Should You Really Be Taking Fish Oil? | Chris Kresser

Should You Really Be Taking Fish Oil?

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Fish oil might not be the cure-all it’s often advertised to be, and in some cases, it may even cause problems.

is fish oil bad for you?
Is there any real value in taking fish oil? DmitriyDanilchenko/iStock/Thinkstock

Note: This article was originally published in June 2015 and was updated in January 2017 to include the latest research. My original recommendations still stand, and the case for high-dose fish oil supplementation has become even weaker.  

Fish oil supplements continue to gain in popularity, but the research supporting their efficacy is shaky.

For over a decade, fish oil has been touted by doctors, nutritionists, and armchair health enthusiasts alike as a near cure-all for health. Whether you have heart disease, depression, diabetes, or joint or skin problems, or you just want to stay healthy and prevent nutrient deficiencies, somebody has probably told you to take a fish oil supplement.

The general notion was that it might help, and at the very least, it couldn’t hurt. Unfortunately, that isn’t necessarily the case.

Does Fish Oil Really Prevent Heart Disease?

It’s safe to say that the benefits of fish oil supplementation for heart health have been significantly overstated. As I mentioned earlier, studies initially found that fish oil was beneficial for heart disease, particularly over the short term and for secondary prevention. (1)

But a majority of the evidence available now suggests that fish oil provides no benefits for preventing or improving heart disease.

For example, two randomized controlled trials (RCTs) published in 2010 found that in adults with preexisting heart disease, long-term supplementation (three-plus years) with fish oil had no significant impact on cardiovascular end points. (2, 3)

A few other trials looked at the effect of short-term fish oil supplementation on atrial fibrillation, and none of them found that fish oil improved patient outcomes. (4, 5, 6)

A meta-analysis of RCTs in 2012, focusing on cardiovascular end-points, found that fish oil did not reduce cardiovascular events or death and concluded that the evidence does not support using fish oil supplements for the secondary prevention of heart disease. (7)

Three other meta-analyses published since then came to similar conclusions. (8, 9, 10)

Some studies do still come up with positive results. For example, one meta-analysis published in 2013 found a protective effect of fish oil for preventing cardiac death, sudden death, and myocardial infarction. (11)

Is it possible that fish oil is beneficial for one person and harmful for another? #fishoil

But there are also studies with negative results. Back in 2010, I wrote an article highlighting one study where long-term fish oil supplementation resulted in an increase in heart disease and sudden death and another that found increased LDL levels and insulin resistance in people who took 3g per day of fish oil. (12, 13)

Overall, the majority of studies show neither benefit nor harm from supplementing with fish oil for heart disease.

Does Fish Oil Improve Metabolic Syndrome?

Metabolic syndrome is a collection of symptoms and biomarkers that often precedes heart disease or diabetes.

On the positive side, a recently published RCT found that in adults with metabolic syndrome, supplementation with 3g/d of fish oil along with 10 mL/d of olive oil for 90 days improved several blood markers. This includes a statistically significant lowering of triglycerides and LDL cholesterol, an improvement in LDL/HDL ratio, and improved markers of oxidative stress. (14)

It’s interesting to note that the fish oil plus olive oil group had better results than either the fish oil or olive oil group alone. One possible reason for this is that olive oil is rich in antioxidants and may have protected against the potentially greater risk of oxidative damage from consuming more polyunsaturated fat.

On the negative side, a recent study in women with metabolic syndrome found that 3g/d of fish oil resulted in an increase in LDL cholesterol, blood glucose, and markers for insulin resistance after 90 days, although they did observe a decrease in blood pressure. (15)

And in overweight men, supplementation with 5g per day of krill and salmon oil resulted in increased insulin resistance after eight weeks, compared with a canola oil control. (16)

Finally, an impressively large RCT involving over 12,500 patients with diabetes, elevated fasting glucose, or impaired glucose tolerance found that supplementation with 1g/d of omega-3s for six years did not reduce disease endpoints compared to placebo. Endpoints measured included incidence of cardiovascular events, death from cardiovascular events, and death from all causes. (17)

As you can see, the evidence for fish oil supplementation for metabolic syndrome is mixed, with some studies showing a benefit, others showing harm, and still others showing no significant effect either way.

Can Fish Oil Prevent Cancer? Or Does Fish Oil Cause Cancer?

Many of you probably recall headlines from 2013 proclaiming that fish oil may increase the risk of prostate cancer (18). But despite the extensive media attention garnered by the study, it’s actually one of the weaker cases that have been brought against fish oil.

