According to Rebecca Lester, the author of “Famished: Eating Disorders and Failed Care in America,” eating disorders are among the most misunderstood medical conditions. For instance, she says there is an assumption that eating disorders are mostly a problem for upper-middle-class white girls. While that’s not completely untrue, it’s just a sliver of the story. In “Famished,” Lester looks closely at the impact of common misconceptions, as well as the way the health care system fails to treat these disorders.