Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise

Jan 21, 2000Journal of applied physiology (Bethesda, Md. : 1985)

Eating medium-chain fats before exercise does not change muscle energy use during exercise

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Abstract

Ingestion of approximately 25 g of medium-chain triglycerides (MCT) did not reduce muscle glycogen oxidation during high-intensity exercise.

Seven well-trained men cycled for 30 minutes at 84% of their maximum oxygen uptake.
Two pre-exercise conditions were tested: carbohydrate alone and a combination of MCT and carbohydrate.
The change in muscle glycogen concentration was similar between the MCT+CHO and CHO conditions (42.0 vs. 38.8 micromol glucosyl units/g wet weight).
Glycogen oxidation rates were also comparable between both conditions (331 vs. 329 micromol.kg(-1).min(-1)).
Resting glucose uptake was significantly higher in the MCT+CHO condition compared to CHO (26.9 vs. 20.7 micromol.kg(-1).min(-1)).
However, during exercise, glucose uptake rates did not differ between the two trials.

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This investigation determined whether ingestion of a tolerable amount of medium-chain triglycerides (MCT; approximately 25 g) reduces the rate of muscle glycogen use during high-intensity exercise. On two occasions, seven well-trained men cycled for 30 min at 84% maximal O(2) uptake. Exactly 1 h before exercise, they ingested either 1) carbohydrate (CHO; 0.72 g sucrose/kg) or 2) MCT+CHO [0.36 g tricaprin (C10:0)/kg plus 0.72 g sucrose/kg]. The change in glycogen concentration was measured in biopsies taken from the vastus lateralis before and after exercise. Additionally, glycogen oxidation was calculated as the difference between total carbohydrate oxidation and the rate of glucose disappearance from plasma (R(d) glucose), as measured by stable isotope dilution techniques. The change in muscle glycogen concentration was not different during MCT+CHO and CHO (42.0 +/- 4.6 vs. 38.8 +/- 4.0 micromol glucosyl units/g wet wt). Furthermore, calculated glycogen oxidation was also similar (331 +/- 18 vs. 329 +/- 15 micromol. kg(-1). min(-1)). The coingestion of MCT+CHO did increase (P < 0.05) R(d) glucose at rest compared with CHO (26.9 +/- 1.5 vs. 20.7 +/- 0. 7 micromol.kg(-1). min(-1)), yet during exercise R(d) glucose was not different during the two trials. Therefore, the addition of a small amount of MCT to a preexercise CHO meal did not reduce muscle glycogen oxidation during high-intensity exercise, but it did increase glucose uptake at rest.

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Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise

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