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Regulatory Role of Dietary Leucine on Plasma Branched-Chain Amino Acid Levels in Young Men^1,2,3,

Department of Nutrition and Food Science and the Clinical Research Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

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.

KEY WORDS: • leucine • branched-chain amino acids • plasma amino acid levels • young men

¹ Supported in part by a contract (No. 12-14-1001-258) from the Human Nutrition Institute, U.S. Department of Agriculture and Grant No. RR-88 from the General Clinical Research Centers Program of the Division of Resources, National Institutes of Health and Swedish Medical Research Council 19X-767.

² Contribution No. 2475 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.

³ The experimental protocols received the administrative approval of the M.I.T. Committee on the Use of Humans as Experimental Subjects and the Executive and Policy Committees of the M.I.T. Clinical Research Center.

⁴ On sabbatical leave. Present address: Institute of Nutrition, University of Uppsala, Box 551, S-75122 Uppsala, Sweden.

⁵ Undergraduate student. Supported by the Undergraduate Research Opportunities Program.

Manuscript received 17 October 1974.