Yes, soy protein contains large amounts of compounds called phytoestrogens, and yes, they’re called that because they look and act awfully similar to the female sex hormone estrogen. (You know, the one that builds fat deposits and generally has zero concern for muscle mass.) But, ironically enough, soy protein can be enormously beneficial for male muscles. For one thing, several studies have conclusively shown that soy promotes muscle growth without affecting testosterone levels. Soy also contains a lot more arginine than whey, which makes it better for blood flow. And those same phytoestrogens just so happen to be powerful antioxidants that have been shown to hasten recovery by reducing the amount of oxidative damage muscle cells incur during exercise.
Add soy to your preworkout and postworkout shakes in a 1:1 ratio with whey.