Macronutrient self-selection pattern in rats under different lighting conditions

The effect of constant darkness (DD) and constant light (LL) on the circadi an pattern of macronutrient self-selection, daily food intake and body weig ht was analysed in rats using an automated computer system. No significant differences in energy intake were observed between groups as regards energy intake or macronutrient preferences. Fat and CHO intakes showed a negative correlation (p < 0.005 in LL and p < 0.0005 in DD and LD), while protein i ntake remained constant, which suggests the existence of separate regulatio n mechanisms governing the intake of protein and energy. Energetic requirem ents can be preponderantly covered by CHO or fat, depending on the preferen ces of the animal. Body weight measurements reflected no significant variat ions between groups at the end of the experiment. However, the circadian pa ttern of wheel-running activity and the intake of the three macronutrients measured in both constant lighting conditions varied with respect to that o bserved in LD. This was particularly true in the case of LL, when constant illumination exerted a decoupling effect on the rhythms. The results indica te that lighting conditions modulate the circadian pattern of wheel-running activity and macronutrient intake. However, changes in temporal organisati on of food intake did not affect macronutrient preferences, daily energy in take, number of meals, feeding duration or body weight, suggesting the exis tence of a double, circadian and homeostatic, control of such variables.