Credit: Binns Johnstone/

At 39-years-old, Jenny McCarthy's still got it goin' on.

The buxom blonde, who celebrates her birthday Tuesday, is known for her sizzlin' bikini body -- but it doesn't come easily.

"I'll be really into health and then I'll be out of health, usually depending on when the McRib is back," Jenny McCarthy joked to Us Weekly in 2010. "I can't even balance a checkbook, let alone my calorie intake."

To stay fit, the Illinois native runs on the treadmill twice a week and does Bikram yoga three times a week. "I hate cardio even though I do it once in a while," she told Us. "Bikram yoga helps you zen out while using every single one of your muscles without having to lift weights."

McCarthy's other secret for looking trim on the beach? "I swear to God, it's 10 days of soup. I just always stick to that," she says. "The soups really do make you feel like you're having a full meal. I have the Montel Williams soup maker. I'm a soup-a-holic."