A Systematic Review of the Measurement of Sustainable Diets^,,

Abstract

Sustainability has become an integral consideration of the dietary guidelines of many countries in recent decades. However, a lack of clear metrics and a shared approach to measuring the multiple components of sustainable diets has hindered progress toward generating the evidence needed to ensure the credibility of new guidelines. We performed a systematic literature review of empirical research studies on sustainable diets to identify the components of sustainability that were measured and the methods applied to do so. Two independent reviewers systematically searched 30 databases and other sources with the use of a uniform set of search terms and a priori exclusion criteria. In total, 113 empirical studies were included in the final review. Nearly all of the studies were focused on high-income countries. Although there was substantial heterogeneity in the components of sustainability measured, the estimated greenhouse gas emissions (GHGEs) of various dietary patterns were by far most commonly measured (n = 71 studies). Estimating the GHGEs of foods through various stages of production, use, and recycling with the use of the Life Cycle Assessment approach was the most common method applied to measure the environmental impacts of diets (n = 49 studies). Many components of sustainable diets identified in existing conceptual frameworks are disproportionately underrepresented in the empirical literature, as are studies that examine consumer demand for sustainable dietary alternatives. The emphasis in the literature on high-income countries also overlooks the production and dietary alternatives most relevant to low- and middle-income countries. We propose 3 methodological and measurement approaches that would both improve the global relevance of our understanding of sustainable diets and attend more completely to the existing multidimensional, multiscale conceptual framing of sustainable diets.

Introduction

The concept of a “sustainable diet” was proposed more than 3 decades ago in reference to a diet that adheres to dietary guidelines for maintaining long-term health while simultaneously avoiding excessive degradation and consumption of natural resources (1). Expanding on this conceptualization, in 2010, a group of international experts proposed the following definition: “Sustainable diets are protective and respectful of biodiversity and ecosystems, culturally acceptable, accessible, economically fair and affordable; nutritionally adequate, safe and healthy; while optimizing natural and human resources” (2). This definition includes ≥10 different components and numerous additional subcomponents (3, 4). Many of these elements require further disaggregation to fully understand the complexity that each one encompasses (e.g., “protective of ecosystems” may include protection of multiple ecosystem goods and services, including genetic resources, nutrient cycling, provision of habitat, regulation of pests and erosion, and aesthetic values). Nonetheless, this broad definition provides a useful conceptual framework for situating the multiple components of sustainability. The breadth and generality of the framework, however, do not allow for easy translation of these components into operationalized metrics of sustainable diets.

However, the need for well-defined, interdisciplinary metrics of the sustainability of diets is increasingly clear. Sustainability has recently become an integral consideration of the dietary guidelines of many European countries and more recently in Brazil and Qatar (5–9). Numerous governmental, nongovernmental, multilateral, and research institutions have also acknowledged the central importance of sustainability for informing food and nutrition policy (10–13). Concerns regarding the environmental impacts of agriculture, post-harvest food supply chains, and excessive food waste have both contributed to the increased attention and urgency that this topic has received, as well as the considerable political traction that has been generated to promote more sustainable diets (14–16). However, operational challenges, and in particular, a lack of clear metrics and a shared approach to measuring the multiple components of sustainable diets have hindered progress toward 1) generating the evidence needed to ensure the credibility of recommendations, 2) tracking the influence of new guidelines, and 3) formulating and implementing relevant policies.

The constructs that researchers and decision makers choose to measure and the metrics used to assess them reflect underlying values and priorities and ultimately drive policy responses (17, 18). Despite the increased attention paid to sustainable diets among policy makers and the importance of clearly and comprehensively measuring sustainability to properly inform new dietary and environmental policies, it is not clear how the different components of sustainable diets are prioritized or operationalized for purposes of measurement. Previous reviews have not systematically examined the measurement of sustainable diets and have emphasized only studies that examined the environmental impacts of diets rather than assessing the many other components of sustainable diets (19, 20).

Guided by an integrated framework that was based on existing conceptual frameworks of the components of sustainable diets (Figure 1), we performed a systematic literature review of empirical research studies on sustainable diets to identify the components of sustainability that were measured and the methods applied to do so. We highlight current research gaps and propose 3 methodological and measurement approaches that would both improve the global relevance of our understanding of sustainable diets and attend more completely to the existing multidimensional, multiscale conceptual framing of sustainable diets.

FIGURE 1.

Conceptual framework of the components of sustainable diets. “Macro political economic context” includes globalization, urbanization, food chain consolidation, and governance systems among other factors; “Global ecological context” includes climate change, fossil fuel, and natural resource depletion among other factors. Adapted from reference 3 with permission.

Methods

We searched 30 databases that encompassed research in the fields of nutrition, public health, agriculture, ecology, economics, social science, environmental and climate science, and public policy and further examined the references of identified articles, prominent policy reports (10, 21, 22), previous literature reviews (19, 20, 23–26), and the archives of select indexed journals (Supplemental Table 1). The search was conducted with a uniform set of search terms with a priori exclusion criteria and no time period restrictions (Supplemental Table 2).

Following standard protocols for systematic literature reviews (27), 2 reviewers performed a first-stage screening of the titles and abstracts of 1508 unique English language peer-reviewed articles. The full texts of 391 articles that were not excluded in the first stage of the review were independently screened by each reviewer for inclusion in the final review (Figure 2). Contradictory assessments of the relevance of articles between the independent reviews were resolved through discussion among all authors. In the second stage of review, we excluded an additional 278 articles that met the exclusion criteria.

FIGURE 2.

Preferred Reporting Items for Systemic Reviews and Meta-Analyses (PRISMA) flow diagram shows identification, screening, eligibility, and inclusion of articles in the systematic review.

We identified the components of sustainability measured in each study according to a thorough review of the data collected and included in empirical analyses. For example, among studies that assessed the environmental impacts of diets, data on the consumption of natural resources (e.g., land or water use), impacts on environmental processes or outcomes (e.g., eutrophication), and management practices associated with the environmental impact of the food supply chain (e.g., food transport distance, organic food production practices) were commonly measured. Among studies that examined determinants of consumer choice related to diet sustainability, authors collected and analyzed data on consumer perceptions of food attributes. In our systematic assessment, we included each distinct attribute, process, practice, outcome, or construct that the investigators of the identified studies measured and analyzed to differentiate either dietary patterns or consumer choices and policy options in relation to diets.

We further identified the methods (i.e., data sources, instruments, modeling approaches) that were used to measure and analyze these components. Because all of the studies assessed different dietary patterns to some extent, we did not examine variation in the measurement of dietary intake. Given the diversity of measurement approaches represented in the literature that examined sustainable diets, we did not conduct a quantitative meta-analysis of the results, but rather we performed qualitative comparisons and descriptive analyses of the reviewed articles. Although we present key findings from each study, we do not assess the weight of evidence for certain findings because this was outside the scope of the objectives of this review.

Results

In total, we included 113 empirical studies in the final review (Table 1). All but 8 of the studies were published in the previous 10 y. Nearly all of the studies were centered in high-income countries, including the United States and countries of Western Europe (92%) (Figure 3).

TABLE 1.

