Experts urge BMI method for calculating weight in kids with eating disorders

January 4, 2012

An exact determination of expected body weight for adolescents based on age, height and gender is critical for diagnosis and management of eating disorders such as anorexia nervosa and bulimia. However, there are no clear guidelines regarding the appropriate method for calculating this weight in children with such disorders.

In a study to be published online Jan. 4, 2012, in the journal Pediatrics, researchers from the University of Chicago, the Harvard School of Public Health and the University of Rochester Medical Center compared three common methods for calculating expected body weight of adolescents with eating disorders and found that the body mass index (BMI) percentile method is recommended for clinical and research purposes.

"There are no clear guidelines in the adolescent field," said study author Daniel Le Grange, PhD, professor of psychiatry and Director of the Eating Disorders Program at the University of Chicago. "We set out to do something that is relatively straightforward that hasn't been done before, and that is look at some of the most frequently used methods of calculating weight in the pediatric and adolescent eating disorder populations, and see whether we can come up with a gold standard for clinical as well as for research purposes."

Le Grange and his colleagues analyzed data from adolescents seeking treatment for eating disorders at the University of Chicago. They calculated expected body weights using the BMI method along with two other commonly used measures: the McClaren and Moore methods. The BMI method compares a patient's current BMI to the 50th percentile BMI for a patient of the same age, height and gender according to charts published by the Centers for Disease Control and Prevention. That percentage can help determine whether a patient has an eating disorder.

Their analysis showed that of the three, the BMI method was the most useful for children and adolescents of all ages, heights and weights, and could account more accurately for very short and very tall patients as well.

By publishing their study in Pediatrics, the premier journal in the pediatric community, Le Grange hopes to reach a wider audience of pediatricians who may not be as familiar with eating disorders. "Pediatricians are at the forefront of making these diagnoses," he said. "We wanted to make a clear statement to the pediatric and adolescent eating disorder community that we should all talk the same language and move forward in this way."

The study also recommends that researchers cite the method used to calculate expected body weight in their research and stresses the importance of using the term "expected" instead of "ideal" to describe body weight to avoid unrealistic body image expectations in patients with eating disorders. "I think it's a good clear clinical guide, and I hope pediatricians in the community feel they can pick it up and have a handy tool in their clinical practice," Le Grange said.

The paper, "Calculation of Expected Body Weight in Adolescents with Eating Disorders," appears as an early release online in Pediatrics [doi:10.1542/peds.2008-1536]. Other authors include Peter M. Doyle, Kali Ludwig and Catherine Glunz, University of Chicago; Sonja A. Swanson, Harvard School of Public Health; and Richard E. Kreipe, University of Rochester Medical Center.

Funding for this work was provided by the National Institutes of Health.