This cephalic secretion of insulin in preparation for the act of eating provides yet another mechanism that may work to induce hunger, weight gain, and obesity in a world of palatable foods, which could mean, of course, simply those foods that induce excessive insulin secretion to handle the unnaturally easy digestibility of their carbohydrates. The idea was suggested in 1977 by the psychologist Terry Powley, who was then at Yale and is now at Purdue University. Powley was discussing the obesity-inducing effect of lesions in the hypothalamus and speculated that the lesions cause the animal to hypersecrete insulin when just thinking about, smelling, or tasting food, and this amplifies its perception of hunger and palatability. The result would be what Powley called a “self-perpetuating situation”—i.e., a vicious cycle. “Rather than secreting quantities of insulin and digestive enzymes appropriate for effective utilization of the ingested material,” Powley wrote, “the lesioned animal over-secretes and must then ingest enough calories to balance the hormonal and metabolic adjustments.”

Powley did not go so far as to suggest that this same phenomenon was at work in humans, but his then colleague Judith Rodin did. Rodin reported in 1980 that those individuals whose eating behavior is most responsive to the smell or sight of food—a grilling steak, in her experiments—were those who also had the greatest cephalic-phase insulin response. Insulin had to be considered a “major candidate,” Rodin suggested, “for an intervening physiological mechanism that might be responsive to environmental stimuli.” By 1985, Rodin was speculating that the chronic hyperinsulinemia of the obese would also exacerbate this phenomenon. “A feedback loop is suggested by these findings in which hyperinsulinemia in turn leads to increased consumption, which, unless compensated for, could lead to further weight gain,” she wrote. “Because acute hyperinsulinemia can also be produced in some individuals by simply looking at or thinking about food, it, too, can in turn lead to increased consumption and possible weight gain.”

The possibility that insulin determines what Le Magnen called the metabolic background of hunger also explains two observations we discussed in the sections on fattening and reducing diets.

The first is the observation by Ethan Sims that he could stuff his convict subjects with as much as ten thousand calories a day of mostly carbohydrate and they would still feel “hunger late in the day,” and yet subjects fed eight hundred superfluous calories of fat “developed marked anorexia.” On a more familiar level: why is it that most of us can imagine eating a large bag (twenty ounces) of movie popcorn—more than eleven hundred calories if popped in oil,*137 as it typically is—but not so the equivalent caloric amount of cheese: say, fifteen slices of American cheese, or a cup and a half of melted Brie?