Kelly Clarkson losing weight for her boyfriend

He may have limited some of her songwriting subjects – especially those angry, brokenhearted ones – but Kelly Clarkson says her boyfriend has fueled her desire to work out.

"I would love to say that it had something to do with my work, but it doesn't," Clarkson, 30, whose new singing competition Duets premieres Thursday, told reporters during a conference call. "I have a boyfriend, and if I'm being completely honest, no one likes to be not toned when you are dating someone."

"I tone whenever I want, and I chose to now because my boyfriend and I are both really into it," she says. "But we don't work out together. We did that once and I didn't like huffing and puffing," she continues. "I didn't like looking all red and gross, so I don't do that."