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1 A Review of the Physiology and Nutrition in Cold and in High-Altitude Environments
Pages 3-58

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From page 3...
... Physiological Responses at High Altitudes .
From page 4...
... . 42 .42 .43 44 INTERACTIONS OF COLD AND n~ At111 Unto 46 SUMMARY 46 REFERENCES 47 PROJECT OVERVIEW Military operations are frequently conducted in locations where soldiers are exposed to desert, arctic, and high-altitude environmental extremes.
From page 5...
... on basal energy requireDoes cold or altitude exposure alter the requirement for nutrients other than energy? What is the sodium requirement for hard physical work in a cold environment?
From page 6...
... Aside from increased energy demands, do cold or high-altitude environments elicit an increased demand or requirement for specific nutrients?
From page 7...
... Military operational rations are the principal source of nutrients provided for the soldier in military operations in all environments. Therefore as 7
From page 8...
... In cold environments the basic three-ration per day provision is augmented with an additional fourth MRE or an energy supplement providing extra kcal. While the MRE can be consumed cold, individual ration heaters are provided since hot rations are more acceptable to soldiers in a cold environment.
From page 9...
... .. Metabolic Heat Production Heat production occurs as the result of voluntary muscular work, by involuntary (central nervous system [CNS]
From page 11...
... 11 ~ to ~ ~\ it # C`l ~t — x ~ ~ c~ ~ to ~ x ~ to =^ - ^ N ~ Ed to en ~ ~ \~)
From page 12...
... If voluntary exercise does not maintain body core temperatures during cold exposure, involuntary shivering responses are initiated, and heat production then may result from both forms of muscular work. Maximal energy expenditure by skeletal muscles may be reduced by cold exposure, if temperatures decline in muscle, body core, and/or blood.
From page 13...
... Severe losses of body weight associated with the complex stresses of prolonged military operations could also complicate the normal physiological responses to cold. Emphasis on maintaining an adequate intake of operational rations to prevent excessive weight loss in severe operational environments is important to sustain normal physiological responses to cold (IOM, 1 995a)
From page 14...
... For this discussion of cold stress, it is important to note that the CNS fails to maintain its temperature regulating functions during REM sleep (Jennings et al., 1993~.
From page 15...
... Prior exercise, prior food intake, and the menstrual cycle all influence core body temperatures during sleep. Giving meals on a precise time schedule appears to help synchronize the temperature regulating clock.
From page 16...
... Additional studies confirmed the value of mixtures of ephedrine with caffeine or theophylline in increasing heat production, decreasing heat debt, and reducing the lowering of body temperature in cold exposed individuals (Astrup et al., 1985, 1992; Dulloo and Miller, 1986; Dulloo et al., 1990~. These interesting results warrant additional studies to define further the benefits and disadvantages of the proposed treatment in improving the cold tolerance of human subjects, including further refinement of the most effective treatment modality.
From page 17...
... Other Causes of Cold-Induced Losses of Body Water Losses of respiratory water may also contribute to cold-induced dehydration. Water vapor pressure of cold air is considerably less than under thermoneutral conditions, so additional water can be lost when exhaling fully
From page 18...
... The obvious countermeasure to dehydration is to drink fluids, but this practice is not always possible. Major problems can arise from the logistical constraints in delivery of drinking fluids during military operations in cold environments.
From page 19...
... Until recently, attempts to determine the magnitude of the increase in energy requirements in the cold focused on estimation of food intake, under the assumption that in healthy, weight-stable individuals, intake represents need (Kark et al., 1948~. Studies of energy needs of troops living in cold environments, based on food intake, have suggested that energy needs range from 3,100 to 3,900 kcal/d, (41 to 52 kcal/kg/d for a 75 kg man)
From page 20...
... The answer to the question of whether undernutrition is a problem in the cold may hinge upon the activity levels of the personnel in question as well as the amount of rations consumed. In summary, energy requirements of 41 to 57 kcal/kg/d have been estimated for troops operating under conditions of arctic cold.
From page 21...
