MCT may help with appetite control via their satiating properties. The satiating properties of MCT involve multiple pre-absorptive and post-absorptive mechanisms. First, MCT appear as a thin, light-yellow, clear, and odorless oil, with a nearly neutral or slightly bland taste, whereas MCFA are characterized by an odor of goat and strong bitterness (Bach et al., 1996). This repulsive quality is extremely strong, as a concentration of 0.1% makes a meal unfit for human consumption (Bach et al., 1996). These palatability properties are important determinants of feeding behavior of an individual, in particular satiation.
The effect of dietary MCT versus LCT on short-term food intake has been compared in rats (Maggio and Koopmans, 1982; Furuse et al., 1992). The satiating effect of these two triglycerides appears to be related to their caloric content rather than to chain length (Feinle et al., 2001; Westerterp-Plantenga, 2004a). In addition, the ingestion of MCT as a bolus does not stimulate contraction of the gallbladder nor raise the plasma cholecystoki-nin (CCK) level in the manner in which it occurs following LCT ingestion (Hopman et al., 1984). This gastric relaxation by MCT is not sufficient to induce satiation; therefore, the nutrient-induced gastric relaxation occurs through other mechanisms than CCK (Furuse et al., 1992; Barbera et al., 2000). According to Maas et al. (1998), MCT inhibit gastrin-stimulated gastric acid secretion, but less so than LCT. Overall, it has been determined that the satiating effects of a fat depend on the fatty acid chain length, and moreover that the role of CCK and gastrin-stimulated gastric acid are minor.
Post-absorptive properties of MCT, including hepatic exposure to fatty acids, may lead to greater beta-oxidation by the liver than that following LCT intake. Enhanced beta-oxidation may in turn lead to increased satiety (Westerterp-Plantenga, 2004b). Thus, MCT consumption in sufficient quantities over the long term may lead to decreased caloric intake and consequently decreased body weight and fat. Van Wymelbeke et al. (2001), conducted a study demonstrating that ingestion of a MCT-containing lunch resulted in less food consumed at dinner in comparison with the other non-MCT-containing meals, indicating that MCT have a higher satiation power than other fats and carbohydrates. This increased satiety may also be due to greater fat oxidation after the MCT lunches. Krotkiewski (2001), demonstrated a similar decrease in hunger feelings and increase in satiety with MCT intake, related to a higher concentration of plasma ketone bodies and lower nitrogen excretion. These differences were observed during the first 2 weeks of treatment and then gradually declined during the third and fourth weeks. However, it is important to note that the increase of ketone bodies paralleled the intensity of hunger feelings, demonstrating that beta-oxidation may lead to increased satiety. These effects gradually declined, indicating subsequent metabolic adaptation, as was demonstrated in studies of MCT-related EE (Krotkiewski, 2001). Long-term effects of a diet rich in MCT or LCT on subjective appetite and ad libitum energy intake were compared in 24 men by St-Onge and Jones (2003) and St-Onge et al. (2003b). There was a trend towards decreased appetite and ad libitum energy intake during MCT compared with LCT consumption. Correspondingly, the average fat oxidation tended to be greater with MCT compared with LCT intake on day 2, but not on day 28. Conversely, Bendixen et al. (2002) observed no differences in fat oxidation, appetite, or ad libitum energy intake after intake of any one of three randomly provided, modified MCT-rich meals. The contradictory results between the studies may be due to different study lengths - one meal versus several days. The initial accumulation of ketone bodies may produce increased satiety, but there may be no further satiating effects when the body adapts to the higher levels of ketone bodies. Further research is required to confirm the short- and long-term appetite-suppressing effects of MCT supplementation in relation to beta-oxidation.
Although MCT have been shown to induce satiety and stimulate hormone secretion, no single hormone has been clearly associated with MCT digestion. Therefore, the exact mechanism for the satiating effects of MCT is unknown, but may possibly be explained by the distinct energy density of MCT or the increase in fat oxidation that they promote.
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