Effects of Protein-Amino Acids, Lipid, and Carbohydrate on the Conversion Ratio of Tryptophan to Niacin

Abstract

Vitamin niacin is biosynthesized from an essential amino acid tryptophan and one defines it as the conversion ratio of tryptophan to niacin. As a lot of tryptophan exists in the body, the pathway is very important because niacin can be efficiently supplied even when the body emergently needs niacin. Therefore, it is very important to know factors affecting the conversion ratio of tryptophan to niacin. The conversion ratio is calculated by the comparison of (sum of the urinary excretion of nicotinamide and its metabolites, N^1-methylnicotinamide, N^1-methyl-2-pyridone-5-carboxamide, and N^1-methyl-4-pyridone-3-carboxamide (mol/day) /tryptophan intake (mol/day). The conversion ratio is decreased with increasing with dietary protein levels when diets contain sufficient of protein, while, when rats are fed with low protein and tryptophan-limiting diets, the conversion ratio is the lowest. In the effects of fat, feeding diets containing unsaturated fatty acids increased the conversion ratio, while feeding diets containing saturated fatty acids did not affect. In the effects of carbohydrate, the conversion ratio was higher in diets containing starch than in diets containing sucrose.