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Anorexia nervosa and bulimia nervosa are characterized by severe disturbances of eating behavior. The salient feature of anorexia nervosa (AN) is a voluntary restriction of food intake relative to caloric requirements leading to an inappropriately low body weight. Bulimia nervosa (BN) is characterized by recurrent episodes of binge eating followed by abnormal compensatory behaviors, such as self-induced vomiting. AN and BN are distinct clinical syndromes but share common features. Both disorders occur primarily among previously healthy young women who become overly concerned with body shape and weight. Many patients with BN have past histories of AN, and many patients with AN engage in binge eating and purging behavior. In the current diagnostic system, the critical distinction between AN and BN depends on body weight: patients with AN are, by definition, significantly underweight, whereas patients with BN have body weights in the normal range or above. Binge eating disorder (BED) is a more recently described syndrome characterized by repeated episodes of binge eating, similar to those of BN, in the absence of inappropriate compensatory behavior.

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Epidemiology

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Among women, the lifetime prevalence of the full syndrome of AN is approximately 1%. AN is much less common in males. AN is more prevalent in cultures where food is plentiful and being thin is associated with attractiveness. Individuals who pursue interests that place a premium on thinness, such as ballet and modeling, are at greater risk. The incidence of AN has increased in recent decades.

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Etiology

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The etiology of AN is unknown but appears to involve a combination of psychological, biologic, and cultural risk factors. Some factors, such as sexual or physical abuse and a family history of mood disturbance, are best viewed as nonspecific risk factors that increase vulnerability to a range of psychiatric disorders, including AN.

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Patients who develop AN are inclined to be more obsessional and perfectionist than their peers. The disorder often begins as a diet not distinguishable at the outset from those undertaken by many adolescents and young women. As weight loss progresses, the fear of gaining weight grows; dieting becomes stricter; and psychological, behavioral, and medical aberrations increase. Eating disorders, including AN, may develop among individuals with type 1 diabetes mellitus and are associated with poorer glycemic control and an increased frequency of complications (Chap. 344).

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Numerous physiologic disturbances, including abnormalities in a variety of neurotransmitter systems, have been described in AN (see below). It is difficult to distinguish neurochemical, metabolic, and hormonal changes that may have a role in the initiation or perpetuation of the syndrome from those that are secondary to the disorder. The resolution of most of these abnormalities with weight restoration argues against an etiologic role.

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Genetic factors contribute to the risk of development of AN, as its incidence is greater in families with one affected member and the concordance in monozygotic twins is greater than ...

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