Medium Chain Triglycerides (MCT): What are They and Should You Care?

First let's explain what are triglycerides, also sometimes called triacylglycerols. Triglycerides, as the name (tri) implies, contain three fatty acids attached to the 3-carbon alcohol, glycerol. Fatty acids come in all "shapes and sizes" and most forms are familiar to most people: saturated fatty acids, unsaturated fatty acids, trans-fats, omega-3 polyunsaturated fatty acids (PUFA), etc. Trans-fats are the worst for humans and their inclusion in foods is banned in the US and many other industrialized countries. Saturated fats are, for the most part, unhealthy, however, significant important physiological differences related to carbon atom number do exist for saturated fatty acids. The healthiest fatty acids are the unsaturated, in particular those of the PUFA family. Indeed, diets high in PUFA protect the heart and the blood vessels from disease, reduce unwanted inflammatory processes, reduce the potential for type 2 diabetes, and most important of all promote development of the fetal brain in utereo and during the early post-natal period.

Essentially 100% of fatty acids in animal tissues consist of an even number of carbon atoms because of the pathways for their synthesis in cells. Some plant-based fatty acids have an odd number of carbon atoms. With respect to size, fatty acids are categorized as short-chain (2-6 carbon atoms), medium-chain (6-12 carbon atoms), long-chain (12-22 carbon atoms), and very long-chain (22 or more carbon atoms).

Triglycerides are crucial components of dietary fats and are the storage form of fat in our adipose tissue (body fat). When consumed in the diet the fatty acids are released from the triglycerides through the action of enzymes released by the pancreas. When stored in adipose tissue the fatty acids are released from the triglycerides in response to energy needs, such as during fasting, and in response to stress. With respect to dietary fats, the bulk of our intake is in the form of triglycerides with the majority of that being triglycerides composed of long-chain fatty acids (abbreviated LCT). However, certain foods are enriched in triglycerides composed of medium-chain fatty acids (abbreviated MCT). The most significant sources of MCT are coconut oil and palm kernel oil. The fatty acids in the MCT of coconut oil are the 8-carbon saturated fatty acid called octanoic acid (commonly called caprylic acid) and the 12-carbon saturated fatty acid called lauric acid. I recently blogged about the beneficial fatty acids one should include in their diets:

Beneficial Dietary Oils: Fats Are Not Always Bad For You

The biochemical and physiological differences between dietary MCT and LCT are dramatic. I will only briefly review the biochemical differences so if you need more info read more in my website:

When LCT are consumed the fatty acids are removed while in the intestines by pancreatic enzymes. The fatty acids and the glycerol are taken up by the intestinal cells, the triglycerides are reformed and packaged into a lipid particle called a chylomicron. These particles are transferred to the lymphatic system and delivered to the blood up in the neck which bypasses the liver. These LCT are degraded within the blood and the majority of the fatty acids are taken up into adipose tissue and stored. When MCT are consumed the released fatty acids are transferred directly into the portal circulation (the large vessel carrying blood from the intestines to the liver) and rapidly taken up by the liver where they can be rapidly metabolized, either completely to CO2 and H2O or to the ketone precursor, acetyl-CoA (a 2-carbon compound).

So what, if any, is the health significance to this difference between dietary MCT and LCT? First and foremost, since the fatty acids in MCT are rapidly mobilized to the liver and there metabolized they do not contribute, to any significant extent to the pool of stored fatty acids in adipose tissue. Therefore, MCT do not contribute to obesity to the extent that LCT clearly contribute and thus, sources of MCT (such as extra virgin coconut oil) should be considered for the diets of overweight and obese individuals. Although, in general, saturated fatty acid consumption results in increased levels of blood cholesterol, medium-chain saturated fatty acids, such as lauric acid, have been shown to reduce the levels of so-called "bad" cholesterol, LDL (low density lipoprotein). In addition, the rapid metabolism of medium-chain fatty acids in the liver to the ketone body precursor acetyl-CoA, results in increased ketone body synthesis (ketogenesis) which has protective effects in the brain. In normal conditions fasting and starvation (resulting in lack of glucose intake and reduced synthesis in the body) lead to increased ketone body production as a means to make a fuel the brain can use to continue making the energy it needs. Disturbances in ketone body production are frequently seen in type 1 diabetics (diabetic ketoacidosis, DKA) which can lead to fatal outcomes. However, the level of ketogenesis when consuming MCT is much less dramatic than during a prolonged fast or as is seen in the case of DKA. The level of ketone body production in a diet containing MCT has been shown (in a small number of studies) to enhance cognitive function and is suggestive of a therapeutic role for MCT diets in the treatment of Alzheimer disease.

So what is the TAKE HOME: Eat more plant-derived fats, that are enriched in MCT such as coconut oil and palm kernel oils, in the preparation and cooking of your foods. The only downside to this recommendation is that these oils are, unfortunately, more expensive than say canola oil. I for one use coconut oil when I bake cookies and the flavor enhancement is substantial!!!

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