Effect of endogenous carbohydrate availability on oral medium-chain
triglyceride oxidation during prolonged exercise.
Jeukendrup, Asker E, Wim H M Saris, Richard Van Diesen, Fred Brouns,
Anton J M Wagenmakers.
Department of Human Biology, Nutrition Research Center, University
of Limburg, Maastricht, The Netherlands
APStracts 2:0485A, 1995.
The present study examined the medium chain triglyceride (MCT)
oxidation rate of oral CHO+MCT supplements after a glycogen depletion
trial (low glycogen, LG) and in the glycogen loaded state (normal to
high glycogen, HG). Eight elite athletes cycled 4 times 90 min at
50%Wmax (57% VO2max). In 2 trials they followed a LG-protocol to
achieve low glycogen stores in the leg muscles the evening prior to
the experiment and in 2 trials they followed a HG-protocol. Subjects
received a bolus of 4 ml.kg-1 at the start and 2 ml.kg-1 every 20 min
during exercise of either a 15% CHO (long chain glucose polymer)
solution or an equicaloric CHO+MCT suspension. Exogenous MCT
oxidation was measured by adding a [1,1,1-13C]- trioctanoate tracer
to the MCT oil and measuring 13CO2 production in the breath. The
results show that 85% of MCT ingested was oxidized in LG and 69% in
HG during the 60-90 min period. There was no statistically
significant difference in MCT utilization in LG and HG. Peak
oxidation rates were 0.15 g.min-1 and 0.13 g.min-1 respectively. MCT
contributed 7.6% (LG) and 6.5% (HG) to total energy expenditure
during the 60-90 min period. Total fatty acid oxidation was
significantly elevated in the LG-trial, but was not influenced by MCT
ingestion. Concomitantly carbohydrate oxidation was reduced in LG,
but no effect of MCT was observed. We conclude 1. that the
contribution of MCT to total energy expenditure was small and 2. that
strenuous exercise the day prior to the experiment followed by a low
CHO intake, leading to a low CHO availability, substantially
increased total fat oxidation but did not significantly increase MCT
oxidation.
Received 5 July 1995; accepted in final form 24 October 1995.
APS Manuscript Number A714-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95