Comparison of dual-energy x-ray absorptiometry to four other methods to determine body composition in underweight patients with chronic gastrointestinal disease

Assessment of body composition may provide important information about the nutritional status. The applicability of two safe and convenient methods fo r body composition analysis, bioelectrical impedance analysis (BIA) and dua l-energy x-ray absorptiometry (DXA), in underweight patients with chronic g astrointestinal disease has been sparsely elucidated. Our objective was to compare measurements by DXA with four other methods. Furthermore, we compar ed total body water (TBW) by BIA using three different BIA equations with m easurement of TBW by tritium dilution (TBW-(H2O)-H-3). Nineteen clinically stable underweight patients with chronic gastrointestinal disease were incl uded in the study (body mass index [BMI], 19.3 +/- 1.2 kg/m(2)). Body compo sition was assessed using total body potassium (TBK), isotope dilution of t ritium ((H2O)-H-3), anthropometry (skinfold thickness [SF]), BIA, and DXA. Fat-free mass (FFM) by DXA was in reasonable agreement with body compositio n measurements by TBK (mean difference(TBK.DXA) = -1.61 kg, r = .88, standa rd error of the estimate [SEE] = 4.66 kg) and (H2O)-H-3 (mean difference(3H 2O.DXA) = 0.98 kg, r = .93, SEE = 3.34 kg). Although mean values for FFM by DXA differed significantly versus BIA and SF, we found highly significant correlations between the measurements (r = .97 and r = .97, respectively). The mean TBW by BIA was overestimated by 1.9 and 3.1 L compared with TBW-(H 2O)-H-3 when prediction equations for normal-weight subjects were used. We conclude that the DXA method is a valuable addition to the list of methods available for body composition studies in clinically stable underweight pat ients. Our data show that BIA equations for normal-weight subjects overesti mated TBW in the patients studied. Copyright (C) 2000 by W.B. Saunders Comp any.