Flavor preference conditioning as a function of fat source.
Rats learn to prefer foods based, in part, on postingestive nutrient actions. This study compared the effectiveness of intragastric (IG) infusions of fat emulsions which varied in their fatty acid composition (chain length and saturation) to condition preferences for flavored saccharin solutions. In Experiment 1, food-restricted rats were trained (30 min/day) with one flavor (CS+CO) paired with IG corn oil (CO) and a second flavor (CS+MCT) paired with IG medium chain triglyceride (MCT); the fats were prepared as isocaloric emulsions. A third flavor (CS-) was paired with IG water. The rats subsequently showed a strong preference for the CS+CO (84%) and a weaker preference for the CS+MCT (65%) relative to the CS-. In a direct choice test, the CS+CO was preferred to the CS+MCT by 75%. In Experiment 2, new rats trained with flavors paired with IG corn oil and beef tallow (BT) infusions learned to prefer both the CS+CO (89%) and the CS+BT (82%) relative to the CS-, and preferred the CS+CO to the CS+BT by 67%. The same rats were trained with three new flavors paired with IG infusions of corn oil, vegetable shortening (VS), and water. The rats strongly preferred both the CS+CO (91%) and CS+VS (86%) over the CS-, and they preferred the CS+CO to the CS+VS by 64%. In Experiment 3, new rats trained with corn oil and safflower oil (SO) paired flavors preferred both the CS+CO and CS+SO to the CS-, and equally preferred the CS+CO and CS+SO in two-bottle tests. The rats were also given one-and two-bottle tests with the various fat emulsions and their preference profile was consistent with their conditioned preferences for the flavored saccharin solutions. These findings demonstrate that many different fat sources can condition flavor preferences. Fats with high polyunsaturated content and/or lower saturated fat content are the most reinforcing.