Evidence is steadily growing about links between many of the FSN and mental health constructs measured by included studies, and the EGM makes this clear. Studies on depression and studies on BMI dominated the map overall. Anxiety, stress and mental wellbeing, and IYCF were the least represented in the literature. There may be strong evidence on how food security, certain nutrients (e.g., Vitamin D), dietary patterns, and BMI are associated with depression. On the other hand, evidence seems sparse on the relationships between other nutrients (e.g., selenium, antioxidants), IYCF practices, or child growth related to mental health or vice versa.
Regarding study design, experimental studies were mostly about nutrient intakes; very few intervened on other FSN measures or mental health interventions with FSN outcomes. Overall, experimental, quasi-experimental studies and systematic reviews with meta-analyses were far less common than the plethora of cross-sectional and cohort studies. Only 34% of systematic reviews were accompanied by a meta-analysis. There was much less qualitative or mixed methods evidence.
Geographically, studies from United States, Australia and United Kingdom dominated the evidence. Although almost a quarter of studies came from LMIC, 77 of these 446 came from China and 75 from Iran, with few from Arab countries or Latin America. The studies from Africa (n=81) mostly came from only three countries (South Africa, Ghana and Ethiopia). Three quarters of studies from South America were from Brazil. Of the LMIC countries represented in the EGM, evidence is largely based in industrialised countries, which suggests that the LMIC literature doesn’t capture the diversity of less industrialized, poorer, or more rural countries.
Most studies that measured FSN in one population group and MH in another were about mothers’ mental health and their children’s nutrition or growth status. Very rarely were FSN indicators in children investigated for their effect on parents’ mental health. Fewer studies still focus on fathers or parents together. As the focus on women in LMICs can sometimes hone in on their reproductive roles with less concern for women as individuals, we highlight the lack of studies from LMICs that examine mental health impact on women’s nutritional status and vice versa.
Despite studies showing that FSN and mental health are related in many ways, there are still large gaps across the EGM of studies investigating causal mechanisms of these relationships. There were many studies showing relationships between FSN and mental health, but less with the combined design, contextual factors and analysis to provide information most needed to design effective programs and policies.
That said, there is scope to further investigate the shared and underlying determinants of FSN and mental health. From the existing literature, these include poverty (although interestingly poverty alone does not account for these burdens alone (30)), lack of women’s agency, other poor health conditions, environment and climate change, as well as conditions of violence, conflict, instability, and social strife (31–34). Most of these factors have been identified through the respective bodies of literature on each, but some new work on the topic has tried to understand common determinants and mechanisms between FSN and mental health through innovative theoretical framing, study design and more advanced statistical models (26, 35). Recent interventions that at the least measure and at the most include programmatic components of both FSN and mental health have begun to give insight into some of these mechanisms as well (36).
Through this systematic synthesis and mapping, we were able to combine various intersections of measures, populations, study types and cross-cultural settings into an interactive resource. This is the first paper to systematize the body of evidence linking FSN to mental health. The EGM can be used in various ways by selecting and describing the nature and extent of literature on this topic.
We employed rigorous, expert-led screening and coding processes, including a search strategy designed by an information specialist using an index list of known literature. We followed state-of-the-art guidance on creating an EGM, which stop short of offering a synthesis effects observed but do include interactive filters to sort evidence according to study characteristics. Conducting a meaningful and feasible quality assessment of almost 2000 studies or pool results was beyond the scope of this EGM.
We also created parameters that limited evidence in certain ways. We searched only from 2000, did not search non-English repositories or include grey literature, and our chosen databases may not have been as likely to include qualitative reports, all which may have introduced some bias. That said, we are confident that collectively, the large number of studies identified and included serve as a robust basis from which to draw conclusions about trends, gaps, and characteristics of the available evidence on FSN and mental health.
The most important exclusion criteria were for studies in populations with underlying health problems, such as diabetes, cardiovascular disease, HIV, tuberculosis, or hospitalized patients, as well as niche characteristics (e.g., female endurance athletes or male textile factory workers). Although there is literature relevant for these populations, we aimed to identify evidence that minimized the confounding nature of these other health burdens or niche characteristics. We also excluded FSN measures that were not direct measures of food security, intake, or nutrition status, such as eating behaviours, stimulant foods or breastfeeding intentions.
In line with current trends to measure mental health globally through a symptom-based framework rather than a diagnostic criterion (which can bias and confound locally appropriate constructs of mental health) (37–39), we included mental wellbeing and mental health quality of life measures. We also aimed to include qualitative literature on the topic, which might not fit within the traditional depression, anxiety, and stress groupings. However, measures of mental wellbeing were often difficult to disaggregate from general happiness, life satisfaction or other physical health quality of life measures. Many were mixed across these domains. We thus relied on expert guidance from Teachers College Global Mental Health Lab, who assessed each measure identified across all categories for eligibility and classified them.
We propose that this EGM(s) is a tool to navigate a diverse literature base which will be primarily driven by the interests and expertise of the user. It can identify key gaps in the literature and thus direct novel efforts in research. This might include planning new primary studies or synthesis of existing primary research. When interpreting cells with fewer studies, it is important to carefully examine the quality of those studies and the clinical or practical relevance of research efforts to fill the gaps. Some research may be less strategic from a policy and planning perspective, for instance conducting new studies on IYCF related to anxiety and stress may have more application than new studies on minerals related to mental wellbeing, both of which appear as gaps on the EGM.
Furthermore, a cluster of studies in a cell (particularly certain study types – such as RCTs and reviews – commonly deemed further up on the hierarchy of evidence) still might prove worthy of further investigation. For instance, the most common subject of studies in the EGM is adiposity and depression, and there are several large, rigorous reviews with meta-analyses included on this topic. However, there is no pooled analysis of this relationship in low-income settings, where the observed effects may be quite different. This example highlights that the EGM as a whole can bring focus to understudied regions or populations: if used to highlight broad contextual factors, this might spur research that changes the conclusions we draw from either combining all available evidence (which may not all act in the same direction) or making assumptions based on the most prevalent literature (e.g. from high-income settings).
The overarching goal of building the EGM was to lay the groundwork for an evidence-based, empirical framework highlighting linkages that are known and hypothesized between FSN and mental health. This would entail selecting and synthesizing the strongest evidence within each cell, insofar as combining certain groups of studies is appropriate. This will serve to direct and support future inquiries into these relationships, as well as systematize our knowledge on the topic. Furthermore, a new understanding of and emphasis on these relationships can become part of advocacy, programs, strategic planning, and policy to support progress towards health goals such as the SDGs and others.