An International Systematic Review of Decarbonisation Interventions in Diabetes and Obesity Pathways: Health and Environment Outcomes (Protocol)

Background

The introduction of the United Nations (UN) Sustainability Development Goals which were adopted by 193 member states in September 2015 sparked change and awareness in relation to how we perceive sustainable development including protection of the planet through environmental awareness. The UN Sustainable Development Goals are broken into seventeen targets with number thirteen written as ‘take urgent action to combat climate change and its impacts’ which is particularly relevant for this systematic literature review. Such goals were introduced on January 1^st, 2016, which marks a 10-year anniversary since this universal call to action (United Nations, 2015).

The concept ‘Net Zero’ has become a popularised term in relation to climate action and healthcare sustainability. Net zero is achieved when anthropogenic greenhouse gas emissions are balanced by anthropogenic carbon removals by a specific period. The term was developed prior to the UN sustainability goals through climate science, but the UN played a decisive role in turning science into global policy (United Nations, 2015). On the foot of this came the Paris Agreement in December 2015 introducing a basis for Net Zero and setting quantified carbon emission reduction targets for many countries, including the European Union member states (United Nations, 2016). Both policies were very influential, although in different but complementary ways. The Sustainability Development Goals built the foundation for a broader awareness and understanding of sustainability while the Paris Agreement drove specific climate action and accountability but together created a change from a niche concern to a mainstream global priority (United Nations, 2015, 2016). To date, the next most influential policy change in the 21^st century is the ‘European Green Deal’ which was created in 2019 with the aim of making Europe the first climate neutral continent by 2050 ( European Commission, 2019). As part of this comprehensive roadmap came the ‘Fit for 55 Package’ (European Commission, 2020) which introduced EU laws designed to cut emissions by at least 55% by 2030 and the ‘EU Circular Economy Action Plan’ (CEAP) strategy to focus on the entire lifecycle of products to reduce waste while encouraging a transition from linear to circular economy ( European Union, 2020).

The healthcare sector is a significant contributor to climate change with approx. 4–5% of the worlds greenhouse gases generated by healthcare every year (Rodríguez-Jiménez et al., 2023). As a result, the World Health Organisation (WHO) has created the ‘Alliance for Transformative Action on Climate and Health (ATACH) with 45 countries pledging a net zero commitment out of the 95 countries involved. Stakeholders involved include government entities, intergovernmental entities and non-state actors with the aim of promoting the integration of health nexus and climate change awareness into regional, national and international plans (World Health Organisation, 2026a).

In the Irish context, such EU and global level commitments place clear expectations on all national infrastructure systems including the health care system to reduce its environmental impact and contribute to national climate goals. In 2023, the Health Service Executive (HSE) released a document outlining its intentions to contribute towards Net Zero through the ‘HSE Climate Action Strategy 2023-2050’ which sets out actions across the services facilities including energy use, transport, procurement, waste, and models of care (HSE, 2023a). This was created to align with the Government of Ireland Climate Action Plan which requires that all public bodies to meet structured sectoral emission standards and embed improved sustainability practice into everyday operations (Government of Ireland, 2019). As a result, the healthcare sector must strengthen climate action awareness, integrate greater environmental considerations into clinical and managerial decision making, successfully adopt sustainability practices such as decarbonisation while maintaining high quality patient care. To assist in this task, the international organisation Health Care Without Harm (HCWH) have established a strategy named ‘Operation Zero’ for European countries with a vision of every country having a structured national decarbonisation plan for its healthcare sector (HCWH, 2026).

Conceptual framework

Decarbonisation is the process of reducing the amount of carbon emission released and the method of implementation will follow an emissions reduction goal trajectory such as aligning with Paris agreement (United Nations, 2016). In Ireland, healthcare emissions similarly impact national greenhouse gas emissions (GGEs) and failure to reduce these emissions could result in Ireland receiving severe financial penalties under EU climate targets. Therefore, reducing the carbon footprint of healthcare is critical, particularly in chronic disease management where care delivery and associated treatments can contribute substantially to the environmental burden (HSE, 2023b).

