Do an Internet search on “soy, menopause,” and you’ll typically find a couple of schools of thought: soy is dangerous because the phytoestrogens in soy increase breast cancer risk. Or, soy helps relieve perimenopause and menopause symptoms thanks to those same phytoestrogens.

So, is soy dangerous?

No. Eating a moderate amount of whole-soy foods will not increase your risk of breast or any other kind of cancer, even if you’ve had breast cancer or have a family history of the disease.

Why do we think soy is dangerous?

Concerns about soy and a link to breast cancer date back to a study done in 1996 and published in Cancer Epidemiology, Biomarkers, & Prevention. The study seemed to indicate that soy protein could stimulate the growth of breast cancer cells.

Researchers had known prior to the study that isoflavones, an estrogen-like compound found in soy and may other foods, can mimic the natural estrogens of the body. And since higher estrogen levels can increase the risk of breast cancer, it followed that isoflavones could have the same effect.

However, Dr. Omer Kucuk, medical oncologist at Emory University’s Winship Cancer Institute, told CNN, there are two estrogen receptors in our bodies, alpha and beta. Binding to alpha receptors may increase the risk of breast cancer by making breast cells grow.  

“Soy isoflavones bind preferentially to estrogen receptor beta,” says Dr. Kucuk, and may actually have a protective effect against breast cancer. Hence the lower cancer rates in high-soy-consumption parts of the world like Japan and China where people consume soy throughout their lives.

There may be negative effects for people with thyroid issues, especially in women. If you take medication for hypothyroidism, soy may interfere with your body’s ability to absorb that medication. However, says the Mayo Clinic, if you take your medication as prescribed and wait four hours after taking your medication before consuming soy, you can enjoy whole soy-based foods without concern.

What are the benefits of soy?

The jury is still out on many of the claims soy proponents have made through the years, but evidence that soy is genuinely good for us is piling up.

How can we safely consume soy?

While the experts still disagree on exactly the benefits and risks of soy, most agree that soy is best consumed as “whole” as possible.

Look for minimally processed versions such as edamame, tofu, tempeh, and miso. Avoid or limit highly processed vegetarian meat or cheese substitutes which can contain a whole lot of other stuff, negating the benefits of soy. Lots of protein bars contain soy, but the processing and the added sugars may make those foods less than healthy.

Additionally, soy or isoflavone supplements may not be a good way to enjoy the benefits of soy, as large-scale studies on soy supplements haven’t really been conducted to date, says Dr. Kucuk. In fact, says Katherine Zeratsky, RD LD, for the Mayo Clinic, some studies suggest the higher levels of isoflavones in supplements may actually increase the risk of breast cancer.

As with most nutrition, it’s best to meet your needs with real food: “25 grams a day” was the amount several nutrition experts gave as a guideline for safe consumption of soy, and “fermented” likely yields the highest nutritional value (natto, tempeh, miso).

Does soy help with menopause symptoms?

OK, so the phytoestrogen in soy won’t cause breast cancer, but will it end hot flashes?

Great question. Results, as with All Things Menopause, are mixed. Some studies seem to show that isoflavones reduce the severity and frequency of hot flashes – this study, unfortunately, centered on the use of soy supplements, which, as discussed above, aren't ideal.

Another, earlier study found no evidence that plant-based estrogens like soy or red clover had any beneficial effect.

The protective and beneficial effects of soy may also depend on how long a woman has consumed it. Women who’ve eaten soy regularly over their whole lives seem to receive greater benefits than women who come to it later.

However, given the low-or-no risk and the very real health benefits of eating soy, why not try it? As ever, if you’re making a significant change to your diet, running it past your doctor is never a bad idea, especially if you’re on medication and have concerns about interactions. And if your morning miso soup results in fewer, less disruptive hot flashes, so much the better.

Do you eat soy? Why or why not? If you’re a soy lover, how about sharing some recipes with the rest of us? You can talk with us in the comments below, in our community forums (you'll need to join our community first, if you haven't already), on our Facebook page, or in Midlife & Menopause Solutions, our closed Facebook group. 


Shannon Perry

January 25, 2019
Director of Programming & Media

Medically Reviewed By

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