Tryptophan-niacin interrelationships during acute fasting and caloric restriction in humans

Abstract

The niacin status of normal adults was evaluated in three studies of caloric restriction for 10-day periods. Although niacin excretions were practically unchanged from control values, the N1MN excretions were increased by 2 to 5 times during caloric restriction. This could be due to two factors: 1) the synthesis of niacin from tryptophan liberated during the catabolism of body protein and, 2) the niacin utilized after its release from catabolized tissue. These data suggest that under conditions of caloric restriction, the daily minimal allowances of niacin are influenced by the caloric and protein intake, the degree of negative nitrogen balance, and the subsequent protein catabolism. The suggested tryptophan/niacin conversion ratio of 60:1 may not apply during conditions of caloric restriction.