Dietary Environmental Impact in the SWITCH Study

Abstract

Food systems contribute substantially to environmental degradation and are closely linked to non-communicable diseases. Sustainable dietary transitions are therefore important for improving both planetary and human health. This thesis evaluated the environmental impact of dietary intake within the SWITCH study and examined associations with dietary target adherence, blood lipid biomarkers, and environmental database choice. Dietary intake data from 113 participants were analysed across three study visits during a 13-week intervention period. Environmental impact was estimated by linking 24-hour dietary recalls to the RISE Climate Database and the SAFAD framework. Linear mixed-effects models were used to assess changes over time and associations between dietary carbon footprint, adherence to SWITCH dietary targets, and blood lipid biomarkers. Agreement between RISE and SAFAD carbon footprint estimates was evaluated using correlation and Bland–Altman analysis. Dietary carbon footprint decreased from baseline to week 7 and increased again by week 13 in both RISE and SAFAD, although these changes were not statistically significant after correction for multiple testing. In contrast, several SAFAD indicators changed significantly during the intervention. Cropland use, nitrogen input, ammonia emissions, and biogenic methane decreased by week 7, whereas carbon dioxide emissions and animal welfare loss increased. By week 13, biodiversity loss, pesticide use, and carbon dioxide emissions had increased from baseline, while ammonia emissions remained reduced. Higher overall adherence to the SWITCH dietary targets was not associated with lower dietary carbon footprint, and no significant associations were observed between dietary carbon footprint and blood lipid biomarkers. This may partly reflect that the adherence score focused on increased intake of selected foods and did not account for reductions in carbon-intensive foods such as red and ruminant meat. SAFAD consistently produced higher carbon footprint estimates than RISE, although the two databases were strongly correlated. Overall, dietary environmental impact changed across study visits, with significant changes in several SAFAD indicators but not in dietary carbon footprint. Higher adherence to the SWITCH dietary targets was not associated with lower dietary carbon footprint, nor was carbon footprint associated with blood lipid biomarkers. SAFAD produced consistently higher carbon footprint estimates than RISE, although the databases were strongly correlated.