Committee on Military Nutrition Research: Activity Report 1992-1994 (1994)

Military personnel must often perform heavy physical activity in very hot environments during training or under combat conditions. The high sweat rates can lead to dehydration, resulting in performance decrements through elevated heart rates, reduced sweat rates, and elevated body temperature and threats to health. Glucose-electrolyte solutions have been found useful in rehydration and in preventing dehydration. Carbohydrate is essential as it facilitates sodium and water absorption. Other ions may or may not be needed, depending on losses in sweat or from the gastrointestinal tract. Advances in exercise physiology demonstrate the value of carbohydrate solutions in providing energy for muscular activity in vigorous endurance events that last at least one hour. A carbohydrate-electrolyte beverage, therefore, could be useful in providing glucose to sustain muscular activity in troops involved in heavy physical activity for long periods. The sodium in these beverages might also be especially important since garrison or field rations may be reduced in sodium to meet prudent dietary guidelines.

In February 1989, the Committee on Military Nutrition Research held a workshop on the subject of fluid replacement and military performance at the request of the U.S. Army Medical Research and Development Command. The Committee was asked specifically to address twelve questions on the potential utility of fluid replacement, including carbohydrate-electrolyte beverages, in enhancing sustained military performance in military operations. The Committee's report, Fluid Replacement and Heat Stress, (Marriott and

Rosemont, 1991) responds to these questions and makes recommendations for future research. Fifteen papers were presented at the workshop, ranging in subject from the body's accommodation to heat and exercise to palatability issues in enhancing fluid intake. The committee report includes these invited papers. This summary is prepared for the third printing of Fluid Replacement and Heat Stress (Marriott, 1994), a report that continues to be popular and for which there is a steady demand for copies.

At a decrease of 3 percent in body weight due to dehydration, the capacity to perform physical work decreases substantially. Research reported at the workshop made evident that a fluid replacement solution may play an important role in preventing fluid, electrolyte, and glycogen depletion, thereby maintaining or improving a soldier's performance. Depending on the physical demands of the military activity and prevailing environmental conditions, the composition of the replacement fluid might vary.

The Committee recommended that the Surgeon General of the Army evaluate the use of carbohydrate-electrolyte fluid replacement products as an aid to maintaining proper hydration of soldiers and assess their effectiveness in maintaining and enhancing the physical and cognitive performance of the soldiers during training activities and field operations. Specifically, the Committee recommended that fluid-replacement products provide approximately 20 to 30 meq of sodium per liter, 2 to 5 meq of potassium per liter, and chloride as the only anion. Carbohydrate content was recommended in a concentration of 5 to 10 percent as glucose, sucrose, malto-dextrin, or other complex carbohydrate.

The workshop provided investigators and product formulators with guidance in the development and testing of carbohydrate-electrolyte fluid replacement products for use by the military. Continued research is needed on energy, electrolyte, and fluid requirements in different environmental and operational conditions that require different types of physical activity. More studies are also needed to provide a better understanding of the factors affecting liver and muscle metabolism and injury during heat stress and those important in preventing muscle injury during heat stress and enhancing muscle recovery. The Committee also recommended research into manipulating the flavor and color of fluid replacement products to promote fluid intake, and to

the potential benefits of adding additional magnesium, bicarbonate, and phosphate to compensate for gastrointestinal losses due to diarrhea or other disturbances.

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The full conclusions and recommendations from this report are included in Appendix H.