Time to Adopt New Measures of Severe Obesity in Children and Adolescents

* Abbreviations: ΔBMIp95 — : BMI minus BMI at the 95th percentile BMIp95 — : BMI as a percent of the 95th percentile BMIz — : BMI z score CDC — : Centers for Disease Control and Prevention The ideal measure of weight gain and loss should distinguish children and adolescents across the distribution of weight and height and should include the capacity for changes in weight adjusted for height over time. Over short intervals, in which there is little growth in height, absolute changes in weight or BMI provide suitable indicators of weight gain or loss. However, over longer intervals, during which height increases significantly, weight change must be adjusted for changes in height and age by sex. BMI, which is calculated as weight (in kg) divided by the square of height (in m2), adjusts body weight for height. Although the correlation of BMI with various measures of body fat percentage is modest across the distribution of BMI, the correlation of BMI with body fat improves at the upper part of the body fat distribution. Increases in BMI greater than the 95th percentile are associated with increases in body fat.1,2 In addition, BMI has benefits in feasibility, reliability, and measurement and clinical validity.3 Changes in BMI, BMI percentiles, or changes in BMI expressed as an SD score (BMI z score [BMIz]) provide a reasonably … Address correspondence to William H. Dietz, MD, PhD, George Washington University, Sumner M. Redstone Global Center for Prevention and Wellness, 950 New Hampshire Ave, NW, Washington, DC 20052. E-mail: dietzwcd4{at}gmail.com