https://orcid.org/0009-0006-0516-2983
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Abstract
Current food production and consumption practices are impacting both human and planetary health. Though these challenges are multifaceted, shifting to healthy dietary choices from sustainable food systems is one solution. Food-based labelling is a common public-health strategy aimed at influencing consumption practices, primarily displaying front-of-pack nutrition labelling to encourage healthier choices. Due to the dual impact of food on human and planetary health there is a growing need to additionally include environmental impact information. However, this potentially conflicting information could overwhelm consumers, necessitating a simplified approach that combines both nutritive and environmental values. Previous work has identified existing models, termed sustainable food profiling models, for labelling of individual food products based on their environmental impacts and nutritive value. Foods are rarely eaten in isolation and are often consumed as composite meals, which aggregate to diets. Therefore, it is important to identify indices that exist to assess or rank meals and diets according to their nutritional and environmental impacts. Following the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) 2015 guidelines, our systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 01 May 2024 (PROSPERO registration ID = CRD42024537149). In the present protocol the methodology to identify and review existing food-based indices for the assessment of nutritive value and environmental impact of meals and diets and their intended public health purpose is described. Our primary research questions are: (i) what food-based indices assessing nutritive value and environmental impact exist for classification or ranking of meals or diets? and (ii) what are the methods used to create, and the key characteristics of, these indices?. The results are expected to increase understanding of, and highlight the variation in, the creation of combined measures for the assessment of nutritive value and environmental impact for meals and diets. Additionally, findings can be used to inform researchers, business, and policy actors on future approaches for labelling foods, meals, or diets in a way that supports healthy and sustainable meal choices and diets.
Citation: Thomas E-L, Livingstone D, Nugent AP, Woodside JV, Brereton P (2024) Food-based indices for the assessment of nutritive value and environmental impact of meals and diets: A systematic review protocol. PLoS ONE 19(12): e0315894. https://doi.org/10.1371/journal.pone.0315894
Editor: Sayyed Mohammad Hadi Alavi, University of Tehran, ISLAMIC REPUBLIC OF IRAN
Received: September 2, 2024; Accepted: December 3, 2024; Published: December 20, 2024
Copyright: © 2024 Thomas et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: No datasets were generated or analysed during the current study. All relevant data from this study will be made available upon study completion.
Funding: This systematic review is funded by a Postgraduate Research Studentship from the Department for the Economy, Northern Ireland. Funders had no role in the development of the protocol.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Human and planetary health are negatively impacted by current food production and consumption practices. Food production and agriculture contributes to over a quarter of the world’s anthropogenic greenhouse gas emissions, occupies around half the world’s habitable land, and uses 70% of valuable global freshwater withdrawals [1–4]. Simultaneously, current dietary intakes across developed and developing nations has caused the double burden of malnutrition, defined as the simultaneous manifestation of both undernutrition and overweight and obesity [5]. One of the five outline strategies by the World Health Organization to act across the food system and work towards tackling these issues is to shift to sustainable consumption patterns by promoting and creating demand for healthy and sustainable diets [6]. Sustainability, in relation to food production and consumption, incorporates an increasing number of dimensions [7]. Sustainable diets are defined by the FAO as “those diets with low environmental impacts which contribute to food and nutrition security and to healthy life for present and future generations. 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.” [8]. Though frameworks outlining global food system transformation for planetary and human health exist, one of the barriers to shifting towards sustainable diets is limited consumer knowledge and awareness of what constitutes such diets [9, 10].
Food nutrition labelling is a commonly used public health tool that aims to inform consumer choice and shift consumption patterns [11]. Due to the growing awareness of the need for healthy diets from sustainable food systems, there is now an increasing interest across the food system to include the environmental impacts of food on front-of-pack (FOP) labelling, known as eco-labelling [12]. However, an unintended consequence of eco-labelling is the health halo effect, where consumers have been found to misperceive foods with eco-labelling as healthier, though low environmental impacts and healthfulness are not mutually exclusive [13]. Presenting both the nutritive value and environmental impacts of foods on FOP labelling could mitigate this health halo effect and is a potential way to overcome the barrier of low consumer knowledge of sustainability of foods.
Labelling initiatives combining nutritive value and environmental impacts of foods are now appearing within the literature. A previous systematic review identified ten food labelling initiatives that scored individual foods according to at least two environmental impacts, of which six additionally scored individual foods based on nutritional quality, which authors termed sustainable food profiling models [14]. The decision to focus on nutritive value and environmental impacts as opposed to the all-encompassing definition of sustainability comes from the lack of consensus on wider dimension definitions alongside immature understanding and supporting standards for such dimensions to be used in a pragmatic index, which could further confuse the consumer. For the purposes of this protocol these labelling initiatives will be referred to as nutritive and environmental combined indices.
