http://www.jbc.org/content/87/3/651.full.pdf
> Two normal men volunteered to live solely on meat for one year, which gave us an unusual opportunity of studying the effects of this diet. The term “meat,” as used by us, included both the lean and the fat portions of animals. The subjects derived most of their calories from fat and the diet was quite different from what one, who uses the term “meat” as including chiefly lean muscle, would expect.
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> 11. In these trained subjects, the clinical observations and laboratory studies gave no evidence that any ill effects had occurred from the prolonged use of the exclusive meat diet.
People in the Arctic circle like the Inuit always lived almost entirely off of meat and Mongolians and other steppe pastoralists come very close, adding dairy.