Comparison of foot-to-foot and hand-to-foot bioelectrical impedance methods in a population with a wide range of body mass indices.

Background: Several techniques are currently used for measurement of body composition. Bioelectrical impedance assessment (BIA) is a simple, noninvasive method of assessing body composition. We aimed to compare multifrequency hand-to-foot (HF-BIA) and foot-to-foot (FF-BIA) bioelectrical impedance analysis techniques to assess fat-free mass (FFM) in a population with a wide range of body mass indices (BMI).
Methods: This was a cross-sectional study of 198 adult subjects. Anthropometric and BIA measures (HF-BIA with Hydra ICF/ECF, Xitron Technologies and FF-BIA with Tanita, model TBF-300A) were recorded after a 12-h fast.
Results: Participants had a mean age of 42 years and BMI of 33.50.7 (range, 17.7-65.6) kg/m2. Mean FFM with HF-BIA (FFM BIA/HF) and FF-BIA (FFM BIA/FF) were 61.31.3 kg and 58.10.9 kg, respectively (P < 0.001). In subjects with BMI <25 kg/m2, FFM BIA/FF was not significantly different compared to FFMBIA/HF (-0.2 kg; P=0.8). However, FFM BIA/FF was significantly lower in subjects with BMI 25-30 kg/m2 (-2.0 kg; P=0.009), 30-34 kg/m2 (-1.8 kg; P¼0.04), 34-42 kg/m2 (-4.7 kg; P<0.001) and >42 kg/m2 (-8.0 kg; P=0.001). Pearson correlations between both methods were very high for FFM (r=0.92), fat mass (r=0.91), and % fat mass (r=0.85), all P<0.001. Correlation coefficients for FFM were high in each quintile of BMI. FFM BIA/FF was the only significant independent predictor of FFM BIA/HF (P<0.001) in linear regression analyses using clinical and FF-BIA variables, but introducing BMI in the model added precision.
Conclusion: FFM BIA/FF correlates closely with FFM BIA/HF across all quintiles of BMI, but FF-BIA gives lower FFM in overweight and obese subjects.