Carrie Underwood says she let her haters be her motivators, and it turned her life around.

In a cover interview with Women's Health, the country star reveals that she dealt with a lot of online trolls after being thrust into the spotlight on American Idol, but that people's negative opinions about her weight and body became positives for her health.

It was 2005, and Underwood had become an overnight star. She told herself she "shouldn’t care what other people think about me," but that she knew she could be better for herself. "And I let my haters be my motivators," she recalls.

As she and her fellow Idol finalists embarked on the American Idol Live! Tour, Underwood decided to swap her pasta and quesadilla diet for healthier options. She began consciously reading food labels and even counting calories, and she start to feel better.

Women's Health

However, Underwood admits her health mission became extreme — to the point that she was prioritizing exercise over food, some days taking in just 800 calories.

As time went on, it was harder to stick to her diet plan of starving her body, which lead to her overindulging. "I would ‘fall off the wagon,’ then feel terrible and repeat the cycle," she explains. "Your body is screaming out, 'I need more calories, I need more carbs!'"

Now 36, Underwood eventually found a regimen that worked for her, and her passion for fitness became an important part of her image. These days, she's a fan of "rules" when it comes to food consumption and strikes a balance of 45 percent carbs, 30 percent fat and 25 percent protein in her diet.

"This is how I feel good about myself, and this is how I operate," she insists.

The "Southbound" hitmaker offers fans a detailed look at her healthy lifestyle in her new book, Find Your Path, which was released on Tuesday (March 3). She also launched a corresponding app, Fit52, that provides users with tools and activities to stay fit like her.

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