The calorific cost of a 590ml soft drink? How about a five mile walk.

Signs telling children how far they will have to walk to burn off the calories in their bottle of soft drink are an effective way of encouraging them to choose a healthier option.

Researchers at the School of Public Health at John Hopkins University in the US found that 40% of people who saw such signs when they went to buy a drink decided to make a different selection.

They said their findings added to the argument that simply putting a calorie count on a product may not be enough.