Affiliation:
1. Clinical Research Center and Laboratory of Human Nutrition, School of Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142; and
2. Rowett Research Institute, Bucksburn, Aberdeen AB21 9SB, Scotland
Abstract
In two groups of five adults, each adapted to two different dietary regimens for 6 days, the metabolic fate of dietary [1-13C]leucine was examined when ingested either together with a mixture of free amino acids simulating casein (extrinsically labeled; condition A), along with the intact casein (extrinsically labeled; condition B), or bound to casein (intrinsically labeled; condition C). Fed state leucine oxidation (Ox), nonoxidative leucine disposal (NOLD), protein breakdown, and splanchnic uptake have been compared using an 8-h oral [1-13C]leucine and intravenous [2H3]leucine tracer protocol while giving eight equal hourly mixed meals. Lower leucine Ox, increased NOLD, and net protein synthesis were found with condition Ccompared with condition A (19.3 vs. 24.9; 77 vs. 55.8; 18.9 vs. 12.3 μmol ⋅ kg−1 ⋅ 30 min−1; P < 0.05). Ox and NOLD did not differ between conditions B and C. Splanchnic leucine uptake calculated from [1-13C]- and [2H3]leucine plasma enrichments was between 24 and 35%. These findings indicate that the form in which leucine is consumed affects its immediate metabolic fate and retention by the body; the implications of these findings for the tracer balance technique and estimation of amino acid requirements are discussed.
Publisher
American Physiological Society
Subject
Physiology (medical),Physiology,Endocrinology, Diabetes and Metabolism
Cited by
95 articles.
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