Energy expenditure and requirement while climbing above 6,000 m

Humans survive the low barometric pressure of altitudes above 6,000 m only by making a complex series of adaptations. However, the effects of such adaptations on energy metabolism have not been widely studied. To determine daily energy requirement at extreme altitude, energy expenditure (EE) was measured by doubly labeled water (DLW) and energy intake-balance (IB) methods in five men and one woman while climbing between 5,900 and 8,046 m over a 7-day period. Energy intakes were determined by dietary record (13.8 +/- 2.0 MJ/day). Change in body energy stores, estimated from differences in body weight, skinfold thickness, limb circumference, and isotope-dilution techniques, was -5.1 +/- 1.6 MJ/day. DLW (19.4 +/- 1.2 MJ/day) and IB (18.9 +/- 2.7 MJ/day) measurements of EE provided similar estimates of group mean EE. These results suggest that IB and DLW techniques can yield comparable estimates of group mean EE at extreme altitude. It is concluded that problems of meeting energy requirements while climbing at extreme altitude are related to energy intakes amounting to only roughly 70% of EE.