Do you know how long you need to run to burn off a standard-size chocolate bar? Or that a quarter of a large pizza can send the eater to a walk for an hour and 23 minutes? There is a certain idea in Britain - aimed at tackling Britain's obesity crisis - and that is to label food with information how much exercise is needed to work off calories. The idea is backed by Shirley Cramer, chief executive of the Royal Society for Public Health. Ms Cramer said: "The objective is to prompt people to be mindful of the energy they consume and how calories relate to their everyday lives."