Hamad N., Travis S.
Climbers lose weight above 5,000 m, which impairs physical performance and reduces safety margins. Although widely assumed to be due to energy imbalance, with expenditure exceeding nutritional intake, weight loss has been observed in mountaineers at rest at high altitude. Basal metabolic rate is increased and some evidence points to carbohydrate malabsorption. This chapter examines how the normal physiological processes of carbohydrate, fat, and protein absorption change at altitudes above 5,000 m, in a standard format briefly describing normal physiology, experimental models, and then field studies at altitude. Other aspects of gut function, from gastric acid secretion to mucosal morphology, mesenteric blood flow, motility, liver function, and the effect of hypoxia inducible factor on gut function are then described before gastrointestinal diseases in short-term visitors and residents at high altitude are addressed.