After serving as the spokesmodel for the Jenny Craig weight-loss program for the past three years, Kirstie Alley is stepping aside.

“Although Kirstie will not appear in future advertising endeavors for us, she does remain on Jenny Craig’s maintenance program and is confident that our program has helped her incorporate positive lifestyle changes that should last a lifetime,” Scott Parker, vice-president of marketing for Jenny Craig, tells PEOPLE.

“Now that Kirstie has ‘passed her maintenance baton’ to Valerie [Bertinelli,]” adds Parker, referring to the inclusion of the former One Day at a Time star to the ad campaign beginning last August, “you’ll see a new campaign with a new celebrity client emerge, in 2008 … one that promotes health with Queen Latifah

Citing Alley’s “losing 75 lbs. and maintaining that weight loss for over a year,” Parker goes on to say, “She’s proud to have been able to participate in the creation of Jenny’s award-winning, integrated advertising campaign, and says she’s thankful for the opportunity to help so many other people lose weight and keep it off.”