They also found carbohydrate-selective diets to be better than categorically low-carbohydrate diets, in that incorporating whole grains is associated with lower risks for cancers and better control of body weight. Attention to glycemic load and index is "sensible at the least." Eating foods that have high glycemic loads (which Katz says is much more relevant to health outcomes than glycemic index—in that some quality foods like carrots have very high indices, which could be misleading) is associated with greater risk of heart disease.

Finally, in a notable blow to some interpretations of the Paleo diet, Katz and Meller wrote, "if Paleolithic eating is loosely interpreted to mean a diet based mostly on meat, no meaningful interpretation of health effects is possible." They note that the composition of most meat in today's food supply is not similar to that of mammoth meat, and that most plants available during the Stone Age are today extinct. (Though it wouldn't surprise me to learn that Paleo extremists are crowd-funding a Jurassic Park style experiment to bring them back.)

Just because Katz is not one to abandon his scientific compass under duress of passion does not mean he is without passion, or unmoved by it in his own ways. The subjects of media headlines and popular diet books are dark places for Katz. "It’s not just linguistic, I really at times feel like crying, when I think about that we’re paying for ignorance with human lives," he told me. "At times, I hate the people with alphabet soup after their names who are promising the moon and the stars with certainty. I hate knowing that the next person is already rubbing his or her hands together with the next fad to make it on the bestseller list."

"The evidence that with knowledge already at our disposal, we could eliminate 80 percent of chronic disease is the basis for everything I do," Katz said. Just as he was finishing his residency in internal medicine in 1993, influential research in the Journal of the American Medical Association ("Actual Causes of Death in the United States") put diet on a short list of the lifestyle factors blamed for half of deaths in 1990. "Here we are more than 20 years later and we’ve made just about no progress."

A nod to the fact that popular media is not totally lost, Katz borrows from the writer Michael Pollan, citing a seminal 2007 New York Times Magazine article on "nutritionism" in concluding that the mantra, "Eat food, not too much, mostly plants" is sound. "That’s an excellent idea, and yet somehow it turns out to be extremely radical."

Though Katz also says it isn’t nearly enough. "That doesn't help you pick the most nutritious bread, or the best pasta sauce. A member of the foodie elite might say you shouldn't eat anything from a bag, box, bottle, jar, or can." That's admittedly impractical. "We do need to look at all the details that populate the space between where we are and where we want to be."