The earliest symptom of malnutrition, fatigue, may easily be attributed to other conditions or ignored.

The basal metabolic rate (BMR) changes with age. It rises from birth to about age five and then declines until adolescence, when it peaks again. During adulthood, the BMR drops in parallel to decreasing activity levels and shrinking muscle mass. In women, it may spike during pregnancy and breastfeeding, when caloric requirements likewise increase. Table 18.10 shows changes in the BMR for adults who are healthy and engage in regular, light exercise.

For all ages, weight gain occurs when energy in exceeds energy out, and weight loss happens when energy out exceeds energy in. Age fifty seems to be a key point in energy balance. For most people, energy balance is positive, and weight is maintained before this age, but afterwards, weight may creep up. However, being aware of a decrease in activity, and curbing food consumption accordingly, enables many people over the age of fifty to maintain their weight.

|| What is an adequate diet?

B What factors influence individual needs for nutrients?

B How can the food pyramid plan help consumers make wise food choices?

B What is primary malnutrition? Secondary malnutrition?

B What happens to the body during starvation?

B How do marasmus and kwashiorkor differ?

U How do anorexia nervosa and bulimia differ?

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