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 (BAI(Δ) , BMI(Δ) , and %BF(Δ) ) quantified adiposity change over a mean of 1.6 (SD = 0.7) years. Lin's concordance correlation (ρ(c) ) and Bland-Altman limits-of-agreement assessed agreement between BAI and %BF. RESULTS: In examining adiposity change, BAI(Δ) showed poor agreement with %BF(Δ) in the overall sample (ρ(c) = 0.41), African-American women (ρ(c) = 0.36), and Caucasian women (ρ(c) = 0.43). BAI(Δ) estimated %BF(Δ) with minimal bias (+0.4%) but low precision (±6.3%BF limits-of-agreement). %BF(Δ) had weaker correlations with BAI(Δ) (rs = 0.38-0.48) than with BMI(Δ) (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.