Regulatory role of dietary leucine on plasma branched-chain amino acid levels in young men.

Four healthy young men were studied to explore the effects of dietary leucine intake on plasma levels of leucine,isoleucine and valine. Leucine-, valine-, leucine-valine-, and leucine-isoleucine-valine-free amino acid mixtures were studied during four-day experimental diet periods. The effects of giving amino acid mixtures with high-carbohydrate, low-fat or low-carbohydrate, high-fat diets were also studied. Deficient leucine intake increased plasma levels of valine and isoleucine, but a valine-free diet did not affect plasma levels of the other branched-chain amino acids. Leucine influence was evident during the postprandial and fasted phases. Valine and isoleucine levels were less markedly reduced when diets devoid of these amino acids were also leucine-free, as compared with a diet providing adequate leucine. Changes in the major dietary energy source failed to influence the qualitative effects of dietary leucine adequacy on the branched-chain amino acid levels in plasma. The results suggest that leucine facilitates both tissue uptake of branched-chain amino acids and their intracellular metabolism.