Obesity in Auckland school children: a comparison of the body mass index and percentage body fat as the diagnostic criterion

OBJECTIVES: First, to determine obesity rates in Auckland school children according to their ethnic group using two different criteria: the body mass index (BMI) and percentage body fat (PBF) derived from bioelectrical impedance analysis (BIA). Second to examine the relationship between BMI and body composition across ethnic groups to determine if BMI references from European children accurately reflect obesity in other ethnic groups. DESIGN: A total of 2273 Auckland school children, aged 5-10.9y had their height, weight and bioelectrical impedance measured. Using these measurements, each child's BMI, fat free mass, fat mass and PBF were derived. RESULTS: In all 14.3% of children were obese using the recommended definition of obesity (BMI) greater than the 95th percentile). There was no clinically significant difference in the relationship between BMI and body composition in different ethnic groups. Obesity rates varied with ethnicity (P < 0.0001) and were higher in Pacific Island (24.1%) and Maori (15.8%) than in European children (8.6%). Obesity rates also varied with age (P < 0.03), with the highest rates in older children. PBF levels were higher in females than males (P < 0.0001). Using a definition of obesity based on percentage body fat (PBF > 30%), obesity rates were higher in all ethnic groups. CONCLUSIONS: Obesity rates are high in Auckland school children and there are clear differences in obesity rates in different ethnic groups. If BMI criteria are used to define obesity in our population, we recommend the same standards be used for children of all ethnicities.