I have no idea why one would want to use soy over whey. I swear when I used to sell supps, every guy and I mean every guy who walked in the store asking for whey looked like a a complete weiner. It has a very low, if not the lowest biological value of all proteins and the one I used tasted like shit. It was the supro bags you find in most places... I got the idea to use it when reading mm2k about 10 years ago. There was talk about soy increasing throid levels while dieting. I used to hold my breath and drink it down it tasted so bad. Any way, I don`t know of any advantage to use soy over whey. The pussy`s who wanted to buy the stuff wanted it because they thought it was not "full of chemicals" like the other stuff in the store.