What are MCTs?
MCTs are medium-chain triglycerides, mostly found in coconut oil and palm oil. Medium-chain triglycerides are smaller than long-chain fats, and it is believed that this property makes them more likely to be used for energy (via ketogenesis) than stored as fat. Another possibility is that MCTs might increase thermogenesis (body temperature), and this might contribute to weight loss.
What do studies show?
Preclinical (animal) studies have reported that MCTs can enhance satiety, reducing food intake. Studies in humans, however, have had mixed results.
A meta-analysis of 13 clinical trials, published in 2015, reported that “Replacement of LCTs with MCTs in the diet could potentially induce modest reductions in body weight and composition without adversely affecting lipid profiles” (Mumme 2015). The authors noted, though, that there were concerns about the quality of the studies and that more research was needed to determine long-term effects and optimal doses.
More recently, a clinical trial tested supplementation of MCT (20 grams a day) for obese women as part of a very low calories ketogenic diet (Vertrani 2023). The authors report that MCT supplementation enhanced weight loss over 45 days, as well as reduced levels of a biomarker of inflammation, C-reactive protein (CRP). This effect was bigger (somewhat) when the MCT supplementation began 5 days before beginning the diet.
So – overall, it does seem that MCT may be able to enhance weight loss, especially in the context of a very low-calorie diet. MCTs do seem to be safe.
My main concern is the same as for all weight loss regimens: in the absence of long-term follow-up data, it’s hard to know if the loss will be maintained. And unless issues with food habits or emotional meanings of food are addressed, it is most likely that the weight will come back, and maybe more.
How do they affect the gut?
Now, for the gut, I have anecdotal good news. We have a “GI kitty” who has suffered from what seems to be a feline version of cyclic vomiting disorder. She barfed multiple times daily and lost so much weight that she looked like a skeleton. It was suggested that we add some coconut oil to her food. After a week of coconut oil, her fur became softer and thicker, and her vomiting declined to the level of most cats (more often than we would like but not so concerning). And she gained back her weight.
So, in this case, the coconut oil helped with gaining weight rather than losing it, although I have no idea of the mechanism. It may simply be that the smallness of the fat allows it to be absorbed more easily by her disturbed gut.
References
Mumme K, Stonehouse W. Effects of medium-chain triglycerides on weight loss and body composition: A meta-analysis of randomized controlled trials. Journal of the Academy of Nutrition and Dietetics, 115:249-263, 2015
Vertrani C, Verde L, Savastano S, Colao A, Muscogiuri G, Barrea L. Supplementation with medium-chain fatty acids increases body weight loss during very low-calorie ketogenic diet: a retrospective analysis in a real-life setting. Translational Medicine, 21:29, 2023