Diagnostic value of body mass index versus bioelectrical impedance analysis for detection of overweight and obesity among Mexican young adults

Background: The Body Mass Index (BMI) is widely used for nutritional status assessment; nevertheless, it has limitations due to the fact that it doesn't evaluate the body fat. Objective: Identify the diagnostic value of the BMI versus Bioelectrical Impedance to determinate overweight and obesity in young Mexican adults. Methods: A cross-sectional study of validation in young adults of Mexican universities. The height was measured by SECA 215, weight and body composition by InBody 270 with trained and qualified personnel. Comparisons were made by sex with Mann-Whitney U and Chi2; and we calculated Spearman correlations between BMI and total body fat percentage (BFP). Sensitivity (s) and specificity (e) with ROC curves by comparing BMI and PBF were calculated to diagnose overweight or obesity. Analyses were carried out using STATA 14 and p -value of <0.05 was considered significant. Results: 351 university students with a median age of 19 years old were evaluated. 42.2% were diagnosed with overweight or obesity by BMI and 48.1% were diagnosed with the same condition by PBF; there were significant differences between the sexes with the diagnostic by PBF. The correlation between BMI and PBF was high for the whole sample (r=0.68) and higher by sex (r=0.85 men and r=0.81 women) The AUC for diagnosing obesity in women was 0.90, with a high sensitivity (100%) and specificity (80.4%); for overweight diagnosis, the AUC was 0.52 with a low sensitivity (31.5%) and a regular specificity (73.1%). The AUC for diagnosing obesity in men was 0.84, with a high sensitivity (80%) and specificity (88.9%); for overweight diagnosis, the AUC was 0.63 with a low sensitivity (32.5%) and a high specificity (94.3%). Conclusions: A high and very high correlation between BMI and BFP was detected in both men and women. The BMI is a useful and reliable indicator for diagnosing obesity, but not for diagnosing overweight in young Mexican adults.