When it comes to fish oil, more is not better

Article summary

  • The benefits of fish oil supplementation have been grossly overstated
  • Most of the studies showing fish oil benefits are short-term, lasting less than one year
  • The only fish oil study lasting more than four years showed an increase in heart disease and sudden death
  • Fish oil is highly unstable and vulnerable to oxidative damage
  • There’s no evidence that healthy people benefit from fish oil supplementation
  • Taking several grams of fish oil per day may be hazardous to your health

A new study was recently published showing that 3g/d of fish oil in patients with metabolic syndrome increased LDL levels and insulin resistance.

Unfortunately, I don’t read Portuguese so I can’t review the full-text. But this study isn’t alone in highlighting the potential risks of high-dose fish oil supplementation. Chris Masterjohn’s latest article on essential fatty acids, Precious yet Perilous, makes a compelling argument that fish oil supplementation – especially over the long-term – is not only not beneficial, but may be harmful.

This may come as a surprise to you, with all of the current media hoopla about the benefits of fish oil supplementation. Yet the vast majority of the studies done that have shown a benefit have been short-term, lasting less than one year. The only trial lasting more than four years, the DART 2 trial, showed that fish oil capsules actually increase the risk of heart disease and sudden death.

A 2004 Cochrane meta-analysis of trials lasting longer than six months suggests that the cardiovascular benefits of fish oil have been dramatically over-stated. They analyzed 79 trials overall, and pooled data from 48 trials that met their criteria. The only effect that could be distinguished from chance was a reduced risk of heart failure. Fish oil provided no reduction in total or cardiovascular mortality.

Too much fish oil can wreak havoc in your body

Omega-3 fatty acids are highly vulnerable to oxidative damage. When fat particles oxidize, they break down into smaller compounds, like malondialdehyde (MDA), that are dangerous because they damage proteins, DNA, and other important cellular structures.

A study by Mata et al demonstrated that oxidative damage increases as intake of omega-3 fat increases. The results of this study were summarized in the Perfect Health Diet, by Paul and Shou-Ching Jaminet:


Notice the clear increase in TBARS (a measure of oxidative damage of the LDL particle) with omega-3 fat. It’s important to note that this was only a 5-week trial. If it had gone on for longer than that, it’s likely the oxidative damage caused by omega-3 fats would have been even worse. This isn’t surprising if you understand the chemical composition of fats. Polyunsaturated fats (PUFA) are highly vulnerable to oxidative damage because they’re the only fatty acids that have two or more double bonds, and it’s the carbon that lies between the double bonds that is vulnerable to oxidation (as shown in the figure below):

diagram of chemical structure of EPA

Another thing worth noting, if you haven’t already, is that intake of saturated and monounsaturated fats does not increase oxidative damage by a significant amount. This is illustrated in both the table and the diagram above: saturated fats have no double bonds, which means they are well protected against oxidation. MUFA is slightly more vulnerable, since it does have one double bond, but not nearly as much as PUFA which has several double-bonds.

A randomized, double blind, placebo-controlled trial likewise showed that 6 grams per day of fish oil increased lipid peroxides and MDA in healthy men, regardless of whether they were supplemented with 900 IU of vitamin E. And consumption of fresh, non-oxidized DHA and EPA has been shown to increase markers of oxidative stress in rats.

Fish oil not as beneficial as commonly believed

To be fair, at least one review suggests that fish oil supplementation is beneficial in the short and even intermediate term. A recent meta-analysis of 11 trials lasting more than one year found that fish oil reduced the relative risk of cardiovascular death by 13 percent and the relative risk of death from any cause by 8 percent.

But the effect seen in this review was mostly due to the GISSI and DART-1 trials. They found that fish oil may prevent arrhythmia in patients with chronic heart failure and patients who have recently survived a heart attack.

However, there is no evidence that people other than those with arrhythmia and chronic heart failure benefit from taking fish oil or that doses higher than one gram of omega-3 fatty acids per day provide any benefit over smaller doses. And then there’s the rather disturbing result of the DART-2 trial, the only fish oil study lasting more than four years, showing an increase in heart disease and sudden death.

It’s logical to assume the effects of oxidative damage would take a while to manifest, and would increase as time goes on. That’s likely the reason we see some benefit in short- and intermediate-term studies (as n-3 displace n-6 in the tissues), but a declining and even opposite effect in the longer-term DART-2 trial (as increased total PUFA intake causes more oxidative damage).

