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My Experience With MCT Oil: Benefits vs. Side Effects

MCT oil side effects

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 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 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 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?


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.

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

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.

John O'Connor

John O'Connor is the founder of Gene Food, a nutrigenomic startup helping people all over the world personalize nutrition. John is the 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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  1. Stephanie says:

    Omg !!!! I have been taking MCT oil with my morning coffee for a few months because i do intermittent fasting and a wellness physician recommended it. I had no idea it could be harmful ! I have been having extreme fatigue and palpitations for awhile now. Been to lots of drs had lots of tests and nothing showed up. This has made me depressed and anxious. My quality of life is suffering . I am nauseous again this morning and decided to look up can MCT oil cause nausea? And i found this forum and am gonna stop the MCT oil now and see if my heart palpitations go away. I am hopeful that this is the cause. Anybody else have severe fatigue and / or arms tingling and weak ?

    • Terry martz says:

      I have had upper stomach pain and bouts of severe diarrhea and with doing some research I’ve decided not take the MCT oil any longer. Thank so much. No palpitations

  2. Mcohen says:

    I have been on keto for 3 wks and taking mct oil- a tablespoon in the morning, and a tsp at lunch- this weekend the acne hit! All over both cheeks! I am not happy! Knew it had to be something new that i was eating so thru process of elimination arrived at mct oil. Started researching so happy to have found this forum! I agree with person who said that this supplement needs closer scrutiny before being sold as harmless! I have also had buzzing in my head! Time to drop the mct oil! Thank you everybody!

  3. Dina Barzilai says:

    shocked at all the negative effects people experienced. Wondering if some is just toxins exiting their body…I had diarrhea for the first 2-3 days i started, a couple of zits which aren’t typical for me but can’t say for sure was the oil…then nothing. Did not even notice any benefits, either, altho i only took it a week or so before running out…my boss gave me about 1/2 bottle of Asprey’s Brain Octane…haven’t ordered more but planned to…trying to improve brain function and lose weight.

  4. Sangeeta Kauchhur says:

    I’ve been using 2 tsps of MCT oil daily with my coffee and noticed weight gain despite being on keto diet!! I’m 55 years old.

    Has anybody had similar experiences? All reviews advocate MCT oil for weight loss so Im extremely confused!


  5. Tonja Bartlett says:

    I nearly died from MCT oil. I didn’t even eat it, just put a little bit on my face. Woke up with my heart going so fast I needed to go to the ER….if you have any kind of health issue, especially heart problems, I would NOT recommend it. I have an irregular heartbeat and it sent my heart rate through the roof. Also turned my skin yellow so obviously affects the liver as well. NOT a very safe product in my opinion. I am certified in fitness and nutrition and believe me I would never tell anyone to use this stuff.

  6. Laurie says:

    Has anyone had pain in their feet? I’ve been experiencing pain that seems to be in the bones of my feet. I took MCT oil for several months (October – December) and then stopped because I finished the bottle. At that time my feet were hurting making walking painful, but the pain seemed to disappear on its own after a couple of weeks.
    Approximately two months later I purchased another bottle, and since I have been using it (March – June) the pain has returned. Maybe it’s a coincidence, but I’m wondering if anyone has had a similar experiences.

  7. Ashlee says:

    I have been using MCT oil and have ended up with Keto Rash and also really bad acne on my face. I don’t have a gallbladder and had gastric bypass back in 2015. I don’t understand why the MCT oil would cause me to have acne.

    • Domica Nelson-Polk says:

      I’ve been taking it for the last couple of weeks & now I too have acne! WTF?! And it’s bad acne! I’m not going to continue taking it. Thanks for ur comment bc I never would hv known it was the oil for I’ve added a couple different natural supplements that I was taking along w the oil.

    • MiMi says:

      I’ve been taking it for the last couple of weeks & now I too have acne! WTF?! And it’s bad acne! I’m not going to continue taking it. Thanks for ur comment bc I never would hv known it was the oil for I’ve added a couple different natural supplements that I was taking along w the oil.

