Originally Posted by SnakePit
Soy is a complete (all the essential amino acids for growth) source of protein.
It's not prefered because many people believe it can act as estrogen in the human body. I personally am mixed but have eaten a bit of soy my entire life and have most of a beard, extremely deep voice, and gain muscle very easily @ 19. So I doubt that to an extent.
I wouldn't recommend loading up on it though.
Soy does act like estrogen in the body. however, what few people realize is that when you have a rise in estrogen, your body will automatically raise it's testosterone. Vice versa, if you take a testosterone booster- your estrogen will automatically rise to match it to keep your body in homeostasis (or balance). so if you take a testosterone booster you also need an estrogen blocker.
what i'm saying is, dont avoid soy for fear of an estrogen increase. there is an increase, which is negligible at best, and is immediately countered by a rise in testosterone.
something else to consider is that soy is lower in cholesterol than whey and egg products.