Weight Watchers via Facebook

Singer-actress Jennifer Hudson is poised to be an American fitness idol as she begins the New Year, flaunting her transformed size 4 body in a new Weight Watchers ad campaign.

Check out the amazing new musical Weight Watchers commercial here.

The "Dreamgirls" star rocks multiple sexy looks in the campaign reportedly styled with the help of Project Runway's Tim Gunn, that features her flaunting her still curvy, but considerably leaner frame.

The mom-of-one has reportedly gone from a size 16 to a size four by following Weight Watchers Points Plus program, a diet that emphasizes portion control and healthy choices, and working with personal trainer Harley Pasternek.

Pasternek also takes credit for the taut curves of celebrity clients including newlywed Katy Perry, Eva Mendes and pantless-brave Lady Gaga.

Hudson played coy about exactly how much weight she's lost during a recent interview with Access Hollywood where she's shown taping her commercial for the weight-loss brand.

"Feeling good is the perfect way to express how I feel right now," she told the program.

To celebrate her new look on a high note, Hudson belts out the classic "It's a New Day," in the ad featured on Weight Watchers' Facebook page. She'll also be singing the tune tonight on "Dick Clark's New Year's Rockin Eve" with Ryan Seacrest on ABC.

In an interview to support the campaign she says,"'I've tried diet after diet, plan after plan and I've only gotten so far, but never this far."

"I feel like I have a new life, I feel like a brand new person," she says, adding she wanted to sing about her new body as a way of inspiring others.

StyleList thinks that's a better plan than the skintight bodysuit she recently wore to the airport.

Her fitness tip for the New Year, "Don't just sit on the couch and eat."

Hudson will have plenty to keep her off the couch in 2011. Her son, David Daniel Otunga Jr., born in Aug. 2009, is entering his toddler stage and she'll be busy promoting her new role in the biopic, "Winnie" about the ex-wife of former South African President Nelson Mandela.

Speaking of dramatic transformations, read about what Kelly Osbourne had to say about her 50 pound weight loss.

And read why reality star Heidi Montag regrets her decision to have a drastic 10 plastic surgeries last year.

Also find out why Ginnifer Goodwin has been on Weight Watchers since she was nine!