Nitrogen Balance in Experimental Human Deficiencies of Methionine and Cystine ∗

Abstract

The studies reported herewith form part of a program which was designed to throw light on the amino acid requirements of man. We have previously reported 1 2 that human subjects deficient in tryptophane or in lysine were unable to maintain their nitrogen balance, indicating that these amino acids were essential in human diets. Observations on male subjects on a diet deficient in arginine 3 indicated that, for the male at least, arginine is a dietary essential, normal spermatogenesis being maintained only when arginine was present in the diet.

The present report deals with observations on nitrogen balance in subjects deficient in one of the sulfur-containing amino acids-methionine and cystine. Three experiments were carried out on each deficiency, 2 of them on males and one on a female subject. Each subject was kept upon the deficient diet for a period of 24 days. This was preceded by a control period of 4 days on an identical diet supplemented with the missing amino acid. A similar control period of 8 days followed the deficiency period. As in our previous studies the experimental diet consisted of fats, sugar, and certain fruits and vegetables selected for their low nitrogen content. These fruits and vegetables supplied approximately 10% of the daily nitrogen requirement, the remainder being supplied by an amino acid mixture. The daily amount of this mixture was adjusted to the weight of the subject such that his total nitrogen intake was maintained at 0.1 g per kilo per day, both in the deficient and the control periods. The remaining portion of the diet, consisting of nautural foods poor in protcin was not adjusted to the weight of the subject, but for the sake of convenience in preparing the diet an identical quantity was given to each subject.