6. Renee Zellweger
For her roles in movies like Bridget Jones’ Diary and Chicago, Renee Zellweger probably wins the award for most drastic yo-yo dieter in Hollywood. To play the average-looking Jones, the actress gained close to 25 pounds, then dropped it all (and more) in time to become sexy murderess Roxy Heart. But that isn’t all. For the Jones sequel and her Oscar-winning performance in 2003’s Cold Mountain, Renee Zellweger gained another 30 pounds.