Fidelity of BMI, Waist, and Waist-to-Height Ratio as Adiposity Measures in Normoglycemic Black vs White American Adults.

Objective: To assess ethnic disparities in the association between indirect and direct measures of adiposity in African American (AA) and European American (EA) adults.

Methods: We analyzed the indirect [weight, body mass index (BMI), waist circumference (WC), waist-to-height ratio (WHtR)] and direct [total fat, trunk fat, fat-free mass (FFM)] adiposity measures in healthy AA and EA adults. Assessments included anthropometry, oral glucose tolerance test, body composition by dual-energy X-ray absorptiometry (DXA), and calculation of direct-to-indirect adiposity ratios (total fat/BMI, trunk fat/WC, trunk fat/WHtR, and FFM/weight).

Results: A total of 314 subjects (167 AA, 147 EA) underwent DXA. All participants (mean age 44.2 ± 10.6 years) had normal fasting and 2-hour glucose values. The BMI (AA vs EA) was 31.2 ± 7.42 kg/m² vs28.8 ± 6.78 kg/m² (P = .0014); WC 95.3 ± 16.0 cm vs 92.9 ± 15.0 cm (P = .15). Significant correlations (P < .0001) were observed between BMI and total fat (r = 0.68), WC, and trunk fat (r = 0.61) and WHtR vs trunk fat (r = 0.77) for the combined cohort, with heterogeneity in the strength of association by sex and ethnicity. Fat-free mass was higher in AA vs EA participants (P = .03). Total fat/BMI was lower in AA vs EA participants (P = .0047); trunk fat/WC (P = .004) and trunk fat/WHtR (P = .0026) were lower in AA men vs EA men.

Conclusion: The BMI overestimated body fat in AA participants vs EA participants, and WC overestimated trunk fat in AA men vs EA men. These data indicate ethnic disparities in the fidelity of indirect measures of adiposity and argue for ethnic-specific BMI thresholds for determination of overweight/obesity.