Relationship of BMI z score to fat percent and fat mass in multiethnic prepubertal children
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 0.05). 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.