When Marie Osmond was on "Dancing with the Stars," she made no secret of the fact that one of the reasons she was on the show was for the "Dancing" diet. Now she talks to ET's Kevin Frazier about keeping the weight off -- and Kirstie Alley's failure to do so.

"I can't motivate you; you can't motivate me, you have to motivate yourself," says Marie, who combined the exercise from "DWTS" with NutriSystem for a 50-pound weight loss, when asked about battling the bulge. "I had a setback for eight years," she jokes. "[The weight came off] once I set my mind to it, but I had to set my mind to it. You can't just say, 'I need to lose weight.'"

That said, the mother of eight feels Kirstie's pain. "I love her," she says. "She is one of the funniest women. I admire her abilities. She is gorgeous no matter what size she is. [I would tell her], 'Don't beat yourself up.' She is still the same person inside. I feel bad when people have to finger point and put other people down to feel better. I think it is a bad disease we have."

Marie also believes that it is not possible to lose weight unless you are doing it for the right reasons.

"It is not about looking good for people," she says. "It is not about being a size two. It is about life, health and happiness. Then you can conquer it."

Kevin spoke to Marie at the signing for her new book Might As Well Laugh About It Now, where she looked fabulous. Keeping busy helps. She continues to perform with brother Donny five days a week in Las Vegas, and she is working on an inspirational CD, which will be released on her 50th birthday.

She says what she is enjoying most about her book signings is the feedback she gets from women on how she has served as an inspiration to them.

"What has been really fun through all of this is, every night when I sign, there are a handful of women that come up to me and say, 'I have lost 30 pounds because of you.' I say to them, 'How do you feel?' They say, 'I feel fantastic.' And I say, 'And your knees don't hurt anymore?' The only snap, crackle and pop I have anymore is from my kids' cereal."

For more of Marie's interview with Kevin, tune in to tonight's ET.