Human energy expenditure, allocation, and interactions in natural temperate, hot, and cold environments

Objective: The aim of this research is to analyze how energy is allocated differently in temperate, hot, and cold environments among National Outdoor Leadership School students. Method: Basal metabolic rate, physical activity, thermoregulation, and the thermic effect of food were estimated to determine the total energy expenditure and energy allocation differences among a group of healthy, highly active adults (N=59) participating in National Outdoor Leadership School courses in the western United States. Two of these courses took place in both hot and temperate climates (N=22) and the other two in both temperate and cold climates (N=28). Data from a pilot study (N=6) in a temperate climate were also included. Each climate regime lasted for one month. Results: Total energy expenditure values were statistically equivalent in temperate and hot climates (p=.97). However, subjects experienced significantly higher total energy expenditures in cold climates (p<.0001), expending an additional similar to 1550 kcal day(-1). There is a significant interaction between physical activity and thermoregulation, such that physical activity reduces thermoregulatory costs in cold climates, but increases it in hot climates. Conclusions: Dissection of the energy budget revealed that total energy expenditure is significantly higher in cold climates. This is due to a combination of high levels of physical activity and high thermoregulatory costs. High levels of physical activity may substantially lower the cost of thermoregulation in cold climates, and this interaction should be taken into account when estimating TEE.