Carrie Underwood has a secret for eating healthy: accountability!

"I'm slightly obsessive-compulsive about what I eat, more than I should be. I write down everything I eat," the American Idol, 24, champ dishes in Glamour magazine's January issue. "I started doing it last year. And in the last year is when I've gotten more healthy and lost weight."

What does she eat? Well, no meat. She's been a vegetarian since age 13. (Listen up, Chace Crawford: "I don't think I could kiss someone after they ate a hamburger 'cause they would probably taste like it, and that would gross me out," she tells Glamour.)

Underwood also says she she enjoys cardio and "that big exercise ball."

Last month Us Weekly praised her dramatic style transformation from country casual to fashionista.

"I'll go home and one of my friends will say, 'Oh my, gosh, those shoes are so cute,' Underwood says. "And I'll say, 'Oh, they're Christian Louboutins.' They're like, 'What?' So yeah, I've definitely learned more names."

Underwood is set to join with Keith Urban on a 24-city tour beginning in January.

But she might need extra room for her luggage: "I have a giant makeup case, more makeup than any girl should have in her lifetime."

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