Food deprivation reduces rats' oil preference.

Rats normally prefer dilute oil suspensions over vehicle, but this preference can be abolished by exposing them to dilute oil suspensions during a period of food deprivation. In the first series of experiments, rats were given a choice of 0.5-0.9% triolein vs. vehicle for 4 consecutive days each week for 3 weeks. Food was available ad libitum on days 1, 2 and 4; no food was available on day 3. Preference for oil suspension dropped sharply after, but not during, each occasion that food was withheld. Similar experiments using starch, Polycose, or sucrose did not show comparable deprivation-induced changes in preference. The second series of experiments included separate control and experimental groups. The experimental group was food deprived for 1 day when test fluids were available. The control group was food deprived the day after the test fluids were available. Food was returned and the test fluids were removed for a few days. Fluid preference was then retested with food available ad libitum. After this cycle of two preference tests was repeated 1-2 times, the experimental group showed substantially lower oil preference than did the control group. Similar results were obtained with 0.5% triolein, 0.5% soybean oil, and 5% soybean oil. A similar experiment in which a vanillin-citral flavor was used instead of oil did not show such an effect. However, preference for the vanillin-citral flavor was decreased in rats exposed to a mixture of this flavor and oil while they were food deprived. It is proposed that rats readily learn to associate oil flavor, but not other flavors, with the aversive effects of food deprivation.