Does the body burn muscle first??

I told a friend that I was doing the Master-Cleanse - (I am on day 8) he claims that your body will burn muscle before it will start buring fat for energy? I looked though the FAQ and I do not see a answer for this- I have been going to the gym for a year now and have built up some muscle I am doing the Master-Cleanse for the cleaning but I not if I will lose the muscle I have built- just confused from reading different things.