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Supplementing With MCT Oil: Benefits vs. Side Effects

Genes Mentioned

MST Oil supplements are popular in many circles, but what is the evidence for and against using this “healthy fat?”

MCT Oil Side Effects

MCT Oil Can Raise “Bad Cholesterol”

As we discuss as part of our core message at Gene Food, no two people respond in exactly the same way to food, saturated fat included. Much of the evidence for the “new thinking” on saturated fat centers around comparisons of a diet high in saturated fat vs. a diet high in vegetable oils. For example, the Minnesota Coronary Survey, a study oft quoted by Nina Teicholz of The Big Fat Surprise fame. 1 A diet that was 10% lower in saturated fat and about 10% higher in polyunsaturated fat was shown to have no meaningful difference for cardiovascular disease on a group of institutionalized men and women in a mental hospital.

The findings of this study, and others like it, have more to offer on the dangers of vegetable oil than they do the benefits of saturated fat. The Minnesota Coronary Survey does not make it safe for all of us to consume a diet that is very high in saturated fat.


Because, as we learn from the Retterstøl study, the variability in response to a diet high in saturated fat is tremendous. Some will see no difference in their levels of “bad cholesterol,” others will see massive spikes. The people who see the big increases are known as “hyper responders,” meaning they see a large uptick in LDL-C when eating a lot of fat. The low carb and paleo diet world loves to deny the causal role of LDL in heart disease, and it is true that it takes more than just LDL to cause cardiovascular health to decline, however, in our view here at Gene Food, the weight of the evidence is not on their side.

Bottom line is heavy use of MCT oil can increase levels of bad cholesterol in some people. That is a known side effect. From there, it’s up to you and your doctor to decide where you would like to see LDL levels stay for optimal health.

Wondering whether you’re more likely to be a hyper responder? Check out our custom nutrition plan product. We use response to saturated fat as one of the ways we categorize customers into their unique diet type.

MCT Oil and heart palpitations

Many people who take MCT oil experience heart palpitations.

MCT Oil and Upset Stomach

This is a really common side effect of MCT oil, probably the most common. It’s well known that if you take too much, the “disaster pants” kick in resulting in diarrhea and unwanted trips to the bathroom.

Forum Accounts of MCT Oil Side Effects

When you start digging around online, you come across a number of forum discussions with people reporting some of the issues with MCT use that I experienced. I’ve included links below.

Man reporting MCT oil caused heart palpitations

Man reporting heart racing after upping coconut oil intake and after supplementing with MCT oil

Man reporting heart palpitations after drinking Bullet Proof coffee and going on high fat diet 

Overcoming MCT Oil Side Effects

It could be that some people do best staggering use of MCTs to once or twice a week to get benefits on those days, but avoid regular use so as not to trigger the side effects that come as making MCTs part of your daily routine. As with anything else, proper dosing is key.

Some find that they tolerate MCTs quite well at lower doses and when they use on a very occasional basis (twice a year). It is usually after multiple days of use that the worst side effects kick in.

Not sure what to eat?

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What are the benefits of MCT oil?

Ok, so I began with the downside. Now on to the benefits I have seen from using MCT oil on rare occasions.

MCT Oil and Ketones

Will MCT oil get you into ketosis?


MCT oil is a precursor to Beta-hydroxybutyrate, a “ketone” or fat molecule the body can use for energy. 3 There are two places you can get ketones from – you can eat them in supplement form or you can get them when your body burns its own fat stores. Supplemental ketones are known as “exogenous” ketones whereas fat you burn for energy produces “endogenous” ketones. MCT oil is popular for those following ketogenic diets and one of the best known exogenous ketone sources since your body can use it as a quick source of fat energy.

See also: The best MCT oil for ketosis

MCT as an Antimicrobial Agent

There is some evidence that MCT oil can act as an anti-fungal and anti-microbial agent.

Some studies have shown the lauric acid found in coconut oil inhibited the growth of Clostridium bacteria, a major cause of antibiotic associated diarrhea.4

Others have found the medium chain fatty acids found in MCT oil were effective at killing multiple harmful pathogenic bacteria strains.5

Best MCT Oil for Killing Bacteria and Fungal Pathogens

It is important to keep in mind that most MCT oil has the lauric acid removed, since lauric acid doesn’t function as an immediate energy source like caprlyic or capric acid does. If your goal is the antimicrobial activity of lauric acid, it’s better to just take a spoonful of coconut oil rather than resorting to MCTs.

Capric acid is a known anti-fungal agent, and has shown the ability to kill Candida in vitro (in test tubes).5 In light of the antimicrobial and anti-fungal capabilities of capric and lauric acid, one of the causes of MCT oil side effects for some people could be an overload of toxins known as a “die off reaction.” Essentially, those with immune systems compromised by pathogens get flu like symptoms when the bad guys die off faster than their bodies can process the toxins.

