The best way to keep in good health is to follow a healthy nutritious diet (with your age, conditions and activity levels in mind) and a balanced workout (including any aerobic activity, muscle work and stretches).
Without wanting to comment on the efficacy of these slimming institutes, considering there are no guidelines they follow, one would be suspect to the success of the process or the safety of the outcome. And from what is understood, if not following a healthy diet and getting some amount of exercise, they prove to be as inefficient. So you'd be better off doing it the tried and tested way!