Background: Medium-chain triacylglycerols (MCTs) are reported to enhance human energy expenditure (EE), although few studies have involved women and the duration of such effects is only known for periods of approximately 7 d.
Objective: This study was conducted to determine whether women consuming mixed, MCT-enriched or long-chain triacylglycerol (LCT)-enriched diets showed changes in EE or substrate oxidation after 7 and 14 d.
Design: Twelve nonobese, premenopausal women were fed isoenergetic mixed diets enriched in either MCTs or LCTs during separate, 14-d feeding periods. Each meal contained 40% of energy as fat (80% of which was the treatment fat), 45% as carbohydrate, and 15% as protein. On days 7 and 14 of each trial, basal metabolic rate (BMR, kJ/min), total energy expenditure (TEE, kJ/min), and thermic effect of feeding (deltakJ/min) after a standardized breakfast were measured by respiratory gas exchange.
Results: On day 7, the mean (+/-SEM) BMR (3.58+/-0.11 kJ/min) with the MCT diet was greater (P = 0.0003) than that with the LCT diet (3.43+/-0.11 kJ/min). The mean postprandial TEE on day 7 was significantly greater (P = 0.04) with the MCT diet (4.36+/-0.04 kJ/min) than with the LCT diet (4.23+/-0.04 kJ/min); by day 14, postprandial TEE was still greater with the MCT diet, but not significantly so. No significant differences in the thermic effect of feeding were evident between diets.
Conclusions: Results from this longest controlled MCT feeding study to date suggest that short-term feeding of MCT-enriched diets increases TEE, but this effect could be transient with continued feeding.