Dieting

A diet is the daily allowance of food and drink. In order to grow and function properly, the body needs certain essential nutrients. These nutrients are supplied through the diet, and a nutritionally adequate diet is one that provides these nutrients in the specific amounts required by the individual. An adequate diet is one that is made up of a variety of foods, for there is no single food, nor even any combination of a few foods, that supplies adequate amounts of all the essential nutrients.

Five basic types of nutrients are essential, either for themselves or for materials supplied through their metabolism. These five nutrients are protein, fat, carbohydrate, vitamins, and certain minerals. Water, although not considered a nutrient, is also essential for life because it is necessary for all the biochemical activities that occur in the body. In addition to requiring each of the essential nutrients, the body needs sufficient amounts of nutrients to supply it with enough energy to carry on all of the vital life processes. Food energy, which is measured in units called calories, is supplied mainly by fat and carbohydrate, but may also be supplied by protein. (In this article the term "calorie" refers to the larger, or kilogram, calorie, which equals 1,000 small, or gram, calories.)

Specific amounts of essential nutrients recommended for healthy individuals in the United States have been established by the Food and Nutrition Board of the National Research Council. To meet these recommendations, a person must eat several basic types of foods each day. According to the U.S. Department of Agriculture's plan entitled A Daily Food Guide, there are four main food groups that should be represented in the daily diet. These groups are known as the milk group, the meat group, the vegetable and fruit group, and the bread and cereal group. In addition, sufficient calories to meet the needs of the individual must be furnished, either from the foods in these groups or from foods not included in the groups. For adults, the food guide recommends a daily intake of at least two glasses of milk (or its equivalent), two servings from the meat group, four servings from the vegetable and fruit group (including one dark green or yellow vegetable and a citrus fruit or tomatoes), and four servings from the bread and cereal group. For children under 9 years of age, the guide recommends a daily intake of 2 to 3 cups of milk; for those 9 to 12 years old, 3 or more cups; and for teen-agers, at least 4 cups. The rest of the food group recommendations for children and teen-agers are the same as for adults, with modifications in amounts made to meet individual caloric and nutrient needs. See also nutrition of man.

Modified Diets. Certain diseases may cause an individual's requirements for essential nutrients to be considerably higher than those of healthy individuals. Diets designed for treating diseases, therefore, are planned as modifications of the normal diet. The basic premise of such diets is that normal allowances be met whenever possible and if the diet modification is such that these allowances cannot be met by foods alone, other measures must be taken.

The treatment of disease through diet is referred to as diet therapy, or therapeutic nutrition. Diet therapy has always been a part of medicine; one of the earliest mentions of diet therapy is found in the writings of the ancient Greek physician Hippocrates. Over the years, diet therapy has undergone many changes, and today it is an integral part of the treatment of a great variety of diseases.

One of the basic principles of diet therapy is that any modification of the normal diet should relate to a specific physiological condition. Accordingly, a single diet may then be used to treat any disease in which the same physiological condition exists. A diet restricted in sodium, for example, may be prescribed for a person with any disease in which there is an abnormal retention of fluid in the body, since sodium normally aids in the retention of fluid in the body tissues.

Therapeutic diets may be classified into two broad groups: those in which the modifications are qualitative and those in which they are quantitative. Qualitative modifications are used in treating disorders that are not as yet directly related to food metabolism. Most of the gastrointestinal diseases, such as ulcers, fall into this category. Quantitative modifications are used for treating disorders that are directly related to food metabolism. These disorders include obesity, underweight, diabetes, and the many diseases involving inborn errors of metabolism, such as phenylketonuria (PKU) and galactosemia. In many of these disorders, the deficiency or complete absence of a particular hormone or metabolic enzyme has been found to be the causative factor.

Whenever the normal diet is modified quantitatively, a specific level of nutrient or calorie intake should always be indicated. Thus, the phrase "low calorie diet" should never be used. Instead, the specific level of calories should be indicated, as in a "1,200 calorie diet."

Therapeutic diets should never be undertaken except when prescribed and supervised by a physician. Once a therapeutic diet is prescribed, qualified dietitians and nutritionists can help the individual in interpreting the prescribed diet to meet his particular needs. A well-planned therapeutic diet is one that adjusts to the individual's religious, ethnic, social, and economic background as well as to his personal preferences.

One of the first diseases to be treated through diet was diabetes. The need to control the patient's intake of carbohydrate was recognized for many years, and until the discovery and general availability of insulin, the restriction of carbohydrate was extremely strict. Today, however, a more liberal diet is possible for diabetics, and they are able to consume a nutritionally adequate diet made up of a wide variety of foods.

When doctors and dietitians were developing special diets for diabetics, a committee representing the American Dietetic Association, the American Diabetes Association, and the U.S. Public Health Service devised special lists, called exchange lists, to aid in meal planning. There are six different exchange lists, each one corresponding to a basic food group—milk, vegetables, fruits, breads, meat, and fats. The foods in each group are roughly equivalent in composition and caloric value. The use of these lists allows an individual to plan a varied and interesting diet that assures adequate nutrition.

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