Women should not be so willing to criticise each other for being supposedly overweight, Jo Swinson, the equalities minister, has said.

She said unrepresentative images of thin women were too pervasive in advertising and the media, and has written an open letter to magazine editors saying that if they promote post- Christmas “miracle diets” they could be endangering the health of their readers.

Swinson, who is also a business minister, started campaigning on the issue of body image anxiety long before she entered government. Although in interviews on Thursday she largely focused on criticising the media, she also said women could do more to help each other ignore media pressure to be thin.

“The imagery that we’re presented with has just one type of so- called ideal which is very, very slim, generally very, very young as well, late teens or early 20s, and it is something which is unattainable and, indeed, not reflective of the true diversity of beauty that’s out there,” she said.

“There’s a resolution here that we all could make, women up and down the country. [Magazines] have got these features because they think people want to read them and part of that is because there is an obsession about being thin, so maybe one of the things we all need to do is support each other not to be so self- critical.

“So when your sister or your friend is standing there and moaning about whether she looks really fat, and actually she looks gorgeous, tell her so and support each other. Very often this kind of criticism, and self- criticism, is something which goes unchallenged and I think there’s a resolution there for everyone to challenge that default setting.”

Swinson said she was writing to magazine editors now because some of the diets they were promoting, such as one promising “lose seven pounds in seven days”, were dangerous.

“Every January we see these fad diets promoted. These aren’t promoting healthiness, these aren’t promoting a way of embracing exercise and eating fruit and veg and doing things which will actually help people. They’re actually suggesting that you can suddenly lose lots of weight very quickly and there are no negative health consequences.

“We actually know most diets don’t work and if you go on a crash diet there can be really negative health consequences … So this is a myth that’s being perpetrated trying to tempt people to buy these magazines and I think it’s time they change their record, frankly.”