Abstract 777 Poster Session IV, Tuesday, 5/4 (poster 50)

Although data from several sources suggests that the BMI of children is increasing in developed countries, we know of no data to verify that this increase is due to an increase in fat mass rather than lean body mass. Further, it is not clear that the same BMI standards for obesity can be applied to all ethnic groups because of possible differences in body composition. We therefore tested the hypothesis that lean body mass and fat mass are closely correlated to BMI in all groups of an ethnically diverse population and tested the implication of defining obesity based on percent body fat.

Methods: We measured height, weight and foot to foot bioelectrical impedance (BIA) of 2273 school children from 5 to 10.9 years old and body composition by dual energy x-ray absorptiometry (DEXA) in a subgroup of 63 children.

Results: DEXA and BIA techniques for evaluation of body composition gave closely correlated results for lean body mass (LBM) (r=0.97), fat mass (r=0.98) and percentage fat (r=0.86) in the subgroup of 63 children, validating foot to foot BIA to evaluate body composition in children. In 2273 children, using BIA results, we found close relationships between BMI and lean body mass (r=0.68), BMI and fat mass (r=0.90) and BMI and % fat (r=0.75) which was valid for all ethnic groups.

Using NHANES reference data BMI of >95th percentile as our definition of obesity, 14.3% of all children were obese. Age, gender and socioeconomic classification of the school area did not influence obesity rates. The percentage of obese children differed significantly (p<0.0001 by ANOVA)among the ethnic groups. Obesity rates varied considerably depending on which arbitrary definition of obesity was used, as shown in the table below as a percentage of children in each ethnic group fulfilling the specified definition of obesity.

Table 1 No caption available
Full size table

Conclusions: 1.Childhood obesity is prevalent in 5-11 year olds in Auckland. 2. Obesity is established by the time of school entry at 5 years old. 3. Ethnic differences in obesity rates are clear and cannot be explained by differences in body composition. 4. Foot to foot BIA is a valid method for determining body composition in children. 5. The optimal definition of obesity is not clear and the implication of different definitions for public health planning is considerable.