Plasma amino acids and nitrogen retention of human subjects who consumed isonitrogenous diets containing rice and wheat or their constituent amino acids with and without additional lysine.

Six diets furnished 6.0 g of nitrogen to adult human subjects as follows: a combination of rice and wheat; mixtures in which either 100 or 50% of the amino acids in rice and wheat were replaced by their constituent amino acids; and similar diets in which lysine was increased from 1.2 to 1.8 g. Nitrogen retention was greater (P less than 0.01) and concentrations of several amino acids in plasma were lower when the cereals were supplemented with lysine than when all other diets were fed. Data obtained with mixtures of amino acids apparently cannot always be used interchangeably with that from cereal-based diets, even when amino acid content is the same. Changes in plasma amino acids are a useful indicator of utilization of dietary amono acids when nitrogen balance also is determined.