Body Composition and Body Weight Changes at Different Altitude Levels: A Systematic Review and Meta-Analysis

Muscle structural changes during typical mountaineering expeditions to the Himalayas were assessed by taking muscle biopsies from 14 mountaineers before and after their sojourn at high altitude (greater than 5000 m for over 8 weeks). M. vastus lateralis samples were analyzed morphometrically from electron micrographs. A significant reduction (-10%) of muscle cross-sectional area was found on CT scans of the thigh. Morphologically this loss in muscle mass appeared as a decrease in muscle fiber size mainly due to a loss of myofibrillar proteins. A loss of muscle oxidative capacity was also evident, as indicated by a decrease in the volume of muscle mitochondria (-25%). In contrast, the capillary network was mostly spared from catabolism. It is therefore concluded that oxygen availability to muscle mitochondria after prolonged high-altitude exposure in humans is improved due to an unchanged capillary network, supplying a reduced muscle oxidative capacity.

High altitude exposure is often accompanied by weight loss. Postulated mechanisms are a reduction of nutritional energy intake, a reduction of intestinal energy uptake from impaired intestinal function and increased energy expenditure. Beyond the field of altitude, there are good reasons for renewed interest in the relationship between hypoxia and energy balance. The increasing prevalence of obesity and associated comorbidities represent a major health concern. Obesity is frequently associated with sleep disorders leading to intermittent systemic hypoxia with deleterious cardiovascular and metabolic consequences. Hypoxic regions may be present within hypertrophic white adipose tissue leading to chronic systemic inflammation. Among the increasing number of people commuting to altitude for work or leisure, obesity is a risk factor for acute mountain sickness. Paradoxically, exposure to intermittent hypoxia might be considered as a means to lose body mass and to improve metabolic risk factors. Daytime exposure to intermittent hypoxia has been used to treat hypertension in former Soviet Union countries and is now being experimented elsewhere. Such intermittent hypoxic exposure at rest or during exercise may lead to improvement in body composition and health status with improved exercise tolerance, metabolism and systemic arterial pressure. Future research should confirm whether hypoxic training could be a new treatment strategy for weight loss and comorbidities in obese subjects and elucidate the underlying mechanisms and signalling pathways. © 2013 The Authors. obesity reviews © 2013 International Association for the Study of Obesity.

The reason for weight loss at high altitudes is largely unknown. To date, studies have been unable to differentiate between weight loss due to hypobaric hypoxia and that related to increased physical exercise. The aim of our study was to examine the effect of hypobaric hypoxia on body weight at high altitude in obese subjects. We investigated 20 male obese subjects (age 55.7 +/- 4.1 years, BMI 33.7 +/- 1.0 kg/m(2)). Body weight, waist circumference, basal metabolic rate (BMR), nutrition protocols, and objective activity parameters as well as metabolic and cardiovascular parameters, blood gas analysis, leptin, and ghrelin were determined at low altitude (LA) (Munich 530 m, D1), at the beginning and at the end of a 1-week stay at high altitude (2,650 m, D7 and D14) and 4 weeks after returning to LA (D42). Although daily pace counting remained stable at high altitude, at D14 and D42, participants weighed significantly less and had higher BMRs than at D1. Food intake was decreased at D7. Basal leptin levels increased significantly at high altitude despite the reduction in body weight. Diastolic blood pressure was significantly lower at D7, D14, and D42 compared to D1. This study shows that obese subjects lose weight at high altitudes. This may be due to a higher metabolic rate and reduced food intake. Interestingly, leptin levels rise in high altitude despite reduced body weight. Hypobaric hypoxia seems to play a major role, although the physiological mechanisms remain unclear. Weight loss at high altitudes was associated with clinically relevant improvements in diastolic blood pressure.