Ever been in the middle of a hard workout and noticed that you smell like ammonia? That smell means you are burning protein, probably from your muscles. I have only ever seen this during extended exercise, but the same thing during a fast would be a clear indicator you are burning muscle.
So that's what that is! I used to notice that a lot when I first started cycling aggressively in college. Once I got into better shape it mostly went away. Thanks for the tip.
I haven't noticed any muscle lost -- but then again I put on muscle /very/ easily (a bit too easily actually, I get hypertrophia if I do too much sport).
For energy, it turns out your body /does/ have some to burn, and once you made the switch to burning fat, well, usually there's a nice source of energy... I also wonder if you don't get a small dose of adrenalin in too, which would explain the 'high' you get after a couple of days.. but don't quote me on this..
But as I mentioned, the fruit juice input in the morning does help get the day started. Oh, and the coffee contains some nutrients too, so it's not like I'm totally starving.
Also, how do you keep sufficient energy to perform daily tasks and things like intense programming sessions?