The danger of reductionist thinking in nutritional research

The current fish oil craze highlights the danger of isolated nutrient studies, which unfortunately is the focus of nutritional research today. Kuipers et al. eloquently described the risks of this approach in a recent paper:

The fish oil fatty acids EPA and DHA (and their derivatives), vitamin D (1,25-dihydroxyvitamin D) and vitamin A (retinoic acid) are examples of nutrients that act in concert, while each of these has multiple actions(7,8).

Consequently, the criteria for establishing optimum nutrient intakes via randomised controlled trials (RCT) with single nutrients at a given dose and with a single end point have serious limitations. They are usually based upon poorly researched dose–response relationships, and typically ignore many possible nutrient interactions and metabolic interrelationships.

For instance, the adequate intake of linoleic acid (LA) to prevent LA deficiency depends on the concurrent intakes of α-linolenic acid (ALA), γ-LA and arachidonic acid (AA). Consequently, the nutritional balance on which our genome evolved is virtually impossible to determine using the reigning paradigm of ‘evidence-based medicine’ with RCT.

Interest in fish oil supplementation started with observations that the Inuit had almost no heart disease. It was assumed their high intake of marine oils produced this benefit. While this may be true, at least in part, what was overlooked is that the Inuit don’t consume marine oils in isolation. They eat them as part of a whole-food diet that also includes other nutrients which may help prevent the oxidative damage that otherwise occurs with such a high intake of fragile, n-3 PUFA.

It’s also important to note that there are many other traditional peoples, such as the Masai, the Tokelau, and the Kitavans, that are virtually free of heart disease but do not consume high amounts of marine oils. What these diets all share in common is not a large intake of omega-3 fats, but instead a complete absence of modern, refined foods.

Eat fish, not fish oil – cod liver oil excepted

That is why the best approach is to dramatically reduce intake of omega-6 fat, found in industrial seed oils and processed and refined foods, and then eat a nutrient-dense, whole-foods based diet that includes fatty fish, shellfish and organ meats. This mimics our ancestral diet and is the safest and most sane approach to meeting our omega-3 needs – which as Chris Masterjohn points out, are much lower than commonly assumed.

Some may ask why I continue to recommend fermented cod liver oil (FCLO), in light of everything I’ve shared in this article. There are a few reasons. First, I view FCLO as primarily a source of fat-soluble vitamins (A, D, K2 and E) – not EPA and DHA. Second, in the context of a nutrient-dense diet that excludes industrial seed oils and refined sugar, and is adequate in vitamin B6, biotin, calcium, magnesium and arachidonic acid, the risk of oxidative damage that may occur with 1g/d of cod liver oils is outweighed by the benefits of the fat-soluble vitamins.

So I still recommend eating fatty fish a couple times per week, and taking cod liver oil daily, presuming your diet is as I described above. What I don’t endorse is taking several grams per day of fish oil, especially for an extended period of time. Unfortunately this advice is becoming more and more common in the nutrition world.

More is not always better, despite our tendency to believe it is.

Note: As always, I’m open to discussion and dissenting views. But please don’t link to short-term studies on the efficacy of fish oil, because as I’ve explained in this article, it’s the long-term effects that we’re primarily concerned with. I’d be interested in seeing any studies longer than 2 years showing that 1) fish oil benefits extend beyond reducing arrhythmia in patients with chronic heart failure and patients who have recently survived a heart attack, 2) doses higher than 1g/d produce a larger benefit than doses of 1g/d, and (most importantly) 3) doses of >1g/d or higher do not increase the risk of heart disease or death

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  1. Craig Giddens’s avatar

    I think people are going to get confused when they are told something is good, but then told it could be harmful.

    “I think fish oil is a much better choice than aspirin. Both have blood thinning effects, but fish oil has other benefits like balancing the omega-6 to omega-3 ratio and isn’t harmful to the liver.”

    Chris Kresser

  2. Ron Lavine’s avatar

    This is an interesting sharing of ideas. The last few months I’ve been convinced that a “balanced fatty acid” pill with fish oil, borage, and flax seed is the way to go, but now I’m not so sure. I was unfamiliar with the idea of fermented cod liver oil – that sounds like its worth checking out.

    Fundamental to a lot of this discussion seems to be the issue of how badly screwed up an individual’s diet is to begin with before we try to modify it and/or supplement it. And also how much an individual can be motivated to change it.

