Good Calories, Bad Calories

I first heard this notion in 1998, when I interviewed William Harlan, then associate director of the Office of Disease Prevention at the National Institutes of Health. Harlan told me that public-health experts like himself assumed that if they advised all Americans to eat less fat, with its densely packed calories, weights would go down. “What we see instead,” he said, “is actually weights have gone up, the portion sizes have gone up, the amount we eat has gone up…. Foods lower in fat became higher in carbohydrates and people ate more.”

The result has been a polarization on the subject of nutrition. Most people still believe that saturated fat, if not any and all fat, is the primary dietary evil—that butter, fat, cheese, and eggs will clog our arteries and put on weight—and have reduced their intakes. Public-health experts and many in the media insist that the obesity epidemic means the population doesn’t take their advice and continues to shun physical activity while eating fatty foods to excess. But a large number of people have turned to the message of Banting and one remarkably best-selling diet book after another: Eat Fat and Grow Slim (1958), Calories Don’t Count (1961), The Doctor’s Quick Weight Loss Diet (1968), Dr. Atkins’ Diet Revolution (1972), The Complete Scarsdale Medical Diet (1978), The Zone (1995), Protein Power (1996), Sugar Busters! (1998), and The South Beach Diet (2003). All advocate an alternative hypothesis: that carbohydrates are the problem, not fat, and if we eat less of them, we will weigh less and live longer. All have been summarily dismissed by the American Heart Association, the American Medical Association, and nutritional authorities as part of a misguided fad.

But is it? If 150 years of anecdotal evidence and observation suggest that carbohydrates are uniquely fattening, it would be unjustifiable scientifically to reject that hypothesis without compelling evidence to the contrary. Such evidence does not exist. My purpose here is to examine the data that do exist and to demonstrate how we have reached the conclusions we have and whether or not they are justified.

There is a more important issue here as well, and it extends far beyond the ideal weight-loss diet. Prior to the official acceptance of the low-fat-is-good-health dogma, clinical investigators, predominantly British, had proposed another hypothesis for the cause of heart disease, diabetes, colorectal and breast cancer, tooth decay, and half-dozen or so other chronic diseases, including obesity. The hypothesis was based on decades of eyewitness testimony from missionary and colonial physicians and two consistent observations: that these “diseases of civilization” were rare to nonexistent among isolated populations that lived traditional lifestyles and ate traditional diets, and that these diseases appeared in these populations only after they were exposed to Western foods—in particular, sugar, flour, white rice, and maybe beer. These are known technically as refined carbohydrates, which are those carbohydrate-containing foods—usually sugars and starches—that have been machine-processed to make them more easily digestible.

In the early 1970s, the hypothesis that refined carbohydrates cause heart disease and other chronic diseases competed directly with the dietary-fat hypothesis of heart disease. Carbohydrates could not cause heart disease, so the argument went, because fat seemed to cause heart disease. Moreover, any diet that contained a suitably low proportion of calories as fat would, by definition, be high in carbohydrates, and vice versa. The only caveat was that the fat hypothesis was, indeed, only a hypothesis, and the evidence to support it was ambiguous at best. By the mid-1970s, the carbohydrate theory of chronic disease had been transformed into a more politically and commercially acceptable version: it wasn’t the addition of refined and starchy carbohydrates to the diet that caused chronic disease, but the absence of fiber or roughage, removed in the refining process, that was responsible. This conclusion, however, has not been supported by clinical trials, which have shown that fiber has little or no effect on the incidence of any chronic disease.