The actress and husband John Travolta welcomed son Benjamin Hunter Kaleo in November 2010.
Talking to People, she confessed that she preferred not to think about dropping pounds and prefers to let nature take its course.
"I haven't been working out. At all," she explained. "Maybe that's the secret. Don't stress about it!"
"It certainly would be better if I started to exercise, but I had a c-section so my stomach muscles weren't very strong. I wanted to do some dance classes but it was a little too much. I was down for the count!"
However, she went on to say that one thing has helped her regain her old figure, adding: "I've been lucky because I've been breastfeeding so that's really helped me lose the weight. That really is the secret."
Preston recently revealed that baby Benjamin often takes flights with Travolta.