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Kirstie Alley stepped off the scale to be a guest on "The Late Show with David Letterman" on Tuesday night. All in the name of fun, the quick-witted host and star quipped back and forth.

After welcoming Kirstie to the show, Letterman confessed that he has cracked jokes about her before. "I'm embarrassed now and if I need to apologize, I'd like to apologize," he said asking for forgiveness. "No, you don't need to because we make fun of you at my house too," whipped Kirstie.

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The star of "Cheers" fame admittedly "went off the wagon" after a stint as a Jenny Craig spokeswoman. "I'm really skinny now, just on a different planet."

Letterman and Alley discussed diet tactics. Comparing the addictive chemicals in cigarettes to food ingredients, he theorized, "Everybody would like to lose weight...I blame the American food producers because…we get addicted to the food and the grease and we love it. Cake frosting, forget it, that's all I eat."

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Alley agreed and is taking steps to change her habits. "That's what I'm working on now, is getting all the chemicals out of my life, out of all the foods, the pesticides, the insecticides, the herbicides, fungicides, all the antibiotics, all the hormones that are in food. It really is what's making us fat because I've always eaten a lot and I wasn't fat," she explained.

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On a mission to shed the pounds, Kirstie will star in a reality series to track her progress. "To see myself fat was hard. It's cathartic," she admitted. "I think other people are struggling with my weight more than I am. I'm losing weight now. I've lost about 24 pounds and I'm on my way on the downhill."

"Kirstie Alley's Big Life" premieres Sunday, March 21 on A&E.

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