1. It has been suggested previously that people in developed countries do not expose themselves to cold severe enough to induce a metabolic response. The energy expenditure, as both heat production and total heat loss, of nine women was therefore measured continuously while each lived for 30 h in a whole-body calorimeter on two occasions, one at 28° and the other at 22°. All subjects followed a predetermined pattern of activity and food intake. The environmental conditions were judged by the subjects to be within those encountered in everyday life. In the standard clothing worn, 28° was considered to be comfortably warm but not too hot, while 22° was judged to be cool but not too cold.
2. Heat production for 24 h was significantly greater at the lower temperature, by (mean ± SE) 7.0 ± 1.1%. The range was between 2 and 12%. Total heat loss was also significantly greater, by 6%, and there was a large change in the partition of heat loss. At the lower temperature sensible heat loss increased by 29% while evaporative heat loss decreased by 39%.
3. Resting metabolism measured in the morning 12–13 h after the last meal was significantly greater at 22° than at 28°, whereas there was no difference when the resting measurement was made for 2.5 h following a meal.
4. In conclusion: (a)environmental temperature may play a more important role than was previously recognized in the energy balance of those living in this country, and (b) there is an indication of at least a partial replacement of cold-induced by diet-induced thermogenesis in man.
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