Congrats on embracing fasting nate - you should link some of your earlier posts to inspire others who find it pretty unconsciable to go more than 12 hours without food.
Regarding burning muscle and fat, you'll know if you fast longer that its definitely not fat then muscle: you'l lose plenty of muscle while still retaining fat. The consolation offered is that muscle growth tends to come back improved (Longo noted this anecdotally and suggested it seems plausible - I believe it is buried in here somewhere - also he has done a recent interview with Bowes on llama podcast where he states that the 18-6 turns out be harmful)
Initially, I was rather confused as to why, during the fasting cycle, given the body perceives a lack of resource and heightened need for competition, it metabolises muscle in order to conserve fat. Then it become obvious - while a muscled-down body may possess a reduced capacity to compete for resource, it'll take far longer to burn through a pound of fat than its beefed-up counterpart. So it kind of makes sense in the early stages to burn fat, since a day or so without food is unlikely to be an indicator of survivability-risk.
Interestingly, in case you didn't know, HGH levels sky-rocket after a fast of 16 hours or so (which perhaps indicates the likely priority at this stage) it has become popular with body builders and, if you do, this may indicate why you haven't noticed this effect.)
Edited by ambivalent, 24 July 2018 - 08:28 PM.