Exploring Sustainable Diet Drivers: An Extended TPB Approach to Alternative Protein Acceptance in Southern Italy

Background/Objectives: This study investigates how consumers decide to adopt alternative proteins—specifically insect-based, cultured meat, and plant-based options—as part of a transition towards environmentally sustainable diets. Building on an extended Theory of Planned Behaviour (TPB), the analysis adds personal moral norms and environmental concerns to better capture the ethical and normative drivers of food choice. Methods: Survey data from 948 residents of the Campania region (southern Italy) were analysed using partial least squares structural equation modelling (PLS-SEM) to assess the relationship among classical TPB constructs, personal moral norms, environmental concerns, and behavioural intention towards alternative protein consumption. Results: Personal moral norms emerge as the strongest predictor of behavioural intention, directly and indirectly influencing attitudes and environmental concerns. Subjective norms also affect intention, primarily by reinforcing moral norms and perceived behavioural control, although their direct impact is not significant. Classical TPB constructs show limited direct effects. Conclusions: The findings suggest that consumers’ sustainable food intentions are more strongly shaped by moral identity and the surrounding social context than by attitudes alone. The evidence supports the development of culturally sensitive strategies designed to strengthen moral and normative motivations and foster the adoption of alternative proteins.