Star Bodies: Too Thin?

KATE BOSWORTH

THEN: Bosworth (left, in 2003), who has always maintained she's "naturally small," once worked out five hours a day to pack on close to 20 lbs. of muscle for her surfer girl role in Blue Crush.

NOW: She recently turned heads at New York's Fashion Week – not for her style, but for her startling frail look. An insider who saw the 23-year-old actress told PEOPLE, "She's so small, it's frightening."

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NICOLE RICHIE

THEN: Richie (left, in 2004) told PEOPLE last year, "I gained weight in rehab [in 2003]. It's been slowly coming off. I've actually never dieted."

NOW: Richie – who attributes her gaunt appearance to stress, not an eating disorder – recently admitted she "wouldn’t mind gaining a few pounds."

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KEIRA KNIGHTLEY

THEN: Though Knightley (left, in 2004) has admitted she’s not completely happy with her body, the actress told British Elle,: "I'm trying to go, 'F– it!,' and have bowls of pasta or whatever makes me happy."

NOW: Her gaunt look at the London premiere of Pirates of the Caribbean: Dead Man's Chest sparked rumors of an eating disorder. "I had no idea that I was (anorexic)," says the actress. "But I'm quite sure I don't have it."

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BEYONCé

THEN: Beyoncé (left, in 2004), whose hit "Bootylicious" gave women everywhere a reason to flaunt their curves, has said, "I'm very conscious of being a curvy woman and I'm very happy that I am a curvy woman."

NOW: The singer-actress confessed she went on a liquid diet to lose 20 lbs. for her role in the upcoming movie Dreamgirls, but claims she's put the weight back on: "I am no smaller or bigger than I've always been. It was strictly for the movie."

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VICTORIA 'POSH' BECKHAM

THEN: The former Spice Girl (left, in 1996), once known as much for her curvaceous good looks as her sassy style, claims bandmate Geri Halliwell got her addicted to dieting.

NOW: Following the birth of her first son Brooklyn in 1999 (during which she reportedly gained a mere 14 lbs.), the mother of three's weight has been a hot issue in the British press. Even Posh confesses in her 2001 autobiography Learning to Fly that she's been "obsessed" with her appearance.