The body will create ketones from fat first - your body does not harvest protein until the very end (which makes sense if you think deep about it). Ketones are VERY good energy source for body/brain. Furthermore, fatty meats are better than lean meats because too much protein can actually raise insulin levels. This is contrary to common Government agency advance today!

I think the best research says if you are fasting, anything over 48-72 hours and you 'could' end up eating into muscle. The wide time span is different metabolism.

But the amino acids in protein (especially red/colored meat) are vital to life - and you can NOT get them all from plant diets (so much supplement). So you are 100% right on the protein consumption!

Great book, "Change you diet, change your mind" - which will lead to several other very good books.