To answer the original question - this is a good idea because/if/when it teaches us something we didn't know, or gives a definite answer to something we've been guessing at until now. And I don't think the question really was "will they lose weight". I think it was more along the lines of "is it possible, by extreme measures, to kick-start a process that saves lives but that also takes a long time, has a high drop-out percentage and is risky because people can actually die before they get that far".

Personally I think it's fascinating that short-term intervention can have such drastic results on serious medical problems. I hope it can get put to good use somehow.