My philosophy is that you want to put the minimum possible stress on the body to get the results you want. If your body is already in cleanse mode, I don't think there is any reason to start fasting, fasting will increase cleansing in the body. Fasting should be used when your body is physically strong, with no stress in your life but your body is not cleansing, when used properly, it can be a powerful tool, juice fasting is also great and can be even more effective if you understand the effects that specific juices have on the body.