The veteran star, 54, admits she has gradually piled on the pounds since her days as a Hollywood pin-up following her turn as Princess Leia in the original Star Wars trilogy, but her weight really ballooned in 2008 when she hit the road to perform her one-woman stage show, Wishful Drinking.
Fisher's lack of exercise and unbalanced diet caused her waistline to spiral out of control and at her heaviest, she tipped the scales at 180 pounds (81.6 kilograms).
She says, "I would just graze, but I didn't do it healthy - it was like putting on the feed bag."
She gained even more weight following the death of her father in September (10), when she indulged in calorie-packed ice cream bars: "That was bad. I was in denial."
But Fisher, who previously battled drug and alcohol problems, recognised her need to shed the pounds in November (10) and turned to Jenny Craig experts to help transform her lifestyle.
She has lost 12 pounds (5.4 kilograms) since starting the new diet, although she insists she still has a long way to go.
She says, "I'm fat. All the clothes in my closet belong to another chick. They have to make a new alphabet for my bra size!"
The actress reveals she was driven to do something about her growing figure after becoming fed up with rude taunts about her size from gossip bloggers.
She adds, "I look on the Internet and they say, 'Whatever happened to Carrie Fisher? She used to be so hot and now she looks like Elton John.' I was really hurt."
Fisher's new lifestyle includes work-out sessions five days a week, reports People.com.
She joins newlywed actress Valerie Bertinelli and Sara Rue as Jenny Craig representatives.