This is limited intake alone.
The research i've read says that you grow additional fat cells when your intake exceeds your expenditure, and your fat cells empty when your expenditure exceeds your intake. Empty fat cells scream at your brain to eat to fill them up again, making it easy to lose a bit of weight but difficult to keep it off. The article I read wasn't clear on how long empty fat cells stay empty before they are eliminated, but i don't think it was particularly fast.
I'm not sure if the article (can't find it anymore) was quackery or actually backed by proper research but it seemed a reasonable explanation for why surgery (cutting out fat from the body) becomes the only option for really obese people. Obviously if they had the self control to lose weight they probably wouldn't be in this situation in the first place.
Stomach stapling would reduce the ability to eat but leave the person in the hell of wanting to eat without being able to. This new invention might be a better solution, although I think that the act of eating primes the body for the nutrients about to be delivered, and messing with that (eg removing the foot before it hits the intestines) might not be a particularly good long term solution...