The objective of the study is to evaluate neonatal body composition determined by the isotope dilution method compared with the total-body electrical conductivity (TOBEC) method. An oral dose of 18O- and 2H-labeled water was given to 40 healthy term newborns, and 26 infants successfully completed the protocol. The isotope concentrations in urine samples were measured by gas-isotope ratio mass spectrometry. Fat and percent body fat (%F) estimated by isotope dilution were correlated with fat and %F estimated. Total body water measured by isotope dilution of 18O and 2H was 2.44 ± 0.36 and 2.49 ± 0.35 kg, respectively (p < 0.001). Fat and %F estimated by 18O, 2H, and TOBEC were 0.48 ± 0.20 kg and 13.7 ± 5.1%, 0.48 ± 0.19 kg and 13.7 ± 4.6%, and 0.38 ± 0.21 kg and 10.9 ± 5.0%, respectively. Neither fat nor %F estimates by isotope dilution showed good correlation with the TOBEC estimates (r = 0.22–0.57). Because of the wide variation of water content in individuals, the isotope dilution method may not be the optimal way of assessing body composition, and specifically body fat, in newborns.

Keywords:
Neonatal body composition, Body fat, Total body water, Isotope dilution, Total-body electrical conductivity
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© 2002 S. Karger AG, Basel
2002
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