Obese and lean Zucker rats differ in preferences for sham-fed corn oil or sucrose

Obese Zucker rats show greater preference for fatty foods in dietary selection studies than do lean rats. We wished to evaluate the preference for dietary fats in Zucker rats in the absence of postingestive cues. Zucker rats (6 lean and 6 obese) were fitted with gastric cannulas for sham feeding. All sham-feeding tests lasted for 30 min. On training days, rats were sham fed 100% corn oil or, on alternate days, rats were sham fed various concentrations of sucrose in volumes yoked to intakes of corn oil. On preference test days, rats were offered 100% corn oil and one sucrose concentration simultaneously for sham feeding. During preference tests, obese rats preferred 100% corn oil to 10% sucrose, whereas lean rats preferred 10% sucrose to 100% corn oil. Obese rats equally preferred 17.5% sucrose and 100% corn oil, whereas lean Zucker rats equally preferred 2.5% sucrose and 100% corn oil. When sucrose concentration was increased to 20% both obese and lean Zucker rats preferred sucrose to 100% corn oil. These results combined with our previously reported results showing that intraduodenally administered fats do not differ in satiating potency for obese and lean Zucker rats (6) strongly suggest that the preference of obese rats for fatty foods is largely mediated by orosensory mechanisms.