Obesity is a public health problem defined as an excess accumulation of body fat. The obesity has an increasing prevalence, affecting more than 650 million adults worldwide. The World Health Organization recommends assessing obesity using a body mass index (BMI) ≥ 30 kg/m2 as the cutoff point for obese individuals. However, the BMI classification has its limitations because it is not able to discriminate fat mass from lean mass. In addition, with aging, changes in body composition occur, such as a reduction in lean mass and an increase in body fat, without changes occurring in BMI.

To establish a cutoff point for total fat mass to identify obesity in community-dwelling Brazilian elderly women.

This was a cross-sectional study involving elderly women evaluated at the Laboratório de Fisiologia do Exercício at the Universidade Federal dos Vales do Jequitinhonha e Mucuri from June 2016 to June 2017. Participants were submitted to anthropometric (weight, height, and BMI) and body composition (total fat mass) assessments measured using dual-energy X-ray abdominmetry (DXA Lunar Type DPX, 2005 software). The sample was categorized by nutritional status based on the obtained BMI. Data were analyzed using the receiver operating characteristics curves and the Youden Index determined the cut-off point. Statistical significance was set at 5%.

One hundred and sixty-one elderly women aged between 65 and 96 years (74.32±7.16) participated in the study. According to BMI, 47.8% of the sample was categorized as obese (BMI ≥ 30 kg/m2). The area under the curve value was satisfactory (AUC: 0.94) and the ROC curve calculated. The cut-off point for the prediction and determination of obesity in community-dwelling elderly Brazilian women was 25.4 kg of total fat mass (Sensitivity: 0.81; Specificity: 0.94). In addition, the cutoff point presented satisfactory positive and negative predictive values ​​(93.94% and 84.21%, respectively), demonstrating good accuracy in identifying obesity.

Obesity is a chronic condition commonly associated with other comorbidities throughout life. Therefore, its early identification is crucial for monitoring and interventions in the context of obesity. Considering the variety of body composition assessment instruments, it is clinically important to propose an alternative for the diagnosis and a cutoff point for the total fat mass that is capable of identifying the obese individual, using DEXA, which is known to present a high accuracy of body composition measurement.

The findings of this study may support future studies that investigate obesity or sarcopenic obesity using a gold standard instrument for assessing body composition.