Define Basal Metabolism and Energy Expenditure at High Altitude?
The energy and nutrient requirements depend upon total energy expenditure and metabolic rate of the individual. Total energy expenditure (TEE), as you may recall studying in Unit 2, has three components i. e, basal metabolic rate (BMR), diet induced energy expenditure and expenditure related to activities. Short-term measurements or gas exchange during field studies suggest that altitude hypoxia increases BMR. Some studies show these acute increases (20-30%) to be sustained for 1-2 weeks while others show elevation to be maintained throughout a three week stay. The decline in BMR with acclimatization seems to be the result of an inadequate energy intake and a decrease in metabolically active tissue that accompanies weight loss. The decrease in metabolic rate is expected to be approximately 20-25 Kcal /dl kg lean tissue lost. Finally, the stress of high altitude (HA) decreases over a period of time as indicated by a decrease in the epinephrine levels in both men and women.
Increased energy expenditure ranging from 6.9 to 25% has been reported. As regards the energy cost of various activities under stationary conditions, there is no variation as compared to the sea levels. Increased energy expenditure may be due to the heavier load carried by the troops, as cold protective garments and efforts in walking in snow bound hilly terrain.