Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
28 Apr

Is Fish Oil Linked to Prostate Cancer?

This is a special guest post from expert study-dismantler Denise Minger. (Read Denise’s previous guest posts – Will Eating Whole Grains Help You Live Longer? and High Fat Diet Linked to Breast Cancer? – and her blog at Raw Food SOS.) Enter Denise…

Like salmon? Pop fish oil? Got a prostate? Then listen up. A new cancer study rolled in this week, and at first glance, it looks like bad news for any fish-loving men out there. A team of researchers at the Fred Hutchinson Cancer Research Center found a disturbing link between blood levels of DHA – that darling omega-3 fat abundant in seafood – and the risk of developing aggressive, “high-grade” prostate tumors.

The eyebrow-raising results of the study showed that:

  • Compared to folks with low DHA levels, men with the highest levels were 2.5 times more likely to wind up with aggressively growing prostate tumors.
  • Men with the highest blood levels of trans fatty acids were the least likely to get aggressive prostate cancer. (Say what?)

According to the researchers, very few of the study subjects were supplementing with fish oil – so these findings probably don’t reflect unbridled mega-dosing of omega-3 fats. Despite its consistent role in boosting heart-health, it looks like fish oil could be a double-edged sword. And maybe a stick of trans-fatty margarine is really a cancer cure. Intriguing, eh?

Something’s Fishy

The researchers weren’t shy about expressing their surprise. Team leader Theodore Brasky stated that he and his colleagues were “stunned to see these results,” and the article’s full-text discussion notes that the findings were the exact opposite of what the team expected.

To top that off, this study derails the otherwise consistent train of research showing that DHA seems protective at best (and neutral at worst) when it comes to prostate health. In 2001, a study of over 6,000 Swedish men found that the folks eating the most fish had drastically lower rates of prostate cancer than those eating the least. Another study from New Zealand found that men with the highest DHA markers slashed their prostate cancer risk by 38% compared to the men with the lowest DHA levels. And yet another study tracking Japanese men in Japan and Brazil found that omega-3 levels in the blood were consistently linked with a reduction in prostate cancer.

Obviously, fish is only bad for you if you’re American.

For the science savvy, there are even some biological pathways explaining how DHA could lower prostate cancer risk. Which brings us to another predicament: We haven’t sleuthed out any mechanism that could explain why DHA (but not other polyunsaturated fats) promotes rapid tumor growth. Nor do we know of any way trans fats could save a prostate from malignant doom. This is a classic case of correlation clashing with biological plausibility – and it highlights why observational studies, with their slew of undocumented variables and contradictory findings, can’t tell us anything definitive about food and disease.

But that doesn’t mean this study is worth ignoring – just that it might warrant an extra dollop of scrutiny. Let’s take a look at exactly what these researchers uncovered, and see whether fish is really off the proverbial hook.

DHA in Your Blood Versus DHA in Your Mouth

First things first: Can we really conclude that the men with high DHA levels were eating more fish (or fish oil) than the rest of the gang?

The answer is a resounding “nope” – and this is why the current fish-condemning media coverage is a load of hooey. Although consuming more DHA can definitely boost your serum levels, the reverse isn’t always true: elevated DHA doesn’t automatically mean you’re a sushi fiend or loyal fish-oil guzzler. Guess what else can increase omega-3 fats in your blood? You’ll get a hoot from this one: low-fat diets.

Check out this intervention study from 2001, which measured changes is serum fatty acids after feeding folks either a low fat (20% of calories) or high fat (45% of calories) diet. Although the low-fat dieters didn’t get any special omega-3 boost, the levels in their blood rose disproportionately by the end of the trial. The study concluded that “Consumption of a low fat diet alters fatty acid patterns in a manner similar to that observed with feeding of (n-3) long-chain fatty acids.” In other words, fat restriction caused blood levels of omega-3 fats to resemble that of seafood lovers.

So what does this mean for our current study? For starters, if there is a legitimate link between high DHA levels in the blood and aggressive prostate cancer, we could point the finger at low-fat diets just as easily as fish. Is dietary DHA a trigger for tumor growth, or is it some consequence of fat reduction – such as the higher intake of grains or sugar that often fills the caloric void? Since this study didn’t document any diet variables, there’s no way to tell for sure. But what we do know is fish can’t be charged guilty by this particular chunk of research.

More to the Story

One final problem with this study is that it only documented a handful of the fatty acids present in the blood. Here’s a low-carb pie chart for your viewing pleasure:

The labeled slices show the eight types of fatty acids this study examined. But see that big green Mystery Slice? It’s the placeholder for the all the saturated and monounsaturated forms the study didn’t report. That’s a whole lotta’ mysteriousness. And because the researchers looked at fatty acid levels as percentages rather than absolute concentrations (a method that may have some major limitations in studies like these), it means that whenever the proportion of one fatty acid rises, at least one of the others has to drop. The higher DHA levels in the aggressive-tumor-ridden men had to go hand-in-hand with lower levels of a different fat. It’s not beyond the realm of possibility that whatever’s going on in the Mystery Slice plays more of a role in tumor growth than DHA.

