Jessica Simpson appears at Dillard's Lakeside Shopping Plaza on October 8, 2011 in New Orleans, Louisiana. Credit: Kevin Mazur/

Jessica Simpson is in it to win it!

As part of a $4 million deal with Weight Watchers, the 31-year-old first-time mom is psyching herself up revamp her eating and fitness routines -- and is she sharing the journey with her 5.5 million Twitter followers.

"What we put in our bodies mirrors our Self-Worth!" the singer and fashion mogul wrote. "#INSPIRED."

One example of junk-food-loving Simpson's dietary evolution? The one-time lover of Scotch and margaritas kicked back last Saturday night with a big glass of…water!

"Responsibility has drastically changed my life "Saturday night drink of choice.... WATER! :)" said the star, who welcomed daughter Maxwell Drew Johnson May 1 with fiance Eric Johnson.

Back in late winter, the then-heavily pregnant star told ELLE mag abstaining from booze was a challenge at first.

"Givin' up my Scotch? My Macallan 18? That was hard for me! Though now being pregnant, you crave other things. A big thing of water sounds great!"

According to a source, the star gained 70 pounds during her pregnancy.

"[Weight Watchers] focuses on healthy habits for the long-term (and I can still indulge in my guilty pleasures every now and then, too)," the new mom explained on Facebook. "I have actually gotten a group of friends together who are going to be doing it with me."