Most of the research on the antimicrobial benefits of coconut oil have been focused on lauric acid and capric acid, rather than the ketone boosting caprylic acid.

MCT Oil and Brain Health

While I, and many others, experience a noticeable cognitive boost from supplementing with MCTs, what about the medical literature? Are there studies which back up this effect?

I couldn’t find many (if you have some good ones please share in the comments).

There is this study which looked at the ability of MCT oil to increase ketones levels in the brain of Alzheimer’s patients as a way to make up for impaired glucose metabolism.

The study found that MCT use doubled consumption of ketones in the brains of Alzheimer’s patients. For more on Alzheimer’s and diet, see this blog post.

Key Takeaways

MCT oil offers an immediate source of fat energy that can bring with it noted benefits such as a boost in mood and cognitive performance.

However, supplementing with MCT oil is not without side effects. In some people it may cause calcium levels to rise in the blood leading to heart palpitations and a racing feeling. In others, digestive distress will be an issue.

Dr. Aaron Gardner, BSc, MRes, PhD

Dr. Aaron Gardner, BSc, MRes, PhD is a life-scientist with a strong background in genetics and medical research, and the developing fields of personalized medicine and nutrition. Read his full bio here.

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  1. Allison says:

    Encephalitis survivor and trying to start a new eating and fitness plan

    Tried MCT oil looking for brain and fitness benefits as well help for controlling seizures

    Made we very sick feeling- like acid stomach, diarrhea etc etc
    Took 1T serving twice the first day—
    Will this go away ?
    Are there things to look for when purchasing
    Any and all comments are appreciated- this would be beneficial for me if I can take it

    • Thanks for the comment Allison. Always best to discuss side effects with your doctor. In terms of MCT oil being beneficial, it’s not clear to me why anyone would need to take MCT oil. MCT oil “benefits” are primarily driven by heavy marketing from companies that sell MCT oil. I would suggest checking out the work of Dr. Valter Longo.

      • Elizabeth Cornell says:

        I experienced an awful ‘die off’ of toxins I guess with only 1 tbl. lots of diarrhea. flu like symptoms like you mentioned in your article. does this mean I’m unhealthy? ugh. Staying away from it.

        • Elizabeth,

          Thank you for the comment. While it is definitely useful to have stories like yours, of severe MCT oil side effects, shared, we can’t say in a forum like this what the implications are. Best to take this issue to your doctor.

  2. Carol Sidofsky says:

    A few years ago, I started to try various Vitamin D3 (Chole-calciferol) oral supplements, for example by Thorne. The ingredients included ARTIFICIAL “MCT’s” (Medium Chain Triglycerides). I had awful side effects, no matter how much I diluted the ARTIFICIAL “MCT’s”. The side effects included RACING HEART, INSOMNIA, etc. I finally figured out that it was the ARTIFICIAL “MCT’s” that were causing my side effects. Then, I discovered that COCONUT OIL/FAT never gave me those awful side effects, even though coconut oil/fat is a NATURAL/GOOD source of MCT’s (Medium Chain Triglycerides). So, my advice is to READ LABELS with a good MAGNIFYING GLASS, and avoid ARTIFICIALLY PRODUCED “MCT’s” (Medium Chain Triglycerides), and instead, get your MCT’s NATURALLY, from Coconut products or any other natural products. Sincerely, Carol Sidofsky (77 and hanging in there): [email protected]

  3. Randy says:

    Bought nutiva MCT oil from Costco, took 1 tbsp straight up two days ago noticed slight upset stomach nothing serious. Today put 1 tbsp in my coffee felt fine all day but earlier this evening my stomach started gurgling. I was watching TV and all of a sudden was overheating to the point where I had to take my shirt off. Went to bed started with bad gas then ran to the bathroom, went back to bed and felt heart palpitations and anxiousness, got up to drink some water. Googled “MCT upset stomach”and came across this forum, previous search’s just showed beneficial effects so this is interesting. Will keep researching.

    • sarah says:

      Randy, almost the same thing happening with me. It was my first time using it and it upset my stomach greatly. Also, I felt like I was having an anxiety attack. Not fun!

      • Donna says:

        My husband and I have been taking at least a tbsp in our coffees daily for 3 years. (we put a squirt with every coffee and guess that we get 1 tbsp total). We are usually on low carb or in ketosis.When we first began it upset our stomachs. It definitely makes us more alert and faster mor thorough in our thinking. Now I have tested very high for my B12 levels over the last 3 years. All my other blood work is good. I am 64 this is highly unusual. Any ideas?

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