One guy at a GNC tried to talk me out of buying a nutrition bar once because he said "it will cause my breasts to start lactating." I said cool and bought it. Anything in large doses can cause problems.

Use common sense, eat plenty of fruits, veges, and lean meats. Avoid low carb diets if you plan on training alot. Oh yeah, I spoke to a well respected Cardiologist who is an avid exerciser and he said soy protien is one of the best protiens for your body.