Population based data may underestimate the true prevalence of obesity for youth with mobility disabilities

Body Mass Index (BMI), based on body weight and height, has been widely used as an indicator of health. However, BMI may not be an accurate estimate of adiposity in individuals for whom the proportion of lean, fat and bone tissue varies considerably from the norm, such as youth with mobility disabilities. The purpose of this study was to evaluate the validity of BMI as a screening tool for obesity among adolescents with mobility disabilities. The study involved youth, ages 14–17 years, with cerebral palsy, spina bifida, and spinal cord injury (n=20). The BMI-based body weight status of the youth was compared with that obtained from their body fat percentage using triceps skinfold and dual x-ray absorptiometry (DEXA). Results indicated that there were considerable discrepancies between body weight status as classified by BMI and those derived from two different direct measurements of body fat. Although BMI indicated that only 5.6% of the youth were obese, their body fat percentage based on triceps skinfold measurement classified 38.9% as obese. Further, DEXA scans revealed that 72.2% of the youth with disabilities were obese. Of the 20 youth measured, 18 youth came up as false negatives for obesity (BMI indicated underweight, healthy, or overweight status, although the true status per DEXA was overweight or obese). This research shows that using BMI as a criterion for obesity in youth with mobility disabilities significantly underestimates the risk of obesity in this population. Future research should indentify more accurate, cost effective methods for this population.