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

Dear Mark: Is Flax Bad?

flax seedsDear Mark,

I’ve been researching flax and am ready to pull the plug on my dedicated flaxseed grinder. The kicker was seeing flaxseeds associated with prostate cancer. What’s your take?

Thanks to reader Clare for the thoughtful correspondence on flax. This is exactly why I love doing this blog. Research continues to unfold, and the conversation never fails to engage and inspire me.

As Apples know, I’ve been a flax supporter. Lately, I’ve been mulling that position. While I don’t think a single study’s results should rewrite the book on any issue, when a number of studies suggest that it may be linked to serious illness in some people, that’s enough to give me pause. And, well, it’s enough to incite me to do some digging – and pondering. Flax is one of those cases lately.

The deal is this. Flax seed is rich in a form of omega-3 fatty acids called ALA (alpha-linolenic acid). Omega-3 fatty acids as a whole (group) are especially vital for the development and ongoing well-being of the nervous system and for the health of the cardiovascular system. They improve lipid profiles, thin blood, and combat inflammation like nobody’s business. (You know how I feel about that one, eh?) They can also help curb insulin resistance.

Research time and again supports the role of omega-3s (again, as a group) in overall health; however, some studies and reviews over the last few years have linked high ALA intake (from both flax oil and milled seed) with higher incidence of prostate cancer. ALA blood levels are higher in response to flax oil intake than they are with milled seed intake. (Eating whole seeds isn’t recommended unless you’re looking for some serious abdominal havoc.)

I’ve always maintained that other animal-based forms of DHA and EPA offer more health-related bang for your buck, and I stand by that point. The preponderance of research supports the particular power of EPA and DHA in the omega-3 fatty acids. One study suggests that fish intake (rich in both DHA and EPA) actually reduces the risk for prostate cancer.

The bottom line is ALA doesn’t do much that DHA and/or EPA can’t do and probably do better. As avid Apples know, I suggest that everyone take a fish supplement. In the past I’ve seen ALA as a decent secondary choice for vegetarians and as a useful addition to a healthy Primal eating strategy (e.g. a bit of ground flax seed on some berries). The human body isn’t terribly effective at converting ALA to either DHA or EPA, hence the need for added dietary intake or supplementation. (An interesting side nugget: women’s bodies are a little better at this conversion. Research has shown that young women convert 21% of ALA to EPA (compared to 8% in men) and 9% to DHA (compared to 0-4% in men). The difference, apparently, is linked to estrogen levels.)

Fish Oil Capsules

So, what’s my current suggestion in light of the potential prostate cancer link? If you’re a woman, the obvious point of the research isn’t relevant. Nonetheless, the underlying role of phytoestrogens in flax is nonetheless an important one. I’d say that healthy women can consume low to moderate amounts of flax without concern. Sure, a large amount of research suggests the protective effect of phytoestrogens against breast cancer (in healthy women), and this research includes flax. Nonetheless, a lot of a seemingly good thing isn’t necessarily better or even safe. My advice would be to use fish oil as your primary omega-3 source and keep the ALA on the lower side.

If you’re a man? Particularly an older man? I’d definitely suggest you make fish oil your principal source of omega-3s. Is it time to chuck the flax grinder all together? Based on the research, I’d at least put it into semi-retirement. (I’d suggest forgoing flax oil entirely.) In the meantime, we’ll stay on top of this one and let you know about any new developments on this front.

As always, thanks for your questions and comments. Keep ‘em coming!

diglyesica, tellumo, spdrecrd Flickr Photos (CC)

Further Reading:

Omega 3 Fatty Acids Round Up:

Omega 3 to 6 Ratio

Omega 3 Daily Dose

Omega 3 Food Sources

Cooking Omegas

Modern Forager: The Vaunted Flax Seed

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. This post is somewhat refreshing to me. I have never really been a fan of adding Flax to my diet. Not because I thought it bad for you but more because I have never enjoyed it and have always had difficult fitting it in time, place and taste wise with my diet. I still make sure i get plenty of omega-3’s though! Flax was looked at as almost a mecca back in my bodybuilding days but if more research shows this to be bad thing then I will be glad yet again that I ignored the mainstream hype.

