Fish oil: friend or foe?

Howard LeWine, M.D.

Chief Medical Editor, Harvard Health Publishing

The answer is more friend than foe, especially if the fish oil comes from food sources rather than supplements.

Omega-3s in balance

What’s so special about fish oil? It’s loaded with omega-3 fatty acids. These must come from food, since our bodies can’t make them.

The two-key omega-3 fatty acids are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Fatty fish like salmon, mackerel, and sardines are rich in these omega-3s. Some plants are rich in another type of omega-3 fatty acid, alpha-linolenic acid, which the body can convert to DHA and EPA. Good sources of these are flaxseeds, chia seeds, walnuts, pumpkin seeds, and canola oil.

Omega-3 fatty acids play important roles in brain function, normal growth and development, and inflammation. Deficiencies have been linked to a variety of health problems, including cardiovascular disease, some cancers, mood disorders, arthritis, and more. But that doesn’t mean taking high doses translates to better health and disease prevention.

Fish oil supplements have been promoted as easy way to protect the heart, ease inflammation, improve mental health, and lengthen life. Such claims are one reason why Americans spend more than $1 billion a year on over-the-counter fish oil. And food companies are adding it to milk, yogurt, cereal, chocolate, cookies, juice, and hundreds of other foods.

But the evidence for improving heart health is mixed. In November 2018, a study reported in the New England Journal of Medicine found that omega-3 fatty acid supplements did nothing to reduce heart attacks, strokes, or deaths from heart disease in middle-age men and women without any known risk factors for heart disease. Earlier research reported in the same journal in 2013 also reported no benefit in people with risk factors for heart disease.

However, when researchers looked at subgroups of people who don’t eat any fish, the results suggested they may reduce their cardiovascular risk by taking a fish oil supplement.

Evidence linking fish oil and cancer has been all over the map. Most research, including the 2018 study cited above, has not shown any decreased risk of cancer. However, some earlier research suggested diets high in fatty fish or fish oil supplements might reduce the risk of certain cancers.

Take home message

How food, and its component molecules, affect the body is largely a mystery. That makes the use of supplements for anything other than treating a deficiency questionable.

Despite this one study, you should still consider eating fish and other seafood as a healthy strategy. If we could absolutely, positively say that the benefits of eating seafood comes entirely from omega-3 fats, then downing fish oil pills would be an alternative to eating fish. But it’s more than likely that you need the entire orchestra of fish fats, vitamins, minerals, and supporting molecules, rather than the lone notes of EPA and DHA.

The same holds true of other foods. Taking even a handful of supplements is no substitute for wealth of nutrients you get from eating fruits, vegetables, and whole grains.

What should you do if you currently take fish oil? If your doctor prescribed them—they are an approved and effective treatment for people with high blood triglyceride levels—follow his or her instructions until you can have a conversation about fish oil.

If you are taking them on your own because you believe they are good for you, it’s time to rethink that strategy. If you don’t eat fish or other seafood, you might benefit from a fish oil supplement. Also, you can get omega-3s from ground flaxseed or flaxseed oil, chia seeds, walnuts, canola oil, and soy oil. One to two servings per day can help you avoid a deficiency of omega-3s.

Following food author Michael Pollan’s simple advice about choosing a diet may be the best way forward: “Eat food. Not too much. Mainly plants.”



  1. TN

    Fish oil seems to be a subject of controversy. Some people swear by it, and there are thousands of clinical trials out now trying to study what the latest and greatest thing about the supplement is. The Natural Standard does a really good job collecting and gathering data for those who are interested in delving through what fish oil may or may not be doing to us. Definitive answers, however, may take a little while to get.

  2. James

    It can’t be a problem with fish oil since the Japanese (and others) who have very high consumption of fish are not dying en-mass of prostate cancer but it could be something associated with the supplement form of it. Most stuff is better in it’s natural form. I just wonder how much of the supplements are coming from China –

    Or it may just be that men with otherwise unhealthy diet and lifestyle choices that might lead to prostate problems are just taking the EPA hoping to compensate and it isn’t working out.

    This study stands out in what it didn’t say, not so much for what it did say.

    – James

  3. johnnywhite

    Studies don’t seem to mention blood content of omega 6, or saturated fats–the overall balnce of triglycerides, so they seem to have been done in a “vacuum”. At least, the data is so presented. Also, high protein may be an issue not being tested, but hovering in the background of the participants’ diets. Many “miracle cures”, and I wish it wasnt so, are being not only “debunked”, but “proven” outright dangerous.

  4. Miroslav Besermenji

    I am concern about few things:
    – Fish oil used in examination, quality and source?
    – Any comparison with men in area where sea fish eating are high (as Mediterranean, etc). As far as i know prevalence in these men are low. True?
    – Family predisposition & genetic statement?
    – Exposition to another factors (like THM in water, pollutions like hard metals etc etc).

    • EO

      Good points, Miroslav. Focusing on your 4th point, with so many different formulations on the market that contain various preservatives, only looking at the blood levels of omega-3’s as the flag for increased risk for prostate cancer tends to ignore the fact that certain populations in coastal regions maintain a diet high in omega fish oils and don’t have a marked increase level of prostate cancer, pointing to the fact that another agent may be to blame here.

