Centre de Recherche en Nutrition Humaine - Auvergne - Clermont-Ferrand, France. Correspondence : Patrick RITZ, MD, PhD, Service de Médecine B, Centre Hospitalier Universitaire, F-49033 ANGERS Cedex 01. Phone : 00 (33) 2.41.35.44.99. Fax : 00 (33) 2.41.73.82.30. e-mail : paritz@chu-angers.fr

Abstract: Background and aims : The assessment of body composition and water spaces in elderly persons, especially in disease situations, would be a critical component of the nutritional and hydration management. Bioelectrical impedance analysis (BIA) is a validated bed-side technique for the estimate of total body (TBW) and extracellular (ECW) water. The aim of the present study was to address the reproducibility of estimates of TBW, ECW and fat-free mass (FFM) in healthy elderly individuals (n=24, 61 ± 3.6 yrs). Methods : Repeated measurements of weight, height, skinfold thickness, TBW and ECW (BIA) were obtained (in almost identical experimental conditions) on days 0, 14, 28 and 42. FFM and the hydration fraction of FFM (HF) were calculated with a three compartment model. Results : Analysis of variance for repeated measurements showed that time did not explain a significant part of the variance in water spaces, FFM, and HF. Mean SDs for repeated measurements were well within 1 litre for water spaces, 1 kg for FFM and 1% for HF. Conclusions : We conclude that reproducible measurements of water spaces can be obtained with BIA, which could be used to monitor hydration changes. Given the small variability in HF, FFM, can be derived from BIA with good reproducibility.

Key words: elderly, total body water, extracellular water, fat-free mass, bioelectrical impedance analysis