Not Out of the Water Yet

Even though this study doesn’t give any reason to shun fatty fish or their oils, it’s a nice segue into a related issue: A bad diet plus fish oil is still a bad diet. And given the oxidation-prone nature of all polyunsaturated fats, a massive intake of omega-3’s – despite their brilliance in moderation – could potentially do more harm than good. If you’re trying to restore a healthy ratio of omega fats, avoiding omega-6-rich foods (and supplementing wisely) is a better strategy than chugging fish oil like a frat boy with gin.

All in all, this study is just another drop in the sea of misinterpreted nutritional research. Don’t take the bait!

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. that is fascinating, i had no idea low-fat diets raised serum omega 3’s… not enough to counteract the other effects of the diet though apparently haha

    Burn wrote on April 28th, 2011
    • Similar to the authors mention of the “mystery slice”, my guess would be that a lowered fat consumption led to a decrease in 06 intake relative to 03 and the ratio of the fats actually improved.

      Pandadude wrote on April 28th, 2011
  2. Personally I could go either way with this. I don’t know enough about fish oils or fats in general to really know what I’m looking at here.

    To me it seems neither position is proved or disproved which is kind of unfortunate. I just wish there wasn’t so many conflicting studies out in the world. It makes it hard to really know what the healthiest route is.

    Also a quick question, since I am not living on my own and don’t buy the groceries, I wanted to start taking an omega 3 supplement but with all the grains the family eats, would it even matter or should I just wait until I move out?

    Bobby wrote on April 28th, 2011
    • Do you eat the grains too? I am not positive but I would say supplementing with fish oil is necessary if your balance is off.

      How much seafood do you eat? If you ate seafood a few times a week then fish oil may not be necessary for you.

      Primal Toad wrote on April 28th, 2011
      • no, we rarely eat fish at all actually. I think I’ve had it once in about 6 months.

        Bobby wrote on April 28th, 2011
        • I would then think you should definitely take a fish oil supplement. Do you limit your omega 6 intake? Avoid all nuts except macadamias?

          Primal Toad wrote on April 28th, 2011
  3. Too awesome: “avoiding omega-6-rich foods (and supplementing wisely) is a better strategy than chugging fish oil like a frat boy with gin.”

    This is very interesting but not surprising. Another study that when you dig down deeper proves nothing. I will continue to take my fish oil and eat fish as much as I can. Oh, and live primal too as they obviously matters!

    Primal Toad wrote on April 28th, 2011
    • It’s Geoff! Or is it Jeff? Really, how do you spell your name? I’ve seen you spell it both ways.

      Primal Toad wrote on April 29th, 2011
      • It’s spelled Jeff. With a “J”.

        Geoff wrote on April 29th, 2011
    • Hey if it feels good (and you’re using protection), sure, why not?

      Another Halocene Human wrote on April 30th, 2011
  4. yeah, definitely something fishy about that study..

    however, on the plus side its good to see the researchers didn’t let their pre-conceptions (DHA good, trans-fats bad) prevent them publishing it when their data revealed the opposite of what they expected

    freddy fishface wrote on April 28th, 2011
  5. “A bad diet plus fish oil is still a bad diet.”

    How true. It’s not a magical golden railroad spike in the quest for health and fitness. Clean up your diet and you don’t have a need for high-dose fish oil. What a novel concept!

    Hal wrote on April 28th, 2011
  6. This seems designed to frustrate. I could just as easily say that my cat eats cat food, and never goes bald, therefore Meow Mix is an effective solution for male pattern baldness.

    Two things existing side-by-side does not create a meaningful relationship. Could the DHA in the blood be released in response to inflammation?

    At any rate, I’m pretty sure that a clean, omnivorous diet is the way to go.

    fitmom wrote on April 28th, 2011
    • What???!! Cat food comparison to the human diet?! LAME!!! Intelligent comments only, dammit!!

      Geoff wrote on April 29th, 2011
      • I think you are missing the sarcasm.

        Steph wrote on April 29th, 2011
        • Nope just another stupid comment from yet another stupid person.

          Jeff wrote on April 29th, 2011
        • Chill out Jeff…take a pill…

          Guvno Dom wrote on July 16th, 2013
  7. I just want to ask. and sorry for the repost, but I do think primal is the way to go. I really do. But I also feel like anyone could look at any study and disprove it. I’m sure many high carb lovers out there have looked at the studies that Mark has put up on the site and dissected them in such a way as is done here.

    I’m not saying this is wrong, just that I don’t honestly know where it ends? How are the studies that are done for primal eating structured differently than say this study? If I could get answers to that question I feel I would be more at ease.

