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FLUID REPLACEMENT AND HEAT STRESS
focuses on the first four of these factors in their relation to gastric emptying, with some thought to their application to the needs of the military.
Early studies of gastric emptying conducted by J. N. Hunt and coworkers (Elias et al., 1968) demonstrated that the presence of mono- and disaccharides slowed the rate of gastric emptying. The magnitude of slowing was generally proportional to the CHO concentration in the test meal. Glucose was shown to be more effective, per osmole, in slowing gastric emptying than galactose. Fructose was shown to be relatively ineffective in slowing gastric emptying. The hypothesized mechanism for the delay of gastric emptying by ingestion of CHO was stimulation of duodenal osmoreceptors. This hypothesis has been supported by studies in which the infusion of glucose into the duodenum produced a profound and long-lasting suppression of gastric emptying (Brener et al., 1983). In a paper that defined the paradigm for exercise-gastric emptying work in the United States, Costill and Saltin (1974) noted a progressive decrease in the rate of gastric emptying with increases in the glucose concentration of the test meal. Their results are summarized in Figure 6-1. Coyle et al. (1978) compared the rate of gastric emptying for three commercially availabel drinks, all glucose/sucrose based, and for water. They noted a decrease in the rate of gastric emptying at CHO concentrations greater than 2.5 g per 100 ml. As with the data of Costill and Saltin (1974), the emptying characteristics of the drinks tested by Coyle et al. (1978) seemed to follow osmotic lines (Figure 6-1). Similar data were presented by Foster et al. (1980) with glucose concentrations as great as 40 g per 100 ml (Figure 6-1).
More recent studies with glucose polymers have likewise suggested a reduction in the rate of gastric emptying somewhat proportional to the total CHO concentration. Although these differences are usually presented in the context of the purported advantage of glucose polymers over that of simple CHO relative to gastric emptying, it appears that the same basic response to increasing CHO concentration is followed. This is well illustrated in Figure 6-2, which compares the gastric emptying of various concentrations of glucose and glucose polymers. There has been less systematic work with glucose polymers; however, these early data (Foster et al., 1980) are generally supported in the literature. Seiple et al. (1983) reported no difference between 5% and 7% glucose polymer-fructose drinks. However, Seiple et al. (1983) used 30- and 60-min emptying periods. Examination of