Stars are slimming down for summer to bare those bikini bodies, and “Extra” is giving you the skinny on their secret diets!

Hillary Duff – now heating up the new issue of Maxim magazine and showing off her figure – recently dropped down to 109 pounds!

She told Us Weekly last week she had been “obsessed” with her weight after tabloid headlines said she could lose a few pounds.

After realizing she wanted to be healthy – and not super-skinny – Hillary started eating right and doing Pilates workouts four times a week.

She said that instead of counting calories, she relies on lots of greens, lean protein and fresh fruit.

“You need to find balance,” she told Us Magazine.

Howard Stern’s sassy sidekick Robin Quivers has transformed her body in less than a month, thanks to the Martha’s Vineyard Diet Detox.

“I'm down 24 pounds in 21 days,” Robin happily told “Extra.”

It’s the 21-day juice diet that has Robin crying for joy.

“I was in tears,” Robin said. “I looked at myself in the mirror yesterday and I almost didn’t recognize the person looking at me.”

New mom Kristi Swanson just started the Medifast program to shed the 30 pounds she gained during her pregnancy, and the actress tells “Extra” she’s already seeing results!

“I’ve almost lost seven pounds already, and it’s amazing,” she gushed.

“Desperate Housewives” star Marcia Cross and “Extra’s” own Dayna Devon have also been busy losing baby weight.

Both are featured in the new In Touch Magazine, where Marcia said she shed her 65 pounds of pregnancy weight by staying away from junk food.

And Dayna, who put on 24 pounds with son Cole, also lost it by working out four times a week.

“I walked everywhere,” Dayna said. “It was easy to put it on – it was really hard taking it off!”