    Son of Grok wrote on September 8th, 2008
    • The issue of flax is very complicated. I don’t see anything on the web that would preclude adding flax in moderate amounts to the diet.


      nancy james wrote on August 24th, 2012
    • I am 64 years old and I’ve heard all the arguments for and against flax. I take prostate supplements because I get difficulty in emptying the bladder sometimes.
      But the most relief I get from prostate problems is when I take 2 tablespoons of ground flax seeds every day. My prostate and bladder usually get back in good shape after doing this for a few days.
      So all the studies back and forth don’t mean anything to me. I know what gives me relief and better health.
      Don’t forget the famous cancer cure from Dr. Budwig which consists of flax seeds/flax oil and cottage cheese. This is a proven cure, so the flax is doing something good here.

      steve s. wrote on March 3rd, 2014
    • Here is info from a flax seed study: “In male rats, lifetime 10% flaxseed exposure raised serum testosterone and estradiol levels and produced higher relative sex organ weights and prostate cell proliferation. In contrast, lifetime exposure to 5% flaxseed reduced adult relative prostate weight and cell proliferation, suggesting potential protection against prostatic disease, although sex hormone levels were unaffected. In conclusion, flaxseed can potentially alter reproduction, depending on the dose and timing of exposure.”

      So, at very high amounts for their entire life span, flax seeds increased both testosterone and estradiol and even at 5% of their diets for their entire life, no effects on hormones were found. Conclusion, people recommending men avoid flax oil “because it contains estrogens” don’t have a clue what they are talking about…

      (1) Brzezinski A & Debi A, Eur J Obstet Gynecol Reprod Biol, 85(1): 47, 1999)

      (2) Tou JC, Chen J, Thompson LU.J Toxicol Environ Health A. 1999 Apr 23;56(Cool:555-70.
      – See more at:

      steve s. wrote on March 3rd, 2014
      • I’m curious what’s the consensus here on rats compared to human physiology, in general.

        One of the tenets of Chinese medicine is to test things on humans.

        Justin wrote on April 17th, 2016
    • I am beginning to see that mainstream hype, is now geared towards blundering what is good for us. Each to their own as every human reacts differently to everything they put into their body’s. There’s never gonna be a quick fix for diets. Pure experimentation, and move on. Bottled water in a humid gym = chemical reactions with bottle = carcinogens. There’s no end to opposite opinions being mascaraed from a Chinese Whisper to what we call fact. The Internet confirms what we want to be true but may not be true in the end. I wasn’t aiming this at anyone you where the first post to see. No hard feelings I’m just an outsider

      Raphanator wrote on July 17th, 2014
  2. I think flax is great but it must be used in the right way, the fact that when consumed as seeds (unground) they are a potent Estrogen metabolizes is something very interesting for men…I regularly add the seeds to yoghurt and shakes or even sprinkle some in burgers……I think its also best to mill your own batches of Flax and keep them in the fridge to ensure optimal freshness….

    Chris - Zen to Fitness wrote on September 8th, 2008
    • Just so I understand correctly..flax seeds can help men lower estrogen levels? (And thus reduce the effects of it?)

      Or did I get this backwards?

      Phil wrote on December 24th, 2009
      • no….Flax increases estrogen, it has a lot of estrogen in it along with Soy which is why its so toxic to men, also soy and flax leach the body of Zinc and zink prevents prostate cancers :)

        chris wrote on June 26th, 2013
  3. Mark – thanks for this info. I have a couple of questions.

    1. I have about 1000mg of flax seed oil per day – is this a relatively low amount in the context of this discussion? All this talk of flax grinders makes me think my consumption is probably on the low side, but it would be good to get your view.

    2. I do get a lot of fish oil in my diet both via food and supplementation but had always understood that ALA offers something extra that is needed to complete the omega 3 picture. If this is not true I’ll happily ditch the flax oil and stick to the fish oil – one less bottle on the shelf!


    Methuselah - Pay Now Live Later wrote on September 8th, 2008
  4. I’m not a fan of flax. Interesting, people with certain endocrine disorders can not tolerate flax, including myself. I’d stick with the fish oil or grass-fed meat.

