Thanks to Greg and Robb (and Nicki!) for putting this protein debate together. I really like that it incorporated two scientists in the field, without getting overly technical. I also appreciated that you chose Campbell for the "low-protein" side of the debate, rather than setting up a straw man to be easily defeated by Cordain.
I have to say that I was a bit disappointed that Dr. Campbell didn't provide references for his assertions. Without these references, it becomes a bit easy for Cordain to look more knowledgeable, especially when he refers to Campbell's own studies. Furthermore, Campbell brings up some scary points - increased protein intake being correlated with cancers and other diseases, etc - but then cites no evidence. These are serious assertions, especially in this community which consumes a fair amount of protein, perhaps even more than 15%.
If the evidence is that compelling, please show us where it is! Thankfully, he does a bit of referring in his rebuttal. However, these citations don't back up his claims connecting protein intake with cancer (other than his own study).
Also, I do not find his assertion that "the ancestral line giving rise to humans was strongly herbivorous" compelling. Those monkeys didn't have our brains, and thus our brain energy requirement, and they lived in warmer climates with ready access to food. When we began to leave those lush environments, finding energy-dense food became more of a challenge than it would have been in the tropical areas where you can stumble across all sorts of edibles.
Furthermore, he spends nearly all of his rebuttal time telling us why nutrition should not be seen through the eyes of evolutionary biology and very little time telling us why excess protein is bad for us. Campbell seems to assume that we have a good knowledge of his work. I do not, and my only knowledge of his book comes from a perusal of the reviews at Amazon. Without that knowledge or references to these protein-damning studies, his arguments about protein being bad and causing this or that disease sound like little more than pleading assertions.
Finally, the last point in his rebuttal is bizarre. It's a vague reference to anecdotal evidence from his colleagues. (My brother's girlfriend's roommate's cousin had the opposite experience, so therefore Campell is wrong.
) This reads more like discussion board flame war tripe than scholarly argument and is a weird addition to an otherwise cogent paper.
However, Cordain's argument is also disturbing in suggesting that saturated fat, not protein is the CVD boogeyman. My understanding is that the science behind that particular line of reasoning is pretty flimsy (see Gary Taubes' The Soft Science of Dietary Fat
) and Cordain's allusion to it is not reassuring.
All in all though, I thoroughly enjoyed the debate. I learned a lot and have a bunch of papers to look up now. This sort of honest evaluation of both sides of an idea is far too rare. Thanks for providing it! Will we perhaps see a debate on fat or ketosis in the future? (Please, please!) In any case, thanks again to the PM crew for putting this together and kudos to Campbell and Cordain for taking on the challenge.