1. Introduction

The intrinsic relationship between nutrition and the environment is well established, as eating patterns affect the environment and vice versa [1, 2]. Technological advances, globalization and changes in agricultural systems have stimulated changes in the human diet [3] and the current global food system is increasingly associated with harm to health ranging from food insecurity to significant environmental losses [1]. Thus, there is a need for sustainable diets that are culturally acceptable, economically accessible, safe and healthy, that minimize negative impacts on biodiversity and ecosystems and optimize both natural and human resources [4].

In 2019, the EAT-Lancet Commission Summary Report delineated a combination of food groups and intake ranges that would enhance the multiple benefits for health and the planet. The Commission’s aim was to develop global scientific goals for achieving healthy and sustainable diets, called the "Anthropocene Diet", which were proposed to optimize human health without pushing the limits of the planet and which, if adopted, could significantly reduce the environmental impact of food production [5].

The current food production system has a significant impact on the environment, contributing around 20–30% of total greenhouse gas emissions (GHGE). In addition, approximately 24% of arable land suffers some degree of soil degradation, depending on the agricultural model adopted. Intensive land use for monoculture and livestock farming results in deforestation and alarming loss of biodiversity [6–8]. However, environmental problems are not only restricted to the food production phase; they also extend to processes included in the supply chain, such as transportation, processing and food preparation. Waste and residues generated along the food supply chain also contribute to the aggravation of these environmental problems [9].

A universal healthy reference diet (planetary health diet or EAT–Lancet diet) served as the basis for the development of indexes of sustainable diets that integrate multiples indicators as environmental, social, economic and health [3, 10–13]. The proposed diet consists of vegetables, fruits, whole grains, legumes, moderate or low amounts of seafood and poultry and little or no red meat, refined grains, added sugars and starchy vegetables [5].

This initiative sparked discussions on the need for changes in contemporary food systems through health sustainable diets [11] to reformulate a global food system, as continuing with the same attitudes is no longer an option [1] and, if nothing is done, the world runs the risk of not meeting the Sustainable Development Goals established by the member countries of the United Nations on the 2030 agenda [5, 14, 15].

Changes in dietary patterns and lifestyles of populations around the world in recent decades stimulate the need for the adoption of sustainable diets and tools to measure these diets, as recommended by the Commission which proposed that this transformation be achieved equitably and across different populations and food system contexts [16, 17]. The remodeling of concepts requires updating existing indices and the way these indices measure diets, as new recommendations have emerged with a planetary scope as reference [3, 11, 12, 18–20]. This scoping review aims to give an overview of the analysis of the available evidence related to the sustainable diet indices that have been developed based on the EAT-Lancet Commission.

2. Materials and methods

3. Results

3.1 Article selection process

The search of the databases led to the retrieval of 1458 papers: 77 in PubMed, 15 in Embase, 165 in Web of Science, 124 in Scopus and 1077 in Science Direct. After the removal of duplicates, the papers were screened based on the title and abstract. Incomplete papers (pre-prints), animal studies, in vitro studies, those focused on the transportation/distribution of food, those that offered only political analyses and surveys of public opinion were excluded. Thirty-two potentially eligible papers were submitted to full text analysis. Those that did not address sustainable diet indices and those that assessed food systems or the climatic impact of food products were excluded. Fourteen papers met the eligibility criteria and were included in the present scoping review. The evidence selection process was done as shown in the flowchart formulated based on the PRISMA recommendations [13] (Fig 1).

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Fig 1. Flowchart of the study selection process.

https://doi.org/10.1371/journal.pone.0296026.g001

3.2 Overview and characteristics of studies

The 14 papers were conducted in 12 countries: eight in Europe (France (n = 3) [19, 25, 26], United Kingdom (n = 2) [18, 27], Sweden (n = 1) [28], Hungary (n = 1) [20] and Albania (n = 1) [29], three in the Americas Brazil [3, 30, 31], two in Asia (Israel (n = 1) [11] and Vietnam (n = 1) [12] and one multicenter study conducted in low- and middle-income countries located in South America, Africa and Asia (Democratic Republic of the Congo, Ecuador, Kenya, Sri Lanka and Vietnam) (n = 1) [32]. The aim of the studies and the sustainable diet indices employed are presented in Table 1.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 1. Overview of papers included in present scoping review (n = 14).

https://doi.org/10.1371/journal.pone.0296026.t001

The papers were published between 2019 and 2022, with the greatest production in 2021 (8/14), demonstrating that interest in this field of research is recent. All papers selected were in the first or second quartile of the Journal Citation Reports and all were published in English.

