Skin and sinus improvements seem to come quickly. No more dandruff or dry skin for me and your sinuses will most likely function far better than you may like during a fast. Smells that were bearable before the fast, like the stench of a smoker, will be almost intolerable while you are fasting. many have reported cellulite disappearing.
Why not just do it? You've got nothing to lose but a stone or so.