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Flaxseeds & Breast Cancer Prevention

Young women at high risk for breast cancer given just a teaspoon of ground flaxseeds a day showed fewer precancerous changes.

April 5, 2013 |
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Supplementary Info

Sources Cited

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C. Eliasson, A. Kamal-Eldin, R. Andersson, P. Aman. High-performance liquid chromatographic analysis of secoisolariciresinol diglucoside and hydroxycinnamic acid glucosides in flaxseed by alkaline extraction. J Chromatogr A. 2003 Sep 19;1012(2):151-9.

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A quarter century ago, a theory was put forth as to why those eating plant-based diets have lower cancer rates.  Vegetarians appeared to have about twice the level of lignans circulating within their bodies, related to the amount of grains and other plant foods they were eating. Back in 1980 a new compound was described in human urine, a compound X, originally thought to be a new human hormone, but later identified to be from a large group of fiber-associated compounds widely distributed in edible plants known as lignans. Population studies suggest that high intake reduces breast cancer risk, but where's it found? Seeds, whole grains, vegetables, fruits and berries. So why isn't it just like the fiber story where lignan intake is just a surrogate marker for healthy plant food intake. Well in a petri dish lignans do directly suppress the proliferation of breast cancer cells but only after the plant lignans are converted into human lignans by the bacteria in our gut. That's why we want to use antibiotics judiciously, because a few days on antibiotics dramatically drops your body's ability to make these anticancer compounds from the plants that we eat, and it can take weeks for our gut bacteria to recover. That's why women with urinary tract infections may be at higher risk for breast cancer, because every time they took a course of antibiotics they were stymying their good bacteria's ability to take full advantage of all the plants they were eating, though this remains little more than a hypothesis or educated guess at this point. This is the National Cancer Institute study that provided the strongest evidence to date that there may indeed be something special about this class of phytonutrients for breast cancer prevention. They took a bunch of young women at high risk for breast cancer, meaning they had a suspicious breast biopsy, showing either atypical hyperplasia or carcinoma in situ, or already had breast cancer in the other breast, and gave them a teaspoon of ground flaxseeds every day for a year before getting a repeat needle biopsy to see if there was any change. Yes, there are lignans in sesame seeds, nuts, whole grains, legumes, certain fruits, and veggies, but they're most concentrated in flax seeds. They could have instead asked women to eat ten cups of strawberries a day for a year, but they'd probably get better compliance with just a teaspoon of flax. So what happened by the end of the year? The primary end point was the expression of a proliferation biomarker associated with cancer called ki-67. In 9 of the 45 women it went up, those in red, but in the other 80% of the women it went down. And indeed on average they found less cellular proliferation in their breast tissue, and fewer precancerous changes. For those that don't like the taste of flaxseeds, sesame seeds may work just as well. Even though flaxseeds have significantly more lignans than sesame, you appear to produce about the same amount of lignans from them, though this was comparing them whole, and when you feed people whole flaxseeds some may not get chewed and they can pass right through you, so ground flaxseed may be best.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.

To help out on the site please email

Dr. Michael Greger

Doctor's Note

Today starts a three-part video series on the role flaxseeds may play in the prevention and treatment of breast cancer. I covered their role in prostate cancer in Flaxseed vs. Prostate Cancer and Was It the Flaxseed, Fat Restriction, or Both?. Then for blood sugar control (Flaxseed vs. Diabetes) and skin health (Flaxseeds For Sensitive Skin).

When I say "why isn't it just like the fiber story" I'm referring to the previous video Fiber vs. Breast Cancer. The graph comparing the lignan contents of various foods is from this video: Breast Cancer Survival and Lignan Intake. Sorry if I covered the UTI-breast cancer connection a little fast—more background on the role our good bacteria play in Flax and Fecal Flora. As I note in the Flaxseeds For Sensitive Skin video, ground flax stays fresh even at room temperature for at least a month.

What if you or a loved one has already been diagnosed with breast cancer, though? Hopefully you'll find the next two videos useful: Flaxseeds & Breast Cancer Survival: Epidemiological Evidence and Flaxseeds & Breast Cancer Survival: Clinical Evidence.