Six studies had a cohort design [9, 10, 18, 25, 27, 28] and eight had a cross-sectional design [3, 11, 12, 20, 21, 27, 31, 32]. Average duration of the cohort studies was 4.8 years. Most studies were conducted with individuals or secondary national data. Only one study involved a multi-country or global approach. A total of 277,911 individuals participated in the studies included.

Adherence to sustainable diets varies around the world as different measurement indices are used making it difficult to compare across different populations. Initially in 2019, an index was developed based on the EAT-Lancet recommendations in the United Kingdom (ELD-I) in which 1 point was assigned for each recommendation met by the population out of a total of 14 points. This study evaluated cardiometabolic risk as an outcome and had scores ranging from 4 to 14 points, with beneficial associations being found for ischemic heart disease and diabetes, but no association with stroke and no clear association with mortality [18].

Xu et al. (2022) found that higher adherence to ELD-I contributes to a lower risk of diabetes [27]. Another study carried out in Albania used the same index with the aim of making associations with the cost of the diet and the place of intake (inside and outside home) and concluded that low adherence was not differentiated by cost, but by place of consumption [29]. Then, a new dietary index was developed based on ELD-I (EAT index) to investigate adherence to the EAT-Lancet diet in a Swedish cohort and its association with mortality and had adherence of, an average of 17.9/42 points was obtained [28].

Studies using the SDI as an index to assess adherence to sustainable diets found an inverse association between adherence and weight gain, overweight and obesity, supporting a potential protective role of more sustainable diets in this context [19]. When applying SDI to outcomes such as cancer and cardiovascular disease risk, greater adherence was found to be associated with a significant decrease in cancer or cardiovascular disease risk [26].

Brazilian studies that used the PHDI presented an average score of 60.4/150 [31] and 45.9/150 [30], respectively. The difference between the scores obtained using the same index may be related to the different populations analyzed. In the first study, the population was composed of federal civil servants, while the second study was conducted using data from a population-based study.

Adherence to sustainable diets when assessed in the general Hungarian population was 2.0/12 points when using a nutrient-based index (NB-EAT) [20]. This score was 5.9/20 possible points in Israel when using the SHED index [11]. When using the WISH index in Vietnamese living in urban areas, adherence was 46/130 points [12].

3.3 Sustainable diet measures

Seven sustainable diet measures were cited: EAT-Lancet diet score (ELD-I) (n = 5) [18, 25, 27, 29, 32], New EAT-Lancet diet score (EAT) (n = 1) [28], Planetary Health Diet Index (PHDI) (n = 3) [3, 30, 31], Sustainable Diet Index (SDI) (n = 2) [10, 18], Sustainable-HEalthy-Diet (SHED) (n = 1) [11], novel Nutrient-Based EAT index (NB-EAT) (n = 1) [20] and World Index for Sustainability and Health (WISH) (n = 1) [12]. The characteristics of these indices are described in Table 2.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Table 2. Characteristics of indices used in papers selected for present scoping review (n = 7).

https://doi.org/10.1371/journal.pone.0296026.t002

3.4 Indicators of sustainability

A total of 21 different indicators were identified. GHGE was the most measured component (n = 13; 93% of sample) [3, 10, 12, 18, 20, 25, 26–32], followed by indices that assessed diet quality with a greater consumption of vegetables and lower meat intake (n = 12; 86% of sample) [3, 11, 12, 18, 20, 25, 27–32]. Other aspects investigated were the benefits of sustainable diets with regards to health outcomes (n = 9; 62% of sample) [3, 18–20, 26–28, 30, 31], food insecurity and costs related to food (n = 4; 29% of sample) [19, 26, 29, 32] and the consumption of organic foods (n = 3; 21% of sample) [11, 19, 26]. Primary energy intake, land occupation, biodiversity, chemical pollution by pesticides, price, support to local producers, household cooking practices, food waste, bottled water consumption and ultra-processed foods were also cited, but in less than 25% of the studies (n = 3) [11, 19, 26]. No investigations were conducted of changes in transportation habits. Components assessed by the sustainable diet indexes can be seen in Fig 2.

