Diagnosis of overweight and obesity in adolescents from the 1993 Pelotas Birth Cohort Study, Rio Grande do Sul State, Brazil: comparison of two diagnostic criteria.

Various cut-off points for body mass index have been proposed to assess nutritional status in adolescents. The aim of this study was to compare two methods for evaluating overweight and obesity. In 2004-5, 4,452 adolescents from the 1993 Pelotas (Brazil) birth cohort study were evaluated, representing 87.5% of the original cohort. Overweight and obesity were evaluated using the methods proposed by the World Health Organization (WHO) and International Obesity Task Force (IOTF). Prevalence of overweight was similar when comparing the two methods (WHO: 23.2%; IOTF: 21.6%). Prevalence of obesity was higher according to the WHO criterion (total sample: 11.6%; boys: 15.1%; girls: 8.2%) as compared to IOTF (total sample: 5.0%; boys: 5.6%; girls: 4.4%). The kappa statistic was around 0.9 for determining overweight and 0.4 for obesity. The IOTF classification showed high specificity in comparison to the WHO criterion for determining overweight and obesity. However, sensitivity was high for overweight but low for obesity. Our data show that the IOTF classification underestimates the prevalence of obesity in early adolescence.