Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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11 Macronutrient Requirements for Work in Cold Environments
11 Macronutrient Requirements for Work in Cold Environments
Pages 189-202
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From page 189... ...
In addition, this information is necessary to ensure optimal performance in military field settings where sizable effort is required to transport required food supplies and associated materiel. During field exercises, either excessive or inadequate food supplies will hamper unit performance capacities.
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From page 190... ...
Studies Showing Increased Requirements Using Energy Intake Data Historically, reports concerning effects of environmental temperature on energy needs began shortly after the Second World War when Johnson and Kark (1947) demonstrated a relationship between climate and reported food intake in several groups of military personnel given unlimited access to food rations.
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From page 191... ...
Food was carefully weighed, and intake data were collected at mealtime, with subjects recording additional snack items separately. Mean caloric intake ranged between 3,100 and 3,400 kcal/d, with a mean of 3,200 kcal/d and no overall body weight change.
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From page 192... ...
In this study, individuals were carefully instructed and repeatedly reminded to be thorough in the self-reporting of food intakes. Military personnel who were training for jungle warfare similarly reported caloric intakes that were about 85 percent of expenditure levels as determined using DLW (Forbes et al., 1989~.
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From page 193... ...
Thus, particularly for experiments conducted in harsh environments, individual energy requirements are better determined using approaches based on energy expenditure. rather than those based on intake and balance.
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From page 194... ...
Studies Measuring Energy Requirements Using Energy Expenditure Data To determine with accuracy the overall caloric needs of military troops in the cold, methods are required that provide integrative, accurate measures of energy expenditure over a representative time period. One such method is DLW, which is well suited to such field studies in that it is noninvasive, does not involve use of radio tracers, and requires minimal subject compliance.
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From page 195... ...
During less extreme activities, energy expenditure averaged 3,632 kcal/d. Over the entire study these subjects' caloric requirements were 62 kcal per kg body weight per day as measured using DLW.
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From page 196... ...
Mechanism of Action of Effects of Cold on Metabolism Johnson and Kark (1947) were the first to speculate on the cause of increased energy requirements in the cold.
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From page 197... ...
The importance of this second component will depend on such factors as adequacy of thermal insulation of clothing worn to protect against heat loss, as well as environmental temperature7 windchill, and duration of cold exposure. It has been suggested that the lack of increased energy requirement observed in some studies is the result of subjects spending long periods indoors (Rodahl, 1954~.
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From page 198... ...
Among military personnel, Johnson arid Kark (1947) showed that troops consumed a consistent ratio of macronutrients regardless of environmental temperature (Table 11-3~.
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From page 199... ...
In summary, there appears to be no tendency on the part of military personnel toward a deliberate shift in the pattern of macronutrients consumed in colder climates. However, consistent with the high-fat diet of the indigenous cultures of the North, there is a suggestion that the macronutrient mixture is modified in the cold.
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From page 200... ...
AUTHORS' CONCLUSIONS AND RECOMMENDATIONS Although the majority of research in which energy requirement determination is based on measured or reported food intake is consistent with an increased requirement for energy in colder climates, some studies have found no difference compared to more temperate environments. The factors that contribute to this lack of difference include possible underreporting by study subjects and prolonged time spent indoors at warmer temperatures and low activity levels.
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From page 201... ...
Further study is required to elucidate the interaction of cold and physical activity on macronutrient utilization. Regardless of which macronutrient is oxidized preferentially in cold conditions, a major objective of field feeding studies should be to minimize body weight loss and, if possible, perfonnance capacity.
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From page 202... ...
Boyd In Comparison of energy intakes determined by food records and doubly labeled water in Press women participating in a dietary intervention trial.
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