important to note that drinking slowed before plasma dilution had become significant. The attenuation of drinking was attributed to changes in sensations, such as stomach fullness and decreased mouth dryness (Rolls et al., 1980). In contrast to these young men, healthy elderly individuals do not experience normal thirst following fluid deprivation and do not rapidly restore their body fluids to predeprivation levels (Phillips et al., 1984b). In future studies, special consideration should be given to those factors that influence rehydration in the elderly.
A number of studies indicate that prolonged dehydration in situations such as intense exercise or thermal dehydration in a desert environment is associated with voluntary dehydration in which insufficient fluid is consumed to restore body fluids (Hubbard et al., 1984). It is clear, however, that the taste and temperature of the availabel fluids can influence the rate of rehydration.
The taste of the availabel drinks is a major determinant of the amount consumed. There are many factors that influence how good a particular drink tastes to an individual. For example, the cultural background of the individual (Rozin and Vollmecke, 1986), previous experience with the drink (Pliner, 1982), and the time of day (Birch et al., 1984) can affect palatability. Even within an individual, palatability is not constant. Dehydration can increase the pleasantness of fluids, whereas rehydration decreases the pleasantness (Rolls and Rolls, 1982). The decrease in pleasantness can, however, be specific to the particular fluid being consumed, so if the goal is to increase fluid intake, switching to a different drink will help to maintain consumption (Rolls, 1986). It has been shown that variety can increase fluid consumption. Nondeprived subjects, under the pretext of a tasting experiment, consumed three drinks successively, with a 10-min period allowed for each drink, under three different conditions: three different flavors (low-calorie orange, lemon, and lime drinks), one flavor only, or water alone with no flavor. More (22%) was consumed in the three-flavor condition than in the no-flavor condition, and more (99%) was consumed in the one-flavor condition than in the no-flavor condition (Rolls and Rolls, 1982).
It is well known that adding sweeteners to drinks leads to increased fluid intake (Rolls, 1987). Soft drinks are consumed in large quantities in the absence of physiological need. This excess fluid does not matter as long as the kidneys are functioning normally, but palatable drinks can potentially induce dangerous overhydration when kidney function is impaired (Rolls et al., 1978). Surprisingly little is known about the effects of soft drinks on the