Myself and a number of my friends tried this plan with ultimately very negative results. Yes, you do lose weight very rapidly - too rapidly. I remember being hungry ALL the time and often dizzy. I couldn't work out since I didn't have the energy. It is expensive, the staff is less than kind and I think health wise, it is just dangerous. We all gained the weight back and then some.

Besides working very fast, there is nothing positive about your experience!
It costs almost $200 a week, you get a painful injection 3 days a week which leaves bruises and you barely eat!
I remember one meal consisting of a slice of fat free process cheese and 4 low sodium triscut crackers!!
Furthermore, the nurses are rude and cold. I had the same experience at 2 different centers so I'm not being biased.
Of course, you gain it all back and then some once you go off since your body is no longer in a state of keytosis.
Save your money!