Purpose

To compare estimates of change in percent body fat (Delta% 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;% 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 Delta% 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 (beta=-0.05; P= 0.006), DeltaBMI (beta= 0.98; P< 0.001), and Delta% BFDXA (beta=-0.71; P< 0.001), indicating that the larger the change, the greater the discrepancy between methods.

Conclusion

The difference between methods regarding Delta% BF was statistically significant, but it was of small magnitude. However, with increasing Delta% 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.