Believe it or not, the study in question actually had nothing to do with fish oil, or even omega-3 supplements. The researchers simply measured circulating levels of omega-3 fatty acids in men with and without prostate cancer and found that men with prostate cancer tended to have higher concentrations of omega-3s in their blood.

There are several reasons this could be the case; for instance, some evidence indicates that having prostate cancer might itself increase blood levels of omega-3s, or that certain genetic polymorphisms can increase both circulating omega-3s and cancer risk.

It didn’t take long for other researchers to publish a slew of comments pointing out these possibilities, but the media had already taken the “fish oil causes cancer” stance and run with it.

More recently, a meta-analysis found that in general, omega-3 consumption is associated with a decreased risk of prostate cancer, but that the correlation is too weak to be statistically significant. (19) In 2016, a massive meta-analysis looked at 44 studies and concluded overall that higher omega-3 supplementation had no effect on prostate cancer mortality (20).

A handful of reviews found that fish oil intake was associated with a lower risk of breast cancer, although no distinction was made between fish oil supplements and fish consumption. (21, 22) And one RCT published in 2012 found that supplementation with 600mg of omega-3s per day had no effect on cancer risk in men, but increased cancer risk in women. (23)

As with heart disease and metabolic syndrome, the research on omega-3 and fish oil supplementation on cancer is decidedly mixed.

High Levels of Oxidative Products Found in Fish Oil Supplements

Recently, attention has been drawn to the quality of over-the-counter fish oil supplements. Long-chain polyunsaturated fatty acids, including DHA and EPA, are especially susceptible to oxidation due to double carbon bonds at multiple locations.  Light, oxygen exposure, and heat can all contribute to oxidation. Oxidized lipids have been linked to a number of health issues, including organ toxicity and accelerated atherosclerosis—the exact opposite outcomes usually desired by those who supplement with fish oil. (24)

In 2016, the top three selling fish oil supplements in the United States were shown to have oxidation levels up to four times higher than recommended “safe” levels. (25) One caveat of this alarming study is that oxidation levels were normalized per 1g of omega-3s in the supplements, instead of the industry standard of normalizing per 1g of fish oil. Although this does inflate their three measures of oxidation, all three fish oil brands were still above acceptable levels of peroxidase and TOTOX levels, while one (instead of the study’s reported two) was above acceptable anisidine levels if instead normalized per 1g of fish oil.

As oxidation level measurements of omega-3 supplements have increased over the last several years, this has been the common finding. Studies examining fish oil supplements available around the world, including in Canada, New Zealand, and South Africa, consistently show that a vast majority (up to 80 percent!) exceed at least one of the measures of acceptable oxidation levels. (26, 24, 27) Also noteworthy is that most of these supplements contain lower levels of DHA and EPA than the labels claim, probably partly due to oxidation.

Furthermore, the most recent study from 2016 demonstrated that over-the-counter omega-3 supplements had a decreased ability to inhibit small, dense LDL oxidation in a laboratory setting compared to pure omega-3 fatty acids. (25) This means that whatever supposed benefits omega-3 supplements should have on blood lipids could likely be completely counteracted by the oxidized lipids also contained in the pills. Overall, I am quite wary of most over-the-counter products out there.

Should You Take Fish Oil?

To avoid making this article so long that nobody will read it, I haven’t included research on fish oil and other aspects of health, including mental health, skin health, pregnancy, and cognitive function. As you might imagine, the research on fish oil supplementation to prevent or improve these conditions is also somewhat mixed, with some studies showing significant benefit and others showing no change.

This is certainly an important topic, and I’m glad to see such a strong interest in it in the research community. I will continue to follow the literature and update my recommendations if and when new evidence comes to light, but for the time being this is what I would suggest:

If you are generally healthy, the best strategy is to consume about 12 to 16 ounces of cold-water fatty fish or shellfish each week. When possible, whole foods are always my first recommendation. Most studies show an inverse relationship between fish consumption and heart disease and mortality, so while fish oil may not protect you, eating fish does seem to. Perhaps this is because fish and shellfish contain many other beneficial nutrients that fish oil does not, including selenium, zinc, iron, and highly absorbable protein. (Fortunately, most cold-water fatty fish and shellfish are also low in mercury and other toxins, and mercury in fish may not be as big a problem as some have led us to believe.)

