Western Diet Impairs the Ability to Use Energy State Cues in Appetitive Control

Rats can learn about their deprivation states to predict the delivery of sucrose pellets. Previous research indicates that learning about internal cues competes with learning about external cues in chow-fed rats. The present research examined the effects of consuming a diet high in saturated fat and carbohydrates, the Western diet (WD), on the ability to use interoceptive energy state cues relative to external, food-related cues in discriminative control. In Experiment 1, male rats were first trained to asymptote on a deprivation intensity discrimination problem. Training was then suspended, and rats were matched on performance to receive WD or chow. Following 6 weeks on the diets, retention performance was assessed. External light and tone cues were then introduced to form compound discriminative stimuli with deprivation cues. After training with the compound, rats' learning about deprivation cues was tested first by removing external cues and finally by reversing the external cue reinforcement contingency while the deprivation cue contingency remained constant. When external cues were absent or reversed, WD-fed animals showed weaker discrimination compared to the end of training baseline, while CHOW-fed animals' performance did not differ from baseline. Experiment 2 investigated how rats' susceptibility to WD-induced weight gain affects the relative salience of internal deprivation versus external food cues in the acquisition of a compound external cued deprivation discrimination problem. Following 20 days on WD or chow, rats were categorized as diet-induced obese (DIO) or diet-resistant (DR). They were then trained and tested, along with chow controls, on the compound cued deprivation discrimination. Throughout the study, DR rats gained significantly more weight than CHOW rats and significantly less weight than DIO rats. While Groups DIO and DR showed discrimination deficits when external cues were removed or reversed, CHOW rats maintained discrimination throughout the experiment. These results suggest that WD consumption diminished these rats' ability to use energy state cues relative to food cues in discriminative control. A WD-induced impairment in the ability to use deprivation cues to control appetitive behavior could promote excess intake and obesity.