Effect of Fasting on Muscle Proteins and Fat in Young Rats of Different Ages

¹ From the Laboratory of Nutrition and Endocrinology, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

Rats 30–70 days of age were fasted for 3 or more days and changes in the amounts of various protein fractions and fat were measured in the thigh muscle. Only two protein fractions in the muscle, myosin and ‘water-soluble’ (sarcoplasmic) proteins, were decreased; the stroma and nonprotein nitrogen fractions were unchanged. It was found that only 20–27% of the calories that came from the thigh muscle were derived from protein and the rest, from fat. These findings are in agreement with many other reports that during fasting body proteins contribute only a small proportion of the calories that are needed for survival. There was no evidence of edema or ‘water-logging’ in the muscle of these fasting animals.