    There are days when I feel on target and that I can be a good motivator of patients. On other days I’m not so sure. The secrets of being influential in how inspiringly we share information (not just on the technical correctness of our information) seems critical.

  3. Chris Kresser’s avatar


    I am always learning and growing as a practitioner and a researcher. I try keep an open mind, consider other points of view, and change my approach when new information warrants such a change. I understand that this can be frustrating and confusing for those that come here hoping for answers.

    That said, the statement you quoted above doesn’t necessarily contradict what I’ve written in this article. I mentioned that fish oil has been shown to benefit those with pre-existing heart disease or those who’ve had a recent heart attack. Many people who take aspirin for cardiovascular protection fall into this category. Note that I was not recommending high dose fish oil supplementation in any of those previous articles, either.

    Also, I still do believe that taking 1-2g/d of fish oil is less harmful than taking aspirin. These aren’t black or white issues. For example, aspiring is less harmful than statins, but that doesn’t mean it’s benign. Likewise, high-dose fish oil is probably less harmful than aspirin, but nor is it benign.

    I do need to revise the series on EFAs to reflect this new information. Hopefully I can get to that in the next couple of weeks.

  4. Chris Curley’s avatar

    Hi Chris,

    a few questions:

    I am a newbie to Fermented CLO. Oxidation occurs both within and without the body. If CLO is fermented does this not allow oxidation to occur?

    What are your thoughts on Krill oil. Krill oil contains a natural antioxidant astaxanthin(?) inherent in its makeup and is presumably less susceptible to oxidative damage.

    I have been hot on the trail of this subject for about a month as well and have come to find a product by Europharma called vectomega. It is a “whole food” supplement of purportedly whole salmon heads pressed into a pill. The manufacturer claims that this phospholipid based form allows for easier assimilation and less oxidation. Are you familiar with this product?


  5. Chris Kresser’s avatar

    Oxidation will still occur. It’s a matter of scale. I believe the benefits of taking FCLO every day (vitamins A, D, K2, E & quinones in their naturally occurring form) outweigh the potential risk of oxidative damage, provided overall intake of PUFA is low and B6, magnesium, and other nutrients that support fatty acid metabolism is adequate.

    I’ve never heard of vectomega. One possible advantage of krill oil, as I wrote about in my article on fish oils in the EFA series, is that the omega-3s are in phospholipid form, which should be better absorbed. But my thoughts on krill oil in general are the same as my thoughts on fish oil.

  6. JB’s avatar

    Thanks for the post very interesting. I have a couple questions. When you say 1g/d of fish oil are you referring to total fish oil or just the EPA/DHA? The fish oil I am currently taking is 1200mg capsule with 410 EPA and 274 DHA. Would you you be recommending 1 capsule (1200mg) or 2 (1368 mg EPA/DHA)? I also saw you recommended a “higher dose” for children. Do you have specific numbers for that? I have 2.5 and 4 year old boys.


  7. Alan’s avatar

    I know that you advocate eating fish such as canned alaskan salmon.

    The question I have is why can’t whole fish oxidize in your body just like fish oil? Or is it just the degree of potential oxidation! Does the whole fish have more antioxidants and greatly prevents oxidation.

    As usual, another great post. Thanks for your effort.

  8. Ahrand’s avatar

    And once again Weston A Price is right, do not take ‘nutrients proven by science ‘ but take food proven by generations of healthy families : grassfed butter, liver, fish bone broths. We are not (yet) smart enough to determine exactly what nutrients in which combination have which advantages.

    Look at healthy populations and try to emulate and be vary wary of refined and extended shelf life foods.

  9. Chris Kresser’s avatar

    JB: the 1g/d refers roughly to the total amount of polyunsaturated omega-3s. So it depends how much of the 1200 mg capsule is omega-3, not just EPA & DHA. For kids, “higher” dose refers to higher relative to their body weight, not higher in an absolute sense. So very young kids can take maybe 1/2 the adult dose, or a little less, and it will still be higher relative to body weight.

    Alan: yes, it’s the degree of potential oxidation and the fact that whole foods like salmon have more antioxidants.

    Ahrand: I agree completely.

  10. Razwell’s avatar

    TREMENDOUS article, Chris. I am so glad this information is getting out there. I always have felt the whole Inuits thing was based on some faulty assumptions. They eat whale blubber and meat, and this contains all the nutrients working in concert, not processed fish oil pills.

