How Healthy Is Soy?

Does soy promote cancer? Does it make men less manly? Weighing the merits of tofu

By Maia Szalavitz, published on May 1, 2006 - last reviewed on June 9, 2016

Soy is the epitome of health food: Perhaps only yogurt has a stronger reputation as a food that Americans eat primarily "because it's good for you."

Touted as being a heart protector, cancer fighter and a safer alternative to hormones during menopause, soy has long been seen as a miracle food.

Yet the soybean has gotten a bit of a bad rap, thanks to studies linking soy's estrogen-like chemicals with breast cancer. As a result, many women now shun the food and some men believe tofu will make them less manly.

No need to panic. The research linking animal fat to heart disease and cancer are far stronger than those connecting soy to any health problems. So, if you are considering substituting soy for meat or milk, the soybean still shines in comparison, according to Ethan Balk, associate director of the Tufts-New England Medical Center's Evidence-Based Practice Center, who reviewed the studies in 2005.

But if the question is whether to eat large amounts of soy or take supplements, the answer is far more elusive. Here's what the latest findings suggest:


The most solid evidence on soy credits it with reducing levels of "bad" LDL cholesterol. Balk's review found that eating large amounts of soy foods or taking supplements was linked to a small, but measurable, positive effect. For every 1 percent reduction in LDL levels, there is a corresponding 1 percent reduction in the risk of heart attack or stroke. Additionally, the studies found that the higher a person's LDL levels, the more soy can help.

However, soy's impact on cholesterol wasn't large enough for the American Heart Association, which reversed its position favoring soy supplements, saying that their effects were too small to warrant recommendation.

Bottom Line: It's worth a shot.

Menopausal Symptoms

Because of soy's estrogen-like effects, it has been promoted as an alternative to hormone-replacement for the relief of menopausal symptoms. But Balk's research has found little agreement among the findings. Some studies found large effects, some small, some found none at all.

Bottom Line: Inconclusive.

Breast Cancer

Certain types of breast cancer are fueled by estrogen, so there has been concern that soy might be harmful to women with a genetic predisposition to this disease. Studies in cell culture and in mice found that soy increased the growth of breast cancer cells. On the other hand, Asian women, who tend to eat a soy-based diet, have a threefold lower risk of breast cancer than Western women do—and their risk increases if they immigrate and switch to a Westernized diet. Further, a study found that soy blocked estrogen receptors in monkeys at risk for breast cancer due to high estrogen levels. This suggests soy might be protective for women at high risk.

Bottom Line: Wait and see.

The Upshot

Soy is a great form of low-fat protein, especially for people seeking to cut down on the saturated fat from meat. However, until scientists determine whether large quantities of soy are helpful or harmful to people at risk for breast cancer, moderation is best. As an alternative to fattier animal proteins, it still deserves health-food status.