For me personally, when I went on a juice fast I would always get severely sick...thought it was just die off or toxins being moved...I think people metabolize foods differently, so what is ok for one person is not ok for the next.
I did much better on liquid, raw kefir, raw eggs, raw milk, beet kvass ect...than with juicing. I didn't get nearly so sick and was able to make it for 7 days where before every time I would fail after 2 days.