If you don’t eat fish (for whatever reason), I’d suggest supplementing with 1 teaspoon of high-vitamin cod liver oil. In addition to about 1.2 g of EPA + DHA, it is rich in the active forms of vitamin A and vitamin D, both of which are difficult to obtain elsewhere in the diet. There are very few studies suggesting the possibility of harm from supplementation with 1 gram or less of fish oil per day, and so I think one teaspoon of cod liver oil a day is likely to be safe even for those eating fish regularly—and beneficial for those not eating liver or other foods that contain active vitamin A. My current favorite cod liver oil is Rosita Extra Virgin Cod Liver Oil, as this company has consistently demonstrated very low levels of oxidative products from independent laboratory testing.

Based on the evidence I’ve reviewed in this article, I would not recommend consuming high doses of fish oil (i.e., more than 3g/day) over the long term. If you do choose to take a higher dose of fish oil, I would make sure to consume plenty of antioxidant-rich foods, like olive oil; blueberries; nuts; dark, leafy greens; and dark chocolate.

I think we still have a lot to learn about this subject. One of the challenges is that the effects of polyunsaturated fats on overall physiology are complex and probably depend on multiple factors that can vary individually, including uncontrolled oxidation, eicosanoid production, cell membrane effects, and signal transduction via specialized fatty acid receptors (i.e., PPAR receptors).

This could explain why we see such a wide variation in study results. Is it possible that 3g/d of fish oil is beneficial for one person and harmful for another? Absolutely. Unfortunately, at this point it’s difficult to predict that individual response with accuracy and certainty, so I think the conservative approach I suggested above is probably the most sensible until we learn more.

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  1. I am almost done with a Quicksilver Scientific Detox protocol so I really need to avoid mercury. Does Rosita Cod Liver Oil contain mercury?

    • I was curious how the Quicksilver Scientific Detox worked for you, did you get a test done once the detox was complete? Did you see an improvement in symptoms?

    • I’m like Nathan… I’d appreciate hearing about before and after testing following the Quicksilver detox. What Quicksilver protocol did you use (exactly, if you don’t mind sharing)

  2. Just wanted to confirm that the recommendation to limit intake to 3 g is for FISH OIL (3 g would be about 2/3 of a teaspoon daily), or for EPA + DHA (i.e., not more than about 2 teaspoons of a fairly typical product).

    Thanks.

    • My naturopath demonstrated to us that a normal flatware soup spoon does not hold a TBS. If you measure a tsp of water and put it in a soup spoon, it fills it with a just little margin around the edge. That is the dosage she recommends for FCLO from Green Pastures. I have been taking that dosage for 5 years and my husband for about 3 years with zero negative effects. I didn’t get sick all winter. But if I had, I would have doubled the dose for a week or so. I know there is controversy re Blue Ice, but judging only from my own health, it seems to be working exactly as it should. Yay!

      • Rami Nagel, the author of “Cure Tooth Decay” and a huge supporter of fermented fish oil died of cancer.

  3. I have read Dr. Kresser’s prior article on Omega 6 v. Omega 3. I was not sure where to post this comment. I have been a big proponent of fish oils in my patients with mixed results and recommending based on prevention research, etc. with outcomes difficult to monitor in one’s own patients without rigorous follow up, etc. I was speaking with my colleague Dr. Rowen who does not recommend fish oils and referred me to his book, The PEO Solution, as the explanation was a long one. I found the information most enlightening and missed even by the brightest and well read. Consider reading and I would enjoy Dr. Kresser’s comments or even a podcast with one of the authors.

    • The PEO Solution is an article that we recently came across,too! I would like to hear Dr Kresser’s opinion on it. I wasn’t totally convinced and am at a loss on whether to take high quality fish oil or not for my cardio issues. It seems like taking nothing would be best except a few supplements. In my opinion, the fermented cod liver oil is a rancid oil and dangerous.

  4. I have taken fish oil (higher DHA) for the past three and a half years. I felt like I did benefit from it (hair, skin, mood). I have been buying from a very reputable brand (Nordic Naturals). Recently, I have read some things about gelatin that bother me. They use a beef gelatin, so I have started looking for other sources of DHA/EPA. I bought some of their liquid fish oil–but I worry about this going rancid fast….I would love to just eat salmon a few times a week–but worry about mercury and other contaminants with that……not sure what to do….? I wish I had never read about the gelatin risks. I know they are small, but it still bothers me…..Any suggestions or ideas would be great 🙂

    • I take Nordic Naturals in the liquid form and store it in the refrigerator. When the oil in a gelatin capsule goes rancid you cannot tell until it gives you indigestion. I’ve had problems with the capsules so avoid them regardless of the source of the gelatin.

