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What You Need to Know About Consuming Soy

By BCRF | September 26, 2014

Dr. Moshe Shike answers your questions

Earlier this month, a new study about soy made waves in the breast cancer community. With support from BCRF, grantee Dr. Moshe Shike and his coauthors, including Scientific Director Dr. Larry Norton, published a study in the Journal of the National Cancer Institute. The randomized trial discovered that, for some women with breast cancer, taking soy protein supplements promoted the expression of tumor genes associated with an increase in tumor cells.

We chatted with Dr. Shike to learn more about what this study means for women.

The study focused on women with estrogen-receptor positive breast cancer. Should women with all types of breast cancers be cautious about their soy consumption or only those with that particular type?

All women with any type of breast cancer should exercise caution. We did not have enough patients in the study to discriminate or to come up with specifics based on estrogen receptor breast cancer — or, for that matter, any other specific kind. Women should be moderate in their intake of soy. We’re not saying don’t take soy at all; we’re just saying the results of this study may indicate some increased risk, so it’s prudent to be cautious.

The amounts of soy supplements provided to each woman in the study were two doses of 25.8 grams each. What does this translate to in terms of a normal diet? Is there a “safe” amount?

The amount of soy each woman had in the study was a relatively high dose, equal to about 3.5 cups of soymilk or about 16 oz. of tofu, which is a lot for the average woman. In this particular study, it showed that large amounts might drive proliferation of breast cancer in some women. Most women are not getting that much soy in a day.Although soy has anti-estrogenic effects, we are not sure how these effects might impact breast cancer risk. Women should avoid extremes — there’s no need to cut out soy completely, but they also shouldn’t consume large quantities.

This study included only women who currently had breast cancer. Most were post-menopausal. Should younger women or those who don’t have the disease be concerned about their soy intake?

We haven’t examined this yet. But I would advocate that this principle of moderation be applied to all women across the board, even those without breast cancer or who are younger in age. Also, we only know about breast cancer in women who have already been diagnosed. There are women walking around with very early stages of breast cancer that haven’t been detected yet. Because we don’t know the effect of soy on normal breast tissue yet, both types of women should exercise caution in the amounts of soy they consume daily.