Examining Classic Bioimpedance Vector Patterns Between BMI Classifications Among Community-Dwelling Older Women

Body mass index (BMI) is not equipped to adequately detect obesity in individuals, leading to conditions such as normal-weight obesity, which disproportionately impact older women. Bioelectrical impedance vector analysis (BIVA) is a non-invasive and accessible method for assessing body composition and cellular health (e.g., resistance/height, reactance/height, phase angle), yet little is known about how BMI categories differ in cellular health. This cross-sectional study compared bioimpedance and adiposity across BMI classifications (normal weight, overweight, and obese) among 196 community-dwelling older women (age: 74.5 ± 7.0 years, BMI: 30.3 ± 6.3 kg/m²) using a one-way ANOVA and BIVA software. Individual and group bioimpedance were plotted within tolerance and 95% confidence ellipses. Body fat percentage (F = 70.6, p < 0.001, η_p² = 0.42) and resistance/height (F = 36.4, p < 0.001, η_p² = 0.27) differed between normal-weight, overweight, and obese groups. Reactance/height (F = 36.4, p < 0.001, η_p² = 0.27) and phase angle (F = 4.77, p = 0.01, η_p² = 0.05) only differed between normal-weight and obese groups. When plotted with 95% BIVA confidence ellipses, BMI categories occupied distinct positions from each other (T² = 16.1 - 66.6, D = 0.68 - 1.48, p < 0.05). Within BIVA tolerance ellipses, overweight and obese categories fell in the "obese" quadrant, while the normal-weight category fell in the "athletic" quadrant. However, individual participants were predominantly scattered throughout the "cachectic," "obese," and "athletic" quadrants regardless of BMI. These findings suggest that BMI appears to be adequate for assessing population averages but not individual body composition. Future research should investigate the utility of bioelectrical resistance as a marker of obesity.