Chronic Disease is considered one of the largest burdens in healthcare worldwide both in overall impact and resource intensiveness due to long term persistence compared to acute illness (Hacker, 2024). Diabetes can be subdivided into three main categories, Type 1 diabetes (insulin dependent), Type 2 diabetes (insulin resistant) and gestational diabetes. Type 2 diabetes is the most common diabetes type worldwide. Although both diabetes and obesity are independent conditions, they are closely connected as obesity is a major modifiable risk factor for diabetes Type 2 development (Grant et al., 2021). It is estimated that ~6% of the Irish population are diabetic, 88.6% of which are Type 2 diabetics (HSE, 2024a). Ireland also has one of Europe’s highest rates of obesity with 60% of adults and over 20% of children and young people living with overweight and obesity (HSE, 2024b). As a result, both conditions generate substantial direct and indirect healthcare costs and environmental impacts. As Ireland also has an aging population, the number of people diagnosed with chronic disease including diabetes and obesity is set to continue to rise into the future and timely considerations of how this will impact our environment is an urgent requirement. Decarbonisation interventions are a key element in achieving net zero by 2050 and is the core objective of the EU Green deal ( European Commission, 2019). Although there has been an increased interest in healthcare sustainability through policy introduction over recent years, many interventions to date are system led rather than disease specific. As a result, pathway-specific decarbonisation opportunities remain under-explored.

The term ‘care pathway’ can be used interchangeably with phrases such as clinical pathway, integrated care pathway and patient pathway (Chawla et al., 2016). Vanhaecht (2007) described a care pathway as a “complex intervention for the mutual decision-making and organisation of care processes for a well-defined group of patients during a well-defined period”. Taking that description, this case would involve a planned sequence of clinical interventions and services using evidence-based recommendations involving a multidisciplinary health care team provided for those diagnosed with and managing diabetes and/or obesity to ensure optimal clinical management across the continuum of care (Grant &Chika-Ezerioha, 2014).

For this review, care pathways encompass:

Screening and diagnosis of initial identification and confirmation of diabetes and/or obesity will not be included as part of the pathway due to the population focus being on those who have a diabetes and/or obesity diagnosis.

Due to each care pathway having its own set of procedures, a wider system only plan would not be sufficient in reducing carbon emissions effectively in these circumstances. Although diabetes and obesity care are typically described and designed with structured linear pathways in mind, the lived experience for patients is often heterogenous and fragmented involving varying combinations of primary care, specialist services, lifestyle interventions and pharmacological treatments, all of which influence patient engagement, outcomes and shape their quality of life.

The implementation of decarbonisation should also incorporate health equity considerations, defined here as fair and just distribution of health resources and outcomes, including access to care and impacts on vulnerable or underserved populations (World Health Organisation, 2026b). This is consistent with UN sustainability goal number thirteen which recognises that climate change ‘disproportionately affects vulnerable populations and marginalised communities’, including those with chronic diseases (United Nations, 2015). Any efforts to improve local environmental quality and resilient healthcare access should directly support health equity goals.

Decarbonisation opportunities at pathway level could include pathway delivery changes (e.g. virtual clinics, telemedicine), waste reduction, lifestyle education changes delivered at local community level, clinical (e.g. greener prescribing and therapeutics use, co-morbidity clinics) and device, consumables and pathway procurement changes (e.g. reusable equipment rather than single use).

In this review patient health outcomes refer to the clinical effectiveness and quality of life for adults receiving diabetes and/or obesity care. Mental health and social wellbeing outcomes are beyond the scope of this review. This information will be used to identify potential intervention opportunities, gaps for missed opportunities which can both be utilised to investigate how such interventions may be incorporated into Irish diabetes and obesity pathways to improve carbon reduction efforts. Furthermore, such outcomes will be used to inform project next stages.

Aim

To review the current international literature on decarbonisation interventions which have been implemented for diabetes and obesity care pathways, to evaluate impacts on patient health, environmental outcomes and health equities.

Objectives

Objective 1. To examine and document what decarbonisation interventions have been implemented within diabetes and obesity care pathways internationally.

Objective 2. To identify gaps in the current evidence relating to decarbonisation interventions in diabetes and obesity pathways.

Objective 3. To evaluate the reported impacts of such decarbonisation interventions primarily on patient health and environmental outcomes, and secondarily on health equity.

Protocol and registration

This protocol describes the systematic review process for synthesising existing evidence of decarbonisation interventions implemented for diabetes and obesity care pathways. This review is registered with PROSPERO (CRD420261302156). The review will be reported in line with the PRISMA guidelines (Page et al., 2021).

