Dr. Saguy, a sociologist at U.C.L.A., methodically teases out all the overtones of the loaded words we use to describe big bodies in her book, “What’s Wrong with Fat”. These bodies are, after all, neither good nor bad, just big. But “fat” often implies the coexistence of sloth, gluttony and self-indulgence. “Obesity” equals disease to medical professionals, while in the world of public health it is a raging epidemic with substantial global mortality. Those immersed in the conventional ideals of beauty see being overweight as an aesthetic disaster, but others find it sexually irresistible, and to activists “fat” has become a rallying cry, with weight-based discrimination a violation of social justice as deplorable as that stemming from race or gender.