Naturally occurring in coconut oil and palm kernel oil, medium chain triglycerides (MCTs) are a class of fatty acids that, like all triglycerides, consist of a glycerol backbone with three fatty acid molecules; in MCT's, though, the carbon chain is only 6-12 atoms long, far fewer than in its long-chain sibling. Because MCTs require significantly less energy for uptake and storage in the body than long-chain triglycerides yet still provide 8.3 calories/g, they make an appealing choice for athletes looking for an easy-to-digest and energy-dense fuel source.

Unlike long-chain triglycerides, MCTs do not require the presence of the amino acid Carnitine to transport them into the mitochondria, the energy-producing factories that lie within muscle cells. The result is more rapid conversion to a molecule called acetyl-CoA, which is a key intermediate involved in the production of energy. It is thought that these attributes could produce an ergogenic effect by boosting energy output and, by sparing carbohydrate, thereby enhancing endurance.

Athletes may benefit from increased energy levels and enhanced endurance during moderate- to high-intensity exercise. Animal data have indicated increased levels of metabolic enzymes along with significant improvements in exercise time to exhaustion with a diet containing 80 g MCT plus 20 g long-chain triglycerides (LCT)/ kg over 6 weeks.

Commercially available MCT supplements undergo a process called fractionation, which allows the MCT to be separated from other oils and concentrated, making the total content greater than what is naturally found in coconut oil or palm kernel oil. MCTs are also available in several medical food products, generally for use in a clinical setting. Taking 1 tbsp (20 g) of pure MCT, or 5 tsp of coconut oil, 1-3 times daily with food is the current research-supported supplementation protocol.

In one study of endurance-trained cyclists, MCT supplementation produced gastrointestinal distress, primarily intestinal cramping, in half the subjects. Additional reported symptoms include diarrhea, nausea, vomiting, and irritability. Most symptoms occur when 80 or more g (equivalent to 4+ tbsp) of MCT are taken as a single dose. MCTs also contain over 100 calories/ tbsp, and thus consuming large amounts without making other dietary adjustments to achieve energy balance can lead to weight gain. Supplementation at doses of 18-24 g/day provides a boost to fat oxidation and aids overall weight and body-fat loss.