Amino Acid Balance and Imbalance

Abstract

Amino acid imbalances have been induced in diets containing low levels of fibrin by the addition of (1) relatively small amounts of methionine and phenylalanine and (2) amino acid mixtures lacking in a single amino acid. The imbalance induced by the former method can be observed when as little as 0.25 to 0.5% of a mixture of methionine and phenylalanine is added to a diet containing 6% of fibrin. The growth depression can be corrected by supplementing this diet with relatively small amounts of the limiting amino acids, leucine, isoleucine, valine and histidine. The effect of an imbalance in increasing the need for the limiting amino acid has been examined by using amino acid mixtures lacking in leucine, isoleucine, valine or histidine and measuring the growth responses to graded levels of each of these in turn. Measurements of food intake in these experiments indicated that an imbalance reduces the efficiency of utilization of the limiting amino acid. The depression in growth caused by the addition of methionine and phenylalanine occurs only when the diet contains 6% of fibrin and involves a delicate balance with the next limiting amino acids leucine, isoleucine, valine and histidine. In contrast, the growth depression caused by an amino acid mixture lacking histidine can be demonstrated over a range of fibrin levels.