Differential reinforcing and satiating effects of intragastric fat and carbohydrate infusions in rats

Food intake and preferences are modulated by the postingestive satiating an d reinforcing actions of nutrients. This experiment compared the feeding ef fects of isocaloric intragastric (i.g.) carbohydrate (maltodextrin) and fat (corn oil) infusions in food-restricted rats fed low-fat (12% fat kcal) or high-fat (48% fat kcal) diets. In Experiment 1, the rats were given one fl avored saccharin solution (CS+C) paired with i.g. carbohydrate infusions, a second flavor (CS+F) paired with i.g, fat infusions, and a third flavor (C S-) paired with i.g. water infusions during 30-min one-bottle training sess ions. In subsequent two-bottle tests, the rats preferred both CS+s to the C S- (68-83%) and the CS+C to the CS+F (68-70%). In Experiment 2, the feeding inhibitory effects of the nutrient infusions on an ongoing meal (satiation test) or a subsequent meal (satiety test) were compared. The intake of a p alatable Polycose+saccharin solution was suppressed by a concurrent carbohy drate infusion but not by a fat infusion. Also, i.g. carbohydrate preloads suppressed the intake of a subsequent (30-180 min) mixed carbohydrate+fat t est meal more than did i.g. fat preloads. The satiety effects of the fat pr eloads were more pronounced in rats fed the low-fat diet than in rats fed t he high-fat maintenance diet. Diet composition did not reliably influence t he preference conditioning and satiation effects of the nutrient infusions. These results confirm prior reports that fat is less satiating than carboh ydrate, and further demonstrate that i.g. carbohydrate infusions condition a stronger flavor preference than fat infusions. (C) 1999 Elsevier Science Inc.