From what I've read ketosis doesn't start until day 8 so you shouldn't be experiance it yet, and yes eating anything could slow that down. From my understanding ketosis is a reaction from your body having NO calories at all and as a result will start to feed on itself.
As for your muscle mass loss I have no idea the longest fast I've ever done was 21 days and though I didn't measure my muscle mass but when I returned to the gym my streangth was improved from prior to the fast.