This video segment, adapted from NOVA, documents a ballerina's experience with a potentially deadly eating disorder: anorexia nervosa. Research suggests that a brain chemical called serotonin plays a prominent role in regulating appetite: a key factor in eating disorders. The disruption of serotonin levels by dietary changes can lead to a vicious cycle that prolongs the disorder. By restoring nutrition to her diet, however, the dancer in the video is tackling her eating disorder and resuming her career. [4:29]