  8. Travis says:

    I recently took a small dose of the MCT oil from the bulletproof brand on a Monday, then again on Tuesday. Two days later I got the worst headache of my life, I don’t get migraines or headaches at all. The pain was a 9/10! I can’t say for sure yet that it was the MCT oil. I’m still working with Doctors to figure out what this is. My head pain is gone finally after 6 days and now my head just doesn’t seem the same. I feel light headed and just out of it. For now I’m going to stay away from the MCT oil. I’m trying to do research on the oil to see if someone else has had these same symptoms.

    • Chris says:

      Exactly the same experience, 9/10 unprecedented headache for days. Added maybe a half-Tbsp of MCT Oil to coffee, a day or two passed, then brutal headache for a day. Didn’t connect the two, so a week or so after that, added a Tbsp (maybe more) of MCT Oil to my coffee. Two days later was utterly laid out with unilateral, constant headache. I’ve never been had headaches, and I surely have never experienced headache like this. It has been going on for four days and nights now, and is just starting to diminish. I was scared to take ibuprofen, I thought I might have a brain bleed! I can’t even bend down at the waist–the added blood pressure is excruciating. This is the fourth day I’ve spent lying down with my head elevated. There’s no headache ‘onset,’ it’s just ongoing. It’s not made worse by light. There’s been some nausea, fever, and chills as well. It can’t be flu, because this bizarre headache is far above and beyond anything one would get with flu, or any illness or infection I’ve had. MCT Oil can’t be on shelves until this is explained and people at risk can be warned. No one would be able to work, drive, or take care of their children with this kind of pain.

  9. Helen Bush says:

    I also have had my gallbladder removed. When I take the MCT oil to break my fast or sometimes after I also experience cramping, gas and sometimes moderate nausea followed by large amount of loose stool. This is with only 2 teaspoons of MCT. Any advice anyone can provide would be appreciated.

    • PeaJay says:

      Your symptoms are normal for someone having their gallbladder removed when consuming a concentrated oral dose of fatty oil. I haven’t had a gallbladder for over ten years. If I eat a meal of deep fat fried foods, or oily salad dressing, or ice cream, etc. I get the same symptoms.

  10. Shannon T. says:

    I had my Gallbladder removed 6 years ago, I have been doing keto diet an taking MCT oil.
    I get so sick, cramping ,light headiness, where I want to pass out and run to the bathroom. If the oil goes right thru me I am getting any benefits from the MCT OIL? Is there something else I could take instead of MCT oil?

  11. Kate says:

    I tried MCT oil and loved the mental clarity in sports. However, by afternoon I would hit a hard crash of needing to sleep. Read somewhere adrenals could be affected, so stopped the oil.

    I now have started with some brain boosting supplements and am seeing good results in my focus in the sports. However, again I’m hitting the hard crash in the afternoon. I thought I’d take a 20 minute nap and woke up over 1.5 hours later. More of an exhaustion.
    I’m searching to try and find out why.
    I think I will do as is suggested to not use every day. Which I haven’t been, but at 3 times a week it seems to take me down physically later in the day.

    Wondered if anyone else has had this problem? I loved the stuff!!! I used the Bulletproof Brain Octane.

    • Brenda Dominguez says:

      Yes I eat mostly same foods everyday , I started taking xct oil in the morning, at first the first few days I felt awesome thought wow I have mental clarity a lot of energy for the whole day I started with tsp . The second week I just felt extremely fatigue lightheaded and my heart beat was abnormal. I knew the only new thing I added was the xct oil . I was taking 1 tablespoons of coconut oil never had any problem but I had heard xct oil and Mac oil were great sources of energy and it is at first until few days later there are side effects !

  12. Yonah says:

    Almost a year ago I had an anaphylactic reaction to a shake I made with MCT oil. I thought it was another ingredient, not the oil. I laid off the shakes and oil until about a week ago. All good for about 3 shakes until today, when I had another allergic reaction. This time I was aware of what was happening and took Benadryl before it got out of control.
    Anybody? Anaphylactic reaction to MCT oil?