      Side note, fish oil’s popularity as a supplement recently has come from the observation that inuits of Greenland have a high omega-3 containing diet. But this is a natural source. For more information on omega-3 check out the information provided on the Natural Standard website.

  5. Dr.Ambrose | Health Care Specialist & Dietician |

    High levels of the oils in blood samples were linked with a 71 per cent increased risk of developing an aggressive and dangerous form of prostate cancer, according to the research. That study, if I recall correctly, mentioned concern about men eating fish more than a certain number of times a week having a 54% increased risk of developing prostate cancer.

    • Trish

      What? Are you serious? What kind of fish are we talking about? High on the food chain? Smoked? Nitrate Laden?
      Are we talking rancid fish oil capsules?
      Weston Price linked fish that was transported greater than a hundred miles (read greater than a day old without refrigeration) to health concerns.

  6. knuth becker

    Great article,
    In Denmark we have the same problem with fish oil. Alot of it is not very good.

  7. Current News

    I must say that overall I am really impressed with this particular site.You can easily see that you are passionate about your writing. If perhaps I’d your writing ability I look forward to more updates and will be returning.

  8. C. Clayton

    Even healthy oils form trans fats when heated. Each oil has a different temperature at which it forms its own trans fats. Generally, when the oil begins to smoke is when trans fats are formed. Did this study consider how and at what temperatures the fish were cooked? Are some of the suppliments heated before being made into capsules? Did it also consider that many types of fish have dangerous levels of mercury?

    • Richard

      You “beat me to the punch.” despite labels, cured meats , aged fats, as well as those heated to a high enough temperature all have trans bonds. Fish that offer high amounts of Omega-3 also often are high in mercury. I was fortunate to have a very good teacher for experimental design. One should be careful to assume that a study actually measures what it claims to and without “confounders” Confounders are parts of the study that complicate the the “logic” of the design. Also, were other fat contents measured or controlled? It would be reasonable to suspect that those with higher levels of Omega-3 could have higher levels of Omega-6, fats in general , High levels of protein, higher levels of testosterone, or lower levels of certain hormones. In addition, statistical studies do not and have never indicated a causal relationship. I have a fear of how much we have begun to rely on statistical correlational studies which are at the end of the day”soft” science.

  9. Jael

    Fish oil has some of the healthiest benefits and a regular intake of this oil can keep up with the nutritional requirements of the body. But for strict vegetarians, consuming fish oil can go against a vegan following…

  10. Doktor Taffi

    I’m ujsing a lot of fish oil and i think it’s healthy. But i need to say that the whole article is very interesting 😉

  11. Rixx

    how much in a day is ideal. by the way, most of people nowadays don’t like food contain too much oil

  12. Peter

    How much is the ideal dose of fish oil daily?

    • Trish

      Up to 4 grams a day to lower triglycerides. Take with food to reduce burping, but if you are burping fishy smell, the capsules are probably rancid. Switch to a higher quality brand! Or eat fish low on the food chain! Sardines anyone?

  13. Paul

    High levels of the oils in blood samples were linked with a 71 per cent increased risk of developing an aggressive and dangerous form of prostate cancer, according to the research.
    Is this true? I am a fish oil fan..

  14. Je suis plutot d’accord sur le principe, mais pouvez vous developper un peu plus…

  15. ryan

    This seems to cement what we learned from 2004 out of the UK re. prostate cancer and Japanese men. That study, if I recall correctly, mentioned concern about men eating fish more than a certain number of times a week having a 54% increased risk of developing prostate cancer.

    I don’t recall all the particulars,and maybe i am offbase in my memories so please google and double check, but i was thinking it expressed concern about fish consumption in men.

  16. Alex

    But its NOT just the supplements. The warning is about eating fish also. I have been eating a can of bumble bee salmon a day for years and now I have to worry about whether I have been poisoning myself?
    If this stuff really increases the cancer risk as described, then cigarettes are to lung cancer what oily fish is to prostate cancer. Warnings should be everywhere.

  17. John Wilson

    While it is interesting to define the increased risk, that is not a very significant statistic absent a clear statement of the underlying risk of prostate cancer in the male population as a whole.

    • ryan

      Excellent point.

      • roy

        It must be kept in mind that prostate issues have been found to be the result of the fact that men who suffer prostate issues are found in males who’s testosterone levels dropped to dangerous levels. If one bothers to research this fact it will be found that studies show that testosterone controls estrogen levels and as such estrogen levels get out of control and begin to create problems the likes of which our society is suffering right now.

  18. Mitch

    yes, Hg was not a factor here.

    However, the referred study was anything but definitive. DHA has been previously tied to increased prostate C risk however EPA has been tied to reduction in risk, possibly due to well known anti-inflammatory effects, although as mentioned results are all over the map.

    Meanwhile, blood levels of DHA and EPA are very transitory, reflecting what an individual consumed only recently, while of course prostate cancer has a markedly longer progression. The study was not designed to isolate omega oil :: prostate cancer relationships, so conclusion would be weak. Seems likely to me that when faced with a serious disease, men suddenly begin to try living “right” in a hurry.

    Nor addressed in the current hubbabaloo is the fact that Japanese men have far higher typical DHA/EPA intake than American men, while having a very small fraction of US prostate cancers.

    The claims and conclusion of this study are at very best unsupported, more like irresponsible.

  19. Patricia

    Did the study take mercury levels into account?

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