The Accuracy of Body Mass Index and Gallagher’s Classification in Detecting Obesity among Iranians

Background: The study was conducted to examine the comparability of the BMI and Gallagher’s classification in diagnosing obesity based on the cutoff points of the gold standards and to estimate suitable cutoff points for detecting obesity among Iranians. Methods: The cross-sectional study was comparative in nature. The sample consisted of 20,163 adults. The bioelectrical impedance analysis (BIA) was used to measure the variables of interest. Sensitivity, specificity, positive predictive power (PPV), and negative predictive power (NPV) were used to evaluate the comparability of the two classification methods in detecting obesity. Results: The BMI wrongly classified 29% of the obese persons as overweight. In both classifications, as age increased, the accuracy of detecting obesity decreased. The Gallagher’s classification is better than MBI in detecting obesity in men with the exception of those older than 59 years. In females, the BMI was better in determining sensitivity. In both classifications, either female or male, an increase in age was associated with a decrease in sensitivity and NPV with the exception of the BMI for the 18 year olds. Gallagher can correctly classify males and females who are less than 40 and 19 years old, respectively. Conclusion: Gallagher’s classification is recommended for nonobese in both sexes and in obese males younger than 40 years old. The BMI is recommended for obese females. The suitable cutoff points for the BMI to detect obesity are 27.70 kg/m2 for females and males, 27.70 kg/m2 for females, and 27.30 kg/m2 for males.