In Defence of Bread, Professor Mike Gibney’s fourth and final popular science book, we are treated to a passionate plea for reason and evidence in the formulation and use of food classifications systems. Food based dietary guidelines, often presented as the food pyramid or food plate, have been used for decades as an effective tool in public health. They portray a simple message to communicate the basic concepts of nutrition – eat a balanced diet. But this approach to nutrition advice, is coming under fire from a version of populist science growing within the online community of food commentators. A range of classification systems have emerged, based on the concept of ultra-processed foods, and the accompanying advice that these foods should be avoided. But these classification systems are inconsistent and lacking robust evidence linking to actual health outcomes. Professor Gibney has never tolerated bad science, and in this posthumous publication, which he worked on until his death in February 2023, he brings his brilliant wit and clarity of communication to bear on this divisive topic.