Phytoestrogen – What’s the Big Concern For Breast Cancer?

Phytoestrogen – What’s the Big Concern for Breast Cancer?

The role of phytoestrogen – which essential means plant-derived estrogen – especially with regard to its interaction with estrogen receptor positive (ER+) breast cancer, is a subject about which I am frequently asked. So frequently, in fact, I decided to shoot a video about it, so that I can save time answering the question!

I don’t mean to sound flippant – it’s an important subject, for sure. As breast cancer patients and survivors, we are frequently told to avoid phytoestrogens in the management of ER+ breast cancer, but is that good advice?

Please watch the video and find out what I have learned to be true over the years.

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Soy Proven To Be Good For Breast Cancer Survivors

Image source:

Soy Proven To Be Good For Breast Cancer Survivors

Just in case we had any lingering questions in our minds as to whether it is safe to eat soy after breast cancer, a brand new study confirms that it is not only safe but protective. We have a BUNCH of these studies now, yet this is one of the things I am asked with great frequency. I have written several articles about it for my website (links below) but there still seems to be so much misinformation given to women with breast cancer about soy.

If you don’t want to read this entire article, here’s the bottom line – minimally processed organic soy foods are considered safe and healthy to eat. The important takeaway – if you are going to eat soy for preventive purposes, it needs to be the type of soy that is not highly processed – whole soy such as tempeh, miso, edamame, tofu, soy milk, soy sauce. And always choose organic, non-GMO soy.

Do I eat soy? Yes! I do choose frequently to eat and enjoy whole organic soy foods. Things like miso, tofu and edamame are things I include in my diet fairly often. There are so many great recipes and dishes that include these healthy soy options. And yes, soy does need to be organic because so much of it is now genetically modified and that has not been proven to be safe for us.

Now for the rest of you that want all the nitty gritty research…

I love reading new research, especially when it helps us understand new things that relate to breast cancer. I love it when new research debunks old ways of thinking because it helps you to decide for yourself whether or not to give something a try. PLEASE don’t base your decision to not have soy products on something your doctor told you – mainly because many doctors are not up to speed on the latest nutrition research. I believe it’s up to us to teach them!

What’s The Perceived Problem with Soy and Breast Cancer?

The main reason we have, in the past, been warned off having soy products after breast cancer is because soybeans contain compounds known as isoflavones. Isoflavones act like weak estrogens, also termed phytoestrogens. The estrogen-like properties of soy have raised concerns in the past for women with estrogen-receptor-positive breast cancer, which is the main type of breast cancer. The worry is that the phytoestrogens might potentially influence cancer to grow. But that theory has not been proven, quite the contrary. What we are finding is that phytoestrogens occupy estrogen receptor sites on cells, preventing stronger estrogen from the body (and also environmental estrogens known as xenoestrogens) from exerting their more powerful influence. So phytoestrogens appear to have a protective and balancing effect on hormones.

The New Research

The latest study, appearing in the journal Cancer in June 2017  1 investigated the effects of soy isoflavones on breast cancer survivors. The National Cancer Institute-funded study collected data from the Breast Cancer Family Registry for 6,235 breast cancer patients over a period of 113 months (9.4 years). The program collected clinical and dietary data on participants and researchers specifically analyzed the soy intake of these women. They found that:

1. Eating foods rich in soy isoflavones was associated with reduced all-cause mortality;

2. A 21 percent decreased risk of death was enjoyed among women eating the highest amount of soy foods. This was also true for women with hormone-receptor-negative breast cancer AND women who did not have hormone therapy.

This is really interesting! The study tells us that soy isoflavones have a beneficial impact on women with breast cancer, regardless of whether their tumor was hormone-receptor positive or negative, also regardless of whether or not the women received hormone therapy such as Tamoxifen.

But Wait… There’s More!

This is not the only study on soy and breast cancer. I have four other, older, studies to share with you. In May 2012 a joint study 2 between Chinese and American researchers, published in the American Journal of Clinical Nutrition followed 9,514 breast cancer survivors in America and China between 1991-2006. Those who consumed soy and its isoflavones had significantly reduced mortality from breast cancer and a “statistically significant reduced risk of recurrence.”

Canadian researchers investigated the same thing in 2013. The title of the study was Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review 3. Basically, they investigated various medical databases looking for human interventional or observational data relating to the safety and efficacy of soy and red clover isoflavones for patients with breast cancer, or at high risk. They concluded: “Soy consumption may be associated with reduced risk of breast cancer incidence, recurrence, and mortality. Soy does not have estrogenic effects in humans. Soy intake consistent with a traditional Japanese diet appears safe for breast cancer survivors. While there is no clear evidence of harm, better evidence confirming safety is required before use of high dose (=100mg) isoflavones can be recommended for breast cancer patients.

In addition to that, an American study published in Anti-Cancer Agents in Medicinal Chemistry in 2013 4 also reviewed past studies and compared the available literature, looking at the anti-cancer vs cancer-promoting effects of soy isoflavones in humans and animals. Researchers concluded “it appears that soy isoflavones do not function as an estrogen, but rather exhibit anti-estrogenic properties. However, their metabolism differs between humans and animals and therefore the outcomes of animal studies may not be applicable to humans. The majority of breast cancer cases are hormone-receptor-positive; therefore, soy isoflavones should be considered a potential anti-cancer therapeutic agent and warrant further investigation.

In a 2014 meta-analysis, which is a study that analyzes all of the research on a particular topic, published in the journal PLOS-One by Chinese researchers 5, it was found that eating soy helped to prevent breast cancer in women of all ages. Researchers found that eating soy cut the risk of breast cancer by a whopping 41 percent!

