Effect on nitrogen retention by adults of different proportions of indispensable amino acids in isonitrogenous...

Nitrogen retention of adults who consumed diets in which cereals furnished 6.0 g N and 0.9 g of lysine was improved by increasing lysine to 1.8 g without altering other amino acids. In a second experiment, 70% of the 6.0 g of dietary N was supplied by rice + wheat and 30% by mixtures of amino acids so designed that the total intakes of amino acids were equivalent to those in diets containing 6.0 g N from whole egg (E), egg + potato (EP), rice + wheat (RW), rice + soy (RS), wheat + milk (WM) or corn + beans (CB). Mean N balances of young men in descending order were, g/day: E 0.69 +/- 0.23, RS 0.44 +/- 0.15, EP 0.43 +/- 0.09, WM 0.24 +/- 0.16, CB 0.16 +/- 0.13 and RW -0.02 +/- 0.10. In the same order, these diet provided, g/day: lysine 2.6, 1.9, 2.3, 1.6, 1.4 and 1.0; S-acids 2.2, 1.7, 1.6, 2.2, 1.9 and 2.3; and tryptophan 0.7, 0.4, 0.6, 0.5, 0.3 and 0.4. N balances resulting from diets E, RS and EP did not differ significantly from each other but E was superior to CB and RW (P less than 0.01). Relative amounts and propertions of the essential amino acids could be varied without altering nitrogen retention until at least one amino acid became limiting. Several patterns of indispensable amino acids therefore may be equally effective in meeting needs of adults, but both amounts and relative proportions should be considered.