Anorexia nervosa is an eating disorder characterized by abnormally low body weight, an intense fear of gaining weight, and a distorted perception of weight. Physical symptoms include excessive weight loss, fatigue, dizziness, and absence of menstruation. Emotional and behavioral symptoms include restricting food intake, excessive exercise, binge eating followed by purging. Risk factors include genetics, environmental pressures to be thin, life transitions, and dieting. Complications can include heart problems, bone loss, electrolyte imbalances, and even death in severe cases.