Introduction

The global population is increasing through an unprecedented and sustained demographic transition, characterized by increasing longevity and reduced fertility rates [1]. In 2017, the global population was 7.6 billion, and is projected to peak at 9.7 billion in 2064 before falling to 8.8 billion by 2100 [2]. Older adults comprise an ever growing proportion of the current global population [1, 3]. As such, multimorbidity and disability levels are expected to rise, creating pressure on health and social care systems, thus emphasising the vital role of preventive interventions [4] to maximise healthy ageing i.e., developing and maintaining physical and mental capacities for both healthy and unhealthy people, and across the life-course, to improve well-being in older age [3].

The number of Africans aged ≥60 years is expected to triple in the next three decades: from 74.4 million in 2020 to 235.1 million in 2050 [5]. This reality calls for interventions to facilitate healthy ageing and to cushion economies and health systems, from negative impacts of rapid and unhealthy ageing [6]. To ensure cost-effectiveness and reduce resource waste, interventions should be informed by local and contextual evidence [7]. However, research and evidence synthesis on health ageing in older adults in Africa are scarce, although emerging. For example, Naidoo et al. [8] are currently synthesising current evidence on physical activity interventions in older people in sub-Saharan Africa (SSA) to inform future interventions [8]. Apart from physical activity [9], diet is a fundamental determinant of, and risk to, healthy ageing [9]. Healthy diets (e.g., high in fruit and vegetables, fish, whole grains) are associated with longevity, and better cognitive, musculoskeletal and cardiometabolic health [10], while less healthy diets (e.g., high in sugar and sodium, low in fruit and vegetables) are important risk factors of chronic diseases such as cancer, cardiovascular disease, and type 2 diabetes [11].

Our preliminary literature search has found that available reviews on nutrition in older adults in Africa have synthesised descriptive studies and focussed on: nutrition and health status [12], nutrition status and associated factors [13] and food insecurity [14]. Of these three reviews, all urgently called for nutritional interventions: however, our preliminary literature search did not identify any existing or ongoing reviews focussed on any aspect of nutrition interventions targeted at older adults in Africa. Nevertheless, we identified a few studies documenting the implementation of nutrition interventions among older adults in Africa. Therefore, to inform current and future nutrition interventions in older adults in Africa, this protocol describes a scoping review aiming to synthesise available evidence on nutrition and nutrition interventions for older people. Particularly, the review will seek to explore the types, design, implementation, delivery, and evaluation of such interventions. The review will comprise of three interlinked phases described in more detail in the methods section: Phase 1 (review of reviews on nutrition in older people in Africa); Phase 2 (review of empirical studies describing nutrition interventions (both nutrition-specific (e.g. supplementation) and nutrition-sensitive (e.g. cash transfers)) in older people in Africa); and Phase 3 (consultation with local stakeholders on Phase 1 and 2 findings to gain contextual insights not in the published literature). The scoping review will inform the development of nutrition interventions in Africa, and more specifically and immediate a healthy ageing intervention in Zimbabwe as part of a wider project on health ageing in Africa.

Methods

A scoping review is appropriate for evidence synthesis in this case, as this design is ideal for areas where evidence is emergent, few randomised trials relevant to a given context exist, and where the aim is to generate evidence beyond intervention effectiveness [15]. This scoping review will be conducted using steps from a framework proposed by Arksey and O’Malley [16] and further proposals by Levac et al. [15] as described below.

Research questions

Table 1 shows the intervention characteristics, research questions, and related review phases.

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Table 1. Intervention aspects and research questions to be addressed by the review and relevant review phases.

https://doi.org/10.1371/journal.pone.0313036.t001

Literature search and selection

Phase 1: Review of nutrition reviews.

Published reviews will be searched in five databases MEDLINE and EMBASE (through Ovid); Web of Science, African Index Medicus and African Journals Online. Systematic searches, without time restrictions, will combine four concepts and their synonyms: older adults, nutrition, review, and Africa. An initial MEDLINE search strategy, informed by published and relevant reviews [18, 19], has been developed by one author (AMM) and checked by an experienced systematic reviewer and librarian–see S1 File. This search strategy will be adapted for EMBASE (through OVID), and the Web of Science; however, the African Journals Online and African Index Medicus databases do not allow for advanced searching, so simple searches using the website search function will be used. The searches will involve multiple searches combining relevant concepts using ‘AND’ (e.g., nutrition and review and older adults; diet and review and elderly). For feasibility, only the first 100 results of each search output (where multiple searches are used) will be screened [20, 21]. Furthermore, to capture reviews that have been conducted by non-academic authors (such as non-governmental organizations), relevant website searches (e.g. HelpAge International website) will be performed (using the simple search strategy already described) and the first 100 search outputs of each search screened [20, 21].

