Galactose consumption induces conditioned flavor avoidance in rats

Recent findings revealed that intragastric infusions of galactose conditioned a flavor avoidance in adult rats. To determine whether the galactose-conditioned avoidance was due to the infusion procedure, we investigated the flavor conditioning effect of orally consumed galactose. Food-restricted rats drank a flavored galactose solution, a flavored fructose solution and a flavored saccharin solution in separate one-bottle training sessions; grape, cherry and orange flavors were used. Because fructose is sweeter than galactose, saccharin was added to the galactose solution to increase its palatability. Pre- and posttraining preferences for the galactose and fructose solutions were evaluated in two-bottle choice tests. Also, preferences for the sugar-paired flavors were evaluated in two-bottle tests with the flavors presented in saccharin. In Experiment 1, rats were trained with flavored 80 g/L fructose, 80 g/L galactose + 2 g/L saccharin, and 2 g/L saccharin solutions (20 mL/d). Their preference for the flavored galactose solution changed (P < 0.01) from 76% (pretraining) to 19% (posttraining). The rats also avoided (P < 0.05) the flavor paired with the galactose solution in choice tests with the fructose-paired flavor and the saccharin-paired flavor. Similar pre- to posttraining preference reversals were obtained in Experiments 2 and 3, which used 20 g/L galactose and fructose solutions, and 20 g/L galactose and fructose solutions mixed with 20 g/L glucose, respectively. These findings, together with the intragastric infusion data, demonstrate that galactose has aversive postingestive consequences in adult rats even at low concentrations (20 g/L). Unlike lactose intolerance, which is due to intestinal malabsorption, this galactose-induced flavor avoidance is presumably due to the slow and incomplete postabsorptive metabolism of galactose.