Moreover, foods are not consumed on an ingredient level, they are predominantly consumed as composite meals, which aggregate to reflect an individual’s diet. Therefore, it is important to identifying nutritive and environmental combined indices designed for the assessment of meals and diets, beyond individual foods. Bunge and colleagues highlighted how research filling this gap could act as a public health tool potentially increasing informed consumer choice in settings such as restaurants or to underpin public health policy, such as menu reformulation or marketing restrictions [14].
These underline the motivation for the current systematic review that aims to provide insights into the food-based indices that exist that assess both nutritive value and environmental impacts of meals and diets, to highlight the methodological variety in the design of these indices and outline their intended public health purposes.
The key PICO (Population, Intervention, Comparison and Outcomes) framework [15] has been adapted to the following systematic review. There is no restriction on population as nutritive and environmental combined indices for the assessment or ranking of meals or diets should be applicable and suitable for all population groups. Nutritive value and environmental impact indices for assessment or ranking of meals and diets are considered the intervention with no comparator. the outcomes considered are the number of combined indices including a nutrition score dimension and an environmental impact dimension for the assessment or ranking of meals or diets, methodology of combination, key characteristics, and public health purpose.
The present study protocol is described to understand what food-based indices assessing nutritive value and environmental impacts exist for classification or ranking of meals or diets? And what are the methods used to create, and the key characteristics of, these indices?
Nutrient profiling, defined as “the science of classifying or ranking foods according to their nutritional composition for reasons related to preventing disease and promoting health” [16], is used to define the nutritive value of foods. There is no definition for environmental impacts profiling models, however, Environmental Impact Assessment (EIA) can be used and is broadly defined by the European Commission as “a study of the effects of a proposed project, plan or program on the environment”, [17]. More specifically, environmental impacts in relation to this systematic review can be described as a metric (e.g. numeric score or letter) quantifying the effect of meals and diets on the natural environment.
The secondary research question for this systematic review is to explore what the intended public health purpose of these indices are.
Materials and methods
This systematic review protocol follows the PRISMA-P (Preferred reporting items for systematic review and meta-analysis protocols) checklist for recommended items to address in a systematic review protocol [18, 19]. The 17 items that are considered necessary to report a systematic review protocol are formed in a checklist (S1 File) [18].
Bibliographic databases and database management
A structured search was conducted in six bibliographic databases: MEDLINE, EMBASE, Web of Science (science and social science citation index), Scopus, CAB abstracts and Food Science and Technology Abstracts, in April 2024. These databases were identified as the most appropriate and relevant to the research field. The database searches were done under the existing subscriptions of the organisations of the authors.
Search string scoping
Relevant papers were identified from the reference lists of previous systematic and non-systematic reviews [14, 20]. Keywords from these relevant papers were identified and grouped into themes based on the PICO elements of this systematic review (S1 Appendix in S2 File). The most frequently used keywords were used to adapt and update a previously reported word string [14]. To optimize the search string a scoping exercise was carried out in Web of Science where different key words and narrower or wider search strings were tested. A list of the most relevant papers identified in each search was created and the retrieved results from each trialed word string were compared to this list to identify the most appropriate search strategy. Key papers identified as work of Rӧӧs et al. (2015) [21], Seconda et al. (2019) [22] and van Dooren et al. (2014) [23]. This enabled a balance between specificity (reducing the number of irrelevant studies) and sensitivity (ensuring the maximum number of relevant studies were identified) to be struck. The search string that identified the key papers was used to search the selected bibliographic databases.
Search string formulation
A search string using the Boolean operators OR, AND, and, AND NOT was used to conduct a search in all six bibliographic databases to retrieve relevant literature that combines terms for the following components: nutritive value, environmental impact, model, and meal / diet, and removes terms related to animals (Table 1). The search string shown in Table 1 was adapted to the requirements of the abovementioned databases, but the same terms and search fields were used (title, abstract and keywords). The search string details for each database can be found in the S2 Appendix in S2 File.
Article screening
Screening strategy.
EndNote version 21.4 will be used to catalogue retrieved articles and will be used to remove duplicates where more than one bibliographic database has returned the same article. Article data will be exported from EndNote, a reference management software package, and imported into Ryyan, a web-based systematic review software, for a two-staged screening strategy by two independent, blinded authors.
