Equalities Minister Jo Swinson is spearheading a government drive to promote better body confidence.
She has previously campaigned about unrepresentative images of thin women being too pervasive in the media.
Ms Swinson said that too many shop windows did not accurately reflect the shapes and sizes of modern women.
The average dress size of a British woman has grown from a size 12 to a size 16 in just over a decade, yet many shops still typically display clothes in size 10 mannequins.
The Liberal Democrat MP for East Dunbartonshire has praised the example of Debenhams, which is preparing to display a range of size 16 mannequins in its Oxford Street store.
She said: "I would really like to see more retailers doing the same. Many customers want to see more realistic images in magazines, TV and on the high street."
"The images we see in the world of fashion are all much the same - it's as if there's only one way of being beautiful."
Susan Ringwood, chief executive of Beat, a charity that advises ministers on tackling eating disorders, welcomed the move.
However John Munro, a spokesman for the British Retail Consortium, said UK retailers already worked hard to promote body confidence.
He said: "Ultimately, individual retailers decide what approach to take based on their customers' feedback and preferences."