340 Feeding and Eating Disorders
Criterion A requires that the individual’s weight be significantly low (i.e., less than
minimally normal or, for children and adoles cents, less than that minimally expected).
Weight assessment can be challenging because normal weight range differs among indi-
viduals, and different thresholds have been published defining thinness or underweight
status. Body mass index (BMI; calculated as weight in kilograms/height in meters2) is a
useful measure to assess body weight for height. For adults, a BMI of 18.5 kg/m2 has been
employed by the Centers for Disease Control and Prevention (CDC) and the World Health
Organization (WHO) as the lower limit of normal body we ight. Therefore, most adults with
a BMI greater than or  equal to 18.5 kg/m2 would not be considered to have a significantly
low body weight. On the other ha nd, a BMI of lower than 17.0 kg/m2 has been considered
by the WHO to indicate moderate or severe thinness; therefore, an individual with a BMI
less than 17.0 kg/m2 would likely be considered to have a significantly low weight. An
adult with a BMI between  17.0 and 18.5 kg/m2, or even above 18.5 kg/m2, might be consid-
ered to have a significantly low weight if clinical history or other physiological informa-
tion supports this judgment.
For children and adolescents, de termining a BMI-for-age percentile is useful (see, e.g.,
the CDC BMI percentile calculator for children and teenagers. As for adults, it is not pos-
sible to provide definitive standards for judgin g whether a child’s or an adolescent’s weight
is significantly low, and variations in deve lopmental trajectories among youth limit the