Okay - there is a technical explanation...the research says that VLCDers are no more or less successful at keeping it off than other diets - the same thing happens to everyone, you put your body into weightloss mode for several weeks and months. Your hormones, thinking they are doing you a favour have no idea what you've just done, they think there was a famine, so as soon as food comes back your hormones, chiefly ghrelin and leptin start playing games with you to get you to eat far more than you usually would to compensate for the undereating. This seems more dramatic and obvious in VLCDers because they lose weight so quickly so any weight gain is just as noticeable, poor old VLCDers are often in the spotlight because of their dramatic losses, so I suspect (there's no research on this bit to my knowledge) that any small weight gain has a negative impact and creaties negative affirmations, particularly as so many people whisper on the sidelines 'She lost it too quickly, she'll put it all back on'.
There is some reserach that suggests that beyond the stepping up through the programmes you should spend several months eating a little below your actual calorie requirements (ie for me, about 2000 a day - my BMR when I do an hour of exercise a day at a BMI of 23 is 2200) until you have totally stabilised, and then gradually try to find your ideal zone!
The people who stick within a few pounds of their finish weight on a VLCD (and other diets for that matter) work at it, a lot of them eat low GI and calorie count. You don;t get to maintain for several years without remaining completely conscious of your weight.
I screwed up, I came back. No shame in that, VLCDs work. It's me that's wonky!