Fatty acid oxidation is directly regulated by carbohydrate
metabolism during exercise.
Coyle, Edward F., Asker E. Jeukendrup, Anton J. M. Wagenmakers, and
Wim H. M. Saris.
Department of Human Biology, University of Limburg, Maastricht, The
Netherlands and Department of Kinesiology and Health Education. The
University of Texas, Austin TX 78712 USA
APStracts 4:0090E, 1997.
We determined if increased glycolytic flux from hyperglycemia and
hyperinsulinemia directly reduces fatty acid oxidation during
exercise. Fatty acid oxidation rates were measured during constant
rate intravenous infusion of trace amounts of a long-chain fatty acid
(1-13C-palmitate; PAL) vs. a medium-chain fatty acid (1-13C
-octanoate; OCT). Six endurance-trained men cycled for 40 min at 50%
VO2max : 1) after an overnight fast (FAST); and 2) following
ingestion of 1.4 g/kg of glucose at 60 min and again 10 min before
exercise (GLU). GLU caused hyperinsulinemia, a pre-exercise blood
glucose of 6 mM and a 34% reduction in total fat oxidation during
exercise due to an approximately equal reduction in oxidation of
plasma FFA and intramuscular triglycerides (all P<0.05). Oxidation
of PAL was significantly reduced during GLU compared to FAST (i.e.;
70.0+/-4.1% vs. 86.0+/-1.9% of tracer infusion rate; P<0.05).
However, GLU had no effect on OCT oxidation, which is apparently not
limited by mitochondrial transport. Furthermore, GLU reduced plasma
FFA appearance 36% (P<0.05), indicating a coordination of effects
on adipose tissue and muscle. In summary, substrate oxidation during
exercise can be regulated by increased glycolytic flux which is
accompanied by a direct inhibition of long-chain fatty acid
oxidation. These observations indicate that carbohydrate availability
can directly regulate fat oxidation during exercise.
Received 22 January 1997; accepted in final form 27 March 1997.
APS Manuscript Number E33-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 13 May 1997