The effect of low energy diets on postprandial gallbladder motility. The effect of a low energy diet on the postprandial biliary response was examined in four male volunteers. Gallbladder volume and ejection rate were measured by real-time ultrasonography before and after 6-7 days on a low energy diet (2400 kcal/day). Two diet types were examined: isocaloric, isovolumic; and hypocaloric, isovolumic. These diets differed in that a nonnutrient fluid was administered intravenously during the postabsorptive phase of the hypocaloric diet. The postprandial gallbladder contraction response was the same on the two diets and increased following oral and intravenous infusions of glucose (50 g), corn oil (50 g), and Na acetate (100 mg). The results of these experiments suggest that the gallbladder ejection rate and contraction response to a meal are unaffected by a decrease in energy intake. Therefore, the gallbladder volume tends to become larger and the frequency of gallbladder contraction increases after a low energy diet. These data suggest that gallbladder volume is influenced by the amount of energy consumed but is not affected by the type of diet.