— https://www.healthline.com/nutrition/11-myths-fasting-and-meal-frequency#section9 says ( and I choose to believe )

Some people believe that when you fast, your body starts burning muscle for fuel. There is evidence for and against this claim.

Contrary evidence — studies indicate that intermittent fasting is better for maintaining muscle mass. A study showed a modest increase in muscle mass for people who consumed all their calories during one huge meal in the evening (Trusted Source).

Intermittent fasting is popular among many bodybuilders, who find that it helps maintain muscle alongside a low body fat percentage.