Another worrying statistic in the survey included more than a quarter of 14-year-olds saying they had considered having plastic surgery or taking diet pills.
Almost a fifth said they were "already suffering from an eating disorder" such as anorexia or bulimia.
The girls were also asked which celeb they thought had the best female body.
Britney came first, but stars with more rounded figures - including Beyonce and J-Lo - also made the top five.
Hear story 
Watch Ellie Criselle's report
Body image Hotseat: Bliss editor 
Are celebs too thin?
There's too much pressure on us to look good
