"A lot of girls put so much emphasis on cardio, but for me, my body changed when I just gave up cardio and started lifting weights," she told ET's Katie Krause. "The more muscle you have, the more fat you burn."
Cavallari, who welcomed her third child with husband Jay Cutler in November, suggests avoiding processed foods, soda and alcohol while gearing up for bikini season.
"I try to be healthy 80 percent of the time and then 20 percent, I indulge, I eat whatever I want and I enjoy life," she confessed, adding that she's set her sights on writing a cookbook. (And, yes, she's still got her vices!)
"I'm a big, big pasta girl. The carb and sweet girl," she says. "My dad's Italian. He has this amazing recipe for meatballs."
Earlier this year, the former reality star released a different kind of book -- Balancing in Heels: My Journey to Health, Happiness, and Making it all Work -- and spoke with ET about why she's turned down offers to return to reality TV.
"We get offered it all the time," she revealed. "We want our kids to live as normal a life as possible."