The essential features of Anorexia Nervosa are that the individual refuses to maintain a minimally normal body weight, is intensely afraid of gaining weight, and exhibits a significant disturbance in the perception of the shape or size of his or her body. In addition, postmenarcheal females with this disorder are amenorrheic. (The term anorexia is a misnomer because loss of appetite is rare.)
The individual maintains a body weight that is below a minimally normal level forage and height (Criterion A). When Anorexia Nervosa develops in an individual during childhood or early adolescence, there may be failure to make expected weight gains (i.e., while growing in height) instead of weight loss.
Criterion A provides a guideline for determining when the individual meets the threshold for being underweight. It suggests that the individual weigh less than 85% of that weight that is considered normal for that person's age and height (usually computed using one of several published versions of the Metropolitan Life Insurance tables or pediatric growth charts). An alternative and somewhat stricter guideline (used in the ICD-10 Diagnostic Criteria for Research) requires that the individual have a body mass index (BMI) (calculated as weight in kilograms/height in meters) equal to or below 17.5 kg/m. These cutoffs are provided only as suggested guidelines for the clinician, since it is unreasonable to specify a single standard for minimally normal weight that applies to all individuals of a given age and height. In determining a minimally normal weight, the clinician should consider not only such guidelines but also the individual's body build and weight history.
Usually weight loss is accomplished primarily through reduction in total food intake. Although individuals may begin by excluding from their diet what they perceive to be highly caloric foods, most eventually end up with a very restricted diet that is sometimes limited to only a few foods. Additional methods of weight loss include purging (i.e., self-induced vomiting or the misuse of laxatives or diuretics) and increased or excessive exercise.
Individuals with this disorder intensely fear gaining weight or becoming fat (Criterion B). This intense fear of becoming fat is usually not alleviated by the weight loss. In fact, concern about weight gain often increases even as actual weight continues to decrease.
The experience and significance of body weight and shape are distorted in these individuals (Criterion C). Some individuals feel globally overweight. Others realize that they are thin, but are still concerned that certain parts of their bodies, particularly the abdomen, buttocks, and thighs, are "too fat." They may employ a wide variety of techniques to estimate their body size or weight, including excessive weighing, obsessive measuring of body parts, and persistently using a mirror to check for perceived areas of "fat." The self-esteem of individuals with Anorexia Nervosa is highly dependent on their body shape and weight. Weight loss is viewed as an impressive achievement and a sign of extraordinary self-discipline, whereas weight gain is perceived as an unacceptable failure of self-control. Though some individuals with this disorder may acknowledge being thin, they typically deny the serious medical implications of their malnourished state.
In postmenarcheal females, amenorrhea (due to abnormally low levels of estrogen secretion that are due in turn to diminished pituitary secretion of follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) is an indicator of physiological dysfunction in Anorexia Nervosa (Criterion D). Amenorrhea is usually a consequence of the weight loss but, in a minority of individuals, may actually precede it. In prepubertal females, menarche may be delayed by the illness.
The individual is often brought to professional attention by family members after marked weight loss (or failure to make expected weight gains) has occurred. If individuals seek help on their own, it is usually because of their subjective distress over the somatic and psychological sequelae of starvation. It is rare for an individual with Anorexia Nervosa to complain of weight loss per se. Individuals with Anorexia Nervosa frequently lack insight into, or have considerable denial of, the problem and may be unreliable historians. It is therefore often necessary to obtain information from parents or other outside sources to evaluate the degree of weight loss and other features of the illness.