Download:

• PPT
  PowerPoint slide
• PNG
  larger image
• TIFF
  original image

Fig 2. Components assessed by the sustainable diet indexes.

https://doi.org/10.1371/journal.pone.0296026.g002

4. Discussion

The present scoping review investigated different tools that identify sustainable diets, which are fundamental for analyzing sustainability, establishing goals and following up the evolution of the subject as well as political decision making on the local, national and planetary levels. In our study, we found that the indices that measure sustainable diets present robust evidence in relation to what is recommended by the EAT-Lancet Commission. They are multidimensional and consider various sustainability indicators (environmental, health, economic and social); most of them allow for a gradual score that includes all the intermediate values of individual food consumption, favoring a better distinction between the degrees of adherence of individuals. In addition, they also consider interchangeable food groups, allowing adaptations to different populations, as recommended by the reference diet.

There has been an evolution over time in the development of indices to assess sustainable diets, with indicators and data used to assess the sustainability of diets adapted to each specific territory. When discussing sustainable diets, it is essential to promote an inclusive and sensitive approach to local particularities, considering the food culture, production systems, socio-economic characteristics and environmental impacts specific to each place. In this way, we can develop effective and tailored strategies to promote food sustainability in different geographical contexts [5, 6, 33]. Adherence to health and sustainable diets varied according to the population studied and assessment methods employed. Countries with less economic development had lower scores and, consequently, lower scores of adherence [12, 29, 30, 31, 34], which may be related to social and economic issues of the food system [25]. Sex, age and income are variables for which the most distinctions are found in different populations, as it is well established the adherence to this type of diet is greater among the female population, individuals with a higher income per capita, older age groups and residents of urban areas [29–31].

The lower adherence may be related to the contemporary eating pattern, with inadequate quantities of fruits, vegetables and plant-based proteins [35]. Similar findings were reported in studies conducted in Mexico and India [36, 37]. The stimulation of plant-based foods, which involve a lower generation of GHGE, could result in an increase in cost for some population groups [38]. Indeed, there is evidence that the EAT-Lancet diet is beyond the reach of needy families because nutrient-rich foods tend to come with a higher price tag compared to starchy staples and items rich in sugar and fat [39], which explains the lower adherence in developing countries [40]. Kesse-Guyot et al. (2021) pointed out the affordability of a sustainable and healthy diet, they found that participants with high EAT-Lancet adherence had the highest diet cost [25]. However the EAT-Lancet report it largely deals with the need to make a healthy and sustainable diet accessible to everyone from an economic point of view and gives suggestions to how to make it real [5]. There is also the issue of the stigmatization of this plant-based eating pattern for disrupting social conventions related to food, as the fear of stigmatization can be a barrier to avoiding meat consumption, which can be an obstacle to implementing the Eat-lancet diet [41, 42]. A healthy, environmentally sustainable diet should be accessible, which could limit indices that do not consider the cost of food [12].

Regarding structure among the indices analyzed, the ELD-1 and NB-EAT use a binary score, with 1 attributed if the participant met a goal and 0 if the goal was not met; the result is the sum of the nutritional goals met [18, 20, 25, 27, 29, 32]. The SHED index records agreement on a Likert scale ranging from 1 to 4 [11], whereas the EAT, WISH, PHDI and SDI have a gradual score proportional to the consumption of foods [3, 12, 19, 26, 28, 30, 31]. This method is encouraged by the EAT-Lancet report for the obtainment of intermediate values, which are common and more faithful for the assessment of food intake [5]. Food intake was addressed mainly in groups. Only the NB-EAT was based on nutrients [20]. The use of interchangeable groups is encouraged in the creation of indices based on the EAT-Lancet Commission. However, the use of nutrients enables a less precise assessment of adherence to these recommendations due to the provision of nutrient composition values of sustainable diets in a more restrictive, less informative way [5].

To define environmental sustainability indicators in the food sector, it is necessary to consider the different environmental dimensions impacted, such as GHGE, water resource use, land degradation and biodiversity loss [7, 9]. Among the main outcomes analyzed, the anthropogenic emission of GHGE was the most reported component and several researchers found a positive correlation between the total GHGE related to the diet and total energy and grams of the foods consumed [3, 12, 18, 19, 25–32]. Only the SHED index [11] is limited in this respect, as it does not quantify GHGs, which is the main metric to assess environmental burden, but by building on the EAT-Lancet reports, the SHED index assesses environmental burden indirectly by encouraging the consumption of a more plant-based and red meat-restricted diet to achieve the United Nations 2030 sustainable development goals and alleviate the burden of non-communicable diseases [5, 33, 43, 44].

