Alteration of glucose tolerance by dietary L-tryptophan in rats

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 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.