“She’s breast-feeding Max and wants her to get the best nutrition,” a source told Us Weekly magazine.
“She has to cut down on fast food. Besides, it’s a great way to jump-start the massive diet ahead.”
Simpson recently revealed she’s keen to lose her baby weight.
“I think anybody who’s gone through a pregnancy, after they have the baby, it’s like, ‘I need to do something about this,’ ” she told People magazine.
“For me, I really want to do something that is a lifestyle, because in the past, I’ve been known to yo-yo diet.
“I was like, ‘I’m going to enjoy my pregnancy,’ and I did.
“I ate very healthy, but I did indulge some of my cravings — and that’s okay because I know I can work it off now.
“There’s not a goal weight — I just want to feel normal and fixate on inches.
“I really want to set small goals, so I’m constantly reaching goals and not looking at something so far ahead.”