M Wilkes1,2,3, J Thornton4, M Horlick4, A Sopher3, J Wang4, E M Widen1,5, R Pierson4, D Gallagher1,4,6. 1. New York Obesity Research Center, Dept. of Medicine, College of Physicians and Surgeons, Columbia University, New York, NY, USA. 2. Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, NY, USA. 3. Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, NY, USA. 4. Body Composition Unit, St. Luke's-Roosevelt Hospital, New York, NY, USA. 5. Department of Nutritional Sciences, University of Texas at Austin, Austin, TX, USA. 6. Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY, USA.
Abstract
OBJECTIVE: The objective of the study is to examine the validity of body mass index z score (zBMI) as a measure of percent body fat in prepubertal children. METHODS: One hundred eleven multiethnic, healthy, Tanner 1 children aged 6-12 years had fat percent and fat mass measured by the four-compartment method as part of the Paediatric Rosetta Body Composition Cohort. Multiple regression models were developed with fat percent as the dependent variable and zBMI, age, sex and ethnicity as independent variables. RESULTS: Body mass index z score predicted fat percent, adjusted for age in both girls (P < 0.001, RMSE 5.67 and R2 0.54) and boys (P < 0.001, RMSE 4.71, R2 0.69). The average model percent error was 20.3% in girls and 21.6% in boys. zBMI2 predicted fat mass when adjusted for age and zBMI in both girls (P < 0.001, RMSE 2.27 and R2 0.82) and boys (P < 0.001, RMSE 2.08 and R2 0.81). The average percent error was 7.2% in girls and 8.7% in boys. Age was associated with percentage body fat (P < 0.01), while ethnicity was not (P > 0.05). CONCLUSIONS: Given the relatively large error in the models, zBMI are not a useful indicator of fat mass in healthy, Tanner 1 children. zBMI2 scores are associated with significantly lower absolute percent errors in girls and boys.
OBJECTIVE: The objective of the study is to examine the validity of body mass index z score (zBMI) as a measure of percent body fat in prepubertal children. METHODS: One hundred eleven multiethnic, healthy, Tanner 1 children aged 6-12 years had fat percent and fat mass measured by the four-compartment method as part of the Paediatric Rosetta Body Composition Cohort. Multiple regression models were developed with fat percent as the dependent variable and zBMI, age, sex and ethnicity as independent variables. RESULTS: Body mass index z score predicted fat percent, adjusted for age in both girls (P < 0.001, RMSE 5.67 and R2 0.54) and boys (P < 0.001, RMSE 4.71, R2 0.69). The average model percent error was 20.3% in girls and 21.6% in boys. zBMI2 predicted fat mass when adjusted for age and zBMI in both girls (P < 0.001, RMSE 2.27 and R2 0.82) and boys (P < 0.001, RMSE 2.08 and R2 0.81). The average percent error was 7.2% in girls and 8.7% in boys. Age was associated with percentage body fat (P < 0.01), while ethnicity was not (P > 0.05). CONCLUSIONS: Given the relatively large error in the models, zBMI are not a useful indicator of fat mass in healthy, Tanner 1 children. zBMI2 scores are associated with significantly lower absolute percent errors in girls and boys.
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