Important precautions: Supplements and protein powders containing soy protein isolate and concentrated sources of isoflavones DO appear to stimulate the growth of estrogen-dependent tumors and should be avoided. Also avoid highly processed soy products such as soy flour, soy oil, silken tofu, TVP (texturized vegetable protein) and soy isoflavone supplements. These are not proven to be good for our health. Lastly, always choose organically grown soy because so much of our soy is now genetically modified and this has not been proven to be safe for human consumption.

In the end, you must do whatever feels right for you. If it’s not a good fit for you, for instance if you hate the taste or texture of tofu, no problem! Move on to something else. There are plenty of anti-cancer foods – see my page Diet and Cancer for more ideas. If you have soy allergies, obviously eating soy is not going to help you. But eating a mainly plant-based diet is hugely beneficial and helps to cut the risk of breast cancer by a huge degree (especially when combined with exercise).

Other articles that may be of interest: Phytoestrogens – Harmful Or Beneficial For Hormone Driven Breast Cancer?
Is Soy Bad For Women with Breast Cancer? A Definitive Answer


[1] Dietary isoflavone intake and all-cause mortality in breast cancer survivors: The Breast Cancer Family Registry –

[2] 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 –

[3] Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review –

[4] Soy and its Isoflavones: the Truth Behind the Science in Breast Cancer –

[5] 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 –

GET MY BEST TIPS on getting through breast cancer and preventing recurrences by signing up for my free e-newsletters and e-books on the right. You can also “like” me on Facebook (Marnie Clark, Breast Health Coach) to get my inspirational snippets, news and updates. I promise to do my utmost to keep you informed and empowered on your healing journey… and beyond.

Is Soy Bad For Women With Breast Cancer? A Definitive Answer.

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 –

If you would like to receive my best tips about getting through breast cancer in an inspiring and ultra-healthy way and preventing recurrences, please sign up for my free e-newsletters and e-books on the right, and/or “like” me on Facebook (Marnie Clark Breast Health Coach).  It is my honor and my goal to help you through this so that you emerge from breast cancer feeling better than before, thriving!

Chinese Study Examines the Role of Soy, Tamoxifen, Estrogen in Breast Cancer Survival

Last week I received a copy of a very interesting 2009 study which examines the role of soy, tamoxifen and estrogen receptors in breast cancer survival.

The study was published in the esteemed Journal of American Medical Association (JAMA) on December 9, 2009.  If you’d like to read the entire article, here it is:  Soy Food Intake & Breast Cancer Survival 2009 study.

The objective of the study, called the Shanghai Breast Cancer Survival Study was to evaluate the association of the intake of soy foods after a breast cancer diagnosis.  It was quite a large study – over 5,000 female breast cancer survivors aged 20-70 years with diagnoses between March 2002-April 2006 were followed up through June 2009.  It was one of the largest population-based studies of breast cancer survival when it was published.  I’d encourage you to read it, it’s interesting.

Many are Confused About Whether Soy is Safe or Not

I’m writing about this today, some 3 years after publication, because there still seems to be quite a lot of confusion about the role of soy’s phytoestrogens (plant-based estrogens) among breast cancer survivors and those actively battling breast cancer.  We are often told by our doctors and their nurses to be wary of too much soy. Their advice is well-meaning, but flawed – that because the phytoestrogens in soy can supposedly act as weak estrogens, those who had estrogen receptor positive tumors (meaning estrogen appeared to fuel the growth of the tumors) should exercise caution and not eat too much soy.

This study makes it clear that this is not how soy works. Here’s a direct quote:

In our comprehensive evaluation of soy food consumption and breast cancer outcomes using data from a large, population-based cohort study, we found that soy food intake was inversely associated with mortality and recurrence. The inverse association did not appear to vary by menopausal status and was evident for women with ER-positive and ER- negative cancers and early and late-stage cancers.”

For those not accustomed to the language used in scientific studies, “inversely associated with” means that the more soy foods that were eaten, the less mortality and recurrence was exhibited in the study participants.

Soy Phytoestrogens vs. Our Estrogen

The Study also found that soy isoflavones compete with the body’s estrogen in the binding of estrogen receptors, they increase the synthesis of sex hormone-binding globulin (thus lowering the bioavailability of sex hormones like estrogen), they reduce estrogen synthesis and increase the clearance of steroid hormones from circulation.  It is thought that these anti-estrogenic effects may be one of the underlying mechanisms through which the consumption of soy foods is associated with better breast cancer outcomes.

Soy Phytoestrogens vs. Tamoxifen

Additionally, the study found that soy food intake was associated with improved survival, regardless of tamoxifen use.  Interestingly, the study concluded that for women who took tamoxifen and had low soy intake, the tamoxifen helped their overall survival rates.  For those who ate high levels of soy foods, tamoxifen was not related to further improvement of survival rates.  More importantly, women who had the highest level of soy food intake and who did not take tamoxifen had a lower risk of mortality and recurrence rate than women who did take tamoxifen and who had the lowest level of soy food intake.  This suggests that high soy food intake and tamoxifen use may have a comparable effect on breast cancer survival.

I know which one I’d rather take!

How much is enough?

The study indicated that 11 grams per day of soy protein was sufficient to confer the benefits they observed. For an idea of how much that is:

1 cup of soy milk = 6-7 grams soy protein

1 cup soy yogurt = 6 grams soy protein

1/4 cup roasted soy nuts = 11 grams soy protein

4 oz organic tofu = 13 grams soy protein

1/2 cup edamame = 11 grams soy protein

Please choose organic soy whenever you are eating it because in some parts of the world, it is a genetically modified crop.

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