You should tackle your health first and rebuild THAT right now. Your body is amazing, it really is, and I really doubt you will lose very much muscle tone. You body doesn't want to get rid of healthy tissue, it wants to get rid of things it does not need. I commend you so much for what you are doing, but in my personal opinion you need to focus on your health first, and your conditioning second. I do know that whey protein even in the purest form (Isopure is a really good kind by the way) will take a bit of digestive work and that is kind of defeating the purpose of the cleanse, don't you think?
My opinion only, you decide what is best. I am no expert, that is for sure, and whatever you decide, post the results, okay? It will be interesting to hear and something to consider for others who train.