Ashlee Simpson has adopted fitness guru Jackie Keller’s 30-day “Body After Baby” plan in a bid to shed the 30 pounds she gained during her recent pregnancy.

Ashlee, who welcomed son Bronx Mowgli with husband Pete Wentz in November, has started the workouts with Nutrifit meals and snacks, delivered daily.

“She’s swapping french toast and sugary syrup for multi-grain bread and berries,” a pal of the 24-year-old singer tells OK!.

Earlier this week, Ashlee dashed to the defense of her “portly” big sister Jessica Simpson, writing on her blog that, “all women come in different shapes, sizes, and forms and just because you’re a celebrity, there shouldn’t be a different standard.”