Requirements of Adult Human Subjects for Methionine and Cystine

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Abstract
Two experiments relative to utilization of methionine and cystine by adult human subjects were conducted, using a basal diet that supplied part of the amino acids as flour and the remainder in crystalline form. Total daily nitrogen intake was 6.00 g. Under these conditions, requirements of young men varied from 700 mg methionine plus 100 mg cystine to 260 mg methionine plus 280 mg cystine. The quantities of sulfur-containing amino acid present in 142 g white wheat flour were adequate for five of six men. Nitrogen balances did not differ significantly when methionine was increased from 310 to 910 mg in the presence of 340 mg cystine, but differences between subjects were significant (P < 0.05). Several subjects retained more nitrogen at the highest than the lowest methionine level, but others did not. Urinary sulfate was dependent on dietary methionine and cystine.