Flavor preferences conditioned by high-fat versus high-carbohydrate diets vary as a function of session length

Intragastric (i.g.) infusions of fat and carbohydrate condition flavor preferences in rats, but different results have been obtained in studies using pure and mixed nutrient infusions. This experiment compared the preference conditioning effects of mixed high-carbohydrate (HC) and high-fat (HF) diet infusions during short-term and long-term sessions. In Experiment 1 food-deprived rats were given one flavored saccharin solution (CS+HC) paired with i.g. infusions of an HC liquid diet, a second flavor (CS+HF) paired with HF diet infusions, and a third flavor (CS-) paired with i.g. water infusions during 30-min one-bottle training sessions. In subsequent two-bottle tests (30 min/day), the rats preferred both CS+s to the CS- and preferred the CS+HC to the CS+HF. In Experiment 2, the same rats were trained and tested with the CSs and paired infusions during 22 h/day sessions with chow available ad lib. Both CS+s were again preferred to the CS-, but now the CS+HF was preferred to the CS+HC. When given additional 30-min choice sessions in Experiment 3 the rats showed no reliable preference for the CS+HC versus CS+HF under food-deprived or ad lib conditions. In Experiment 4, the rats were given 22-h CS+HC versus CS+HF choice sessions every other day. They showed no reliable CS preference during the first 30 min of each session, but reliably preferred the CS+HF during the remaining 21.5 h. These findings indicate that previously reported differences in preferences conditioned by pure versus mixed nutrient infusions are due to training procedures (session length, deprivation state) rather than to the type of nutrient infusions per se. The rats displayed different CS+HF versus CS+HC preferences as a function of test duration even after being given both short- and long-term training. Thus, short-term choice tests do not always predict the long-term intakes and preferences for high-fat and high-carbohydrate foods.