I am living proof that fasting doesn't eat your muscle away, barely if at all.
I had a week where I stayed home sick with a cold. I fasted for 4 days straight. After a few weeks later I came back stronger in the gym.
Anyone would have to be moron to think or even hope that fasting makes you stronger. But I am just sure by now that it won't hinder your gains over the long term, if you have storage fat to spare.
With extra storage fat available, your body will go for that while fasting. It will only really go after the muscle if there is no fat available.
So much for worrying about nutrition and recovery. It's all just a bunch of marketing dogma based only on belief and zero proof.