For what it's worth, my cortisol felt way, way lower on a water fast than it did on a juice feast. I agree with CD about feeling the calmest I've ever felt on a water fast (and I only did 5 days). My personal suggestion for juice feasting (unless CD objects) is to start it off with two days of water fasting - this will get you calm quicker and get you over hunger quicker. You'll also appreciate the fuck out of the juice rather than it being a letdown.