PHENYLALANINE AND TYROSINE KINETICS FOR DIFFERENT PATTERNS AND INDISPENSABLE AMINO-ACID INTAKES IN ADULT HUMANS

In a previous paper (Am J Clin Nutr 1993;58:670-83) we described resul ts for plasma amino acid changes, leucine kinetics, and body leucine a nd nitrogen balance in 20 young men receiving diets for 3 wk. The diet s were based on the 1985 FAO/WHO/UNU amino acid requirement pattern (m odified FAO diet; n = 7), the Massachusetts Institute of Technology (M IT) requirement pattern (MIT diet; n = 7), or the egg-protein pattern (Egg diet; n = 6). It was concluded, in comparison with the MIT and Eg g diets, that the modified FAO diet was not capable of maintaining bod y amino acid homeostasis or balance. Here we report results from trace r studies with L-[O-H-2(5)]phenylalanine and [H-2(2)]tyrosine that wer e carried out within the same experiment. The modified FAO diet failed to maintain a mean body phenylalanine balance as determined from rate s of phenylalanine hydroxylation (corrected for deuterium-isotope-kine tic effects); balance was achieved with the MIT and Egg diets. These r esults further underscore the inadequacy of the internationally propos ed amino acid requirement pattern for healthy adults. We recommend int erim use of the MIT, tentative amino acid requirement values in all co nsiderations of adult human amino acid requirements and nutrition.