Image copyright Thinkstock Image caption How much exercise would it take to burn this off?

People like to have information about their food - but working out how much exercise you'll need to do to burn off the calories in your favourite treat is not straightforward.

In this week's Scrubbing Up, Shirley Cramer, chief executive of the Royal Society for Public Health, says a simple icon on food packaging could be the answer.

Picture, if you will, your favourite chocolate bar.

You may take note of how many calories it has - and wonder just how these calories relate to your everyday life. Given the average consumer spends six seconds looking at food before making a purchase this is a lot to cram in.

So how about we make life easier for people?

We think a clearer way of making people more mindful of the calories they are consuming is for a food or drink product to also show on the front of the packet a small icon which would visually display just how much activity you would need to do to burn off the calories it contains.

Take, for example, a medium coffee mocha. Who'd have thought that this could contain nearly 300 calories?

But what does that actually mean for our daily lives? If instead we showed that you'd need to walk for nearly 50 minutes to burn the calories off or run for 30 minutes, maybe we wouldn't be so blasé about the number.

This is not meant to scare people, or to create a society of obsessives. But instead it is meant to show to the public very clearly just how active we need to be if we are to consume the diets we do and not put on weight. Or how we might need to readjust our diets to match our inactive lives.

Why does this matter? Firstly, we are facing an obesity epidemic - two in three of us are either overweight or obese.

And one of the main reasons for this is we are consuming far more calories than we are actually expending.

We recognise that just to live and breathe we need to consume a certain number of calories every day - for a man that's about 2,500 and for a woman 2,000.

But anything more than this, without a more active lifestyle, could lead us to gain weight.

Can you lose weight without counting calories?

Are we being fooled by food labels?

What's the easy way to get healthy?

We also think these little icons could gently prompt people to be a bit more active in their everyday lives.

Almost half of us aren't getting enough physical activity. Perhaps that bar of chocolate showing how long we need to walk might encourage us to either put down the chocolate bar, or get off the bus or tube a stop earlier and walk.

However, we also know that you can't out-run a bad diet, so there are limits to how much activity we can do to compensate for how many calories we consume.

Introducing activity-equivalent calories labelling should be a fairly simple step.

We know the calories contained in many food and drink items. And we know how these equate to activity equivalents.

This doesn't require legislation. There are one or two food companies already doing it!

Retailers or food companies could show some real leadership on this issue and make life a lot easier for us. And perhaps they'd make consumers lives healthier into the bargain.