MCT oil: what it is and how it works

MCT oil became popular thanks to the ketogenic diet, "butter coffee," and products for athletes. It is called a "fast fat" that the body uses almost like carbohydrates. The editorial team explains what medium-chain triglycerides are, how they differ from ordinary fats, and which properties are backed by science.

What MCTs are

MCT (medium-chain triglycerides) are triglycerides in which fatty acids with a chain length of 6 to 12 carbon atoms are attached to glycerol. For comparison: most fats in an ordinary diet — olive oil, sunflower oil, butter, meat — consist mainly of long-chain fatty acids with 16–18 carbon atoms.

The medium-chain group includes caproic (C6), caprylic (C8), capric (C10) and lauric (C12) acids. Commercial MCT oils are based on C8 and C10, because these are the ones whose metabolism differs most characteristically from long-chain fats. C6 has an unpleasant smell and irritates the throat, so it is usually removed.

The status of lauric acid (C12) is debated. Formally it is medium-chain, but in terms of absorption it largely behaves like a long-chain acid: a significant part of it is incorporated into chylomicrons and enters the lymph. That is why many researchers do not consider C12 a "true" MCT from a metabolic standpoint.

MCT oil is produced by fractionating coconut or palm-kernel oil: the required fatty acids are isolated from them and re-esterified with glycerol. The resulting product is a clear liquid with no pronounced taste that does not solidify in the refrigerator.

MCT oil and coconut oil: not the same thing

You often hear that coconut oil is a "natural source of MCTs." Formally that is true, but its composition differs substantially from commercial MCT oil. The largest share of fatty acids in coconut oil is lauric acid, while C8 and C10 together make up only a comparatively small part.

This has practical consequences. A study by Vandenberghe and colleagues (2017) compared the ketogenic effect of different oils and showed that pure tricaprylin oil (C8) raises blood ketone levels far more strongly than coconut oil or blends with a larger share of C10 and C12.

Coconut oil also contains a significant amount of saturated fats, which affect LDL cholesterol levels. Therefore it is incorrect to transfer MCT research data to coconut oil — these are different products with different effects.

On an MCT oil label it is worth looking for the ratio of C8 to C10. Markings such as "C8/C10 60/40" or "100% C8" give an idea of the composition and the expected effect.

How MCTs are absorbed and oxidized

The key difference between MCTs and ordinary fats is the absorption route. In the intestine, long-chain fatty acids are packed into chylomicrons, enter the lymphatic system, and only then the blood. Medium-chain fatty acids are mostly absorbed directly into the blood of the portal vein and travel to the liver (Bach, Babayan, 1982).

The second difference is entry into the mitochondria. Long-chain fatty acids require the carnitine transport mechanism for this, which is tightly regulated. Medium-chain acids largely enter the mitochondria independently of it, so they are oxidized faster.

Because of these features, MCTs are deposited less in adipose tissue and are used more quickly as an energy source. They are also slightly less caloric than ordinary fats: roughly about 8.3 kcal per gram versus approximately 9 kcal for long-chain triglycerides.

At the same time, MCTs are still fat, and excess calories from any source contribute to weight gain. Faster oxidation does not make MCTs "calorie-free" or "fat-burning" in the literal sense.

MCTs and ketone bodies

Since a significant part of MCTs goes straight to the liver, their oxidation there produces a large amount of acetyl-CoA. Part of this acetyl-CoA is converted into ketone bodies — acetoacetate and beta-hydroxybutyrate. That is why MCTs are called ketogenic fats.

The ketogenic effect of MCTs depends on several factors: the composition of the oil (C8 yields more ketones than C10), the dose, whether the oil was taken on an empty stomach, and the overall carbohydrate content of the diet. Against the background of an ordinary diet, the rise in ketones is small and short-lived.

It is precisely the ketogenicity of MCTs that has historically been used in medicine: a modified ketogenic diet with MCTs allows people with epilepsy to consume more carbohydrates and protein than the classic keto diet while maintaining a therapeutic level of ketones. Such a diet is carried out only under medical supervision.

Compared with exogenous ketones, MCTs give a weaker but longer-lasting effect, since ketones are formed gradually. We write in detail about the comparison of these approaches in separate materials on ketone supplements.

Where MCTs are used

The medical use of MCTs has the longest history. They are used in clinical nutrition for fat malabsorption, diseases of the pancreas, liver, and lymphatic system, as well as in specialized formulas for premature infants. In such cases the advantage is precisely the independence from chylomicrons and bile.

In sports nutrition, MCTs have been studied as an additional energy source for endurance. The results turned out to be modest, and large doses caused gastrointestinal discomfort. More on this — in our article on the evidence base for MCTs in athletes.

• Clinical nutrition:malabsorption, diseases of the pancreas and liver, chylothorax.
• Ketogenic diets:the MCT variant for epilepsy, under a doctor's supervision.
• Sports nutrition:an experimental energy source, limited evidence base.
• Weight management:a moderate effect as part of a calorie-deficit diet.

For weight management, a meta-analysis by Mumme and Stonehouse (2015) showed that replacing part of long-chain fats with MCTs in the diet was associated with a small additional reduction in body weight. The effect is modest and appeared in the context of the overall diet, not because of the mere fact of adding the oil.

The most common side effects of MCTs are nausea, cramps, and diarrhea, especially when taken in large amounts on an empty stomach. That is why it is advised to start with small portions, gradually increasing the amount. People with liver diseases need a doctor's consultation.

Editorial conclusions

MCT oil is a fat with medium-chain fatty acids, mainly caprylic and capric, which is absorbed and oxidized differently from ordinary fats: faster, via the portal vein and liver, with partial formation of ketones.

MCT oil and coconut oil are different products. Coconut oil contains predominantly lauric acid and has a much weaker ketogenic effect, so transferring MCT data to it is incorrect.

The most proven use of MCTs is clinical nutrition. In sport and weight loss the effects exist, but they are moderate and depend on the dietary context.

We also recommend reading our materials "The benefits of MCT oil for athletes: the evidence base," "Exogenous ketones: what they are and how they work," and "What to combine exogenous ketones with."

References

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3. Vandenberghe C, St-Pierre V, Pierotti T, et al. Tricaprylin alone increases plasma ketone response more than coconut oil or other medium-chain triglycerides: an acute crossover study in healthy adults. Curr Dev Nutr. 2017;1(4):e000257.
4. Mumme K, Stonehouse W. Effects of medium-chain triglycerides on weight loss and body composition: a meta-analysis of randomized controlled trials. J Acad Nutr Diet. 2015;115(2):249–263.
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6. Puchalska P, Crawford PA. Multi-dimensional roles of ketone bodies in fuel metabolism, signaling, and therapeutics. Cell Metab. 2017;25(2):262–284.