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Leucine metabolism during fasting and exercise.

J Knapik1, C Meredith, B Jones

  • 1US Army Research Institute of Environmental Medicine, Natick 01760-5007.

Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 1, 1991
PubMed
Summary

Fasting increases leucine oxidation during rest and exercise. A 3.5-day fast significantly elevates whole body leucine kinetics, particularly during physical exertion, impacting energy metabolism.

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Area of Science:

  • Exercise Physiology
  • Nutritional Biochemistry
  • Metabolic Research

Background:

  • Leucine kinetics are crucial for understanding protein metabolism.
  • Exercise significantly impacts amino acid oxidation.
  • Prolonged fasting alters whole-body metabolic responses.

Purpose of the Study:

  • To investigate whole body leucine kinetics during rest and exercise following a 3.5-day fast.
  • To compare leucine flux and oxidation rates between a postabsorptive state and a fasted state during physical activity.

Main Methods:

  • Utilized a primed constant intravenous infusion of L-[1-13C]leucine in healthy young men.
  • Measured leucine kinetics at rest and during cycle ergometer exercise (45% maximal O2 uptake).
  • Analyzed blood samples for isotopic enrichment and expired gas for 13CO2.

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Main Results:

  • Resting leucine flux was higher after fasting (FS) compared to the postabsorptive state (PAS).
  • Leucine oxidation increased during exercise in both states but was significantly higher in the FS group.
  • During exercise in FS, leucine oxidation rose to 75 +/- 21 mumol.kg-1.h-1 compared to 52 +/- 17 mumol.kg-1.h-1 in PAS.

Conclusions:

  • A 3.5-day fast further elevates the high rate of leucine oxidation observed during exercise.
  • Fasting significantly impacts leucine metabolism, increasing its oxidation during both rest and physical activity.
  • These findings highlight the metabolic adaptations to prolonged fasting and exercise.