Major fast food companies in New South Wales have been ordered to list the amount of energy in their foods on menu boards.

A government survey from last year showed more than half of the state's adults are overweight or obese.

The State Government has demanded fast food companies list the amount of kilojoules in their foods next to the prices.

They will also have to show the average daily adult intake of 8,700 kilojoules.

Companies with more than 20 outlets in the state or 50 shops nationally must comply with the rules, which start in February next year.

Premier Kristina Keneally has set up a reference group of health and industry professionals to implement the scheme over 12 months.

She says businesses and health groups have supported the move and if successful, other nutrients such as saturated fat and salt could also be listed.