ENERGY-BALANCE AT HIGH-ALTITUDE OF 6,542-M

Weight loss due to malnutrition and possibly intestinal malabsorption is a well-known phenomenon in high-altitude climbers. Up to similar to 5,000 m, energy balance may be attained and intestinal energy digesti bility remains normal. To see whether 1) energy balance may also be at tained at 6,542 m and, if not, 2) whether decreased energy digestibili ty would play a significant role in the energy deficit, energy intake (EI), energy expenditure, body composition, and energy digestibility o f 10 subjects (4 women, 6 men; 27-44 yr) were assessed during a 21-day sojourn on the summit of Mt. Sajama, Bolivia (6,542 m). EI was measur ed during two 3-day intervals: EI1 (days 7-9) and EI2 (days 17-19). To tal fecal energy loss during EI1 was calculated from fecal energy meas ured by bomb calorimetry. Average daily metabolic rate (ADMR) at altit ude was measured in six subjects (2 women, 4 men) using doubly labeled water over a 10-day interval (days 9-19). Basal metabolic rate was me asured before and after the expedition by respiratory gas analysis. Bo dy composition was estimated from skinfolds and body mass before and d uring the altitude sojourn. Subjects were in negative energy balance t hroughout the observation period (EI1 - ADMR = -2.9 +/- 1.8 MJ/day and EI2 - ADMR = -2.3 +/- 1.8 MJ/day based on a gross energy digestibilit y of 95%). The activity level, expressed as ADMR to basal metabolic ra te, was 1.56-2.39. The loss of fat mass (3.7 +/- 1.5 kg) represented 7 4 +/- 15% of the loss of body mass. Energy content of the feces was 21 kJ/g dry wt, and gross energy digestibility amounted to 85%. The ener gy deficit increased to 3.5 MJ/day after correction for the decreased energy digestibility. In conclusion, energy balance was not attained a t 6,542 m. The resulting energy deficit appeared to result mostly from malnutrition, and only a limited part could be attributed to malabsor ption.