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.
Obesity Unit, Department of Medicine, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, SWEDEN
Address for correspondence: Martin Neovius, Ph.D., Obesity Unit M73, Karolinska University Hospital Huddinge, SE-141 86 Stockholm, Sweden; E-mail: Martin.firstname.lastname@example.org.
Submitted for publication February 2007.
Accepted for publication August 2007.