For some context, please also check out my associated blog posts: Treating Sensitive Skin From the Inside OutFlax and Breast Cancer Prevention , and Flax and Breast Cancer Survival 

If you haven't yet, you can subscribe to my videos for free by clicking here.

  • Audrey Pellicano

    Dr. Gregor,

    According to Jeff Novick, chia seeds are better utilized by the body as keeping flax seeds fresh is difficult. I had estrogen receptor positive Breast Ca in situ, stage 1 in 2009. Since then I use chia seeds in my morning smoothie. Are there sufficient lignans in chia seeds? I don’t grind them, should I?

    • MacSmiley

      Milled chia seeds are being marketed now, so I expect yes.

      I’d like Dr Greger to evaluate any further research on chia versus flax. So far, he’s favored flax versus chia, though including both in one’s diet is great for variety.

      Storing ground flax is not “difficult”. That sounds like marketing.

      • cambria

        Whole seeds are stable for long long time against oxidation. Even Flax. Research shows that even ground flaxseed is stable for a month at room temperature. A cheap coffee grinder makes short work of a tablespoon of flaxseed. Grind daily if you are concerned. I dearly wish I could tolerate it myself! Good luck

        • MacSmiley

          I grind a half pound at a time and store in a mason jar in the fridge. Can’t be bothered with daily cleanup or with watching the calendar. ;-)

    • Darryl Roy

      Unlike flax (with its lignans) or soy (with its isoflavones), there’s no phytoestrogen modulating normal estrogen binding in chia.

      Some (eg. bodybuilders) prefer chia for this very reason.

      Chia fats are readily absorbed without milling, unlike flax.

    • gc

      Put them in the fridge. Problem solved.

    • Toxins

      Dr. Greger covers this here

      Flaxseeds win out in terms of lignans.

  • MacSmiley

    For those who don’t like the taste of flaxseeds, golden flax seeds have a much milder flavor. And that’s why I prefer the dark ones.

    • Thea

      MacSmiley: Funny you should say this. I found a website describing the difference between golden and brown and they said the brown ones are milder. :-)

      Perhaps the thing to do it for people to try the other type if they haven’t yet. Also, I think the easiest thing to do is mix it up in something where you won’t be tasting the flax seed at all. I don’t taste them in my chocolate oatmeal and others don’t taste them in their smoothies.

      How do you eat your flax seed?

      • MacSmiley

        To each his own.

        I eat one tablespoon a day of ground brown flaxseed. Half a tablespoon goes in my smoothie and half in my oatmeal. (Take old-fashioned rolled oats, add boiled water and flaxseed, and let it sit for 5 minutes.) I then pour a little of my smoothie into the oatmeal for flavor.

        • Thea

          Interesting! Thanks for sharing.

          • MacSmiley

            I’ve never liked cooked oatmeal but always loved granola and oatmeal cookies. So I was grateful to Dr. Esselstyn for pointing out in an interview that rolled oats are already cooked. The grain is steamed before it is rolled flat. It’s the only processed food I eat.

          • Thea

            I do not like cooked rolled oatmeal either! I believe it is mostly a texture problem for me.

            A couple years ago, I discovered steel cut oatmeal. That was a big moment for me. All of sudden, I was liking oatmeal, at least the way I started preparing it.

            More recently, I modified an idea that I got from (I think) Dreena Burton: I take whole, raw (organic) groats (the whole grain oatmeal) and grind them up in my blender to pretty much a powder. Than each morning, I mix some fo that with: ground flax seed, alma powder pinch, cocoa powder, home-made date paste and almond milk. Microwave for 2 minutes. Stir. Then microwave for 1-2 more minutes. I then mound it up in the center of the bowl and poor in a moat of almond milk before eating. I love it. This idea works with other grains too such as wheatberries and millet.

            Just thought I would share some oatmeal ideas.

          • MacSmiley

            Texture. You nailed the problem. Glad you found a solution suited to your preference.

