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My Experience With MCT Oil: Benefits vs. Side Effects

MCT oil side effects

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I originally wrote this post to highlight side effects of MCT oil that weren’t frequently discussed in other forums. Reading this post will give you all of that information, as well as the reasons some people may benefit from taking MCT oil, even if smaller doses is all they can handle.

For those of you who aren’t yet familiar, MCT oil stands for “medium chain triglycerides.” It is a form of fat that your body can use right away.

Because we believe the side effects are perhaps a tad underreported, we will start there.

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. I believe that vegetable oils may be even worse for some people than diets high in saturated fat, or at least they play to a draw. That was the key takeaway of the Minnesota Coronary Survey, a study oft quoted by Nina Teicholz of The Big Fat Surprise (View on Amazon) 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.


Hyper responders and MCT Oil

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 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 to decide what level you are comfortable having your LDL rise to.

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 Vitamin D Side Effects

One side effect I developed when taking high doses of Vitamin D alongside MCT oil was heart palpitations. I now realize this could have been caused by the increase in calcium circulating in my blood on high doses of Vitamin D. The bioactive form of Vitamin D is called calcitriol, which helps your body absorb and use calcium.2 Some VDR genotypes will absorb a greater amount of calcium from taking Vitamin D and since Vitamin D is fat soluble, MCT oil will up-regulate the absorption process. A ton of calcium in the blood isn’t a good thing which is why many Vitamin D supplements like Thorne’s (View on Amazon) are paired with Vitamin K2, which helps to absorb the calcium.

In light of my VDR genotype, I try not to take vitamin D supplements alongside MCT oil. Aaron and I came up with a genetic hypothesis linking variants in the VDR genes to MCT oil sensitivity. Those of us with VDR “mutations” may want to avoid the combination of high IU doses of vitamin D with MCT oil, as the combo may increase serum calcium levels to uncomfortable levels. This is a theory we’re advancing based on our research, it is not yet proven. We lay out the details of that theory in this post titled VDR Fok1, Vitamin D, Fat and 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.

It’s also important to have an idea of how your body will react to saturated fat from a lipid standpoint. New studies are teaching us that based on variability in LDL receptor activity due to mutations in genes like PCSK9, people respond very differently to high fat diets.

I now find that I tolerate MCTs quite well at lower doses and when I use on a very occasional basis. It is usually after multiple days of use that I get the worst side effects.

I currently take MCT oil in the form of Dave Asprey’s “Brain Octane” oil (View on Amazon) in low doses a few times a month for an energy boost. Taking it more often seems to increase my lipids to levels I don’t like, so this is a very occasional supplement for me.

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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?


You can confirm using at home testing (View on Amazon).

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 one of the best known exogenous ketone sources since your body can use it as a quick source of fat energy.

For more on ketosis, see our first podcast episode titled – Ketogenic Diets: the Good, the Bad and the Genetic

Best MCT Oil for Ketosis

The MCT oil I used originally was comprised of 55% caprylic acid, 36% capric acid, and only 0.2% lauric acid.

Initially, I saw the power of MCT oil and loved the benefits. However, the product I used was lower on caprylic acid, which is the important ingredient for ketosis.3 To this end, the best MCT oil for ketone production are the products that have higher amounts of caprylic acid or C8.

If you want an MCT oil that will produce the most ketone “bang for your buck,” look to Bullet Proof’s Brain Octane Oil (View on Amazon), which is almost all caprylic acid. Note that this is not the case for Bulletproof XCT oil.

My experience: Small doses of MCTs, even 1-2 teaspoons, gave me a significant increase in brain function, and a burst of energy. This was due to the uptake of ketones as a fat fuel source.

I normally function at a fairly high level cognitively, but the MCTs gave me an “edge” that allowed me to maintain focus for longer periods of time.

My brain felt razor sharp when MCT’s hit me right.

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.

Sports Research MCT Oil (View on Amazon) comprises about 33% lauric acid, and reduced caprylic acid, so it’s not the go-to MCT oil for energy, but it may have added antimicrobial benefits. 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.

John O'Connor

John O'Connor is the founder of Gene Food, host of the Gene Food Podcast and a health coach trained at Duke's Integrative Medicine Program. Read his full bio here.

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