The soy milk we have in the market are sweetened. That means they add sugar.

And drinking A LOTTTTT of soy milk can increase your estrogen level --> man boobs. (This one, I am not sure. I'm just throwing this out so that you can go read more about it.)

Well, that's what I read in one of the issues in Men's Health. It mentioned about a guy with man boobs for drinking tonnes of commercial soy milk daily.
But then again, that's the US, with their GM soy and different soy milk processing.