How well does the body adiposity index capture adiposity change in midlife women?: The SWAN fat patterning study†

Objectives: The body adiposity index (BAI) is a proposed alternative to the body mass index (BMI) that has shown good cross-sectional agreement with percent body fat (%BF) in validation studies. The objective of this study was to examine the ability of BAI to track adiposity change over time in a biracial sample of midlife women. Methods: African-American (n = 159) and Caucasian (n = 206) women, aged 42–60 years, at the Chicago site of the Study of Women's Health Across the Nation were followed from 2002 to 2008. BAI and BMI were calculated from measurements taken at annual assessments. %BF was quantified using whole-body dual-energy X-ray absorptiometry. Difference scores (BAIΔ, BMIΔ, and %BFΔ) quantified adiposity change over a mean of 1.6 (SD = 0.7) years. Lin's concordance correlation (ρc) and Bland–Altman limits-of-agreement assessed agreement between BAI and %BF. Results: In examining adiposity change, BAIΔ showed poor agreement with %BFΔ in the overall sample (ρc = 0.41), African-American women (ρc = 0.36), and Caucasian women (ρc = 0.43). BAIΔ estimated %BFΔ with minimal bias (+0.4%) but low precision (±6.3%BF limits-of-agreement). %BFΔ had weaker correlations with BAIΔ (rs = 0.38–0.48) than with BMIΔ (rs = 0.48–0.59). BAI and BMI showed similar cross-sectional associations with %BF in the overall sample and within each race (rs > 0.74). Conclusions: We conclude that BAI is less accurate than BMI in tracking adiposity change in midlife women, and would not be a suitable replacement for BMI in most research applications involving adiposity change. Am. J. Hum. Biol., 2012. © 2012 Wiley Periodicals, Inc.