    Crystal wrote on September 8th, 2008
  5. i cant see anything past september 6th?

    anna wrote on September 8th, 2008
  6. Thank you for the comment, Anna. We are working on a solution. I apologize for the inconvenience. In the meantime, Firefox seems to be displaying MDA just fine.

    Aaron wrote on September 8th, 2008
  7. As we age, the enzyme (delta-6 desaturase) that converts Omega-3 to EPA/DHA, decreases in activity.

    Thus with less anti-inflammatory EPA/DHA oils, the prostate, as well as other tissues, would become inflamed and dysfunctional.

    I am willing to bet that with increased ALA in the diet, not only prostate cancer, but, other cancers would exist too.

    drcapt wrote on September 8th, 2008
  8. How about the fibre content; is flax seed at least a valuable source of fibre? (Not that anyone following the PB diet needs to add fibre to the bountiful amount that veggies provide!)

    I don’t understand why whole unground seeds pose a potential problem. Would not Grok have nibbled on a few pinches of flax seeds as he found them? Aren’t they whole, unprocessed, natural goodness?

    I don’t know if my smoothies will ever be as good without the flax. :(

    new_me wrote on September 8th, 2008
  9. Hi Mark,

    Can you let me know your thoughts on omega 3’s post workout? I had read somewhere that this is not optimal.


    Brett wrote on September 8th, 2008
  10. Crystal,you said that people with certain endocrine problems cannot handle flax. Is that someone who is hypothyroid?

    Sue wrote on September 8th, 2008
  11. There’s an inaccuracy in this article – there are vegan EPA and DHA supplements from algae.

    Tony wrote on September 8th, 2008
  12. Possibly Sue. There isn’t a lot of info. out there but it is common among hypoT./hypoA. people. It must have something to do with the conversion causing stress. Others think it’s a goitergen and should not be eaten.

    Some people are intolerant to flax worsening a nervous/emotional disorder—but what is described is actually low cortisol IMO.

    Crystal wrote on September 8th, 2008
  13. Hello Mark,

    Any opinion on chia seeds as an omega source, flax alternative?


    DC wrote on September 8th, 2008
  14. I use a high-quality liquid fish oil as my main supplement to combat inflammation and have really cut back on the flaxseeds (ground) after talking with my natural doctor. He suggested trying hemp seeds.

    I would also be interested in similar research (if it exists) on both chia and hemp seeds.

    greg wrote on September 9th, 2008
  15. Tony – The article doesn’t say there aren’t vegan sources; only that ALA is an option for vegetarians.

    Thanks for the link.

    Aaron wrote on September 9th, 2008
  16. DC – Thanks for the question. I think we have a chia seeds post in the works. Check back!

    Aaron wrote on September 9th, 2008
  17. Aaron, thanks for your response. Actually, Mark does say that there aren’t any vegan options for DHA and EPA:

    “I’ve always maintained that other animal-based forms DHA and EPA offer more health-related bang for your buck, and I stand by that point.”

    He says that DHA and EPA are “animal-based forms” of Omega-3s. This isn’t true and weakens his conclusion that fish oil is the best solution for those trying to get a healthy balance of Omega-3s.

    Tony wrote on September 9th, 2008
  18. Tony – I’m still not sure how you get that Mark is saying vegan sources of DHA and EPA don’t exist. He is simply saying that he has always said that it is better to get Omega 3s via animals than flax. At least this is how I read it. Nevertheless I am pretty sure this is what was meant…

    Aaron wrote on September 9th, 2008
  19. Hey Aaron. In the passage I quoted above Mark specifically says that EPA and DHA are animal-based.

    “He is simply saying that he has always said that it is better to get Omega 3s via animals than flax.”

    No, he isn’t simply saying that fish oil is better than flax – what he’s saying is that he recommends fish oil as the best source of a good balance of omega 3s (out of all options, not just compared to flax). Without any mention of plant-based EPA and DHA this conclusion seems hasty at best.