The first stage will assess the relevance of each article based on the title and abstract. Articles that clearly meet the exclusion criteria will be excluded and articles that seemingly meet the inclusion criteria will be included for stage two screening. This will involve assessment of article relevance through a review of their full text. Articles that meet any of the exclusion criteria will be excluded, with the exclusion reasons during this stage being noted for each article. If additional information is mandatory to determine eligibility, up to three attempts to contact the original study authors will be made. If no response is received, the paper will be excluded. Once all full text articles have been screened blinding will be turned-off and conflicts will be discussed between the two reviewers. Where there is uncertainty, the article will be marked for review by a third author.
Ryyan provides the number of conflicts between authors, from this a decimal (amount of agreements / number of papers screened) can be calculated. This value can be used as the Kappa value and a Cohen’s kappa can be interpreted [24].
Eligibility criteria.
The PICO framework was used to develop the eligibility criteria to ensure only relevant articles are included in the final analysis. The following inclusion and exclusion criteria (Table 2) will be used to screen retrieved studies:
- Study type:
The criteria will include relevant observational studies, consumer experiment studies, modelling and optimization studies as well as protocol and methodological studies. To ensure consistency and accessibility, only full-text peer-reviewed articles published, and not withdrawn by authors, in the last 15-years will be included (2009–2024).
- Participants:
No specific group of participants or populations will be included or excluded as meals and diets that are nutritionally adequate that have a low environmental impacts should not be restricted. Policies, initiatives, and concepts combining nutritive value and environmental impacts for the assessment or ranking of meals or diets should be applicable and suitable for all population groups.
- Intervention:
The criteria will review indices (including models, tools, or frameworks) that include the nutritive value and at least one environmental impacts appropriate for the assessment or ranking of meals or diets. Therefore, studies describing the nutritive or environmental impacts in relation to meals or diets without presenting this as an index will be excluded. Studies will also be excluded if they assess nutritive value or environmental impacts solely, refer to an index that has already been included in the review, for example a validation or follow-up study, or detail an index that does not have scope to be used for the assessment or ranking of meals or diets, for example are designed specifically for the assessment of individual food items or food systems.
- Outcomes:
The number of combined indices including a nutrition score dimension and an environmental impacts dimension for the assessment or ranking of meals or diets as well as the methodology of dimension combination and key characteristics of the index are the main outcomes of this review.
Therefore, included studies need to specify nutritional quality and at least one environmental impacts of a meal or diet quantitatively. Indices that use qualitative measures (e.g., scoring based on dietary behaviours) to define nutritional quality or environmental impacts of meals or diets will be excluded. Studies will also be excluded if there is no clear methodology outlining the combination, assessment, or ranking of the two dimensions.
A secondary outcome for this review is to define the public health purpose of the index. Hence, studies that do not refer to the intended public health purpose of the index will be excluded.
Study records
Study validity assessment.
This review will narratively synthesise the number of and existing approaches to the creation of indices that simultaneously assess nutritive value and environmental impacts of meals and diets. All studies that meet the inclusion criteria will be included in the synthesis regardless of their risk of bias. The methodological quality of the studies will be assessed using an amended criteria previously defined by Bunge et al. (2021), known as the model replicability assessment [14], re-termed the index replicability assessment and included in the data extraction spreadsheet. Replicability will be assessed on a scale from 1 (replicable), where equations, system boundaries, final scoring and cut-offs are included and data sets are referenced and fully available, to 7 (not replicable), where the methodology is not described, no equations, system boundaries or final scoring is included, and datasets are not referenced.
Two authors will be involved in the quality assessment. Any discrepancies will be discussed and resolved via consensus. If consensus cannot be reached, a senior reviewer will review the eligible paper and make a final decision.
Data extraction (data categorisation).
Information on studies included in this review will be extracted and collected in a piloted data extraction Excel spreadsheet, which will be accessible to all study authors. The following data, if available, will be extracted from each eligible paper based on the PICO framework for this review:
- Index name
- Year indices was launched / published
- Country of publication
- Type and name of institution
- Geographical scope
- Aim
- Target population
- Application (e.g., (A) meal, (B) diet, or (C) scope for meals/diets
- Index classification (e.g. (A) composite / combined single index or (B) multiple-score index)
- Dimensions (e.g. (A) nutritive value and environmental impacts or (B) nutritive value, environmental impacts, and other factor (e.g., economic or socio-cultural consideration)
- Name of nutritional score and equation
- Name of environmental score and equation
- List of nutrient values
- List of environmental impact indicators
- System boundaries
- Reference amount
- Approach to combining nutritional and environmental components (e.g. algorithm or calculation and weighting)
- Cut off value for healthy meal/diet
- Cut-off value for environmentally friendly meal/diet
- Cut off value for healthy and environmentally friendly meal/diet
- Public health purpose
- Database(s)
Table 3 shows how the data extraction points will be categorised.
