Background Future priorities of public health must consider how the global food system is inextricably linked with diets and nutrition, and subsequently faces numerous challenges in meeting different individual, societal, and global health objectives. The current model leads to unhealthy dietary patterns, exceeds planetary boundaries, and is vulnerable to food insecurity. Food production releases more than 25% of all Greenhouse Gas Emissions (GHGE), depletes natural resources, and pollutes waters with agrochemicals. Synergies must be built between diets and health, environmental sustainability, and food system resilience. Although much of the focus is on animal-sourced foods, particularly red meat, it is important that a reductionist approach does not override the complexity of shifting to sustainable dietary patterns by overtly focusing on a single food group and neglecting the quality of the diet in its totality.

Methods A priori assessed dietary patterns were used to construct diet quality indices that quantify the healthiness of dietary patterns based on scientific consensus. Consumption data was obtained from the Mitchelstown Cohort Study conducted between 2010–11 among Irish adults (n= 1,862) aged 46–73 years (mean= 59 years). A Food Frequency Questionnaire assessed dietary intake of participants. The DASH and Mediterranean diet scores were calculated for each participant to determine if higher adherence was associated with lower environmental impact. Environmental impact was assessed by linking food items to GHGE (kg of CO2 equivalents (kgC02eq)) and water use (L) impact factors.

Results There was medium adherence to both dietary patterns among the population, DASH (male 24.9 ± 5.0; female 28.5 ± 5.1), MED (male 4.4 ± 1.9; female 4.1 ± 1.6). A minimal difference was observed in GHGE between the MED diet adherence levels (T1 6.1 vs T3 6.3 kgCO2eq (CO2eq) per person per day). Higher DASH diet quality scores resulted in the lowest GHGE among the population when compared to low adherence (Q5 5.3 vs Q1 6.9 kgCO2eq per person/day). A weak negative correlation was observed between DASH diet adherence and dietary GHGE (r = -0.19, p < 0.001). No correlation was observed for the MED diet. Results differed for water use and diet quality scores.

Conclusion Balancing the requirements of diets and food supply is of great planetary and public health importance. Debate on how food systems should be positioned to ensure resilience while safeguarding planetary boundaries continues, but nutrition and long-term health outcomes must remain at the foundation of any proposed dietary change, specifically for older adults.