Although it's often lauded as a healthy, cholesterol-free, cheap, low-fat protein alternative to meat, not all soy is healthy for you, Berkowitz says. "Soy protein, soy isolate, and soy oil are present in about 60 percent of the foods on the market and have been shown to impair fertility and affect estrogen in women, lower sex drive, and trigger puberty early in children," she says. "Soy can also add to the imbalance between omega-6 and omega-3 fatty acids."
The main problem is that 92 percent of soy products in the U.S. are genetically modified, Berkowitz adds. "If you really can't avoid it or are considering going vegetarian or vegan, try to stick with organic soy and don't eat more than three servings a week." She recommends beans, nuts, or sprouted grains such as quinoa or millet as good vegan protein sources, as well as cage-free eggs for vegetarians.