We have done this because we either didn't eat the best food, or we didn't take enough exercise to burn off the bad stuff we ate.
Me, I did a lot of drugs and smoked a lot of cigs years and years ago. My body did some healing, but now...it's really healing and I'm happy to have gone two days and look forward to more.
Even if you don't do the purist lifestyle, you can still be healthy and eat some of the crap out there.
I think moderation is the key. I've got a few boxes of Girl Scout cookies in the freezer that are calling my name, and I told them to shut up until I'm done wiht the fast. Then I will feast on the glory. Yet, I've never been the type to eat a box at time either. LOL
I also have learned new eating habits lately so this will only compliment my new ways as I return to food.