Relationship between body mass index and adiposity: Comparison of ethnic differences in urban college females

Body Mass Index (BMI) has been used to diagnose obesity and it is often used as a surrogate estimate of body fat because of its ease of measurement, non-invasive nature and low cost. This study tested the hypothesis that BMI is representative of body fatness independent of age and ethnicity in college females. A total of 336 undergraduate female students from a major urban university participated in the study (Mean age =23.69 (SD=5.25); Caucasians 44.3%, Asians 30.1%, African-Americans 13.1% and Hispanics 12.5%). Age-adjusted multiple linear regression models were utilized to assess ethnic differences in the relationship between BMI (independent variable) and Fat Mass (FM) as well as Percent Body Fat (PBF) (dependent variables).  Overall, BMI was significantly associated with FM (R² = 82%, p<.001) and PBF (R² = 63%, p<.001). Thus, BMI alone explained 82% and 63% of the between-individual differences in FM and PBF, respectively. Ethnicity explained another 1% of variance in FM (R² = 83%, P<.001) and 2% variance in PBF (R² = 65%, p<.001).Specifically,  Asians had significantly lower age-BMI adjusted FM and PBF as compared to Caucasians (FM β=-4.37, p<. 001; PBF β=-2.18 p<.010) and African-Americans (FM β=-6.00, p<.001, PBF β=-4.02, p<.001). No difference was observed between any other ethnic groups. The results of this study support the recommendation that BMI can be used as a surrogate estimate of FM and PBF. However, caution is warranted when applying BMI across ethnic groups.