Total body water and fat-free mass: evaluation of equations based on bioelectrical impedance analysis in infants and young children in India

The association of early postnatal growth with diseases in adults such as hypertension, type 2 diabetes and CHD has generated interest in studying postnatal growth. Bioelectrical impedance analysis (BIA) is a useful measure to estimate total body water (TBW) and fat-free mass (FFM). We evaluated three published equations (Fjeld et al. (Pediatr Res (1990) 27, 98-102), Bocage (MSc Thesis (1988) University of West Indies) and Kushner et al. (Am J Clin Nutr (1992) 56, 835-839) to measure TBW and derived FFM based on BIA, using (H2O)-H-2 dilution as a reference method for suitability in infants in India. In a cross-sectional study in seventy-eight apparently healthy infants aged 6-24 months from the urban poor attending an immunisation clinic at a hospital in Kolkata, we measured their length to the nearest 0.1 cm, weight to the nearest 10 g, resistance at 50 kHz using BIA and TBW using (H2O)-H-2 dilution. TBW was derived using three published BIA-based equations and compared with TBW using (H2O)-H-2 dilution. Based on the BIA equations of Fjeld et al., Bocage and Kushner et al., the mean TBW values were 2.46% (P<0.001), 4.62% (P<0.001) and 9.50% (P<0.001) lower than the reference (H2O)-H-2 method, respectively. All three published BIA-based equations consistently underestimated the TBW and FFM and appeared inadequate for studying infants in India. The equation described by Fjeld et al. gave the smallest deviation from the reference method and may be used for field studies. New equations based on population-specific data are desirable for a more precise measure of TBW.