Approximately 3 percent of women develop anorexia, and another 8 percent develop bulimic syndromes at some point in their lifetimes. Eating disorders cause considerable morbidity and even mortality, and their prevalence may be increasing. These disorders often begin during adolescence, but the etiology may be obscured by comorbidities and retrospective recall. Patton and colleagues prospectively studied a cohort of Australian teenagers to elucidate risk factors for eating disorders.

The three-year study of 1,947 14- and 15-year-olds was conducted in two stages. Data were gathered on height, weight, dieting and eating patterns, exercise and psychiatric morbidity. Every six months during the study, previous cohorts were re-assessed and a new cohort added.

By the age of 15 years, 8 percent of the girls reported dieting at a severe level, and an additional 60 percent dieted at a moderate level. The prevalence of eating disorders was 3.3 percent in girls and 0.3 percent in boys. Partial bulimic disorders were most common, followed by bulimia and anorexia. The rates of development of eating disorders were 21.8 per 1,000 person-years for girls and 6.0 per 1,000 person-years for boys. The most important predictor of eating disorders was severe dieting. Girls who reported severe dieting were 18 times more likely to develop eating disorders than those who did not diet. Moderate dieting in girls was associated with a fivefold increase in the incidence of eating disorders.

Psychiatric morbidity was independently associated with the development of eating disorders. Those with the highest psychiatric morbidity had a sixfold increase in the risk of developing an eating disorder. When adjustments were made for dieting history and psychiatric morbidity, factors such as exercise, body mass index and sex did not predict the development of eating disorders.

The authors conclude that a history of dieting is the most important predictor of eating disorders. Although girls who reported dieting at a severe level were at highest risk, two thirds of new cases of eating disorders occurred in girls who reported moderate dieting. Psychiatric morbidity was also an important predictor. The authors recommend promoting exercise in adolescents as the preferred method of weight control.