Feeding frequency and protein metabolism

¹ Department of Biochemistry, Medical Research Institute, Michael Reese Hospital and Medical Center, Chicago, Illinois

Normal young adult male rats were allowed to eat a diet of a specified protein content ad libitum, or were pair-force-fed the same diet twice a day. At the end of 14 days of controlled feeding, the animals were killed and analyzed for total body lipids. These analyses showed that the fat content of the force-fed animals, relative to those that ate ad libitum, became progressively greater as the dietary protein was increased in quantity from 0 to 67% of the diet. Furthermore, it was observed that force-fed animals excreted about 37% more urea nitrogen over a 7-day period than pair-fed animals eating ad libitum. Abruptly reversing the feeding habits of the rats immediately reversed the relative amounts of urinary nitrogen they excreted. The results of both types of experiments suggest that the intermediary metabolism of protein is related to feeding frequency (or load of absorbed nutrients to be metabolized per unit time). With fewer feedings but with total 24-hr intake constant, less dietary protein appears to participate in protein anabolic reactions since larger amounts of nitrogen are lost in the urine.