Since those carnivorous days in the 1970s, soy foods have gone from a niche product for the vegetarian-environmentalist crowd to a four-billion-dollar-a-year food industry. Soy is now on nearly every sushi bar menu and is used as a vegetable oil, as a meat and dairy substitute，and as an inexpensive additive to increase the volume and improve the texture of many processed foods. The legume is so ubiquitous that it has found its way into everything from peanut butter to canned tuna. Many studies have shown the possible health benefits of eating soy, so most people consider it a “health food”. After all, it，s high in protein and has zero cholesterol—wbat could be wrong with that?

Plenty, some say. Recent research has shown that soy may contain dangerous levels of isoflavones, natural chemicals that are similar to human estrogen. Isoflavones can affect fertility in men and may increase the incidence of breast cancer in at-risk women. Because of these concerns, the Israeli Ministry of Health has had a warning in effect since 2005. According to reports, the ministry suggests that adults moderate their soy consumption, that infants be given soy formula only when breast milk or cow's milk is not an option, and that parents limit the amount of soy their children eat. Health officials in France and Great Britain are concerned, too. French food manufacturers have been asked to reduce the isoflavones in soy formula, and are required to put warning labels on soy foods. The British Dietetic Association has warned parents against using soy formula during the first six months of a baby's life.

Not surprisingly, the Soyfoods Association of North America doesn’t necessarily agree with these concerns. Nancy Chapman, the group’s executive director, says that the Israeli Ministry of Health’s warning was largely based on research that used rats, whose hormonal makeup and reproductive system don’t accurately predict what may happen in the human body.

“Every time a study comes out that the soy industry doesn’t like, they respond in one of two ways: It’s poorly designed, or it’s old” says Kaayla T. Daniel, Ph.D., a nutritionist and author of The Whole Soy Story. “Israel had a committee of more than a dozen distinguished nutritionists, researchers, pediatricians, and toxicologists who looked at the body of evidence, and concluded there was a risk.”

Daaiel is one of an increasingly vocal group of nutritionists and scientists who are concerned about the possible risks of consuming too much soy. “The soy industry can never prove safety,” she tells me. “They’ll trot out studies showing a benefit, and act as if all the others indicating a risk are not a problem.”

Muddying the waters further are scientific studies that have reached very different conclusions. Soy can reduce the risk of breast cancer {Journal of the National Cancer Institute, 2006); it has no effect (Cancer，2007); it can actually increase the risk (Cancer Research, 2001); soy can help memory in postmenopausal women {Menopause, 2003); no, it can’t (Journal of the American Medical Asso-ciation, 2004).

What is clear today, according to the Harvard School of Public Health, is that when it comes to soy and health, “some of the claims...go far beyond the available evidence.” The AHA still says that it’s perfectly fine to eat soy as part of a varied diet, and Van Horn continues to recommend soy to some of her patients, and to eat it herself.

So what’s the bottom line? If you’re a woman who has been diagnosed with or has a family history of breast cancer, it’s probably safest to avoid soy. Men hoping to father children should probably limit the amount of soy they eat, and parents would be advised to follow the Israeli guidelines in serving soy foods to their kids, especially infants and toddlers.