Research suggests that a genetic predisposition to anorexia may run in families. If a girl has a sibling with anorexia, she is 10 to 20 times more likely than the general population to develop anorexia herself. Brain chemistry also plays a significant role. People with anorexia tend to have high levels of cortisol, the brain hormone most related to stress, and decreased levels of serotonin and norepinephrine, which are associated with feelings of well-being.