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Nitrogen Retention in Men Fed Varying Levels of Amino Acids from Soy Protein with or without Added L-Methionine¹

Department of Nutritional Sciences, University of California, Berkeley, California 94720

A metabolic study was undertaken to determine methionine requirements of six young men fed soy protein isolate (SB) for 9-day periods. Formula diets contained 9 g of nitrogen from intact proteins with glycine and alanine added. Nitrogen derived from intact protein was, g per day: reference eggwhite (EW), 3.0, 4.5, and 6.0; and SB, 3.0, 4.5, 6.0, and 7.5. SB diets were fed with and without addition of L-methionine to raise the total amount of sulfur amino acids (SAA) to 900 mg. Mean nitrogen balance was positive with diets containing at least 4.5 g EW, 6.0 g SB, and 4.5 g SB with methionine added. Individual requirements for SAA were: for one man, between 320 and 480 mg; for three, between 480 and 640 mg; for one man, between 640 and 800 mg; and for the sixth man, between 640 and 900 mg. Thus 900 mg, stipulated by the 1973 FAO/WHO Committee as being necessary for the 70 kg reference man, was sufficient for all participants. Nitrogen balance was equally improved by increasing the SB nitrogen level by 1.5 g or adding methionine at each level of SB fed.

KEY WORDS: • L-methionine requirements • soy protein • amino acid supplementation • nitrogen balance

¹ Supported by USPHS Grants AM 10202 and 5A02AH00095 and by a gift from Procter and Gamble. Submitted in partial fulfillment for the degree of Doctor of Philosophy in Nutrition, University of California, Berkeley. Presented in part at the 58th Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, N.J. (1974) Federation Proc. 33, 712 (Abstr.).

Manuscript received 8 August 1975.