I used to do a two day juice fast...I had to stop because I passed out once (I think either my blood sugar or pressure bottomed out) and decided that I'd rather be alive than lose ten pounds in two days, lol...
However, I used prepared juice that was specifically for that purpose. And, I'm not telling you what to do--I have blood sugar issues so it was a bad idea for me. I think if you can do it, then* by all means. Sorry I couldn't be of more help.