Soybeans Image Source / Ponsulak

Is Soy Bad For Women With Breast Cancer?

The topic of the safety of soy continues to be hotly debated amongst health professionals and women with breast cancer, as well as those looking to reduce their risk. This question deserves careful consideration.

Just a few weeks ago I was told by a health professional to avoid soy like the plague because “soy disrupts hormones”.  Since I have been an advocate for soy, particularly as it relates to breast cancer, ever since I started this website, I was shocked and dismayed by this advice.  Did I get it wrong?

No, I Didn’t Get It Wrong – Whole Soy is GOOD For Us!

Fortunately, Dr Ian Gawler, one of my thought leaders and someone whose advice I value, has just written a couple of really good, well-researched articles about the safety of soy on his blog, here are the links:

Is Soy Safe? Part 1 (July 29, 2013)

Is Soy Safe? Part 2 (August 6, 2013)

To summarize these two articles,  research shows that whole soy products (not soy isolates or processed soy products) are indeed safe for women with breast cancer, read Part 2 very carefully. I particularly appreciated Dr Gawler’s discussion on how breast cancer is affected by estrogen, the three estrogen-like chemicals in soybeans, and his information on how isoflavones may possibly stimulate the growth of existing estrogen-sensitive breast tumors.

As we know, if a breast tumor is estrogen receptor positive (ER+), that means the tumor has estrogen receptors on its surface and estrogen will speed up the progression of this kind of tumor.  We don’t need anything we are eating to also act in this manner, and the issue of whether soy acts like estrogen in the body has been hotly debated.

Please read the two articles I’ve linked to above to fully appreciate the information Dr Gawler has shared with us.  He’s an excellent researcher, and is really good at taking a difficult subject and unraveling the research studies so that we can understand it better.

In a nutshell, we are safe eating traditional, non-processed soy foods such as tofu, soy yogurt and soy milk.  They are good for us and, in fact, current research suggests traditional soy foods, eaten in traditional amounts, are felt to be safe and may well be helpful in reducing recurrences and extending survival rates.

Update: February 2017

Dr Michael Greger over at has released an excellent video, backed by research on actual people, that demonstrates conclusively that soy IS not only safe but helps to turn on tumor suppressor genes.  Check it out: Should Women at High Risk for Breast Cancer Avoid Soy?

6 Tips for Eating Soy Products When You Have Breast Cancer

  1. Traditional soy foods such as organic tofu, organic soy yogurt and organic soy milk are safe to eat if you have breast cancer – research shows it to be beneficial.  You can safely eat up to 3 servings per day.  Fermented soy products are also safe to consume and that includes tamari, miso and tempeh (again, best if organic);
  2. Soy protein isolates and concentrated sources of isoflavones such as powders and supplements do appear to stimulate the growth of estrogen-dependent tumors and so should be avoided.  We should also avoid highly processed soy products such as soy flour, soy oil, silken tofu and TVP (texturized vegetable protein);
  3. Soy does NOT interfere with the action of Tamoxifen.  In an American study released in 2007, soy intake had no effect on levels of Tamoxifen or its metabolites [1]. In another study done by American researchers in 2007, it was demonstrated that the combination of Tamoxifen and genistein actually inhibited the growth of human breast cancer cells and worked synergistically [2].
  4. Eating soy foods during childhood and adolescence appears to significantly reduce the risk of breast cancer later in life for women;
  5. Because of the fact that so much soy is genetically modified in the USA, make sure your whole soy foods are organic;
  6. Research indicates that soy consumed with green tea is beneficial – the two appear to work synergistically against cancer cells.

One Last Bit of Research

One further note, I received an email recently from one of my subscribers who is an RN and certified in plant based nutrition, and she also felt that whole soy products are quite beneficial for those with breast cancer, but noted “Soy supplements in the form of pills and powders are very harmful because of the way they are processed, so I would not recommend anyone ever taking those.”

She shared with me another study performed jointly with Chinese and American researchers, published in the American Journal of Clinical Nutrition dated May 2012 [3]. This study followed 9,514 breast cancer survivors between 1991-2006 and demonstrated a significantly reduced recurrence rate for those who consumed soy isoflavones.

I hope you found this information helpful and thanks to Ian Gawler for his excellent articles, to Susan G for bringing that last bit of research to our attention, and to Dr Michael Greger at whose excellent videos and articles keep us up to date with the latest health news and research.


[1] Tamoxifen, soy, and lifestyle factors in Asian American women with breast cancer –

[2] Genistein sensitizes inhibitory effect of tamoxifen on the growth of estrogen receptor- positive and HER2-overexpressing human breast cancer cells –

[3] Soy food intake after diagnosis of breast cancer and survival: an in-depth analysis of combined evidence from cohort studies of US and Chinese women –

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