BMI does not capture the high fat mass index and low fat-free mass index in children with cerebral palsy and proposed statistical models that improve this accuracy

Background/objectives Children with cerebral palsy (CP) are at risk for having a misclassified overweight/obesity status based on BMI thresholds due to their lower fat-free mass and similar fat mass compared with typically developing children. The primary objective was to determine if BMI could predict fat mass index (FMI) and fat-free mass index (FFMI) in children with CP. Subjects/methods Forty-two children with CP and 42 typically developing children matched to children with CP for age and sex participated in the study. Dual-energy X-ray absorptiometry was used to assess body composition. Children with CP who could ambulate without assistance were considered ambulatory (ACP) and the rest were considered nonambulatory (NACP). Results Children with CP had higher percent body fat (% Fat) and FMI and lower fat-free mass and FFMI than controls (p < 0.05) but no difference in fat mass (p = 0.10). When BMI was statistically controlled, NACP had higher % Fat, fat mass and FMI and lower FFMI than ACP and controls (p < 0.05). NACP also had lower fat-free mass than controls (p < 0.05). ACP had higher % Fat and FMI and lower fat-free mass and FFMI than controls (p < 0.05). BMI was a strong predictor of FMI (r(2) = 0.83) and a moderately strong predictor of FFMI (r(2) = 0.49) in children with CP (both p < 0.01). Prediction of FMI (R-2 = 0.86) and FFMI (R-2 = 0.66) from BMI increased (p < 0.05) when age, sex and ambulatory status were included. Conclusion Compared with typically developing children, children with CP have a higher FMI and lower FFMI for a given BMI, which is more pronounced in NACP than ACP. The finding suggests that the prevalence of overweight/obesity status may be underestimated in children with CP.