Comparison of obesity classification methods among college students

The purpose of this study was to compare obesity classification methods (body mass index (BMI)), abdominal girth (AG), and body fat percentage (BF%)), among college students. College students (n = 5943) completed an objective fitness assessment, where height and weight (used to calculate BMI), AG, and BF% (using Bioelectrical Impedance Analysis) were assessed. Correlation and chi-square tests for independence analyses examined relationships between variables and obesity classification methods; and, the sensitivity and specify of BMI using AG and BF% were calculated. Significant correlations were found between BMI and BF% for men (r = 0.775, p < 0.001) and women (r = 0.849, p < 0.001); BMI and AG for men (r = 0.868, p < 0.001) and women (r = 0.858, p < 0.001); and, BF% and AG for men (r = 0.749, p < 0.001) and women (r = 0.767, p < 0.001). There were significant associations between BMI, AG, and BF% for both sexes. Obesity categorization differed significantly between methods. In men and women, respectively, 47.6% and 44.1% classified as normal weight based on BF% were classified as overweight or obese based on BMI (Men: χ2 = 1547, p < 0.001; Women: χ2 = 1127, p < 0.001). In men and women, respectively, 48.3% and 24.0% classified as normal based on AG were classified as overweight or obese using BMI (Men: χ2 = 1274, p < 0.001; Women: χ2 = 996, p < 0.001). Comparing AG and BF%, 25.1% of men and 18.6% of women classified as normal based on AG were classified as overweight or obese using BF% (Men: χ2 = 1412, p < 0.001; Women: χ2 = 421, p < 0.001). Obesity classification differed significantly between methods, and BMI demonstrated relatively poor predictive value with respect to obesity classification. Thus, caution should be applied when using BMI to diagnose obesity among college students.