What’s So Special About Medium-Chain Triglycerides (MCTs)?
Before diving into the what, the how, and the why on MCTs, let’s cover some background for better understanding. Ketosis is a natural metabolic state of the body defined by increases in the primary ketone body, beta-hydroxybutyrate (BHB), to levels above 0.5 mmol/L. At these raised levels, the body transitions away from using glucose for fuel and toward using ketones and free fatty acids for energy. Entering a state of ketosis can be achieved by fasting, calorie restriction, and/or consuming a ketogenic diet.1 BHB can also be elevated temporarily through supplementation by exogenous ketones1—which is a fancy way to say using ketone supplements. Today, exogenous ketones are commonly found on the market as ketone salts (ketone body bound to a mineral salt or amino acid) or ketone esters (ketone body bound to a ketogenic precursor via an ester bond).1
Interestingly, MCTs, even though not produced outside the body, act similarly to exogenous ketones in that they can help elevate blood ketone levels without restriction of carbohydrates and protein to the extent that the classical ketogenic diet (i.e. 4 parts fat to 1 part protein and carbohydrates) does.2 That is what makes them pretty special!
What are MCTs?
MCTs are fat molecules that contain a glycerol backbone attached to three medium-chain fatty acids that may be 6 carbons (C6 or caproic acid), 8 carbons (C8 or caprylic acid), 10 carbons (C10 or capric acid), or 12 carbons (C12 or lauric acid) in length. Based on taste, accessibility, and the way they are digested, the MCTs you find on the shelves of your health food store are predominantly C8 and C10. In addition, C8 is the most ketogenic of the MCTs, with C10 following close behind.3 However, C6 is known to cause digestive issues, and C12 is digested more like long-chain fatty acids.4 Long-chain fatty acids range from 14-22 carbons in length and are the predominant fatty acids found in the diet. Short-chain fatty acids are any fatty acid less than 6 carbons in length and are not commonly consumed in the diet; rather, they are primarily produced by the gut microbiome during the fermentation of insoluble fiber.5
Fun fact: One of the primary short-chain fatty acids produced in the gut is butyrate, a molecule that is structurally similar to the ketone body beta-hydroxybutyrate, and can contribute to ketogenesis.6 Learn more about fiber and the ketogenic diet here.
How are MCTs digested differently from other dietary fats?
The length of fatty acids dictates how the body digests and utilizes the fats consumed. Medium-chain fatty acids are unique in that they are absorbed directly into the bloodstream through the hepatic portal circulation and transported to the liver. A lot more work goes into the digestion of long-chain fatty acids, as they require pancreatic enzymes and bile acids for their breakdown, are further packaged into chylomicrons, and are finally delivered to the liver via lymphatic and vascular circulation to be oxidized for energy or stored in adipose tissue. Thus, MCTs are metabolized and utilized much more rapidly than other fatty acid types.3
MCTs to ketones—using MCTs with the ketogenic diet
In order to use fats for fuel, fatty acids must enter the mitochondria of our liver cells, since this is where the bulk of our cellular energy (ATP) is made. Normally, fatty acids require the help of L-carnitine for entry into the mitochondria; however, MCTs do not require L-carnitine, and as a result their entry into the mitochondria is much more rapid than other fatty acids. Inside the mitochondria, free fatty acids quickly generate acetyl-CoA via beta-oxidation, which go on to make what we are all after: ketone bodies! This rapid assimilation and conversion to ketones makes MCTs much more likely to be used as energy than to be stored as fat.
Due to their ketogenic properties, incorporating MCTs into the ketogenic diet can allow you to be more liberal with protein and nonsugar/nonstarch carbohydrates (e.g. fibrous vegetables) to sustain nutritional ketosis (i.e. BHB > 0.5 mM).
Figure 1. MCTs to Ketone Bodies: Medium-chain fatty acids can freely cross the inner mitochondrial membrane (compared with other types of fatty acids, which can enter in a more regulated manner). This more rapid absorption into the inner mitochondrial space quickly increases acetyl-CoA and ketone body formation.
MCFA=medium-chain fatty acids; OM=outer membrane; IM=inner membrane
Sources of MCTs
Whole-food sources of MCTs are found primarily in coconut oil and palm oil and small amounts in butter or ghee.7 However, they are only found in minute fractions, and the predominant type of MCT in all examples is lauric acid (C12).8 As mentioned previously, the ketogenic properties of MCTs are primarily in response to the smaller length C8 and C10 MCTs.9 This is where concentrated MCT oils and powders shine. Concentrated MCT oil and powder have become widely available as the popularity of this supplement has grown. These oils come from natural sources such as coconut and palm fruits, which adds to their appeal as being a natural supplement. There are many ways to consume MCTs, and in addition to their many benefits, they can even make foods taste more delicious!
Get ketogenic tips and more by visiting the Metagenics blog.
This content is not intended as a substitute for professional medical advice, diagnosis, or treatment. Individuals should always consult with their healthcare professional for advice on medical issues.
Resources:
- Evans M et al. J Physiol. 2017;595(9):2857-2871.
- Harvey CJDC et al. PeerJ. 2018;6:e4488.
- Cunnane S et al. Front Mol Neurosci. 2016;9:53.
- A C Bach et al. Am J Clin Nutr. 1982;36(5):950–962.
- Tan J et al. Advances in Immunology. 2014;121:91-119.
- St-Pierre V et al. J Functional Foods. 2017;32:170-275.
- Nagao K et al. Pharmacological Research. 2010;61:208-212.
- Kinsella R et al. Physiology & Behavior. 2017;179:422-426.
- Khabbush A et al. Epilepsia. 2017;58(8):1423-1429.
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