Journal of Applied Physiology, Vol 80, Issue 6 2217-2225, Copyright © 1996 by American Physiological Society

ARTICLES

Effects of medium-chain triglyceride ingestion on fuel metabolism and cycling performance

C. G. Van Zyl, E. V. Lambert, J. A. Hawley, T. D. Noakes and S. C. Dennis
Liberty Life Chair of Exercise and Sport Science, University of Cape Town Medical School, Observatory, South Africa.

On three occasions separated by 10 days, six endurance-trained cyclists rode for 2 h at 60% of peak O2 uptake and then performed a simulated 40-km time trial (T-trial). During the rides, the subjects ingested a total of 2 liters of a [U-14C]glucose-labeled beverage containing a random order of either 10% glucose [carbohydrate (CHO)], 4.3% medium-chain triglycerides (MCTs); or 10% glucose + 4.3% MCTs (CHO+MCT). Although replacing CHO with MCTs slowed the T-trials from 66.8 +/- 0.4 (SE) to 72.1 +/- 0.6 min (P < 0.001), adding MCTs to CHO improved the T-trials from 66.8 +/- 0.4 to 65.1 +/- 0.5 min (P < 0.05). Faster T-trials in the CHO+MCT trial than in the CHO trial were associated with increased final circulating concentrations of free fatty acids (0.58 +/- 0.09 vs. 0.36 +/- 0.06 mmol/l; P < 0.05) and ketones (1.51 +/- 0.25 vs. 0.51 +/- 0.07 mmol/l; P < 0.01) and decreased final circulating concentrations of glucose (5.2 +/- 0.2 vs. 6.3 +/- 0.3 mmol/l; P < 0.01) and lactate (1.9 +/- 0.4 vs. 3.7 +/- 0.5 mmol/l; P < 0.05). Adding MCTs to ingested CHO reduced total CHO oxidation rates from 14 +/- 1 to 10 +/- 1 mmol/min at 2 h and from 17 +/- 1 to 14 +/- 1 mmol/min in the T-trial (P < 0.01), without affecting the corresponding approximately 5 and approximately 7 mmol/min rates of [14C]glucose oxidation. These data suggest that MCT oxidation decreased the direct and/or indirect (via lactate) oxidation of muscle glycogen. A reduced reliance on CHO oxidation at a given O2 uptake is similar to an endurance-training effect, and that may explain the improved T-trial performances.

This article has been cited by other articles:

				M. S. Thorburn, B. Vistisen, R. M. Thorp, M. J. Rockell, A. E. Jeukendrup, X. Xu, and D. S. Rowlands Attenuated gastric distress but no benefit to performance with adaptation to octanoate-rich esterified oils in well-trained male cyclists J Appl Physiol, December 1, 2006; 101(6): 1733 - 1743. [Abstract] [Full Text] [PDF]

				B. Vistisen, L. Nybo, X. Xu, C.-E. Hoy, and B. Kiens Minor amounts of plasma medium-chain fatty acids and no improved time trial performance after consuming lipids J Appl Physiol, December 1, 2003; 95(6): 2434 - 2443. [Abstract] [Full Text]

				T. R. Thomas, K. E. Horner, M. M. Langdon, J. Q. Zhang, E. S. Krul, G. Y. Sun, and R. H. Cox Effect of exercise and medium-chain fatty acids on postprandial lipemia J Appl Physiol, April 1, 2001; 90(4): 1239 - 1246. [Abstract] [Full Text] [PDF]

				J. F Horowitz and S. Klein Lipid metabolism during endurance exercise Am. J. Clinical Nutrition, August 1, 2000; 72(2): 558S - 563. [Abstract] [Full Text] [PDF]

				D. R. Pendergast, J. J. Leddy, and J. T. Venkatraman A Perspective on Fat Intake in Athletes J. Am. Coll. Nutr., June 1, 2000; 19(3): 345 - 350. [Abstract] [Full Text] [PDF]

				D. J. Angus, M. Hargreaves, J. Dancey, and M. A. Febbraio Effect of carbohydrate or carbohydrate plus medium-chain triglyceride ingestion on cycling time trial performance J Appl Physiol, January 1, 2000; 88(1): 113 - 119. [Abstract] [Full Text] [PDF]

				J. F. Horowitz, R. Mora-Rodriguez, L. O. Byerley, and E. F. Coyle Preexercise medium-chain triglyceride ingestion does not alter muscle glycogen use during exercise J Appl Physiol, January 1, 2000; 88(1): 219 - 225. [Abstract] [Full Text] [PDF]

				R. C. Hill The Nutritional Requirements of Exercising Dogs J. Nutr., December 1, 1998; 128(12): 2686S - 2686. [Abstract] [Full Text]