ABSTRACT
The branched-chain amino acids (BCAA) - leucine, isoleucine, and valine — are required preformed in the diet by mammals. Unlike the other indispensable amino acids, lysine, threonine, and methionine, BCAA are rarely limiting in the diet, accounting for an estimated 50% of the total essential amino acid content of most foods. 1 Consequently, naturally-occurring deficiencies of BCAA are rarely encountered in our environment. Little attention was given to the BCAA during the early 1900s when most protein nutrition research was concerned with improving the nutritional quality of food proteins. Much of the nutritional research conducted on BCAA metabolism has dealt with the effects of excessive intakes of individual BCAA, particularly leucine, as the result of studies during the mid-1900s which indicated that nutritional antagonisms could be demonstrated among the three BCAA. 1–3 In the classical BCAA antagonism, addition of excessive quantities of leucine to a low protein diet causes growth and food intake depression along with marked depletion in the body pools of isoleucine and valine. Alleviation of these effects are observed after supplementation of the diet with small quantities of isoleucine and valine.
