Policy synergies and trade-offs: reviewing the land use and biodiversity implications of adopting national dietary guidelines

There is growing interest in analysing potential sustainability trade-offs and co-benefits when it comes to national dietary guidelines (1,2) . However, biodiversity is one area that is often left out of these analyses. This scoping review explores the range of studies measuring potential land use impacts of aligning diets or food supply with national dietary guidelines, with a secondary aim to identify how often biodiversity is included. Scopus, Food Science and Web of Science were searched for peer-reviewed articles which focused on dietary guidelines, land use and future scenarios or modelling, following the Joanna Briggs Institute scoping review method (3) .The 1,481 papers retrieved were uploaded to EPPI Reviewer, and 191 duplicates were removed. After screening, a final set of 40 papers were included. Data on the methods used, dietary and environmental impacts, and policy recommendations were extracted. Due to the variation in how impacts were measured, it was not possible to carry out any statistical analysis. The majority (75%) of papers were published in the last 5 years. In most studies aligning diets with dietary guidelines involved reducing meat (-7% to -74%) and sugar (-3% to -100%), and increasing fruit and vegetables (+17% to +207%), compared to current diets. Only one Australian study found an increase in meat (21%). Results for dairy were mixed with two papers identifying a reduction, based on diets in England and Wales, and Germany. Two papers indicated no change in dairy, while all other papers which included dairy indicated an increase, one with an increase of 500%. Greenhouse gas emissions were the most common additional environmental factor included (n=30), followed by water (n=19), fertiliser (n=9) energy (n=7) eutrophication (n=3). Biodiversity was featured in only three papers, two of which found both reductions and increases in threats to biodiversity. The third study found most dietary guidelines are incompatible with Aichi biodiversity target to limit rate of cropland change. Twenty-four authors made the following policy recommendations; incorporate environmental sustainability into dietary guidelines (n=8), having holistic and coherent food systems approaches (n=5), implement policies to change food production and promote sustainability (n=5), combine supply and demand side approaches (n=4), consider socioeconomic factors of food-environment nexus and related policies (n=3), use regional approaches to develop food policy (n=2), and implement measures to encourage dietary change (n=2). Dietary results were relatively consistent across studies and regions, with most suggesting increasing fruit and vegetables, and reducing meat and sugar. Mixed environmental impacts highlight the need to include multiple environmental factors in diet and land use modelling, for a broader picture of potential trade-offs or co-benefits. Considering the importance of biodiversity to the food system, it is essential that it is included in more studies modelling the land use impacts of dietary guidelines.