Carbohydrate- and protein-conditioned flavor preferences: Effects of nutrient preloads

Abstract

Food-deprived rats were trained to associate one flavor (CS Prot) with intragastric (IG) infusions of protein (PROT; 10% calcium caseinate), a second flavor (CS CHO) with IG infusions of carbohydrate (CHO; 10% protein), and a third flavor (CS−) with IG water infusions during 30 min/day training sessions. (The CS flavors were cherry, grape, and orange saccharin solutions.) In subsequent two-bottle tests the rats reliably preferred both the CS Prot and CS CHO to the CS− and equally preferred the CS Prot and CS CHO. The preference for the two nutrient-paired flavors was not altered by IG preloads of PROT or CHO delivered CS Prot + IG PROT 45 min prior to test selectively increased the preference for the CS Prot and CS CHO, respectively. In subsequent gastric-only and oral-only tests single IG preloads of PROT and CHO, but not CS Prot and CS CHO preloads, selectively altered the rats' preference for CS CHO vs. CS Prot. In a second experiment with new rats, oral + gastric preloads again selectively altered the preference for the CS CHO vs. CS Prot, but gastric-only preloads failed to have this effect. These results demonstrate that rats can learn to associate different flavors with the postingestive effects of different nutrients, and modify their flavor preferences after nutrient preloads. Oral + gastric preloads were most effective in altering flavor preferences, whereas gastric-only preloads had inconsistent effects and oral-only preloads were ineffective.