Is There a Risk to Eating Soy for a Breast Cancer Survivor?

Have you wondered if soy is ok?  I mean it’s one of the forbidden foods for breast cancer survivors especially if you had a hormone receptor positive tumor.  Right?

Wrong!  Yep, surprise…this is one of the persistent pieces of misinformation about nutrition that breast cancer survivors hear.  

I would like to explain to you why this is not true and why you may want to add a little soy to your diet.

So why believe me and not what your oncology team (or your Aunt Sally or your neighbor or the lovely lady who sat in the next chemo chair) told you?  Well, first, because I am going to talk to you about the clinical studies that have been done that show that soy is not harmful to breast cancer survivors.  Then I am going to explain why it might make physiologic sense that soy could be good for you.

And just what makes me the expert?  I am an Integrative Oncologist which means I help breast cancer patients integrate lifestyle changes and complementary therapies with conventional treatment so that they can get through treatment easier and help improve their survival after treatment.  It also means that I did some extra training and research to learn about nutrition that your well-meaning oncologist may not have done.

So let’s get down to the truth about soy for breast cancer survivors.

Oncologists for many years recommended that ER/PR+ (or hormone positive) breast cancer patients avoid soy.  You see soy contains phytoestrogens, which are very weak, plant-based estrogens.  But the clinical research has not supported this recommendation.

And there is a physiologic reason why this might be the case.  There are multiple receptors for estrogen in the body.  Some of these receptors promote the growth of breast cancer and some of these receptors actually inhibit the growth of breast cancer.  It is possible that soy, containing very weak phytoestrogens, stimulates the receptors that protect us from breast cancer.

There are some clinical trials to back up the assertion that soy is not harmful for breast cancer survivors.  There was a meta-analysis that looked at all the observational research that had been done in the US and China.  These studies examined soy intake in breast cancer patients.  What the research uncovered is that women who had the highest levels of soy consumption compared to women who had the lowest, had a 26% decrease in their risk of breast cancer recurrence.  So not only was soy not a problem, it might have been helpful at protecting against breast cancer in these women.

There was another review of four large trials involving breast cancer survivors and looking at soy consumption.  What this review found was that there was no harm in consuming soy.  There was no increased risk of recurrence in this group of breast cancer survivors and no change in their survival no matter what their soy intake was.

So, at the very least we can say that soy is probably not harmful at all in breast cancer survivors, and it may help reduce the risk of recurrence.

Soy is a great source of protein especially for vegetarians who may have trouble meeting their protein needs. In fact, it is the only complete plant-based protein (meaning it contains all of the essential amino acids).

The bottom line is that soy is safe to consume.  One or two servings a day might actually decrease your risk of a breast cancer recurrence.  It is important to note that this applies to soy foods like tofu, edamame, soy nuts, soy milk, and tempeh.  These studies did not involve soy supplements or soy protein powders.  The soy supplements and powders may contain a large amount of phytoestrogens that are not found in soy foods.

Here’s what you need to know about soy.  First, there are several different types of estrogen receptors in the body, and the phytoestrogens found in soy foods may actually interact with the estrogen receptors that protect you from breast cancer.  Second, we do have clinical research to back up the assertion that soy foods are not harmful to breast cancer survivors and may actually protect them from a recurrence. It would be helpful to have a randomized clinical trial to support this before we make a strong recommendation on consuming soy foods, but at least it appears that soy foods are not harmful for breast cancer survivors.  Third, it is important to note that we are talking about soy foods and not soy supplements or powders.

For more information about nutrition and lifestyle changes that can reduce your risk of breast cancer recurrence, join me in the THRIVE Beyond Breast Cancer program.  You can find out how to join now on my website by clicking here.


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