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.

Previous studies of the erythropoietic response to hypoxia in high-altitude natives suggest that the hematocrit and hemoglobin values in Himalayan natives (Sherpas) are lower than expected for the altitude, perhaps because of a genetic adaptation. However, differences in sampling techniques and experimental methods make comparisons difficult. Our studies were carried out to compare the erythropoietic response with the same altitude in age-matched natives of the Himalayas and Andes by the same experimental techniques. Healthy male subjects were selected in Ollagüe, Chile (n = 29, 27.3 +/- 5.9 yr) and in Khunde, Nepal (n = 30, 24.7 +/- 3.8 yr). Both of these villages are located at 3,700 m above sea level. Hematologic measurements confirmed lower hematocrit values in Nepal (48.4 +/- 4.5%) than in Chile (52.2 +/- 4.6%) (P less than 0.003). When subjects were matched for hematocrit, erythropoietin concentrations in Chile were higher than in Nepal (P less than 0.01). Detailed measurements of blood O2 affinity in Nepal showed no differences in shape or position of the O2 equilibrium curve between Sherpas and Western sojourners. Our results indicate that although Quechua Indians have higher hematocrits than Sherpas living at the same altitude, nevertheless they may be functionally anemic.

Physical performance and regeneration after exercise is enhanced by the ingestion of proteins and carbohydrates. These nutrients are generally consumed by athletes via whey protein and glucose-based shakes. In this study, effects of protein and carbohydrate on skeletal muscle regeneration, given either by shake or by a meal, were compared. 35 subjects performed a 10 km run. After exercise, they ingested nothing (control), a protein/glucose shake (shake) or a combination of white bread and sour milk cheese (food) in a randomized cross over design. Serum glucose (n = 35), serum insulin (n = 35), serum creatine kinase (n = 15) and myoglobin (n = 15), hematologic parameters, cortisol (n = 35), inflammation markers (n = 27) and leg strength (n = 15) as a functional marker were measured. Insulin secretion was significantly stimulated by shake and food. In contrast, only shake resulted in an increase of blood glucose. Food resulted in a decrease of pro, and stimulation of anti-inflammatory serum markers. The exercise induced skeletal muscle damage, indicated by serum creatine kinase and myoglobin, and exercise induced loss of leg strength was decreased by shake and food. Our data indicate that uptake of protein and carbohydrate by shake or food reduces exercise induced skeletal muscle damage and has pro-regenerative effects.

Plasma renin activity (PRA), serum angiotensin-converting enzyme (ACE) activity, and plasma aldosterone concentration (PAC) were measured in 15 subjects at sea level and at high altitude. Previous work has shown that on first ascent to altitude PAC and ACE are reduced, whereas PRA may be raised or reduced. After 2-4 wk at 6,300 m all hormones had returned to within +/- 10% of sea-level values. In seven subjects PRA and PAC were measured when exercise stopped. PRA and PAC were both elevated, PRA more than PAC; i.e., the PAC response to PRA was markedly blunted. Since ACE activity was normal, it is suggested that there may be down regulation, i.e., reduction in density of angiotensin II receptors on the adrenal cortex and/or induction of enzymes which degrade angiotensin II. This mechanism apparently protects the subjects from very high levels of PAC and sodium retention when hypoxia and exercise raise PRA to very high levels.

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