Research and see what kind of life change you can stick with.  Once you have decided make sure the doctor agrees that you are healthy enough of such diet changes.

I did the six week body make over and it is fantastic, I ate healthy, I didn't stick to it one hundred precent but I still lost weight and I had energy.  But it is a way of life for you, if you give up fast food for example and lose, then go back to fast foods it will come back.  When I first went on the 6WBMO plan I felt a sudden burst of energy, then I got sick and it was due to the toxins leaving my body and a week or so later I felt great.  I went off the plan and now I am ready to go back on it, I feel terrible.