Effect of Hypercaloric versus Isocaloric Lipid Diet Ration on Diurnal/Nocturnal Eating Pattern in Self-Selecting Rats

Analyses of rats diurnal/nocturnal feeding behaviour were made according to the caloric density of the lipid ration. Adult male Sprague-Dawley rats were simultaneously offered three pure macronutrient diet rations: protein, carbohydrate, and lipid. The last was either kept isocaloric to protein and carbohydrate rations or was hypercaloric. Measurements of the food intake were recorded at 12-h intervals with respect to the dark phase and to the light phase of the circadian cycle (24 h). Rats fed the hypercaloric lipid diet ration showed a significantly higher total energy intake compared with animals fed the isocaloric lipid diet ration. Also, in the hypercaloric group, the percentage of energy ingested as protein was significantly higher during both the light and dark phases, whereas the percentage of energy ingested as carbohydrate was significantly lower during the light phase and the 24-h cycle when compared with that of the isocaloric group. These results indicate that the caloric density of the lipid diet ration has differential effects on the diurnal/nocturnal energy intake and macronutrient choice and suggest that these feeding patterns may modify the outcome of experiments using macronutrient diet rations with different caloric density.