Oxidation of exogenous medium-chain free fatty acids during prolonged exercise: comparison with glucose

Oct 1, 1992Journal of applied physiology (Bethesda, Md. : 1985)

Burning medium-chain fatty acids from outside the body during long exercise compared to glucose

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Abstract

Over a 2-hour exercise period, 13.6 ± 3.5 g of ingested medium-chain triacylglycerols (MCT) and 36.4 ± 8.2 g of glucose were oxidized.

Both MCT and glucose began to be oxidized within the first 30 minutes of exercise.
The oxidation rate of both substrates increased progressively until the end of the exercise.
MCT contributed approximately 119 ± 31 kcal, while glucose contributed around 140 ± 36 kcal to total energy expenditure.
MCT and glucose represented 7% and 8.5% of total energy expenditure, respectively.
The amounts of MCT and glucose oxidized were 54% and 64% of the total ingested amounts.

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The purpose of this study was to compare the oxidation rate of exogenous 13C-labeled medium-chain triacylglycerols (MCT) with that of an isocaloric amount of exogenous [13C]glucose and to evaluate their respective effects on endocrine and metabolic responses to moderate prolonged exercise. To take into account changes in isotopic composition of 13CO2 arising from oxidation of endogenous substrates because of exercise and/or substrate ingestion that overestimates the oxidation rate of exogenous substrates, two levels of 13C enrichment were used for each substrate. Six young healthy males (20-26 yr of age) completed five 2-h periods of exercise at 65 +/- 3% maximal O2 uptake (VO2max) on a cycle ergometer at 7-day intervals: one control exercise with water ingestion, two trials with ingestion of 25 g of [13C]MCT (trioctanoate) 1 h before exercise, and two trials with 57 g of [13C]glucose (dissolved in 1,000 ml of water) ingested during exercise. Exogenous MCT and glucose began to be oxidized within the first 30 min of exercise, and the oxidation rate increased progressively until the end of exercise for both substrates. Over the 2-h period of exercise, 13.6 +/- 3.5 g of ingested MCT and 36.4 +/- 8.2 g of exogenous glucose were oxidized, which represent 54 and 64%, respectively, of the total amount ingested. The contribution of MCT (119 +/- 31 kcal) and glucose (140 +/- 36 kcal) was not significantly different and represented 7 and 8.5%, respectively, of the total energy expenditure.(ABSTRACT TRUNCATED AT 250 WORDS)

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Oxidation of exogenous medium-chain free fatty acids during prolonged exercise: comparison with glucose

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