Lysine and tryptophan in cereal-based diets for adult human subjects.

A basic diet containing rice, wheat, and corn that furnished 6.0 g of nitrogen per day was consumed by health young adults. Two levels of lysine, 900 and 1800 mg, and three of tryptophan, 260, 390, and 520 mg, were tested. Lysine exerted a significant effect (P less than 0.05) on nitrogen retention but tryptophan did not. When consumed in conjunction with at least twice the reported minimal requirements of other essential amino acids, 900 mg of lysine induced mean daily balances of 0.15 +/- 0.18, 0.19 +/- 0.14, and 0.22 +/- 0.21 g, respectively, in response to the three levels of tryptophan; and 1800 mg of lysine caused retentions of 0.75 +/- 0.14, 0.77 +/- 0.21 and 0.71 +/- 0.15 g. These findings are discussed in relation to fulfillment of protein and amino acid requirements of adult human subjects.