Triglycerides are composed of a glycerol backbone with three free fatty acids attached. In the case of medium-chain triglycerides (MCTs) these fatty acids are made up of a mixture of C6 to C12 medium-chain fatty acids. Unlike long-chain triglycerides, the MCTs are liquid at room temperature and are relatively soluble in water.
For example, the water solubility of a C8 saturated fatty acid is 68 mg/100 mL at 20°C versus 0.72 mg/100 mL for a C16 saturated fatty acid. Also, as discussed above, long-chain fatty acids require the carnitine transport system to enter the mitochondria. Medium-chain fatty acids (MCFAs) cross the mitochondrial membrane rapidly through a diffusion process 190 and therefore can be oxidized into CO2 at a faster rate than long-chain fatty acids.
The liver is capable of producing ten times more CO2 from a C8:0 fatty acid than from a C16:0 fatty acid. However, when MCTs are consumed, there is an increase in ketone body production. Because of the increased rate of oxidation of MCFA, there is an excess of acetyl-CoA, and Krebs cycle intermediates will be in short supply, resulting in a large part of the MCFA being directed toward ketone body production.
The reason MCTs have been used in the treatment of obesity is of interest because the research does not necessarily support its use as a weight-loss product, especially in humans. Furthermore, a mechanism as to why fat intake would result in fat loss has not been provided.
Several studies have investigated the potential use of MCTs in weight reduction. However, the results are equivocal and many of them have not reported a significant effect from MCT supplementation. One possible mechanism by which MCT may function is throughenhanced thermogenesis induced by MCT. However, this study has only appeared in abstract form and has not been verified.
Of the few human studies to be conducted that have investigated the use of MCTs as a fat-loss supplement, none have reported a significant effect. These studies have primarily used obese subjects on a restricted caloric intake (500 to 1200 calories per day). One study, however, reported that MCTs decreased food intake during the day when the MCT was consumed with breakfast. In general, the results of these studies have failed to provide any evidence in favor of MCTs providing any benefit during dieting. For example, one study reported that obese women consuming a 550-kcal diet containing 30 g of MCTs lost the same amount of weight as when MCTs were replaced by sugars.
Safety and Toxicity
For some populations, there is some concern regarding MCT supplementation. MCTs are ketogenic in the normal individual and even more so in a diabetic. A ketogenic state (ketosis) can result in acidosis. In this condition, homeostasis is compromised, leading to dehydration, hypovolemia, and hypotension caused by an increase in Na+ and K+ excretion in the urine. Furthermore, the acidosis and dehydration can lead to a state of unconsciousness, and in severe cases, coma. For the normal, healthy individual, there appears to be no risk in consuming MCTs.