Meal to meal energy balance in rats

Meal to meal energy balance was examined in thirty-eight simultaneous recordings of feeding pattern and O2 consumption in six rats. The mean difference between energy intake in a meal and energy expenditure until the onset of the next meal was found positive at night and negative during day time. At night the excess of meal intake over meal to meal expenditures was decreasing from the beginning to the end of the night and was strongly correlated to meal sizes. During day time meal to meal deficit was decreasing from the beginning to the end of the period but was not correlated to meal sizes. These meal location and size effects on the meal to meal energy balance were not determined by an effect of these factors on metabolic rate. No indication was provided that meal to meal energy balance was influenced by a "meal induced thermogenesis." Rather an evolution from the beginning to the end of the night of the correlation between meal size and durations of meal to meal intervals was found to be parallel to the evolution of positive meal to meal energy balance throughout the night. From these data it is concluded that at night a dual utilization of meal caloric intake (current energy metabolism plus fat storage) and a dual source of fuel during the day (food plus mobilized fats) determine time and mechanism of meal onset.