... As discussed above, the increase in energy requirements in the cold is attributable to thermoregulation and to increased physical activity. In Chapter 7 of this volume, Young and colleagues review the energy requirements for thermogenesis, which occurs as a result of increased voluntary muscular activity, or in the absence of voluntary activity, involuntary muscle activity (shivering)
From page 22...
... The question of whether shivering thermogenesis, like voluntary muscle activity, is dependent upon glucose derived from glycogen and can be enhanced by increasing dietary carbohydrate has attracted a great deal of interest since the discovery of the crucial role of muscle glycogen in voluntary muscle activity and the effect of dietary carbohydrate loading in improving physical performance. Contradictory findings have emerged concerning the contribution of blood glucose versus muscle glycogen stores as energy sources for involuntary shivering (Jacobs, 1993; Martineau and Jacobs, 1989; Young et al., 19893.
From page 23...
... In summary, energy is needed in the cold to fuel both voluntary physical activity and involuntary shivering. As in thermoneutral conditions, voluntary muscular activity is fueled primarily by carbohydrate, and at high levels of activity, a minimum of 400 g carbohydrate is recommended per day to replace depleted glycogen stores.
From page 24...
... The authors commented, however, that the protein content of an MRE plan is too high for cold weather consumption. This is because the increase in urea excretion that would result from metabolism of the extra protein would increase the requirement for water, and the availability of drinking water is often restricted in cold environments.
From page 25...
... The use of the lower protein ROW or supplementation of the MRE with primarily fat- and carbohydrate-containing supplements would be beneficial in minimizing the increase in protein in the face of scarce water supplies. A protein snack prior to retiring to sleep could provide some benefit from the thermic effect of protein in cold environments.
From page 26...
... APPETITE AND BEHAVIOR CHANGES IN THE COLD In several long-term studies in cold environments, significant body weight pains were observed (see LeBlanc Chapter 12 in this volume)
From page 27...
... Changes in diet alone seem unlikely to be the cause of the weight gain since the foods used in some of the studies were reported to be less palatable than foods consumed before the study. It is well known that a reduction in food intake does not simultaneously occur with a reduction in physical activity.
From page 28...
... and over. Integration of these various studies can be difficult due to: · numerous confounding variables (e.g., duration and severity of any coexisting physical activity, harsh environmental conditions and temperatures, and/or variations in fluid and food intake)
From page 29...
... The curve "breaks" at about 14,110 ft (4,300 m) , at which point hemoglobin saturation is already decreased to 85 percent of that seen at sea level.
From page 30...
... Plasma volume falls, and heart rate increases. Basal energy requirements are elevated in individuals living at altitude, and total energy requirements are elevated in those performing work at altitude.
From page 31...
... Few studies have had adequate experimental controls for the insufficient dietary intake observed. This dietary insufficiency could result in diuresis from the excretion of breakdown products of lean and fat tissues.
From page 32...
... At moderately high altitudes, losses of body fluids are proportional to losses in body weight, and there are significant decreases in plasma volume (Jain et al., 1980, 1981; Singh et al., 1986, 1988, 1990~. In addition, there are uncontrolled shifts of fluid out of the vascular compartment, which, along with the initial fall in total body water, help lower the stroke volume.
From page 33...
... Work Capacity (VO2 max) Months to Years 1~ ~~:J~: FIGURE 1-1 Approximate size, direction, and temporal changes that occur during acclimatization to 14,000 to 15,000 ft (4,267 to 4,572 m)
From page 34...
... Subacute Mountain Sickness A new syndrome, termed subacute mountain sickness, was observed in healthy young soldiers who had spent several months at extremely high altitudes of approximately 22,000 ft (6,706 m) (Anand et al., 19909.
From page 35...
... . As pointed out above, some of this weight loss may be a result of diuresis, other contributing factors include a decline in appetite, which accounts for a deficit of almost 200 kcal/d in most studies, and an increase in basal energy needs, which accounts for almost 300 kcal/d.
From page 36...
... Some investigators claim that women acclimatize better than men (Hannon et al., 1976) in that basal metabolic rates and appetite appeared to return toward sea level values more rapidly in women studied at high altitudes than in men.
