Greenhouse gas emissions of environmentally sustainable diets: Insights from the Icelandic National Dietary Survey 2019–2021

Background: Health authorities are increasingly integrating environmental sustainability considerations into food-based dietary guidelines. However, concerns persist about the accuracy of the data used to assess environmental impacts, as well as the extent to which these guidelines are followed in practice. Aim: To compare dietary greenhouse gas (GHG) emissions estimates using different top-down and bottom-up life cycle assessment (LCA) databases; and to estimate GHG emissions of food consumption within the ranges set for meat and dairy in recently proposed environmentally sustainable diets. Methods: Dietary GHG emissions were estimated for participants in the 2019–2021 Icelandic National Dietary Survey (n = 822) using three publicly available LCA databases from Denmark, the US, and France. GHG emissions among participants whose consumption was aligned with the EAT-Lancet diet, the 2021 Danish food-based dietary guidelines and the 2023 Nordic Nutrition Recommendations were also quantified. Results: The mean dietary GHG emissions among participants were 6.3, 6.1, and 6.1 kg CO-eq/day based on the Danish (top-down), US (bottom-up), and French (bottom-up) databases, respectively. The relative ranking of foods was also consistent across all three databases. For example, the relative contribution of total CO-eq (% range for the three databases) was highest for red meat (39–51%), followed by dairy (10–17%) and beverages (9–13%). The contribution from plant-based foods (6–10%), seafood (4–11%), and poultry/eggs (<5%) was modest. The dietary habits of most participants (86%) were outside the ranges for meat and dairy consumption as set by the three sustainable diets. However, participants reporting consumption within the ranges for meat and dairy had mean GHG emissions ranging between 4.2 and 4.7 kg CO-eq/day, depending on the diet. In comparison, the mean for participants not adhering to the sustainable diets was 7.7 kg CO-eq/day. These results are higher than those reported in other Nordic and European studies, likely due to high consumption of lamb, beef, and dairy, and low consumption of plant-based food. Conclusion: All three LCA databases provided similar estimates for total dietary GHG emissions and relative ranking of different food groups. Based on current dietary habits in Iceland, adherence to environmentally sustainable diets would lead to a substantial reduction in dietary GHG emissions.