  5. Unfortunately this article makes no distinction in the research to the amounts of EPA/DHA that were given, many of these studies are comparing apples to oranges. 3 grams of fish oil means nothing, the important thing is how much EPA/DHA is being given. 1 gram of a low quality fish oil may only contain 150-200 mg of EPA per gram while a triple strength, pharmaceutical grade product may contain 500-600 mg of EPA per gram. The research that shows that there must be enough EPA/DHA, generally in the 1000-1500 mg range of EPA.

    Fish oil works, just google Lovaza and Omacor. Do you think these would be prescription products if they didn’t. You just have to get enough EPA/DHA. You can get similar products from amazon, search pharmaceutical grade, triple strength fish oil.

    For me, the antidepressant effect of fish oil is life saving. I do not want to take pharma antidepressants. I take 2 enteric coated capsules(2.8 grams) of a triple strength fish oil that totals 1300 mg of EPA and 500 mg of DHA. I have been on this amount for several years, when I go off of it, depression sets in after about a week. I have cycled off of it several times and felt this happen everytime. My tryglycerides also dropped from 158 to 75 after starting fish oil. I take it with antioxidants (Beta cartotene, Vit C, E, and selenium) with breakfast.

    Check out Dr. Stephen Illardi’s book “The Depression Cure” and TED talk, also the Omega 3 Connection

    • I’m glad you posted this because in my experience of fish oil, I dive into depression about a week after no consumption of the supplement. I switched to krill oil and I’ve noticed even more benefits with even greater mental clarity and sharpness along with overall energy! Trying to make a blanket statement for all to follow is tough because we all have diff DNA. Clearly, my brain benefits from the fat / needs more fat, but I cannot consume a high fat diet because it over works my digestive system, so the supplements help! I also consume extra virgin coconut oil, too.

  6. i have two questions:

    1. What are your views on flaxseed oil ?

    2. What are your views on moderate daily alcohol consumption?

    • Flaxseed oil is great but as Chris Kresser has commented a number of times “research indicates that the conversion of ALA to EPA and DHA is extremely limited. Less than 5% of ALA gets converted to EPA, and less than 0.5% (one-half of one percent) of ALA is converted to DHA”

  7. I have worked in the health and fitness industry for about 7 years. Have various PT certs and and two nutrition certs (one precision nutrition).

    I fell on a basketball court once and braces my fall with my left elbow. I had severe pain for about a week then lots of swelling but after a week the pain reduced, butthe swelling stayed and I had occasional pain while working out. This continued for 6 months.

    I then met an RD who told me to take an entire bottle of Omega 3 fish oil. I thought she was nuts but I tried anyway. I woke up the next day and the swelling in my elbow was completely gone and the pain only surfaced if I tried to find it (moving different ways, pressure points, messages).

    I understand the research on fish oil, but it personally helped me reduce inflammation greatly.

    Just my input…

  8. The author asks: “Does fish oil really prevent heart disease?”

    He then states for his first study a group who had pre-existing heart disease. This is not a group in which to prevent it because they already have heart disease, right?

    Ummm…

    I stopped there.

  9. Hi,
    Thanks for writing such an informative, engrossing, enticing post for us.
    I am a health enthusiast and I have tried anything to everything under the name of superfood to supplements.
    I firmly believe there are several factors attached to bring a positive and negative when we follow something.
    I have taken this supplement and seen changes in my body, hair, and skin texture.
    The golden rule to follow os moderation and to be on the move so that body can come up with real results.
    No food is entirely good or entirely bad. Rest we must focus on the food and food groups that are from our own soil and locally available. “Eat local and think global”

  10. If you are taking in good amounts of antioxidants I don’t see a problem with taking fish oils. I take fish oils shortly after juicing greens (of course adding most of the fiber back into the diet). There’s no way that fish oils or even an iron supplement could counter the massive release of antioxidants from juicing greens.

  11. I finally read your discussion of fish oil, just not all the comments (yet). I take a tsp/day of FCLO, Green Pastures Blue Ice. I know the jury is still out and different testing labs use different methods so it’s hard to tell exactly what we are getting. But I haven’t been sick all winter so I think the Vit D must be in there. I have been doing GAPS for ~4yrs and take it for general good health. I am concerned about any processed fish oil, especially if it doesn’t taste fishy. My question is, if I am not trying to heal cancer or heart disease, do you recommend NOT taking FCLO for a while, or taking breaks of some interval? I also eat Wild Planet anchovies and sardines and salmon, but not always once/week. I will share your response with my GAPS support group. We are all taking FCLO but of course we all have different health profiles. Thanks.

