Let's get this straight: The number of dieters who go from fat to thin, and stay there, statistically rounds down to zero.

Every study says so. No study says otherwise. None.

Oh, you can lose a ton of weight with diet and exercise. You'll gain it back. Here's one study running the numbers. Here's a much larger analysis of every long-term weight loss study they could find. They all find the exact same thing: You can lose and keep off some minor amount, 10 or 15 pounds, for the rest of your life -- it's hard, but it can be done. Rarer cases may keep off a little more. But no one goes from actually fat to actually thin and stays thin permanently.