Good Calories, Bad Calories

the efficacy of carbohydrate-restricted diets. That someone might find living without starches, flour, and sugar to be difficult, and that there might be physical symptoms accompanying the withdrawal process, does not speak to the possibility that they might be healthier and thinner for the effort. No one would argue that quitting smoking (or any other addictive drug) is not salutary, even though ex-smokers invariably miss their cigarettes, and many will ultimately return to smoking, the addiction eventually getting the better of them. The same may be true for these carbohydrates.

It also makes us question the admonitions that carbohydrate restriction cannot “generally be used safely,” as Theodore Van Itallie wrote in 1979, because it has “potential side effects,” including “weakness, apathy, fatigue, nausea, vomiting, dehydration, postural hypotension, and occasional exacerbation of preexisting gout.” The important clinical question is whether these are short-term effects of carbohydrate withdrawal, or chronic effects that might offset the benefits of weight loss. The same is true for the occasional elevation of cholesterol that will occur with fat loss—a condition known as transient hypercholesterolemia—and that is a consequence of the fact that we store cholesterol along with fat in our fat cells. When fatty acids are mobilized, the cholesterol is released as well, and thus serum levels of cholesterol can spike. The existing evidence suggests that this effect will vanish with successful weight loss, regardless of the saturated-fat content of the diet. Nonetheless, it’s often cited as another reason to avoid carbohydrate-restricted diets and to withdraw a patient immediately from the diet should such a thing be observed, under the mistaken impression that this is a chronic effect of a relatively fat-rich diet.

In 1963, when Robert Kemp discussed his clinical experience with carbohydrate-restricted diets and the apparent problem of carbohydrate addiction, he made the point that the necessary step was to establish beyond reasonable doubt whether carbohydrates indeed were the cause of obesity and overweight. By doing so, we could then make informed decisions about the risks and benefits of our cravings. Many former cigarette smokers would likely still be smoking today without the certain knowledge that tobacco causes lung cancer. “At least half of our patients, win or lose, cannot be persuaded that they must permanently alter their eating habits to save their lives,” Kemp wrote. “This is undoubtedly a battle for the mind where unfortunately the patient is completely unsettled by the confusion of advice offered from both professional and lay sources.” This statement is still true today. Carbohydrate-restricted diets will always be tempting, if for no other reason than their efficacy at inducing weight loss. But to make a permanent change in diet requires the confidence that we will be healthier for doing so. For that, we need the support of physicians, nutritionists, and the public-health authorities, and we need advice that is based on rigorous science, not century-old preconceptions about the penalties of gluttony and sloth.

EPILOGUE

The community of science thus provides for the social validation of scientific work. In this respect, it amplifies that famous opening line of Aristotle’s Metaphysics: “All men by nature desire to know.” Perhaps, but men of science by culture desire to know that what they know is really so.

ROBERT MERTON, Behavior Patterns of Scientists, 1968

The first principle is that you must not fool yourself—and you are the easiest person to fool.

RICHARD FEYNMAN, in his Commencement Address at Caltech, 1974

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 deja 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.”