Ketosis Part V: Medium-Chain Triglycerides

We have covered a lot of ground so far in looking over the literature on ketosis and ketogenesis.  We have seen what ketone bodies our body actually uses, and how they are regulated on many levels.

We already know that a high-fat diet is a great way to induce ketogenesis.  However a question many of you may be asking is “Do all fats have the same ketogenic potential?”  Well, the answer to that is no, some fats are better at inducing ketogenesis than others.  The most ketogenic fats we have are the medium-chain fats.

We consume many different kinds of fats, and all these fats vary in two different ways, chain length and saturation.  Saturation refers to the number of double bonds a fatty acid chain has, with no double bonds being a saturated fat, and one or more double bonds being an unsaturated fat.  The medium-chain fatty acids we will talk about here are all saturated fatty acids.  They are called medium-chain because they have between 6 and 12 carbons in their chain (1).  Here are a couple of diagrams of some of these medium-chain fats.

Caproic/Hexanoic Acid

Caprylic/Octanoic Acid

Lauric/Dodecanoic Acid

We usually refer to these as medium-chain triglycerides, because we usually encounter them in the triglyceride state, which just means we have three of the above fatty acid chains connected to a glycerol molecule to keep them together.

What makes these fats so ketogenic?  Well it all comes down to the special properties they have based on chain length and saturation.

Absorption and Liver processing

Medium-chain triglycerides (MCTs) are preferentially dealt with by pancreatic lipases in our small intestines (2).   This means that they will be broken down into individual medium-chain fatty acids (MCFAs) first, which is the state they need to be in to be absorbed.  Not only are they preferentially broken down, but also they are absorbed into the portal vein and transported straight to the liver.  This is in direct contrast with other fats, as they are absorbed by the lymphatic system and travel through the periphery before reaching the liver.  This has the distinct of advantage of making MCTs unable to be stored by adipose tissue, since they never encounter the tissue.

Once in the liver MCFAs are able to cross the mitochondrial membrane without the need for a special transport molecule.  Once inside of the mitochondria, their even number chain lengths facilitate their rapid breakdown into acetyl-CoAs (2). As we have seen time and time again, the production of acetyl-CoA is absolutely necessary for ketogenesis.  These new acetyl-CoAs are mainly destined to become ketone bodies, however as with all ketone body generation it is still dependent on low levels of oxaloacetate, as we can see from this abstract (3). 

So, as we can see from our biochemistry, MCTs are easily turned into ketone bodies by our liver and then sent out to the periphery for use.  While other fats can be turned into ketone bodies, none of them have the unique characteristics that MCTs do that make them ideal for ketone body creation. 

I found one nice study that discusses a lot of the questions still out there about MCTs, like how ketogenic are they alone, and when eaten with other foods, especially glucose.  The first experiment gave rats either 10mL/kg body weight MCT oil or corn oil, and looked at their ketone levels (4). Rats in the MCT oil group had ketone body levels that increased by as much as 22 fold over 4 hours after treatment.  Also the treatment with MCTs was shown to increase ketone levels in as little as 30 minutes after treatment.  However, the rats given the corn oil only managed to increase ketone body levels 2 fold over the same time period.  With this data alone we can see the ketogenic power of MCTs. 

Now how about what happens when you give these same rats some glucose with these fat treatments? In the next experiment from the same paper the authors gave 3.75g/kg body weight glucose to the rats, in addition to 5mL/kg body weight MCT or corn oil. 

We can see from this graph that while we do get a significant amount of total ketone body production, we get nowhere near the 22 fold increase we saw with just the MCT treatment. However, I think this level still constitutes a ketosis state.

Summary

Well I think that was pretty much all I wanted to cover with MCTs and ketosis.  We can see through the biochemistry that MCFAs are ideal for producing ketones in liver mitochondria.  This is because they are preferentially sent to the liver through the portal vein, they readily cross the mitochondrial membrane, and are easily broken into acetyl-CoA since they are even numbered chains.  Also, we have seen just how ketogenic MCTs are, and can increase ketone body levels up to 22 fold in rats.  Also, they are still able to induce ketosis when glucose is present, which is something we have not seen with the other ways we know to enter ketosis.

We will wrap up this series next time with how ketogenic diets can be therapeutic, and in what cases.  Then, finally, we will end with my practical recommendations.