    I know people find it obnoxious when vegans go on about their diets, but the reason we’re prone to preach is because the diet is so frequently unfairly maligned. I think it’s obvious that any reader will come away from the above article thinking that eating animals (in some form) is the only way to optimal health. This is a damn shame because it’s just not true, and while I’m sure it’s not Mark’s intent to knock veganism, by completely ignoring vegan DHA and EPA and coming to an ill-informed conclusion, that’s the effect his article has.

    Tony wrote on September 9th, 2008
    • Because someone might come along and read this later: I cannot go vegan unless I want to bleed out through my uterus. You can’t get real vitamin A from a vegan diet. I find that if I go low on vitamin A, my cycle gets all messed up. I am not the only one with this experience. A friend of mine on FB heard about my problem and tried vitamin A in her own health regimen and had the same results I did. And charity clinics in developing countries often use vitamin A to cure dysmenorrhea (sp?) in women of those countries. Not to mention it is vitamin A capsules, not golden rice, which are used to prevent blindness in children. (Kids under five can’t even convert beta carotene!)

      You also can’t get B12 in a vegan diet. You MUST supplement. If you *have* to get a nutrient from a pill in order to follow the rules of your diet, by definition your diet is not healthy. There’s a difference between just missing out on a nutrient because you didn’t eat enough of a food allowed in your dietary pattern, and *having* to supplement because the nutrient isn’t in any allowed foods at all.

      There isn’t anything unfair about maligning a diet that, followed properly, results in malnutrition. Vegans can only be vegans because you have an industrial support system that makes supplement pills for you. Follow it if you want. But we’re not the ones making inferior dietary decisions. It’s foolish to rely on machines for all of your intake of any nutrient, and even more foolish to cite farm animals not being fed species-appropriate diets as your excuse for not following a species-appropriate diet yourself.

      Dana wrote on January 18th, 2012
      • It’s true that with our hyper-sanitized food supply nowadays that vegans must supplement with B12. B12 of course, is a bacterium, not an animal product per se.

        Donald Watson, the gentleman who coined the term vegan, lived on a purely plant-based diet for over 55 years (most likely without B12 supplementation for all those years), and died at the ripe old age of 95. Not bad for someone subsisting on a diet that “results in malnutrition.”

        Omnivores must supplement with B12 as well, as they get older:

        “Many older adults, who do not have enough hydrochloric acid in their stomach to absorb the vitamin B12 naturally present in food. People over 50 should get most of their vitamin B12 from fortified foods or dietary supplements because, in most cases, their bodies can absorb vitamin B12 from these sources.”

        Mike wrote on October 18th, 2013
      • Want vitamin A on a vegan diet–just eat sweet potatoes or pumpkin
        and you’ll get plenty.

        mike wrote on May 6th, 2014
  20. The algae supplements come from Switzerland. Are they available in other countries?

    I think its a lot easier to achieve optimal health on a diet that includes meat. It could possibly be achieved on a vegetarian diet but with a lot more thought and possibly a lot more supplements.

    Sue wrote on September 9th, 2008
  21. I stopped grinding flax a year or so ago based on the mixed research, some of it is pretty strong, same thing with soy, too much risk, there’s proof to suggest they are unsafe, that’s enough for me, other things like cod liver oil have down sides (pro oxidant, rancidity, heavy metals etc) but the research is more favourable, so i still consume it.

    JC wrote on September 10th, 2008
  22. Hey Sue, I don’t really know of any other vegan DHA and EPA supplements, but I do remember reading about others in development a few years ago when V-Pure came out. Although they’re based in Switzerland I think they deliver to the states. Supposedly they’re also working on an algae-based b12 supplement, more good news for vegans.

    “I think its a lot easier to achieve optimal health on a diet that includes meat.”

    I think in general this is true – planning a vegan diet in our meat-obsessed culture can take some time. However, there are lots of health problems associated with meat that vegans don’t deal with at all. Aside from the correlation with heart disease etc (which can be avoided if you eat the right meats), I am mainly thinking of accumulated toxins. Of course, you can buy free-range, grass-fed, no-antibiotics etc etc, but this can be difficult and costly. I’m guess what I’m trying to say is that for truly optimal health (which includes no toxins) it might be easier to just go vegan (also wayyyyy cheaper). There aren’t even really many supplements – b12 is the only one you absolutely need and then the omega-3s.

