An extensive search of numerous sources was conducted to ensure an unbiased sample of both published and grey literature for the period Jan 1, 2010, to Feb 30, 2021. The timeline was purposely chosen as it represents an overlap between the last five years phase of Millennium Development Goals (MDGS) implementation and the first phase of Sustainable Development Goals (SDGS) which provides a desirable comprehensive transition interphase in terms of policies and strategic plans appraisal, re-formulation or formulation while addressing unfinished agenda with the shift to SDGs [3] [4]. The method used adopted guidelines on preferred reporting for systematic reviews [19] and the Cochrane principles [20] where applicable. We searched Ovid MEDLINE/PubMed, Embase, African Journals OnLine (AJOL) and PsychINFO databases for relevant articles. Database and repository searches were conducted in English language. An asterisk (*) was used to pick up multiple word endings for instance Afric* to pick up Africa and African and the following keywords/phrases were identified and used in various combinations with boolean operators (and, or): “sub-Saharan Afric*” or Afric* or “Afric* countries” and agricultural diversification or agriculture diversity and policy*; dietary diversity or dietary assessment or nutrition diversity or nutrition assessment and policy*; diet* and assess* and policy*; nutrition* and assess* and policy*. With regard to AJOL, the search string was modified due to differences in database functionality to “sub-Saharan Africa” and “agricultural diversification policy” or “dietary diversity policy” or “nutrition diversity policy”. Building on the experience of prior research on systematic review of grey literature and its significance [21], additional technical reports with a focus on sub-Saharan Africa were retrieved from relevant institutional websites (like the Africa Union, Agriculture for food security 2030 (AgriFoSe2030) and Food and Agriculture Organization of the United Nations (FAO) in January 2021. The search outputs were exported to endnote for review of titles and abstracts. A total of 1113 relevant research articles outputs (Figure 1) were collected in the initial search.

The inclusion criteria were applied by the reviewers to all studies at title and abstract level. Whenever it was not clear whether a study met the criteria, the reviewers consulted further. Relevant studies included all studies that have reported on policy and agricultural diversification, dietary diversity or nutrition outcomes in sub-Saharan Africa context. Besides, for each study to be included, it had to pass the following specific criteria: 1) relevant policy direction in relation to agricultural diversification, dietary diversity, and impact and/effect on nutrition; 2) relevant subject: precision agriculture used in the general areas of agriculture and/or diversification, nutrition and/or diversification, agriculture and/or economic outcomes.

The exclusion criteria were applied at both title and abstract level. The studies were excluded at the title level if the title was outside the geographic scope of SSA or the title was not within the general topics of agricultural diversification,

dietary diversity, and nutrition. At the abstract level, studies were excluded if the abstract was not in English, abstract not available, abstracts outside the general topics of agricultural diversification, dietary diversity, and nutrition, abstracts that mention agricultural diversification, dietary diversity, and nutrition concepts without any policy component on their findings and application in SSA. The applied selection criterion is summarized in Figure 1.

A qualitative synthesis of the information was conducted, and information obtained categorized in three main themes. First, identified agricultural diversification policies in relation to dietary and nutrition diversity was reviewed, synthesized and described. Next, policy outlook in guiding structural transformations in agriculture is presented. Finally, an exploration of policy implications for addressing challenges associated with malnutrition in SSA was done. The findings are presented using narrative summaries.

It is evident, agricultural development policies, implementation strategies, guidelines and action plans are cognizant of the fact that, there is no one-size-fits-all solution for fostering agricultural diversification in SSA as an entry point for stimulating agricultural modernization and enhanced productivity particularly for the smallholder farmers who are the majority. At regional and national level, the various policy documents and related monitoring and/or implementation research evidence address different but thematically inter-related dimensions of agricultural diversification vis-a-vis dietary and nutrition diversity [4] [10] [22] [23] [24] [25] [26]. The interlinked dimensions of focus as observed in our review entail: 1) governments commitment in supporting subsidies and enhancing public expenditure in agriculture diversity, 2) more efforts directed towards creating an enabling environment for competitive market locally and globally, 3) increased investment in agricultural research and development, 4) the need to strengthen nutritional awareness advocacy, 5) better land administration in terms of land and water tenure policies and laws to ensure equitable access and tenure security, and 6) more resilient agroecosystem through on-farm diversification aimed at invigorating climate shocks adaptation resilience, better dietary diversity at household level and agribusiness incentives [4] [10] [22] [23] [25] - [31].

