Anorexia nervosa is a serious eating disorder that is characterized by an intense fear of weight gain, a distorted body image, severe weight loss and the absence of menstruation (in females who have already had their first menstrual period). For instance, individuals with anorexia nervosa often believe they are fat despite being extremely underweight.

Anorexia nervosa is more prevalent in females than males, especially adolescents and young adults. The disorder is more common in industrialized, economically developed nations. 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.

There are two types of anorexia nervosa:

• Binge-eating/purging type. The most common type of anorexia nervosa in which patients regularly engage in binge eating and/or purging behaviors to control their weight. Sometimes, individuals with this type of anorexia nervosa do not binge eat, but regularly purge (e.g., vomit, use laxatives) after consuming even small amounts of food.
  
  
• Restricting type. In this type of anorexia nervosa, patients do not engage in purging methods to accomplish weight loss. Rather, individuals with restricting anorexia nervosa attain weight loss mainly by dieting, fasting and/or excessive exercise (anorexia athletica).

It is important to note that anorexia nervosa differs from another eating disorder called bulimia nervosa. Although individuals with bulimia nervosa also may engage in purging behaviors, they 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.

Medical health experts are unsure what causes anorexia nervosa, but it is believed to result from a combination of biological, psychological and environmental factors.

Patients with anorexia nervosa frequently have other types of mental illnesses,  including depression, anxiety disorders (e.g., obsessive-compulsive disorder) and substance abuse. Patients often exhibit symptoms, including an excessive preoccupation with food, extreme unhappiness or concern about body shape and size, absence of menstruation, dry skin, hair loss, chronic fatigue and damage to the teeth and gums from repetitive vomiting.

Anorexia nervosa is usually diagnosed after a physical examination by a physician, which includes a medical history. Patients may be referred to a psychiatrist or other mental health professional for an evaluation.

Due to the complex nature of eating disorders, anorexia nervosa usually requires a comprehensive treatment plan including medical care and monitoring of health complications (e.g., malnutrition), psychotherapy and dietary counseling by a nutritionist. Sometimes, residential care that involves the patient remaining in a facility that specializes in treating anorexia nervosa may be necessary, especially in the case of chronic relapses or when patients have not been able to reach a significant degree of medical and psychological stability from their initial treatment plan.

Receiving support from family members and friends is important because often patients with anorexia nervosa are in denial and resist treatment, believing they do not need help.