I use whey protein powder. I chose it over soy only because at the time I had mold in my house and it helps kill the mold that could be in my system. I talked to my specialist and he said either soy or whey were good. If you have a health food check with them. I buy mine at the military exchange, so much cheaper than the health food store. I'd just research them. I try to only buy vanilla because then I can change the flavor to anything that I want. They didn't have it this time so I got cookies n cream, close enough to vanilla