Accuracy of the WHO's body mass index cut-off points to measure gender- and age-specific obesity in middle-aged adults living in the city of Rio de Janeiro, Brazil.

INTRODUCTION: Obesity is defined by the World Health Organization (WHO) as a disease characterized by the excessive accumulation of body fat. Obesity is considered a public health problem, leading to serious social, psychological and physical problems. However, the appropriate cut-off point of body mass index (BMI) based on body fat percentage (BF%) for classifying an individual as obese in middle-aged adults living in Rio de Janeiro remains unclear.

MATERIALS AND METHODS: This was a prospective cross-sectional study comprising of 856 adults (413 men and 443 women) living in Rio de Janeiro, Brazil ranging from 30-59 years of age. The data were collected over a two year period (2010-2011), and all participants were underwent anthropometric evaluation. The gold standard was the percentage of body fat estimated by bioelectrical impedance analysis. The optimal sensitivity and specificity were attained by adjusting BMI cut-off values to predict obesity based on the WHO criteria: BF% >25% in men and >35% in women, according to the receiver operating characteristic curve (ROC) analysis adjusted for age and for the whole group.

RESULTS: The BMI cut-offs for predicting BF% were 29.9 kg/m2 in men and 24.9 kg/m2 in women.

CONCLUSIONS: The BMI that corresponded to a BF% previously defining obesity was similar to that of other Western populations for men but not for women. Furthermore, gender and age specific cut-off values are recommended in this population.