    Thanks again, and again I am commited to the primal diet, I just always have a questioning mind, and seeing how these studies differ from primal leaning studies would help

    Bobby wrote on April 28th, 2011
    • I think if you feel good. Wake up fresh and your mouth tastes good. your energy levels are as you want them. not many energy swings. no aches, foggy mind, more clarity all studies are moot. keep doing what you are doing. sometimes our beliefs creates issues when none exists. placebos are prime example of that. i have cut down grains…eat lotsa vegetables, some meat, fish lotsa oils..occasional treat ones or twice a month…and things have improved in health and ur good health..cheers

      A wrote on April 29th, 2011
  8. Excellent critical analysis, and very clever too. Prepare for the impending marriage proposals!

    I had the same criticism that serum DHA isn’t necessarily indicative of dietary DHA. What we care about is CELLULAR DHA. And if it’s cellular DHA then it appears that it prevents cancer. I have seen too much evidence to the contrary of this so I just dismissed it outright. That’s not to say that I’m in favor of tons of DHA, just enough to have low levels of inflammation and good brain health.

    Another thing to note is that prostate cancer is a very unlikely disease to get and so you can triple the rate in a population without increasing all-cause mortality. You gotta die from something and if something protects massively from heart disease and neurodegeneration then it might just appear to “raise” the risk in the population.

    Stabby wrote on April 28th, 2011
    • Prostate cancer is unlikely in the fact that half of us don’t have prostates. However, in the African American population 1 in 4 will get prostate cancer and 1 in 20 will die of it. Certainly not something to ignore. Get your screenings guys!

      That said, this one study shouldn’t be cause to lower fish consumption. Love Denise’s comments as usual.

      Real Food RD wrote on April 28th, 2011
      • Hmm, maybe not so uncommon, especially amongst African Americans. Though generally if you prevent one disease in a population you increase another one, that’s the luck of it.

        Stabby wrote on April 28th, 2011
        • African-Americans also get higher than average rates of high blood pressure and type 2 diabetes. I wouldn’t be surprised if the prostate cancer is related somehow.

          Dana wrote on April 30th, 2011
      • “Get your screenings guys!”

        It’s important to note that screenings do not improve survival rates. Don’t be so quick to recommend, especailly when screeings can actually cuse more problems than good.

        Dan wrote on May 2nd, 2011
    • Also note that no fatty acid was related to the most common mild form of prostate cancer. It was only in the small sub-group with “aggressive” disease that showed these apparent relationships with fatty acids.

      Tim wrote on April 28th, 2011
      • A friend of mine, who is a cancer researcher at Davis, looked at this study for me and one of his comments was that you can’t make the statement that due to the lack of more milder forms of prostate cancer found that somehow EPA/DHA levels made the cancer more aggressive. It is more likely that higher levels of EPA/DHA were helpful in reducing these milder forms of cancer but were not able to help with the more aggressive forms.
        I too will continue to eat paleo, try and eat grass fed protein vs grain fed, try and eat meats in appropriate amounts vs. the over large servings that I am used to ( I am such a carnivore at heart!), try to get more fish in my diet, which I tend to not like as much) and take my fish oil to balance my 3:6 ratio.

        Rich wrote on July 31st, 2013
    • Errr, prostate cancer is incredibly common – it’s the most common of all cancers. In fact, there’s a saying in the medical community that if you’re a man and you live long enough, “it’s not a question of if you’ll get prostate cancer, but when”.

      james wrote on April 28th, 2011
      • Unless you, like, die of something that isn’t prostate cancer, in which case you won’t.

        Yes yes I was mistaken, it’s common. Being that it is common if you reduce heart disease risk you can expect to get more prostate cancer, since you gotta die of something.

        Stabby wrote on April 28th, 2011
    • More intelligent thoughts by Stabby!

      Primal Toad wrote on April 29th, 2011
    • Excellent post Denise and great point about low-fat diets elevating tissue DHA levels.

      So if DHA promotes cancer, the low-fat dieters are in the most trouble.

      However, there is a growing body of evidence linking high DHA levels to cancer and other diseases of pathological angiogenesis. And there is a known mechanism. I’ve blogged about it this week in two posts:

      My second post also has a few reflections on your post.

      Your conclusion, that moderate omega-3 consumption is beneficial but high consumption is harmful, is the right one. Nice post!

      PS – Please let Stabby down gently!

      Paul Jaminet wrote on April 29th, 2011
      • Paul, I think you have missed a key issue in assuming that high oral intake of DHA has a direct connection to and is the cause of high blood levels of DHA and cancer. Not to be too harsh, but was this just a plug for your blog?

        While your blog touches on a couple good points about the oxidation-prone nature of fats and the ramifications of too much anti-inflammatory inputs (e.g. DHA), your message here is a little to simplistic and reductionist. An overly simple cause-and-effect is assumed. Here you throw the baby out with the bathwater and ignore the systemic nature of our bodies and the importance of the *quality* of our inputs, like DHA.

        Not only the studies, but our bodies’ systems too are full of confounding factors and multiply-inter-related processes. Modern scientific analysis is great, but it is still growing up in terms of analyzing complex systems.

        Tony wrote on April 29th, 2011
        • Hi Tony,

          No, I didn’t miss that issue. High oral intake of DHA does have a direct connection to high blood levels of DHA. It is not the only factor, of course, which is Denise’s point.

