Medium-chain triglycerides (MCTs) are the saturated fatty acids that contain 6-12 carbon atoms (caproic acid C6, caprylic acid C8, capric acid C10, and lauric acid C12) — they are found in high concentrations in the coconut oil (approximately 50-60% MCT), in the palm kernel oil (approximately 50-60% MCT), and in the dairy fat (approximately 10-15% MCT). The MCTs are unique among the dietary fats because they are absorbed directly from the intestine into the portal vein (without the need for the bile acids or for the formation of the chylomicrons), they are transported directly to the liver (without the chylomicron transport through the lymphatic system), and they are rapidly oxidised in the liver (where they are either used for the energy production through the beta-oxidation or converted to the ketone bodies). This unique metabolic pathway of the MCTs makes them the preferred fuel for the liver and for the ketogenesis — and it explains why the MCT supplementation has been shown to improve the energy metabolism, to increase the ketone production, to enhance the cognitive function, and to support the weight management. Without adequate MCTs and their unique metabolic effects, the liver relies on the long-chain triglycerides (which are the dominant dietary fat and which require the bile acids and the chylomicron formation for the absorption and the transport), the ketone production is reduced, and the cognitive function declines — the hallmark of the MCT deficiency and of the impaired ketogenesis.
MCTs and the Ketone Production
The ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone) are the water-soluble energy substrates that are produced by the liver from the fatty acid beta-oxidation during the periods of the fasting, of the carbohydrate restriction (ketogenic diet), or of the intense exercise — when the glucose availability is limited and the liver must rely on the fatty acid oxidation for the energy production. The ketone bodies are not just the byproduct of the fasting metabolism — they are the essential fuel for the brain (which cannot use the fatty acids directly because they do not cross the blood-brain barrier), for the heart (which prefers the ketone bodies over the glucose for the energy production), and for the skeletal muscle (which uses the ketone bodies during the prolonged exercise). The MCTs are the preferred substrate for the ketogenesis because they are rapidly oxidised in the liver and because they generate the acetyl-CoA at a faster rate than the long-chain fatty acids — making them the most efficient dietary stimulus for the ketone production. The C8 (caprylic acid) and the C10 (capric acid) MCTs are the most ketogenic MCT species, and they are the primary components of the MCT oil supplements that are used for the ketogenic diet, for the cognitive enhancement, and for the therapeutic ketosis.
The clinical importance of the MCTs for the cognitive function is underscored by the observation that the MCT supplementation improves the cognitive function in people with the cognitive impairment and in the healthy older adults. A study in 20 subjects with the Alzheimer’s disease found that the MCT supplementation at 20g daily (as C8 MCT oil) for 3 months significantly improved the cognitive scores (as measured by the ADAS-Cog and the MMSE) in the subjects who were APOE4 negative — suggesting that the MCTs may be a useful adjunctive therapy for the cognitive impairment and for the early Alzheimer’s disease.
Practical Application
For general MCT supplementation for the energy support, for the ketogenic diet, and for the cognitive enhancement, the evidence-based approach is to supplement with 15-30g of MCT oil daily (as the C8 and C10 MCT oil, which are the most ketogenic species). The MCT oil should be started at the low dose (5g daily) and titrated gradually to the therapeutic dose (to minimise the gastrointestinal side effects of the rapid fat absorption — nausea, cramping, diarrhoea). The MCT oil should be taken with the meals (to enhance the absorption and to reduce the gastrointestinal side effects), and it should not be used in the pure form for cooking (because the MCTs are volatile and can be destroyed by the high heat). For comprehensive ketogenic diet and cognitive support, MCTs pair well with the omega-3 fatty acids (which provide the essential fatty acids and which have complementary effects on the brain function), with the exogenous ketone salts (which provide the exogenous ketone bodies and which work synergistically with the MCTs for the ketogenesis), with the magnesium (which is a cofactor for many of the enzymes of the energy metabolism), and with the caffeine (which enhances the ketone production and the cognitive function through the activation of the sympathetic nervous system).
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