model.<sup>1</sup> These costs are in turn components of their much larger $12 trillion (13.8% of global GDP) estimates of hidden costs of global agrifood and land use systems. These larger costs use a planetary rather than a human health framework, incorporating environmental costs.

The “double burden” of malnutrition refers to: (1) the co-existence of undernutrition (as evidenced by child stunting, child wasting, women thinness) and adult or child overweight at country level; (2) the co-existence of one or more individuals with wasting, stunting, or thinness and one or more individuals with overweight or obesity within the same household and; (3) the underlying developmental origins biology on what is termed the Developmental Origins and Health and Disease (DOHAD), originating in the work of Barker (2004). The DOHAD theory posits a biological basis for why diets with inadequate energy and nutrients levels during early pre-conception and pregnancy predispose offspring 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 nonpregnant 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 among individuals whose body mass index is within the healthy range (i.e., 18.5-24.9 kg/m2) (Mwangome and Prentice 2019).

Recent UN statements have referred to “malnutrition in all its forms,” for example in Sustainable Development Goal 2. Countries facing both stunting and obesity encounter more complications in policies; Hawkes et al. (2020) propose ten ways to reorient nutrition interventions to address both burdens simultaneously and Luo, Zyba, and Webb (2020) propose an index to measure nutrition in all its forms.

The discussion proceeds as follows. We first outline the important definitions being used throughout this Working Paper and present a basic conceptual framework. We then discuss issues of measurement, and review data sources, focusing on healthy diet metrics collected at national-level across a wide array of countries. This is followed by a brief summary of previous related costing studies, mainly focused on the costs of malnutrition in all its forms. We then propose a methodology for estimating the economic costs of unhealthy diets, along with preliminary cross-country empirical work. The concluding section summarizes key findings in terms of etiological pathways, nutrition and health outcomes, and economic effects, and notes key gaps and areas for future work.

# 2. Definitions and Conceptual Framework

The 2021 UN Food Systems Summit used the following definition: “A healthy diet is health-promoting and disease-preventing. It provides adequacy without excess, of nutrients and health-promoting substances from nutritious foods and avoids the consumption of health-harming substances.” (Neufeld, Henriks and Hugas 2019). Healthy diets respond to the universal principles of nutrient adequacy, dietary diversity, macronutrient balance, and moderation (Verger et al. 2023). In what follows we consider three different diet aspects: energy sufficiency, nutrient adequacy, and food choices which promote health, using Figure 1 published by FAO (2020). These three aspects are also consistent with the “triple burden” of malnutrition discussed above.

**Energy insufficient diets** have large economic consequences in terms of disability-adjusted life-year (DALY) losses from high child mortality and direct costs of treatment of acute malnutrition. Key pathways

> 1 Conversions from the amounts in $ trillion in FOLU (2019), for 2018, to percentage of GDP were undertaken by the present authors, using $86.4 trillion as global GDP in 2018.

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