I've never known anyone who has gone on a diet and lost the weight they wanted to lose and then keep it off once they completed the diet. The people I've known who struggled with their weight seem to be constantly yoyo-ing. From the outside looking in I'll say this...diets don't work. The people who are successful are those who made for real lifestyle changes. The runners, the daily exercisers, the ones who completely rehauled their food intake THE RIGHT WAY.
I've never read something that made more perfect sense than what this guy says in this article: The 7 Things I Did To Lose 220 Pounds Without Dieting
That guy laid it all out there. He's lived it and beat it. Dude is a rockstar.