Women and Thinness

Along the same lines, competitive escalation is a dynamic among women too. A well argued commentary in an audio file (NPR) about the pecularities of women's sizing:

Gaining Weight, Losing Perspective: When Sizes Grow
Obesity is becoming a bigger and bigger problem in the United States. An estimated 30 percent of Americans are obese, and the number is going up. But commentator Lori Gottlieb observes that it's getting harder to tell how much weight you've gained -- if you're gauging by your pants size.

Lori Gottlieb is the author of Stick Figure and I Love You, Nice to Meet You.

Spanish fashion show rejects too-skinny models:
Women with very low body-mass index not allowed on runway

MADRID, Spain - Spain’s top fashion show has turned away a slew of models on grounds they are too skinny — an unprecedented swipe at body images blamed for encouraging eating disorders among young people.

Just not attractive, IMO

When Is Thin Too Thin?

Girls aged seven 'have anorexia'

Men lust for hourglass curves, say researchers