I work with a guy who did the gastric bypass surgery thing. He looked great for years. Now? Not so great. He slowly slipped back into his old eating habits (like eating an entire sleeve of Chips Ahoy cookies for breakfast) and back into his fatter clothes as a result.
I'll bet when he decided to become a trainer he pictured himself working with young Olympic athletes in the peak of physical condition... and here he is taking a brisk power walk with a fat old no-self-control sloppy broad.