12/18/2012 AT 03:05 PM EST
Almost seven months after giving birth to daughter Maxwell Drew
, Jessica Simpson
posed for a series of sexy shots showing off her post-baby body.
The Weight Watchers spokeswoman lost 50 lbs. of her pregnancy weight and looks svelte in her new "Expect Amazing" ad campaign, which will begin airing Dec. 25. PEOPLE has a sneak peak at the images of Simpson, which were shot on location in the California desert in late November.
Shortly after becoming a mom, Simpson, 32, admitted that she felt self-conscious about her post-baby body – but said she was ready to get back into shape.
"I think anybody who's gone through a pregnancy, after they have the baby, it's like, 'I need to do something about this!' " she told PEOPLE
in May. "For me, I really want to do something that is a lifestyle, because in the past I've been known to yo-yo diet."
So, when Weight Watchers asked her to be their new spokesperson, the fashion mogul eagerly said yes, and signed her friends up for the program, too.
"Weight Watchers changed my relationship with food, and I feel so much more prepared to make the right choices," she says. "It feels pretty incredible."