By Cliff Harvey
Dietary medium chain triglycerides (MCTs) are a class of triglycerides in which two-to-three of the fatty acid chains attached to a glycerol backbone are medium in length. Medium-chain fatty acids (MCFAs) are fatty acids comprised of 6–12 carbons in chain. The MCTs are: caproic (C:6), caprylic (C:8), capric (C:10) and lauric acid (C:12) (1). So how do these particular fatty acids aid ketogenic and low carb high fat diets?
What is the difference between the long and medium chain Triglycerides?
Long-Chain Triglycerides (LCTs) are the most common dietary fats and include the majority of both saturated fatty acids (SFAs) and Monounsaturated Fatty Acids and Polyunsaturated Fatty Acids (MUFAs and PUFAs respectively). In digestion long chain fatty acids (LCFAs) associate with bile and phospholipids to enable diffusion into the cells of the intestinal epithelium. Once within this cell the fatty acids are resynthesized into triglycerides and bundled into chylomicrons (a lipoprotein transport molecule) for deposition into the lymphatic system before delivery via the vena cavae to the greater circulatory system.
Medium Chain Triglycerides do not require the same actions of bile nor standard micellar-chylomicron mediated absorption and transport as LCTs but instead are largely passively diffused into the hepatic portal vein for transport to the liver where they are preferentially converted to bio-available ketone bodies. Thus rates of cholecystokinin release and gastric motility (and thereby bile response) are dependent on fatty acid chain length (2).
The rates of diffusion into the hepatic portal vein appear to be inversely proportionate to the chain length of fatty acids. This has been demonstrated in studies comparing lymphatic vs portal deposition of fatty acids in rats in which lymphatic deposition of fatty acids at the following (mean) rates were observed: stearic acid C:18 = 91%, myristic acid C:14 = 74%, lauric acid C:12 = 36% and capric acid C:10 = 11% (3).
What does the research say?
Animal studies have also demonstrated the ketogenic effect of MCTs (4) and indicated an approximately nine-fold increase in ketone body production after ingestion of 10ml of MCT per kilogram of bodyweight versus an equivalent amount of LCT (from corn oil) (5). Because of this, dietary MCTs promote both ketonaemia and ketogenesis (increased availability and production of BOHB (and other ketone bodies) respectively) (6) and therefore may encourage a more rapid induction of functional ketosis.
So how do they promote ketosis?
Medium Chain Triglycerides (MCTs) promote ketonaemia and ketogenesis (increased availability and production of BOHB respectively) (6) and may encourage a more rapid induction of functional ketosis. MCTs encourage ketogenesis and nutritional ketosis, as evidenced by both the direct observations of increases in BOHB levels with application of MCTs and by the ability to induce ketosis with a lower fat intake if sufficient MCTs are provided. As mentioned earlier an absolute reduction of 20% calories of fat less (25% relative reduction) or around 60% of calories from MCT, results in nutritional ketosis if sufficient MCTs are included in the diet as compared to standard dietary fats, which are predominantly LCTs, in which around 80% of calories need to be ingested to adequately ensure ketogenesis at the required level to encourage nutritional ketosis. Additionally the substitution of LCTs with MCTs in the diet may provide a greater thermic effect, resulting in a net increase in calorie usage and thus may offer a benefit for weight-loss (7).
There is a dearth of research on a more moderate application of MCTs to a ketogenic diet. However a 2001 study published in the International Journal of Obesity and Related Disorders compared participants allocated to one of three very low calorie diets (VLCD) for two weeks, of approximately 578.5 calories, one including 29.7 MCT, one with 26.4 LCT (or 9g fat in a ‘low-fat’ group) per day. The MCT group exhibited greater weight-loss, higher proportion of fat loss and increased lean tissue retention, with reduced hunger and improved satiety (proportionate to increases in blood BOHB) (8). This suggests that a more moderate intake of MCT oil as a supplement (as compared to a substitutive macronutrient approach) may also moderately increase ketonaemia, ketogenesis and therefore by the increased earlier availability of the ubiquitous cellular fuel BOHB, serve to reduce symptoms associated with the induction of ketosis that may result in part from a reduced provision of glucose (by way of reduced dietary carbohydrate), and thereby improve clinical outcomes by encouraging greater compliance with a dietary strategy that has been clinically indicated to be of benefit for several conditions and for desired outcomes such as obesity.
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