I think it started in the 1920's with the thin, stick-straight flapper dresses (I'm actually writing a research paper on this topic for my Mass Communications class lol), and then elevated in the 1940's when women were urged to "tighten their belts" because of food shortages during WWII. That's when fat began to be seen as unpatriotic, sinful even. Then it re-emerged to a new extent in the 1960's with Twiggy and women suddenly wanted to look like they were 12 years old (prepubescent). The fashions in the 1960's were not designed for very curvy women - they were straight up an down again. Also you had the shrinking bikini's and miniskirt that encouraged small legs, thighs and stomaches. Then in the 1980's you had the aerobic fitness model craze, and with the 1990's came the deathly "heroin chick" thanks to Kate Moss. According to the fashion industry, you are not beautiful unless your ribs stick out. It's that whole "tiny girl in big clothing" look now, your clothes must blouse around.