Lipolytic suppression following carbohydrate ingestion limits fat
oxidation during exercise.
Horowitz, Jeffrey F., Ricardo Mora-Rodriguez, Lauri O. Byerley, and
Edward F. Coyle.
The Human Performance Laboratory. Department of Kinesiology and
Health Education and Division of Nutritional Sciences. The University
of Texas at Austin, Austin, TX 78712
APStracts 4:0145E, 1997.
This study determined if the suppression of lipolysis following pre
-exercise carbohydrate ingestion reduces fat oxidation during
exercise. Six healthy-active men cycled 60 min at 44+/-2% VO2peak,
exactly 1h after ingesting 0.8 g/kg of: 1) glucose (GLU), 2) fructose
(FRU), or 3) after an overnight fast (FAST). The mean plasma insulin
concentration during the 50 min before exercise was different among
FAST, FRU, and GLU (8+/-1, 17+/-1, and 38+/-5 [mu]U/ml, respectively;
p<0.05). Following 25 min of exercise, whole-body lipolysis was
6.9+/-0.2, 4.3+/-0.3, and 3.2+/-0.5 [mu]mol/kg/min and fat oxidation
was 6.1+/-0.2, 4.2+/-0.5, and 3.1+/-0.3 [mu]mol/kg/min during FAST,
FRU, and GLU, respectively (all <0.05). During FAST, fat oxidation
was less than lipolysis (p<0.05), whereas fat oxidation
approximately equaled lipolysis during FRU and GLU. In an additional
trial, the same subjects ingested glucose (0.8 g/kg) 1h before
exercise and lipolysis was simultaneously increased by infusing
Intralipid_ and heparin throughout the resting and exercise period
(GLU+LIPID). This elevation of lipolysis during GLU+LIPID increased
fat oxidation 30% above GLU (4.0+/-0.4 vs. 3.1+/-0.3 [mu]mol/kg/min;
p<0.05), confirming that lipolysis limited fat oxidation. In
summary, small elevations in plasma insulin before exercise
suppressed lipolysis during exercise to the point where it equaled
and appeared to limit fat oxidation.
Received 13 February 1997; accepted in final form 25 June 1997
APS Manuscript Number E068-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 10 July 1997