          You might look at some of Dr William Davis’s posts on the ability of high-dose fish oil to raise the Omega-3 index, which is a blood level measure.

          This was a plug for these two posts, which provide a much more in-depth look at the issue than you’ll find elsewhere.

          I’m not assuming anything about cause and effect. I’m merely reporting scientific observations of causes and effects.

          You’ll notice my conclusions are not different from Denise’s.

          Best, Paul

          Paul Jaminet wrote on April 29th, 2011
        • Excellent. Thanks for the additional details!

          [This is a reply to Paul Jaminet’s “No, I didn’t miss that issue” message. If this appears out of order, it is because there was no “Reply” link visible after the post.]

          Tony wrote on April 29th, 2011
  9. Good call Stabby.

    Will you marry me?

    chima_p wrote on April 28th, 2011
    • If Denise can marry us too.

      Stabby wrote on April 28th, 2011
      • Thanks for another great post, Denise!

        Sue wrote on April 28th, 2011
      • We could start our own reality TV show: Brother Husbands!

        chima_p wrote on April 28th, 2011
      • +1

        Primal Toad wrote on April 29th, 2011
        • A-ha!!! Now I’m starting to see the “Geoff”/”Jeff” comments and quibs regarding and questioning all of your sexualities! The above comments are certainly not helping him to stop gripping! I too, am a little sickend by your off-topic lovefest.

          Ian wrote on April 29th, 2011
        • Yeah. Primal Toad’s super-gay.

          Geoff wrote on April 29th, 2011
      • I think that’s only legal in Utah. I’ll be your flower girl, though!

        Denise Minger wrote on April 29th, 2011
  10. I hope Ms. Minger’s day job pays her based upon her brain power. She will surely be a millionaire in a very short time.

    Phocion Timon wrote on April 28th, 2011
    • Ha. Having smarts is like a strong back… employer will pay you as little as they can get away with, because it’s a commodity, like any other.

      Remember what Henry Ford told Congress: I don’t have to know the answer to that question, because I can pick up my interoffice phone and have a man to answer any question you put to me.

      That leaves going into business for yourself, but good luck actually capitalizing it with all the sharks in the water (other companies, investors, lawyers) trying to profit off your ideas and hard work for themselves.

      Only ‘creative’ fields pay well for intelligence (and it has to be of the right kind) because they’ve figured out if you put the right mix of brilliant people together, magic happens.

      Another Halocene Human wrote on April 30th, 2011
  11. Looks like this interpretation is based on a subgroup analysis that only includes 125 cases of high-grade cancer.

    If you are comparing two groups of cancer with 10 different fatty acids, that is 20 comparisons. Doing that on a small number of cases is quite risky from a statistical viewpoint.

    Tim wrote on April 28th, 2011
  12. I am so suspicious of anything that the American doctors put out…they push pills..suggest idiot diets..use us as test animals..and leave huge holes in the studies they take…My daughter is a bio-chemist and says that if you look for one thing..GUESS WHAT! will probably find it..while of course completely ignoring the other factors around it..I love the just goes to show that ALL the information has not been posted…just what the folks supplying the $$$ for the studies want them to post…because if they posted the Whole truth..They would not get the grants to do more studies..BIG business at work as usual…

    DAVE PARSONS wrote on April 28th, 2011
    • The studies that showed that trans fatty acids cause heart attacks caused were deeply unwelcome to the big food businesses. Similarly, do you think the tobacco companies welcomed scientists investigating the health effects of their products?

      If you look at the big picture, your argument doesn’t hold water.

      Tim wrote on April 28th, 2011
      • The tabacco companies had to do something because doctors were being sued by patients for getting cancer…because doctors prescribed cigarettes back in those days!
        And then the ball got rollin’ all the way to the head of the tabacco company.

        If great masses suffer the same illness and have 1 thing in common…it’s too obvious to ignore.

        Donnersberg wrote on April 28th, 2011
        • You think the tobacco companies sponsored the research that proved their products were harmful, in response to lawsuits from patients that were prescribed cigarettes by their doctors?

          That is an interesting idea, but the facts are very different. You can read about the history of tobacco research in this review

          Tim wrote on April 28th, 2011
  13. Fitmom and Stabby, good possibilities. I am going to add some more.

    The elevated DHA levels in the blood seem to me a lot like the situation where there is elevated cholesterol. In analyzing seemingly correlated conditions, the interpretation gets cause and effect backwards.

    From what little I’ve learned, the volumes of these substances are not free-floating reflections of dietary intake. Instead they indicate the body’s response to some condition that it is trying to remedy.

    For example, if a person has a low-fat diet, their cells and processes are going to suffer in certain ways. In response, the body may dump lots of DHA into the blood to get it to where it is needed. The prostrate cancer could be 1) coincidental, 2) a concurrent result of the low-fat diet or other deficiency, or 3) a result of the body having to rob DHA from one place in order to fix another.

    Tony wrote on April 28th, 2011
    • Interesting that another study, mentioned in NY Times article, found that extremely low levels of cholesterol correlated with increased risk of prostate cancer. Again, this was not what researchers were expecting since low cholesterol levels are assumed to be good.

