Articles were included if they assessed a dietary exposure that was food-based (as opposed to specific nutrients), including breastmilk, food groups or categories (e.g. animal source foods, dairy products, sugar-sweetened beverages) or measures of diet quality (e.g. diet adequacy, diet diversity and different ways of defining healthy or unhealthy dietary patterns, which focus more on balance and moderation). We included studies assessing salt intake (not just sodium in foods) as condiment/seasoning. Articles were excluded if the dietary exposure was a specific nutrient (e.g. omega-3 PUFA, cholesterol, protein), therapeutic diet (gluten-free, DASH diet), uncommon individual food item (e.g. sesame seed), micronutrient supplement (including micronutrient powders, smallquantity lipid nutrient supplements), therapeutic food (e.g. RUTF), food supplement or fortified food product. Dietary behaviours (e.g. initiation of breastfeeding, frequency of feeding, fast food restaurant frequency), and food insecurity were not considered to be a dietary exposure.

Articles were included if they assessed the relationship between the diet exposure and one or more nutrition or health outcomes relevant to our theoretical framework, including stunting, wasting, overweight, obesity, anemia, micronutrient deficiencies, raised fasting blood glucose, raised blood pressure, and maternal and neonatal outcomes during pregnancy and the perinatal period (e.g. gestational diabetes, gestational hypertension and the hypertensive disorder known as pre-eclampsia, preterm birth, low birthweight, small-for-gestational-age). Other disease outcomes associated with dietary intake were not included (e.g. depression, asthma, kidney or liver disease). We focused on two of the most critical metabolic risk factors for a range of diseases, namely high blood pressure (referred to hereafter as hypertension) and high blood glucose (referred to hereafter as diabetes) (World Cancer Research Fund International and The NCD Alliance 2014). In much of the literature found, high blood glucose and type 2 diabetes mellitus (T2DM) were used interchangeably. We did not include type 1 diabetes mellitus, an autoimmune condition that is not diet related. In the second literature search, articles were further limited to original systematic review articles that included a meta-analysis of observational study data (e.g. crosssectional and prospective or retrospective cohort studies). Systematic review articles were excluded if they reported only on intervention trials (RCTs) or did not report an estimate of the effect size or odds ratio for the risk of the outcome associated with the diet exposure. We did not include experimental studies because we were interested in estimates based on normal population dietary intake. Articles were excluded if they reported evidence specific to high-income countries only.

# **Information sources**

To identify relevant articles, we conducted the first search in April 2023 using the Web of Science Core Collection database and Cochrane Database of Systematic Reviews. We conducted the second search in January 2024 using the same two databases. The search strategies were developed by life stage group and health/nutrition outcome, with search terms for each of the three components (diet exposure, outcome and cost) combined to identify relevant studies. The list of search terms for each life stage group and health/nutrition outcome are shown in **Annex 1.** The electronic database search was supplemented by scanning the reference lists of selected articles and other relevant reviews.

A team of six reviewers assessed the eligibility of the search results, with two reviewers for each search list (by life stage group/outcome). In the first step, each reviewer independently screened the list of articles based on the title and abstract. In the second step, one reviewer scanned the full text of the article and noted the presence or absence of each of the components required by the inclusion criteria. Disagreements on study selection were resolved by consensus and discussion with other reviewers.

# **Approach to data charting and synthesis of results**

A standard data charting table was jointly developed by two reviewers and data from eligible studies were charted by the lead reviewer, grouped by life stage. The table columns captured the relevant information on key study characteristics (e.g. author, publication year, study design, sample size), age and geographic location of study participants, type of diet exposure and metric used, type of nutrition/health outcome(s) and measure used, type of economic cost and measure used, and relevant key findings (e.g. strength of association observed, economic cost 6