Soy may be good for the heart, but if you’re trying to keep the ticker healthy and happen to be a breast cancer patient as well, then it’s not so clear how beneficial soy products may be for you.
The studies so far haven’t helped. Soy contains isoflavones that are similar to estrogen in chemical structure, and when these isoflavones bind to estrogen receptors on cells, they can either stimulate or inhibit estrogen-driven functions in tissues. That explains why some studies have shown that eating soy can reduce the risk of recurring breast tumors, while others have shown that soy foods can increase the chances that a cancer will return. (More on Time.com: Special Report: Advances for Breast Cancer Patients)
Now researchers from China report that soy lowers the risk of recurring breast cancers among women with estrogen-positive tumors, just the cancers that might be more sensitive to soy’s tumor-promoting effects. Comparing the volunteers who ate the least amount of these foods including tofu, to those eating the most (eight times the daily dose), the researchers found that the high consumers lowered their risk of having a recurrent breast tumor by 33%.
“This study helps us to move one step forward from where we are now,” says Dr. Banu Arun, co-director of clinical cancer genetics at MD Anderson Cancer Center, in commenting on the results. “It shows potential beneficial effects, so it helps us to move forward with other studies that need to be done that might include more patients and will give us additional information about why soy is beneficial, and why higher doses might be more effective.”
The heaviest soy consumers in the trial ingested about 59 mg of isoflavones a day, while the lowest consumers still got about 6.5 mg a day. The average American only eats about 1 mg to 3 mg daily. That’s an important consideration for U.S. women at risk of breast cancer who are thinking of increasing their soy milk or tofu consumption, says Arun. “The effect of taking soy might be different in the western patient population where they aren’t eating as much soy. This [Chinese] patient population was primed with soy and its good effects, so there may be a favorable milieu in the tissue so after breast cancer they continue to see its benefits. But perhaps in breast tissue or other organs that haven’t been exposed to soy before, all of sudden starting to increase soy consumption might have other effects; we don’t know.” (More on Time.com: Photos: The Landscape of Cancer Treatment)
The findings hint that there may be some ways in which the isoflavones are beneficial, particularly since the subjects in the trial were all taking hormone-based drugs to treat their cancer. Some experts have speculated that soy may enhance the activity of these medications in inhibiting tumor growth, and if that’s the case, then further studies like this one might expose which doses and which regimens of soy are most effective in fighting cancer.
In the meantime, is it safe for women worried about breast cancer to eat tofu and other soy foods? Yes, says Arun. “I wouldn’t say don’t eat soy. Moderate consumption should be fine. I just wouldn’t convert to a soy rich diet yet to reduce breast cancer recurrence since we don’t have the data yet for a western population.”
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