How long are you planning to fast for? I don't know if you said. Maybe I missed it. At any rate, I'm planning to do another fast. Last time I made it to 10 days I believe, but this time I would like to fast to completion; however, my lifestyle, while not busy, might be /slightly/ too strenuous, so if it gets to be too much, I might have to alternate a juice day or two in there. We'll see.
And to answer your question. When you feel it necessary. Idk what you're fasting for, but I am fasting for my health and quality of life. It's not an ideal situation. I'm kind of desperate. But it gives me the motivation to continue. A blend of the both of us might be ideal!