I don't do the Master-Cleanse but I usually fast with either water or lemon juice or sometimes apple cider vinegar. The longer I fast the better the flush and the longest I have fasted before a flush is 5 days. I also use a tincture of liver herbs while fasting (milk thistle, dandelion, schizandra, gentian, golden seal). Like the previous post I find it very hard in winter as I get very cold. If you try it please post your results.