What are MCTs?

Medium-chain triglycerides (MCTs) are types of fat, and they have been shown to have benefits to health and performance^{[1, 2]}. Triglycerides are the main constituents of fats and each triglyceride is made up of three fatty acids with a backbone of glycerol. The majority of fats found in our food are long-chain triglycerides (LCTs). MCTs are triglycerides where the fatty acids in their structure are 6 to 12 carbon atoms in length. There are four main fatty acids that makeup MCTs – known as medium-chain fatty acids (MCFAs) – and the number denotes their chain length:

• C6:0 Caproic acid
• C8:0 Caprylic acid
• C10:0 Capric acid
• C12:0 Lauric acid

Lauric acid is an interesting fatty acid as some information sources dispute it as an MCFA^[1]. However, because of the significant difference in its properties relative to longer-chain fatty acids, it fits better classed as an MCFA, in particular because nearly half of it is absorbed in the same way as other MCTs; also the mitochondrial metabolism of lauric acid doesn't rely on the carnitine-shuttle process as is the case with long-chain fatty acids (LCFAs)^[3].

MCTs are actually types of saturated fat; therefore they are not oxidised and also contribute to the saturated fat content of a food as labelled. This is despite not being treated like other saturated fats in the body^[4].

Digestion, absorption and metabolism of MCTs

As well as being structurally different to LCTs, MCTs are absorbed and metabolised in a different way and are treated more like an energy-dense carbohydrate source than a fat. Indeed, they are slightly less energy-dense than LCTs in that they provide approximately 8.3 kcal per gram compared to 9.0 kcal per gram. After digestion, MCTs are absorbed differently to other fats in that they passively cross the small intestine wall. LCTs, on the other hand, are absorbed into the lymphatic system. Also, MCTs do not require bile salts for digestion so humans find MCTs easier to digest and metabolise. The rate at which MCTs are absorbed is similar to that of glucose and faster than that of LCTs^[2].

Uses of MCTs

As you can see, MCTs are a very efficient and energy-dense nutrient, properties that allow MCTs to have numerous applications in clinical nutrition, sports nutrition and for general good health.

Athletes, especially long-distance runners and cyclists, often prefer to supplement with MCTs, including them as a significant contribution to calorie intake, especially in the run-up to an event. Often these athletes may even prioritise their intake of MCTs over additional carbs, as MCTs provide an equally efficient source of energy, but in a more concentrated form; i.e. you need less for a similar amount of energy (carbs provide 4 kcal per gram).

As MCFAs are metabolised differently to LCFAs, high levels of MCFAs do not produce energy through the typical metabolic processes following food intake. Instead, MCFAs – with the exception of lauric acid – are more likely to be used for ketogenesis^[1]. Ketogenesis is a metabolic state where ketone bodies are produced and is a survival mechanism where the brain and heart muscle use ketone bodies in order to keep functioning. A typical ketogenic diet is where an individual consumes a very low carb intake, a fairly low protein intake and a high fat intake and this leads to the body being in a ketotic state. However, MCFAs do not require the same physiological conditions for ketogenesis, which can occur even in the presence of a higher carbohydrate intake, so they are particularly useful for those wanting to follow a ketogenic diet.

MCTs in foods

MCTs are not that common in foods, but are found in small amounts in dairy fats like butter (about 8.3g per 100g) and some types of cheese (for example, Cheddar cheese is typically 1.9g per 100g), but the richest sources are coconut oil (about 58.7g per 100g) and palm kernel oil (about 54.2g per 100g).

References

1. Examine. Medium-chain triglycerides. Date Accessed: 19/08/15. [Available from: https://examine.com/supplements/mcts/].
2. Dean W, et al. NutritionReview. Medium Chain Trigylcerides (MCTs). Date Accessed: 19/08/15 [Available from: https://nutritionreview.org/2013/04/medium-chain-triglycerides-mcts/].
3. Dayrit FM. Lauric acid is a medium-chain fatty acid, coconut oil is a medium-chain triglyceride. 2014; 143:157-66.
4. Takeuchi H, et al. The application of medium-chain fatty acids: edible oil with a suppressing effect on body fat accumulation. Asia Pac J Clin Nutr. 2008; 17 Suppl 1:320-3.