    • Based on the extensive work of Dr. Raymond Peat and others, some of whom appear in The upcoming documentary ‘On The Back Of A Tiger’ all polyunsaturated fatty acids (PUFAs) are detrimental for human consumption in any regular concentrated form. The vitamin A and D in those FCLO capsules are probably helpful and unfortunately are also naturally occurring with PUFAs in the fish oil.

      Please check out this extensively referenced article by Dr. Peat along with his other articles about oils

      http://raypeat.com/articles/articles/fishoil.shtml

      Mostly people think in terms of the most mentioned PUFAs; Omega 3 and 6 DHA and EPA
      Here is the content of the FCLO you are using which you can find on their FAQ blog:

      DHA has a typical range of 10% of the FCLO +/-
      EPA has a typical range is 15% +/- of the FCLO. Use the same calculation as above

      Total Omega 3 will typically be in the 30-40% of the FCLO.

      If you are consuming Skate Liver oil, the DHA will make up 14-16% of the oil +/- and EPA will be in the 10-12% of the oil +/-.

  12. Why do you ignore the immense work of Gilbert Ling, Gerald Pollack, Mae-Wan Ho , and Harold Hillman ckesrlyvdhowing ghat cells are complex gels generating boundaries due to the EZ liquid crystalline be state of water in the body. This eliminates most of the arguments in terms of the need for “essential fatty acids whether omega 6 or 3

    • That is to say that crlls have no bilayer membranes . If you have not read their work which has produced NOBEL prizes forbothers, I suggest you take the time to do so. The documentary “On the Back Of A Tiger ” should be coming out soon about this and much more.

  13. I was diagnosed with Von Willebrand Disease this year. It’s a blood clotting disorder where I bleed more than I should. Taking fish oil makes it dramatically worse. So I take a very small dose of a high quality oil once in a while if I’m not eating fish. And not otherwise. Because otherwise I bruise by leaning against a table.

    • You need high dose Vitamin C (maybe also Vitamin K)!

      Forget the name the Allopaths have giving your blood clotting disorder, just look at the symptoms they are almost identical to Scurvy! (I.e massive Vitamin C deficiency)

      Go research Dr Linus Paulings and the other Orthomolecular medicine literature on the wonders of mega dose C

      (Again it could also be a Vit K defiecny but I would be confident Vit c will deal with it)

  14. I’ve taken about 2g of fish oil for almost 10 years with some breaks. I have metabolic syndrome and high morning blood sugar indicating insulin resistance. The resistance seems to be increasing as blood sugar levels have been creeping up. I try to keep a tight rein on carbs and have stopped drinking coffee and dairy which helps. I will probably decrease the amount of fish oil I’m taking, switch to cod liver oil or maybe stop all together for a while. I take a high quality fish oil that I get from health practitioners. I was told to take fish oil after cancer diagnosis to reduce inflammation.

    • You have significant inflammation much of which probably stems from endotoxins in your gut. Look into the use of low dose tetracycline like 1/3 dose per day for several weeks along with decent probiotics 2 hours after antibiotics, and/or eat a carrot salad every day as per Ray Peat, take Floraphage, twice a da and 500 mgs of Aspirin uncoated, add K2 regularly, check your thyroid and consider getting progesterone using it for some Time in the form of Progest E . Maybe some sodium bicarbonate regularly like full teaspoon in 4 ounces of water twice a day, and learn to reduce your breathing as undoubtedly you are over breathing a lot. Begin by training yourself to only breathe through your nose even when exercising. You may have to slow your exercise speed and intensity down for a while to do this and you will build back up. Learn about the importance of sea salt and iodoral from David Brownstein, MD too

  15. It was recommended to me to get my DHA/EPA from taking an algae supplement instead of fish oil….thoughts?

  16. I’ve taken fish oil regularly for years ( for multiple benefits) but what I’ve noticed the most is how much it’s helped with my dry eyes. When I run out for a couple days, I notice a significant difference in my eyes feeling dry and scratchy.

  17. Hi Chris, Yay for chocolate endorsements! I think keeping an eye on your omega 6 to omega 3 ratio is more important that pumping yourself full of fish oil and nuts and seeds. But everyone is different. Glad you did not make this a black and white conversation.