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Nitrogen Requirement of Normal Men on a Diet of Protein Hydrolysate Enriched with the Limiting Essential Amino Acids¹

Seven Figures

The Hektoen Institute for Medical Research of the Cook County Hospital and the Department of Physiology, University of Illinois College of Medicine, Chicago

Nitrogen balance experiments were performed in 7 normal male human subjects to determine the nitrogen requirements for equilibrium when the only significant source of nitrogen was a lyophilized modified casein hydrolysate⁸ given orally. Then in the same subjects the nitrogen requirement for equilibrium was determined for the same hydrolysate fortified with DL-tryptophan, L-phenylalanine, and DL-methionine in quantities that made the quantitative pattern of essential amino acids in the supplemented product equivalent to that found by Rose in his estimation of the minimum requirements of the individual amino acids in human subjects.

The corrected mean nitrogen requirement for equilibrium with the unsupplemented hydrolysate was 52.2 mg per kilogram per day, with a standard deviation of 3.5 mg. For the supplemented product the mean nitrogen requirement for equilibrium was 38.5 mg per kilogram per day, with a standard deviation of 2.1 mg, a reduction of 26%. This reduction was found to be statistically significant.

Nitrogen equilibrium was reached with the unsupplemented product when L-tryptophan and methionine were present in the diet in quantities of the order of the minimum amounts found to be required by Rose. Therefore, these amino acids were the limiting factors determining the amount of nitrogen in the product required for equilibrium. On the other hand, nitrogen equilibrium was reached with the supplemented products when all the essential amino acids were still present in twice as great a quantity as Rose had found necessary to meet the minimum requirements. Therefore the limiting factor in the supplemented product appeared to be the total quantity of nitrogen present. This conclusion was corroborated in a short experiment in which the addition of 15 gm of glycine changed from negative to positive the balance produced by a diet of 30 mg per kilogram per day of the supplemented product.

⁸ See footnote 3, page 124.

Manuscript received 2 December 1950.

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