AN is characterized by three primary symptoms:
- Restriction of caloric intake relative to the person's energy expenditure, leading to significantly low body weight (usually defined as BMI ≤ 17 kg/m2 or below the 5th percentile for height) or a failure to make appropriate weight gain milestones.
- Intense fear of weight gain, significant fear of becoming fat, or persistent behavior that prevents weight gain (such as excessive exercising).
- Disturbed body image, including undue influence of body weight or shape on the person's self-esteem, failure to recognize the seriousness of one's low body weight, or a seriously distorted perception of one's weight or shape.
The onset of AN typically occurs during or after puberty, although earlier onsets have been observed. A child or adolescent with AN may globally fear becoming fat, or may believe that he or she is generally thin but that certain body parts are unacceptably fat. Of note, some younger children may not recognize or acknowledge a fear of weight gain; therefore, collateral reports should be used. Checking behaviors are common; these can include measuring body parts, excessively weighing oneself, and excessively looking at oneself in the mirror. Preoccupation with food and food-related hoarding behaviors are also common. AN can be associated with poor insight; people with AN may consider their weight loss to be an accomplishment or sign of self-discipline, rather than a symptom of a serious illness.
Children or adolescents with the binge-eating/purging type of AN engage in binge eating (eating an unusually large amount of food in a very short period of time) and/or purging (self-induced vomiting or misuse of laxatives, diuretics, or enemas). The binge-eating/purging type of AN is distinguished from bulimia nervosa primarily by the presence of significantly low body weight in AN. Individuals with the restricting type of AN do not engage in binging or purging behavior. For these individuals, weight loss is maintained primarily through dieting or fasting. Crossover between these types is fairly common; therefore, these specifiers are used to describe current behaviors (i.e., within the past three months).