Principal objectives, cited components of sustainable diets, methods applied, and the key findings reported from articles identified in the systematic review¹

Study (reference), y, country	Objective	Components of sustainable diets cited	Data and measurement of sustainability	Key findings
Environmental impacts of different dietary patterns
Herrin and Gussow (28), 1989, United States	Examine the feasibility of encouraging the adoption of more localized seasonal diets	Locally produced fruits and vegetables; nutritional adequacy of diets	“Disappearance" food consumption data; national diet guidelines (1977)	Nutritionally adequate diets that used only locally available seasonal foods were possible to create; consumer knowledge and acceptance could prevent adoption
Carlsson-Kanyama (29), 1998, Sweden	Assess impact on GHGEs of carrot, tomato, potato, pork, rice, and dry pea production	GHGEs; energy use	LCA (before consumer purchase)	Crop management and animal husbandry practices have more relevant environmental impacts than other aspects of the food supply chain
Kramer et al. (30), 1999, Netherlands	Assess GHGEs of Dutch food consumption according to household expenditure	GHGEs, including CO2, N2O, CH4	LCA (hybrid; agricultural production and transportation)	Cattle farming was responsible for most CH4 emissions, whereas crop farming strongly influenced N2O emissions; non-CO2 GHGEs should be included in food LCAs
Jungbluth et al. (31), 2000, Switzerland	Assess constraints and options for environmentally friendly food purchases	GHGEs; pesticide use; energy use; acidification; 6 others2	Process-based LCA (production, transportation, processing, home use, waste)	Not purchasing air-transported products and reducing meat consumption have largest impacts on reducing diet-related GHGEs; packaging is of minor importance
White (32), 2000, Global	Assess how differences in diet affect the distribution of land use	Land use; equality of food distribution; calorie availability	Ecological footprint data (land use); food balance sheet data; Gini coefficient	Meat-intensive diets are associated with inequality in land use to a greater extent than inequality in calorie distribution
Carlsson-Kanyama et al. (33), 2003, Sweden	Assess food-related life cycle energy inputs and energy efficiency of meals	CED	Process-based LCA (storage, (production, processing, transportation, preparation)	Swedish food consumption patterns require yearly life cycle energy inputs ≤21,000 MJ/person; one-third of total energy inputs is from snacks, sweets, and drinks
Pimentel and Pimentel (34), 2003, United States	Assess land and energy use associated with meat-based and lacto-ovovegetarian diets	Fossil fuel energy use; land use; water use	None specified	Long-term sustainability of both diets is limited because of heavy fossil energy requirements, although meat-based diets require more energy, land, and water
Wallén et al. (35), 2004, Sweden	Assess GHGEs associated with production of different foods	GHGEs; primary energy use; protein from animal-source foods	LCA (variable; indirect energy sources assumed for some foods)	Decreasing fossil fuel use from food production, processing, and distribution is more important than dietary change for reducing GHGEs
Gerbens-Leenes and Nonhebel (36), 2005, European Union	Assess the association of food consumption patterns and agricultural land use	Land use	Total per capita land requirements calculated from investigators’ previous research	Food consumption patterns associated with greater wealth (i.e., cheese, beverages, fruits, and meat) require more agricultural land; see also Gerbens-Leenes and Nonhebel (37)
Sonesson et al. (38), 2005, Sweden	Assess environmental impact of homemade, semiprepared, and ready-to-eat meals	Eutrophication; acidification; GHGEs; energy use	LCA (full life cycle except for sewage treatment of food waste after consumption)	Small differences in environmental impacts of different meals; agriculture was the predominant contributor to energy use and eutrophication
de Boer et al. (39), 2006, European Union	Assess the contribution of different protein sources (plant compared with animal) in diets	Reducing meat consumption	Survey data of dietary intake, food expenditures; food balance sheet data	Largest intercountry variance was across those with high supplies of protein from vegetables and cereals and those with high supplies from milk
Eshel and Martin (40), 2006, United States	Compare GHGEs of red meat, fish, poultry, lacto-ovovegetarian, and mean US diets	GHGEs	LCA (production only; consequential method)	At isocaloric amounts, the mean US diet was associated with 1485 kg CO2-equivalent greater emissions than the plant-based diet
Zhu et al. (41), 2006, European Union	Assess GHGE impact of reducing meat consumption by substituting novel protein foods	GHGEs from agriculture; meat consumption	Agriculture-related NH3, CH4, N2O emission factors	Increased consumption of novel protein foods leads to reductions in agriculture-related GHGEs
Baroni et al. (42), 2007, Italy	Assess environmental impacts of different diets derived from organic compared with industrial agriculture	Land use; eutrophication; water consumption; GHGEs; energy use	LCA (raw material extraction, production, transportation, distribution, use, disposal)	Animal products were associated with greater environmental impacts across production systems; water consumption was the largest contributor to environmental impacts
Peters et al. (43), 2007, United States	Assess impact of fat and meat intake on land requirements for agriculture in New York State	Annual per capita land requirements	Land use calculated from dietary intake, crop yields, livestock feed requirements	Higher per capita land requirements were associated with more meat overall in the diet, and low-meat diets were associated with higher dietary fat
Davis and Sonesson (44), 2008, Sweden	Assess environmental impacts of homemade compared with semiprepared chicken meals	GHGEs; eutrophication; acidification; ozone layer depletion; energy demand	Attributional LCA (agricultural production through sewage treatment)	Reducing food waste and car trips to supermarkets and improving energy efficiency for semiprepared foods are important for reducing environmental impacts of foods
Weber and Matthews (45), 2008, United States	Assess GHGEs associated with food production compared with food transportation	GHGEs; “food miles” local purchasing	Input-output LCA, assumed standard energy intensity of transport per mode	Consuming fewer meat and dairy foods was more effective in reducing GHGEs than buying local
Carlsson-Kanyama and González (46), 2009, Sweden	Assess GHGE of 22 food items and analyze GHGE impacts of simple meals	GHGEs	Process-based LCA (agricultural production, transportation)	Plant foods have the lowest GHGEs except for those transported by plane; animal products are associated with higher GHGEs, especially ruminant meats
Coley et al. (47), 2009, United Kingdom	Assess the difference in carbon emissions from 2 different food distribution systems	GHGEs; energy use; local procurement (i.e., “food miles”)	Annual energy consumption data from 1 United Kingdom organic vegetable supplier	Driving >7 km to buy local vegetables leads to greater GHGEs than purchasing food through the industrial system
Risku-Norja et al. (48), 2009, Finland	Assess agricultural GHGEs for 4 diet scenarios and organic compared with industrial production	GHGEs; organic production	Per capita GHGEs (production only) calculated for foods from published sources	Primary source of GHGEs from agricultural production is soil management practices (62%); organic production has greater GHGEs because of greater cultivated acreage
Stehfest et al. (49), 2009, Global	Assess impact of dietary changes toward less meat on environmental outcomes	GHGEs; land use; energy use; carbon cycling; animal- compared with plant-based diets	Integrated assessment model framework to assess long-term dynamics of global change	Consuming less meat would dramatically reduce land use and emissions of methane and nitrous oxide and would allow for greater carbon uptake through regrowth of vegetation
Arnoult et al. (50), 2010, United Kingdom	Assess impact of changes in land use and landscapes on healthy diets	Land use; landscape character; profitability of agriculture sector	Quadratic programming modeling and land use allocation model	Reduced intakes of cheese or meat and increased intakes of fruit and vegetables would result in loss of grazing management and land abandonment in pastoral landscapes
Chen et al. (51), 2010, China	Assess agricultural land requirements (1980–2006) for rural food consumption	Land use requirements	Grain equivalents by using energy conversion efficiency to calculate land requirements	Although consumption of animal products has increased, higher productivity of arable land has meant lower land use requirements from food production
Davis et al. (52), 2010, Spain and Sweden	Assess environmental benefits of incorporating grain legumes into dietary patterns	Global warming potential; ozone layer depletion; 7 others3	Process-based LCA (agricultural production through sewage treatment)	Replacing meat with peas has positive environmental impacts, especially lower GHGEs, although pea burgers use the same amount of energy as other meat-based meals
Muñoz et al. (53), 2010, Spain	Assess the environmental impact of human excretion in the context of food intake	Global warming potential; acidification; primary energy use; eutrophication	LCA (production, processing, transport, storage, preparation, excretion, waste management)	Food production has the largest environmental impact, although human excretion has high eutrophication potential and is the second most important source of GHGEs
Pathak et al. (54), 2010, India	Assess GHGEs of various vegetarian and non-vegetarian Indian diets	GHGEs	LCA (agricultural production, processing, transportation, and preparation)	GHGEs were higher for non-vegetarian than vegetarian diets; GHGEs were substantially higher from rice than from milk in lactovegetarian diets
Popp et al. (55), 2010, Global	Assess impact of changes in food consumption on non-CO2 GHGEs from agriculture	Non-CO2 GHGEs (N20, CH4) associated with agricultural land use	National emissions variables (production) applied to global land use allocation model	Non-CO2 GHGEs from agriculture are expected to increase in the next 40 y, especially with increased meat and milk consumption
Smedman et al. (56), 2010, Sweden	Estimate GHGEs from production of different beverages	GHGEs; nutrient density of beverages	LCA (production, processing, packaging, transport)	Milk has the highest nutrient density overall and in relation to GHGEs of compared beverages (i.e., soft drinks, beer, orange juice, wine, carbonated water, soy and oat drinks)
