Does soy act like estrogen in the body?

A. Soy does contain estrogen-like substances, but the jury is still out on health effects. Soy is rich in plant-based protein, sans the saturated fat of meat, and has been found to have a mild benefit on blood cholesterol levels. But as the reputation of soy has grown as a health food that may relieve symptoms of menopause and lower heart disease risk — so have doubts.

One of the most hotly debated areas is soy’s possible effect on cancer. Some evidence in human populations suggests that high soy intake might have a preventive effect on breast and endometrial cancers in women, and on prostate cancer in men. But animal studies have noted that high amounts of phytoestrogens, or plant-derived estrogens, may actually promote cancer.

Frank Hu, a professor of nutrition and epidemiology at the Harvard School of Public Health, says that studies in Asian populations have found that diets high in soy products correlate with lower cancer rates. Studies in Western populations have been less clear, in part because fewer people consume a lot of soy. As for determining safe levels of soy consumption, Hu says, “soy consumption has been very high historically in Asian populations, and there is no reason for them to reduce their consumption.’’ For Western populations not accustomed to such high levels of dietary soy, he recommends eating a moderate level of soy-based foods until more is known.

That advice aligns with a 2006 statement by the American Heart Association, which recommends eating soy products such as tofu, soy butter, soy nuts, and some soy burgers as part of an overall heart-healthy diet, but does not recommend taking isoflavone (a phytoestrogen found chiefly in soybeans) supplements or pills because of their uncertain health effects.