CARBOHYDRATE-CONDITIONED AND PROTEIN-CONDITIONED FLAVOR PREFERENCES -EFFECTS OF NUTRIENT PRELOADS

Food-deprived rats were trained to associate one flavor (CSProt) with intragastric (IG) infusions of protein (PROT; 10% calcium caseinate), a second flavor (CSCHO) with IG infusions of carbohydrate (CHO; 10% pr otein), 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 reliabl y preferred both the CSProt and CSCHO to the CS- and equally preferred the CSProt and CSCHO. The preference for the two nutrient-paired flav ors was not altered by IG preloads of PROT or CHO delivered as three l oads 120, 40, and 5 min prior to testing. However, single oral + gastr ic preloads of CSCHO + IG CHO and CSProt + IG PROT 45 min prior to tes t selectively increased the preference for the CSProt and CSCHO, respe ctively. In subsequent gastric-only and oral-only tests single IG prel oads of PROT and CHO, but not CSProt and CSCHO preloads, selectively a ltered the rats' preference for CSCHO vs. CSProt. In a second experime nt with new rats, oral + gastric preloads again selectively altered th e preference for the CSCHO vs. CSProt, but gastric-only preloads faile d to have this effect. These results demonstrate that rats can learn t o associate different flavors with the postingestive effects of differ ent nutrients, and modify their flavor preferences after nutrient prel oads. Oral + gastric preloads were most effective in altering flavor p references, whereas gastric-only preloads had inconsistent effects and oral-only preloads were ineffective.