Health Journal - WSJ.com

Explains medical reason why people tend to gain weight back after losing...

Interesting!

Also a link to this interesting study about how people who kept food diaries lost twice as much weight over the same time period as those who didn't journal their intake...:

Writing down every morsel doubles weight loss - Diet and nutrition - MSNBC.com

I think thie last paragraph sums it up nicely:

How do some people manage to overcome the leptin effect and keep weight off? Generally by watching their food intake very carefully and continuing to increase their physical activity. "Anybody who has lost weight and kept it off will tell you that they have to keep battling," says Dr. Rosenbaum. "They have essentially reinvented themselves, and they are worthy of the utmost admiration and respect."