American Journal of Clinical Nutrition, Vol 17, 360-366, Copyright © 1965 by The American Society for Clinical Nutrition, Inc.

Evaluation of Nitrogen Balance of Young Women Fed Amino Acids Proportioned as in the FAO Provisional Pattern and as in Egg, Oats, Milk and Peanuts

¹ From the Human Nutrition Research Division and Biometrical Services, Agricultural Research Service, U. S. Department of Agriculture, Beltsville, Maryland

Data on nitrogen balances of twenty-four young women, at three locations, fed purified amino acids proportioned as in the FAO pattern were combined and analyzed. The analysis showed (1) significant differences among balances within locations but none between locations and (2) a significant regression of nitrogen balance on essential amino acid nitrogen intake. Mean balances on intakes of 0.20 gm. tryptophan and less, with other amino acids as required to maintain the pattern, were negative and not significantly different but differed significantly from mean balances on intakes of 0.22 gm or more. This is interpreted as indicating that these young women, when fed amino acids proportioned as in the FAO pattern, required a minimum of 0.22 gm. tryptophan and other essential amino acids as in this pattern in order to maintain nitrogen balance.

Also analyzed were nitrogen balance data for subjects at each location fed purified amino acids and/or a food to provide the FAO pattern and the food pattern. Mean balances were significantly higher for two of the food patterns studied (oat and milk) than for comparable levels of the FAO pattern regardless of whether amino acids were furnished in a purified form or by the food; the same was true for the egg and peanut patterns when furnished as purified amino acids.

Balances tended to be higher when the same amounts and proportions of amino acids were provided as food than as purified amino acids, but differences were significant in only three of the eight comparisons.

The results of these studies suggest that the nutritional value of a protein depends in part on factors other than the amount of its limiting amino acid as determined by comparison with the FAO provisional pattern.