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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations (1993)
Institute of Medicine (IOM)

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. "6. Energetics and Climate with Emphasis on Heat: A Historical Perspective." Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press, 1993.

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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations

TABLE 6-10 Possible Reasons for an Increase in Metabolic Rate in Hot Environments

Lack of acclimatization

Inefficient physical activity, psychomotor stress

Q10 effect, elevated body temperature

Greater sweat gland activity

Tachycardia

Increased pulmonary ventilation

Increased anaerobic metabolism

Increased RQ

Increased O2 debt

Increased lactate

Increased muscle glycogen utilization

Increased blood glucose utilization

Lessened skeletal muscle blood flow

NOTE: Q10 = adjustment in metabolic rate in relation to temperature change; RQ = respiratory quotient.

TABLE 6-11 Possible Factors That Would Tend to Reduce Metabolic Rate in Hot Environments

Complete acclimatization

Lower basal metabolic rate

Reduced physical activity, particularly intense activity

Lighter-weight clothing

Decreased appetite and associated dietary-induced

thermogenesis

ACCLIMATIZATION/ACCLIMATION

A finding that has been repeatedly documented is that unacclimatized personnel suffer the consequences when suddenly exposed to stressful environments, whether the environmental stress is heat, cold, or altitude. The psychological and physical stresses associated with combat only complicate the adverse situation. At issue is inadequate acclimatization, which with sudden exposure to heat, not only perpetrates physiological strain but lessens initiative and appetite, which negatively affects nutritional status including water balance. The acclimatization process with exposure to hot environments proceeds rapidly, being virtually complete in the working soldier within 10 days (Adolph, 1947; Buskirk and Bass, 1957; Dill, 1938). During this time, body weight is invariably lost due to undernutrition, but the weight may be subsequently regained in toto or in part. Johnson (1946), in his review, concluded that following acclimatization, dietary require-

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107
Front Matter (R1-R14)
Part I: Committee Summary and Recommendations (1-2)
1. Introduction and Backgrounds (3-44)
2. Conclusions and Recommendations (45-52)
Part II: Invited Presentations (53-54)
3. Physiological Responses to Excercise in Heat (55-74)
4. Effects of Excercise and Heat on Gastrointestinal Function (75-86)
5. Water Requirements During Excercise in the Heat (87-96)
6. Energetics and Climate with Emphasis on Heat: A Historical Perspective (97-116)
7. The Effect of Excercise and Heat on Mineral Metabolism and Requirements (117-136)
8. The Effect of Excercise and Heat on Vitamin Requirements (137-172)
9. Heat as a Factor in the Perception of Taste, Smell, and Oral Sensation (173-186)
10. Effects of Heat on Appetite (187-214)
11. Situational Influences on Food Intake (215-244)
Part III: U.S. Army Presentations: A Reevaluation of Sodium Requirements for Work in the Heat (245-246)
12. Responses of Soldiers to 4-gram and 8-gram NaCl Diets During 10 Days of Heat Acclimation (247-258)
13. Endocrinological Responses to Dietary Salt Restriction During Heat Acclimation (259-276)
14. Subjective Reports of Heat Illness (277-294)
Part IV: Committee Discussion Paper (295-296)
15. Food Intake, Appetite, and Work in Hot Environments (297-304)
Appendixes (305-306)
Appendix A: Military Recommended Dietary Allowances, AR 25-40; 1985 (307-328)
Appendix B: Nutritional Needs in Hot Environments -- A Selected Bibliography (329-352)
Appendix C: Biographical Sketches (353-362)
Index (363-378)