Image copyright Getty Images

Food packs should display how much exercise a person would need to take to burn off the calories contained in the product, UK researchers say.

Appreciating it would take four hours to walk off the calories in a pizza or 22 minutes to run off a chocolate bar creates an awareness of the energy cost of food, they say.

The labels would help people indulge less, exploratory studies suggest.

The aim is to encourage healthier eating habits to fight obesity.

According to the researchers from Loughborough University, who looked at 14 studies, this type of labelling could cut about 200 calories from a person's daily average intake.

About calories

The amount of energy in an item of food or drink is measured in calories (kcal)

Men need about 2,500 kcal a day and women about 2,000 kcal to provide enough energy for your body to function - for everything from breathing to running

Eating more calories than you burn off causes obesity because the excess calories are stored as fat

Even eating a little bit too much every day adds up

This may not sound like much but, they say in the Journal of Epidemiology and Community Health, it would have an impact on obesity levels across the country.

More than two-thirds of adults in the UK are overweight or obese.

Lead researcher Prof Amanda Daley said: "We are interested in different ways of getting the public to make good decisions about what they eat and also trying to get the public more physically active."

And labelling food with "exercise calories" made it easier for people to understand what they were eating and nudge them into making better choices.

Prof Daley said many people would be shocked to realise how much physical exercise would be required to burn off calories from certain snacks and treats.

"We know that the public routinely underestimate the number of calories that are in foods," she said.

"So if you buy a chocolate muffin and it contains 500 calories, for example, then that's about 50 minutes of running.

"This definitely isn't about dieting.

"It's about educating the public that when you consume foods, there is an energy cost, so that they can think, 'Do I really want to spend two hours burning off that chocolate cake? Is the chocolate cake really worth it?'"

'Triggering' risk

The Royal Society for Public Health would like to see the labelling introduced as soon as possible and says it is a move many consumers would also welcome.

It says: "This type of labelling really does put an individual's calorie consumption in the context of energy expenditure and knowing how out of kilter we can be partly explains the record levels of obesity we face.

"Small changes can make a big overall difference to calorie consumption, and ultimately weight gain."

Prof Daley hopes a large food chain or company will be willing to try the new labels on their products so the system can be given a "real life" trial.

But concerns have been raised about labelling food in this way.

Tom Quinn, from the eating disorder charity Beat, said: "Although we recognise the importance of reducing obesity, labelling food in this way risks being incredibly triggering for those suffering from or vulnerable to eating disorders.

"We know that many people with eating disorders struggle with excessive exercising, so being told exactly how much exercise it would take to burn off particular foods risks exacerbating their symptoms."