Caloric regulation in the rat: evidence for a calibration mechanism

Rats were given access to small quantities of a 50% oil/water mixture on each of 7 baseline days. On the eighth day, a 30 min compensation test was conducted during which control rats had access to the 50% oil/water mixture and experimental rats had access to either a more concentrated or a more dilute oil/water mixture. Experimental rats given the more concentrated mixture consumed significantly less than controls, while rats given the dilute mixture consumed significantly more than controls. These results suggested that rats can immediately adjust their food intake in response to changes in the caloric density of their diets. In a second experiment, immediate adjustment for caloric change was inhibited by giving rats a supplementary meal directly after access to the 50% oil/water mixture during the baseline phase. These results were discussed in terms of a hypothetical "calibration" mechanism which allows rats to estimate the density of novel caloric concentrations on the basis of a standard concentration.