    Also as you say, the Maasai, Kitivans do fine without all the marine oils.

    Take care,


  11. David’s avatar

    What about fish oil for depression?

  12. Chris Kresser’s avatar


    For depression, my recommendation is the same as it is for general health: the first step is to dramatically reduce omega-6 consumption. Then, eating fatty fish like salmon 2-3x/week and adding a moderate amount of fermented cod liver oil should help balance the n-3/n-6 ratio. That’s the intention behind fish oil, after all, but this is a safer way to do it.

    That said, if someone has done all that and they’re still not getting the results they want, and additional fish oil provides a benefit, I’d choose that over an SSRI any day of the week.

  13. Bentzurm’s avatar


    You have not mentioned the omega3-index blood tests in your excellent fish oil posts. Would you agree that the following would be wise:
    - reduce dietary omega6 to a minimum, while taking moderate amounts of fish oil (or FCLO) for 6 months (to reverse years of SAD).
    - test your membrane fatty profile and either increase or decrease fish oil accordingly.
    - retest in 6-12 months and repeat.

  14. Chris Kresser’s avatar


    Yes, that would be wise. I did mention the omega-3 index in this article. Scroll down about 2/3 of the way.

  15. Vin Kutty’s avatar

    Hi Chris, an interesting counter-point here…but I have not read the full study, just the abstract. Frankly, I wasn’t even aware of this journal.

    Mas E, Woodman RJ, Burke V, et al. The omega-3 fatty acids EPA and DHA decrease plasma F(2)-isoprostanes: Results from two placebo-controlled interventions. Free Radic Res. Jun 2010.


  16. Suzy’s avatar

    From the Green Pastures link you posted for their “Product Test Data” – under additional comments it says “Majority of D is D2″. I’m concerned – I thought it would’ve been D3 – do you know why that is?

    Also, do you know what this means: “below .090 PPM PCB WHO/exceeds Prop 65″ ?

    Thanks for the very informative post.

  17. Chris Kresser’s avatar

    Suzy: it has D2 because that’s what naturally occurs in the cod livers, apparently. We know less than we think about how all of the various constituents of vitamin and mineral complexes behave.

    The second part means that the detectable levels of PCBs exceed the WHO and California Prop 65 standards.

  18. Suzy’s avatar

    Chris, thanks for your reply. So now I’m confused because from my understanding it’s the D3 we’re after. I was hoping to use FCLO as a somewhat whole food source of vitamin D (more for maintenance than boosting my levels). But now it looks like it’s actually the wrong kind of vitamin D? Could you please shed some light on this for me?

    As for the second part about Prop 65, that’s what I was worried it meant, but was hoping that I had misunderstood it. I’m surprised to hear that their FCLO exceeded the standards. I always thought that FCLO was one of the “safer” alternatives. Could you please share your thoughts on this?

    Thank you.

  19. Chris Kresser’s avatar

    Suzy: exceeds the standards means “is better than”.

    Eating vitamins in their natural whole food form is always the best choice. When supplementing, D3 is more desirable than D2, but that doesn’t mean we would avoid cod liver oil because it has more D2 than D3. As I said in my previous reply, there’s still a lot we don’t understand about the various constituents and how they work together.

  20. Suzy’s avatar

    Chris, yes of course. I was so focused on toxins exceeding safe levels or allowable limits, that I completely misread the “standards” part. Thanks for your insight re: FCLO.

  21. andy’s avatar

    thx for another great article.
    Prof. Brian Peskin has been advocating agains fish oils for a long time, more info
    Also google ‘IOWA study on fish oils’, and you also see that fish oils makes worse

    B.Peskin has been advoacing for consuming good ratio of omega 3:6, and then body would be able to produce enough DHA and EPA. Whilst consuming fish oils we get pharmacological doses of DHA and EPA, which is harmful, could even lead to diabetes, CVD, cancer.
    He got a term parent essetial oil (PEO), – which basicly means high quality omega 3 and 6 (alfa linolenic and linoleic fatty acids)

  22. Bruno’s avatar

    Hi Chris,

    What is the dose recommended of omega 3 caps? 1 gram a day???

  23. Chris Kresser’s avatar

    Best to just eat fatty fish 2-3 times a week, and take 1/2 tsp/day fermented cod liver oil from Greenpasture.org.

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