Nutrition and the responses to extreme environments.

The calorie requirements of adequately clothed men living and working in a cold environment are not increased, except for the 2-5 percent increase in matabolic rate due to the "hobbling" effect of the heavy clothing. The energy requirements in the cold, as in a temperate environment, are primarily a function of body weight and level of physical activity. The discrepancies between studies of persons living in a hot environment are explainable and are primarily due to the level of protection from the heat. The increased requirements are probably due to the increased heat load imposed on the body by solar radiation and the extreme heat. The increased requirements, in all likelihood, are a combination of increased action by blood in heat transport, increased ventilation and heart rate, and increased action of the sweat glands plus the increase in metabolic rate due partially to elevation in body temperature. In view of some strong new evidence, the energy requirements are increased for individuals living and working in extremely hot environments. There is no evidence showing that modification of macro nutrient composition of the diet will enhance either heat tolerance or cold adaptation in humans. Recent studies indicate that high carbohydrate diets will improve tolerance during high altitude exposure.