Daily moderate exercise at neutral energy balance does not affect
total 24-h leucine oxidation or nitrogen retention in healthy
men.
El-Khoury, Antoine E., Anders Forslund, Roger Olsson, Anders Sjodin,
Agneta Andersson, Alan Atkinson, Ambalini Selvaraj, Leif Hambraeus,
and Vernon R. Young.
Laboratory of Human Nutrition, School of Science and Clinical
Research Center, Massachusetts Institute of Technology, Cambridge,
Massachusetts 02142, and Department of Nutrition, University of
Uppsala, Uppsala, Sweden
APStracts 4:0093E, 1997.
Short-term metabolic experiments have revealed that physical exercise
increases the oxidation of leucine, which has been interpreted to
indicate an increased requirement for dietary protein in physically
active subjects. Because it may be inaccurate to extrapolate
measurements of amino acid oxidation made over a few hours to the
entire day we have carried out a continuous 24h, intravenous 1-13C
-leucine/15N-urea tracer study in eight healthy adult men. Their diet
supplied 1 g protein.kg-1day-1 and exercise (mean 46% VO2max) was for
90 min during the 12h fast and 12h fed periods of the day. Subjects
were adapted to the diet and exercise regimen for 6 days. Then on day
7 they were dressed in the UPPCAL direct calorimeter suit, connected
to an open hood indirect calorimeter and received the tracers.
Exercise increased leucine oxidation by about 50% and 30% over pre
-exercise rates, for fast and fed periods respectively. This increase
amounted to about 4-7% of daily leucine oxidation. Subjects remained
in body leucine equilibrium (balance -4.6 + 10.5 mg.kg-1.d-1; -3.6 +
8.3% of intake; P = NS from zero balance). Therefore, moderate
exercise did not cause a significant deterioration in leucine
homeostasis at a protein intake of 1 g.kg-1.day-1. These findings
underscore the importance of carrying out precise, continuous 24h
measurements of whole-body leucine kinetics and this model should be
of value in studies concerning the quantitative interactions between
physical exercise, energy/protein metabolism and diet in humans.
Received 24 December 1996; accepted in final form 14 March 1997.
APS Manuscript Number E624-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 13 May 1997