Healthy AND Sustainable DietsSymposium Presentation
Climate change and environmental degradation present major threats to humanity. In recent years, recognition of the significant environmental impact of food production has prompted research into the relationships between diets and environmental sustainability. The term sustainable diets was defined by the Food and Agriculture Organization as “those diets with low environmental impacts which contribute to food and nutrition security and to healthy life for present and future generations”. This definition is most easily conceptualized if we think of sustainable diets as having four dimensions: nutrition and health, environment, economic, and sociocultural.
Existing research on sustainable diets is diverse, including studies on single foods, dietary patterns, habitual diets, and diet modelling. Most studies assessing the environmental footprint of food consumption rely on life cycle assessments (LCA), an international standard by which to quantify the environmental impacts incurred at each of the stages of a food’s life, including production, transportation, and processing, among others. Meta-analyses of global LCA studies have generally shown plant-based foods as having lower environmental impacts compared to animal-source foods. However, factors such as agricultural practices, transportation, and energy consumption determine the environmental footprint of a given food, which can vary widely among regions of the world. Furthermore, the choice of functional unit by which to compare foods (e.g., weight, calories) can have a marked influence on the interpretation of foods’ environmental impacts. Therefore, it is difficult to make inferences on the environmental sustainability of diets based on estimates of single foods alone.
To quantify the environmental footprint of dietary patterns and habitual diets, studies have linked LCA data on single foods to food intake data captured in nationwide nutrition surveys. Estimates of environmental impact are aggregated for quantities of foods consumed as dietary patterns (e.g., omnivorous, vegetarian, etc.) or habitual diets. The bulk of these assessments have been conducted in European countries and more recently, in the US. Most studies find diets containing greater amounts of plant-based foods as having a lower environmental footprint relative to those containing animal-source foods. However, this conclusion is not as clear-cut when environmental impacts are weighed against nutrient adequacy. Indeed, more comprehensive analyses employing replacement scenarios and diet modelling as tools to analyze the nutritional and environmental trade-offs of foods and diets report reductions in environmental impact associated with the replacement of animal-source foods with plant-based alternatives up to a threshold, as the removal of animal products poses implications on nutrient adequacy.
Despite the limitations of existing research, evolving national dietary guidelines are placing emphasis on sustainability. In January of 2019, the EAT-Lancet Commission convened to establish global scientific targets for healthy diets and sustainable food production. The Commission defined a planetary health diet as one that contains large amounts of vegetables, fruits, whole grains, legumes, nuts, and unsaturated oils, includes a low to moderate amount of seafood and poultry, and includes no or a low amount of red meat, processed meat, added sugar, refined grains, and starchy vegetables with optional moderate amounts of dairy. In combination with technological and management-related changes in food production and reductions in food loss and waste, the Commission proposed the adoption of the planetary health diet as necessary for staying within planetary boundaries, defined as the biophysical limits within which humanity should operate to ensure a stable Earth system. While there are merits to the EAT-Lancet Report, there are also limitations with respect to nutrient adequacy that we must account for when discussing the potential implications of adopting a planetary health diet.