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When It Comes to Fish Oil, More Is Not Better


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Update: I now recommend Extra Virgin Cod Liver Oil from Rosita as my preferred cod liver oil product. For more information, read this article. You can purchase EVCLO here.

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.

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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 dissenting views, but I’m not convinced by short-term studies on the efficacy of fish oil. 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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Join the conversation

  1. I tried high strength fish oil when it came out a few years ago. Only taking the recommended dose on bottle. After a few days I felt I was foggy and drunk. It happened no matter the brand. Never on normal fish oil capsules. I now only eat Salmon. Best to eat real food only, nature is already perfectly balanced no need to mess with it to extract only one component of a perfectly balanced combination.

  2. Thought I’d add my experience. Been taking small doses of fish oil for many years. Recently though, it so happened that I was on a very low omega-6 diet. I just decided to eat healthier, therefore the only oils I eat are olive oil and oils form meat and dairy. Since about a month or two, omega-3 been making me sick for about 48 hours every time I eat it.. Chia seeds and walnuts seem to make it the worst, but so does fish. I’d have very strange anxiety where I can’t seem to shut of negative thinking and I’ll feel I’m going crazy, also experiencing disassociation and feeling very sad in general. Normally, I feel very well mentally except for a few anxiety issues, but those are not usually related to sad feelings, just feeling nervous. I tried adding more omega-6, but still, any time I eat fish, walnuts or god forbid, chia seeds I’d get that “crazy” feeling for 24-48 hours…After that I’d be fine…Very weird. Any thoughts?

  3. I am an optometrist who just so happens to be very interested in nutrition and how poor diets are affecting my patients. I see dry eye so commonly, and a staple dry eye treatment is fish oil. We were taught to recommend 1000-2000mg of fish oil to patients with dry eye. The products that we are taught to use are highly filtered fish oil with the ethyl alcohol removed so that is better absorbed (brands that I believe do this are Nordic Naturals and PRN). They are sourced from anchovy, sardines, and mackerel. It is assumed that patients are going to be taking these supplements long term. My question is, what is your take on this approach, and would you recommend doing something different with my dry eye patient? Should I go against the fish oils my peers recommend and do cod liver oil instead? Also, some fish oil products also contain lutein and zeaxanthin which we recommend for macular health. Now I am afraid to recommend these long term.

    • Hi Shannon, thought I’d reply to your comment, it’s always great for me to speak to Optomotrists dealing with Dry Eye symptoms directly in patients.

      I head up a company that provides ‘triglyceride’ omega 3, this is omega 3 with the ethyl esters removed. In answer to your question, when you actually look at the studies the figures are not really showing Fish oil is dangerous, although some ‘writers’ have used it to create controversy.

      The DART 2 study actually showed that 18% of men taking fish oil died, whereas 17% of men eating fish died, it hardly seems possible to suggest Fish oil increases the risk of death. The fish oil group also had more serious health problems to start with.

      • Thank you for the response. I’m not as fearful to recommend fish oil to my dry eye patients now!

      • Actually, I have one more question for you. Should I continue recommending the anchovies/sardine fish oil or should I switch to cod liver oil?

  4. I am 69 years old. People tell me I look to be in my early fifties. I have been taking 25 — 40 grams of fish oil per day for twelve or fifteen years now, with no apparent ill effects. I ate a sensible diet. I also work out at the gym every day—weights plus cardio.

    • What type of fish oil are you taking to provide you with 20 -40 grams per day? Are you aware of the potential excessive bleeding that could result in so much fish oil? FDA comments on GRAS (generally recognized as safe) up to 3 grams/day.


      • Apparently didn’t happen to him. Taking for 15 years!!! It is working for him. Not everyone is the same. I believe this article is to get me to take prescription drugs? ?, not all of us have the luxury to get fresh cod even twice a week. Try everything in moderation and keep track if it is working.

