I wouldn't view the Master-Cleanse as a diet for losing weight. Weight loss is a nice side effect but the detox and rejuvination of organs is the primary goal. You can only lose 2-3 lbs of fat a week in a healthy manner and once you go back to working out and eating wisely you should continue to lose the fat at that rate. But don't get to crazy with the exercise when you are only consuming around 600 calories a day.
By my estimate the Master-Cleanse delivers around 600-700 calories a day which is flirting with the "starvation" mode as it is. Your body will begin to feed on muscle tissue if you start burning too many calories and not taking calories in.
Don't starve your body and work it hard at the same time. The happy path is in the center, not at the extremes. I lost 40 lbs over 12 weeks just doing good food combining and light exercise. The Master-Cleanse will clean you up but it is not a "diet".