Kelly says the criticism started as early as her season on American Idol -- in 2002, she became the first winner ever of the hit Fox reality singing competition.
"I was the biggest girl in the show too," she recalls. "And I wasn't big, but people would call me big. Because I was the biggest one on Idol, I've kind of always gotten that."
Still, Kelly says that the mean-spirited comments hurts her more when it comes to her fans than it does her own self-esteem.
"I think what hurts my feelings for people is that I'll have a meet and greet after the show and a girl who's like bigger than me will be in the meet and greet and be like, 'Wow, if they think you’re big I must be so fat to them,'" she explains. "And it's like, you're just who you are. We are who we are -- whatever size. And it doesn't mean that we're gonna be that forever."
For example, Kelly herself admits that her fluctuating size depends on her mood.
"Sometimes we're more fit. Like, especially me," she says. "I'm such a creative person that I yoyo. So sometimes I'm more fit and I get into kickboxing hardcore. And then sometimes I don't and I'm like ... I'd rather have wine."