Protein absorption and energy digestibility at high altitude

and energy digestibility at high altitude. J. Appl. Physiol. 73(6): 2425-2431, 1992.-To test the hypothesis that malabsorption of dietary protein is partly responsible for the weight loss ob-served during prolonged altitude exposure, six healthy male subjects [31.8 t 4.5 (SD) yr] received 15N-labeled soya protein by mouth and [15N]glycine intravenously at 122 and 5,000 m. From the subsequent 4-day total urine and fecal pools, the dif-ferent fractions of the administered 15N were determined by mass spectrometry. Weight and skinfold thickness were mea-sured at the beginning and end of the altitude exposure. In addition, the overall digestible energy of the diet at altitude was assessed by a &day diet control and adiabatic bomb calorime-tric assessment of the energy content of the corresponding fe-cal pool. The average decrease of the subjects ’ weight during altitude exposure was 3%. Loss of fat mass at altitude esti-mated from the skinfold measurements was 9%. Protein ab-sorption, calculated as 100- [fecal excretion of 15N after inges-tion of 15N soya protein ( % of dose given)- fecal excretion of 15N after injection of i5N glycine ( % of dose given)], was not significantly impaired at altitude compared with sea level (96 vs. 97%, respectively), and overall digestible energy at altitude, calculated as 100- percent undigested gross energy in the feces, amounted to 96%. It is concluded that, at least up to an altitude of 5,000 m, malabsorption does not play a role in alti-tude-related weight loss, malabsorption; weight loss; body composition; climbing; hyp-oxia; nutrition SEVERAL STUDIES have reported weight loss during high-altitude exposure, and most authors consider this occur-rence to be an inevitable consequence of chronic hypo