    • Vera says:

      Hi Yonah, I too had a reaction to MCT oil that sent me to the hospital. Be careful!
      It also dorpped my blood pressure to the point that I was loosing consciousness and was unable to link MCT oil to the problème until after four months of hell, I stopped the oil and am now recovering.

  13. Laurel says:

    Just wanted to put this in the mix. I have taken 3 scoops a day for 2 month and experienced heart palpitations that I think are a result of MCT oils. Also taking exogenous ketones very minor amount. Anywho, I just had a severe tachycardia episode with heart rate over 200 and couldn’t get it to stop and never had before. None of the things they think could trigger something like this I don’t do, like smoke, drink, caffeine, etc. ON top of that I’ve felt horrible for a good 3 weeks. I mean they did discover a UTI in the emergency room but that’s all. I cannot find anything on the Inet about daily dosages and just wanted to throw this out there in case any one else experiences this. I have to make a cardiologists appointment but I bet he doesn’t find a thing that caused it but will update so as not to throw MCTs under the bus if it’s not necessary. BTW haven’t taken MCT for 3 days and no heart palps since.

    • Dan says:

      It’s not toxic, it’s simply more concentrated as MCT oil since natural coconut is basically ~50% (approximately) MCT. The idea is to use less, since MCT oil essentially a concentrate.

    • Ned Meyers says:

      “Processed MCT oil is toxic.” Yeah. No it’s not. I visited two U.S.-based MCT oil producing facilities to research my dissertation on human dietary fat adaptation. The MCT oils are naturally extracted from coconut oil through a process of steam and semi-permeable membranes. If “processed” MCT oil is toxic then so is coconut oil.

  14. Usman says:

    I don’t know anything about MCT oil and Iam just thinking about using it for weight loss which product you think is best for me To start. Thanks

  15. Cherie says:

    I started taking 2 Tbls a day with breakfst and dinner about two weeks ago. I have Celiac’s and I can see that it is helping recover after being “glutened” after eating out. It is definitely helping gut health, fat loss, and absolutely has made an improvement in speeding up memory and thinking quickly and clearly again. .I exercise consistently I am seeing a shift in my metabolism of FAT enough that people are starting to notice the change even the scale is just barely creeping down. But, the last two days I’ve experienced what I think is a side effect of getting hot and my head POURing sweat. I’m 60 and haven’t had hot flashes in years and this isn’t typical of those either. This is just my head that sweats. I’ll experiment with a lower dose.

    • Maria says:

      Hello I will be turning 60 and I wanted to know what MCT oil you use, that was helpful in your fat burning and clearer thinking?
      John O’Connor did mention in his article above that if you take Vit D with MCT oil then that could cause the symptoms you are experiencing. He said to take lower doses of the MCT oil and not with D vitamin.
      Thank you

  16. Virginia says:

    Is Purely Inspired 100% pure MCT Oil a good brand. I have Hashimoto’s and n matter how I cut back on carbs, drink a lot of water and do moderate exercise, I keep gaining weight. I thought the MCI Oil would speed up my metabolism.

  17. Diane Bailey says:

    I’m curious to know if MCT oil can cause detox that manifests as long bone pain. Specifically femur shank. I once experienced severe extremity pain…bone pain…when a D.N. suggested a detox regime that was too aggressive. Just curious. Not severe enough that I”m going to abandon use.

    • Arlie Staab says:

      I’ve been taking two tbsp of MCT oil a day and on the sixth day I woke up with severe pain in long bones of both legs. I couldn’t imagine what was going on. I’m a retired RN and was checking off what all it might be. Also had a headache. Finally decided I was coming down with a flu bug and took an extra strength pain pill and went to bed all day. The next day woke up, same problem. Decided to do some on line research about MCT oil and found this site,

  18. John T. says:

    Began using NOW MCT about Dec 6, 2018. I don’t particularly measure amounts that I use I just pour some on top of cider three times a day. Noticed that seemingly incurable to fungus is starting to disappear. I’m 79 years old and began taking MCT mostly for short term memory improvement, it helps. Side effects for me, reduced belly fat, better short term memory,
    anti bacterial and fungus obvious. Good stuff for aging body I am sure.

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