From page 37...
... Military operations at high altitudes may require even greater increases in energy expenditure. Basal metabolic rates at altitude may initially be elevated 20 to 30 percent above those at sea level.
From page 38...
... However, no research in human subjects has been able to attribute the anorexia of acute mountain sickness to a possible physiological mechanism. The metabolic fuels used to supply energy requirements during military operations at high altitudes are derived from both dietary sources and preexisting body stores.
From page 39...
... The implication of these data is that the loss of lean body mass and resulting negative nitrogen balance are due entirely to the negative energy balance caused by anorexia and increased metabolic rate and not to an increase in protein requirements per se. Butterfield et al.
From page 40...
... should be employed to encourage soldiers to eat their rations and thereby meet their energy needs and avoid negative nitrogen balance. Vitamins As in the case of cold exposure, no scientific basis was found to recommend increasing dietary recommendations for vitamins A, D, or K for individuals working at high altitudes (see Reynolds, Chapter 13 in this volume)
From page 41...
... Therefore, there appears to be no reason to advocate dietary intakes of iron greater than MRDA levels because of high-altitude exposure. Urinary excretion of zinc was not increased during an expedition carried out at moderate altitudes (8,000-14,000 ft t2,438~,267 m]
From page 42...
... The general and REM sleep deprivation may contribute to personality changes. The Effect of Altitude on Cognitive Performance and Mood States Physiological changes associated with exposure to altitudes above 10,000 ft (3,048 m)
From page 43...
... . In addition, the reduced food intake and body weight loss associated with hypoxia at high altitudes may exacerbate direct chemical effects of high altitudes on brain chemistry and function.
From page 44...
... Military Considerations As described in this report, the many adverse physiological reactions, physical, or cognitive performance difficulties, and mood changes at high altitudes, when combined with increased risks for mountain illnesses, trauma, ~ ,
From page 45...
... Increased energy needs at high altitudes result from an increase in basal energy needs as well as from strenuous activity. In order to prevent loss of body weight and muscle mass, the foods required to supply these needs must be provided, and they must also be compatible with logistical constraints.
From page 46...
... In both, diuresis occurs at least initially, energy requirements for work are increased, carbohydrate is well tolerated, and there appears to tee no advantage of extra protein over the usual requirement. Cold exposure tends to increase appetite and, over time, body weight may increase, whereas at high altitudes, appetite tends to be depressed, and body weight may decrease.
From page 47...
... Bhandari, and P Wahi 1990 Adult subacute mountain sickness a syndrome of congestive heart failure in man at very high altitude.
From page 48...
... Reeves 1992 Increased energy intake minimizes weight loss in men at high altitude.
From page 49...
... Sharp 1989 Field use of D2'8O to measure energy expenditure of soldiers at different energy intakes.
From page 50...
... Cymerrnan 1991 Doubly labeled water measurement of human energy expenditure during strenuous exercise.
From page 51...
... 1994 Food Components to Enhance Performance, An Evaluation of Potential PerforrnanceEnhancing Food Components for Operational Rations. A report of the Committee on Military Nutrition Research, Food and Nutrition Board.
From page 52...
... Askew 1993 Cold weather field evaluation of the 18-man Arctic Tray Pack Ration Module, the Meal, Ready-to-Eat, and the Long Life Ration Packet. Milit.
From page 53...
... Pandolf 1988 Respiratory and cardiovascular responses to cold stress following repeated cold water immersion. Undersea Biomed.
From page 54...
... Issekutz, Jr. 1962 Effects of dietary protein on physical work capacity during severe cold stress.
From page 55...
... Banderet, and H.R. Lieberman 1991a Relationships between symptoms, moods, and performance, and acute mountain sickness at 4700 meters.
From page 56...
... Terzioglu, M., and R Aykut 1954 Variations in basal metabolic rate at 1.85 km altitude.
From page 57...
... Pandolf 1989 Thermoregulation during cold water immersion is unimpaired by low muscle glycogen levels.


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