Medium Chain Triglycerides (MCTs) have been promoted to bodybuilders as a supplement to promote weight loss, and to endurance athletes as a supplement to enhance performance capacity. But is there scientific evidence to back either claim?

What are they?

They are a type of fat. Most of the fats in our diet are long chain triglycerides (LCTs). This means they contain long chain fatty acids, which are basically … well … long! In contrast, medium chain triglycerides (MCTs) contain shorter (i.e. medium length!) fatty acids. For those scientifically inclined: long chain fatty acids have over 12 carbons strung together in their backbone, whereas medium chain fatty acids have 6-10 carbons.

The shorter fatty acids chains make MCTs faster digesting and more soluble than other fats. This means that when we eat them they rapidly enter the blood and are delivered to tissue – including muscle – where they can be used as fuel to produce energy for work … which might include muscle contraction. Studies indicate that MCTs are available for use in tissue up to 250 times faster than LCTs!!

The only real natural sources of MCTs in the human diet are coconut oil and palm kernel oil; MCT supplements are made by extracting the medium chain fatty acids from these sources.

MCTs and Endurance Performance

Why would MCTs enhance endurance performance? The hypothesis was that because they can be rapidly delivered to muscle tissue and used to produce energy, taking them before or during endurance exercise might mean MCTs are used in fuel instead of carbohydrate. We fatigue as carbohydrates run out, and so if MCTs “spare” carbohydrates then we may be able to exercise for longer at higher capacity.

However, the research in humans doesn’t seem to support this hypothesis! Although some changes in fat metabolism have been observed when MCTs are consumed before or during endurance events, no consistent performance improvements have been observed to date – at least at the levels of MCTs that are tolerable … typically we can only consume around 30g before suffering gastro issues … not ideal in an endurance race!

MCTs and Weight Loss

So, what about weight loss? As MCTs are rapidly used to produce energy, they are not typically stored in the body as fat. They have also been shown to promote satiety, have fewer calories per gram (8.4 versus 9) and a slightly higher thermogenic effect (calories used by our bodies to use them!) than LCTs. So, it was hypothesised they may promote weight loss, if they replace LCTs in the diet gram for gram.

There is some evidence to suggest this could be the case, however further research is needed. Moreover, it is questionable how feasible it would be to replace the LCTs in the diet with MCTs considering they are found in so few foods. They certainly are unlikely to promote weight loss if eaten on top of a normal diet … in this instance they will just contribute further calories to the diet!

In summary …

To date, the evidence does not support taking MCTs for endurance performance or weight loss! To read more on MCTs and other fat based supplements, Jeukendrup and Aldred have published a great review:

Jeukendrup, A., Aldred, S. Fat supplementation, health, and endurance performance. Nutrition. 20:678-688, 2004.