Janet Jackson is famous for her chart-topping songs, her dance moves and being from one of the best-known musical families in pop music history.

But she's also well known for fluctuations in her body weight. At times, she'll appear in public with rock-hard abs, and at others, she'll be significantly fuller and curvier.

In a new campaign for Nutrisystem, the weigh-loss program for which Jackson is a spokeswoman, she is revealing a newly trimmed and toned figure.

In a video for the new campaign, which starts today, a slender-looking Jackson wears a form-fitting white blouse, black pants and a black belt that highlights her waist.  She holds out her arms, smiles and says: "This is what success looks like."

And in a striking photo, Jackson wears an orange dress and high, platform pumps. The 45-year-old appears slim and shapely.

Jackson has admitted that even when she was in top shape, she felt insecurity about her body.

"If it isn't our arms, it's our thighs, it's our butt, it's our stomach," she said in a December 2011 interview with ABC News' Juju Chang. "I could easily pick myself apart. That's what I would do, that's what I did."

The singer said she had been teased by her older brother, late pop legend Michael Jackson, and said producers asked her to lose weight when she appeared on the hit 1970s sitcom "Good Times."

"I remember them asking me, my first show, the wardrobe woman said, 'We are going to bind your chest.' I was developing at a very young age. Then the following season they told me I need to lose weight," she said.

"I look back on those episodes and I go, 'Oh, my gosh, I'm not a heavy kid by any means,'" she continued. "I internalized it and I never told anyone about it, and kept it inside for years."

As her career skyrocketed,  she turned to snack food for comfort and her weight ballooned. At her heaviest,  Jackson, who stands 5 feet, 4 inches tall, weighed 180 pounds.

Jackson isn't the only celebrity to take her weight-loss battle public. Singer Mariah Carey is a spokeswoman for Jenny Craig, and Jennifer Hudson, a Weight Watchers spokeswoman, has undergone a dramatic transformation.