Modern food consumption harms both the environment and human health, contributing to diseases like cardiovascular conditions, type 2 diabetes, and cancer. Current food systems also drive climate change and biodiversity loss. Sustainability challenges differ by context: in low-income settings, the priority is economic access to nutritious diets; in high-income settings, reducing the overconsumption of red meat is key due to its high environmental footprint. This thesis examines sustainable diet strategies in Ghana, Ethiopia, and Finland through four key domains of diet sustainability: nutrition and health, economics, society, and environment. In this thesis, Ghana is considered a low-income setting, reflecting its focus on low-income households rather than national income classification.

In low-income settings, sub-studies I and II utilised linear programming to design nutritionally adequate and affordable diets for low-income families in Ghana and Ethiopia. While theoretically achievable, rural Ghanaian households below the extreme poverty line would have to rely on wild foods to meet their nutritional needs, raising concerns about feasibility. In Ethiopia, diets that were more diverse and culturally acceptable were attainable but more costly, highlighting affordability as a major constraint. However, the modelling did not account for nutrient bioavailability, behavioural factors, or the feasibility of long-term adherence.

In high-income Finland, sub-studies III and IV investigated nudging and policy interventions aimed at reducing red meat consumption. The “Dish of the Day” strategy and altering dish sequence had no effect, suggesting the need for stronger or culturally tailored approaches. Meat reduction policy acceptance was driven by perceived fairness, followed by environmental risk perception and political trust.

In conclusion, transitioning to sustainable diets requires context-specific strategies that take into consideration nutrition, economic feasibility, cultural acceptability and environmental impacts. Cultural and structural differences shape the effectiveness of interventions, which highlights the need for localised evaluation. Future research should include larger and more diverse samples and investigate strategies to enhance both the efficacy and public acceptance of sustainable diet policies.