I do an 80 hour fast/cleanse three times a year. I always start the day of my dentist visit, love having the dentist clean feeling for days! Any longer I've read that the body starts attacking/eating muscles to support the vital organs. Anyhow on day one I drink hot lemon water, (stopped eating the night before) and that makes me almost shit in my pants! It goes right through me. After the first morning it's just water and that's it.