A better index of body adiposity

Abstract

Obesity is a growing problem in the United States and throughout the world. It is a risk factor for many chronic diseases. The BMI has been used to assess body fat for almost 200 years. BMI is known to be of limited accuracy, and is different for males and females with similar %body adiposity. Here, we define an alternative parameter, the body adiposity index (BAI = ((hip circumference)/((height)(1.5))-18)). The BAI can be used to reflect %body fat for adult men and women of differing ethnicities without numerical correction. We used a population study, the "BetaGene" study, to develop the new index of body adiposity. %Body fat, as measured by the dual-energy X-ray absorptiometry (DXA), was used as a "gold standard" for validation. Hip circumference (R = 0.602) and height (R = -0.524) are strongly correlated with %body fat and therefore chosen as principal anthropometric measures on which we base BAI. The BAI measure was validated in the "Triglyceride and Cardiovascular Risk in African-Americans (TARA)" study of African Americans. Correlation between DXA-derived %adiposity and the BAI was R = 0.85 for TARA with a concordance of C_b = 0.95. BAI can be measured without weighing, which may render it useful in settings where measuring accurate body weight is problematic. In summary, we have defined a new parameter, the BAI, which can be calculated from hip circumference and height only. It can be used in the clinical setting even in remote locations with very limited access to reliable scales. The BAI estimates %adiposity directly.

Figure 1

Relation between hip circumference (cm) and height (m). Note the overall lack of correlation (R = 0.005, P = 1.0) suggests that each can contribute independently to a adiposity index.

Figure 2

Calculated suggested body adiposity index values with varying values of power (x axes). Note the maximum at X = 1.48. BAI, body adiposity index; DXA, dual-energy X-ray absorptiometry.

Figure 3

%Body fat (from dual-energy X-ray absorptiometry (DXA)) vs. body adiposity index (BAI); blue for males and yellow for females from the BetaGene study. Relationship between body adiposity index and %body fat, and measured by DXA is represented by the green line. Note that the slope of the relationship (0.93) is fortuitously not different from unity, such that an estimate of %fat can be obtained by calculating BAI and subtracting 15.

Figure 4

Bland and Altman’s limits-of-agreement plot between %body adiposity and BAI-18 for the BetaGene cohort. BAI, body adiposity index; DXA, dual-energy X-ray absorptiometry.

Figure 5

Relationship between DXA-measured %body fat and BMI in the BetaGene study, for males vs. females. DXA, dual-energy X-ray absorptiometry.

Figure 6

Bland and Altman’s limits-of-agreement plot between %body adiposity and BAI-18 for the TARA cohort. BAI, body adiposity index; DXA, dual-energy X-ray absorptiometry.