Skinny models don't necessarily sell more products

Each ad was made twice, once using a size eight model and the other featuring a size 12 model.

The Sydney Morning Herald reports that when Diedrichs showed the ads to 400 young people, she found no difference in the likelihood of respondents buying the advertised products depending on whether they had seen the skinnier ad or the one showing the bigger woman.

She did report, however, that women aged between 18 and 25 felt better about their own body image if they had viewed the images of the larger models than those shown the thinner women.

She told the SMH: "For anything to change, research has to be convincing not just to government and health researchers but also to people in advertising who actually make the decisions. Often people make the argument that thinness sells, and that's why they use [slim models]."

Unilever brand Dove has also made a big deal of its campaign using "real women" and highlighting how much imagery in advertising is manipulated.

The company has subsequently been criticised for using more traditional imagery to promote other brands, such as Lynx/Axe deodorant, which feature a succession of skinny models.

There have been concerted campaigns to cut back on the use of ultra-thin "size zero" models, with fashion weeks in Madrid and Milan attempting to ensure that all the models appearing on the catwalk are of a weight that is deemed healthy by the Body Mass Index measure.

However, fashion editors maintain that they must use thin models because clothing companies supply samples in small sizes.