Sting, the rock star, stays super fit with yoga. For many years now he's been practicing Ashtanga Yoga and he typically spends an hour and a half a day performing the exercises.
Ali lost 100 pounds in one year. She did this with the help of a personal trainer. She is very tall at 6'1' and she now weighs 175 pounds. When she first met her trainer and weighed 278 pounds, he told her she wasn't eating enough! 
The Daily Beast site has a great slideshow and discussion about how 10 stars and celebritites went about losing weight. They include 
Lisa Key-Blair has lost 50 pounds in one year. She is featured in this months Fitness magazine. See her before and after photo at the link.
Actress and model Rebecca Romijn has lost nearly 60 pounds after giving birth to twins on December 28th last year. She says she lost the first 35 pounds within the first three weeks. (We must be counting the baby weight here too.) She says breastfeeding is the very best diet she's been on. See her story here.
Marie Osmond, age 49, lost 45 pounds 2 years ago and has managed to keep it off. 
A high protein diet is increasingly being recommended for fast weight loss. A friend of mine needs a hernia operation and he was told he had to lose almost 25 pounds in less than three months before the operation. A hernia operation is much less risky if there is less stomach fat. He has been placed on a high protein, low carb diet. It's not recommended for the long term, but as a fast way to lose the extra weight.