      Robin wrote on April 28th, 2011
    • Interesting. That would make sense in my father’s case. He got prostate cancer, but eats extremely healhty in comparison to SAD, but is a low-fat adherent. He eats a ton of fish (living on the coast) and veggies, and no processed food. But he was diagnosed with high cholesterol, so was always working to correct it. Hmm, how sad would that be if all of his effort at eating well actually led him to prostate cancer? *sigh*

      Julie wrote on April 29th, 2011
  14. How come the reviewers don’t shred the findings, like Ms Minger does, before they are published?

    kem wrote on April 28th, 2011
    • So if you had reviewed this, what possible reasons would there be for saying that the paper shouldn’t be published?

      The methods have no obvious flaws. They discuss the strengths and weaknesses of their study in the discussion and don’t push any particular view. In fact they specifically state that the results they saw were the exact opposite of what they expected! Indeed, the association may be real and the fact that there is no known mechanism may just mean that we haven’t been looking for one.

      This paper is not the last word on fatty acids and prostate cancer. however, it will certainly spur other people to look at this question, so the picture will become clearer in time.

      Tim wrote on April 28th, 2011
      • I agree with Kem,
        Why were the flaws that were found by Denise, and so many other intelligent reviewers of this study, not discussed before its publication and leaking to the newspapers?
        I spoke to a lipid researcher at Holman, an Omega 3 test kit company that I use in my practice, what he thought about this very subject and he said that it looked like the journal, which has a good name in the research community, most likely had the article reviewed by specialists that specialized in the research technique but likely didn’t have an extensive background in lipid research because they should have picked up the flaws. who knows for sure though.

        I am most upset with the poor investigative reporting of this before this information hit the public. The reporters simply sensationalized this and put a massive scare into the public rather than reporting a quality story. These people have potentially harmed the public’s already poor health by doing so.
        there are hundreds, if not thousands of studies on the benefits of having a balanced 3:6 ratio and having a healthy consumption of fish and fish oil in your diet. Are all of these studies to be disregarded because of this one poorly designed study?

        Rich wrote on July 31st, 2013
  15. The last point that you touch upon–that a bad diet with fish oil is still a bad diet–is a really important point. Many people seek a magic bullet to cure all of their health problems and physical incapablities, however it never works out. The real “magic bullet” is hard work, discipline, and going back to the essentials. This involves eating simpler, non-processed food and a return to primal movement patterns like squatting, deadlifting, and pressing.

    Jeremy Priestner | Art of Lifting wrote on April 28th, 2011
  16. Fitmom, Stabby, and Tony have some trenchant criticisms in addition to Denise’s excellent analysis. There are many possible explanations for this odd correlation.

    In the face of conflicting or unclear studies, evolutionary theory fills the void. We know that evolving humans had lots of access to the marine food supply; O3s are essential to our distinctive large brains, among other evidence. So dietary DHA is probably not the culprit. We also know that the prostate’s primary role is to concentrate nutrients from the bloodstream, so it only makes sense that it might concentrate carcinogens as well.

    I happily conclude that the most logical prophylactic against prostate cancer remains a primal diet combined with frequent ejaculation.

    Timothy wrote on April 28th, 2011
    • LMAO :) I concur!

      Robin wrote on April 28th, 2011
  17. Flaxseed oil has been linked to prostate cancer growth. ALA from flaxseed oil is converted to DHA via enzymes in humans. So a question would arise whether those with cancer and high in DHA obtained their DHA from conversion of sources such as flaxseed oil that might also promote prostate cancer. More study would be needed to determine whether DHA from fish is implicated.

    Since essential PUFA’s are extremely fragile and vulnerable to rapid degradation by light, heat, and age, there also arises the question whether the men studied obtained their DHA from degraded sources.

    Paleo Man wrote on April 28th, 2011
  18. Any of these studies that don’t control for other factors are almost useless. Of course that is part of the reason for duplicating a study

    bbuddha wrote on April 28th, 2011
  19. I don’t think the study had any huge methodological flaws. I definitely appreciate the criticism (it’s important that we look critically at all science) but I get a little tired of valid studies being portrayed as if they are bunk. I think this post might be a little more effective if it focused more on the media response and debunking that than the actual article itself.

    WolfGirl wrote on April 28th, 2011
    • It didn’t appear that Denise was really pointing out methodological flaws (and actually, having a relative small n, considering the large number of lipid types studied, as well as such a large amount of blood lipids catagorized as “other” are pretty significant flaws, IMHO) so much as she was pointing out alternative conclusions that could be made from the study findings.

      True, it is not entirely the fault of the researchers if the media decides to propegate the idea that fish consumption might be linked to increased incidence of prostate cancer. But it is the responsibility of the skeptic and guardians of the scientific process to investigate.

      And don’t worry too much about “valid” studies having holes poked in them–the rigorous scientific process encourages this. If a study is valid, it will stand up to this test. At any rate, a study can be entirely valid, mostly free of methodological flaws and still suffer from flawed conclusions.

