Factors Influencing Survival of Rats in Fasting

Metabolic Rate and Body Weight Loss

¹ From the Department of Physiology, University of Western Ontario, London, Canada

The individual duration of survival of adult rats in complete fasting varied considerably; the range at an environmental temperature of 22°C was 6–16 days, at 2–5°C, 1–7 days, and in thyroidectomized animals at 22°C, 15–25 days. This variation in survival was not closely related to the initial body weight but was related to the individual proportionate body weight loss per day and the total proportionate weight loss sustained before death. The individual proportionate rate of weight loss has been correlated with the metabolic rate indicating that the former reflected the metabolic rate of the animal. The duration of survival in fasting has been correlated with the individual metabolic rate, whether measured before or during fasting. Since fasting did not obliterate or reduce the individual differences in metabolic rate, it was possible to predict the individual duration of survival from knowledge of the prefasting metabolic rate. The total proportionate weight loss, which also influenced the survival time in fasting, was altered by changes in the environmental temperature and probably by other factors. The previous diet whether high in protein, fat or carbohydrate had little effect on the duration of survival. Fasting caused a decrease in the metabolic rate of intact rats at 22°C but no change in that of thyroidectomized rats or of rats living in the cold.