Recently, an ominous sounding article snaked its way through the breast cancer community.

It freaked A LOT of people out.

With the message it conveyed; it well should have.

And that made me a little crazy.

The article stated that certain foods containing an estrogen-mimicking compound “appear to reverse the effects of a combination drug therapy used in postmenopausal women with estrogen receptor (ER) positive, metastatic breast cancer.” Of course that information was concerning, given this drug combination was shown in a clinical trial to double the progression-free survival in this population. (1)  

20%-30% of women with early stage breast cancer go on to develop metastatic disease (Stage 4). Metastatic breast cancer is treatable with drug therapy, but not curable. The five-year survival rate for Stage 4 is 22%. The median survival is three years. (2)

Approximately 70% of all breast cancer cases are hormone-dependent and ER-positive. (3) Medications that reduce circulating levels of estrogen are prescribed for these types of breast cancer, and one of the two drugs in this combination therapy does exactly that.

Can you imagine taking a medication to extend your life, only to learn that something as innocuous as the food you eat could potentially REVERSE its impact? Even more unsettling, the article didn’t exactly indicate which foods are problematic.

It highlighted two types of compounds found in two groups of foods (grains and soy), suggesting that women who take this drug combo consider “LIMITING EXPOSURE” to foods containing this compound.

But WHICH foods? Some soy? All soy? Oatmeal? Rice? Wheat? ALL “carbs”?

As I read the article I imagined it fueling food fears; fears based on existing erroneous nutrition recommendations around soy and carbs.


What IS This Ominous Compound?

The estrogen-mimicking compound charged with wreaking all this havoc is called a “xenoestrogen.” The Greek origin of “xeno” translates to foreign or stranger. Estrogen formed in the body is called endogenous estrogen, meaning, originating from within.

Xenoestrogens, whether synthetic or natural, imitate endogenous estrogen. A number of anthropogenic (something relating to, resulting from or influenced by humans on nature, i.e. anthropogenic pollutants) agents are xenoestrogens, and defined as endocrine-disrupting chemicals (EDC). (4)

The two natural xenoestrogens identified in this article are called “common dietary xenoestrogens;” zearalenone, produced by fungi that colonize maize, barley, wheat and other grains”, and genistein, “produced in certain plants including soybeans and often highly concentrated in phytoestrogen-rich food supplements.”

Having read that, would YOU know which specific foods the article was referencing? Or how common those foods are in your diet? Or how much or how little to actually eat?

I didn’t think so. I wouldn’t know that, either.

Looking Closely at the Research

This research was conducted on CELL LINES, which are essentially cell cultures (not humans). Cell line outcomes can provide good information for further study and to help develop strong hypotheses, but they don’t offer the assuredness of a randomized control trial performed using actual human subjects – the gold standard.

Don’t get me wrong. I’m all for breast cancer research, particularly when that research involves food and nutrition. What I adamantly am NOT for is broad, sweeping nutrition recommendations based on outcomes that are unproven and unclear.

Women diagnosed with breast cancer are understandably nervous and unsure about what foods to eat or avoid, eagerly gravitating to nutrition research headlines in hopes of more knowledge to help manage their disease or reduce the risk of recurrence.

An article such as this does nothing to allay their fears.

And Then, There Was Clarity

There’s legitimate cause for concern about xenoestrogens in food and water, as well as synthetic xenoestrogens like bisphenol A, phthalates and parabens. We desperately need more definitive research and to educate the public on the connection to breast cancer.  

But there are still too many unknowns. If you read closely, you’ll see the authors use “appear to” and “suggests”, yet it can be difficult for the lay public to catch those nuances.

That’s where we nutrition professionals come in, providing clarity, frame of reference, and guidelines for putting new research findings into practice – or not. That’s one of the constants in my (and others’) work as a dietitian in the breast cancer community.

So I shared this article with my oncology dietitian colleagues, knowing they would likely be fielding questions and concerns from their own patients. 

In response, I received thoughtful comments showcasing how we’re trained to use critical thinking to best interpret research for our clients/patients. I also have permission to share them. 

If you’re confused about nutrition and breast cancer research, seek out legitimate nutrition experts who can help you make sense of it. We’re here to help, and love nothing more than the opportunity to do so.

“My thought is that this comes with a lot of limitations and caveats. My first thought is that this effect may be very different in vivo, i.e. there may be counteracting metabolites from the same or other foods in the diet or that the metabolic effect in vitro may be of little or no significance. Don’t we already have some epidemiological data to refute this?  In other words, are women in Asian countries who regularly consume soy treated with the same drugs and what are their outcomes?

While this is certainly an interesting study that probably requires further exploration, it is dismaying when journalists and/or researchers ring alarm bells and suggest dietary changes based this type of data/study.

I’ll be interested to hear what others have to say. For now, I’ll continue to say what I’ve been saying: eat a plant-based diet with a variety of vegetables, fruits, and whole grains, include soy if you like it, and avoid dietary supplements containing phytoestrogenic compounds.” – Angela Bruce, RD, CSO. Board Certified Specialist in Oncology Nutrition, Laurel Amtower Cancer Institute and Neuro-Oncology Center, San Diego, CA


“I find it interesting that the article states “The palbociclib/letrozole combination therapy was approved by the U.S. Food and Drug Administration in 2015 after a clinical trial showed it doubled the progression-free survival time in postmenopausal women with estrogen receptor (ER) positive, metastatic breast cancer.” I’m assuming the original clinical trial participants were allowed to eat while on the trial and were not instructed to limit food and water based on xenoestrogen content. Maybe I’m looking at this all wrong, but if clinical trial participants had statistically significant improvement in progression-free survival when compared to placebo/standard of care, then how could “xenoestrogens largely reverse the metabolomic impact of the cancer drug”. Of course there are a lot of assumptions in this thought, such as maybe the outcomes would have been greater if the participants limited their exposure to xenoestrogen, but I don’t think it is fair to say that exposure to xenoestrogens is going to reverse the effects of the drug.” – Laura Brown, MS, RD, CSO, CNSC. Oncology Dietitian, SCL Health, Lafayette, CO

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  1. Estrogen-mimicking compounds in foods may reduce effectiveness of breast cancer treatment
  2. Living with stage 4
  3. Treatment of estrogen receptor-positive breast cancer
  4. Environmental exposure to xenoestrogens and oestrogen related cancers: reproductive system, breast, lung, kidney, pancreas, and brain