Fit at Any Size

Trimmer may still be healthier, but staying active is replacing weight as the true standard of beauty

Eric Espada / Cal Sport Media / Zuma

Prince Fielder of the Milwaukee Brewers.

Nikki Blonsky is exactly the role model most parents dream of for their kids. She's happy, she's successful, she's overcome obstacles--no wonder her young fans adore her. She's also overweight--by some measures very overweight--in a culture that fetishizes thin.

There was a time when that alone would have been enough to keep the 19-year-old star of the movie Hairspray out of the fan magazines and off the posters decorating grade-schoolers' bedroom walls. But that time may at last be ending. The national obesity epidemic did not happen in a vacuum. It occurred in an era in which fashion models have got...