The thing is that you'll need to forever eat a rather low-calorie diet (more so than someone who was never overweight) and often this leads to frustrating, pervasive cravings for food that aren't that different from what people who have undergone starvation experiences report. Not for some finite period of time, but forever.

http://www.slate.com/articles/health_and_science/medical_exa...

> For instance, much of the research assumes that when fat people lose weight, they become “healthy” in the same ways as a thinner person is healthy. The evidence says otherwise. “Even if someone loses weight, they will always need fewer calories and need to exercise more,” says [UNC pediatrician Asheley] Skinner. “So we’re putting people through something we know will probably not be successful anyway. Who knows what we’re doing to their metabolisms.”

> Debra Sapp-Yarwood, a fiftysomething from Kansas City, Missouri, who’s studying to be a hospital chaplain, is one of the three percenters, the select few who have lost a chunk of weight and kept it off. She dropped 55 pounds 11 years ago, and maintains her new weight with a diet and exercise routine most people would find unsustainable: She eats 1,800 calories a day—no more than 200 in carbs—and has learned to put up with what she describes as “intrusive thoughts and food preoccupations.” She used to run for an hour a day, but after foot surgery she switched to her current routine: a 50-minute exercise video performed at twice the speed of the instructor, while wearing ankle weights and a weighted vest that add between 25 or 30 pounds to her small frame.

> “Maintaining weight loss is not a lifestyle,” she says. “It’s a job.” It’s a job that requires not just time, self-discipline, and energy—it also takes up a lot of mental real estate. People who maintain weight loss over the long term typically make it their top priority in life

That link says the chance of keeping lost weight off for 3 years is 3% but of doing so for 5 years is 5%? Seems odd.

Anyway, I'd like to see a credible source on the claim that "Even if someone loses weight, they will always need fewer calories and need to exercise more". And even IF that's true, it doesn't change the fact that that person can still, by eating fewer calories, maintain their weight loss.

The case with Debra Sapp-Yarwood says she eats 1800 calories, or 7500kJ/day. That's not a severe caloric restriction. For a "small-framed" but active 55-year-old woman that's an entirely appropriate intake.