The Quantitative Amino Acid Requirements of Young Women III. Tryptophan

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Abstract
The tryptophan requirement has been studied using 8 young women as subjects. On a semi-purified diet nitrogen balances were determined on daily intakes which began with 307 mg of L-tryptophan, were reduced to 82 mg and then to 63 mg, and finally raised to 157 mg. The lowest daily intake of tryptophan which maintained all of these subjects in nitrogen balance (excretion within 95 to 105% of the intake), was 157 mg. This level of tryptophan was fed to 8 additional subjects in a ration which contained minimum amounts of threonine, valine, phenylalanine, and leucine. These subjects remained in nitrogen balance. The figure of 157 mg of L-tryptophan is rounded to 160 mg and suggested as a tentative minimum daily requirement for young women similar to those studied here.