Jessica Simpson and 8 Other Celebrities Who Endorse Diet Plans

(Associated Press)

Kirstie Alley served as a Jenny Craig spokeswoman from 2005 to 2008. More recently in 2010, she founded her own weight loss program called Organic Liaison. READ: Kirstie Alley Talks About Her Cocaine Addiction (Associated Press)

Kirstie Alley brought Valerie Bertinelli on board as a Jenny Craig ambassador in March of 2007. Less than two years later, she was posing in a bikini on the cover of People magazine. (Reuters)

After being called "the big girl" when she was a contestant on "American Idol," Oscar-winner Jennifer Hudson slimmed down with the help of Weight Watchers, for whom she became a spokesperson in April of 2010. WATCH: Jennifer Hudson Talks About How Her Weight Loss Is Saving Lives (Reuters)

Currently a spokesperson for Nutrisystem, Marie Osmond credits the weight loss program with helping her shed 50 pounds. (Reuters)

Reportedly inspired by the success of pal Valerie Bertinelli, the "Seinfeld" star signed on as a Jenny Craig spokesman in 2010. READ: Seinfeld Imagines What A 'Seinfeld' Reunion Would Look Like (AP)

Following the birth of her twins in 2011, the songstress signed on with Jenny Craig and shed 30 pounds. (Reuters)

After struggling for years to lose her post-pregnancy weight while the British tabloids called her "the Duchess of Pork," Sarah Ferguson, the Duchess of York, became a spokeswoman for Weight Watchers in 1997. (Reuters)

Charles Barkley is the face of Weight Watchers' "Lose Like a Man" ad campaign. While on the program, the former NBA star reportedly dropped 42 pounds from his 6-foot 6-inch frame. (Reuters)