Enhanced postprandial energy expenditure with medium-chain fatty acid feeding is attenuated after 14 d in premenopausal women

Background: Medium-chain triacylglycerols (MCTs) are reported to enhance hu man energy expenditure (EE), although few studies have involved women and t he duration of such effects is only known for periods of approximate to 7 d . Objective: This study was conducted to determine whether women consuming mi xed, 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 di ets enriched in either MCTs or LCTs during separate, 14-d feeding periods. Each meal contained 40% of energy as far (80% of which was the treatment fa t), 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 (Delta kJ/min) after a standardized breakf ast were measured by respiratory gas exchange. Results: On day 7, the mean (+/-SEM) BMR (3.58 +/- 0.11 kJ/min) with the MC T 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 +/- 0.03 kJ/min) than with the LCT diet (4.23 +/- 0.04 kJ/min); by day 14, postprandial TEE was still greater with the M CT diet, but nor significantly so. No significant differences in the thermi c effect of feeding were evident between diets. Conclusions: Results from this longest, controlled MCT feeding study to dat e suggest that short-term feeding of MCT-enriched diets increases TEE, but this effect could be transient with continued feeding.