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Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise
J F Horowitz1, R Mora-Rodriguez, L O Byerley
1Department of Kinesiology and Health Education, The Human Performance Laboratory, The University of Texas at Austin, Austin, Texas 78712, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|January 21, 2000
Summary
Adding medium-chain triglycerides (MCT) to a pre-exercise carbohydrate (CHO) meal does not reduce muscle glycogen use during high-intensity exercise. However, MCT did increase resting glucose uptake in trained athletes.
Area of Science:
- Sports Science
- Human Physiology
- Nutritional Biochemistry
Background:
- Muscle glycogen is a primary fuel source during high-intensity exercise.
- Medium-chain triglycerides (MCT) are proposed to spare muscle glycogen.
- The effect of co-ingesting MCT with carbohydrates on glycogen use needs further investigation.
Purpose of the Study:
- To determine if ingesting a tolerable amount of medium-chain triglycerides (MCT) reduces muscle glycogen utilization during high-intensity exercise.
- To assess the impact of MCT co-ingestion with carbohydrates on substrate oxidation rates.
- To examine the effect of MCT on glucose uptake at rest and during exercise.
Main Methods:
- Seven well-trained men performed two 30-minute high-intensity cycling trials (84% maximal O2 uptake).
- Participants ingested either carbohydrate (CHO) or MCT+CHO 1 hour pre-exercise.
- Muscle biopsies and stable isotope dilution techniques were used to measure glycogen concentration and substrate utilization.
Main Results:
- Muscle glycogen concentration change was not significantly different between MCT+CHO and CHO trials.
- Calculated muscle glycogen oxidation rates were similar in both conditions.
- Co-ingestion of MCT+CHO increased resting glucose uptake but not during exercise.
Conclusions:
- A small amount of MCT added to a pre-exercise CHO meal does not spare muscle glycogen during high-intensity exercise in trained individuals.
- MCT may influence glucose metabolism at rest, but this effect does not translate to glycogen sparing during intense exercise.
- These findings suggest MCT supplementation may not be effective for reducing muscle glycogen depletion during prolonged, high-intensity exercise when consumed with carbohydrates.