While you will certainly get more results with a longer fast, anytime you take to clean out toxic sludge from your body and give you organs time to heal is benificial. This said, the Master-Cleanse is great for jump starting a better eating lifestyle (especially if you eat typical stardard American diet). Only if you make changes to what you eat will you see long term effects. Otherwise you are taking out the garbage just to leave room for more gunk.