Aussie researchers say fast food lunch will take hours to burn off

If you care for a slice though, pizza from Dominos, Pizza Hut and Crust all came under the 1,300 kilojoule mark, but with serving sizes measured at just 100 grams, or one slice of pizza, workers will need to keep a close eye on how many slices are eaten.

For the office workers out there, where possible, bring food from home as you have more control of what and how much you are eating, Petersen said.

"If you buy food out, be aware of what you are eating," she said.

"Making small changes such as choosing menu items lower in kilojoules may help to prevent weight gain or achieve weight loss."

But if you think a simple salad will suffice, think again as they are laden with sauces and dressings which increase the amount of kilojoules, such as a small ancient grain peanut orange salad from local chain Sumo Salad, requiring a run of more than an hour to burn off.