  • Jeff and Karen Hay

    Aloha Dr. Greger,

    You cover in this video the adverse effect that antibiotics have on gut flora which raises a question for us as to other substances, foods, beverages etc. that could adversely affect gut flora. We are wondering specifically about alcoholic beverages generally and in particular red wine.

    Thank you

  • Vicki Bowman

    This is quite the best site I have found on the web.

    • rebecca allen


  • GC

    Your posts are fascinating and informative. Thanks for the science lessons, which should be common sense.

  • cambria

    This is the real Mayo Clinic I think, saying some really cautionary stuff about flaxseed:

    When you ignore the “balance” and tout the wonderfulness of something you are obviously sold on you put yourself on par with Dr. Oz (BARF!). Isn’t the Mayo some of the science that your read so we don’t have to?

    I love you, you save many lives …among them mine. This question sounds harsh on rereading…becasuse i have no tact. forgive me but I have been so sick for so long trying to get the goodness of flax. I blow up with major IBS flare up everytime I grind up a tablespoon of flaxseed into my porridge. No Flax = wonderful quality throne time.

    • Veganrunner

      Cambria wouldn’t you then just decide flax isn’t for you? Don’t eat it. We hear so much about the benefits of turmeric but it doesn’t like me. (Mad rush to the toilet) That doesn’t mean I wouldn’t still recommend someone with joint pain give it a try to see if they get relief. Better than a daily dose of NSAID.

      • WholeFoodChomper

        I agree, just like wheat or certain whole grains may not be for someone who is gluten intolerant, and nuts may not be for someone who has nut allergies, it seems that flax seeds can be put in this category as well. Although, I do have to say that the Mayo web-site link did mention some interesting cautionary effects regarding flax seed safety, side effects, and warnings; some directly counter to what has been stated on this site. I’m not sure if the Mayo claims should be ignored, either.

  • Jeannie

    does toasting flax seed kill it’s value?

    • Darryl Roy

      From studies on flax processing (most behind paywalls) the lignan content (and hence estrogen antagonist effect) seems uneffected by sterilizing heat, though broiler heat is higher. Recovery of flax α-linolenic acid (its anti-inflammatory omega-3 fat) goes down by about a quarter when flax is baked in goods.

      Sesame lignans can stand microwave roasting for 30 minutes losing only about 20%.

      There’s not a lot in the literature, but it seems toasting would reduce beneficial compounds somewhat, not kill them.

      • Toxins

        Great response!

  • AliceJ

    On the news this morning was an item about organic apples and pears being sprayed with antibiotics. As a result, antibiotic resistant bacteria are developing. Apparently there is a loophole for farmers to do this. I don’t want to give up these fruits. How safe is it to eat them and what can we do to protect ourselves, if we do? Thank you. –AliceJ

  • LailaShoshana

    Does flaxseed oil have any of the benefits like ground flaxseeds?

  • thilo

    Whats about flaxseeds and cadmium and cyano glycoside and these study:

    Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen
    and progestin activity: a controlled crossover trial ? Thank you for an answer. By the way excuse my bad grammar because i´m from germany.

  • Louise Sawyer

    Dr. Greger,
    Thank you for making empirically based nutrition information so easily accessible! After watching your videos regarding nutrition and breast cancer prevention and survival I am wondering if there is any specific information regarding nutrition and premenopausal breast cancer associated with inherited mutations of the BRCA1 and BRCA2 genes? These women are at high risk (60-80% increased risk from what I’ve read); were they included in this study? If not, is there data on this anywhere? Thanks!

  • a belgian

    I don’t know if the beech tree is very common in the States, but here in Europe I often go beech nut gathering. It strikes me that linseed, which I’ve only recently been adding to my morning oatmeal, has a somewhat similar taste. Has the beech nut come up in any nutrional studies?
    Thanks for all the hard work doctor.

  • Jmix

    I have heard that flax has estrogenic effects & therefore, women should be cautious. I am a healthy middle-aged female & eat whole flax daily. Should I be concerned?