Doughnuts, custard tarts, hot chickens and other ready-to-eat supermarket meals will come with a label displaying their kilojoule content, in the hope consumers will think twice before indulging.
NSW Premier Barry O'Farrell launched the mandatory labelling on Tuesday morning as part of the government's 8700 kilojoule campaign, aimed at providing consumers with more information about what they eat.
"It is my view that people who want to lose weight and get healthier need to take personal responsibility for their food and lifestyle choices," Mr O'Farrell said.
''But I believe it is essential consumers are equipped with nutritional information to encourage them to make balanced food choices.''
Obesity cost the NSW economy about $19 billion each year, he said, with more than half of the state's residents overweight or obese.
Nationally, more than 60 per cent of people are overweight or obese.
The Heart Foundation NSW director of cardiovascular health Julie Anne Mitchell said research had shown people significantly underestimated the kilojoule content of foods.
''Which is why it's important to give people the facts," she said.
"For foods that currently don't have any nutritional information, having the 8700 kilojoule campaign in supermarkets is a great step forward in the fight against obesity.''
The 8700 kilojoule campaign is named after the recommended average daily kilojoule intake for an adult, with a smartphone app of the same name available to help people monitor their intake.
Woolworths director of public affairs Andrew Hall welcomed the roll-out.
"At a glance, customers can now see the energy value of many popular ready-to-eat items and make a decision on how those products can fit into their daily energy needs," Mr Hall said.
A professor with the University of Sydney's School of Public Health Louise Baur said the labels had been a long time coming. She hoped it would lead to a change in bad eating habits.
''This sort of thing doesn't happen overnight,'' she said. ''Industries have to work out kilojoule content of their food and that may be worrying to them as foods may look somewhat less appealing when people realise the kilojoule content.''
Kilojoule content also differed depending on how the food was cooked, she said.