Don't swear off soy just yet, guys

Phytoestrogens have very weak estrogenic activity in humans, said La Barbera. "You would need to consume enormous quantities to affect anything," he said. He added that the current study doesn't prove a causal relationship between soy and sperm -- it just suggests a correlation. And though the study accounted for men's smoking, caffeine and alcohol consumption and differences in age, it didn't rule out other dietary or behavioral factors that may have accounted for the variations in sperm.

Soy has come under fire before -- studies of varying quality have linked tofu to dementia, soy infant formula to immune system damage and soy products to an increased risk of bladder cancer. It's also, of course, been praised -- as a way to prevent prostate and breast cancers, osteoporosis, hot flashes and heart disease.

The pendulum will likely continue to swing as researchers undertake studies of different sizes, designs and lines of inquiry. Case in point: Since 1999, the Food and Drug Administration has allowed soy foods containing at least 6.25 grams of soy protein per serving to bear labels claiming they can help prevent heart disease, based on soy's demonstrated ability to lower levels of LDL or "bad" cholesterol. But in 2006, an American Heart Assn. committee revisited the evidence and concluded that soy protein has only minimal cholesterol-lowering abilities.

Still, the committee said, soy foods could be a boon to those hoping to reduce their risk of heart disease. Tofu, tempeh, soy milk and the like may not be "superfoods," but they're still pretty healthful, naturally low in saturated fat and high in fiber, vitamins, minerals and protein.

And, of course, phytoestrogens.

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