Smallholder farmers across the region maintain de facto agricultural diversity with a strong association between small scale production diversity and self-consumption for food and to a large extend cash income [4] [10] [22] [27] [28] [30]. Subsequently, policy decisions to improve food security in SSA have significantly enhanced a positive interplay between agriculture diversity and household dietary consumption behaviors thus positively influencing household nutrition outcomes and agriculture related climate change resilience due to alternative paths for food and income security [4] [10] [24] [27]. On the other hand, implementation assessment of the policies, strategies, guidelines and action plans across different nations in SSA reveal that, mechanism by governments in supporting subsidies, ensuring access to agricultural technologies, agricultural advisory services, training, timely and relevant information as well as trickledown effect of public expenditure targeting smallholder cadre of farmers who are majorly in remote rural settings remain poorly streamlined for farmers access and benefit [8] [10] [25] [30] [31]. Even though implementation of some of the policies and guidelines has uplifted agribusiness, they have equally fallen short of actualizing enabling environment for market access. The persistent and much needed enabling agricultural diversification stimulus environment across the region is in two domains. First, the need of an enabling physical investments and support that entail rural-rural and rural-urban transport connections in terms of road networks, communication services like mobile and internet network, climate change prediction information flow, quality of farm inputs and favourable costs and guaranteed human and agribusiness investments security. Secondly, provision of agricultural extension advisory services, training and timely and relevant information, tailored to different types of farmers across regions within a nation in order to sustain existing and emerging interest of investment in agricultural diversification at large.

The existing empirical evidence with regards to establishing the direct causal link between agriculture diversification and nutrition is mixed. For instance, in Kenya, small livestock assets such as poultry, cattle ownership and milk consumption as well as pulses farming among the ultra-poor labour-constrained farmers were positively correlated to household nutrition [32]. Besides, in Ghana, agriculture production diversity has been demonstrated to be important for household dietary diversity and nutrition with much attention linked to its value for an income effect [33]. Among rural small holder farmers in Zambia, while agricultural diversification was associated with the household dietary diversity score, the relationship was not significant and that behavioural change communication should be factored as a critical component of agricultural diversity advancement programs [34]. The behavioural change advanced, resonates with the fact that, food seeking behaviours influence individual food consumptions patterns and dietary diversity, hence the need for a better understanding of the link between dietary diversity, nutrition security and the associated factors [35] [36]. In Mali, findings on impact of crop diversification on household nutrition, socioeconomic influences were proven to have a positive influence on food consumption and household nutritional security [37]. Thus, to improve crop diversification and the nutritional quality, there is need to invigorate diversification through subsidies among other measures that can then translate to impactful nutritional status [37]. The mixed outcomes outlined by the case examples demonstrate that agricultural diversification alone is not adequate to contribute to a positive change in nutrition outcomes, and mirrors the inherent needs, challenges and opportunities as concerns African Agriculture and its effect on food security resilience and nutrition [23] [38].

Globally, agricultural production transformation has been shaped by forces of globalization while related policies and programs are established in particular political, social and economic contexts with a broader aim to bring nutritious diets within reach of the poor [39] [40]. Therefore, examining policy and programmes interplays that shape agriculture production can contribute to better understanding of policy implementation, uptake and impact by identifying policy levers, obstacles and windows of opportunity [39] [40]. Across the SSA nations, there is a great variety of agroecological zones and large differences in land, labour and other resources but there is a wide overlap in the national and regional agricultural policies in place [41] [42] [43].

