What's one to make of it?
Soy, which comes in many forms and is derived from soybeans, has long had the reputation of being a near perfect health food - offering loads of protein with little calories and fat.For years, the government and nutritionists have praised soy, pointing to the health of Asian populations where soy is a diet staple.
When soy started hitting the mainstream, it was reportedly supposed to lower cholesterol, alleviate menopause symptoms, even help prevent cancer.
But soy has its detractors, too. Some nutritionists complain not only are soy's benefits overstated, but there are also plenty of drawbacks as well. They say a diet laden with soy can impact fertility, affect the thyroid and even cause heart problems.
Critics also point out that the type of soy Americans eat is different from that of Asia, which is mostly fermented forms such as tempeh and miso. Much of the soy consumed in the United States is both highly processed and made from genetically modified soybeans. The upshot: Even though Asian populations don't seem to suffer any ill effects from soy, like reduced fertility, that doesn't necessarily translate to U.S. consumers.
So what's a lover of soy - which is in everything from edamame to soy milk to Boca burgers - to make of it all? Is it time to put soy on the shelf with the seemingly ever-expanding list of shouldn't-eat foods?
As in all things, the truth lies between the two extremes, said Joan Rupp, a professor of nutrition at San Diego State University.
While there have been some animal studies that have found such side effects as reduced fertility and thyroid issues, those problems have not been established in any long-term human studies. As far as the current research goes, Rupp said, it supports the belief that a diet with moderate soy consumption is both safe and healthy because substituting animal protein for plant protein is always a good way to cut saturated fat from your diet. Still, eating soy is not the health panacea that some might envision.
"There's a place for soy, but you don't want to go overboard with it," she said. "Everyone is always looking for that magic pill in terms of their health. From what it looks like now, soy isn't going to be it."
Still not sure what to make of soy? Here's a rundown of some of its potential benefits and drawbacks.
Does soy lower cholesterol?
Sure, but not by much. Studies have found that a soy-rich diet can reduce LDL, or bad, cholesterol between 3 percent and 6 percent. Those with extremely high cholesterol may benefit the most. Just remember that overloading on soy, consuming beyond the recommended limit of 25 grams a day, won't bring your cholesterol down any further.
Does soy reduce fertility?
Not so far as we know, say most nutritionists, physicians and researchers. They point to Asian populations where there are no such fertility problems. Still, a recent Harvard study found that men who eat approximately half a serving of soy did experience a reduced sperm count. But many studies have found no conclusive evidence that soy causes fertility problems in humans although there have been some issues in animal studies. Soy does have phytoestrogen, a plant form of the female hormone estrogen, but the American Academy of Pediatrics says it is not worried about the hormonal effects on children.
Is soy-based baby formula dangerous?
The American Academy of Pediatrics says no. Still, there's no real reason to use soy formula instead of formula derived from cow's milk, said Dr. Frank Greer, who recently studied the soy formula issue for the organization.
Does soy help with menopause symptoms?
Maybe, a little bit. According to the National Institutes of Health, some studies suggest that soy supplements may reduce hot flashes in women after menopause. However, the results have been inconsistent.
Does soy help prevent breast cancer?
It might if soy consumption begins at a very young age but the science is inconclusive. That goes for prostate cancer, too. But nutritionists and physicians say women who have breast cancer should be careful of eating soy because of the estrogen component. As the NIH puts it, women at risk of developing hormone-sensitive conditions such as breast cancer or ovarian cancer should consult with their doctor about their soy intake.
Does soy help prevent heart disease?
Since it lowers a person's cholesterol, it can. Still, soy's overall heart benefits are in question. The American Heart Association has scaled back its earlier recommendation of a soy-rich diet because of the limited benefit in preventing heart disease. One study of male mice genetically programmed to develop heart disease found that those with a soy-rich diet were more prone to heart failure than those on a dairy diet. Typical caveat: It's still unclear if that study has any relevance for humans.