Category Archives: Phytoestrogens

Phytoestrogens – Harmful Or Beneficial For Hormone Driven Breast Cancer?

Image Source: / ba1969
Image Source: / ba1969

Phytoestrogens – Harmful Or Beneficial For Hormone Driven Breast Cancer?

The subject of phytoestrogens and their role in hormone driven breast cancer comes up at least once per week (and usually WAY more than that) amongst breast cancer patients and survivors, so I decided to present to you what I have discovered on the subject over the past few years.

What Exactly Is A Phytoestrogen?

The word phytoestrogen means “plant estrogen”.  Phytoestrogens are a group of chemicals found in plants that can act like the human hormone estrogen.

Phytoestrogens are found in many foods, chiefly soy and legumes, flaxseed, high fiber foods, beans, alfalfa, red clover and some herbs.

I found a brilliant description of the way phytoestrogens work in this article on the Physicians Committee For Responsible Medicine website.  See the second paragraph.

The Controversy

Many doctors and websites will warn you against anything containing phytoestrogens, the argument being that phytoestrogens may increase the amount of estrogens in your body and if you have hormone-driven cancer, would be something better avoided.

With reference to red clover in particular, I came across a few websites that warned against phytoestrogens for those with breast cancer.  The American Cancer Society states on their website “Women who have had estrogen receptor-positive cancers or who are pregnant or breastfeeding should not use this herb.”   The National Center for Complementary and Alternative Medicine stated on their website: “It is unclear whether red clover is safe for women who are pregnant or breastfeeding, or who have breast cancer or other hormone-sensitive cancers.”  The webMD website stated: “Red clover might act like estrogen. If you have any condition that might be made worse by exposure to estrogen, don’t use red clover.”

These same warnings appear with relation to other phytoestrogens as well – soy, in particular.  Phytoestrogens have to be one of the most misunderstood plant compounds on the planet.

The View Of Natural Therapists

Natural therapists have been using phytoestrogens for their patients with hormone-driven cancers for several decades.  Successfully.  We have relied on the anecdotal evidence of the patients that were successfully treated with them.  So we just had to know what we knew – that phytoestrogens have been shown to be beneficial and protective – and wait for the research to back us up.

The understanding of most natural therapists is that phytoestrogens exert a much weaker influence in the body than the body’s own estrogen.  How phytoestrogens appear to work is to occupy estrogen receptor sites on cells, preventing stronger estrogens from the body (and also environmental estrogens termed “xenoestrogens”) from exerting their stronger influence.  Through this mechanism phytoestrogens appear to prevent cancer growth and have a balancing effect on the hormonal system. This is why so many of the herbs used to treat menopause are rich in phytoestrogens.


The research is finally starting to come to light, although it can still be quite conflicting. Many of the studies I read admitted that further study needed to be done.  Here are the ones I found most helpful.

Flaxseed and its lignans in particular have been much studied for their beneficial effects for those with breast cancer.  One particular study titled Flax and Breast Cancer: A Systematic Review 1 published in September 2013 indicated that flaxseed had beneficial effects on hot flashes and breast density, as well as possible anti-angiogenic activity, offered decreased risk of primary breast cancer, better mental health, and lower mortality among breast cancer patients.  Flaxseed exerted antiproliferative effects in the breast tissue of people at risk of breast cancer, decreased the risk of breast cancer and reduced mortality risk among those living with breast cancer.

A newer study, dated June 2014, Flaxseed and its lignan and oil components: can they play a role in reducing the risk of and improving the treatment of breast cancer? 2 indicates that flaxseed reduces tumor growth in breast cancer patients, and that lignans reduced the risk of breast cancer in premenopausal women. The authors stated “Mechanisms include decreased cell proliferation and angiogenesis and increased apoptosis through modulation of estrogen metabolism and estrogen receptor and growth factor receptor signalling pathways. More clinical trials are needed but current overall evidence indicates that FS and its components are effective in the risk reduction and treatment of breast cancer and safe for consumption by breast cancer patients.”

Soy is also considered a phytoestrogen and some feel that it should be avoided by those with hormone driven cancers.  I found this particular November 2013 study compelling: Soy, red clover, and isoflavones and breast cancer: a systematic review 3 .  The study authors specifically state “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 (≥ 100 mg) isoflavones can be recommended for breast cancer patients.”

Another interesting study titled Soy and its isoflavones: the truth behind the science in breast cancer 4 published in October 2013 stated “Although the specific quantities and constituents responsible for the observed anti-cancer effects have not been elucidated, 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. ”

Professor Trevor Powles, an authority on breast cancer, and former head of the Breast Unit at The Royal Marsden Hospital in Surrey, UK, refers to phytoestrogens as “anti-estrogens”, because of how they block the action of human estrogen in the cancer process.  Prof Powles believes that phytoestrogens have the ability both to block the receptor sites to which human estrogens attach, and also in some cases to even denature aggressive human estrogens.

Another reliable source of information is The Block Center for Integrative Oncology and their recommendations on soy appear in this article :  Soy And Breast Cancer (see point 3 especially).  Please also note the advice that soy supplements (especially those containing soy protein isolate) are not recommended and that GMO soy is to be avoided.

I hope you found this helpful.  I believe that the latest research shows phytoestrogens to be not only safe but very beneficial for those with hormone driven breast cancer.  I will keep you posted as new research comes to light.

1.  Flax and Breast Cancer: A Systematic Review –
2.  Flaxseed and its lignan and oil components: can they play a role in reducing the risk of and improving the treatment of breast cancer? –
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  –

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