from what I've seen if you lose it fast it'll come back jsut as fast.
As well as this if you lose..........say 26lbs in 4 weeks then you have a problem and that problem is your skins elasticity. You'll have big folds of flabby skin from losing the weight too fast. You might look alot thinner but once the clothes come off and the skin starts hanging you may as well not have bothered. Work out properly, its the only way to go.