Overlaps observed largely driven by regional agricultural policies as envisioned by regional economic communities (RECs) which have overlapping memberships [42] [44]. For instance, Agriculture for food security 2030 (AgriFoSe2030), a think-tank programme that targets the UN Sustainable Development Goal 2 in low-income countries, in its focus on SSA, synthesizes and translates existing science into policy and practice, and develops capacity to achieve the goal [41] [45]. Yet, in its membership and thematic scope for example in theme 1 (social and economic dimensions of smallholder based agriculture and food security) in the focus countries for example, there is Tanzania being both a member of EAC and SADC while Kenya being a member of both EAC and COMESA, and Malawi and Zambia being a member of both COMESA and SADC among others [41] [42]. By virtue of these overlaps, harmonized implementation of various structural transformations such as those aimed at raising smallholder productivity, combating hunger and improving rural livelihoods through improving technology use to enhance women’s participation and stimulate inclusive and efficient markets is hampered by factors like variable scale of technological advancement in the different countries [46] [47].

Even so, right through the respective national and regional economic communities policies, the aim of the various policy and implementation strategies in guiding the structural transformation in agriculture to help realize multiple goals (including affordability and availability of diverse food, ensuring high quality and safe food for the population, especially the vulnerable groups) is centered on agriculture commercialization and intensification [47] [48] [49]. In the same framework, other than focusing on smallholder farmers, there is gradual integration of women and youth in order to actualize sustainable intensification geared towards enhancing food security. The SSA context of policy support in agricultural diversification, guiding structural transformations, dietary and nutrition diversity is summarized in Table 1. While empirical analyses have shown clear relations between farming diversity and food security, and a linkage to nutritional diversity in SSA, mixed findings have been reported on how market orientation influences the relationship [27] [33] [50]. Therefore, is need for a strong private public partnership multi-sectoral approach to focus on niche product markets, certification schemes, price and credit incentives to promote diversification, while intensifying production systems [23] [28] [33] [38] [50].

On the other hand, despite enormous potential in agriculture, many SSA nations are struggling to meet their food needs [51] [52] [53]. According to African development bank, 65% of the world’s arable land is in Africa despite the continent being a net importer of food with $35 billion expenditure on food imports annually. Over 80% of 874 million hectares of land that is considered suitable for agricultural production suffers from serious soil fertility challenges or other limitations to achieving high and sustained productivity [54] [55] [56] [57]. While climate change is predicted to significantly affect arable land health and agricultural output, the demand for food in Africa is expected to rise by over 60% by 2050 due to population growth and improvements in nutrition [54] [55] [56] [57]. Africa requires a significant improvement in agricultural productivity and resilience to achieve sustainable growth and development. Accelerating key elements highlighted in Table 1 would guarantee improved agricultural systems in SSA countries in tune with the targets of SDG 1 and 2.

Although climatic and/or biophysical, socio-economic, markets, institutional and policy factors greatly influence agricultural diversification decisions, it is often policies, both national and international, that have a decisive impact on agricultural diversification, dietary diversity and nutrition outcomes [68]. Thus, we further examine policy implications for addressing challenges associated with malnutrition in SSA in which we group policies into three (3) broad categories under policies and programmes for improving nutrition: 1) international initiatives - making nutrition a development priority; 2) national initiatives - policies and programmes; and 3) priorities and approaches for responding to threats to nutrition from climate change and biofuel demand.

The majority of international commitments support nutrition programs that reduce infant and maternal mortality, advance women and girls empowerment, and promote lifelong health development. In light of the shifting nutrition environment, the COVID-19 and other potential pandemic related challenges and impact, modern agricultural productivity, population shifts, and climate change, a larger, “multi-sectoral food systems approach” is required to establish robust food systems with beneficial nutrition and health outcomes [69]. Almost all countries have action plans related to agricultural diversification, dietary diversity and nutrition, as well as overall national vision documents (e.g., South Africa Vision 2030, Nigeria Vision 2030, Kenya Vision 2030, Rwanda Vision 2020, Senegal Vision 2035), national development plans, national green growth development strategies, all often based on international declarations or strategies [10]. Many have also put in place sectoral food security, agriculture and climate change policies and strategies that indicate their treatment of nutrition. Most countries recognise the value of agricultural diversification for dietary diversity and improved nutrition, yet some have declared the pursuit of agricultural specialisation and intensification as important for national economies, while some advertently or inadvertently promote specialisation under the pretext of improving national food security.

