## **_Impact of interest_**

**Third, the impact of these health and nutrition outcomes is the economic costs to individuals and society.** Economic costs are defined as the direct and indirect impacts of malnutrition on individual and national economic activity, including the costs of preventable mortality, costs of medical care and income lost to ill health, costs of impaired physical growth, and costs and losses linked to impaired cognitive growth (Global Panel 2016).

The measures of economic impact (i.e. cost) include disability adjusted life years (DALYs), the monetary value of losses of goods and services production in a country each year (gross domestic product, GDP), as well as various measures of human capital, such as years of educational attainment and value of future income/wage earnings. Studies on the cost of diet-related NCDs also frequently report the annual per capita health care costs associated with health services (hospitalization, consultations) and treatment of NCDs (medications), as well as indirect health care costs, such as work absenteeism and reduced work productivity.

# Literature search approach

We chose to conduct a scoping review as this type of review is useful for presenting a broad overview of the evidence for a specific topic, examining emerging aspects of research on that topic, clarifying key concepts and identifying gaps (Tricco et al. 2016). The scoping review aimed to assess the extent to which research on the contribution of unhealthy diets to nutrition and health outcomes and their associated economic costs in LMICs has been undertaken. This implied mapping the types of evidence available on which subpopulations (life stage groups) are represented, which diet metrics (or specific dietary factors) are used, and which outcome types and economic costs are considered.

As a first step, we conducted a comprehensive literature search to identify primary research articles that included all three components described in our conceptual framework, namely: a diet metric (or a specific dietary factor), a nutrition or health outcome, and economic cost. These criteria yielded a body of literature that was limited in scope, especially in terms of the life stage groups represented.

For this reason, we conducted a second comprehensive literature search that expanded the inclusion criteria to include systematic review papers that assessed the evidence for the contribution of a diet exposure measure to a nutrition or health outcome described in our conceptual framework and reported an estimate of effect size based on a meta-analysis of observational study data. This was expected to help the mapping of evidence from the first literature search in two ways. First, the biggest gap from the first search was the lack of evidence on the contribution of diet to nutrition and health outcomes for the various life stage groups (beyond adulthood). Second, while there are a reasonable number of studies which provide estimates of the cost of undernutrition and overweight/obesity in LMICs (Horton et al. 2024), there are very few studies that incorporate the contribution of the diet to these outcomes. Since conducting a full literature review on the diet and outcome components would yield a very large body of evidence on these relationships without necessarily providing the desired information on the effects, we chose to limit the second search to studies that consolidated this body of evidence in a systematic way, including calculation of effect sizes. See **Table 1** for a PICO summary of the elements that guided Search 2.

## **Eligibility criteria**

Peer-reviewed journal articles were included if they were: published during 2000-2023 (arbitrary cutoff used to focus on evidence produced with a recent timeframe since dietary patterns are changing rapidly in LMICs), written in English, and involved human participants of any age living in a low- or middle-income country (using the World <u>Bank’s classification</u> in 2023 fiscal year). Articles were excluded if they were case reports, editorials, letters to editors, comments, conference abstracts, short communications, or qualitative studies.

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