During a workout at a CrossFit gym, a gathering spot for lots of paleo-enthusiasts, Durant told me it's no longer a challenge for him to avoid the onslaught of bagels and pizza at every street corner. The paleo approach is to eliminate grains and processed food, which are relatively new to the human diet. And, as a result, Durant says, he no longer gets the spikes and dips in his moods, and he feels better.

Now, everyone from the American Cancer Society to the American Heart Association and popular food writers such as Mark Bittman tells us to eat less red meat.

But Durant says it's a meat-based diet that was fundamental to early human development. (Check out our tongue-in-cheek Time Traveler's Cookbook: Meat Lover's Edition for more on this.)

My colleague Chris Joyce has reported on how a meat-based diet helped make us smarter.

And paleoanthropologist John Hawks at the University of Wisonsin, Madison, agrees: "We definitely evolved to eat meat."