Good Calories, Bad Calories

ON FEBRUARY 7, 2003, THE EDITORS OF Science published a special issue dedicated to the critical concerns of obesity research. It included four essays written by prominent authorities, all communicating the message of the toxic-environment hypothesis of the obesity epidemic and the belief that obesity is caused by “consuming more food energy than is expended in activity.” The one article that offered a potential solution to the national and global problem of burgeoning waistlines—other than the promise of future obesity-fighting drugs—was written by James Hill of the University of Colorado, John Peters of Procter & Gamble, and two colleagues. Hill and Peters introduced the concept of an “energy gap” that could purportedly explain the existence of the obesity epidemic and illuminate a path of action by which it might be halted or reversed. By their calculation, the obesity epidemic represented an energy gap of a hundred calories per person among the American public per day that had been consumed but not expended. To undo the epidemic, Hill and Peters suggested, Americans would have to make either comparable increases in daily energy expenditure—walking one extra mile, perhaps—or decreases in energy consumption, such as “eating 15% less (about three bites) of a typical premium fast-food hamburger.” Two years later, when the U.S. Department of Agriculture released the sixth edition of its Dietary Guidelines for Americans, it offered similar advice based on the identical logic: “For most adults a reduction of 50 to 100 calories per day may prevent gradual weight gain.”

This proposition should evoke a distinct sensation of déjà vu, because it is the precise argument that Carl von Noorden made over a century ago. Hill, Peters, and the USDA authorities, like von Noorden, were treating the regulation of body weight as though it were a purely arithmetical process, in which a small excess of calories consumed, day in and day out, accumulates into pounds of flesh and then tens of pounds, and a small deficit, day in and day out, does the opposite. That this argument is now the cornerstone of the official U.S. government recommendations for obesity prevention made the single caveat in Hill and Peters’s Science article all that much more remarkable. Speaking of the hundred-calorie energy gap, they said that their “estimate is theoretical and involves several assumptions”—in particular, “Whether increasing energy expenditure or reducing energy intake by 100 kcal/day would prevent weight gain remains to be empirically tested.”

The more important point, though, which Hill and Peters did not discuss, was why a century of research had not produced such an empirical test. Two immediate possibilities suggest themselves: Either the accumulated research and observations on weight regulation in humans or animals had never provided sufficient reason to believe that such a proposition should be true, which is a necessary condition for anyone to expend the effort to test it; or, perhaps, nobody cared to test it. In either case, we have to wonder whether the individuals involved in the pursuit of the cure and prevention of human obesity, as Robert Merton would have put it, have the desire to know that what they know is really so.

In the 1890s, Francis Benedict and Wilbur Atwater, pioneers of the science of nutrition in the United States, spent a year in the laboratory testing the assumption that the law of energy conservation applied to humans as well as animals. They did so not because they doubted that it did, but precisely because it seemed so obvious. “No one would question” it, they wrote. “The quantitative demonstration is, however, desirable, and an attested method for such demonstration is of fundamental importance for the study of the general laws of metabolism of both matter and energy.”

This is how functioning science works. Outstanding questions are identified or hypotheses proposed; experimental tests are than 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. In science, as Merton noted, progress is made only by first establishing whether one’s predecessors have erred or “have stopped before tracking down the implications of their results or have passed over in their work what is there to be seen by the fresh eye of another.” Each new claim to knowledge, therefore, has to be picked apart and appraised. Its shortcomings have to be established unequivocally before we can know what questions remain to be asked, and so what answers to seek—what we know is really so and what we don’t. “This unending exchange of critical judgment,” Merton wrote, “of praise and punishment, is developed in science to a degree that makes the monitoring of children’s behavior by their parents seem little more than child’s play.”