Xue and Landis (57), 2010, United States	Compare carbon and nitrogen footprints of food groups throughout the life cycle	Eutrophication; carbon and nitrogen footprint; animal- compared with plant-based diets	LCA (production, processing, packaging, transport)	Meat and dairy products require more nitrogen than cereals; dairy products and chicken/eggs have high nitrogen footprints and low carbon footprints
Zhen et al. (58), 2010, China	Compare land requirements of diets in Guyuan District and other regions of China	Land use	Cultivated crop area and arable land requirements combined with yield data	Per capita land requirements are higher in rural Guyuan than in all of China because of higher wheat consumption and larger household sizes in Guyuan
Fairchild and Collins (59), 2011, United Kingdom	Assess nutritional value and environmental impacts of secondary school meals	Ecological footprint (energy and land use); adequacy and limits of dietary nutrients	School nutrition guidelines; standardized environmental–economic national accounts	Secondary school meals in Cardiff, United Kingdom, did not meet nutritional standards and had an ecological footprint >2 times that of average residents; see also Collins and Fairchild (60)
Fazeni and Steinmüller (61), 2011, Austria	Examine how dietary changes influence GHGEs from Austrian agriculture	CED; GHGEs; agricultural land availability	LCA (production only); CED derived from inventory analysis	Lower meat consumption could lead to more arable land, lower CED, and reduced GHGEs (i.e., 30–38%)
González et al. (62), 2011, Sweden	Assess environmental impact and protein efficiency of animal- and plant-based foods	GHGEs; energy use; protein availability; animal- compared with plant-based foods	LCA (production through delivery to wholesaler)	Animal-based foods are associated with high energy use and GHGEs; protein delivery efficiency was higher for plant-based foods (increased as protein in food increased)
Thibert and Badami (63), 2011, Canada	Assess impacts of diet type and modes of production on environmental outcomes	Land, irrigation water, and energy use; organic; 3 others4	Calculated energy accounts and ecological footprint from published sources	Vegetarian meals had lower total energy relative to meat-based meals because of land use; total energy was similar for organic and nonorganic vegetarian meals
Tukker et al. (64), 2011, European Union	Assess environmental impacts of 3 different recommended diets in the European Union	Multiple environmental impacts (1200) including energy, water, and land use	Environmentally extended input-output model (waste, consumption, production)	Reducing meat consumption reduces environmental impacts but not greatly; losses in domestic meat markets will be compensated for by higher exports; see also Wolf et al. (65)
Virtanen et al. (66), 2011, Finland	Assess the contribution of the Finnish food chain to GHGEs	GHGEs (CO2, CH4, N2O)	National economic input-output model LCA	Agricultural production contributed the largest food chain share of GHGEs (69%); industrial processing and retail contributed the most GHGEs to ready-to-eat meals
Aston (67), 2012, United Kingdom	Assess impacts on health and environment from consumption of red and processed meat	Red and processed meat consumption; chronic disease risk; GHGEs	LCA (system bounds not specified)	Reduced consumption of red and processed meat was associated with reduced GHGEs and reduced risks of diabetes in women and colorectal cancer in men
Berners-Lee et al. (68), 2012, United Kingdom	Assess impact on GHGEs of different dietary choices	GHGEs	LCA (to point of sale only)	Reducing food waste and choosing plant-based foods, seasonal produce, and produce transported by ship can reduce GHGEs
Macdiarmid et al. (69), 2012, United Kingdom	Assess impact of different dietary choices on GHGEs and affordability	GHGEs; adequate dietary energy and nutrients; cost of diets	LCA (to regional distribution center)	Eliminating meat and dairy foods from diets is not necessary for reducing diet-related GHGEs
Meier and Christen (70), 2012, Germany	Assess impact of sex-specific diets on environmental outcomes	Global warming potential; ammonia emissions; land use; water demand	LCA (including life cycle inventory and life cycle impact assessment)	Diets of men have higher environmental impacts than diets of women primarily because of the higher share of meat and meat products in the usual diet of men
Saarinen et al. (74), 2012, Finland	Assess environmental impact of home-made, ready-to-eat, and school lunches	GHGEs; eutrophication	LCA (production through consumption plus plate and food preparation waste)	Ready-to-eat lunches had lower environmental impacts than home-made lunches because of raw materials; school lunches had the least impact
Scarborough et al. (72), 2012, United Kingdom	Assess impact of diets on climate change and mortality from chronic disease	GHGEs; cardiovascular disease and cancer mortality	None specified for GHGEs; model of aggregate mortality risk (meta-analysis of trials)	Chronic disease mortality and climate change impacts were both reduced when consumption of all meat and dairy products was reduced
Vieux et al. (73), 2012, France	Estimate GHGEs associated with self-selected diets	GHGEs	LCA (agricultural production, processing, packaging and transportation to retail outlet)	Meats contributed the most to GHGEs; substituting fruits and vegetables led to equal or increased GHGEs because higher amounts were needed to maintain dietary calories
Briggs et al. (74), 2013, United Kingdom	Model the effect of carbon taxes on food and drink items on chronic disease outcomes	GHGEs; mortality; national revenue	Production and land use GHGEs only; meta-analysis modeling of mortality risk	Applying a carbon tax on foods and beverages with above average GHGEs can reduce mortality and food-related GHGEs
Capone et al. (75), 2013, Italy	Analyze water footprint of Mediterranean compared with non-Mediterranean dietary pattern	Water use (i.e., “footprint”)	Water footprints of crops, animals, and products obtained from published reports	Adherence to the Mediterranean dietary pattern is associated with reduced total freshwater abstraction
de Carvalho et al. (76), 2013, Brazil	Assess impact of red and processed meat intake on dietary quality and GHGEs	GHGEs; overall diet quality; consumption of red and processed meat	Assumed production of 1 kg Brazilian beef generates 44 kg CO2 equivalents	Excessive consumption of red and processed meat has a substantial impact on GHGEs
Geeraert (77), 2013, Sweden	Assess sustainability impacts of dietary changes in Sweden (1960–2006)	GHGEs; energy use; land use	Land, energy use, and GHGE data from published articles; household expenditure data	Increases in consumption of meat and cheese in Sweden are associated with greater land requirement (25%), energy (31%), and GHGEs (31%)
Hoolohan et al. (78), 2013, United Kingdom	Assess GHGEs of different food categories on the basis of realistic consumer choices	GHGEs; intake of energy, macronutrients, sodium; cost	LCA (production, transport, processing, packaging, storage, and supermarket operations)	GHGE reductions can be achieved by consuming pork or chicken in place of lamb and beef and not consuming air-freighted food or food grown in heated greenhouses
Jereme et al. (79), 2013, Malaysia	Assess associations between food consumption and disposal behaviors	Food waste	Household survey of food waste management and disposal behavior (n = 24)	Consuming freshly-cooked foods leads to less food waste; food disposal behaviors are influenced by attitudes and behaviors of neighbors
Meier and Christen (80), 2013, Germany	Analyze the environmental impacts of 4 dietary scenarios in 2006 compared with 20 y before	Greenhouse gas/ammonia emissions; water, primary energy, land, phosphorus use; food waste	Attributional input-output LCA/hybrid-LCA	Changes toward plant-based diets are expected to have the largest positive environmental impacts; impacts from food wastage were lower than from other components
Panzone et al. (81), 2013, United Kingdom	Develop indicator of environmental sustainability of food purchasing behaviors	Consumption of meat, bottled water, fruits and vegetables, organic foods	Fruits, vegetables, tap water, local/organic, online shopping assumed as more sustainable	An index of sustainable shopping behaviors is associated with food-related GHGEs and can assess changes in aggregate sustainability of food shopping
Pradhan et al. (82), 2013, Global	Assess environmental impacts of global dietary patterns	GHGEs	Data on agricultural non-CO2 emissions, output/input energy ratio, feed supply	Developing country diets show similar GHGEs across caloric intakes; high GHGEs from developed country diets are because of production practices and animal foods
Sáez-Almendros et al. (83), 2013, Spain	Assess environmental impact of Mediterranean diet compared with “Western” diet	GHGEs; agricultural land use; energy consumption; water consumption	LCA (agricultural production, processing, packaging, transportation and retail)	The Mediterranean diet is associated with reduced GHGEs, land use, energy and water consumption
Saxe et al. (84), 2013, Denmark	Assess GHGEs of 2 healthy Nordic diets relative to the average Danish diet	GHGEs	Consequential LCA method (production to retail) with the use of Danish LCA Food Database	Diets with less meat and dairy were associated with fewer GHGEs; organic compared with industrial farming may be associated with greater GHGEs
Temme et al. (85), 2013, Netherlands	Assess impact on land use and nutrition of reducing animal source foods consumption	Land use; SFA and iron intake; animal- compared with plant-based diet	Combined amount of crop or feed needed to produce food product with crop yield data	Shifting from an animal-based to a plant-based diet reduces land use and does not compromise the iron status of women
Vanham (86), 2013, Austria	Assess water consumption associated with 4 different diets in Austria	Water use	Published data on green, blue, gray water footprint of foods (consumption and production)	Consumption of animal products accounts for high water consumption; a vegetarian diet would result in the lowest water footprint; see also Vanham et al. (87)
Vieux et al. (88), 2013, France	Assess the relation between the nutritional quality of self-selected diets and GHGEs	GHGEs; adequacy of some nutrients and moderation of others in diets	LCA (all steps except transportation from retail centers to consumers’ homes)	High nutritional quality diets had higher GHGEs than low nutritional quality diets
