Objective: Percentiles for the body mass index (BMI) offer a possibility to epidemiologically assess the linear weight criterion of 85% average body weight commonly used for the diagnosis of anorexia nervosa.
Method: BMI values corresponding to 85% average body weight were calculated and assessed with percentiles derived from epidemiological studies in both the United States and Germany. The underweight range was characterized epidemiologically.
Results: The weight criterion used for the diagnosis of anorexia nervosa corresponds to BMI values between the 5th and 10th centiles in both populations. In epidemiological terms the lowest BMI values in individuals aged 10 years and older occur during adolescence. In the general population BMI values <16 kg/m2 are rarely observed. Upon the use of higher BMI cutoffs in the underweight range females clearly predominate. The BMI increase associated with the 5th or 10th centile in the age range between 18 and 30 years is quite low suggesting that many underweight females in the general population gain only minimal weight during this age span.
Discussion: The diagnostic, epidemiological, and therapeutic implications for anorexia nervosa are discussed.