and the body's countermeasures to heat loss, focusing on thermoregulation and its effects on performance. On the nutritional side, cold-induced diuresis is a concern given the effects of cold stress on fluid balance. Data on energy needs in cold environments are presented in the committee's discussion of macronutrients, vitamins, and minerals. At high altitudes, physiological responses can be detrimental to physical and cognitive performance given the debilitating impact of acute mountain sickness (AMS) and related altitude illnesses. Nutrient requirements at altitude often depend on rate of ascent and duration of stay. The combination of cold and altitude presents new considerations given the differences in physiological response and nutritional needs for these environmental extremes.

The CMNR answers the questions posed by the Army in Chapter 2 before presenting their recommendations, suggestions for future research, and conclusions. For work in cold and in high-altitude environments, the importance of water discipline and the availability of safe fluids for drinking are critical because fluid imbalance is detrimental to performance. To insure that energy intake equals energy expenditure, high energy, palatable rations must be supplied, and troops should be educated regarding changes in physical and cognitive performance at environmental extremes and their countermeasures. In an era of rapid redeployment, soldiers who have not regained lean body mass lost in previous operations should not be sent to cold or to high-altitude environments until lean body mass is regained. Future research in cold and in high-altitude environments should focus on defining water requirements and how to meet them; encouraging the maintenance of body weight and composition; and determining the best ratio of macronutrients, vitamins, and minerals.