Nutritional Disorders

Diet-related problems may originate from an excess or shortage of necessary nutrients. Another issue in the news today is weight control. Food allergies may also affect some people.

Food Allergies

Some people develop clear allergic (hypersensitive) symptoms if they eat certain foods. Common food allergens are wheat, nuts, milk, shellfish, and eggs, but almost any food might cause an allergic reaction in a given individual. People may also have allergic reactions to food additives, such as flavorings, colorings, or preservatives. Signs of allergic reactions usually involve the skin, respiratory tract, or gastrointestinal tract. Food allergies may provoke potentially fatal anaphylactic shock in extremely sensitive individuals.


If any vital nutrient is missing from the diet, the body will suffer from malnutrition. One commonly thinks of a malnourished person as someone who does not have enough to eat, but malnutrition can also occur from eating too much of the wrong foods.
Factors that contribute to malnutrition are poverty, old age, chronic illness, anorexia, poor dental health, and drug or alcohol addiction. In poor and underdeveloped countries, many children suffer from protein and energy malnutrition (PEM). Marasmus is a term used for severe malnutrition in infancy (from Greek meaning “dying away”). Kwashiorkor typically affects older children when they are weaned because another child is born (and the name means just that). A low protein level in the blood plasma interferes with fluid return to the capillaries, resulting in edema. Often excess fluid accumulates in the abdomen as ascites fluid, causing the stomach to bulge.

Overweight and Obesity

The causes of obesity are complex, involving social, economic, genetic, psychological and metabolic factors. It is common knowledge that overweight and obesity have increased in the past several decades in many countries. In the U.S., 35% of adults are overweight and an additional 30% are obese. Obesity shortens the life span and is associated with cardiovascular disease, diabetes, some cancers, and other diseases. The incidence of type II diabetes, once considered to have an adult onset, has increased greatly among children. Some researchers hold that obesity has a closer correlation to chronic disease than poverty, smoking, or drinking alcohol. Scientists are studying the nervous and hormonal controls over weight, but so far they have not found any effective and safe drugs for weight control. For most people, a varied diet eaten in moderation and regular exercise are the surest ways to avoid obesity. One-half hour of vigorous exercise at least four times a week is recommended for health and weight control.
Calculation of body mass index (BMI)
Figure 16-4 Calculation of body mass index (BMI).

Body Mass Index

Body mass index (BMI) is a measurement used to evaluate body size. It is based on the ratio of weight to height (Fig. 16-4). BMI is calculated by dividing weight in kilograms by height in meters squared. (For those not accustomed to using the metric system, an alternate method is to divide weight in pounds by the square of height in inches and multiply by 703.) A healthy range for this measurement is 19-24. Overweight is defined as a BMI of 25-30, and obesity as a BMI greater than 30. However, BMI does not take into account the relative amount of muscle and fat in the body. For example, a bodybuilder might be healthy with a higher than typical BMI because muscle has a higher density than fat.


People who are underweight have as much difficulty gaining weight as others have losing it. The problem of underweight may result from rapid growth, eating disorders, allergies, illness, or psychological factors. It is associated with low reserves of energy, reproductive disturbances, and nutritional deficiencies. A BMI of less than 18.5 is defined as underweight. To gain weight, people have to increase their intake of calories, but they should also exercise to add muscle tissue and not just fat.
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