Megan Fox has lost 13 of the 23 pounds she gained while pregnant with her first son, Noah, but it's not because she's been logging extra hours in the gym.

"I can't work out yet because my body is still too fragile," the 26-year-old actress told Us Weekly at the Dec. 12 Palladium Jewelry-sponsored premiere of This Is 40 in Hollywood. "I try to eat whatever I want, but I don't eat any dairy, and I guess that's the biggest diet tip. Try and stay away from dairy -- especially if you're a woman! It's really hard on your hormones."

Though she's only been a mom since Sept. 27, Fox -- also stepmom to husband Brian Austin Green**'s son Kassius, 10 -- told Us she's eager to expand her brood. "I want a big family," she revealed. "I definitely want to have a couple more kids."

As for her little guy, the actress cooed that he's "getting really chubby!"

"He's super healthy and funny and he's very bossy already," Fox told Us. "He's got a very strong personality, so I'm really in for it!"

Green, 39, is "an amazing dad," the star added. "He does anything that I can't do at the moment because I'm too tired. Whatever's going on, he does. He's with the baby right now. He's the perfect daddy."

This Is 40, which also stars Paul Rudd and Leslie Mann, is in theaters now.

This article originally appeared on Usmagazine.com: Megan Fox: "My Body Is Still Too Fragile" to Work Out After Giving Birth