Energy metabolism increases and regional body fat decreases while regional muscle mass is spared in humans climbing Mt. Everest.

The objectives of the study were to determine regional changes in body composition, energy expenditure by means of doubly labeled water, and net energy balance during exposure to high and extreme altitudes (5,300-8,848 m). This study focuses on a subset of subjects who consumed the doubly labeled water (three base camp personnel and seven climbers). Regional body composition was determined by measuring skinfold thicknesses and circumferences at 10 different sites on the body. Energy expenditure was measured by doubly labeled water excretion. Discrepancies between actual energy expenditure and data obtained from diet records and body weight changes suggested a chronic underreporting of dietary energy intake, especially by those subjects who reached the highest altitudes. This underreporting may be due in part to diminished cognition or to a preferential focus on survival, rather than on filling out diet records accurately. Mean adjusted dietary intakes were 10.50 +/- 0. 65 MJ/d (2510 +/- 155 kcal/d) for those who remained at base camp, and 20.63 +/- 6.56 MJ/d (4931 +/- 1568 kcal/d) for those who climbed above base camp. Energy expenditure averaged 2.5-3.0 times sea level resting energy expenditure. Differential changes in regional body composition suggested a preferential loss of fat mass and a relative sparing of muscle mass, despite insufficient energy intake to maintain body weight.

Intakes of high fat and high carbohydrate foods by humans increased with exposure to increasing altitude during an expedition to Mt. Everest.

The objectives of the study were to determine total energy intakes, distribution of energy derived from the macronutrients, and the effects of increasing altitudes on energy and macronutrient consumption during exposure to high altitudes. High fat, low carbohydrate diets (35% and 50% of energy, respectively) or low fat, high carbohydrate diets (20% and 65% of energy, respectively) were provided to two groups of subjects for a 3-wk period. Groups then consumed the alternate diet for 3 wk, followed by a return to the original diet for the remaining 3 wk of the study. Free choice of individual items and amounts within each diet was permitted. Intake of food and fluid was determined by means of monitored entries in daily food records. Five subjects remained at Base Camp (5300 m) and 10 subjects climbed to altitudes up to and including the summit of Mt. Everest (8848 m). Subjects consumed an average of 10.22 +/- 4.57 MJ/d (2442 +/- 1092 kcal) energy while at Base Camp, with climbers consuming significantly more than Base Camp personnel [11.89 +/- 4. 88 vs. 7.87 +/- 2.98 MJ/d (2841 +/- 1167 vs. 1881 +/- 713 kcal/d), P 0.05). Contrary to previous reports, subjects in this study did not shift their food selections away from the high fat items towards high carbohydrate items.

Consumption of a dehydrated ration for 31 days at moderate altitudes: energy intakes and physical performance.

Energy intake, body weight, maximal work capacity, and measures of muscle strength and endurance were obtained from eight men who consumed a high-carbohydrate (CHO) dehydrated ration during a 31-day period of high activity at moderate altitudes. Data were collected 2 months before exposure to moderate altitudes (PRE), multiple times during the month's expedition at moderate altitudes (ALT), and after return from the expedition (RET). Work capacity per kilogram of body weight increased significantly from the PRE phase to the ALT phase. Mean energy intake averaged 2,354 +/- 71, 3,430 +/- 79, and 3,384 +/- 117 kcal/day during PRE, ALT, and RET, respectively; mean CHO intake during ALT was 595 +/- 13 g/day. Mean weight loss and reduction in body fat were significant: 1.9 +/- 0.9 kg and 18.9 +/- 10.1%, respectively. Energy deficits calculated from changes in body weight and composition during ALT ranged from 473 to 963 kcal/day, whereas the energy deficit estimated from the Harris-Benedict equation was only 194 kcal/day. The rigorous physical activity and exposure to moderate altitudes necessitated a high energy intake, approximating 3,800 kcal/day. The results indicate that physical performance and nutritional status are maintained when a high-CHO diet, consisting primarily of commercially available dehydrated foods, is consumed over a 31-day period of rigorous activity. However, weight loss and gastrointestinal distress were noted. These events might be minimized when a dehydrated ration is consumed, if dietary fat is substituted for some of the CHO.

Treatment of acute mountain sickness: hyperbaric versus oxygen therapy.

STUDY OBJECTIVES: To compare the benefits of simulated descent in a hyperbaric chamber with those of supplementary oxygen for the treatment of acute mountain sickness. DESIGN: A prospective study. SETTING: The Snake River Health Clinic in Keystone, Colorado, which has an altitude of 2,850 m (9,300 ft). TYPE OF PARTICIPANTS: Twenty-four patients who presented with acute mountain sickness. INTERVENTIONS: A simulated descent of 1,432 m (4,600 ft) was attained by placing the patients in a fabric hyperbaric chamber and pressurizing the chamber to 120 mm Hg (2.3 PSI) above ambient pressure. Patients were randomly assigned to either the hyperbaric treatment or treatment with 4 L of oxygen given by facemask; both treatments lasted for two hours. MEASUREMENTS AND MAIN RESULTS: Mean arterial oxygen saturation (SaO2) increased 7% (84 +/- 2% to 91 +/- 1%) with pressurization and 14% (83 +/- 4% to 96 +/- 1%) with oxygen during treatment over pretreatment levels. Symptoms of acute mountain sickness decreased as rapidly with pressurization as with oxygen treatment, despite significantly higher SaO2 in the oxygen-treated group during treatment. Symptomatic improvement was retained in both groups at least one hour after treatment. CONCLUSION: Simulated descent in a fabric hyperbaric chamber is as effective as oxygen therapy for the immediate relief of acute mountain sickness.