"It's like you have to eat 5,000 extra calories a day or you can't produce enough food for them. So, that's been fun as well," the actress tells Extra.
Romijn, 36, has lost nearly 60 lbs. of pregnancy weight since giving birth to twins Charlie and Dolly four months ago – all without exercising.
"I think within the first three weeks, I took off like 35 lbs. without doing anything!" says says. "I haven't been able to work out that much because I have twins. It's impossible to get back into a regular schedule."
But she does acknowledge, "I'm not pretending to be back to the shape I was in beforehand anyway. I still have a ways to go. We've got Spanx underneath almost everything."