Eligibility criteria

Studies will be eligible for inclusion if they include healthcare specific decarbonisation opportunities for adults with either diabetes and/or obesity. A link to the full inclusion and exclusion criteria for studies in this review can be found under extended data.

Information sources

The chosen information sources are five bibliographic databases to identify relevant literature. The chosen databases are:

Search strategy

The search strategy was created with the assistance of a librarian specialist and will combine controlled-vocabulary terms (including MeSH where applicable) and free text terms for diabetes, obesity, carbon footprint and pathway opportunities using database-specific field tags and operators. The full search strategy, including a PubMed search string is available in the extended data.

Selection process

The relevant records identified from database searches will be imported into Covidence which has the function of automatic removal of duplicate search results. Literature screening will be undertaken in Covidence supporting transparency of the process (Covidence, 2026). Two reviewers will independently screen titles, abstracts initially, against the predefined inclusion/exclusion eligibility criteria with conflicts at any stage resolved through discussion with the wider project supervisory team members. Studies deemed as ‘yes’ or ‘maybe’ records will proceed to full text screening. Reasons for exclusion of records at the full text stage will be documented.

The study selection and screening process will be documented using PRISMA flow diagram detailing the number of initial records identified, screened, excluded and included (Page et al., 2021). Prior to screening, a pilot screening exercise will be conducted on approx. 50 random studies generated from the search to ensure consistent reviewer interpretation of the eligibility criteria (Higgins et al., 2022).

Data collection

Data will be extracted from chosen studies using a Covidence template data extraction form using the extraction 2 method (Covidence, 2026). Data extraction will also be conducted by two reviewers as in the study screening process with assistance from a third reviewer if required. Any discrepancies will be resolved as outlined by input from the wider review team.

Outcomes

For each included study, data will be extracted under several headings: Individual study details, setting, population, intervention, outcomes (clinical, environmental/carbon and equity where possible), implementation, quality indicators and overall study findings. These outcomes will include any quantitative metrics and qualitative conclusions reported by the study authors. A link to the full list of the data items can be found under extended data.

Other data items

If the study contains a lifecycle assessment, further data will be extracted where applicable. Studies will be grouped according to type of sustainability intervention and by healthcare setting.

Quality appraisal and risk of bias assessment

All studies that are successfully screened and chosen will be quality appraised and assessed for risk of bias. The type of assessment carried out will depend on the study type. The aim of the quality appraisal and risk of bias assessment is to evaluate the methodical rigor and internal validity of each study and inform the interpretation of generated findings. The proposed assessment technique to be applied are ROBINS-I, RoB-2, CASP and CHEERS/ISO 14040/44 for lifecycle assessments. Two reviewers will independently carry out risk of bias assessment for each study. These assessments will assist in informing the data synthesis strategy and interpretation of generated results.

Data management

Records from database searches will be imported into Covidence as RIS files. Data extraction will be conducted using a Covidence extraction form, with version control maintained on a secure institutional SharePoint OneDrive (Covidence, 2026). All steps will be documented to ensure transparency and reproducibility including a PRISMA flow diagram (Page et al., 2021). Mendeley reference manager software will be used to manage chosen studies and record citations (Mendeley, 2026).

Synthesis

A narrative synthesis will be undertaken. However, where sufficient, consistent and comparable data are available, a statistical meta-analysis will be attempted on comparable interventions e.g. subgroup meta-analysis for a chosen intervention. Studies will be grouped according to intervention type as listed as in phenomenon of interest under the SPIDER framework (Cooke et al., 2012) and by healthcare setting (if comparable).

Findings will be compared across the chosen studies to identify any common strategies or metrics for reducing carbon emissions in diabetes and obesity care pathways and to explore any possible similarities or differences in reported outcomes. Study quality will be considered when interpreting the strength and consistency of the evidence, with greater emphasis placed on findings from higher-quality studies. Results will be presented and described narratively to highlight any key themes and patterns identified across the literature.

Meta bias

Any potential meta biases such as publication bias or selective outcome reporting will be considered throughout the review process. Due to the anticipated heterogeneity of the research topic including study designs, interventions and outcomes, there will be no formal statistical assessment of publication bias. However, to reduce publication bias, multiple bibliographic databases will be searched and associated references lists of included studies will be screened.

Confidence in cumulative evidence

The overall certainty of the evidence for each outcome will be assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach (Neumann & Schünemann, 2024).