A comparative study of methods for diagnosis of obesity in an urban mixed-race population in Minas Gerais, Brazil

Background: Obesity is defined as an excess of total body fat and may be assessed by different methods. The objective of the present study was to establish the discriminatory power of anthropometric data in determining obesity. Methods: The subjects comprised 685 individuals, aged 20-79 years, sampled from a population-based survey. The following indicators were used: body mass index (BMI), waist circumference (WC) and total body fat percentage estimated with both Siri's equation (%BF Siri) and foot-to-foot bioelectrical impedance analysis (%BF BIA). Sensitivity and specificity of different cut-off points for each method were determined using %BF BIA as reference. Results: Of 685 participants, 57.6% were aged >= 40 years, 69.9% were women and 72.6% self-referred themselves as non-white. To classify obesity based on sex and age among women aged < 40 years, the cut-off points were BMI of 26.0 kg m(-2), WC of 84.0cm and %BF Siri of 34.0%; in those aged >= 40 years, the cut-off points were 28.0 kg m(-2), 90.0cm and 37.4%, respectively. The cut-off points among men aged 2 < 40 years were BMI of 26.3 kg m(-2), WC of 86.0 cm and %BF Siri of 22.5%, and in those aged >= 40 years, 26.3 kg m(-2) 89.0 cm and 24.5%, respectively. BMI was the method with the largest area under the Curve (AUC) independent of sex and sex/age, yet no differences were observed in AUC between BMI and WC (P > 0.05). Classifying according to skin colour did not change cut-off points in any indicator. Conclusion: BMI and WC better discriminate obesity among women and men aged >= 40 years from a mixed-race population.