THIN opens with a couple of gripping statistics: Eating disorders affect 5 million people in the United States, and more than 10 percent of those diagnosed with anorexia nervosa will die from the disease. Director Lauren Greenfield lived at the Renfrew Center for six months, gaining access to and earning the trust of both patients and staff. Cameras follow four women between the ages of 15 and 30 who are literally dying to be thin. In the course of telling their stories, the film teaches viewers about the psychology, pathology, and medical consequences of eating disorders. Brittany is a 15-year-old whose eating disorder began when she was 8. Shelly, 25, has a feeding tube put in her stomach when she enters Renfrew after several hospitalizations. Alisa, 30, a divorced mother of two, arrives at Renfrew following five hospital stays in three months. And Polly, 29, has spent years in and out of treatment and often challenges the center's policies and procedures. Theirs is an agonizing story, beginning with 5 a.m. weigh-ins and moving on to struggles with meals, therapy sessions, and group encounters. As the women's lives unfold on camera, a mosaic forms of the compulsion, the denial, and the horrible psychological toll anorexia exacts. Although each woman's fight for recovery is unique, Greenfield paints a cumulative portrait of the disease's hallmarks -- shame, dishonesty, secrecy, and ambivalence about recovery. Some of the women sabotage their own treatment, while others make significant strides. Some will make progress, only to relapse. And still others find their recovery thwarted by insurance companies who won't cover the long-term care they require.