Nitrogen Balance of Men Fed Amino Acid Mixtures Based on Rose's Requirements, Egg White Protein, and Serum Free Amino Acid Patterns

Abstract

Six healthy men were fed formula diets containing crystalline L-amino acids. Ratios of amino acids were designed according to requirements set by W. C. Rose (R); the pattern present in egg white (E); the free amino acids found in serum of fasting men maintained with 75 g egg-white proteins in the diet (S); and an inverse ratio of the serum pattern (MS). Patterns R and E were given at a level of 250 mg tryptophan in diets providing 3.5 or 7 g total amino acid nitrogen. These patterns and S and MS were also fed as diets containing 7 g total nitrogen with one-third more essential amino acids (330 mg tryptophan). Patterns E, S and MS included the nonessential amino acids, as well as the eight essential ones, according to the 250 or 330 mg tryptophan limitation. The remainder of the amino acid nitrogen in these diets and all of the nonessential amino acid nitrogen for the R pattern diets was derived from a mixture of glycine, alanine and glutamic acid. A control diet provided 12 g of pattern E essential and nonessential amino acids (1.125 g tryptophan). Fecal nitrogen content was unaffected by variation in amount of nitrogen fed (0 to 12 g/day) or the pattern of amino acids, so absorption was complete. Nitrogen balance was negative in all subjects fed the R pattern, suggesting that one or more of the eight essential acid requirements established by Rose is more than one-third below the need of our subjects and/or that an essential is missing, probably histidine. Balance was achieved with E pattern when tryptophan was 330 mg and total nitrogen 7 g/day. Patterns S and MS gave intermediate results, confirming that serum aminograms form a less adequate basis for predicting amino acid needs than does analysis of food proteins of high quality.