  5. What do people think about having two omega 3 capsules a week rather than daily to reduce the risk factors?

  6. It’s odd to me Chris that you decided to remove your support to Green Pastures and then go support another company who is less transparent about their practices than Green Pastures and doesn’t even disclose why they add vitamin E and then don’t tell you their source of it. Nordic Naturals and Carlson oils get their fish from the same ocean as Corganic and go through horrific processing to remove contaminants and then add synthetic vitamins back into their oils, what makes Rosita so special that they don’t process their oil? I think it was a poor move on your part and Green pastures has always been transparent and always disclosed its processes and labs and even re-did labs to double check. I’m not convinced Rosita/Corganic is as honest as you are saying.

  7. Hi bare biology fish oils have been tested and they say it is not rancid? What do you think? Is it safe

      • Please direct us to an evidence based quality study so we can review the results. There are so many anecdotal and useless, self-serving “studies,” that are meaningless. Evidence based would be from a clinical study that is double-blinded and which has a reasonable amount of participants. Thanks.

  8. Some interesting points Chris, however the DART 2 study showed that 18% of men taking fish oil died, whereas 17% of men on fish died, it hardly seems possible to suggest Fish oil increases the risk of death.

    Also more importantly, the fish oil group we taking 3g of fish oil twice a week (maxepa). They don’t say exactly how much of that was omega 3, given the study date of 2003 we can assume it’s around 30% so 900mg of omega 3 twice a week. This is way less than even the recommended 500mg per day for everyone, (as opposed to the higher number that would be expected for people suffering from angina).

    How can you expect to see a reduced death risk when the amount of omega 3 taken was significantly less then needed?

    Also it was only in the EPA form, with no DHA, and we must assume the ethyl ester form. Absorption of ethyl esters is way less than it would be from fish, which is obviously in the triglyceride form. So in conclusion the amount of omega 3 in the fish oil supplementation group was completely inadequate.

    Plus the fish, veg and fish and veg groups were given no other dietary advice, how do we know what else they were eating, is it surprising that just simple healthy eating had the lowest death rate, if you are mixing your fish oil capsules twice a week with burgers and doughnuts?

    Also in the TBARS study, you fail to mention that it was conducted in vitro, and they point out in their discussion that animal studies that had shown this in vitro risk did not transfer to atherosclerotic risk in vivo.

    • Thank you Andy. I know this post & your comment is over a year old, but I greatly appreciate your counter points.

  9. My blood results today (this year) shows very high level of Vit B12, cholesterol level of 6.7 and LDL of 4.4.
    I do 90 mins gym 4 days a week and a fair bit of walking on other days. My non veg diet is very healthy with a lot of greens and fruits daily and all home cooked. I do not snack on chips and sweets, etc. However, I take about 4 -2000mgcapsules a day of Fish a I am allergic to fresh seafood. Could this be the reason for my strange reading?

    • What brand is the fish oil you are taking? The FDA says that dietary supplement manufacturers should not recommend taking more than 2,000 mg of omega-3 fatty acids per day. If you are taking 4 x 2,000 mg = 8,000 mg of omega-3’s daily, you are asking for trouble. In addition, if your dietary supplement is in the form of ethyl esters, there are more than 49,000 mandatory reported adverse events reported to the FDA.

    • Check your MTHFR, your test results indicate a possible polymorphism in this SNP.
      (Nutritional Medicine Practitioner/Herbalist)

  10. I’m a 79 year old male. I go to the gym daily and eat vegetarian (plus eggs). I have been taking 15 grams fish oil morning and 15 grams of fish oil evening for about 12 years now. people tell me I look about age 50. I attribute my youthful looks and smooth skin to my megadosing of fish oil for so many years.

  11. Hi Chris,
    Yu said: 1g/d of cod liver oils is outweighed by the benefits of the fat-soluble vitamins.

    What is the best way of measuring out such a small amount from a bottle of fish oil?

    Thanks, Alex

    • Alex,

      I do not know if you ever received an answer for this but the best way is to use a graduated eye dropper/medicine dropper available from any local drug store or pharmacy.