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Alteration of Glucose Tolerance by Dietary L-Tryptophan in Rats

Department of Biochemical Nutrition, Roche Research Center, Hoffmann-La Roche Inc., Nutley, New Jersey 07110

L-Tryptophan is known to have pharmacological effects on carbohydrate metabolism. In a scrutiny for possible physiological relationships, intravenous glucose tolerance was measured in rats fed various diets of defined L-tryptophan content. Within 14 days, animals which had been fed a tryptophan-deficient diet removed excess glucose from their blood at a reduced rate. This decreased tolerance to glucose was dose dependent to dietary L-tryptophan and the intolerance was reversed by feeding a complete diet. The intolerance was not dependent on dietary protein source, not reversed by added niacin or vitamin B-6, not a necessary consequence of decreased food consumption and growth, and not duplicated by a lack of dietary lysine. The results suggest that dietary L-tryptophan is active in physiological regulation of carbohydrate metabolism.

KEY WORDS: • L-tryptophan • tryptophan-free diet • intravenous glucose tolerance

Manuscript received 14 October 1975.