American Journal of Clinical Nutrition, Vol 46, 557-562, Copyright © 1987 by The American Society for Clinical Nutrition, Inc

ORIGINAL RESEARCH COMMUNICATIONS

Leucine, glucose, and energy metabolism after 3 days of fasting in healthy human subjects

KS Nair, PD Woolf, SL Welle and DE Matthews
Department of Medicine, University of Rochester School of Medicine and Dentistry, NY.

Adaptations of leucine and glucose metabolism to 3 d of fasting were examined in six healthy young men by use of L-[1-13C]leucine and D[6,6- 2H2]glucose as tracers. Leucine flux increased 31% and leucine oxidation increased 46% after 3 d of fasting compared with leucine flux and oxidation after an overnight fast. Glucose production rate declined 38% and resting metabolic rate decreased 8% during fasting. Plasma concentrations of testosterone, insulin, and triiodothyronine were reduced by fasting whereas plasma glucagon concentrations were increased. We conclude that there is increased proteolysis and oxidation of leucine on short-term fasting even though glucose production and energy expenditure decreased.

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