Rock your body   Katherine Schwarzenegger does the book fair
By Madeleine Marr  You won't catch Katherine Schwarzenegger on
the latest fad diet. Been there, ate that. The daughter of Maria
Shriver and Arnold Schwarze- negger talks all about her strug-
gles with weight in Rock What You've Got (Hyperion, $22.99),
which she'll discuss at 4 p.m. Sunday at Miami Book Fair
International. Rock's main message is directed to young girls
who don't necessarily fit the size-2 mold seen in magazines and
on screen. "It's unrealistic to compare yourself to models, who
are most of the time airbrushed," says the 20-year-old USC
student.  "It's really important to know what is and isn't
real." A recent example of someone taking things to the extreme
is Disney star Demi Lovato, who entered rehab for body image
issues. ‘‘She's in an industry where that's all anyone focuses
on," says Schwarzenegger, whose favorite splurge is cereal.
"It's a lot of pressure to always be thinking about how you look
on the outside, every single da