"I'm fat," says Fisher, 54. "All the clothes in my closet belong to another chick. They have to make a new alphabet for my bra size."
Jokes aside, as the newest spokesperson for Jenny Craig, the 5'1" (and a ½") actress and author is opening up about her humiliation over gaining weight – she was 180 lbs. at her heaviest – and her determination to slim down.
Fisher, who weighed around 105 lbs. when she starred in the Star Wars trilogy in the late '70s and early '80s, says her weight crept up over the years and grew out of control three years ago when she went on the road with her one-woman show Wishful Drinking, thanks to no exercise and an unbalanced diet.
"I would just graze, but I didn't do it healthy – it was like putting on the feed bag," says Fisher, the daughter of '50s movie sweetheart Debbie Reynolds and crooner Eddie Fisher. She lives in L.A. with her daughter Billie, 18.
For Fisher – whose conquering of drug and alcohol addiction and mental illness became fodder for her best-selling books – food was one of her last great comforts. When her father died in September, she recalls turning to Häagen-Dazs ice cream bars. "That was bad," she says. "I was in denial."
Adding to her humiliation were comments from bloggers. "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,' " she recalls. "I was really hurt."
But now Fisher has reason to be hopeful: Since joining Jenny Craig in late November, she has shed 12 lbs. by eating only plan-approved meals and getting back to exercising five days a week.
For more on Fisher's weight struggle – including how she packed on the pounds and how she's getting back in shape – pick up the new issue of PEOPLE, on newsstands Friday