Search results from OVID and Web of Science will be exported to Endnote for removal of duplicates and then uploaded to Rayyan [22] for title, abstract, and full-text screening by two independent reviewers. Disagreements in screening decisions will be resolved through discussion and/or involving a third reviewer. For efficiency, searching and screening of records (using title and text underneath and if needed accessing full text) in African Journals Online, African Index Medicus and websites will be conducted simultaneously by one author. Records will be included if they document a review of any kind synthesising African evidence on nutrition in older adults.

Phase 2: Review of nutrition interventions.

This Phase will involve searches of empirical studies describing implemented or planned nutrition interventions targeted at older adults in Africa. The literature search and selection approach will be similar to that described for Phase 1, albeit with a different search strategy. In addition to databases used for Phase 1, we will also seek protocols for ongoing research by searching trials registers including the International Clinical Trials Registry Platform and clinicaltrials.gov. S1 File shows the MEDLINE search strategy for this Phase which will combine four concepts and their synonyms: nutrition; intervention; older adults; and Africa. The search strategy was developed using synonyms used in published reviews [18, 19]. Like Phase 1, search results from MEDLINE, EMBASE, and Web of Science will be exported to Endnote for duplicate removal and uploaded to Rayyan [22] for title, abstract, and full-text independent screening by two reviewers. Similar to Phase 1, searches and screening in African Journals Online, African Index Medicus, and grey literature will be conducted simultaneously by one author. Records will be included if they describe any aspect of nutrition interventions (type, design, implementation, evaluation) piloted or implemented in older adults in Africa. Both published articles and grey literature with data on any research question will be included; however, reviewers will decide on whether to include certain grey literature types such as conference abstracts based on comprehensiveness and added value of data presented.

For both Phase 1 and 2, databases’ and grey literature search inclusions will be complemented by screening reference lists of included full texts for relevant records. Additionally, using our professional contacts and networks, we will solicit relevant resources from organisations working on nutrition in older adults and healthy ageing interventions in Africa.

Table 2 shows additional inclusion information based on Population, Intervention, Comparison, Outcomes, and Study design criteria.

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Table 2. Inclusion criteria based on the population, intervention, comparison, outcomes, and study design criteria.

https://doi.org/10.1371/journal.pone.0313036.t002

Synthesis of Phase 1 and 2 findings

All data will be extracted and analysed in Microsoft Excel. Record characteristics will be analysed by one reviewer using frequency counts and percentages and presented in text, tables or graphs. Data relevant to research questions will be analysed using a simple form of thematic analysis [24] and presented in frequency counts and percentages, text or appropriate visualisations. Two authors will independently read through collated text and identify relevant codes/themes after which they will meet to discuss a coding framework that will be applied to all the data by one author. Table 3 summarises the analysis and synthesis that will be used for each of the review questions.

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Table 3. Summary of analysis and synthesis for each of the review questions.

https://doi.org/10.1371/journal.pone.0313036.t003

Conclusion

This review will summarise all previous reviews related to nutrition in older adults, and empirical studies describing development or implementation of nutrition interventions in older adults in Africa. Furthermore, local stakeholders will be consulted to enrich the findings from the published literature. Evidence from this review will inform the development of a healthy ageing intervention for use in Zimbabwe and, if it proves successful, for future nutrition interventions targeting older adults in Africa.

Strengths and limitations

Search and inclusion of journal articles and grey literature will provide a comprehensive synthesis of evidence on nutrition in older adults in Africa. Additionally, consultation with local stakeholders will contextualize the findings and provide insights that are not in the published literature. However, consultation exercises will only be conducted in two countries which may not be generalisable to the African region.

Supporting information

Acknowledgments

The authors would want to thank systematic reviewers at the Musculoskeletal Research Unit, Bristol Medical School, Jane Dennis, and Andrew Beswick, for their help in the development of the search strategy.