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Journal of Nutrition Vol. 101 No. 1 January 1971, pp. 45-59
Copyright © 1971 by American Society for Nutrition
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Plasma Tryptophan Response Curve and Its Relation to Tryptophan Requirements in Young Adult Men1,2,

Vernon R. Young, Mohammed A. Hussein3, Edwina Murray and Nevin S. Scrimshaw

Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

A total of 17 adult human subjects was studied to determine the relationships between the concentration of free tryptophan in fasting and postprandial blood plasma, dietary tryptophan intake, and the daily requirement for this amino acid. The diet, containing an L-amino acid mixture, which was patterned as in egg protein, furnished nitrogen equivalent to 0.5 g egg protein per kilogram body weight/day. In two separate experiments dietary tryptophan intake was varied over a range of 1.0 to 8.7 mg/kilogram body weight. Plasma tryptophan concentration was constant above and below tryptophan intakes of 5 and 3 mg/kilogram body weight, respectively, and changed linearly with altered tryptophan intake within this range. The level of dietary tryptophan above which a linear increase in plasma tryptophan occurred was taken to be the requirement level. Nitrogen balance measurements indicated a tryptophan requirement of 2 to 2.6 mg/kilogram body weight whereas the plasma tryptophan data suggested a requirement of about 3 mg/kilogram body weight. The present nitrogen balance data, which did not include integumental and sweat nitrogen losses, probably underestimated tryptophan needs.

1 Contribution No. 1620 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology.

2 Supported by grant no. 12-14-100-9209 (61) from the U. S. Department of Agriculture. These studies made use of the facilities of the M.I.T. Clinical Research Center, supported by U. S. Public Health Service Grant no. FR88.

3 Present address: Nutrition Institute, Kasr, El-Aini Street, Kasr El-Aini Post Office, Cairo, U.A.R.

Manuscript received 3 June 1970.




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