Precisión diagnóstica del IMC para detectar adiposidad en adultos jóvenes varones físicamente activos

Introduction: The assessment of body composition is particularly relevant in physically active populations, as total body weight may mask actual adiposity. In this context, the Body Mass Index (BMI) has been questioned due to its limited ability to discriminate between adipose tissue and fat-free mass. Objective: To evaluate the diagnostic accuracy of BMI for detecting elevated adiposity in physically active young men, using body fat percentage as an operational comparative criterion. Methodology: A quantitative cross-sectional study was conducted in 203 men aged 18–35 years, recruited from fitness centres. The diagnostic performance of BMI (≥ 25 kg/m²) was contrasted against elevated adiposity defined by ACE criteria (body fat percentage ≥ 18%), estimated using multifrequency bioelectrical impedance analysis. Sensitivity, specificity, predictive values, diagnostic accuracy, and the distribution of concordant and discordant phenotypes were calculated. Results: BMI showed an overall diagnostic accuracy of 63.05%, with a sensitivity of 65.48% and a specificity of 51.43%. Discordance driven by adiposity underestimation predominated, with the phenotype of elevated adiposity and BMI < 25 kg/m² accounting for 28.6%, compared with 8.4% for BMI ≥ 25 kg/m² without elevated adiposity. The negative predictive value was 23.68%. Discussion: The findings describe a pattern of adiposity underestimation by BMI in physically active young men, calling into question its exclusive use as a screening tool in this context. Conclusions: BMI demonstrated limited utility for detecting elevated adiposity in this population. Complementary use of direct body composition assessments is recommended to reduce the omission of individuals with excess adiposity not identified by BMI.