This study of body composition in British schoolchildren has shown that ethnic and gender differences in percentage body fat can be seen as early as 5 years of age and become more evident with increasing age with striking differences in percentage body fat being seen in the teenage years. The largest differences were seen between the South Asian and African‐Caribbean children, and South Asian teenage girls had the highest values for percentage body fat. It is apparent that classification of subjects as overweight or obese by IOTF criteria does not recognise these ethnic differences in percentage body fat. While a higher proportion of African‐Caribbean children are classified as obese, the South Asian children have the highest percentage body fat. Our study has also demonstrated that the prevalence of obesity in our cohort at 7.5% is higher than the previously reported prevalence of 6% in UK children.4
Gender differences in body fat in prepubertal children have previously been recognised. A study in the south west of England using skinfold thicknesses showed that girls at the age of 5 years carried 26% more subcutaneous fat than boys.9
Prepubertal children in New York studied using DXA and skinfold thicknesses also demonstrated clear gender differences, with the girls having greater body fat.10
Ethnic differences in body composition using DXA have been examined in other populations of children and young adults. A study of 358 prepubertal children aged 5–12 years from New York used DXA to examine differences between Caucasian, African‐American and Asian (Chinese and Korean) subjects.10
The Asian children had lower values for extremity body fat in comparison with the Caucasian subjects. Two studies from Houston, Texas11,12
examined body composition in European‐American, African‐American and Mexican‐American (Hispanic) girls and boys aged 3–18 years. Both studies identified the Hispanic subjects as having higher values for fat mass and percentage body fat after adjustment for body size differences. Our study is the first UK study to examine ethnic differences using DXA.
What is already known on this topic
- Ethnic differences in body composition in adults are related to differences in the prevalence of type 2 diabetes.
- African‐Caribbean girls have the highest prevalence of obesity amongst UK children.
What this study adds
- Ethnic differences in percentage body fat can be seen from the age of 5 years.
- Body mass index criteria for obesity do not identify these ethnic differences in percentage body fat.
It is now well established that Asian adult subjects have higher levels of body fat than European subjects with comparable BMI values, which has led to a revision of WHO recommendations for appropriate BMI cut‐off levels in Asian populations.13
Our study has demonstrated that similar differences in body fat are present in South Asian children at comparable levels of body weight or BMI. It is of note that the South Asian boys in our study did not demonstrate a fall in percentage body fat in the teenage years as was seen in the white and African‐Caribbean boys and has also been demonstrated as a normal physiological phenomenon using bio‐impedance in a large cohort of Caucasian children in the UK.14
Although our study did demonstrate higher BMI values in the African‐Caribbean subjects as seen in the Health Survey for England,4
this was not reflected in higher values for body fat. Thus BMI does not accurately indicate percentage body fat and the use of similar BMI criteria for different ethnic groups may lead to errors in identifying obese children. This will be important if BMI criteria are used to identify those children who should be referred for specialist obesity services. The limitations of BMI as a measure of the fatness of an individual has been mentioned in a recent review paper.15
A similar discrepancy between BMI and percentage body fat across ethnic groups has been shown in a study of black and white children and adolescents from Cincinatti.16
If the data are reanalysed with adjustment for height rather than weight, the differences in body composition for the girls from the age of 9 years are no longer significant and may represent the fact that the unadjusted differences are due to body weight and not stature. In the boys significant differences in the younger age groups disappear but remain significant between 13 and 18 years of age. These discrepancies between apparent ethnic differences in body composition after adjustment for height or weight may be explained by environmental and genetic interactions on nutrition, linear growth and proportion of body fat. Further work investigating longitudinal changes are required to provide more insight.
Our study has demonstrated ethnic differences in percentage body fat amongst contemporary UK children that are apparent at an early age prior to the onset of puberty and which become more marked with puberty. We have shown these variations to be related to ethnic differences in insulin sensitivity between South Asian and white adolescents which maybe associated with the risk of developing type 2 diabetes in childhood or adulthood.5
It is currently recognised that in the UK the relative risk of developing type 2 diabetes in childhood is fourteen times greater in South Asian than in white European children.17
Those factors, genetic and environmental, that lead to these differences in body composition at a young age need to be identified and should be the focus of future research.