Jessica Simpson's best pals have signed up for the singer's weight-loss plan in a bid to support the new mum's efforts to shed her post-baby pounds.

The fashion designer's figure ballooned when she fell pregnant with baby Maxwell last year (11), but she has dropped a staggering 40 pounds (18 kilograms) in the months since she became a first-time mother thanks to her spokeswoman deal with WeightWatchers.

Simpson still has a way to go, and to help the Sweetest Sin hitmaker reach her goal, her friends have begun following the diet too - even joining the pop star at her home for weekly Wednesday weigh-ins.

She tells Us Weekly magazine, "We talk about what we've struggled with. It's really encouraging to know you're all going through the same thing. Our meetings are also a great time to celebrate victories... Most people can tell a difference every time they see me, which lets me know I'm making progress."

And her trainer Harley Pasternak, who keeps Simpson on track with gym sessions four times a week, is impressed by the star's dedication.

He continues, "There was one time she stubbed her toe and had to miss an appointment to go to the doctor. So she booked an extra one that week to make up for it and even came in flip-flops because her toe was too sore to put on shoes. She could have easily used that as an excuse, but she didn't."

Pasternak also helps the 32 year old avoid temptation on the set of her U.S. TV show Fashion Star by re-routing her path from her trailer to bypass the catering table.

He adds, "We literally mapped out a different direction from the trailer to the stage so she wouldn't walk by it."