Through the beginning of World War II, the notion that a defect in fat metabolism causes obesity was known as the lipophilia hypothesis. “Lipophilia” means “love of fat.” The term was invoked in 1908 by the German internist Gustav von Bergmann to explain why areas of the body differ in their affinity for accumulating fat—a vitally important phenomenon, one would think, since obesity is a malady of fat accumulation. Bergmann considered the energy-balance hypothesis of obesity to be nonsensical: “It seems just as illogical,” he wrote, “to say: Child, you shoot up in height because you eat too much or you exercise too little—or you have remained small because you play sports too much. What the body needs to grow, it always finds, and what it needs to become fat, even if it’s ten times as much, the body will save for itself from the annual balance.”

Just as we grow hair in some places and not typically in others, Bergmann noted, there are places more or less prone to fatten, and some biological factor must regulate that. Some regions of the body are more or less lipophilic than others. This is the kind of observation that can obsess us individually: Why do we have love handles or a double chin? Why fat ankles, thighs, or buttocks? Why is it that some men accumulate excessive fat in the abdomen (a beer belly) and yet are lean elsewhere? Why do some women have significant fat deposits in their breasts and so are considered voluptuous, whereas other women have little or none? These are all variations on the question of which biological factors determine the regional and local distribution of fat.

The example commonly cited in discussions of the nature of this localized lipophilia was that of a twelve-year-old girl in the early 1900s who burned the back of her hand. Her doctors used skin from her abdomen as a graft over the burn. By the time this girl turned thirty, she had grown fat, and the skin that had been transplanted to the back of her hand had grown fat as well. “A second operation was necessary for the removal of the big fat pads which had developed in the grafted skin,” explained the University of Vienna endocrinologist and geneticist Julius Bauer, “exactly as fatty tissue had developed in the skin of the lower part of the abdomen.” Some biological factor must regulate this, Bauer believed.