Many naturopaths recommend giving the body a break from digestion now and then especially if the person doesn't have a great diet. Acupuncturists however will warn never to fast as Chinese medicine concerns itself with nourishing the organs rather than depleting them. So I had a Acupuncturist once who was also a naturopath and I asked him the question since he should be sitting on the fence on this one. He told me that he thought fasting was a good thing to do once or twice a year but that most known fasts recommended fasting for too long. At the time I wanted to try a fast that including drinking (the master cleanser) a lemonade (as much as you wanted) made of organic lemon juice, maple syrup and cayenne pepper and it was recommended for ten days. He told me he'd only recommend fasting for 3 to 5 days maximum even with this lemonade.
So I did it and tried it a few times and lost 10 pounds every time (in five days) and continued to exercise through it. Personnally now I prefer to eat well and not fast. I didn't realise at the time that I was gluten intolerant on top of being dairy and wheat intolerant. So of course freeing my system of gluten was a great thing for 5 days but I did feel depleted at the end of these fasts.
One day of fasting should be fine with just water or water and lemon juice. I'd probably add a bit of a sweetener just for nourishing the brain which only functions on simple sugar. The whole idea being mostly to give the digestion a break.
If you eat very well, you will have nothing to cleanse. I believe a good cleanse would have to be a diet full of antioxidants. Plus I believe "cleansing" or fasting would just elevate cortisol which would have you sleeping less causing more stress and you won't function very well. I don't know, maybe it's just me but I like staying at peak efficientcy.
I do a fast, but I definitely drink a GREEN drink. Some drink with just wheat grass/other green veggies. Or a powder and drink tons of water.
I do this maybe once or twice a year. I find it is cleansing. (During these fasts I may eat very light meals too). The intention is to super charge my body with liquids, hydrate, and alkalize. The Thrive diet should do this for you. I do believe here and there it is good to fast (by that I mean just have liquids or very lite meals).