Comparison of Foot-to-Foot and Hand-to-Foot Bioelectrical Impedance Methods in a Population with a Wide Range of Body Mass Indices Claudia Gagnon, M.D., Julie Me ´ nard, Ph.D., Annie Bourbonnais, Jean-Luc Ardilouze, M.D., Ph.D., Jean-Patrice Baillargeon, M.D., M.Sc., Andre ´ C. Carpentier, M.D., and Marie-France Langlois, M.D. Abstract Background: Several techniques are currently used for measurement of body composition. Bioelectrical im- pedance assessment (BIA) is a simple, noninvasive method of assessing body composition. We aimed to com- pare 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 33.5  0.7 (range, 17.7–65.6) kg/m 2 . Mean FFM with HF-BIA (FFM BIA/HF ) and FF-BIA (FFM BIA/FF ) were 61.3  1.3 kg and 58.1  0.9 kg, respectively (P < 0.001). In subjects with BMI <25 kg/m 2 , FFM BIA/FF was not significantly different compared to FFM BIA/HF (þ0.2 kg; P ¼ 0.8). However, FFM BIA/FF was significantly lower in subjects with BMI 25–30 kg/m 2 (2.0 kg; P ¼ 0.009), 30– 34 kg/m 2 (1.8 kg; P ¼ 0.04), 34–42 kg/m 2 (4.7 kg; P < 0.001) and >42 kg/m 2 (8.0 kg; P ¼ 0.001). Pearson correlations between both methods were very high for FFM (r ¼ 0.92), fat mass (r ¼ 0.91), and % fat mass (r ¼ 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. Introduction S everal techniques are currently used for measure- ment of body composition. Underwater weighing, the reference method, is impractical for use in large clinical trials and uncomfortable for patients. Assessment of body com- position by dual-energy X-ray absorptiometry (DXA) is more convenient, but costly. Consequently, bioelectrical imped- ance analysis (BIA), a simple, noninvasive, and less expen- sive method, has gained in popularity in the last decade, and is more practical for use in clinical and epidemiological studies. BIA is based on two important principles. The first one is that the resistance of a length of homogeneous conductive material of uniform cross-sectional area is proportional to its length and inversely proportional to its cross-sectional area. Thus, the technique assumes that the body is a uniform cylinder. A second assumption is that water represents 73.8% of the fat-free mass (FFM). Instruments for BIA introduce a current of about 800 A in the body that flows between two electrodes at single or multiple frequencies throughout con- ducting material. 1 The measured impedance, which reflects tissue resistance to electrical current, provides an estimate of total body water (TBW). Various equations are used to de- rive FFM from TBW. FFM is probably the most accurate index recorded by BIA and is a useful parameter to follow in overweight and obese individuals, especially those under- taking restrictive diet programs. Indeed, without exercise, these diet approaches are associated with a decrease in FFM, accounting for about 25% of the total weight loss. 2,3 Department of Medicine, Division of Endocrinology, Centre de recherche clinique Etienne-Le Bel, Faculte ´ de me ´decine et des sciences de la sante ´, Universite ´ de Sherbrooke, Sherbrooke, Canada. METABOLIC SYNDROME AND RELATED DISORDERS Volume 8, Number 5, 2010 ª Mary Ann Liebert, Inc. Pp. 437–441 DOI: 10.1089/met.2010.0013 437