40 Hour Fast and Skeletal Muscle Genes
I'm new to this forum but have been following various forms of IF on and off for a long time. I didn't see this study mentioned here, it suggests that at least 40 hours of fasting can be done without muscle loss.
Ann Nutr Metab. 2006;50(5):476-81. Epub 2006 Aug 24.
Actions of short-term fasting on human skeletal muscle myogenic and atrogenic gene expression.
Larsen AE, Tunstall RJ, Carey KA, Nicholas G, Kambadur R, Crowe TC, Cameron-Smith D.
School of Exercise and Nutrition Sciences, Deakin University, Burwood, Vic, Australia.
BACKGROUND: Skeletal muscle mass is governed by multiple IGF-1-sensitive positive regulators of muscle-specific protein synthesis (myogenic regulatory factors which includes myoD, myogenin and Myf5) and negative regulators, including the atrogenic proteins myostatin, atrogin-1 and muscle ring finger 1 (MuRF-1). The coordinated control of these myogenic and atrogenic factors in human skeletal muscle following short-term fasting is currently unknown. METHOD: Healthy adults (n = 6, age 27.6 years) undertook a 40-hour fast. Skeletal muscle biopsy (vastus lateralis) and venous blood samples were taken 3, 15 and 40 h into the fast after an initial standard high-carbohydrate meal. Gene expression of the myogenic regulator factors (myoD, myogenin and Myf5) and the atrogenic factors (myostatin, atrogin-1 and MuRF-1) were determined by real-time PCR analysis. Plasma myostatin and IGF-1 were determined by ELISA. RESULTS: There were no significant alterations in either the positive or negative regulators of muscle mass at either 15 or 40 h, when compared to gene expression measured 3 h after a meal. Similarly, plasma myostatin and IGF-1 were also unaltered at these times. CONCLUSIONS: Unlike previous observations in catabolic and cachexic diseased states, short-term fasting (40 h) fails to elicit marked alteration of the genes regulating both muscle-specific protein synthesis or atrophy. Greater periods of fasting may be required to initiate coordinated inhibition of myogenic and atrogenic gene expression.