Carbohydrate, fat, and protein condition similar flavor preferences in rats using an oral-delay procedure

Flavor preferences conditioned by carbohydrate (Polycose), protein (casein hydrolysate), and fat (corn oil) were compared using an oral-delay training method. In Experiment 1 separate groups of food deprived rats were trained to associate a CS+ flavor (e.g., grape-saccharin) with the delayed (10 min) presentation of isocaloric carbohydrate, protein, or fat sources. A CS- flavor (e.g., cherry-saccharin) was paired with the delayed presentation of an unflavored saccharin solution. In subsequent two-bottle tests the carbohydrate, protein, and fat trained groups displayed significant preferences for the CS+ over the CS-. In Experiment 2 each rat was trained to associate two new flavors with two of the three nutrients (e.g., orange with carbohydrate, and strawberry with protein). In subsequent two-bottle tests the rats equally preferred the two nutrient-paired flavors. Experiment 3 compared the preferences for the new CS+ flavors vs. the original CS-flavor. The rats displayed similar preferences for carbohydrate-, protein- and fat-paired CS+ over the CS-. The similar preferences obtained with the three different nutrients support the view that preference conditioning is mediated by the nutrients' caloric value. Other studies suggest, however, that nutrient-specific signals are also involved in the conditioning process.