Recalibration of overweight–obesity prevalence from body-mass index in UK children of South Asian and black African origin: cross-sectional study based on National Child Measurement Programme data

Background The accurate assessment of overweight–obesity prevalence in UK children of South Asian and black African origin (in whom its consequences are especially adverse) is an important challenge. However, body-mass index (BMI), the marker of body fatness used in most national surveys, differs in its association to body fatness between ethnic groups, which biases ethnic comparisons of body fatness based on BMI. We recalibrated BMI values for ethnicity to assess overweight–obesity prevalence more accurately in UK South Asian and black African children in recent survey data from the National Child Measurement Programme (NCMP), an inclusive assessment programme in English primary schools. Methods Deuterium dilution measurements of body fat and BMI were collated from four recent UK population-based studies (three in schools selected to provide balanced ethnic representation) in 873 children of South Asian, black African, and white European origin aged 9−11 years. Data were analysed with linear regression models to determine the age-adjusted and sex-adjusted BMI differences in South Asian and black African children compared with white Europeans at an equivalent level of body fatness (denoted by fat mass index [kg/m 5 ], which is uncorrelated with height). These BMI adjustments were applied to NCMP 2012–13 survey data in 489 146 children aged 10–11 years to determine ethnic-specific overweight–obesity prevalences; standard NCMP overweight–obesity definitions were used. Findings BMI adjustments for equivalent body fatness were +1·11 kg/m 2 and +0·98 kg/m 2 for South Asian boys and girls, respectively, and −1·20 kg/m 2 and −1·66 kg/m 2 for black African boys and girls, respectively; these adjustments were applied to NCMP data for South Asian and black African children. Overweight–obesity was recorded in 14 538 of 38 201 South Asian children (38·1%, 95% CI 37·6–38·5) and 9839 of 22 672 black African children (43·4%, 42·8–44·0) before BMI adjustment and in 18 145 of 38 201 (47·5%, 47·0–48·0) and 7065 of 22 672 (31·2%, 30·6–31·8), respectively, after adjustment; overweight–obesity was recorded in 92 002 of 292 467 white European children (31·5%, 95%CI 31·3–31·6). Interpretation Use of ethnic-specific BMI adjustments to obtain comparable assessments of body fatness substantially changed observed overweight–obesity prevalences in ethnic minority groups. Adjusted BMI particularly emphasised the substantial overweight–obesity burden in South Asian children, an important priority for prevention. Funding This research was supported by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care South London and by grants from the British Heart Foundation (PG/11/42/28895), the Child Growth Foundation (GR 10/03), and the Wellcome Trust (WT094129MA).