Updated: Oct 23, 2021
The trend of MCT (Multi-Chain Triglyceride) supplementation came about due to the advent of coconut oil supplementation. Since coconut oil is a rich source of commercial extraction for MCT. However, they are not one and the same. In addition, coconut oil has found rapid and rising integration into a number of food sources. Its popularity has a rather strong influence among Whole food proponents, namely Paleo and Ketogenic circles, which may have hastened the search for quality fat, especially the heart-healthy kind. One of its growing popularity has been its claim to aid in weight loss. However, there are conflicting studies linking MCT consumption negatively to impacting cardiovascular disease risk. However, these studies have focused mostly on only coconut oil, which is comprised of mostly Long Chain Fatty Acids (LCFA) at 39% and Lauric Acid at 47%. These two acids have to utilize chylomicrons for transport, which are then transported to the heart, the body, the liver, through systemic circulation.
Research surrounding MCT supplementation is diverse and extremely compelling. As someone who once worked with neuromuscular patients on an acute rehab neuromuscular floor, I'm especially intrigued by the results and subsequent approval by the FDA for caprylic acid, which is found in MCT oil, as a food supplement for symptomatic treatment of Alzheimer's. A discussion we will have to explore in detail some other time.
MCT's are mostly man-made and refer to the position of the aliphatic (hydrogen carbon compound) tail of 6–12 carbon atoms on a fatty acid.
MCT oil contains 100% Medium Chain Triglycerides. It is a concentrated source of MCTs and is made primarily of a combination of refined raw coconut and palm oil. MCT oils generally contain 50–80% caprylic acid (CH3 (CH2)6COOH) and 20–50% caproic acid (CH3(CH2)4COOH). Both are saturated fatty acids/carboxylic acids.
One of its main and popular, characteristics and claims, is that MCT oil assists with weight loss. This is largely due to how it is metabolized. It passively diffuses from the GI tract to the portal system, as opposed to that of long-chain fatty acids which diffuse into the lymphatic system through chylomicrons, a system that generally carries lymph in the direction of the heart. The portal system directs blood from the GI tract to the liver.
Medium Chain Triglyceride (MCTs) structure allows for it to be metabolized much quicker, easily digestible, and absorbed intact to the liver for energy; requiring less energy for absorption, usage, or even storage.
Therefore, energy is not expended, in order, for immediate energy usage. This is useful for athletes since MCT can be immediately processed much like carbohydrates, in that, it is readily available if needed.
Initially, much of the research conducted on MCT supplementation is/or was being done in animal models, namely mice. In 2016, a study conducted by researchers in China on obese mice directly looking at MCT supplementation yielded promising results and insights. The aim of the research was to study the effect of MCT supplementation on inflammation and insulin resistance related to metabolic diseases. The research was conducted on mice that had been fed for 12 weeks on 3 specialized high-fat diets to see if molecular manipulation is possible in addressing metabolic diseases.  The diets were: An AIN-76 rodent diet, an industry diet composed of a combination of proteins (sometimes in the form of casein), in this case, the fat is 5% corn oil. The second diet was a controlled high-fat diet with 17% lard and 3% corn oil. The third diet was an isocaloric (moderate carb/moderate fat) high-fat diet consisting of 17% MCT and 3% corn oil.
The research found that MCT supplementation had noticeable anti-inflammatory and anti-diabetic effects, noticeably suppressing inflammation and downregulating pro-inflammatory cytokines. The research also found comparably that the combination of High Fat with Carb diet increased glucose serum, whereas MCT supplementation did not contribute to body weight gain and/or accumulation of white adipose tissue.
Meanwhile, human studies related to MCT supplementation are still wrought with inconsistencies because many have solely been focused on the effects of coconut oil, rather than only MCT oil alone. In addition, other studies specifically focused on dietary fats have been around comparing sources of Long Chain-Fatty Acids especially related to Cardiac Health.  In addition, cohort and comparative studies looking at the effects of MCT supplementation have been rather small, less than 100 individuals.
However, a cohort and comparative study on human subjects comparing the effects of olive oil v MCT oil as part of a weight-loss diet examined the effects on metabolic risk profile has provided some interesting insight. This study consisted of thirty-one men and women, ages 19–50 years old, with body mass indexes (BMI) of 27–33 kg/m2. The study lasted 16-weeks as part of a weight loss program. About 12% of oil consumption was from the prescribed energy intakes in the form of muffins and liquid oil. 
In this study, 2 of the 3 subjects in the MCT oil group that had metabolic syndrome at baseline did not have metabolic syndrome at the endpoint. While 2 of the 6 subjects in the olive oil group that had metabolic syndrome at baseline no longer had metabolic syndrome at the endpoint. However, 1 person did develop metabolic syndrome in this group. While 4 subjects did not have any change in their metabolic syndrome status. 
This particular research was interesting since it compared Olive Oil which mostly consists of Monounsaturated Fatty Acids (MUFAs) and the composition consist of long-chain fatty acids of 12 to 20 carbon atoms. While MCT oil comprises mostly medium-chain fatty acids. This study and those similar to it, suggest that though MCT is saturated fat, it can still modulate inflammation and does not adversely affect metabolic profile as once suggested, and even cease metabolic syndrome as part of a weight-loss diet. Of course, there were limitations as mentioned, small sample size and a lack of control, in that, two different oil sources were being compared. However, the questions answered in this study proved compelling especially about the role of MCT oil, a saturated fat source, on metabolic markers associated with cardiovascular risk. This study even went one step further and analyzed its impact on metabolic damage specifically. Specific and larger studies looking directly at MCT oil supplementation are still needed.
Therefore, some research concerning MCT supplementation has concluded that some health benefits of MCT supplementation about 18 to 24 grams a day help to prevent high-fat induced metabolic diseases and high fat-induced insulin resistance by:
-reducing serum lipid levels (cholesterol levels)
-decrease body fat and hepatic lipid accumulation
-increasing fatty acid oxidation
The literature and also the biochemistry suggests that its best used in concert with diet and exercise since it can best be used as fuel.
For athletes, health-oriented athletes, especially those partaking in low-carbohydrate (less processed carb/grain sources) and high-fat diets (high in plant sterols and low on saturated fat sources), MCT supplementation may provide a healthy fat with immediate energy for training purposes.
While also not contributing adversely to cardiovascular risks associated with consumption of high fats as once commonly asserted in literature. We will discuss the topic further. However, by now, many of you know that not ALL FATS/OILS are created equal and essentially MCT oil supplementation has proven that point.
 Geng et al. (2016). Medium‑chain triglyceride ameliorates insulin resistance and inflammation in high fat diet‑induced obese mice. Springer-Verlag Berlin Heidelberg, 55:931–940.
 Neelakantan et al. (2020) The Effect of Coconut Oil Consumption on Cardiovascular Risk Factors. AHA-Circulation, 141 (10): 803-814.  St-Onge, Marie-Pierre et al. (2008). Medium Chain Triglyceride Oil Consumption as Part of a Weight Loss Diet Does Not Lead to an Adverse Metabolic Profile When Compared to Olive Oil. J Am Coll Nutr., 27(5): 547–552.