The eating disorders, anorexia nervosa and bulimia nervosa, may be classified as true psychosomatic illnesses, inasmuch as an underlying biological vulnerability interacts with a particular cultural stress in order to produce behavioral and psychological symptoms. For example, anorexia and bulimia nervosa are more prevalent in industrialized societies, where there is an overabundance of food and where attractiveness in women is linked with being thin, than in agriculturally based societies. Immigrants from cultures in which anorexia nervosa is rare are more likely to develop the illness as they assimilate the ideals of a thin body appearance.
In some ways, the term anorexia nervosa is a misnomer, because the affected individual's appetite and craving for food are usually preserved. Nevertheless, the individual will actively counter the feelings of hunger with disordered thinking, leading to self-imposed starvation. The threshold for defining the amount of weight loss considered to be serious enough to qualify for the diagnosis of anorexia nervosa is computed on the basis of the Metropolitan Life Insurance tables or pediatric growth charts. A body mass index less than or equal to 17.5 kg/m2 (calculated as weight in kilograms/height in meters2) represents an alternative guideline accepted by many researchers. Nevertheless, these standards are only suggested guidelines, and clinicians should also consider the individual's body build and weight history.
Lifetime prevalence rates for anorexia nervosa in females are approximately 0.5–1.0, or 1 in 100–200 individuals. Many more individuals exhibit symptoms that do not meet the criteria for the disorder (i.e., eating disorder not otherwise specified; see later in this chapter), but this is an area for continued research. More than 90% of affected individuals are female, and data concerning the prevalence of the illness in males are scant. Worldwide, the disorder appears to be most common in the United States, Canada, Europe, Australia, Japan, New Zealand, and South Africa; however, few systematic studies of the illness have been conducted in other countries.
The onset of illness is bimodal: One peak occurs in early adolescence (age 12–15 years) and another in late adolescence and early adulthood (age 17–21 years); the mean age at onset is approximately 17 years. The illness rarely appears de novo before puberty or after age 40 years. Often an associated life event, such as moving away from home, precedes the first episode of anorexia nervosa. Although the prevalence of this disorder showed marked increases in the latter half of the twentieth century, more recently this rate of increase has slowed.
The incidence and prevalence of eating disorders have increased greatly in the latter half of the twentieth century. This increase is due in part to cultural pressures in industrialized societies (placed largely on women), including an overemphasis on ...