Food production affects the environment and vice versa, as high environmental GHGE loads and unsustainable use of natural capital, such as overexploitation of natural resources and degradation of ecosystems, leads to environmental problems that have direct repercussions on climate instability. This climate instability, in turn, affects food production, creating additional challenges for food and nutrition security for future generations [6, 41].

The benefits of sustainable diets to human health are well established [41]. The use of different indices for the assessment of sustainable diets obtained positive outcomes for ischemic heart disease and diabetes [18, 27], the risk of weight gain, overweight and obesity [19, 31] and a significant reduction in the risk of cancer and cardiovascular disease [18, 34]. Knuppel et al. [18] found no clear association with mortality, whereas Stubbendorff et al. [28] demonstrated a 25% lower risk of mortality among individuals with greater adherence to the EAT-Lancet diet.

The offer of animal protein conditioned to essential human needs could reduce global morbidity and mortality rates associated with chronic diseases [20]. This would diminish the environmental impact of food production and would be capable of maintaining sustainability linked to the consumption of fresh, seasonal products produced locally and with minimal packaging [41]. It is possible that a balanced diet rich in vegetables is ideal, as the Western eating pattern and contemporary food systems place the health of both humans and the planet at risk [45, 46].

The indices analyzed have limitations that should be considered, such as gaps in the measurement of social dimensions and an intense focus on health (62% of sample), quality of diet (86% of sample) and environmental aspects (93% of sample), this suggests that there is an imbalance in studies regarding the different aspects of sustainability that are rarely recognized or comprehensively assessed when it comes to diets. Social aspects are critical to understanding the capacity of societies to engage in the definition and assessment of who wins and who loses as diets and food systems advance in response to the concerns of sustainability [7]. Previous reviews reported similar findings [7, 41, 47], demonstrating a lack of consideration for such issues in studies.

Another limitation was the lack of uniformity of the indicators assessed in the measurement of sustainable diets. However, this could also be considered an advantage when summarized scores are combined and may be applicable for use in population-based epidemiological studies. The sample size and quality of the papers ensure representativeness and confer reliability to the results, suggesting adequate quality of the evidence presented.

The inclusion and association of other indicators are suggested for the assessment of sustainable diets in indices that were not addressed here, such as changes in food transportation habits that can contribute to rural development and local production, which would consequently would contribute to a reduction in GHGE and global warming [48]. Transportation activities currently account for 23% of CO₂ emissions, which is expected to double by the year 2050 [49].

This review also has strong points, such as the originality of the study with regards to the investigation of updated methods with a planetary scope in sustainable diet indices based on the EAT-Lancet Commission Summary Report. To the best of our knowledge, this is a pioneering synthesis on a subject that is becoming increasingly important. Lastly, a rigorous selection of papers was performed using pre-established inclusion criteria and the results can assist in the planning of public policies and orientations regarding the benefits of a healthy, sustainable diet based on the proposal of the EAT-Lancet Commission.

The findings of the present scoping review underscore the importance of studying indices that summarize components of complex modeling, which, when combined, present integrated structures that can explain the inherent relevance to the concept of healthy, sustainable diets.

There is an increasing need to improve indices of healthy, sustainable diets in the search for well-defined measures for the faithful assessment of the adherence of populations to sustainable diets. The EAT-Lancet Commission proposes scientific goals for these changes that should be reached by 2050 and such knowledge could assist in the adoption of measures that have a positive impact on the transformation of the long-term scenario of sustainability.

5. Conclusions

The evidence from this review highlights the diverse approaches employed by researchers to define sustainable diets based on the recommendations of the EAT-Lancet report. Our analysis significantly contributes to the current body of knowledge, presenting a description of the indexes that evaluate sustainable diets and indicators frequently used in the analyzes of articles (environmental and health). We identified serious barriers that hinder progress towards healthy and sustainable diets, including the difficulty of comparing different indices, the tendency to neglect social aspects and the lack of common definitions and metrics. Despite being challenging, the description of an ’ideal’ index that harmonizes the various indicators, promoting positive changes towards a more sustainable future is highlighted.

Supporting information