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Kristin Cavallari, 24

Height: 5'3½" Weight: 109 lbs.

Was it hard adjusting to photographers catching you in a bikini all the time? I remember filming The Hills and I saw a photo of myself in a bikini and thought I looked really fat, and I went on a crazy diet. It's hard when people judge you.

Do you feel a lot of pressure to stay thin?

Sometimes. The good thing about it is, it makes me healthy. If I wasn't in the public eye, who knows how much I'd weigh. When I first started dating Jay [Cutler, her fiancé and Chicago Bears quarterback] I gained about 8 lbs. And it was like, I've got to get back to the gym. I can't eat like a 6'4" guy!

What's the best bikini cut for your body?

I automatically go to string bikinis. I really have no shape, and it gives me a bit of a butt.

How do you stay fit?

For this shoot, I worked out with my trainer three times a week then did cardio on the treadmill for 40 minutes. But the biggest thing for me was cutting out alcohol; when I'm hungover, I eat whatever I want.

Serena Williams, 29

Height: 5'9" Weight: "I don't step on scales."

When did you realize you're not built like most athletes?

I was 17, playing in the U.S. Open, and this one lady said, "You need to wear a better bra." That's when it clicked for me that I was really curvy. A DD chest is not what you normally see in the locker room.

What do you get the most compliments on?

It's all about my butt. I like Brazilian-cut bikini bottoms in the back. Some people think it's too small, but I'm like, "Whatever!"

Are you insecure about any areas?

Sometimes my stomach poufs out a little bit, and I feel like my legs aren't as tight as I like them to be.

How do you feel when you're photographed on the beach in your bikini?

In the beginning it was weird, but I'm okay with it. I represent ladies who want to be healthy and not starve themselves.

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Paris Hilton, 30

Height: 5'8" Weight: 115 lbs.

What did you weigh at your skinniest?

I was about 105 lbs. Looking back at photos, I was way too skinny. I was single, going out every night and not having full meals. Now that I'm in a relationship [with nightclub owner Cy Waits, her boyfriend of one year], I eat a lot! At my heaviest I was 125. Now I'm 115 lbs.

How did it feel weighing 125-a slim weight, by the way?

Last December I was wearing a skintight leather catsuit and someone said I was pregnant! That was just hurtful.

What changes have you made to your diet and exercise routine?

No more soda, no more fast food. And I have a nightclub upstairs at home that I've turned into a gym.

  • Contributors:
  • CONTRIBUTORS By Thailan Pham/L.A.,
  • Cynthia Wang/L.A.,
  • with Jennifer Garcia/L.A..