Mariah Carey: 'I can fit into my high school jeans'

Mariah Carey may be pushing 40 -- but she can still fit into her high school jeans.

"My jean size went down to my 10th grade size," the 38-year-old singer, who frequently describes herself as "eternally 12," told Oprah Winfrey Monday.

"I got tired to people telling me, 'You need to lose weight'," she said. "It inspired me.

"For me, it's not about a number on a scale," she added. "It's not about necessarily even a size. It's about feeling good and being comfortable in your own skin. Right now, I feel really great. I feel better than I've ever felt."

And with the help of her own diet and nutrition guru, the singing superstar has maintained a very strict diet that limits foods cooked in butter.

And her favorite calorific treat, she says, is Mac and cheese.

"It broke my heart... That's the thing that I have difficulty letting go of because that's comfort food," Carey said. "So basically I'm uncomfortable."

Carey – who recently celebrated her 18th No. 1 single – has also credited her personal trainer for her sexy new physique.

"I don't know why everyone thinks I lost 30 pounds," she told Allure magazine. "This trainer has actually helped me reshape my arms. That's where I gained most of my weight: upper body. That's just one thing you have to lose weight for."