Endogenous fat oxidation during medium chain versus long chain triglyceride feeding in healthy women

OBJECTIVE: To compare the effect of medium chain triglycerides (MCT) vs long chain triglycerides (LCT) feeding on exogenous and endogenous oxidation of long chain saturated fatty acids (LCSFA) in women. SUBJECTS: Twelve healthy female subjects (age 19-26 y, body mass index (BMI) 17.5-28.6 kg/m2) DESIGN AND MEASUREMENTS: In a randomized cross-over design, subjects were fed weight maintenance diets providing 15%, 45% and 40% of energy as protein, carbohydrate and fat, respectively, with 80% of this fat comprising either a combination of butter and coconut oil (MCT) or beef tallow (LCT). Following 6 days of feeding, subjects were given daily oral doses of 1-(13)C labelled-myristic, -palmitic and -stearic acids for 8 days. Expired 13CO2 was used as an index of LCSFA oxidation with CO2 production assessed by respiratory gas exchange. RESULTS: No difference in exogenous LCSFA oxidation was observed as a function of diet on day 7. On day 14, greater combined cumulative fractional LCSFA oxidation (16.9 +/- 2.5%/5.5 h vs 9.1 +/- 1.2%/5.5 h, P < 0.007), net LCSFA oxidation (2956 +/- 413 mg/5.5 h vs 1669 +/- 224 mg/5.5 h, P < 0.01), and percentage dietary LCSFA contribution to total fat oxidation (16.3 +/- 2.3%/5.5 h vs 9.5 +/- 1.5%/5.5 h; P < 0.01) were observed in women fed the MCT vs LCT diet. With the MCT diet, but not the LCT diet, combined cumulative fractional LCSFA oxidation (P < 0.03), net LCSFA oxidation (P < 0.03), and percentage dietary LCSFA contribution to total fat oxidation (P < 0.02) were increased at day 14 as compared to day 7. Day 14 results indicated increased endogenous LCSFA oxidation during MCT feeding. CONCLUSION: The capacity of MCT to increase endogenous oxidation of LCSFA suggests a role for MCT in body weight control over the long term.     

Stimulation of thermogenesis and brown fat activity in rats fed medium chain triglyceride

Gastric intubation of young male rats with 100 kJ/d of medium chain (C8 and C10) triglyceride (MCT) reduced their voluntary intake of stock diet such that total metabolizable energy intake was similar to that of rats intubated with water, and 41% of their energy intake was derived from MCT. Body weight, energy gain, and energetic efficiency were all markedly suppressed in MCT-fed rats, but energy expenditure over the 14-day experiment was significantly increased. Resting oxygen consumption, measured at thermoneutrality, was also enhanced in MCT-fed rats, but this difference was abolished by injection of the animals with the beta-adrenergic antagonist, propranolol. Brown adipose tissue mass was similar for both groups, but the activity of the mitochondrial proton conductance pathway, assessed from the binding of purine nucleotides, was increased by over 70%. These data indicate that the reduced weight gains of animals fed MCT are due to elevated rates of energy expenditure, possibly resulting from sympathetic activation of brown fat thermogenesis.