Sure, a greasy takeaway burger isn't the best food choice you can make, but after a long day at work, its appeal skyrockets because it is convenient and inexpensive.

If a junk food tax was introduced in Australia, that might change. The prices of chips, cakes and lollies would increase in a bid to encourage people to add the healthier option to their shopping trolley instead.

Experts are divided over whether a junk food tax would be a good move. As one of the ideas currently being tossed around as a way to reduce the country's obesity rates, in theory it seems like a great one.

However, price is not the only thing taken into consideration when buying food.

Accredited practising dietitian Alycia Hull says time pressures and other lifestyle factors are a bigger factor when deciding what to eat.

She says overall behaviour change is the key to curbing the obesity epidemic, not bumping up the price of junk food.

"The group I see this being a problem for is the socioeconomic disadvantaged. I don't think adding a tax will necessarily reduce their buying of these foods or change their behaviour."

Denmark introduced a similar initiative last year, taxing all foods with a saturated fat content of more than 2.3 per cent. The tax was repealed last month because it didn't deter people from buying these products, with tales of people driving to Germany to load up on cheap ice cream.

Another problem some see with introducing a junk food tax is determining what is classified as junk food.

"We don't have a clear definition of what foods are considered unhealthy and junk foods," Hull explains, adding that sugar, sodium and saturated fat content would all have to be considered.

But others believe it would be simple to decide what foods would fall under the tax. Heather Yeatman, Associate Professor in Public Health at the University of Wollongong and President of the Public Health Association of Australia says the Australian dietary guidelines and work on food labelling would make it easy to decide what deserved a price rise.

"But the chances of it happening are very small because there's very strong economic policy that governments have that basically doesn't allow this type of tax to be implemented," she says.

Yeatman believes there are many benefits to a junk food tax.