Young women are getting fatter but they are clueless when it comes to shedding those extra kilos, according to a new body image survey.

The Cosmopolitan magazine survey of more than 5000 Australian women aged 18-34 found about 42 per cent considered themselves overweight or obese.

And almost half said if they could change one thing about their life it would be their body.

Ten per cent of respondents were so body depressed they said they would happily trade four or more years off their lives to slim down.

The survey found women today weigh more than a decade ago, with obesity rates up by almost 20 per cent.

And when it comes to doing the right thing by their bodies, women are big on bad habits.

About 37 per cent of respondents regularly skip breakfast, more than one in five relies on coffee to stay energised, nearly half don't eat fruit every day and a quarter exercise once a month or less.

More concerning is that women are abandoning traditional healthy lifestyle measures to lose weight and are resorting to illicit drugs.

Seven per cent of women said they had used cocaine or amphetamines to lose weight and almost one in 10 would rather skip a meal than give up alcohol to purge the pounds.

Their partners too are suffering in the bedroom, with one in six women saying they prefer chocolate to sex.

Cosmopolitan editor Sarah Wilson said the survey had unearthed some disturbing trends about women and body image.

"But the conflicting information out there is also a major culprit," she said.

"Women are yo-yo dieting, based on competing information they're being fed. This kind of eating is throwing out women's metabolisms and stopping them from listening to their bodies."