From an evolutionary standpoint, legumes, milk, and grains are "artificial" food, at least for humans. Agriculture is a recent thing. Would you also endorse the Paleolithic diet movement?
(I do actually endorse the paleolithic diet as probably optimal at the moment and I agree with your central point - I just want to point out that even unprocessed modern diets are already rather unnatural.)
Although agriculture is only about 10,000 years old, humans have been gathering and eating wild grains for 30,000.
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.