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Effects of Excess Intake of Leucine and Valine Deficiency on Tryptophan and Niacin Metabolites in Humans

Department of Nutrition and Biochemistry, Institute of Public Health, Tokyo, Japan

Nineteen healthy humans (2 men and 17 women) served as experimental subjects in 4 experiments using diets having different levels of leucine and also a valine-deficient diet. The effect of an excess intake of leucine, with and without addition of vitamin B-6, and the effect of a deficiency of valine on urinary excretions of N¹-methylnicotinamide, N¹-methyl-2-pyridone-5-carboxamide, nicotinic acid, quinolinic acid, and 5-hydroxyindole acetic acid, and on the level of plasma amino acids were investigated. There was no effect of leucine on the excretion of these metabolites, but a marked decrease in the plasma (or serum) valine level was observed. The same decrease was seen when a valine-deficient diet was fed.

KEY WORDS: • leucine • valine • niacin metabolites

Manuscript received 9 December 1974.