Role of bioelectrical impedance analysis in acutely dehydrated subjects

15 young healthy volunteers were studied to assess the reliability of bioelectrical impedance analysis (BIA) to determine body composition during acute dehydration. Body weight (BW), resistance and reactance measurements were performed before and 4h after a 40 mg intravenous administration of furosemide. BW decreased on average from 69.09 ± 9.83 kg to 67.43 ± 9.72 kg (p < 0·001), while resistance, reactance, and phase angle showed significant increases. The individual variations in bioelectrical parameters were not related to the BW loss. Formulae to derive body composition predicted poorly the true water loss (mean individual error: 40% of real loss). The errors in body composition prediction were unrelated to basal percentage of fat free mass, to body mass index, or to BW loss after furosemide administration. In conclusion, BIA proved unreliable in calculating the body composition of acutely dehydrated subjects.