The fomer Cheers star blamed her latest boost in size on her departure from the Jenny Craig Weight Loss Programme and a switch in her diet.
Alley admitted that she started "screaming" when she weighed herself for the first time in 15 months and discovered that she was her "highest weight ever".
"I was so much more disgusting than I thought," she told People.
Speaking about her eating habits, the 58-year-old said: "My food demons are Chinese food, sugar, butter. A lot of butter.
"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."
Alley famously lost 145lbs after signing up as a Jenny Craig spokesperson, but regained weight after leaving the company in 2008.
"When you're a spokesperson for Jenny Craig, there's responsibility," she said. "You have a person every week standing over you when you get on the scale, and I did it naked because those panties could weigh 30lbs.
"It was amazingly successful. But the first nail in the coffin was when I didn't have to weigh in. I just sort of went wild."
She added: "I messed up along the way, but I'm not going to concentrate on that. I'm gonna go, 'You know what? Get back on the horse, lose the freakin' weight, and then just move forward!'"