Protein Health Article

Protein Requirement and Nutrition

The recommended protein intake for an average adult is generally based on body size: 0.8 grams per kilogram of body weight is the generally recommended daily intake. The recommended daily allowances of protein do not vary in times of strenuous activities or exercise, or with progressing age. However, there is a wide range of protein intake which people can consume according to their period of development. For example, the recommended allowance for an infant up to six months of age, who is undergoing a period of rapid tissue growth, is 2.2 grams per kilogram. For children ages seven through ten, the recommended daily allowance is around 36 total grams, depending on body weight. Pregnant women need to consume an additional 30 grams of protein above the average adult intake for the nourishment of the developing fetus.

Sources of protein.

Good sources of protein include high-quality protein foods, such as meat, poultry, fish, milk, egg, and cheese, as well as prevalent low-quality protein foods, such as legumes (e.g., navy beans, pinto beans, chick peas, soybeans, split peas), which are high in protein.

Protein–Calorie Malnutrition

The nitrogen balance index (NBI) is used to evaluate the amount of protein used by the body in comparison with the amount of protein supplied from daily food intake. The body is in the state of nitrogen (or protein) equilibrium when the intake and usage of protein is equal. The body has a positive nitrogen balance when the intake of protein is greater than that expended by the body. In this case, the body can build and develop new tissue. Since the body does not store protein, the overconsumption of protein can result in the excess amount to be converted into fat and stored as adipose tissue. The body has a negative nitrogen balance when the intake of protein is less than that expended by the body. In this case, protein intake is less than required, and the body cannot maintain or build new tissues.

A negative nitrogen balance represents a state of protein deficiency, in which the body is breaking down tissues faster than they are being replaced. The ingestion of insufficient amounts of protein, or food with poor protein quality, can result in serious medical conditions in which an individual's overall health is compromised. The immune system is severely affected; the amount of blood plasma decreases, leading to medical conditions such as anemia or edema; and the body becomes vulnerable to infectious diseases and other serious conditions. Protein malnutrition in infants is called kwashiorkor, and it poses a major health problem in developing countries, such as Africa, Central and South America, and certain parts of Asia. An infant with kwashiorkor suffers from poor muscle and tissue development, loss of appetite, mottled skin, patchy hair, diarrhea, edema, and, eventually, death (similar symptoms are present in adults with protein deficiency). Treatment or prevention of this condition lies in adequate consumption of protein-rich foods.

SEE ALSO AMINO ACIDS.

Jeffrey Radecki
Susan Kim

Bibliography

Berdanier, Carolyn D. (1998). CRC Desk Reference for Nutrition. Boca Raton, FL: CRC Press.

Briggs, George M., and Calloway, Doris Howes (1979). Bogert's Nutrition and Physical Fitness, 10th edition. Philadelphia, PA: W. B. Saunders.

Johnston, T. K. (1999). "Nutritional Implications of Vegetarian Diets." In Modern Nutrition in Health and Disease, 9th edition. M. E. Shills, et al, eds. Baltimore, MD: Williams & Wilkins.

Robinson, Corrinne H. (1975). Basic Nutrition and Diet Therapy. New York: Macmillan.

U.S. Department of Agriculture (1986). Composition of Foods. (USDA Handbooks 8–15.) Washington, DC: U.S. Government Printing Office.

Wardlaw, Gordon M., and Kesse, Margaret (2002). Perspectives in Nutrition, 5th edition. Boston: McGraw-Hill.

Internet Resources

Institute for Chemistry. "Amino Acids." Available from <http://www.chemie.fuberlin.de>