    Here is a thing from the V-Pure site, about “the dangers of fish oil.” Obviously, V-Pure has a business interest in convincing you of its claims, but then again, so do many proponents of fish oil.

    Again, I’m not trying to preach but it’s just SO frustrating when every single bit of advertising and health advice you see is a paean to the wholly destructive industrial meat industry.

    For a far more detailed rundown of EHA and DPA:

    Tony wrote on September 10th, 2008
  23. This may have been answered already but I can’t find it…I have never found a fish oil that doesn’t “repeat” on me. I have tried (& returned) virtually every one that anyone even suggested would agree with me. I even tried just a liquid which was mixed in with my daily protein smoothie. Yuck & ick! The only one even remotely palatable has been Coromega–but it seems pretty low dosage. Any suggestions? I currently take a 1000 mg “organic” flaxseed oil cap. daily. I’m 63 & take no medications.

    gloria wrote on September 10th, 2008
    • I take Carlson’s Cod Liver Oil Professional Formula with light lemon flavour. I’m not saying it doesn’t ever “repeat” but I take it at night shortly before bed so it doesn’t bother me. I admit if I take it in the morning I can have an issue. Both of my 60 year-old parents take it in the morning, though, and never have a problem.

      I wouldn’t mix any CLO with food, even a smoothie– the taste always comes through. It doesn’t taste wonderful, but with a sip of water I down it like a pill and it’s not too fishy (like some other CLO I’ve tried). I’m a huge baby about taking anything that tastes bad, so if I find it palatable, I think anyone could handle it. Good luck!

      Bridget wrote on November 11th, 2012
  24. **OT, but can’t wait to read the chia post.

    recently had a green bar w/chia..then started reading up on someone making chia drinks, etc. The fiber content is out of this world..

    will check back soon.

    yipper wrote on September 11th, 2008
  25. Ground flax seeds do NOT cause any sort of cancer. This is another paranoid headline-grabbing phenomenon based on dubious science from a tiny study or handful of studies. Who sponsored the research? Think about it- who the heck would pay to study a link between flax seeds and prostate cancer? It wouldn’t surprise me if it was another scare tactic by the meat or pharmaceutical industry. Reminds me of the garbage about too much Vitamin E, too much soy, and most recently drinking too much water. There will always be research that supports or attacks anything ever studied. Intelligent people read a cross section, take note who sponsored which studies, and act in accordance with the majority of independent science. The majority of independent science in regard to flax seeds is clear: they are an extremely beneficial food. Period.

    Peter Sklar wrote on September 11th, 2008
  26. Peter, you said:
    “Ground flax seeds do NOT cause any sort of cancer”

    You can’t make such a statement, where is your proof that it doesn’t cause cancer. Flaxseeds contain phyto-oestrogens so it makes sense that there would be a study examining any links with cancer.

    Sue wrote on September 11th, 2008
  27. Susan-

    In science, one doesn’t normally seek to prove that a substance DOESN’T cause something, (such as cancer); one normally attempts to prove that it DOES. The scary word “phyto-estrogens” literally means plant estrogens. Virtually every healthy food we eat — most vegetables, most fruits, grains, beans, nuts, seeds, and roots — all contain phytoestrogens. Perhaps you didn’t realize that. The preponderance of independent research in fact indicates that phytoestrogens actually PROTECTS tissues from the cancer-causing effects of xenoestrogens and other hormonal pollutants. I repeat my suspicion as to why flax seeds were singled out for such a misleading headline. What’s next- broccoli causes melanoma?

    And I repeat: who sponsored that so-called “research”?

    Anyone here know?


    Thank you. -P

    Peter Sklar wrote on September 11th, 2008
  28. How come there’s no info on who did the study and what they did in the study? We need the proof before we can believe that this is true. To me it sounds like someone just made this up, why only flax and what about the other foods that have ALA in them? If it was the ALA that caused prostate cancer then why is flax the only food to be targeted?

