Background: The concept of ‘processed food' and its classification stimulates debate among professionals across different scientific disciplines, stifling scientific progress and communication. This thesis aimed to understand the perceptions of processed food, of various stakeholders, to better understand the debates surrounding the concept and contribute towards scientific consensus and effective communication.

Scope and approach: The studies explore the conceptualisation of processed food, approached at different levels; 1) A critical review of the underlying basis of classification systems (scientific level); 2) Focus groups and thematic analysis (professional community level); 3) Discourse analysis of representations on Twitter (X) (ideological level); 4) Interviews using word association and sorting techniques (consumer level).

Key findings and conclusions: Classification systems deviate from a food science approach to food processing and draw on sociocultural elements and subjective terms. While classifications were created to link processed foods to nutrition and health outcomes, almost all omit direct assessment of nutrients and other known health impacts of food processing. Discussions are disoriented by tension between the concepts of processed food, food processing and food healthfulness, further convoluted by disagreements on the scope and degree of processing. The social media representation of ‘processed food’ suggests that the concept is used as a heuristic to avoid health risk and demonstrates distrust towards the food industry. Meanwhile, consumer research showed that heuristics such as ‘recognisability’, ‘ingredients’ and ‘shelf life’, may be used to infer degree of processing. Overall, the thesis shows the complexity of the debates surrounding the topic, which relate to the lens through which it is viewed. Further inter-disciplinary dialogue at a food systems level, open communication about scientific certainties and uncertainties, and mechanistic research to clarify processing-related health risks, are warranted.