Effects of Excess Leucine on Growth and Food Selection

Abstract

When 5% leucine was added to a 9% casein diet supplemented with methionine, growth and food intake of rats were depressed. Although isoleucine and valine were found to largely overcome this growth depression the initial reduction in weight and complete restoration to the control rate of growth resulted only after additional supplementation with tryptophan, phenylalanine and threonine. When rats were given a choice between diets containing 5% leucine and a protein-free diet, they invariably chose the protein-free diet. About half of the rats chose the protein-free diet even when the high leucine diet was “corrected” by supplementation with isoleucine, valine, tryptophan, phenylalanine, and threonine. Supplementation of the high leucine diet with a complete amino acid mixture devoid of leucine increased selection of the high leucine diet. Thus, it appears that rats will avoid almost all diets containing 5% leucine, even if the alternate is a much inferior, protein-free diet.