Wilson et al. (89), 2013, New Zealand	Identify diets optimized for cost, health, and environmental sustainability	GHGE; adequacy and limits of dietary nutrients; 4 others5	Process-based LCA (agricultural production only)	Optimized low-cost and low-GHGE dietary patterns had health advantages over the current dietary pattern because of higher vegetable content and lower sodium and saturated fat
Baroni et al. (90), 2014, United States	Assess environmental impacts of omnivorous, lacto-ovovegetarian and vegan diets	GHGEs; land, water and energy use; eutrophication, acidification; toxicants	LCA (raw material extraction, production, transportation, distribution, use, disposal)	Animal foods main determinant of environmental impact, primarily from land and water use, then energy use and emission of toxic inorganic compounds
Biesbroek et al. (91), 2014, Netherlands	Assess associations of GHGEs and land use of usual diets with mortality risk	GHGEs; land use; animal- compared with plant-based diets; mortality	LCA (production, processing, packaging, transport, storage, preparation, cooking, waste)	Dietary-derived GHGEs and land use were not associated with mortality; substituting plant-based foods for meat lowered mortality risk and environmental burden
Eshel et al. (92), 2014, United States	Assess land, water, reactive nitrogen impacts, and GHGEs from animal feed production	GHGEs; land use; irrigation water use; reactive nitrogen	LCA (land, water, nitrogen used for feed production, per crop type and pasture)	Environmental impacts per calorie of dairy, poultry, pork, and eggs are lower than impacts of beef; plant foods show lower impacts than animal-derived calories
Hallström et al. (93), 2014, Sweden	Quantify the impact of meat consumption on diets, GHGEs, and land requirements	GHGEs; land use; meat consumption; adequacy and limits of dietary nutrients	LCA (production only); land area needed for feed production	Reducing meat consumption reduces GHGEs, increases available crop land, and reduces saturated fat, energy, iron, and zinc intakes
Hendrie et al. (94), 2014, Australia	Estimate GHGEs from different dietary patterns	GHGEs	LCA (to point of purchase); environmentally extended input-output model	Recommended dietary patterns in Australia have lowest GHGEs; red meat and energy-dense, nutrient-poor foods contribute most to diet-related GHGEs
Masset et al. (95), 2014, France	Identify affordable foods with low environmental impact and high nutritional quality	GHGEs; air acidification; freshwater eutrophication; nutritional content; cost	LCA (production, transformation, packaging, distribution, use)	Foods with the greatest environmental impact had lower nutritional quality and higher price per weight
Masset et al. (96), 2014, France	Assess the sustainability of low-carbon, high nutritional quality, and sustainable diets	GHGEs; cost; adequacy of some nutrients and moderation of others	LCA (production, transformation, packaging, distribution, use)	Reducing energy intake and increasing consumption of plant-based foods in diets can reduce GHGEs by 20% at no extra cost while maintaining nutritional quality
Meier et al. (97), 2014, Germany	Assess land use impacts of different dietary scenarios (including virtual land imports)	Land use; food waste	LCA (land use factors from environmental-economic accounts)	Reducing consumption of stimulants (e.g., cocoa, coffee, tea, wine) and meat would decrease land use; reducing food waste is less effective on land use
Saxe (98), 2014, Denmark	Assess impacts of New Nordic Diet and organic food on affordability and environment	16 environmental impact categories6; organic, local food; cost	LCA (consequential modeling; system bounds not specified)	Reducing meat consumption and long-distance imports reduced costs and environmental impacts; organic produce was associated with greater environmental impacts
Scarborough et al. (99), 2014, United Kingdom	Assess differences in GHGEs from diets of meat-eaters, fish-eaters, vegetarians, and vegans	GHGEs; meat-based compared with vegetarian diets	LCA (to regional distribution center)	GHGEs from diets of self-selected meat-eaters are twice as high as those from diets of vegans
Soret et al. (100), 2014, United States and Canada	Compare associations of diet patterns with GHGEs and all-cause mortality	GHGEs; meat-based compared with vegetarian diets; all-cause mortality	LCA [farm to farm/factory gate (plant-based foods), final producer/wholesaler (meat)]	Diets lower in animal products are associated with lower GHGEs and reduced risk of mortality
Tilman and Clark (101), 2014, Global	Quantify environmental and health impact of projected future global diets	GHGEs; non-communicable disease incidence and related mortality	LCA meta-analysis (production to farm gate); diet-health meta-analysis	Increased consumption of meat protein and refined sugars is associated with high incidence of disease and GHGEs; plant-based diets are optimal alternatives
van Dooren et al. (102), 2014, Global	Assess healthfulness and ecological sustainability of 6 different diets	GHGEs; land use; “healthfulness” of diet (10 nutritional indicators)	LCA (system bounds not specified)	Reducing consumption of meat, dairy, coffee, tea, and alcohol and reducing overall energy intake are associated with lower environmental impacts
Werner et al. (103), 2014, Denmark	Assess GHGE impact of diets with varying quantities of dairy foods	GHGEs; nutrient density of diets; consumption of dairy	LCA (attributional modeling with the use of life cycle through consumer use and food waste)	GHGE-reducing impact of food substitution depends on both GHGE/kg and energy density of foods
Westhoek et al. (104), 2014, European Union	Assess environmental impacts of replacing animal-based with plant-based foods in diets	GHGEs; land use; nitrogen excretion; mortality; animal- compared with plant-based diets	Biophysical modeling (data from various published source)	Reducing meat and dairy consumption would reduce nitrogen emissions, GHGEs, and land use for crops, improve air and water quality, and lower diet-related mortality
Doran-Browne et al. (105), 2015, Australia	Compare and contrast metrics for assessing GHGEs and nutritional quality of foods	GHGEs; nutrient density	GHGE factors (production through processing) defined by IPCC	Among metrics of GHGEs per unit of nutrient density, food mass, protein, or energy, nutrient density best differentiated nutritional quality and GHGE reductions
Downs and Fanzo (106), 2015, Global	Assess environmental impact of foods associated with a reduced risk of cardiovascular disease	GHGEs; water use; ecological footprint (land use); cardiovascular health	Estimates of water, carbon, land use from Barilla Center Double Pyramid	Fruits and vegetables have low carbon and water footprints; fish have a high ecologic footprint; walnuts and sunflower oil are good choices for health and environment
Gill et al. (107), 2015, Brazil, China, India	Assess environmental impacts of dietary changes associated with the nutrition transition	GHGEs; water use; land requirements; nitrogen and phosphorus cycles (i.e., fertilizer use)	National food balance sheets; various sources of planetary boundaries framework metrics	Diet-related increases in beef production in Brazil and cereal supply in China and India increased water use/GHGEs and affected phosphorus and nitrogen cycles, respectively
Hess et al. (108), 2015, United Kingdom	Assess impact of healthy diet scenarios on water use and scarcity	Water use/scarcity; adequacy of nutrient intake	Water use data used to create stress index; morphological analyses for diet scenarios	The impact of alternative healthy diets on blue water scarcity footprint was modest, although it could have negative impacts on countries with existing high water stress
Marlow et al. (109), 2015, United States	Compare water, energy, pesticide and fertilizer use for plant- and animal-based diets	Water use; energy use; fertilizer use; pesticide use; plant- compared with animal-based diets	Mean input application rates, fuel and water use (production only) from published data	Diets that contain more animal products, especially beef, require more water, energy, fertilizer, and pesticide inputs than diets that contain fewer animal products
Milner et al. (110), 2015, United Kingdom	Assess effects on non-communicable disease mortality of low-GHGE diets	GHGEs; adequacy of nutrient intake; mortality	LCA (bounds not specified); dietary optimization and life table modeling	Diets that meet WHO recommendations are associated with lower GHGEs and prevention of premature loss of life because of non-communicable disease
Pairotti et al. (111), 2015, Italy	Assess environmental impact of Mediterranean diet compared with healthy and vegetarian diets	GHGEs; energy use; adequacy of nutrient intake; vegetarian diet	Hybrid LCA–-input-output analysis (production, transport, trade, waste)	The Mediterranean diet was associated with less energy use and lower GHGEs than the national average diet, although not as low as a vegetarian diet
Röös et al. (112), 2015, Sweden	Jointly assess environmental impact and nutritional quality of diets	GHGEs; land use; biodiversity; adequacy and limits of dietary nutrients	LCA (unspecified bounds); data on land use requirements; species richness by land use	Data reduction by using indicator scores does not allow differentiation of over- and underconsumption or combined assessment of environmental/nutrition impacts
Temme et al. (113), 2015, Netherlands	Evaluate GHGEs of diets in Dutch girls, boys, women, and men	GHGEs	LCA (production, packaging use, processing, transport, storage, preparation, waste)	Higher diet-related GHGEs were associated with more meat, cheese, dairy, and soft drink consumption, higher saturated fat intake, and lower fiber intake
Tom et al. (114), 2016, United States	Measure environmental impacts of shifting from current US diet to 3 alternative diets	GHGEs; water use; energy use	Data from published studies and LCAs (various systems bounds)	Shifting from the current US diet to USDA recommended food patterns with or without caloric reductions increases energy use, blue water footprint, and GHGEs
Determinants of consumer choice related to diet sustainability
Vermeir and Verbeke (115), 2006, Belgium	Assess determinants of consumer choice for purchase of sustainable dairy	Organic food; “ecologically and socially sound” conditions	Questionnaire: perception that dairy products are “ecologically and socially sound”	Certainty and perceived consumer effectiveness affect attitudes toward buying sustainable dairy foods; social pressure from peers predicts intentions to buy
