Fasting is great, not enough people do it. I think 28 days is a tad too much for the average bear. Not a literal bear, as they hibernate (obviously).
Are you going to supplement with ANYTHING??
Hope you've got the extra weight to fuel you through this endeavor, lest you wind up like Alexander Supertramp.
RE: I Quit Eating for 28 Days [Water Fast] : Day 1 (Introduction)