In the UK poor diet is a worrying public health issue, and we rank one of the worst in Europe for levels of obesity, particularly among children. Reformulating the most unhealthy foods to reduce sugar, salt and fat is the food industry’s main strategy to turn things around, and this is echoed by the government. Reformulation has been going on for decades, and there has been some real progress recently, for example reducing sugar in soft drinks and some breakfast cereals. However, overall there is much work still to be done and government sugar reduction targets are way-off being met according to recent figures. The focus on reformulation has always been on reducing the level of ‘bad’ nutrients in food. Now the concept of ‘ultra-processed’ food is calling that strategy into question. It defines food on the level of processing rather than on nutrients – if a product includes ingredients you wouldn’t find in your kitchen and was made in a factory, then it’s probably ultra-processed. UPF food makes up half of the average diet in the UK, and there is growing evidence to show that it’s very likely driving the rise in diet-related diseases, and the global obesity epidemic. So when it comes to nutrients, what are the technical challenges for reformulating our food, and how far can this approach go in improving the quality of ultra-processed food? And if the problem really lies with processing rather than nutrients, do we need a different approach entirely? Presented by Sheila Dillon and produced by Sophie Anton for BBC Audio in Bristol.