"Has it backwards"... What? No, absolutely not. Fasting absolutely eats muscle. Your body requires EAAs to function and they come mostly from skeletal muscle when dietary intake is inadequate. Oliver Owen did the classic fasting research on this and found that 21 days of fasting in obese men led to half of their weight loss coming from lean mass, of which 60% was structural protein (PMID: 9665093). And yes, his research showed it takes about 5 days for protein sparing mechanisms to kick in (see first image), but even at max capacity your skeletal muscle is never "protected" or "spared" in the sense that you can prevent muscle loss. And muscle loss is substantially worse the leaner you get. Abdul Dulloo did a lot of work on this with data from the Minnesota Starvation Experiment and others, finding that the ratio of protein losses to non-protein losses increase exponentially with lower levels of body fat (PMID: 10673906; see second image). Another study observed the same thing and found that protein contributed 2-3 times more energy in normal weight vs obese adults during prolonged fasting (PMID: 10574520). In fact, they didn't even really observe an adaptation in normal weight people like they saw with obese people, with oxidation being consistent for up to a month of fasting.