This chapter will discuss both the direct and indirect effects on caloric intake of drinking water and nonalcoholic beverages. A brief overview of research addressing the sensory, psychological, and environmental influences on fluid consumption will also be presented to provide background information and a rationale for recommendations found at the end of the chapter.

The direct contribution of beverages to caloric intake in the field can be assessed from a data base of field study results that are part of the U.S. Army Natick Research, Development and Engineering Center's (NRDEC) ration testing program. While some of NRDEC's work on drinking behavior involves experiments designed specifically to determine the effects of sensory or situational factors on beverage consumption, other information on drinking behavior stems from the ration testing program in which rations are evaluated in realistic military field settings. The methodology for these field studies includes monitoring food and beverage intake and subjects' body weights and collecting acceptance ratings of rations and associated products such as packaging, heating devices, and utensils. In collaboration with the U.S. Army Institute of Environmental Medicine (USARIEM), NRDEC also monitors urine-specific gravity to assess hydration status. Data from these field studies serve not only as the basis for evaluating rations and related products, but they also provide insight into human eating and drinking behavior.

This discussion will focus on beverage consumption in field studies where the Meal, Ready-to-Eat (MRE) was the sole source of sustenance. The MRE is the primary operational ration when troops are deployed, a time when hypohydration is most common (see Kramer, Chapter 17 in this volume). Beverage consumption data from field studies of the MRE are an excellent source of information to determine the contribution of beverages to daily caloric intake in the field because different versions of the MRE have been tested repeatedly in different environments. The MRE data base is also the most extensive of the ration data bases.

Over the past 10 years, some of the food components in the MRE have been improved, others have been dropped, and new products have been added. A summary of these changes can be found in Chapter 7 of this volume by Darsch and Brandler. The beverage components, all of which are found in powdered form, have also changed over the years. The earliest versions of the MRE included a package of coffee in each meal and cocoa in 7 of the 12 menus. In response to feedback from soldiers and evidence indicating that flavoring enhanced water intake in the field (Engell and Hirsch, 1991), a