[solarmist]

It's not that simple unfortunately. Basically, as I understand it, your body(liver) puts out a call for energy and whatever happens to pick up the signal first will respond. In the same way you can't spot reduce fat (can't choose where you want to lost fat from).

So this means, unfortunately, you will lose muscle while losing fat. Fortunately it is significantly more difficult to extract protein from muscle, so it responds much more slowly than fat.

The minimum seems to be about 40 g (~150 Cal) of protein per day (I don't remember where I got this number, sorry.), but can be as high as 10-30% of Calories supplied by the body.

There are a lot of things you can do to counter and minimize most this though. Working out to signal to your body the muscle mass is still in use and protein shakes (no fat, no carbs) are the most obvious.