Verbeke et al. (116), 2007, Belgium	Assess consumer attitudes toward sustainable fishing and fish consumption	Overfishing; aquaculture management	Questionnaire: perceived importance of fishing practices and fish welfare	Price, convenience, and brand influence purchases more than sustainability; sustainable consumers believe personal choice contributes to sustainability
Avermaete and Mathijs (117), 2008, Belgium	Assess relation between purchase of sustainable compared with healthy foods	Fair trade; seasonal food; local; organic food	Questionnaire: preference for seasonal, local, organic foods; purchases at fair trade shops	There is a positive association between healthy and sustainable food purchasing behavior; healthy food is more valued by consumers than sustainable food
Vermeir and Verbeke (118), 2008, Belgium	Assess determinants of consumer choice for purchase of sustainable dairy	Organic food; respect for animal welfare; fair incomes for producers	Questionnaire: perception of ecological production, respect for animal welfare, fair wages	Attitudes, perceived social influences, perceived consumer effectiveness, and perceived availability affect intention to purchase sustainable dairy
de Boer et al. (119), 2009, European Union	Assess motivations behind consumer preferences for sustainable meats	Limiting meat consumption; consuming free-range meat	Questionnaire: purchase of industrial or free-range (including organic) meat	Consumer purchasing behaviors are influenced by both undesirable and desirable food alternatives
Pieniak et al. (120), 2010, Belgium	Assess determinants of consumer choice and attitudes toward organic vegetables	Inorganic compared with organic vegetable consumption	Questionnaire: consumption, attitudes, and knowledge of organic vegetables	Positive attitudes toward and self-assessed knowledge of “organic” are associated with consumption of organic vegetables; objective knowledge is less associated
Schacht et al. (121), 2010, Norway	Assess consumer acceptance of fish with different origins and management practices	Rapeseed oil (of plant origin) compared with fish oil for aquaculture feeding	Assessment of sensory attributes of farmed salmon fed with rapeseed compared with fish oil	Fish fed by using feed of plant origin is acceptable to consumers; appearance, flavor, odor, and texture of farmed salmon is at least as accepted as wild salmon
Dzene and Yorulmaz (122), 2011, European Union	Assess determinants of consumer choice	Limiting meat consumption; organic foods	Classification maps (no details provided)	Food choice is influenced by cost and quality of foods, income, and other attributes (i.e., sensory health, process, and convenience)
Panzone et al. (123), 2011, United Kingdom	Assess determinants of consumer choice by incentives to purchase sustainable food	Carbon footprint	Market incentives to purchase margarine compared with butter, chicken compared with beef, soda in bottle compared with can	Choosing a sustainable alternative is easiest for soda and most difficult for milk; removing a product is more effective at behavior change than subsidies or labeling
Schosler et al. (124), 2012, Netherlands	Assess attitudes toward meat consumption and meat substitution options	Reducing meat in diets	Questionnaire: dietary intake, meat substitution, portion sizes, food choice motives	Meal contexts, cooking skills, and familiarity with foods influence attitudes toward meat substitution options
Grebitus et al. (125), 2012, Canada	Assess determinants of consumer choice for meat labeled with carbon/water footprints	Carbon and water footprints	Questionnaire: choices between products differing by carbon/water footprints and prices	Consumers with more societal rather than individualistic values have more environmentally-motivated choice behavior
Pearson (126), 2012, Australia	Assess consumer perceptions of diet-related sustainability characteristics	Organic; local; fair trade; animal welfare; 10 others7	Online questionnaire of self-selected adult food shoppers (government employees)	3% of respondents reported purchasing organic food as a priority for achieving a sustainable diet; more than half indicated plans to increase organic consumption
Dixon and Isaacs (127), 2013, Australia	Assess determinants of consumer choice of sustainable and healthy foods	Accounting for “the environment” local food	Ethnography, focus groups: food environment, food preferences, shopping habits	Food purchases are not primarily determined by the sustainability or healthiness of diets, but rather by cost, convenience, and duty of care to family members
Fonte (128), 2013, Italy	Assess determinants of consumer choice	Local; reducing ecological footprint; community building; collective action	In-depth interviews: values and understandings of sustainability	Food consumption behaviors can help to build collective agency, social relations, community identity, and alternatives to the dominant food regime
Kesse-Guyot et al. (129), 2013, France	Assess characteristics of organic food consumers, and associations with nutrition	Organic food	Questionnaire: consumption, organoleptic qualities, and sustainability of organic foods	Consumers of organic foods have a higher level of education, have diets more aligned with dietary recommendations, and are less overweight
van Dam and van Trijp (130), 2013, Netherlands	Assess determinants of consumer choice	Environmental friendliness; animal welfare; waste; fair trade; local; health; natural	Questionnaire: relevance and determinance of sustainability factors to food purchases	Consumers consider sustainability issues relevant to their food choices, but it is not the primary determinant of their choices
Vanhonacker et al. (131), 2013, Belgium	Assess consumer opinions on ecological impact of food choices	GHGEs; ecological footprint; meat alternatives; animal agriculture	Questionnaire: “ecological footprint” concept, sustainable food choices, meat in diet	Consumers underestimate environmental impacts of animal agriculture; consumers are less willing to pay for meat alternatives than to consume them
Pomarici and Vecchio (132), 2014, Italy	Assess determinants of consumer willingness to purchase sustainable wines	Carbon neutral product; social equity/justice	Questionnaire: consumption of/willingness to buy carbon neutral, ethical wine	Urban residence, being female, and older age are associated with purchase of sustainable wines
Clonan et al. (133), 2015, United Kingdom	Assess meat consumption behaviors and perceived sustainability impacts	Climate change; local; organic; free range; animal welfare	Self-administered survey on attitudes, sustainable meat purchasing and intake	Less than one-fifth of respondents agreed that consuming less meat and dairy could reduce climate change; animal welfare was a strong motivator to consume less meat
Monroe et al. (134), 2015, United States	Assess effectiveness of a dietary behavior change intervention among students	Local/organic/fair trade; animal protein/welfare; food waste; antibiotic-free meat	Quasi-experimental online education intervention and behavioral survey	University students improved attitudes and behaviors related to environmentally conscious eating in the intervention group of the study
Siegrist et al. (135), 2015, Switzerland	Examine changes in perceptions of environmental impacts of food consumption	Excessive packaging; regional foods; 14 others8	Self-selected participation in mail-in questionnaire survey; longitudinal follow-up	Increasing health consciousness and conviction in better taste of seasonal produce strengthened beliefs that reducing meat consumption is better for the environment
von Meyer-Höfer et al. (136), 2015, Germany	Identify sociodemographic and psychographic characteristics of sustainable consumers	Fair trade; organic food	Choice experiment: price and labeling of foods as organic, fair trade, or conventional	Sustainable consumers rely on food labels, are more often female, perceive that purchasing behaviors affect sustainable development, and are less influenced by ads
Economic costs of different dietary patterns
Jensen and Poulsen (137), 2013, Norway	Assess economic costs of New Nordic Diet compared with average Danish diet	Cost	Market retail price data and consumer food expenditure data from dietary intervention	The New Nordic Diet (i.e., less meat and more local vegetables) is ∼25% more expensive than the average Danish diet although there is much variation
Barosh et al. (138), 2014, Australia	Assess affordability of a typical compared with sustainable food basket across socioeconomic strata	Cost; water use; biodiversity; nutritional quality of diets; GHGEs	Survey of food outlets: price, availability, weight, price per unit weight of food items	A sustainable food basket had a higher cost than a typical food basket; households in the lowest socioeconomic status neighborhood had to spend proportionately more
Germani et al. (139), 2014, Italy	Assess cost and environmental impact of Mediterranean diet	Cost; GHGEs; land use; water use	Published data on household food expenditure, and carbon, ecological, water footprints	Monthly expenditure of the Mediterranean diet was higher than expenditure for the current Italian diet; the Mediterranean diet was associated with lower environmental impacts
Choice and procurement of food for school meals
Løes and Nölting (140), 2011, European Union	Assess determinants of organic food procurement in schools	Organic food; institutional policy	Questionnaire: school food procurement/policies; focus groups, expert interviews	School policies to promote public procurement of organic food can increase organic food consumption in schools
Lombardini and Lankoski (141), 2013, Finland	Assess effects of forced vegetarian food choice in schools on students’ diets	Vegetarian diets	Natural experiment; direct measurement of plate waste, food taken, lunch participation	Participation in school lunches decreased, students took less food, and plate waste increased with effects strongest in lower-secondary schools
He and Mikkelsen (142), 2014, Denmark	Examine influence of organic food sourcing in schools on school food environments	Organic food; policy environment	Questionnaire: attitude toward organic food in school; note existing policies and practices	Schools that sourced organic produce were more likely to adopt a schoolwide food and nutrition policy
Black et al. (143), 2015, Canada	Assess the integration of environmentally sustainable food initiatives in schools	Minimally processed foods; local/organic food; food waste; vegetarian diets	Direct observations of food environments; interviews with administrators/stakeholders	Most schools provided environmentally sustainable food choices, but no schools reported comprehensive initiatives to integrate environmentally sustainable foods

