Since giving birth to her second child, son Ace Knute Johnson, the star has pinged back into shape.
Now, a source close to Jessica has revealed that her one-year-old daughter Maxwell is partly responsible for her slimmed-down physique.
Apparently, her favourite way to exercise is running around after her toddler and playing with her on the swings in their garden.
Jessica also incorporates regular exercise into her busy schedule, making sure to work out three or four times a week.
The 33-year-old enjoys hiking around her LA neighbourhood, wearing a pedometer to measure how much exercise she's doing.
Jessica recently revealed that she has never felt better in her own skin. Smouldering in new photos for Weight Watchers, the 33-year-old star shows off her incredible figure eight months after welcoming her second baby .
"When I started Weight Watchers, I didn't know what to expect at the meetings," the bubbly blonde says in the latest advert.
"It reminds me that we don't have to do this alone. It's so much better to have some back-up since we all face similar challenges. I can honestly say I've never been happier."
It's not just Jessica’s body confidence that's putting a smile on her face. She is blissfully happy with her fiancé Eric Johnson. "The new year will definitely bring wedding bells, which is exciting… I think it's about time," the Texas-born beauty recently told People.
"Knowing that I have the wedding coming up is an incentive to stay on Weight Watchers, count my points and stay in the gym. I mean, when you see my dress, you'll know."