Nutritive value of N-acetyl-L-tryptophan in man

The nutritive value of N-acetyl-L-tryptophan was investigated by loading tests with deuterated L-tryptophan and deuterated N-acetyl-L-tryptophan in three healthy adults, and by a 7 day-long feeding experiment with deuterated N-acetyl-L-tryptophan in one healthy adult. After loading with deuterated N-acetyl-L-tryptophan, serum levels of deuterated tryptophan and kynurenine were only about 10%, and the amounts of deuterated 5-hydroxyindole-3-acetic acid excreted in 24 h approximately 30% of those found after deuterated tryptophan loading. During the feeding experiment with deuterated N-acetyl-L-tryptophan, the serum level of deuterated tryptophan remained below 20% of total serum tryptophan, and serum protein fell below the normal range. It is concluded that the nutritive value of N-acetyl-L-tryptophan is inferior to that of L-tryptophan. Contradictory findings of earlier studies are discussed.