Amino Acid Balance in the Adult: High Nitrogen — Low Tryptophan Diets

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Abstract
Studies were carried out with adult roosters and with male college students to ascertain the influence of increasing the nitrogen (N) intake of diets suboptimal with respect to an essential amino acid (tryptophan), on N utilization. In experiments with adult male chickens, N retention was either the same or greater when the total amino acid intake was doubled, whereas the level of tryptophan remained unchanged and suboptimal. In one study with human subjects, doubling the N intake, while tryptophan remained suboptimal, resulted in a significant increase in N retention, when the period during which the N intake was doubled followed a period of negative N balance. In a second experiment, the high N — low tryptophan diet was given immediately following a period of strong N retention. In this instance, subjects remained in N equilibrium; they did not retain as much N as they had done previously. In contrast with studies with growing rats and chicks, in all experiments with adult chickens or man, no impaired retention of N as a result of increasing the N intake without a concomitant increase in the limiting amino acid was observed. A tryptophan intake of 200 mg/day was found to adequately meet the requirements of the nine subjects studied in these experiments.