A. Restriction of energy intake relative to requirements, leading to a significantly low body weight in the context of age, sex, developmental trajectory, and physical  health. Significantly low weight is  defined as a weight that is less than minimally normal or, for children and adolescents, less than that minimally expected. 
B. Intense fear of gaining weight or of becoming fat, or persistent behavior that interferes with weight gain, even though at a significantly low weight.
C. Disturbance in the way in which one’s body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or persistent lack of recognition of the seriousness of the current low body weight.
Constipation
Abdominal pain
Fatigue
Weakness
Amenorrhea
Depression
Hair loss
Fine facial and body hair (lanugo)
Brittle hair and nails
Dry, scaly skin
Loss of subcutaneous fat
Breast and vaginal atrophy
Anorexia nervosa
Gastrointestinal disease
Bulimia nervosa
Hyperthyroidism
Metabolic syndrome
Occult malignancies
Hypothyroidism
AIDS