The problem is that protein is much more complicated molecularly (if that's a word) than carbohydrates, and in the breakdown you get such little delights as mercaptans and ketones. Not that I'd have a real problem with a nice porter that smelled like decaying animal flesh but I doubt the marketeers would go for it. Dang capitalists.
Like I said, call it ABB (Atkins bug beer - aka: anyone but bush) and market it to the libs.