In a world where dietary supplements are purported to help with everything from improved sleep to better vision, MCT oil is often promoted as having many of the most desired health benefits. 

Once pushed primarily by bodybuilders and fringe fitness gurus, the supplement has become mainstream, today even wowing celebrities like Kourtney Kardashian, Alicia Vikander and Emma Stone.

Despite its newfound popularity, few of MCT oil's purported health benefits are rooted in science and others aren't supported at all. What's more, experts explain why the supplement isn't for everyone. 

What is MCT oil?

MCT stands for medium-chain triglycerides − dietary fats that occur naturally in food sources like coconut oil, palm oil, and some dairy products such as butter, cheese, yogurt, and cow's and goat's milk. In the case of MCT oil, such fatty acids are extracted from "coconut and palm kernel sources" and made into a clear liquid, explains Caroline Susie, RD, a registered dietician and national spokesperson for the Academy of Nutrition and Dietetics. 

One of the things that makes MCT oil unique is that its molecules are smaller than many other types of fats, making them easier to digest. "Most fats have a more complicated trek through the body," explains Jill Weisenberger, MS, RDN, a Virginia-based registered dietician and author of "Prediabetes: A Complete Guide." Unlike long-chain fatty acids, smaller ones can travel directly to the liver for processing. Because of this, "MCT oil can be used medically because the fats are small enough to be absorbed into the body," she says. 

People can obtain medium-chain triglycerides from the aforementioned food sources, but MCT oil is usually taken as a supplement in liquid or powder form and is often added to coffee, smoothies or even salad dressings.

It's also sometimes used as a topical application to help moisturize or hydrate dry skin. 

What does MCT oil do for a person?

The purported health benefits of MCT oil include improved cholesterol levels, reduced inflammation, increased athletic performance, better brain health and a decreased risk of diabetes − though supporting research for such claims is lacking.

MCT oil is probably most popular as a weight management tool because the oil has been connected to feelings of fullness and people eat less when they aren't hungry, but the science isn't robust on that point either. "Only small studies have shown very small benefits for weight management," says Weisenberger.

Another of MCT oil's studied benefits is as an energy booster, Susie explains. "And some research suggests MCT oil can also increase physical strength," she adds, "but again, more research is needed."

In short, the experts say there are few purported health benefits connected to MCT oil that are actually backed by scientific findings.

Who should not use MCT oil?

Still, including MCT oil in one's diet in small doses is considered safe, per the Cleveland Clinic, but only for healthy individuals. "MCT oils are not for everyone," says Weisenberger. 

She says it's best to avoid MCT oil supplementation for anyone who has a heart condition or for people with fatty liver disease because medium-chain triglycerides are still fats and MCT oil is very high in calories − about 120 calories in a single tablespoon. She adds that even for healthy people considering taking MCT oil, "it's always a good idea talk to your doctor before starting any supplements." 

What is the healthiest oil to cook with?Most have some benefits but these two might be best.