# Introduction

This paper aims to review and summarize the current evidence on the association between diet quality, malnutrition (in all its forms), and related economic costs in low- and middle-income countries (LMICs). Economic arguments are useful particularly for influencing government policy changes that can support societies to adopt healthier diets. Economic arguments have been widely used to advocate for action against undernutrition and are now increasingly being used to advocate for policies to stem the increase in overweight, obesity, and risk of noncommunicable diseases (NCDs). This follows the shift in concern from undernutrition, initially focused on calorie intake, subsequently on inadequacy of micronutrients, and most recently on overweight and obesity. The term “nutrition transition” has been used to describe big shifts in human diets towards consumption of foods high in fat, salt, sugar, and refined carbohydrates, mostly accompanied by low consumption of fiber, fruits and vegetables.

While a broad array of economic, social and environmental factors affect stunting, the agrifood system is strongly implicated in increases in overweight and obesity and hence NCDs. Very rapid changes in the food system, especially in the food retail environment, have led to higher availability and wider variety of ultra-processed foods (UPF) (Reardon et al. 2021). UPF foods are highly palatable, cheap, ready-to-consume food products that are characteristically energy-dense, fatty, sugary or salty (Monteiro et al. 2013).

Although the nature and pace of the nutrition transition has varied by location and income groups, the lowest income LMICs face severe levels of what is termed the double burden of malnutrition (DBM) as the rapid increases in overweight and obesity are not accompanied by equal reductions in child stunting (Popkin, Corvalan, and Grummer-Strawn 2020). The DBM is defined as the simultaneous manifestation of both undernutrition and overweight and obesity within various contexts, such as within the same country, the same household, or even the same individual (where the individual is both stunted and overweight/obese).

The DBM affects most LMICs and has increased in the poorest LMICs, mainly due to overweight and obesity increases (Popkin, Corvalan, and Grummer-Strawn 2020). Between 1990 and 2022, there has been a transition in many countries from underweight dominance to obesity dominance in the DBM, with growing prevalence of obesity among school-age and adolescent children as well (NCD Risk Factor Collaboration (NCD-RisC) 2024). The work of Barker (2004) on what is termed DOHAD (Developmental Origins and Health and Disease) posits a biological basis for why diets with insufficient appropriate nutrients for pregnant women predispose their children to higher risks of obesity and associated NCDs in adulthood (Wells et al. 2020). Furthermore, with recent global estimates that over half of preschool-aged children and two-thirds of non-pregnant women of reproductive age have at least one of three micronutrient deficiencies (Stevens et al. 2022), most LMICs are dealing in reality with a “triple burden” of malnutrition. Micronutrient deficiencies can occur “at either end of the anthropometric spectrum” as well as in individuals with healthy weights (Mwangome and Prentice 2019). The double and triple burdens of malnutrition render greater complexity for policy interventions (Hawkes et al. 2020).

Earlier economic studies of the cost of malnutrition in LMICs have focused on the effects of undernutrition, while those in high income countries focused on overweight and obesity. The nutrition transition and the DBM have led to a growth in studies of the economic cost of malnutrition in all its forms in LMICs (Schneider et al. 2020). However, associating cost with nutritional status does not directly inform policy, as there are multiple factors which determine nutritional status. Recent work has increased focus on the health and economic consequences of diet since this provides an entry point to examine agrifood policies.

A growing number of economic studies attempt to assess the economic cost of unhealthy diets. Candari and colleagues (2017) reported just six studies from Australia, China, the United Kingdom and the United States that generated evidence on the costs of unhealthy diets, but these varied widely in their definition of unhealthy diets and reported a wide range of cost estimates which were sensitive to the study methodology. The majority of recent studies rely on impacts on health using data from the Global Burden of Disease (GBD) project (Institute for Health Metrics and Evaluation, IHME). These include studies by The Food and Land Use Coalition (2019) and FAO et al. (2023). These estimates face methodological issues discussed elsewhere (Beal et al. 2021; Stanton et al. 2022; Horton et al. 2024).

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