Like blue-blocking glasses, collagen peptides, “barefoot” running shoes, and other products some health-minded people can’t imagine life without, medium-chain triglycerides (MCTs) have spawned an entire industry that didn’t exist just a few short years ago. Considering the exploding popularity of these special fats, it’s a good idea to take a closer look at what they are, their purported effects, and whether research substantiates the considerable hype around them.

When people talk about MCTs, they’re usually referring to medium chain fatty acids (MCFAs). Specifically, MCFAs are saturated fatty acids with carbon chains containing between 6–12 carbon atoms. A triglyceride is a molecule composed of three fatty acids bound to one glycerol molecule. Common nomenclature is a little less precise, however, and most people simply say “MCTs” when talking about MCFAs. (See here for our recent primer on different types of fatty acids.) A triglyceride can contain fatty acids of varying chain lengths and degree of saturation. (For example, one triglyceride may contain one molecule each of oleic acid [18 carbons, monounsaturated], palmitic acid [16 carbons, saturated], and arachidonic acid [20 carbons, polyunsaturated]). Using modern technology, however, single triglyceride molecules can be manufactured that contain only MCFAs. Since “MCFAs” can be a mouthful, we’ll abide by convention and use MCTs, but for scientific accuracy it’s worth understanding the distinction between a fatty acid and a triglyceride.

As we explained in a recent post looking at the role of MCTs in supporting cognitive function, MCTs are metabolized differently than other fats. They don’t require emulsification with bile and are absorbed directly into the portal vein, rather than via the lymphatic system, and they’re hydrolyzed more quickly and more completely than longer chain fatty acids. They’re also more water-soluble than longer chain fats and exhibit mild electrolyte activity, with ionization at neutral pH, making them even more soluble in biological fluids. Additionally, MCTs can enter mitochondria without using the carnitine transport system, making them a readily usable source of energy.

As a general category, MCTs have a lot in common with each other, but their differing carbon chain lengths confer unique properties upon them which may have implications when using these special fats for therapeutic purposes. The shortest of these, caproic acid (C6), is found mostly in dairy products. Rich sources of the next two, caprylic acid (C8) and capric acid (C10), include coconut and palm kernel oils. Coconut oil is also very high in lauric acid (C12), as is palm fruit oil (different from palm kernel oil).

Commercially available MCT oil typically contains solely C8 or a blend of C8 and C10, mostly because C6 is a very small component of food sources it might be extracted from, whereas C8 and C10 are more abundant and may be more effective for certain purposes than C12. (Monolaurin, derived from C12, is antimicrobial, antifungal and antiviral, and is highly effective for supporting the immune system, but it is not ordinarily used in MCT oils although some products may include it.)

Interest in MCTs has grown in conjunction with the expanding popularity of ketogenic diets. This is because MCTs are readily converted to ketones even in people not following ketogenic diets, and while carbohydrate restriction is required for some of the beneficial effects seen from ketogenic diets (such as improved blood sugar and insulin levels), for select issues, the ketones themselves may confer a therapeutic effect.

Alzheimer’s disease is one such condition. Alzheimer’s stems from reduced brain glucose usage, and ketones can serve as an alternative neuronal fuel source. For people looking to bridge this brain “energy gap,” MCT consumption has been shown to lead to elevated plasma ketones and slight but promising improvements in cognitive function in individuals with mild cognitive impairment (MCI). Healthy subjects have been used to quantify differences between the ketone-producing effects of C8 and C10. C8 alone was shown to induce the highest plasma ketones for up to 8 hours compared to coconut oil, C10 alone, and a blend of C8 and C10. The blend and C10 alone raised ketones significantly compared to control conditions (no test oil), but C8 resulted in substantially higher plasma ketones (about 3 times higher than C10 alone), so people looking to employ MCTs specifically for the purpose of elevating ketone levels may wish to favor C8.

This doesn’t mean that C10 doesn’t have its place, though. In a study looking at the effects of C8 and C10 on energy metabolism in cultured human astrocytes, C10 promoted glycolysis and increased lactate formation, while C8 did not. Lactate can be exported and used as fuel by neurons, which may be helpful in Alzheimer’s and MCI. In contrast, C8 increased astrocyte ketogenesis, and of course, the ketones may be used by neighboring neurons, so both of these MCTs have a potentially helpful role in conditions associated with reduced or perturbed brain glucose metabolism, such as Alzheimer’s, multiple sclerosis, and Parkinson’s disease.

Another condition for which MCTs may be beneficial is Huntington’s disease (HD). A very specific MCT—heptanoic acid—appears to be instrumental here. Heptanoic acid (C7) is unique in that it’s an odd-chain fatty acid and is metabolized into 5-carbon ketone bodies, as opposed to C6, C8, C10 and C12, which all have an even number of carbon atoms and are metabolized to 4-carbon ketones (acetoacetate and beta-hydroxybutyrate). Unlike the 4-carbon ketones, as opposed to being oxidized for fuel, 5-carbon ketones are anaplerotic and can provide intermediates for the Krebs cycle. Either way, they can contribute to energy metabolism, which is critical for the many conditions associated with impaired brain or neuronal energy. C7 is derived from castor bean oil, and as a medical therapy it is manufactured as triheptanoin, a triglyceride consisting exclusively of C7. Huntington’s is associated with brain energy deficit, and triheptanoin has been shown to make up for some of this energy gap. Oral administration of triheptanoin (1 g/kg body weight per day, divided in 3–4 doses during meals to reduce likelihood for GI Upset) for 1 month in patients with early stage HD resulted in increased brain ATP synthesis and small improvements in the Unified Huntington’s Disease Rating Scale (UHDRS).

Because they are digested, absorbed and metabolized so differently from other types of fats and confer an array of unique effects, MCTs may also have a role in decreasing the incidence and duration of major clinical manifestations of disorders of fatty acid oxidation or lipid absorption. This is an exciting area of research with the potential to yield very helpful findings with real-world clinical implications for patients living with complex and difficult-to-treat conditions.