To ensure repeatability the primary reviewer will extract data from all articles and a second reviewer will extract data from every 5th article and data extraction will be cross-checked. Any discrepancies will be discussed and resolved via consensus. If consensus cannot be reached, a senior reviewer will review the eligible paper and make a final decision. All extracted data will be included in the systematic review manuscript.
Data synthesis
Synthesising extracted data is a key element of a systematic review. Statistical analysis will not be carried out due to the qualitative nature of data that will be collected and therefore conducting a narrative synthesis will allow authors to understand how the interventions work, why and for who, enabling exploration of relationships in the data and allowing for strength of evidence assessment in order to draw evidence based conclusions [25]. Counts will be used to report the number of identified indices and a heterogenous table will be used to report the general information. Summary and matrix tables will be used to present extracted data relating to the intervention and outcomes with supporting narrative synthesis to enable comparisons between the indices included in the review, and to answer the primary and secondary research questions.
Risk of publication bias.
The authors have no conflicts of interest. Two reviewers, with an additional third reviewer where necessary, will participate in study screening and data extraction and minimum threshold of substantial agreement according to Cohen’s kappa [24] will be used to reduce selection bias.
Conclusion
Eating habits are a key modifiable factor influencing personal and planetary health. By identifying the existing indices and assessing the methodology and characteristics alongside their intended public health purpose the results of the systematic review can be used to inform researchers, business, and policy actors in the future development of an index for the purpose of labelling foods, meals or diets in a way that reflects both human and planetary health. For example the adaptation of public health policies or initiatives, such as highlighting the need for meal reformulation or marketing restrictions to support healthy and sustainable meal and diet choices.
Main limitations of this study include the varied methodology used to create nutritive and environmental combined indices as well as the diverse range of key information included in these indices making direct comparison difficult. However, carrying out this systematic review could highlight where the variance in how these indices are created lies and demonstrate the need for standardisation of such indices.
Additionally, there is no exclusion of papers based on language, which may lead to the need for papers to be translated to English. Translation of technical language can be difficult and can lead to the translated text not conveying the intended meaning of the original text or make understanding the original text difficult and therefore could be another limitation in our study. The reasoning behind this is to ensure a thorough search of the literature making sure to capture all combined nutritive and environmental indices regardless of language.
Supporting information
S2 File. Search string development and details for each database.
https://doi.org/10.1371/journal.pone.0315894.s002
(DOCX)
Acknowledgments
We would like to thank Patrick Elliot, Subject Librarian–Biological Science at Queen’s University who assisted with word string formulation and database selection.
References
- 1. Poore J, Nemecek T. Reducing food’s environmental impacts through producers and consumers. Science. 2018;360(6392):987–92. pmid:29853680
- 2. Ritchie H, Rosado P, Roser M. Environmental Impacts of Food Production 2022 [cited 2023 13 November]. Available from: https://ourworldindata.org/environmental-impacts-of-food.
- 3. Crippa M, Solazzo E, Guizzardi D, Monforti-Ferrario F, Tubiello FN, Leip A. Food systems are responsible for a third of global anthropogenic GHG emissions. Nature Food. 2021;2(3):198–209. pmid:37117443
- 4.
Food and Agriculture Organization. The state of the world’s land and water resources for food and agriculture (SOLAW)–Managing systems at risk. Abingdon, Oxfordshire, England.2011 [cited 2023 18 November]. Available from: https://www.fao.org/4/i1688e/i1688e.pdf.
- 5. Popkin BM, Corvalan C, Grummer-Strawn LM. Dynamics of the double burden of malnutrition and the changing nutrition reality. The Lancet. 2020;395(10217):65–74. pmid:31852602
- 6.
World Health Organization. Transform Food Systems 2023 [cited 2023 16 November]. Available from: https://www.emro.who.int/nutrition/food-systems/index.html#:~:text=Transform%20food%20systems&text=Malnutrition%20takes%20many%20forms%20%E2%80%93%20from,%2C%20diabetes%20and%20some%20cancers.
- 7. Johnston JL, Fanzo JC, Cogill B. Understanding Sustainable Diets: A Descriptive Analysis of the Determinants and Processes That Influence Diets and Their Impact on Health, Food Security, and Environmental Sustainability. Adv Nutr. 2014;5(4):418–29. WOS:000339643300005. pmid:25022991
- 8.