      Does this study have value? Of course. Should it have been published? Absolutely–indeed, it’s methodolgy was sound enough to be taken seriously. Is further investigation warrented? Certainly. And I would guess that further study will likely provide us with information supportive of some of the hypotheses provided by Denise.

      fritzy wrote on April 28th, 2011
    • Well, WolfGirl, who cares a whit about the media response? I certainly don’t. They’ll prattle on no matter what we say or do and another demonstration of how the media machine produces lies and half-truths is simply covering old ground. I care about good science and part of that is subjecting evidence to the most rigorous scrutiny, as you admit. No one was harmed in the making of this post; your fatigue notwithstanding.

      Courage wrote on April 29th, 2011
  20. First time visiting vour site – as I just dip my toe in the Primal world. Been familiar w/ the Paleo Diet for some time but this article caught my eye for multiple reasons.

    I’ve just been reading a book Why We Get Fat and What We Can Do About It. Gary Taubes is the author. And in the same vein as this article on fish-oil, he speaks repeatedly as to the mechanics behind how high our LDL gets when lo-fat diets are introduced.

    Just thought I’d mention the book, for those of us interested in learning more as to “why”.

    Interesting site Mark, can’t wait to read more!

    spksea wrote on April 28th, 2011
  21. Fish flax oil tips. The specialists at Barleans offer fresh flax oil to help improve your health.

    Fish flax oil tips wrote on April 28th, 2011
  22. Just so we’re all clear on this: nowhere in the study did the authors ever state that fish oil (or fish consumption) was deleterious–the interpretation of the findings was restricted to *serum* fatty acids.

    And, in fact, if Ms. Minger would have bothered to read the discussion, there is another large prospective study that found a similar association (the EPIC study, one of the most highly regarded studies of diet and cancer to date). She makes out like this is an isolated finding… it is not.

    Just because a finding doesn’t agree with your preconceived notion doesn’t mean that the study is bunk–we simply may not have identified the relevant biologic mechanism.

    So basically her criticisms are (1) you shouldn’t express individual fatty acids as percentages of the total (a position which is debatable) and (2) it all may all be due to a low fat diet (which everyone follows, particularly men [sarcasm]). I fail to see any real value in her critique.

    If there is anything to be concerned about related to this study it would be the overinterpretation by the media, not anything to do with the study itself.

    I’m all for critical evaluation of research findings, and offering some perspective on studies related to diet, but Ms. Minger is making a career out of stirring up $h!t.

    I’m certainly not going to stop taking fish oil any time soon, but I will keep this in the back of my mind…

    Patrick wrote on April 29th, 2011
    • Hi Patrick,

      You wrote: “And, in fact, if Ms. Minger would have bothered to read the discussion, there is another large prospective study that found a similar association (the EPIC study, one of the most highly regarded studies of diet and cancer to date). She makes out like this is an isolated finding… it is not.”

      The EPIC study measured both serum phospholipid fatty acids (like this one did) and actual dietary intake from different food sources, including fish. The study did link higher serum DHA with prostate cancer, *but* it found zero association between fish fat intake and prostate cancer:

      “Our results showed no evidence of an association between the intake of fat from fish and shellfish and the risk of prostate cancer, which is consistent with the results from other prospective studies that have reported intake of fat from fish (20) or intake of the 2 major n-3 long-chain polyunsaturated fatty acids— eicosa- pentaenoic and docosahexaenoic acids—for which fish fat is a rich source (22, 23). Although some findings from in vitro and animal studies have suggested a role for n-3 long-chain poly- unsaturated fatty acids in lowering prostate cancer risk (24) and the association between biomarkers of n-3 long-chain polyun- saturated fatty acids and risk of prostate cancer has been investigated (25–29), only 2 observational studies have reported that a higher proportion of n-3 long-chain polyunsaturated fatty acids reduced the risk of prostate cancer (27, 29).”

      I’m not disputing that this new study found an association between elevated DHA in the blood and prostate cancer. I just want to hammer in that this doesn’t automatically mean food sources of DHA are going to contribute to the disease. Nor that high serum DHA is necessarily a perfect reflection of dietary intake (especially when measured in a percentage rather than absolute value). The study’s authors didn’t try to make those claims (and I only have praise for the way they reported their findings and admitted it ran contrary to what they expected) — but to the 99% of the population who doesn’t have the time or understanding to dig through the actual study, these findings are going to look like a slam against fish and fish oil. That’s why I wanted to do a closer analysis of it.

      “(1) you shouldn’t express individual fatty acids as percentages of the total (a position which is debatable)”

      There are problems with expressing FA’s as absolute concentration as well. I think it would be interesting, though, to see if the pattern with DHA and trans fats would remain if they weren’t measured in relative terms.

      “(2) it all may all be due to a low fat diet (which everyone follows, particularly men [sarcasm]).”

