Outdated NSW menu labelling laws are allowing large food outlets to leave out nutritional information on food delivery apps, a study has revealed.

The University of Sydney study shows that menu items for major food outlets such as McDonald's and KFC on food delivery apps are missing information on food that would help consumers make healthy choices.

The 2011 NSW Menu Labelling Scheme requires large fast-food outlets to display the average kilojoule content on menu items.

But the study's lead author SiSi Jia said that was not being done on online food delivery platforms.

"Just because it is online doesn't mean that the rules or regulations should be different," Ms Jia said.

She said the laws were written in a time when only traditional food environments were in mind, but since the pandemic the use of food delivery apps had increased.

"We need to update them, but we also need to make sure that they're well monitored and enforced," Ms Jia said.

According to market research company Roy Morgan, in 2022 around 40 per cent of people in Australian capital cities were using food delivery apps.

The defintion of large food outlets are franchises or chains with more than 20 locations in the state or 50 locations nationally.

The study reviewed 43 unique large food outlets with a total of 482 menus from UberEats, Menulog and Deliveroo included, with Deliveroo no longer in operation in the country.

Ms Jia told AAP that 94 per cent of menus of large food outlets had incomplete kilojoule labelling.

"We found that less than 6 per cent of menus on third party delivery apps had complete kilojoule labelling," she said.

The research found that there were also inconsistencies between different locations for the same franchise store and between the type of delivery service.

"Displaying the kilojoule content on a menu item is important to help people make more informed health choices," Ms Jia said.

"There are multiple studies that show menu labelling have real world impact."

NSW Agriculture Minister Tara Moriarty said the state government was working with other jurisdictions on a coordinated national approach to menu labelling.

"Food Standards Australia New Zealand (FSANZ) have been requested to prepare a proposal for a food regulatory measure for menu labelling under the Australia New Zealand Food Standards Code," she said in a statement.