Dieters have been misled by the outdated system for assessing the calorie content of food for decades, according to research that could redefine how people attempt to lose weight.

People who eat high-fibre foods such as vegetables and muesli are consuming more calories than they think because the current food labels do not take into account the calories in fibre.

Meanwhile the system overestimates, by up to 20%, the content of some protein-rich foods such as tuna steak that can take more energy to digest than simple carbohydrates such as white bread.

The scientists behind the research also reveal that consumers could reduce their calorie intake by eating raw rather than cooked foods. They argue that the way calories are assigned to foods by manufacturers needs a significant overhaul because calories are currently both over and under estimated by up to 25%.

“There is a lot of misinformation around calories…