Rather not do the "illness weight loss" treatment. You gain it back, anyway, usually.

Indeed, rapid weight loss usually isn't permanent. It's usually water which you'll need to gain back to keep from being dehydrated.

All the decent weight loss sites I recall say that it's best to try to lose at most 2 pounds a week. E.g. [link|http://www.active.com/story.cfm?story_id=7012|this] story from the St. Petersburg Times.

1 pound of fat is about 3500 Calories. 2 pounds is about 7000 Calories. If you can keep your metabolism the same (a big if), then you need to eat about 1000 Calories less a day to lose 2 pounds a week. That's a big task, and that's one reason why most people can't do it for a long period of time. And, as we all know, it's better to exercise too rather than trying to lose weight only through diet. It takes a lot of work to burn off 1000 Calories (e.g. when I NordicTrak, 10 Calories a minute is a pretty active pace).

Cheers,
Scott.