Yes, some breast cancer grows in the presence of estrogen, and yes, soy can
act like estrogen. But there’s no direct link saying soy can cause cancer. In some animal studies, pure isoflavones, the compound in soy bearing the chemical similarities to estrogen, have been shown to promote tumor growth, HuffPost Healthy Living’s
Meredith Melnick reported. However, humans both process isoflavones differently than rodents and isoflavone supplements vary greatly from dietary soy.
Among observational studies of humans
who get high amounts of dietary soy, findings have shown either no link to breast cancer or lower rates of the disease. “Even though animal studies have shown mixed effects on breast cancer with soy supplements, studies in humans have not shown harm
from eating soy foods,” Marji McCullough, ScD, RD, strategic director of nutritional epidemiology for the American Cancer Society wrote for the organization. “Moderate consumption of soy foods appears safe for both breast cancer survivors and the
general population, and may even lower breast cancer risk.”
The concerns about the estrogen-like activities of soy have caused some to worry that soy products could
decrease a man’s testosterone, but clinical studies don’t support this fear. There are at least two reports of men who have experienced feminizing changes in their bodies (one of whom had Type 1 diabetes) after consuming high doses of soy, but
even at higher-than-average rates of consumption — higher even than what’s typical among Asian cultures — science has found no evidence to caution men against eating soy. In fact, men may even benefit from some dietary soy, as it seems to
decrease prostate cancer risk.
.....at least two reports of men who have experienced feminizing changes in their bodies
as it seems to decrease prostate cancer risk.