Anorexia nervosa is characterized by a refusal to maintain a minimally normal body weight (based on a person’s age and body size), a distorted body image, an intense fear of gaining weight and amenorrhea (absence of menstruation) in females who have had their first menstrual period. For instance, individuals with anorexia nervosa often believe they are fat despite being extremely underweight.

Anorexia nervosa differs from another eating disorder called bulimia nervosa. Individuals with bulimia nervosa usually maintain a normal body weight or are overweight. To be diagnosed with anorexia nervosa, a person must weigh more than 15 percent below the normal range for their age and body size and exhibit a distorted body image.

Eating (especially a healthy, well-balanced diet) is necessary for normal functioning of all organ systems. Disordered eating habits (e.g., skipping meals) or prolonged dieting (e.g., calorie restriction) may deplete the body of important nutrients. In some cases, such habits may become chronic and may lead to the development of an eating disorder, such as anorexia nervosa.

Anorexia nervosa can be particularly dangerous because it puts a person at risk for malnutrition. Individuals with anorexia nervosa tend to associate their self-worth or self-esteem with the way their bodies look and attempt to control their weight through harmful methods, including starvation and purging.

People with anorexia nervosa typically achieve weight loss by drastically reducing their food intake. Patients often begin by eliminating high-calorie foods from their diet, but most usually end up with a very restricted diet that is sometimes limited to only a few foods.

Additional methods for weight loss include purging methods, such as self-induced vomiting or misusing laxatives and/or diuretics, in addition to increased or excessive exercise (anorexia athletica). Individuals with anorexia nervosa may also rely on diet pills, recreational drugs (e.g., amphetamines, cocaine) and caffeine (e.g., coffee, caffeinated diet drinks) to suppress hunger and boost energy. Prolonged use of these agents may result in tolerance and withdrawal symptoms, which can be exacerbated in low-weight people who use these substances in excess.

Patients with anorexia nervosa often exhibit other types of mental disorders including depression (due in part to being severely underweight) and anxiety disorders, which may also become exacerbated by prolonged starvation. Obsessive-compulsive features, such as chronic calorie counting and hoarding food, are also prominent among people with anorexia nervosa. However, most individuals with anorexia nervosa are only preoccupied with thoughts of food and weight.

Anorexia nervosa is more prevalent in females than males, especially among adolescents and young adults. According to the U.S. Department of Health and Human Services, it ranks as the third most common chronic illness among adolescent girls in the nation. 

Anorexia nervosa typically begins during adolescence or early adulthood. However, some reports indicate that its onset can occur during childhood, even before children reach puberty, or later in adulthood. It is more common in industrialized, economically developed nations.

Anorexia nervosa can have severe, life-threatening complications. Prolonged starvation can lead to malnutrition and damage of the vital organs, including the heart and brain. In addition, nutritional deprivation often results in the loss of bone mass (osteoporosis), which may result in brittle bones that break easily. Other complications from malnutrition include amenorrhea, anemia (low red blood cell count), infertility (inability to get pregnant), hair loss and a failure to grow in children or adolescents. In the case of patients who engage in prolonged self-induced vomiting, damage to the teeth, gums and upper gastrointestinal tract  can occur. If left untreated, patients with anorexia nervosa may literally starve themselves to death. Limited food intake and purging can also lead to other health problems, such as injuries to the esophagus.