MCT oil: what it is and how it works

MCT oil became popular thanks to the ketogenic diet, “butter coffees,” 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 have confirmation in science.

What MCT are

MCT (medium-chain triglycerides) are fats 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 predominantly of long-chain fatty acids with 16–18 carbon atoms.

The medium-chain ones include caproic (C6), caprylic (C8), capric (C10), and lauric (C12) acids. Commercial MCT oils are based on C8 and C10, since it is precisely these that most characteristically differ from long-chain fats in metabolism. 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 features it largely behaves like a long-chain one: a significant part of it is incorporated into chylomicrons and enters the lymph. Therefore many researchers do not consider C12 a “true” MCT from a metabolic point of view.

MCT oil is produced by fractionating coconut or palm kernel oil: the necessary fatty acids are isolated from them and re-esterified with glycerol. The resulting product is a clear liquid without a pronounced taste that does not solidify in the refrigerator.

MCT oil and coconut oil: not the same thing

You can often hear that coconut oil is a “natural source of MCT.” Formally this is true, but its composition differs substantially from commercial MCT oil. The largest share of fatty acids in coconut oil is lauric acid, and C8 and C10 together account for only a comparatively small part.

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

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

On the MCT oil label it is worth looking for the ratio of C8 and C10. Designations like “C8/C10 60/40” or “100% C8” give an idea of the composition and expected effect.

How MCT are absorbed and oxidized

The key difference of MCT from ordinary fats is the absorption path. Long-chain fatty acids in the gut are packaged into chylomicrons, enter the lymphatic system, and only then the blood. Medium-chain fatty acids are mostly absorbed directly into the portal vein blood and head 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 ones largely penetrate the mitochondria independently of it, so they are oxidized faster.

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

At the same time, MCT are still fat, and an excess of calories from any source contributes to weight gain. Faster oxidation does not make MCT “calorie-free” or “fat-burning” in the direct sense.

MCT and ketone bodies

Since a significant part of MCT immediately enters the liver, their oxidation there yields a large amount of acetyl-CoA. Part of this acetyl-CoA is converted into ketone bodies — acetoacetate and beta-hydroxybutyrate. That is why MCT are called ketogenic fats.

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

It is precisely the ketogenicity of MCT that has historically been used in medicine: a modified ketogenic diet with MCT 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, MCT give a weaker but longer effect, since the ketones form gradually. We cover the comparison of these approaches in detail in separate materials on ketone supplements.

Where MCT are used

The medical use of MCT has the longest history. They are used in clinical nutrition for disorders of fat absorption, 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, MCT were studied as an additional energy source for endurance. The results turned out to be modest, and large doses caused gastrointestinal discomfort. More on this is in our article on the evidence base for MCT for athletes.

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

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

The most common side effects of MCT are nausea, cramps, diarrhea, especially when taking a large amount on an empty stomach. Therefore it is advised to start with small servings, 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, predominantly 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 MCT is clinical nutrition. In sport and weight loss the effects exist, but they are moderate and depend on the nutritional 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.
5. Jeukendrup AE, Aldred S. Fat supplementation, health, and endurance performance. Nutrition. 2004;20(7–8):678–688.
6. Puchalska P, Crawford PA. Multi-dimensional roles of ketone bodies in fuel metabolism, signaling, and therapeutics. Cell Metab. 2017;25(2):262–284.