Carrie Underwood admits internet trolls motivated her to question how she looked during American Idol, which led to a months-long quest to lose weight in 2005, which led to her not feeling very good at all.

In her new book Find Your Path, the now-36-year-old Underwood spends time explaining how she did it wrong during and after winning American Idol. She had already cut red meat out of her diet by the time the show began, and during the competition she cut chicken, too. But she didn't really know how to live a vegetarian lifestyle without sacrificing nutrients.

Simply scrapping meat and counting calories (plus her first organized exercise routine) brought the wanted results at first. Underwood was losing weight and feeling less winded onstage. "But then I started to experiment," she writes.

Her philosophy was simple: If cutting calories was good, wouldn't cutting more calories be better? That lifestyle suppressed her metabolism, she explains, and while she was losing even more weight, she was losing energy and strength, too.

"Some days, I went as low as 800 calories!" she adds.

"I looked thin, but I wasn't feeling great anymore, and I definitely wasn't healthy."

See Carrie Underwood Through the Years:

Underwood's time on American Idol was pre-Twitter and in the early days of Facebook, so she and her competitors weren't ready for public criticism when it came via online message boards. Earlier in the book, she explains how most people were sweet, but the small percent who criticized her performance or how she looked stuck with her. This wasn't all bad, however. Underwood used it as fuel to be better and to eat better — during the competition she admits she snacked on a lot of junk food and wasn't intentional about what went into her body.

"I realized my pants were a lot tighter than they had been. I did have less energy. I wasn't feeling that great or weathering the stress of the show all that well," she says in her new book. "I think seeing those comments was a blessing in disguise."

With help from trainers and some research into nutrition, the superstar learned how to eat better and more, and while it came at the cost of added weight, her body didn't necessarily change. She leaves the chapter letting readers know the journey was worth it.

Find Your Path is in stores and at digital retailers now. This week Underwood has been on a small book tour and has one more planned visit in Los Angeles later this month.

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