MEASUREMENTS OF ENERGY-EXPENDITURE USING ISOTOPE-LABELED WATER ((H2O)-H-2-O-18) DURING AN ARCTIC EXPEDITION

Estimates of energy expenditure using both isotope-labelled ((H2O)-H-2 -O-18) water and dietary intake/body composition changes were made dur ing an attempt by two men (MS and RF) to walk to the North Pole. The i sotope-labelled water technique gave mean estimates of daily energy ex penditure for the 48-day expedition of 28.05 MJ (MS) and 32.38 MJ (RF) , which compared with estimates of 25.66 MJ (MS) and 24.86 MJ (RF) fro m the intake/body composition measurements. Fluid retention and periph eral oedema probably caused a considerable underestimate of the losses in body energy stores when applying the energy balance method, wherea s in the isotope method, uncertainty in the measurements of isotopic b ackground led to minimum errors of -4.9% to +4.0% of the means for MS and -12.7% to +8.2% for RF (95% confidence limits).