Triglycerides are biomolecules comprising of three fatty acids esterified to a glycerol back bone. Medium chain triglycerides (MCTs) are those triglycerides that contain fatty acids of carbon length from 6 to 12. Chain length not only determines the physical and chemical properties of fatty acids, but also plays an important role in absorption. Following ingestion, triglycerides pass to the upper small intestine, where they are digested to free fatty acids, glycerol and monoglycerides by the action of lipases. Bile acids are needed for the emulsification of triglycerides in this process. Long chain fatty acids (carbon length > 12) pass into the enterocytes, where they are re-esterified to form LCTs and packaged into chylomicrons. These chylomicrons then pass into the lymphatic circulation and enter the blood in the left subclavian vein.
MCTs differ in their digestion and absorption in that they do not require incorporation into a chylomicron. Instead, MCTs are absorbed into enterocytes as free fatty acids, where they pass into the portal system and are delivered directly to the liver (along with short chain fatty acids; < C6) (figure 1). The absorption and metabolism of these fatty acids is important in human nutrition because the differing pathways have implications for body weight maintenance, fat storage and energy production. Because LCTs pass into the circulatory system, they are susceptible to the action of hormone sensitive lipase, which can allow the long chain fatty acids to be deposited in adipose tissue. In contrast, MCTs avoid circulation and so can undergo oxidation in the liver producing an instant source of energy for liver cells.
Figure 1. Long and medium chain triglyceride absorption and metabolism1.
The fatty acids present in MCTs are caproic acid (C6), caprylic acid (C8), capric acid (C10) and lauric acid (C12). Coconut oil and palm oil are both high in MCTs. Therapeutically, MCTs are used in the treatment of hypercholesterolaemia and various absorption syndromes. However, research has indicated that in healthy individuals MCTs may have a use in weight loss. For example, research has shown that MCTs may increase thermogenesis is subjects who consume them, when compared to LCTs. This increase in energy expenditure is likely due to the increased oxidation of the medium chain fatty acids. Some evidence also suggests that diets high in MCTs increases satiety when compared to diets high in LCTs. These effects could make MCTs useful in weight control diets or in sports performance where the unique metabolism of MCTs may have beneficial effects.
RdB
