I've been on a 5-2 diet maybe three times now, over a couple of years, because I do indeed put the weight back on if I stop completely. (I really must follow Michael's advice and go on a permanent 1-6 diet if I want to keep it off. Or get serious about exercise.)
So I'm on it again, and I have to say, maybe I like yo-yo dieting. I mean, as I've said before, the fasting days on the diet (600 cal allowed) really make the small amount of food you do eat taste pretty fantastically good. (And, as I scrap up every last morsel of salad or cracker crumb, I am also always reminded of the scene in Empire of the Sun where our young hero carefully gathers all of the weevils from his rice and eats them happily.) There is a sort of feeling of mental focus that can come with the fast days, too.
True, after a few months the novelty wears off, and the reducing speed of the weight loss encourages me to stop at "close enough". But the early weeks of being on the diet - they feel pretty good.
In other diet news, I see that Eddie McGuire and Malcolm Turnbull have apparently both tried a severe fasting diet over 3 weeks and lost something like 15 kg. Yeah, I agree with the experts - that's not a good idea. It might take me a year to lose that much on 5-2, but I can enjoy life on the way. (By the way, I should lose about 7 kg this time - I really did let myself rebound too far this time.)