Food and Agriculture Organization. Food-based dietary guidelines. Dietary guidelines and sustainability. 2023 [cited 2023 18 November]. Available from: https://www.fao.org/nutrition/education/food-dietary-guidelines/background/sustainable-dietary-guidelines/en/.
- 9. Hartmann C, Lazzarini G, Funk A, Siegrist M. Measuring consumers’ knowledge of the environmental impact of foods. Appetite. 2021;167:105622. Epub 20210804. pmid:34363900.
- 10.
Safefood. Building ‘sustainability’ into national healthy eating guidelines. Review of international practice and practical implications for policy. 2023 [cited 2023 17 November]. Available from: https://www.safefood.net/professional/research/research-reports/sustainability-eating-guidelines#:~:text=This%20includes%20reducing%20reliance%20on,diets%20and%20sustainable%20seafood%20consumption.
- 11. Nohlen H, Bakogianni I, Grammatikaki E, Ciriolo E, Pantazi M, Diaz JA, et al. Front-of-pack nutrition labelling schemes: an update of the evidence2022 [cited 2023 12 December]. Available from: https://publications.jrc.ec.europa.eu/repository/handle/JRC130125.
- 12. Brown KA, Harris F, Potter C, Knai C. The future of environmental sustainability labelling on food products. Lancet Planetary Health. 2020;4(4):E137–E8. WOS:000528893800008. pmid:32353291
- 13. Wolfson JA, Musicus AA, Leung CW, Gearhardt AN, Falbe J. Effect of Climate Change Impact Menu Labels on Fast Food Ordering Choices Among US Adults. JAMA Network Open. 2022;5(12):e2248320. pmid:36574248
- 14. Bunge AC, Wickramasinghe K, Renzella J, Clark M, Rayner M, Rippin H, et al. Sustainable food profiling models to inform the development of food labels that account for nutrition and the environment: a systematic review. The Lancet Planetary Health. 2021;5(11):e818–e26. pmid:34774122
- 15. Schardt C, Adams MB, Owens T, Keitz S, Fontelo P. Utilization of the PICO framework to improve searching PubMed for clinical questions. BMC Medical Informatics and Decision Making. 2007;7(1):16. pmid:17573961
- 16.
World Health Organization. Use of nutrient profile models for nutrition and health policies: meeting report on the use of nutrient profile models in the WHO European Region 2021 [cited 2024 25 January]. Available from: https://www.who.int/europe/publications/i/item/WHO-EURO-2022-6201-45966-66383.
- 17.
European Commission. Environmental impact assessment framework 2019 [cited 2024 1 February]. Available from: https://ec.europa.eu/research/participants/documents/downloadPublic?documentIds=080166e5c23b58e2&appId=PPGMS.
- 18. Moher D, Shamseer L, Clarke M, Ghersi D, Liberati A, Petticrew M, et al. Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015 statement. Systematic Reviews. 2015;4(1):1. pmid:25554246
- 19. Shamseer L, Moher D, Clarke M, Ghersi D, Liberati A, Petticrew M, et al. Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015: elaboration and explanation. BMJ. 2015;350:g7647. Epub 20150102. pmid:25555855.
- 20. Grigoriadis V, Nugent Anne., Paul Brereton. Working towards a combined measure for describing environmental impact and nutritive value of foods: A review Trends Food Sci Technol. 2021;112:298–311.
- 21. Röös E, Karlsson H, Witthöft C, Sundberg C. Evaluating the sustainability of diets-combining environmental and nutritional aspects. Environ Sci Policy. 2015;47:157–66. WOS:000349581400015.
- 22. Seconda L, Baudry J, Pointereau P, Lacour C, Langevin B, Hercberg S, et al. Development and validation of an individual sustainable diet index in the NutriNet-Santé study cohort. Br J Nutr. 2019;121(10):1166–77. pmid:30973117
- 23. van Dooren C, Marinussen M, Blonk H, Aiking H, Vellinga P. Exploring dietary guidelines based on ecological and nutritional values: A comparison of six dietary patterns. Food Policy. 2014;44:36–46. WOS:000332751200004.
- 24. McHugh ML. Interrater reliability: the kappa statistic. Biochem Med (Zagreb). 2012;22(3):276–82. pmid:23092060; PubMed Central PMCID: PMC3900052.
- 25. Popay J, Roberts H, Sowden A, Petticrew M, Aria L, Rodgers M, et al. Guidance on the Conduct of Narrative Synthesis in Systematic Reviews A Product from the ESRC Methods Programme. 2006;1(1).