Evidence demonstrates that national agricultural systems in SSA as well as individual farmers and communities are not sufficiently diversified which undeniably leads to vulnerability to malnutrition [52] [70]. Low productive diversification, alongside frequent lack of assets to buffer against risks, exposes farmers to risks of income variability, crop failure, and consequently malnutrition. In some extreme cases, disturbances in production lead to severe malnutrition since poor farming households have low purchasing power to compensate for missing required nutrients especially for children and mothers. Unsurprisingly, poor undiversified farming households also struggle to ensure dietary diversity and nutrition as they have limited resources to supplement the consequential shortfall in dietary diversity and nutrition [10].

Since agricultural diversification, dietary diversity and nutrition features prominently in food security, health and resilience strategies of SSA countries, there is greater need to improve awareness and strengthen agricultural extension with inclusion of nutrition messages. Knowledge and awareness on agricultural diversification are increasingly recognised as a key factor in achieving food security objectives in SSA countries. Though, nutrition outcomes are not always met, especially when the agriculture production is dominated by the production of few crops and/or in some cases one major crop. Maize, for example, accounts for almost half of the cultivated land in six countries: Lesotho (61 percent), Zimbabwe (51 percent), Zambia (49 percent), South Africa (49 percent), Botswana (43 percent), and Malawi (43 percent) [10].

It therefore follows that; policies need to take into account the diversity of conditions in which farmers in Sub-Saharan Africa farm by virtue of respective regional blocks and at national level, if they are to nudge them in the right direction on agricultural diversification. Governments should aim at creating an enabling environment for agriculture where diversification is complementary: as sometimes necessary to boost dietary diversity and nutrition, while other times needed as a step towards greater economic efficiency, higher-added value and ultimately structural transformation. Within this space, public policy should aim to find balance, mindful of important implications that agricultural diversification has for dietary diversity and nutrition, as well as acknowledge the fiscal constraints that might at times argue in favour of alternative interventions.

It is, therefore, important to note that farmers in SSA ’s decision, for example, to diversify does not only rest on their understanding of the resulting impacts but is influenced by the specific context in which the consideration is made. They are mainly constrained by the realities of the environment around them, by the changing public policies and market infrastructure, and by factors specific to the organisation of society and economy in which they live and operate [10]. These specific conditions generate drivers of production decision and nudge the farmer either towards diversification. These drivers would be of particular importance to policy makers since they can be influenced or prepared for by policy decisions and the set-up of institutions. These drivers would be grouped into three broad categories:

1) Environmental drivers—that take cognisance of the climatic or biophysical factors & agro-ecological zones, climate, natural resources, the prevalence of pests/diseases and environmental shocks.

2) Policy and market drivers—that take cognisance of the measures put into place that promote national food security, productivity enhancement and commercialisation, as well as regulatory measures that condition market access.

3) Socio-economic and institutional drivers—that take cognisance of the rules & regulations, subsidies & incentives, practices, factor endowment, power distribution, education, gender and broad conditions within the community(ies).

In the appraisal of various policies, we actualize the fact that, in order to create better performing programmes, policy makers and think-tanks programmes that synthesize and translate existing science into policy and practice, and develop capacity to achieve the goal can take the following lessons learned into account. First, the Agricultural Input Support Programmes (AISPs) need to be clearly and unequivocally aligned with national food security, resilience and nutrition objectives, while reconciling the arguably competing objectives of increasing productivity as well as increasing agricultural diversity. Second, procurement and distribution of subsidised inputs should facilitate the development of competitive private sector-led input markets. Third, parallel investments in the development of relevant infrastructure that promotes overall market-functioning improvements (e.g. roads, market centres, storage facilities, transport and processing equipment for a wide variety of agricultural products) particularly in rural areas will likely enhance the outcomes of AISPs. Finally, subsidies should be part of a holistic approach to enhancing the use of a wide variety of improved inputs and not only fertilizer through the provision of complementary services (e.g., research and extension, irrigation, credit), social policy measures (e.g., productive safety nets, cash transfers) and private sector-led market development (e.g., policy reforms, infrastructure development) [70] [71].