Dietary protein provides essential amino acids necessary for the growth and maintenance of your tissues. Not getting enough protein, while uncommon, can occur in the setting of inadequate dietary protein or lack of an essential amino acid. It can also be due to physiologic stresses such as trauma, burns, illness or surgery. In some parts of the world, protein-calorie malnutrition can lead to conditions known as kwashiorkor and marasmus, which are uncommon in the United States.
Protein Quality
The amount of protein you require depends on what is known as the biologic value of protein, or protein quality. This is a measure of a protein's ability to provide the 8 essential amino acids required for life. Proteins from animal sources have a high quality because they contain all essential amino acids in proportions similar to those in your own body. Plant proteins, which include wheat, corn, rice and beans, have a lower quality and can be deficient in one or more essential amino acids, most notably methionine and lysine.
Protein Intake
The recommended dietary allowance, or RDA, of protein is computed for proteins of mixed biologic value at about 0.36 g per lb. of body weight for adults, or roughly 56 g of protein for a 155-lb. person. However, your requirements vary based on whether your diet is centered around animal or vegetable sources, with meat eaters requiring less than vegetarians.
Protein Deficiency
In the U.S., not eating enough protein is rare. Protein-calorie malnutrition, as this is called, is seen most frequently in hospital patients with chronic illness, or if you suffer major trauma, severe infection or undergo surgery. In these cases, protein requirements markedly increase, and sometimes dietary intake can fail to keep up with your body's demand. In these cases, intravenous administration of protein is often required. In underdeveloped countries, however, the two extreme forms of protein malnutrition can occur.
Kwashiorkor
Kwashiorkor occurs when your protein needs are not met despite adequate caloric intake. This is frequently seen in children after weaning at about one year of age, when their diet consists mainly of carbohydrates, such as grains. Symptoms include stunted growth, swelling of the abdomen, loss of hair color and an enlarged, fatty liver. As a result, such a child frequently shows a plump belly as a result of fluid buildup.
Marasmus
Marasmus occurs when calories are scarce. This is more common in children younger than one year of age when the mother's breast milk is supplemented with thin, watery gruels of native cereals, which can be deficient in protein. Symptoms include muscle wasting, weakness and anemia.
Vegetarians
The protein requirements of vegetarians are higher than for meat eaters, as plant-based sources of protein can lack essential amino acids. However, if you consume adequate calories you are at no risk of protein deficiency. By choosing a varied diet that includes several servings of vegetables as well as legumes such as beans and lentils, it is easy to fulfill your body's protein needs, and combining foods at each meal in order to obtain all essential amino acids is not necessary.
References
- "Biochemistry"; Pamela C. Champe, Ph.D.; 2005
- "Eat to Live"; Joel Fuhrman, M.D.; 2005
- Institutes of Medicine: Dietary Reference Intakes: Macronutrients
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