Fat-free mass in chronic illness: comparison of bioelectrical impedance and dual-energy x-ray absorptiometry in 480 chronically ill and healthy subjects

Assessment of fat-free mass (FFM) and fat mass in ambulatory and hospitalized patients permits optimal adaptation of nutrition support. Recent methods for the determination of FFM are dual-energy x-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA). The purpose of this study was to determine if the BIA-determined FFM as estimated by the formula by Kotler et al.[1] and the Geneva formula [2] could be validated when compared to DXA-determined FFM in subjects with various diagnoses. Body composition was measured by BIA and DXA in 480 subjects including healthy young men and women, elite female runners, and patients with various pathologies (including chronic obstructive and restrictive pulmonary disease patients; cystic fibrosis patients; lung, heart, and liver transplantation patients [both pre- and post-], and hemiplegic and AIDS patients). The present results suggest that BIA is relevant in the clinical assessment of body composition, but BIA formulas appropriate to the subject pool must be used for evaluation of FFM and fat mass. The BIA formula by Kotler et al. [1] is appropriate for healthy subjects and patients with AIDS, cystic fibrosis, and pre- or postliver transplantation. The Geneva formula [2] is more appropriate in pulmonary diseases and hemiplegic subjects with normal weight.