This is a myth – one of many fasting myths that just needs to die.
- Losing Muscle: No you won’t burn/lose muscle when you fast. Here’s why. Our bodies simply are not made that way. Our bodies store food energy as body fat for a reason – to have an energy source to go to when food is scarce. Muscle, on the other hand, is preserved until body fat becomes so low that the body has no choice but to turn to muscle. This will only happen when body fat is at less than 4 percent. If we did not preserve muscle and burn fat instead when no food is available, we would not have survived very long as a species. Almost all mammals have this same ability. Dr Jason Fung explains it this way, “To burn muscle for energy would be like storing firewood and then, as soon as cold weather hits, chopping up your sofa and throwing it into the fire.” (The Complete Guide to Fasting, by Dr Jason Fung with Jimmy Moore.)
Gaining or losing muscle has to do with exercise, not your diet. You can’t eat your way to more muscle and you can’t fast your way out of muscle.
In fact, fasting is one of the most potent stimuli for growth hormone secretion, and increased growth hormone helps maintain lean body mass.