Aim: Body mass index (BMI) metrics are widely used as a proxy for adiposity in children with severe obesity. The BMI expressed as the percentage of a cut-off percentile for overweight or obesity has been proposed as a better alternative than BMI z-scores when monitoring children and adolescents with severe obesity.Methods: Annual changes in BMI, BMI z-score and the percentage above the International Obesity Task Force overweight cut-off (%IOTF-25) were compared with dual-energy X-ray absorptiometry (DXA) derived body fat (%BF-DXA) in 59 children and adolescents with severe obesity.Results: The change in %BF-DXA was correlated with the change in %IOTF-25 (r = 0.68) and BMI (r = 0.70), and somewhat less with the BMI z-score (r = 0.57). Cohen's Kappa statistic to detect an increase or decrease in %BF-DXA was fair for %IOTF-25 (j = 0.25; p = 0.04) and BMI (j = 0.33; p = 0.01), but not for the BMI z-score (j = 0.08; p = 0.5). The change in BMI was positively biased due to a natural increase with age. Conclusion: Changes in the BMI metrics included in the study are associated differentlyAbbreviations %BF, Percentage body fat; %IOTF-25, Percentage above the International Obesity Task Force definition of overweight; BMI, Body mass index; DXA, Dual-energy X-ray absorptiometry. Key notesThe percentage above the International Obesity Task Force overweight cut-off (%IOTF-25) has been suggested as an unbiased alternative with respect to age for the body mass index (BMI) or BMI z-score in children and adolescents with severe obesity. Changes in BMI, BMI z-scores and %IOTF-25 were compared with dual-energy x-ray absorptiometry of body composition. The %IOTF-25 might be a better alternative to BMI z-scores to monitor changes in adiposity.

No abstract