Sham-feeding of corn oil by rats: sensory and postingestive factors.

Previous research indicates that rats fed a high-fat (HF) diet increase their intake and preference for oil compared with rats fed a high-carbohydrate (HC) diet. To assess whether this increased intake was due to the sensory or postingestive properties of oil, rats were adapted to either the HF or HC diet and then allowed to sham-feed pure corn oil daily for 30 min. During the first 4 trials, rats fed the HF diet sham-fed more oil than did rats fed the HC diet; however, this difference diminished with repeated testing and was absent after 8 trials. In both diet groups, 4-5 calories (approximately 25%) of sham-fed oil could not be recovered and may have escaped to the intestine. These results suggest that, compared with rats fed a HC diet, rats fed a HF diet are initially attracted to the sensory properties of oil, but that the differential oil intakes of rats fed the HF or HC diet are maintained by postingestive, rather than sensory factors.