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Soy & Breast Cancer

Should women with estrogen-receptor positive breast cancer avoid soy foods?

September 2, 2008 |
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Supplementary Info

Sources Cited

C.B. Klein & A.A. King. Genistein genotoxicity: critical considerations of in vitro exposure dose. Toxicol Appl Pharmacol, 224(1):1-11, 2007.

R. Villegas, Y.T. Gao, G. Yang, H.L. Li, T.A. Elasy, W. Zheng, & X.O. Shu. Legume and soy food intake and the incidence of type 2 diabetes in the Shanghai Women’s Health Study. Am J Clin Nutr, 87(1):162-167, 2008.

F.H. Liao, M.J. Shieh, S.C. Yang, S.H. Lin, & Y.W. Chien. Effectiveness of a soy-based compared with a traditional low-calorie diet on weight loss and lipid levels in overweight adults. Nutrition, 23(7-8):551-556, 2007.

C.D. Gardner, M. Messina, A. Kiazand, J.L. Morris, & A.A. Franke. Effect of two types of soy milk and dairy milk on plasma lipids in hypercholesterolemic adults: a randomized trial. J Am Coll Nutr, 26(6):669-677, 2007.

A.H. Wu, M.C. Yu, C.C. Tseng, & M.C. Pike. Epidemiology of soy exposures and breast cancer risk. Br J Cancer, 98(1):9-14, 2008.

M. Iwasaki, M. Inoue, T. Otani, S. Sasazuki, N. Kurahashi, T. Miura, S. Yamamoto, & S. Tsugane. Plasma isoflavone level and subsequent risk of breast cancer among Japanese women: a nested case-control study from the Japan Public Health Center-based prospective study group. J Clin Oncol, 26(10):1677-1683, 2008.

B.N. Fink, S.E. Steck, M.S. Wolff, J.A. Britton, G.C. Kabat, M.M. Gaudet, P.E. Abrahamson, P. Bell, J.C. Schroeder, S.L. Teitelbaum, A.I. Neugut, & M.D. Gammon. Dietary flavonoid intake and breast cancer survival among women on Long Island. Cancer Epidemiol Biomarkers Prev, 16(11):2285-2292, 2007.



Soy foods like tofu. Harmful??? Harmless??? Helpful??? Well, if you take Chinese dwarf hamsters— how could anyone ever hurt a hamster? Well, if you feed them the equivalent of 300 cups of soy milk every day they don’t do so well, and you can read all sorts of crazy stuff on the internet but what does the human data show?

Just from the last couple months—eating soy can cut your diabetes risk in half, can help you double your weight loss for those on a diet and drop your bad cholesterol 14%, even just adding soy milk to your diet can have a measurably powerful effect on reducing cardiovascular risk.

Bumping it up a notch, not just soy, but soy for women with active estrogen receptor positive breast cancer. The phytoestrogens, the plant estrogens in soy protect the breast tissue from the more powerful ovarian estrogens, and so in terms of preventing breast cancer, the only question has been does it cut your risk by 30%, or 50%? But what if you already have breast cancer that reacts to estrogen—do you want to be consuming any estrogenic type compounds? This was one of the most controversial questions in nutrition, until now.

Soy intake and breast cancer survival on Long Island. So what do you think? Harmful??? Harmless??? Helpful???

They calculated all-cause mortality for women diagnosed with breast cancer and eating soy or not eating soy, and those eating soy cut their risk of dying by 50%! So not only does soy prevent breast cancer, but women with breast cancer eating soy live longer.

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 Dianne Moore.

To help out on the site please email

Dr. Michael Greger

Doctor's Note

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the Soy and Breast Cancer Survival video and the accompanying blog post. Also, there are 1,449 other subjects covered in the rest of my videos--please feel free to explore them as well!

You may also want to check out my associated blog posts for more context: Eating To Extend Our Lifespan, Stool Size and Breast Cancer Risk, Breast Cancer and Diet and Soy and breast cancer: an update.

  • Michael Greger M.D.

    Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the Soy and Breast Cancer Survival video and the accompanying blogpost. Also, there are 1,449 other subjects covered in the rest of my videos–please feel free to explore them as well!

  • HereHere

    I appreciate the fact that you have raised how researchers are still using animals for studies that have no applicability to human health. It boggles my mind, as I thought the research community was required to look at alternatives to using animals for research, assessing whether there is a human benefit or need for the research on animals, having to pass by an ethics review panel and having to exam opportunities to minimize the number of animals used for the study. I am shocked that this irrelevant research continues as it does.

  • Donna Turner

    There’s so much contradictory information out there, I would like to know your take on this quote that I found in an email I received from “These days, people turn to soy milk. Even if you’re not turned off by the fact that it’s an industrial waste product spun by marketers into a so-called “health food,” you can’t like the numerous health-risks associated with soy. (I’ll be writing more on those later in the week. But as a foretaste of things to come, soy: is thyroid suppressing, blocks absorption of minerals like calcium, causes hormonal imbalance leading to infertility and breast cancer, disrupts protein digestion, can cause growth problems in children).”

  • DrDons

    When reading claims on other websites I would tend to discount the claims unless they cite references with links to abstracts(and articles when free) like Even then the studies can be misleading see Alot of misinformation about soy exists including fertility in males see; the issue re: thyroid and soy … Dr. Greger addressed in a 8/24/11 response… “Soy does indeed have so-called “goitrogenic” compounds (as does broccoli-family vegetables and flax seeds), which can interfere with thyroid function in people with marginal iodine intake. The answer is not to avoid these super healthy foods but to just make sure you get enough iodine”. See his video on Avoiding Iodine Deficiency.. Soy seems to have benefits compared to standard american diet as far as hormones are concerned see and As far as calcium absorption of soy vs cow’s milk see Calf’s milk has calcium but comes with negative factors see Soy appears to be fine based on the science but stay tuned as the science is changing all the time.

  • Michael Greger M.D.

    Also be sure to check out my associated blog post Breast Cancer and Diet!

  • Lois

    I would have to disagree with this report because in the US we use a cheap soy – not the fermented soy used in Asian countries.  When my cousin had breast cancer her oncologist actually ranted some about soy products as she was the third or fourth young women he had seen that day with estrogen related breast cancer.  She ate soy products, health food bars, and soy milk thinking they were healthy.  I won’t touch soy products except on occasion or if natural.  I use coconut milk as I’m allergic to milk.

  • Mark

    Hi Dr. Greger,

    So soy has been shown to have benefits for women, but what about men?
    Surely those phyto-estrogens could create problems, like gynecomastia?

    Thanks Dr.,


  • guesttest

    what about soy and estrogen hormone in men exercising actively in the gym targeting muscle building and fat loss? thanks…