Willpower

likely to go on diets, and their diets caused them to rely on external instead of internal cues. For what is a diet but a plan imposing external rules? Dieters learn to eat according to a plan, not to their inner feelings and cravings. Dieting means being hungry a lot of the time (even if the marketers of diets are always promising otherwise).
    More precisely, dieting means learning not to eat when you are hungry, preferably by learning to ignore those feelings of hunger. You mainly try to tune out the start-eating signal, but the start and stop signals are intertwined, so you typically lose touch with the stop-eating signal, too, particularly if the diet tells you exactly how much to eat. You eat by the rules, which works fine as long as you stick to them. But once you deviate from the rules, as just about everyone does, you have nothing left to guide you. That’s why, even after downing a couple of big milkshakes, dieters and obese people not only continue but increase their eating. The milkshakes filled them up, but they still don’t feel full. They have only the one bright line, and once they have passed it, there are no more limits.
    Now, you could argue that the real lesson of these experiments is that dieters shouldn’t take part in experiments involving milkshakes. If they didn’t go into the lab and drink all those calories, then they wouldn’t cross the bright line and break their daily diet. So if the dieters could just follow their own rules all the time, if they never exceeded the daily limit, then they’d never succumb to the what-the-hell effect. Sure, they’d feel hungry, but they’d never go on a binge as long as they had the willpower to observe the rules.
    All of which makes a certain sense, but only until you actually begin testing those dieters’ willpower with movies, ice cream, and M&M’s, as Kathleen Vohs and Todd Heatherton did in a series of experiments. The psychologists recruited young women, all chronic dieters, and showed them a classic tearjerker, the scene in Terms of Endearment in which the young mother, who is dying of cancer, says good-bye to her two little sons, her husband, and her mother. Half the dieters were instructed to try to suppress their emotional responses, both internally and externally. The other half were told to let their feelings and tears flow naturally. Afterward, all the dieters filled out questionnaires about their mood, and each was taken individually to a different room for what was ostensibly an unrelated task: rating various kinds of ice cream. The ice cream was presented to each dieter in several large and only partly full tubs, which created the impression that the experimenters would not know how much was in there and how much each woman ate.
    But, of course, the tubs had been carefully weighed beforehand, and they were weighed again afterward. The researchers found that there was no connection between the women’s moods and their eating: The ones who were sadder after the movie didn’t eat extra ice cream to drown their sorrows. What mattered was not their mood but rather their will. The dieters who had suppressed emotions during the movie had a much harder time suppressing their appetite. Having depleted their willpower, they ate considerably more ice cream—more than half again as much—as the women who’d been free to cry during the film. This is, of course, just one more demonstration of ego depletion. Still, it bears repeating that eating and dieting can be affected by things that seemingly have no connection to them. Trying to hide your feelings while watching a movie drains your willpower, rendering you more likely to overeat later on in a separate, ostensibly unrelated context.
    In another test of the wills of young female dieters, each one was tempted by a bowl brimming with M&M’s that was placed in the screening room with her as she watched a nature documentary (a nontearjerker about bighorn sheep). For some of the women, the bowl was placed nearby, within easy reach, so they had to continually resist the temptation. For other women, the candy bowl was placed on the other side of the room and hence was easier to resist. Later, in a separate room with no food in sight, the women were given impossible puzzles to solve, that standard lab test of self-control. The dieters who had sat within arm’s reach of the M&M’s gave up sooner on the puzzles, demonstrating that their willpower had been depleted by the effort of resisting