Anorexia nervosa is an eating disorder characterized by an obsessive fear of gaining weight and refusal to maintain a healthy body weight. It is caused by a combination of genetic, psychological, and social factors. Physical symptoms include being seriously underweight, depression, fatigue, and mood swings. Anorexia affects about 1% of people and is most common in teenage white women. It is diagnosed by physicians and treated through psychotherapy and nutrition management, though it can be a very painful and potentially fatal condition if not addressed.