The effect of amino acid imbalance on nitrogen retention (biological value) in rats

1. Three series of nitrogen balance experiments were performed with growing rats to test the effect of amino acid imbalance on protein utilization. In Expt 1 egg protein was fed as a basal diet and supplemented with one amino acid at a time in the amounts originally found in egg protein. In Expt 2 the procedure was repeated with a barley diet, and in Expt 3 egg and potato proteins were fed together in various combinations. 2. Doubling the single amino acids, especially arginine, in an egg-protein diet reduced biological value (BV) markedly. Also the branched-chain and the basic amino acids reduced BV significantly. In the barley-based diets negative effects were also observed when the concentration of the single amino acid was doubled. However, it was assumed that the observed deleterious effects of amino acid excess were partly due to an exaggerated lysine deficiency in the barley protein when non-limiting amino acid excess were added. 3. The results with various combinations of egg and potato proteins showed that as potato protein was increased true protein digestibility decreased linearly, whereas BV decreased curvilinearly. Maximum protein utilization was obtained with egg protein alone.