¹Unique articles appear only one time in this table, even if the components of sustainability assessed in the study correspond to more than 1 of the 4 principal types of analyses described. The main sustainability component assessed in the study was used to categorize the study into 1 of the 4 types of analyses. CED, cumulative energy demand; GHGE, greenhouse gas emission; IPCC, Intergovernmental Panel on Climate Change; LCA, Life Cycle Assessment.

²Additional components of sustainable diets are carcinogenic substances, eutrophication, smog production, heavy metals, radioactive releases, and ozone layer depletion.

³Additional components of sustainable diets are CO₂ from fossil fuels, land use, use of renewable (biomass, wind, and water) and non-renewable (fossil and nuclear) energy resources, eutrophication, acidification, photochemical ozone creation potential, and high NOx areas.

⁴Additional components of sustainable diets are local, seasonal, and vegetarian compared with meat-based diet.

⁵Additional components of sustainable diets are low cost, high vegetable intake, minimal cooking skills required, and cultural familiarity of meal.

⁶Additional components of sustainable diets are primary energy use; global warming potential; acidification; ozone layer depletion; photochemical ozone; eutrophication; nitrogen losses as NO₃, NH₃, N₂O; aquatic and terrestrial ecotoxicity (pesticides used); human carcinogenic and non-carcinogenic toxicity; respiratory inorganics; ionizing radiation; land use; abiotic resources used; water use; respiratory organics; and mineral extraction.

⁷Additional components of sustainable diets are energy use, consumption of meat or dairy, seasonality, food waste, “junk” food, cost, packaging, amount of processing, healthfulness, and bottled water.

⁸Additional components of sustainable diets are energy use, consumption of meat or dairy, seasonality, food waste, “junk” food, cost, packaging, amount of processing, healthfulness, bottled water, organic food, imported foods transported by airplane, seasonal fruits and vegetables, and minimal meat consumption.

FIGURE 3.

Geographic location of the reviewed studies, by country or region, and high-income, upper-middle income, and lower-middle income country status. The x axis shows the number of unique articles that included data from the country or region shown. Definition of high-income, upper-middle income, and lower-middle-income country status are found at the World Bank (144).

