I am glad you mentioned fasting as it is one of the best transformational tool as pointed out in my unusual diet.
From my experience, since I started one meal a day (intermittent fasting), my lean muscles got denser and my body fat rate went below 10%. I use Dexascan to be sure twice a year even though it is expensive.
As long as we have sufficient amount of protein with sufficient good quality fat as energy, the muscle lost is very low possibility. Of course unless we do mindless cardio for 3 to 5 hours in fasted state.
Hope my unusual diet experiment provide a perspective on this.
My Unusual Diet Revealed
Throughout my life, I tried many diets. None of the diets or dietary approaches I tried based on mainstream advice…
The autophagy concept is one of my main reasons to eat only one meal day, to focus on strength training, to practice dry sauna and cold showers. These practices are covered in my new publication on Medium.