Effects Of Feeding Schedule On Circadian Regulation And Physiology In Rats

In mammals, circadian clock affects almost all physiological and behavioral activities. The food cue is a predominant Zeitgeber for peripheral clocks in many tissues. Unhealthy feeding schedule can uncouple the peripheral clocks from the central clock, and results in disordered internal circadian environment. Previous studies mainly focused on the effects of once a day restricted feeding or calorie-restricted feeding on circadian clocks, while studies really simulating the human feeding habits have rarely been reported. We developed a model of daily three meals in rats that mimics the feeding habits of human beings. The aim of this study is to test the impact of different feeding habits on circadian rhythms and development of young rats, and to investigate the potential significance of feeding time on physiological function of aged rats.The present study shows that the feeding time and amount of the first meal determine the peak phase of peripheral oscillators. Less amount of the first meal incuces altered peak phases of clock genes. Thus, the first meal plays an important role in circadian metabolism. Secondly, whether having the last meal or not significantly changes the expression of circadian clock genes in peripheral tissues, especially the hepatic clock genes, thereby influencing the development of peripheral tissues and lipid metabolism. Thus, the last meal plays an important role in energy metabolism. Finally, compared with young rats, food entrainment in aged rats is relatively inefficient. Although the changes of physiological differences caused by feeding habits are not significant, certain trends are still presented, such as no first meal increases body weight of rats, and no last meal leads to lower the metabolic level of physiological function in aged rats. Taken all together, regular daily three meals helps to promote the stability of circadian rhythm and induce balanced metabolic homeostasis.