Evolution should be our best guide for what constitutes a healthy diet. — Gary Taubes

There is no such ambiguity, however, on the subject of carbohydrates. The most dramatic alterations in human diets in the past two million years, unequivocally, are (1) the transition from carbohydrate-poor to carbohydrate-rich diets that came with the invention of agriculture—the addition of grains and easily digestible starches to the diets of hunter-gatherers; (2) the increasing refinement of those carbohydrates over the past few hundred years; and (3) the dramatic increases in fructose consumption that came as the per-capita consumption of sugars—sucrose and now high-fructose corn syrup—increased from less than ten or twenty pounds a year in the mid-eighteenth century to the nearly 150 pounds it is today. Why would a dietary that excludes these foods specifically be expected to do anything other than return us to “biological normality”?

Since none of this research is particularly controversial, it’s hard to imagine why obesity researchers would not take seriously the hypothesis that carbohydrates have a unique ability to fatten humans—or, as Thomas Hawkes Tanner put it in The Practice of Medicine almost 140 years ago, that “farinaceous and vegetable foods are fattening, and saccharine matters are especially so.” Researchers who study carbohydrate metabolism have found this science compelling. In 1991, the Belgian physiologist Henri-Géry Hers, an authority on what are known as glycogen-storage diseases, one of which is named after him, put it this way: “Eating carbohydrates will stimulate insulin secretion and cause obesity. That looks obvious to me.…” but this simple chain of cause and effect has nonetheless been rejected out of hand by authority figures in the field of human obesity, who believe that the cause of the condition is manifestly obvious and beyond dispute, that the law of energy conservation dictates that obesity has to be caused by eating too much or moving too little.

This is how functioning science works. Outstanding questions are identified or hypotheses proposed; experimental tests are then established either to answer the questions or to refute the hypotheses, regardless of how obviously true they might appear to be. If assertions are made without the empirical evidence to defend them, they are vigorously rebuked…. Each new claim to knowledge, therefore, has to be picked apart and appraised….

This institutionalized vigilance, “this unending exchange of critical judgment,” is nowhere to be found in the study of nutrition, chronic disease, and obesity, and it hasn’t been for decades.