Purpose: To compare estimates of change in percent body fat (Δ%BF) between DXA and BIA8 in abdominally obese women.
Methods: Six-month longitudinal study of 106 women (baseline: age 48.2 ± 7.6 yr; BMI 30.4 ± 2.9 kg·m−2; %BFDXA 45.8 ± 3.6%) participating in an exercise-oriented behavior-change program (walking and bicycling). Fatness was measured by DXA and Tanita BC-418 (BIA8). Agreement between methods was assessed, and regression analysis was used to find predictors of the deviation between methods for estimating changes in fat mass percentage.
Results: The methods differed significantly, both at baseline and follow-up (−5.0 and −4.4%BF, respectively; both P < 0.001). The mean Δ%BF was −1.1 ± 2.5%BFDXA and −0.5 ± 2.2%BFBIA8 (mean difference between methods 0.6 ± 1.8%BF; P < 0.001; 95% limits of agreement −3.0 to 4.2%BF), with a range of −14.8 to 3.3%BFDXA and −9.4 to 3.5%BFBIA8. Approximately 49% of the variation in the difference between methods was explained by variations in age (β = −0.05; P = 0.006), ΔBMI (β = 0.98; P < 0.001), and Δ%BFDXA (β = −0.71; P < 0.001), indicating that the larger the change, the greater the discrepancy between methods.
Conclusion: The difference between methods regarding Δ%BF was statistically significant, but it was of small magnitude. However, with increasing Δ%BF, increasing discrepancies were observed, implying that the BIA equipment may have limited validity for detecting larger fat losses. Both clinicians and researchers may benefit from awareness of this potential limitation.