      Not quite. I don’t know if there’s a threshold after which fat intake stops being inversely associated with serum omega-3s. If it’s linear, it could mean the men with the lowest fat intake (even if their diet wasn’t traditionally “low fat”) were somehow at heightened risk for aggressive tumor growth. This is entirely speculation, since I don’t think many (any?) studies have found an inverse link between fat intake and prostate cancer, but it could be reflecting another diet component associated with lower fat consumption (higher processed carbs, “low fat” sugary versions of foods, etc.). Again, only speculation at this point, but I think it’s worth considering.

      “If there is anything to be concerned about related to this study it would be the overinterpretation by the media, not anything to do with the study itself.”

      The misinterpretation by the media is due to not understanding the implications of the study’s results. What better way to clear that up than do an analysis of the study and see what it’s really saying? That was my only goal here. :)

      Thanks for your feedback!

      Denise Minger wrote on April 29th, 2011
      • Hi Denise,

        Thanks for your thoughtful reply. Re: the EPIC study and fish intake: as you know, it’s incredibly challenging to assess associations between intakes assessed via food frequency questionnaire, so it’s not surprising that they find a null association with fish fat intake there. That doesn’t preclude something going on re: serum DHA that we simply haven’t figured out yet. I think your speculation re: low-fat diets and DHA levels is interesting, but I don’t think it really calls any of the findings into question–I find it unlikely that the men in this study were following a low fat diet at the level of the intervention in the study you cite. As you point out, there could be a lot of other things going on (high refined CHO, for example), but you would expect the effects of higher DHA to ameliorate those (potentially inflammatory) effects. This definitely warrants further study.

        As a primal/paleo devotee, and scientist (who, incidentally, does this type of research), I applaud your efforts to have folks critically evaluate research such as this–there’s a lot of crap out there in the nutrition world. I think it’s important to keep some perspective on both sides–judging from some of the comments many of the readers tend to have a totally dismissive attitude to this study now, which is just as ignorant as those who treat it as a reason to eschew fish oil. A former professor of mine used to say when consuming scientific findings “be critical, but not cynical…”

        Patrick wrote on April 30th, 2011
      • So would this point to flax oil as an issue?

        If my wetware RAM still functions, I think in Art De Vany’s book he said something along the lines of “we feed flax to chickens so their livers convert them to EPA/DHA, bad deal for the chickens, good deal for us.” This was part of the discussion about vegan sources of n-3’s and how flax causes problems.

        Perhaps this is part of the same mechanism?

        RayDawg wrote on May 6th, 2011
    • Also regarding the EPIC study: The actual association between serum phospholipid DHA and prostate cancer wasn’t very high (RR 1.39) and wasn’t statistically significant:

      Denise Minger wrote on April 29th, 2011
      • The adjusted relative risk of 1.39 comparing the 5th vs. the 1st quintile would be considered “moderate” by epidemiologic standards, but I agree, hardly worth chucking my bottle of Carlson’s over.

        This contrast was, in fact, statistically significant (RR: 1.39; 95% CI: (1.02, 1.90)) Note that the 95% confidence interval does not include the null value (1). What wasn’t statistically significant was the “trend test” (p-value=0.158), which assesses (roughly) if greater and greater serum DHA was associated with greater and greater risk… so these results seem to suggest that there’s a “threshold” that once you cross it, your risk doesn’t really change. There are some issues I could discuss here related to categorizing DHA levels using percentiles (how it relates to this study as well as implications for comparison to others), but they’re not critical here…

        As an aside, statistical significance isn’t the “holy grail” that some would make it out to be, and is becoming (or is, depending on where you are), a controversial topic in population-based research. I’d be happy to point you to some references if you’re interested.

        Patrick wrote on April 30th, 2011
  23. The world could use a few more Denise Mingers.

    BW wrote on April 29th, 2011
    • Denise Mingers and Patrick’s too! damn the info they just put out was way over my head! A bit of a pissing match but good stuff!

      Rich wrote on July 31st, 2013
  24. I’m curious to see what nationality these “Americans” were. My husband is Filipino and their diet is highly based in fish. Just curious

    Amanda wrote on April 29th, 2011
  25. There is surely some money behind this report somewhere I’ll just say it.

    Trans-fatty acids prevent cancer? Right. I’d hate to see there results on an Aspartame study.

    Rodney wrote on April 29th, 2011

    DAVE PARSONS wrote on April 29th, 2011
    • Oops, what about cervical, anal, and penile cancers, all caused by STIs? Better use protection!

      Another Halocene Human wrote on April 30th, 2011
  27. Nobody in my family and all relatives (total of about 80 people) had any prostate problems…(or breast and ovarian cancer in women).
    Nobody went to the doctors to get ‘screened’. We all ate a low grain diet, high in fat, mostly pork.

    I moved to the states, met my husband (who was his entire life on a heavy grain/brean diet) and is the ONLY 1 with an enlarged prostate and had to have surgery.
    I also met a farmer who sprayed chemicals en mass for a decade and ended up with prostate cancer. He cured it by himself with a primal diet and sold his polluted piece of land.

    If the guys stick to a primal diet I don’t think any of them will ever get cancer, of any kind.