We identified 4 principal types of analyses in the reviewed articles. Eighty-three studies analyzed the environmental impacts of different dietary patterns. These studies examined the differential potential of various diets to affect energy consumption; climate change; air, water, and soil quality; and numerous ecosystem services that were based on differences in food production, processing, and transport activities along the food supply chain. Twenty-two studies focused on assessing determinants of consumer choice related to the purchase or consumption of sustainable diets. These articles examined the value systems, attitudes, purchasing behaviors, and sociodemographic characteristics of consumers whose diets were considered “sustainable.” Three studies primarily assessed the economic costs to consumers of different diets, and 4 additional studies examined impacts on school meal policies and student participation in school meals of introducing sustainable food options into schools.

Components of sustainability

In total, we identified 30 different components of sustainability (Table 2). The estimated greenhouse gas emissions (GHGEs)⁷ of diets were by far the most common component measured (n = 71 studies; 63% of sample). Land use (n = 32 studies; 28% of sample) and consumption of animal-source foods, especially meat (n = 30 studies; 27% of sample), were the second and third most frequently cited components. Energy use and water consumption associated with the production and processing of foods in diets, agricultural management practices, whether food was procured locally, and the nutritional quality of diets were also commonly cited, but in <25% of studies. Considerations of the nutritional quality of diets as a component of sustainability varied greatly from the consumption of sufficient dietary energy or essential micronutrients to moderation in consumption of processed foods, SFAs, free sugars, or sodium (85, 88, 96).

TABLE 2.

Cited components of sustainable diets, keywords used to describe those components, and total number of times they were cited in articles identified in the systematic review¹

Component description and keywords	Citation count, n
GHGEs	71
GHGEs
Non-CO2 GHGEs (i.e., N20, CH4)
Global warming potential
Carbon footprint
Carbon neutral product
Climate change
Carbon cycling
Land use	32
Land use
Land use requirements
Virtual land imports
Nature occupation
Ecological footprint (referring to land use)
Agricultural land availability
Consumption of meat and dairy	30
Animal-source foods
Animal agriculture
Animal-based compared with vegetarian or vegan diets
Consumption of dairy, red meat, or processed meat
Limiting meat consumption overall
Consuming meat alternatives
Diet quality	27
Adequate dietary energy and nutrients
Overall diet quality
Adequacy and moderation/limits of nutrient intake
Nutritional content or quality of diets
Nutrient density of diets
Healthfulness of diets
Consumption of fruits and/or vegetables
Consumption of fish
Calorie availability
Protein availability
Intake of energy, macronutrients, SFAs, trans-fats, total fat, dietary fiber, free sugar, sodium, iron
Amount of processing of foods
“Junk” food
Energy use	26
Primary energy use
Primary energy consumption
Fossil fuel energy use
Cumulative energy demand
Use of renewable and non-renewable energy sources
Management practices/organic food	21
Organic food
Organic production
Free-range meats
Antibiotic-free meats
Water use	20
Water use
Water consumption
Water demand
Water footprint
Water scarcity
Irrigation water use
Local or seasonal food procurement	18
Food miles
Foods transported by airplane
Local purchasing
Local procurement
Local food
Regional food
Seasonal food
Seasonality
Cost of diets and revenue generation	13
Cost of diets
Food costs
Cost of food basket
National revenue
Profitability of agriculture sector
Eutrophication potential	11
Eutrophication potential
Eutrophication
Health	11
Cardiovascular disease
Cancer
Mortality
All-cause mortality
Chronic disease risk
Non-communicable disease incidence
Health or healthfulness
Reactive nitrogen	9
Ammonia emissions
Nitrogen oxides
Reactive nitrogen species
Nitrogen losses, excretion
Fertilizer use
Nitrogen cycle
High NOx areas
Nitrogen footprint
Acidification potential	8
Acidification potential
Acidification
Human toxicity/ecotoxicity	8
Pesticide use
Aquatic and terrestrial ecotoxicity
Human toxicity
Respiratory inorganics
Smog production
Carcinogenic substances
Heavy metals
Radioactive releases
Social equity	8
Fair trade
Fair incomes for producers
Social equity
Social justice
Equality of food distribution
Food waste	7
Ozone layer depletion	6
Ozone layer depletion
Photochemical ozone creation potential
Photochemical ozone
Ecology/environment	5
Ecologically and socially sound
Reducing ecological footprint
Accounting for the environment
Environmental friendliness
Natural
Animal welfare	5
Respect for animal welfare
Fisheries	3
Overfishing
Aquaculture management
Aquaculture feeding
Community	2
Community building
Collective action
Policy	2
Institutional policy
Policy environment
Phosphorus use	2
Phosphorus use
Phosphorus cycle
Bottled water consumption	2
Food packaging	2
Food packaging
Excessive packaging
Biodiversity	2
Biodiversity
Biodiversity damage potential
Cultural appropriateness	2
Requirement of cooking knowledge and skill
Cultural familiarity of meals
Abiotic resource use	1
Mineral extraction	1
Landscape character	1

¹GHGE, greenhouse gas emission.

Measuring the sustainability of diets

Nearly two-thirds of studies that analyzed the environmental impacts of different dietary patterns (n = 49; 59% of sample) applied a Life Cycle Assessment (LCA) approach. LCA estimates the environmental impact of a product through ≥1 “life stages” of its production, use, and recycling, commonly with the use of GHGEs as a metric of impact (145). For foods, these stages may include inputs into agricultural production, processing, packaging, transportation, retail sale, storage, preparation, consumption, and waste disposal (69). All but 5 studies that used LCA used a process-based approach, which entails aggregating data on emissions and resource use of individual food items from published databases (146). Two of these 5 studies applied monetary transaction data toward economic input-output LCA modeling (45, 66), whereas 3 studies adopted a hybrid approach (30, 80, 111). The system bounds of the studies identified varied widely. However, all but 4 LCA studies that identified system bounds (40, 61, 89, 93) included assessment of life stages in addition to agricultural production (e.g., processing, packaging, transport, retail storage, home storage, preparation, postconsumer waste, and disposal) (Table 1). In addition to LCA, among studies that assessed the environmental impacts of dietary patterns, various alternative modeling approaches were also used, including integrated assessment model frameworks (49), quadratic programming modeling (50), and land use allocation models (55).

Sixteen of the 22 articles that examined determinants of consumer choice used a variety of Web, phone, or in-person questionnaires to assess consumers’ dietary patterns, purchasing behaviors, and attitudes and perceptions toward the sustainability of various foods and dietary patterns (Table 1). Attribute-based choice experiments were commonly included as part of these questionnaires (i.e., repeatedly offering the respondent alternative choices, assessing preferences and determinants of preferences). Many of these studies also applied qualitative methods such as in-depth interviews, focus groups, and observational techniques.

The 3 studies that principally assessed the economic costs of different dietary patterns for consumers used secondary market retail price data and collection of primary data through surveys of the prices and availabilities of foods at retail food outlets. Those studies that examined procurement of food for school meals and impacts on student participation in school meals used a variety of measurement approaches from surveys and interviews of school officials to direct measurement of student participation in school lunch programs in the context of a natural experiment that compared schools with different meal patterns.

Conclusions

We systematically reviewed the empirical research literature to identify the main components of sustainable diets that scholars have measured and the methods that they have applied to assess these components. The conceptual framework shown in Figure 1, adapted closely from previous frameworks (3, 4), identifies multiple, equally weighted components of a sustainable diet and emphasizes the multiscaled political, economic, and ecological contexts that constrain or facilitate changes in diets and food systems. Although we identified 30 distinct components of sustainability in this review, neither the distribution nor complexity of components identified in existing conceptual frameworks of sustainable diets is evident in the empirical research that has measured sustainable diets. The global warming potential of diets was by far the most commonly measured component, with land, energy, and water use also frequently assessed. The costs associated with different dietary patterns were assessed as the primary aim of only 3 studies and explicitly measured in only 13 studies. Thus, limited evidence is available to assess important economic trade-offs in selecting alternative diets. Furthermore, despite the paramount importance of consumer demand in shaping the realization of sustainable diet recommendations, far fewer studies assessed consumer preferences for sustainable dietary alternatives than studies that assessed the environmental impacts of diets. Food security and control of productive resources were also disproportionately underrepresented, whereas an examination of cultural heritage and skills, equity, rights, and governance were almost entirely lacking. These social dimensions are critical for understanding the capacity of communities to engage in defining, achieving, and evaluating who wins and loses as diets and food systems change in response to sustainability concerns.