    Michael wrote on September 11th, 2008
  29. It’s always a relief to see a note of reason, in present case, from Peter and Michael. I spend a lot of time finding valid info for consumers, and have seen good double-blind clinical studies [not funded by special interests] which have shown that flaxseed consumption is definitely beneficial in opposing prostate and other cancers. Anyone who has a cause to prove can always find something to back it, of course. The amount of irresponsibility so often seen re: quoting an isolated study [which as Peter and Michael have pointed out was not even identified] is sad. It is doubly so when that’s done by someone who speaks as an authority. This is a position, which once chosen, demands objectivity and thoroughness due to influence on the uninformed. –Linda

    Linda wrote on September 11th, 2008
  30. The study is mentioned above. Just click on the link just after the picture of the flax bottle.

    Sue wrote on September 11th, 2008
  31. I would like to recieve your daily ‘informational’ updates, Thanks,

    sl wrote on September 11th, 2008
  32. I reviewed the study. The final sentence from the authors’ own abstract says it all:

    “It is quite uncertain at present whether the effect on prostate cancer is real.”

    Case closed.

    Thank you.


    Peter Sklar wrote on September 11th, 2008
  33. O.k. One more point.

    And this flimsy, non-conclusive, ambiguous conclusion inspired HEADLINES warning people against flax seeds.

    Mark, with all due respect, how about a bit more homework next time before advising your readers to avoid an extremely healthy and essential nutrient source.



    Peter Sklar wrote on September 11th, 2008
  34. Ok, I have read all of the pro’s and con’s and still have no idea whether I should continue having Flax seeds (3 tablespoons) with my cereal and my salads. I usually have one helping 3tbs per day. I am a male,76 years of age, in good health and take 1 each: 1000mg of Fish Oil Concentrate with Omega-3 Fatty Acids together with Vitamin B-6 (100mg); B-12(1000 mcg);
    Folic Acid (400 mcg); Vitamin D (1,000 IU); Magnesium (250 mg)and a Mature (Kirkland-same as Centrum Silver) Multi Vitamin daily.

    So, with all of the various discussions on this Blog, just where does a guy in my shoes fit into this picture, especially as regards to the possible affects to my prostate of using Flax Seed?? Thanks to anyone or everyone who is able to provide me with substantive info. Thanks

    FLOYD HOLMES wrote on September 11th, 2008
  35. Addendum to Floyd Holmes comment: I also eat salmon (wild) twice a week and red meat once a week.

    FLOYD HOLMES wrote on September 11th, 2008
  36. Uh…I thought it was pretty clear that flax seeds are a wonderful food. Let’s put it this way: I’m a 59-year-old male who researches nutrition daily, somewhat as a hobby and partly related to my work. I read at least a half-dozen health-related publications regularly. I reviewed the above study supposedly establishing a link between flax seeds and prostrate cancer.

    My conclusion? I am continuing to have crushed flax seeds almost daily with my meals.

    I read nothing whatsoever- except a sloppy interpretation of some research, and some paranoid gossip- that would make me concerned.

    Those of you who are now afraid of eating flax seeds- are you going to stop eating most fruits, vegetables, and grains as well? If you’re concerned about phytoestrogens, you absolutely should.



    Peter Sklar wrote on September 11th, 2008
  37. I have been aware of this issue for many years now..that plain Flax seed oil is not beneficial to men and has phtoestrogen qualities and can cause issues with the prostate. BUT the kicker in this is “Plain” flax seed oil. “IF” the flax seed oil is with “Lignans” is has been stated to be okay for men. I believe that any flax seed oil taken should be organic and taken as oil “with Lignans for both men and women” always. The lignans help the nody remove excess estrogen.

    MCM wrote on September 11th, 2008
  38. Another great form of Omega 3s are from Chlorella. Chlorella, spirulina and algaes are all excellent sources and also provide numerous other health benefits. Definitely worth taking.

    MCM wrote on September 11th, 2008

Leave a Reply

If you'd like to add an avatar to all of your comments click here!

© 2016 Mark's Daily Apple

Subscribe to the Newsletter and Get a Free Copy
of Mark Sisson's Fitness eBook and more!