Anorexia nervosa, as categorized by the DSM-IV, is relatively uncommon, affecting 0.5-1% of adolescent and young adult women (8,9), although a much larger percentage experience subthreshold symptoms. Approximately 10% of patients with anorexia nervosa are male (9). There is some evidence that the incidence of anorexia nervosa is increasing among adolescents, but not among adults (10,11). Although most individuals with anorexia nervosa are adolescents or young adults, onset has been reported in prepubertal children and postmen-opausal women (12). It is more common in industrialized societies where food is plentiful and thinness is valued, but anorexia nervosa is found in individuals from all cultures and social strata (13,14).
The prevalence of bulimia nervosa has been estimated at 1-3% of high school and college-age women (8,9), although a much greater percentage engage in bulimic behaviors, such as binge eating and/or purging, that are not of sufficient frequency or duration to meet criteria for the disorder. Five percent to 15% of patients with bulimia nervosa are male (15-17), and it is more frequent in homosexual men (18 and athletes who must ''make weight'' for competition, such as wrestlers (19). Bulimia nervosa is found in all racial, ethnic, and socioeconomic groups (15,16). A substantial subset of patients with bulimia nervosa have previously met criteria for anorexia nervosa (20).
Binge eating disorder (BED) is the most common eating disorder, affecting <3% of the general population (21). The prevalence among overweight persons is higher, with increasing prevalence as degree of obesity and intensity of treatment increases. Although initial reports suggested a prevalence of up to 30% of obese individuals seeking specialized treatment, such as very low calorie diet programs (22,23), diagnosis made by clinical interview shows a much lower prevalence, even in clinical populations, in whom the prevalence is generally 10-15% (21). The prevalence of binge eating disorder among severely obese individuals undergoing bariatric surgery, however, is high even when made by clinical interview, and may exceed 50% (9,24,25). Unlike anorexia nervosa and bulimia nervosa, a large proportion of individuals with BED are men, estimated at 40% in the original field studies (22,23). The age at diagnosis of BED is older than that seen in anorexia nervosa or bulimia nervosa, averaging in the mid-to late thirties; however, age of onset of significant binge eating is often a decade or more earlier. An age-matched study of patients with bulimia nervosa and binge eating disorder showed a younger age of onset of binge eating behavior among those with BED (14.3 vs. 19.8 years), although both groups reported first dieting at similar ages (15.0 vs. 16.2 years) (26). In addition, among those with BED, the age of onset of binge eating as well as age at which symptoms met criteria for BED was significantly lower in those whom reported that age of binge eating preceded age of first diet (27).
The night eating syndrome has been reported in 1.5% of the general population (28), and is more common among obese persons than the nonobese. It may also increase with increasing adiposity. Studies have found a prevalence of 8.9% in an obesity clinic (29), 12% of obese patients in a nutrition clinic (30), and 27% among candidates for obesity surgery (28).
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