Appetite at “high altitude” [Operation Everest III (Comex-’97)]: a simulated ascent of Mount Everest

The hypothesis that high-altitude weight loss can be prevented by increasing energy intake to meet energy requirement was tested in seven men, 23.7 +/- 4.3 (SD) yr, taken to 4,300 m for 21 days. Energy intake required to maintain body weight at sea level was found to be 3,118 +/- 300 kcal/day, as confirmed by nitrogen balance. Basal metabolic rate (BMR), determined by indirect calorimetry, increased 27% on day 2 at altitude and then decreased and reached a plateau at 17% above the sea level BMR by day 10. Energy expended during strenuous activities was 37% lower at altitude than at sea level. Fecal excretion of energy, nitrogen, total fiber, and total volatile fatty acids was not significantly affected by altitude. Energy intake at altitude was adjusted after 1 wk, on the basis of the increased BMR, to 3,452 +/- 452 kcal/day. Mean nitrogen balance at altitude was negative (-0.25 +/- 0.71 g/day) before energy intake was adjusted but rose significantly thereafter (0.20 +/- 0.71 and 0.44 +/- 0.66 g/day during weeks 2 and 3). Mean body weight decreased 2.1 +/- 1.0 kg over the 3 wk of the study, but the rate of weight loss was significantly diminished after the increase in energy intake (201 +/- 75 vs. 72 +/- 48 g/day). Individual regression lines drawn through 7-day segments of body weight showed that in four of seven subjects the slopes of body weight were not significantly different from zero after the 2nd wk. Thus weight loss ceased in four of seven men in whom increased BMR at altitude was compensated with increased energy intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Little is known about weight loss and changes in body composition at extreme altitude. As part of the American Medical Research Expedition to Everest in 1981 we measured body weight, body fat, limb circumferences, dietary intake, 72-h stool fats, and 5-h urine xylose excretion at various altitudes on Caucasian and Sherpa expedition members. In Caucasians, loss of body fat accounted for 70.5% of the mean 1.9-kg weight loss during the approach march at moderate altitude but for only 27.2% of the mean 4.0-kg weight loss during residence above 5,400 m. There was a significant proportionate decrease in arm and leg circumferences during residence above 5,400 m (1.5 and 2.9 cm, respectively). On the other hand, Sherpas, who arrived in Base Camp with half as much body fat as members (9.1% vs. 18.4%), maintained weight and limb circumferences during residence above 5,400 m. Fat absorption decreased 48.5% in three subjects, and xylose excretion decreased 24.3% in six of seven subjects at 6,300 m relative to sea level. It appears that muscle catabolism and malabsorption contribute significantly to weight loss at high altitude. High percent body fat does not protect against loss of muscle tissue. Sherpas do not appear susceptible to some of the changes affecting Caucasians.