How many days till you start losing muscle
You just won’t find an unbiased answer here as you’ll see by how much this post gets down voted.
But think about it no matter what the magic mechanism touted by fast zealots, whether it’s autophagy or hgh your body still needs a certain amount of protein per day as the basic building blocks of cell renewal and it’s not going to be able to recycle all of that for necessary organs AND still have enough for your muscles if you’re not eating anything.
In short, yes you’ll lose muscle on a 3 day fast.