    Donnersberg wrote on April 29th, 2011
    • There’s no link between an enlarged prostate and prostate cancer, nor is there a link between diet and an enlarged prostate. An enlarged prostate has to do w/ hypertrophy of the glandular tissue from dihydrotestosterone & doesn’t require surgery in most cases.

      cody wrote on April 29th, 2011
  28. The study authors hypothesized that high omega 3 diets cause prostate cancer because high prostate cancer rates correspond with high blood omega 3 levels. Denise responded.

    A poster said that neither party proved nor disproved their hypothesis. But Denise did not make a hypothesis. The study authors did. Denise DID disprove the hypothesis by citing a study which showed that a high fat diet causes high omega 3 blood levels. So omega 3 ingestion does not NECESSARILY correlate with high omega 3 blood levels.

    Then a blogger posted that the study results mean that high omega 3 blood levels cause high prostate cancer rates. So according to the blogger “moderate omega-3 consumption is beneficial but high consumption is harmful.” Denise’s response study says nothing of the sort. It says that omega 3 ingestion is not indicative of omega 3 blood concentration, that omega 3 blood concentration can result from a low fat diet.

    So combining the hypothesis study with Denise’s answer study, two things are possible:

    1. Both low fat dieting and high omega 3 dieting can cause high omega 3 blood levels, and that high omega 3 blood levels cause prostate cancer, or

    2. Low fat diets cause elevated blood omega 3 levels and cause prostate cancer.

    The blogger chose number 1. But neither study found that high omega 3 blood levels CAUSE prostate cancer. Given that Denise’s study correlated high fat diets with high omega 3 blood levels, and that the hypothesis study found that high omega 3 blood levels correspond with high prostate cancer rates, wouldn’t number 2 be more likely? ….that Low fat diets cause both elevated omega 3 blood levels and prostate cancer? ….in no particular order?

    At any rate, unlike the blogger contended, the exchange confirmed neither 1 nor 2 above. So we can’t draw conclusions about the proper omega 3 intake rate for avoiding cancer. We can only conclude what Denise said, that high omega intake does not necessarily correlate with high omega 3 blood levels. The hypothesis study is wrong.

    It seems that someone is hiding common sense from public dissemination. Someone please alert science authorities.

    Good work, Denise.

    veggienft wrote on April 29th, 2011
    • The hypothesis that the study authors put forth is that *serum* fatty acids are related to risk of prostate cancer. They make no claim regarding diet–that was put forth by the media (and picked up by Ms. Minger).

      Denise’s critique disproves *nothing*. She offers a *potential* reason that low fat diets are the cause of the elevated DHA levels. There are a number of reasons why I believe that this is highly unlikely, not the least of which is the fact that almost no free-living human follows a low-fat diet. They may not be Paleo/Primal, but they’re not Ornish either. Add that to the fact that this entire line of reasoning is supported by a single, small *interventional* study (which fails to propose a convincing mechanism), and it hardly seems worth mentioning.

      If it holds that the DHA from fish consumption is, in fact, the culprit (again, the jury is not even close to being in on that yet), then It’s more likely that something else related to their fish consumption (preparation, perhaps) would explain the discrepancy between the expected and observed findings. With 2 large prospective studies coming to the same conclusion, there’s definitely something going on, and it warrants more drilling down to find the answer. Saying this is convincing evidence to stop eating fish, or conversely that it’s a worthless study and should be ignored, is an ignorant position either way.

      The first author said it best in the Science Daily article that she linked to above:

      “”What this study shows is the complexity of nutrition and its impact on disease risk, and that we should study such associations rigorously rather than make assumptions…”

      Patrick wrote on April 30th, 2011
  29. Some years ago in the Journal of Clinical Cardiology there was a study of vascular flow and endothelial function following ingestion of olive oil. The surprising results were the ingestion of olive oil caused a deterioration of vascular endothelial function and also diminished flow by 30%. A later study provided further insight – fresh olive oil that had been protected from light, heat, and air and had high natural polyphenol content improved endothelial function and degraded olive oil that had been exposed to light for as little as two weeks lost its polyphenol content and had a negative effect on vascular function. The same may be true of essential Omega 3’s, even more so in light of their fragile nature. If they are regarded, processed, and stored as if they were ageless motor oil, they may have the same health benefits as motor oil. Fragile essential oils probably need to be treated and stored more like raw hamburger, like fresh natural food that can deteriorate, like everything truly primal.

    Paleo Man wrote on April 30th, 2011
    • I can TOTALLY buy that. It’s my personal opinion/hunch/superstition that fats, even normally GOOD fats, that have been exposed to heat or otherwise transformed (oxidation?) are bad news.

      Jeffrey wrote on October 13th, 2011
  30. It is plausible that persons with lower omega-3 fatty acids had higher levels of trans fats. They probably were eating more butter, which is high in trans-fat content (typically ~5%).

    R.Hirsch wrote on April 30th, 2011
  31. Denise rules.

    Roo wrote on April 30th, 2011

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