The limited emphasis on equity and cultural context is particularly important, given the skewed geographic emphasis of studies that measured sustainable diets. Nearly all of the research on sustainable diets was centered in high-income countries. Although these countries have contributed most of the GHGEs associated with agriculture and food systems, the negative effects of climate change and resource degradation reflected in many of the measured components of sustainability are expected to be felt most strongly in low- and middle-income countries (LMICs)—those countries that already bear the strongest burdens of food insecurity, malnutrition, and ill health (147). As sustainable diet guidelines begin to be adopted by LMIC governments or encouraged by international institutions, basing such guidance on evidence derived almost exclusively from high-income countries could fail to identify where the greatest changes are needed and acknowledge the specific needs and potential of LMICs.

The framing of the dietary alternatives in the sustainable diets literature, for example, has tended to overlook the unique disease patterning in LMICs characterized by an increasing “double burden” of undernutrition and diet-related non-communicable illness (148). Nearly all of the studies that examined the nutritional quality of diets emphasized differences between meat-based and vegetarian or vegan diets. These different dietary patterns were shown to be associated with different levels of GHGEs (92). However, the diets of most poor households in LMICs are still predominantly plant-based, not necessarily by choice, but because of the high price of nutrient-dense meat and animal products (149). Therefore, this dichotomy is not nearly as meaningful for LMICs wherein a different set of dietary alternatives may be needed to enhance sustainability while maintaining the nutritional quality of diets. Indeed, the evidence from studies that examined determinants of consumer choice was exclusively derived from high-income countries, nearly all in Western Europe (n = 18 of 22 studies). Organic, fair trade, and local food were among the most common food attributes assessed in these studies. These attributes are either nonexistent in many LMICs (e.g., organic and fair trade certification) or do not adequately discriminate between dietary alternatives in contexts in which informal, local markets are already the principal food source for most consumers (150). Contrasting organically produced food with food produced through industrial agriculture also fails to capture the complexity and variability among agricultural management practices across countries and does not reflect differences in access to wealth and productive resources that in part determine management decisions (151).

Given these incongruities there is a need to broaden the scope of the empirical literature on sustainable diets to include LMICs. More geographic heterogeneity in these analyses will help to elucidate how regional changes in diets and distinct agricultural management systems may have differential effects on sustainability outcomes. Differences in the embodied GHGEs of diets, for example, may differ in high-income compared with low-income countries because of differences in production efficiency or input intensity across these countries (82). Broadening the geographic scope of the research on sustainable diets will also help to ensure that proposed dietary alternatives are economically practical, culturally appropriate, and nutritionally meaningful for diverse global populations.

A major obstacle to reorienting the geographic focus of research on sustainable diets is the availability of data and the reliance on LCA as the principal approach to assessing sustainability. LCA is a powerful tool for comparing the potential environmental impacts of different diets at multiple loci throughout the food value chain (152). However, current LCA data sets are largely limited to data that were based on studies of GHGEs in high-input, industrial production systems from high-income countries. More research is needed to build LCA data sets in LMICs and on alternative agricultural systems (primarily in low-income contexts where resources are limited to collect such extensive life cycle data) (24). LCAs are also primarily used to examine GHGEs and resource use. Although these are two of the most important factors shaping the sustainability of agricultural production and global food and nutrition security (101), a narrow focus on GHGEs neglects many other ecosystem services that are affected by diets and agri-food systems. Life-cycle sustainability assessments that incorporate social and economic dimensions of sustainability hold great promise for expanding the conceptual scope of LCA (24, 153). However, whether through more comprehensive LCA data sets or complementary methods, GHGEs should be assessed within a broader context of trade-offs or synergies among multiple ecosystem services (e.g., nutrient cycling; soil fertility; insect, weed, and disease regulation), and the dynamics of complex social-ecological systems.

Three other approaches can contribute to a more holistic analysis that simultaneously attends to the ecological, sociopolitical, economic, and health dimensions of the sustainability of diets identified in current conceptual frameworks. These include 1) modeling approaches, 2) integrated analytical frameworks, and 3) adaptive, participatory methods. First, considering modeling approaches, partial equilibrium models, common in analyses of complex systems, offer an alternative to LCAs. Modeling approaches such as bio-economic models that couple assessment of economic and biophysical components to analyze trade-offs among distinct social-ecological systems and multi-objective optimization models that assess optimal allocation of resources to benefit multiple ends within food systems are promising approaches to modeling the complexity of sustainable diets (154). These and other analytic techniques for examining complex, adaptive systems (e.g., modeling nonlinear feedbacks, strategic interactions, and heterogeneity across spatial and time scales) can provide meaningful insights to inform sustainable diet policies across contexts (155).

Integrated metrics of sustainable diets are also needed to complement modeling approaches and to be applied independently as another strategy for improving measurement (13). For example, multi-criteria indicator frameworks that quantify ecological, social, and economic dimensions of sustainability are an example of integrated assessment approaches. Such frameworks were applied to assess analogous multidimensional constructs such as poverty (156) and empowerment (157), to evaluate the sustainability of farming systems over time, and to contrast distinct farm management systems (e.g., by displaying indicators with the use of spider diagrams) (158). This approach could easily be adapted to assess the sustainability of contrasting diets across multiple spatial scales. For example, researchers, in partnership with stakeholders, could identify relevant system attributes, leverage points for sustainability, and associated areas of evaluation and then develop specific indicators to measure and track change over time (e.g., GHGEs, soil fertility, dietary diversity, market stability, adult and child anthropometric indexes, soil carbon storage, access to technical assistance or knowledge, etc.).

Finally, methodological frameworks are also needed that allow for participatory analysis and ongoing re-assessments. Food systems are inherently dynamic, context-dependent and can exhibit substitution effects on different sustainability outcomes, depending on the nature and extent of the changes made to diets (103). Therefore, quantitative methods such as complex systems modeling and integrated indicator frameworks should be interpreted within a sociopolitical and place-based understanding, allowing for a critical interpretation of the influence of context on sustainability (159). Because the concept of sustainability itself is contested, metrics and measurement approaches must also attend to questions of who decides what components of sustainability to prioritize, for whom, and with what benefits (160). Multidimensional vulnerability frameworks centered on food insecurity and environmental sustainability, for example, were developed and adapted with the use of participatory methods to capture the complex connections between these phenomena (161). Adaptive management approaches used in resource management and conservation science use an iterative process that engages key stakeholders in trials of new practices, assesses changes and impacts, and iterates on this process by modifying interventions, reassessing priorities, and experimenting with new approaches for measurement on the basis of multidimensional outcomes (162).

Taken together, complex modeling, integrated indicator frameworks, and adaptive, participatory methods can help to account for the inherent complexity of sustainability and can address the research gaps identified in this review centered on the measurement of the multiple, diverse components of sustainable diets. We recognize the challenges in implementing such interdisciplinary approaches. However, the examples highlighted above indicate such approaches are feasible. At a minimum, it is critical to acknowledge the underlying conceptual framework that guides methodological decisions and the assumptions and limitations embodied in a given method or metric. If the sustainability of diets is to gain sufficient political attention as to become a core priority in the shaping of agriculture, food, and nutrition policies, empirical research must better reflect the diverse characterization of sustainability outlined in the aspirational definition of sustainable diets. Integrating environmental, health, and social considerations across scales and contexts can offer a more complete understanding of the opportunities and barriers to achieving more sustainable diets.