Jessica Simpson Shows Off Post-Baby Body, Promotes Weight Watchers On 'Good Morning America'

Jessica Simpson appeared on Good Morning America this morning, Jan. 7, where she debuted her super-thin post-baby body and spoke about how Weight Watchers helped her get back to size following the birth of her second child.

"I believe in it with all of my heart," she told GMA's Lara Spencer of Weight Watchers. "It's a lifestyle. I've tried so many different diets, and you can only stick to something for so long. I feel like with Weight Watchers, it just becomes a part of who you are."

During Simpson's first pregnancy, she allowed herself to completely indulge, and gained a reported 70 pounds. Then, just months later, she became pregnant with her second child, son Ace Knute. Throughout that pregnancy, Simpson remained focused on her health, which, along with the help of Weight Watchers, paid off.

Simpson admitted on GMA that during her first pregnancy with daughter Maxwell, (now 20 months old), she "didn't care" about gaining weight and "just let myself have whatever I wanted!" With son Ace, she wasn't nearly as "relaxed in my eating."

"I had already been on Weight Watchers, and I had already lost over 50 pounds," Simpson explained. "I was just already in a healthier regimen, so I kept walking and staying active-and Maxwell started walking!"

One thing that is keeping Simpson motivated to stay fit is her upcoming wedding to fiance Eric Johnson. Although the pair have yet to set the date, Simpson is already thinking about her potential wedding dress -- and looking great in it.

"We don't have an actual [wedding] date, but we do know that we want it to be this year," she said. "We need to get married! I already feel like we're an old married couple already. Like, if he wanted to run, he could've run when I was hormonal and pregnant."