Eating Habit and Fasting Metabolism of Rats

The rate of fasting metabolism depends on the level of previous food intake. In order to measure the influence on the metabolic rate of any condition which lowers the appetite one must therefore reduce the food intake of controls to that of the experimental animals in order to eliminate the influence of food level. The rats whose food intake is thus reduced but whose appetite is not affected may eat their daily ration at once while their pair mates with their decreased appetite on unlimited food supply extend their food intake over the whole day.

Table I shows the feeding habit of 18 rats during 12 days. The amounts eaten during the various daily periods are expressed in percent of the daily intake. The behavior of 9 rats that had previously been on a restricted ration was essentially the same as that of their controls whose food intake had never been restricted. The previously restricted rats ate, however, during the first 4 hours of unlimited food supply 17 g of food which is more than their later average food intake during an entire day and is 71% of the intake during the first day of unrestricted intake. Does such a difference in the distribution of a given daily ration during the day affect the subsequent fasting metabolism? If such an effect would be found then it would not be sufficient to equalize the daily ration between experimental animals and controls but it would be necessary also to parallel with the controls the feeding habit of the experimental animals.

Method. Six female rats (Long-Evans strain) were given 8 g per day per rat of a food mixture which is considered qualitatively complete. Three of these rats received this ration at one time, at 4 p.m. The other 3 were given their food in 5 portions of 1.6 g at 4 p.m., 8 p.m., 12 p. m., 8 a.m., and 12 noon. Four days after the start of this regime, at the age of 88 days, the fasting metabolism of the 6 rats was measured by a respiration trial.