As with all foods, experts still don’t know everything there is to know about soy. But research in recent years suggests that moderate consumption of minimally processed soy foods (more on what those are later) not only isn’t bad for you—it probably has some benefits. Here’s what we can say about soy in 2017:
1. Soy probably doesn’t raise breast cancer risk, and it might even lower the risk of some cancers.
The majority of recent, high-quality studies have found that soy doesn’t increase breast cancer risk, and very high consumption could even offer some protection. A PLoS One meta-analysis of 35 studies found that soy intake lowered breast cancer risk for women in Asian countries; among U.S. women, soy consumption and breast cancer risk were unrelated. And a Tufts University study, published earlier this year, showed that soy consumption isn’t problematic for women who currently have breast cancer and doesn’t make cancer treatment drugs like tamoxifen less effective. Soy was even linked to longer survival rates for women with certain types of aggressive breast cancer.
Eating soy could help protect against other types of cancer, too. Findings show that soy consumption may slightly lower the risk for gastrointestinal cancers and have a protective effect in prostate cancer survivors. Eating a high-fiber diet is also tied to lower colon cancer rates, and soyfoods like edamame and tempeh both have plenty of roughage. (Here are 5 ways to sneak more fiber into your diet.)
2. Soy might improve fertility and help with hot flashes.
Soy appears to be beneficial for fertility, as long as you don’t eat too much. Women undergoing in vitro fertilization who have environmental exposure to BPA are more likely to get pregnant if they also ate soy. Likely, that’s because soy’s isoflavones help neutralize the BPA’s endocrine-disrupting effects, researchers say.
Just don’t go overboard. Consuming over 100mg of soy isoflavones (the equivalent of 6 oz uncooked tempeh or 16 cups soy milk) daily was linked to reduced ovarian function, found a Journal of Nutrition review. But moderate soy consumption didn’t pose a problem. (Here's a comprehensive table listing the soy isoflavone content of various soy-based foods.)
As for soy solving hot flash problems? It might help, but not for everyone. Among women whose bodies produce the soy metabolite equol, those who consumed the most soy experienced significantly fewer hot flashes and night sweats compared to those who ate the least soy, found one Menopause study. (Between 20% and 50% of North American and European women produce equol. And though some research centers can test for it in a urine sample, there’s an easier option: Try adding soy to your diet for 4 to 6 weeks and see what happens. If it helps, you produce equol. If it doesn’t, you probably don’t, the study authors say.)
Related: 9 Everyday Chemicals That Could Be Messing With Your Fertility
3. You should pay attention to your soy intake if you have thyroid issues.
Soy foods don’t affect thyroid function in people with healthy thyroids, found a Loma Linda University review of 14 studies. But if you have an underactive thyroid, you might want to watch how much soy you eat. Soy foods have been shown to interfere with the body’s absorption of thyroid medication—but only if you overdo it, suggests a 2016 Nutrients review. One small study also found that eating soy could up the risk of borderline hypothyroidism progressing to full hypothyroidism. But the evidence is still far from conclusive, and experts agree that people with thyroid issues don’t need to avoid soy altogether. Just make sure to wait at least 4 hours after consuming soy to take your thyroid medicine, experts say.
Related: 9 Thyroid Symptoms To Look Out For
4. Soy will probably protect your heart, but it’s not a miracle food.
Early research suggested that soy could help lower levels of bad cholesterol. But more recent findings have shown that might not be the case, and in 2008, the American Heart Association said that there wasn’t enough evidence to say for sure that soy lowered the risk of heart disease.
Still, it’s safe to assume that soy has some benefits going for it. In general, replacing animal foods with plant foods like soy lowers saturated fat intake and ups fiber intake, both of which are good for your heart. In other words, swapping that steak out for tofu or tempeh is a heart-smart move. But having steak followed by a bowl of soy ice cream for dessert probably won’t be as helpful.
Related: 7 Worst Foods For Your Heart