Nine healthy subjects were studied to determine their performance and the metabolic and hormonal responses to prolonged exercise
after ingestion of a carbohydrate or a lipid diet. Subjects exercised on a bicycle ergometer (60% VO2max) until exhaustion four times at weekly intervals. The exercise
test was performed I h after ingestion of three different isocaloric meals (400 Kcal) containing either glucose, medium-chain triglycerides (MCTs) or long-chain triglycerides (LCTs). The fourth test was performed after a night fast. The metabolism of these nutriments was followed using [U-13C]glucose, [l-13C]octanoate, and [l-13C]palmitate added as tracers.
The average work time was comparable whatever nutriment used (116 ± 11 min). Oxidation of the ingested nutriment over this period was 80% for glucose, 45% for MCTs, and 9% for LCTs. Glucose ingestion produced an early insulin peak associated at the end of the exercise
with a lower glycemia compared to the fat diets. After MCT ingestion, an increase in ketone bodies was observed. Catecholamine response to physical exercise
was decreased by aII the meals when compared to fasting.
Thus, we conclude that a different lipid meal, MCTs, or LCTs, compared to glucose feeding, do not modify exhaustion time in spite of differences in hormonal and metabolic responses.
©1987The American College of Sports Medicine