To be honest I don't know too much about it, but as I understand it tofu is the curd made from soya milk, and soya protein is some form of the processed whole bean. My thinking that it's soya protein is just from the fact that I've tried a few different brands' soya fake burgers and they all give me the same discomfort.

I don't have any ill effects from tofu either.

The fake stuff usually lists “textured vegetable protein” or soy protein isolate” or things like that. Those are much more processed than tofu. Tofu is more like a curd in so far as the tofu gets minced then settled out of the water. I think it sometimes gets calcium carbon added.