Understanding healthy eating intentions and behaviour through an extended theory of planned behaviour: the role of sustainability beliefs

Healthy eating represents a central objective for public health policies and is increasingly framed as a key pillar of sustainable development. Despite this growing convergence, empirical research grounded in behavioural theories has rarely integrated sustainability-related motivations into explanatory models of healthy dietary behaviour. This study addresses this gap by extending the Theory of Planned Behaviour (TPB) through a multicomponent conceptualisation of perceived behavioural control and the explicit inclusion of healthy diet sustainability beliefs as an additional value-based determinant of healthy eating intention. Drawing on data from a representative sample of 1000 Italian consumers, the proposed framework is tested through Partial Least Squares Structural Equation Modelling. The findings confirm the robustness of the TPB in explaining healthy eating intentions, with attitude and subjective norm emerging as the strongest predictors. Sustainability beliefs of healthy eating significantly enhance intention to eat healthily, underscoring the relevance of environmental concerns in shaping dietary goals. At the same time, actual eating behaviour is strongly shaped by practical and contextual factors, including cooking skills, nutrition knowledge, self-control, financial resources, and time pressure. Notably, quadratic effects emerge for cooking skills and time constraints, suggesting non-linear relationships with healthy eating behaviour. Overall, the findings highlight the importance of combining sustainability motivational drivers with enabling conditions to promote healthy and sustainable diets. By jointly examining sustainability beliefs and behavioural constraints, these findings refine behavioural models of food choice and offer a stronger evidence base for designing integrated public health, sustainability, and food-system interventions.