The fact that appetite and thus calories consumed will increase to compensate for physical activity, however, was lost along the way. Clinicians, public-health authorities, and even exercise physiologists had taken to thinking and talking about hunger as though it were a phenomenon that was exclusive to the brain, a question of willpower rather than the natural consequence of a physiological drive to replace whatever calories may have been expended. When we are physically active, we work up an appetite. Hunger increases in proportion to the calories we expend, just as restricting the calories in our diet will leave us hungry until we eventually make good the deficit, if not more. The evidence suggests that this is true for both the fat and the lean. It is one of the fundamental observations we have to explain if we’re to understand why we gain weight and how to lose it.

Chapter 16

Chapter Sixteen

PARADOXES

The literature on obesity is not only voluminous, it is also full of conflicting and confusing reports and opinions. One might well apply to it the words of Artemus Ward: “The researches of so many eminent scientific men have thrown so much darkness upon the subject that if they continue their researches we shall soon know nothing.”

HILDE BRUCH, The Importance of Overweight, 1957

LET’S ASK A FEW MORE SIMPLE QUESTIONS about the nature of obesity and weight regulation. Even if we accept—just for the moment—that obesity is caused by a positive energy balance and thus some combination of overeating and sedentary behavior, why would anyone willingly continue to overeat or remain sedentary if obesity is the undesirable state it certainly appears to be? Why would energy balance remain positive when there are so many compelling reasons and so much time to stop the process and maybe reverse it? If a positive energy balance can be turned into a negative energy balance with reasonable facility by exercise and calorie-restricted diets, why is it so difficult to lose weight?

This is the paradox that haunts a century of obesity research. As Marian Burros wrote in the New York Times in 2004: “Those who consume more calories than they expend in energy will gain weight. There is no getting around the laws of thermodynamics.” This was the “very old and immutable scientific message,” she explained. And yet the great majority of those who attempt to expend more calories than they consume don’t lose weight. Those who do, lose only a little, and for short periods of time. This suggests that obesity is a disease, “a chronic condition,” as Albert Stunkard described it over thirty years ago, “resistant to treatment, prone to relapse, for which we have no cure.”