Diagnostic criteria: It is a kind of abnormal eating behavior mostly seen in adolescent females, characterized by deliberate restriction of diet to bring weight down to significantly lower than normal standards, for which excessive exercise, induced vomiting and diarrhea are used to reduce weight. There is often an excessive fear of gaining weight, and even has been significantly wasted still consider themselves too fat, even if the doctor to explain also ineffective. Some patients can explain their restricted diet with reasons such as stomach upsets and decreased appetite. There is often malnutrition, metabolic and endocrine disorders, amenorrhea in women, hypogonadism in men, and infantile sexual organs in prepubertal patients. Some patients may have intermittent episodes of binge eating. The disorder is not a physical disease caused by weight loss, and the patient dieting is not a secondary symptom of other mental disorders. Diagnostic criteria] (1) Significant weight loss of more than 15% of the normal average weight loss, or Quetelet body mass index of 17.5 or lower, or failure to achieve the desired physical growth standards before puberty, and delayed or stopped development; (2) self-induced weight loss, at least one of the following: ① avoidance of “fattening foods “(3) there is often a pathological fear of gaining weight: a persistent and unusual fear of gaining weight that is overpriced and the patient sets an excessively low weight threshold that is far below what the pre-morbid doctor considers to be a moderate or healthy weight (4) There can often be widespread endocrine disorders of the hypothalamic-pituitary-gonadal axis. Women present with amenorrhea (menopause of at least 3 consecutive menstrual cycles, but women may experience persistent vaginal bleeding if treated with hormone replacement therapy, most commonly with birth control pills), and men present with loss of sexual interest or hypogonadism. There may be elevated growth hormone, increased cortisol concentration, abnormal peripheral thyroxine metabolism, and abnormal insulin secretion; (5) symptoms have been present for at least 3 months; (6) there may be intermittent episodes of binge eating (only anorexia nervosa is diagnosed at this time); (7) exclude weight loss due to physical disease (e.g., brain tumor, intestinal disease such as Crohn’s disease or malabsorption syndrome). (1) Normal weight expectancy can be assessed by subtracting 105 from the height in centimeters to obtain the normal average weight in kilograms; or by using the Quetelet body mass index = weight in kilograms / height in meters squared; (2) Sometimes anorexia nervosa can be secondary to depression or obsessive-compulsive disorder, making diagnosis difficult or requiring concurrent diagnosis if necessary.