When Kirstie Alley vowed to shed weight, doubters scoffed “fat chance” — but she’s done it!

The “Fat Actress” star has broken her addiction to food — and has a slimmer new look to prove it.

The sitcom queen dropped 20 pounds in the past few months, and her goal is to lose 60 more in the next year.

“Over the past two years, she’s gained a ton of weight — and kept telling people not to worry,” revealed an insider.

“But she was addicted to food — and especially to tacos.

“Privately she worried she was spiraling out of control, even as she put on a devilmay- care air about her weight. But she couldn’t make her craving for fatty foods go away, and she was putting her health at risk.”

Ironically, her reality show forced her to face reality.

“When Kirstie first started seeing the replays while shooting her show, she couldn’t believe how much space she took up,” revealed the insider.

“She says that when she looked in the mirror, she didn’t really seem as shocked at her size and appearance as everyone else was. But the small screen didn’t lie.

“Kirstie could hardly stand to see herself, and to realize that was how everyone else saw her made her vow to lose weight.

“She knew the first things that had to go were the bags and bags of tacos. She realized that would be the hardest part of getting her weight under control.

“Whenever she got the urge to splurge on a Mexican treat, she popped a video of herself into the VCR rather than send her assistant out for tacos.

“She used negative reinforcement and faced her problem head-on. She associated tacos with her overweight appearance on the screen — and when she saw herself, her craving went away.

“After a few weeks of not eating tacos and other junk food, she found she had lost a remarkable seven pounds!

“She’s stayed with the technique of watching herself on a video every time she gets a craving, and she’s lost another 13 pounds.

“The weight’s not coming off as fast as it did at first, but Kirstie’s desire for junk food has been waning.

“She says she wants to lose all the weight in the next year, and she’s started working out again to get back into shape.

Once Kirstie is thin again, it will be difficult for her to continue the fat jokes, but she says her show will move on to other topics.

“Promiscuity, I hope,” she quipped. “Everyone’s pulling for her,” said the insider. “No one liked seeing her as a ‘fat actress.’ She’s so beautiful and full of fun and life and has so much to give.

“Everyone’s hoping she will continue to slim down. But ultimately, it’s up to her.”