Kirstie, who appeared on "The Oprah Winfrey Show" last week to discuss her weight gain after appearing on the show in 2006 to show off a svelte bikini body, told the mag things got out of hand after parting ways with the Jenny Craig program.
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"I didn't have to weigh in," she said. "I just sort of went wild."
The star said that her "food demons" weren't cakes and pies, instead showing a sweet tooth for Chinese food, sugar and butter.
"A lot of butter," she said. "If I'm at the movies, usually I eat popcorn without butter, but I'd say, 'I'm at the movies, so who cares?' And toast with butter. Or let's say I had two cups of pasta and six tablespoons of butter on it. There was a lot of butter going on."
And though she tried being a vegetarian for seven months, that only encouraged her to pack on the pounds.
"A vegetarian would probably be eating vegetables," she said. "But to me, being a vegetarian meant I'm going to eat enchiladas with no meat, and I'm going to eat lots of bread, lots of carbs."
Now, she said, she's ready to get back in shape – which means dropping from 228 pounds, her highest weight ever, down to 140 or better.
"I have to be below 140 to look really good," the 5'8" star said. "I have to work my legs like crazy. My real goal's always too low – I love the way I look at, like, 128… I'm ready to work. I'm gonna go, 'You know what? Get back on the horse, lose the freakin' weight, and then just move forward!"