Writing in The Wall Street Journal, Jonah Lehrer suggests a weight loss drug that may soon be approved by the Food and Drug Administration should cause us to rethink conventional wisdom about why people overeat. Qnexa, which in clinical trials helped subjects lose about one-tenth of their weight on average, combines an appetite-suppressing stimulant with "an anticonvulsant shown to reduce cravings for binge-eaters." Lehrer says it seems to work partly by increasing "activity in the dopamine reward pathway," which "allows dieters to squeeze more satisfaction from every bite." That explanation is consistent with a recent Oregon Research Institute brain-scan study that found teenagers who reported eating the most ice cream showed the least dopamine response when viewing and sipping milkshakes. "This suggests that they were eating more in desperate compensation, trying to make up for their indifferent dopamine neurons," Lehrer writes. "People crave pleasure, and they don't stop until they get their fill, even if means consuming the entire pint of Häagen-Dazs." He says one lesson for dieters is that "it's important to seek pleasure from many sources," since "people quickly adapt to the pleasure of any single food."
This theory that overeaters have "hypofunctioning reward circuits" sounds plausible, although the evidence for it so far seems skimpy. But notice that it contradicts the advice commonly heard from anti-obesity crusaders such as Kelly Brownell and David Kessler, who say the problem is that food is too delicious and too varied. Rats who eat their fill of one food, they note, will begin chowing down again if given something different. Hence variety is the dieter's enemy—not, as Lehrer suggests, his friend.
These clashing perspectives are reflected in the perennial conflict between two dieting dicta: 1) avoid temptation and 2) don't make yourself feel deprived. There is some truth to both views. Sometimes I eat more just because something tastes so good, or because a new item has been introduced and I want to try it. But sometimes I will continue eating after a bland meal even though I am not really hungry, just to make up for the disappointing culinary experience. Eating is a complex behavior, and there is unlikely to be one explanation of it even for a single individual, let alone for people in general (assuming there is such a thing). That is yet another reason to be wary of government-imposed, one-size-fits-all solutions.
Back in 1998, I considered two dueling studies of smoking, one of which posited that people who get more pleasure per puff will be less addicted to the habit; the other said the opposite.