Understanding the nutrition ecology and related distal and proximal research gaps impacting school-aged children’s and adolescents’ functioning— a report from the “Biomarkers of Nutrition for Development: Knowledge Indicating Dietary Sufficiency (BOND-KIDS)” Project Working Group 2

Abstract

Nutrition is critical to the health, development, and well-being of children and adolescents, operating through nutrients and the social and physical influences of dietary behaviors. Child and adolescent growth and development depend on complex biological systems interacting with the nutrition ecology. Here we focus on bi-directional interactions with the multi-level nutrition ecology, including distal systems (climate, geopolitical, food systems), and proximal systems (community food options; health, social, and food services; and school policies and programs), all mediated by the family. Thus, the impact of nutrition on children’s and adolescents’ functional outcomes is dependent on understanding the multilevel nutrition ecology. Interdependencies between the nutrition ecology and children’s health, development, and well-being have been examined during early childhood, with limited attention to corresponding relations among school-age children and adolescents. This age grouping represents 3 unique developmental phases: primary school-age (pre-puberty; approximately 5–9 years of age), early adolescence (puberty; approximately 10–14 years of age), and late adolescence (post-puberty; approximately 15–19 years of age). The 4-paper “Biomarkers of Nutrition for Development: Knowledge Indicating Dietary Sufficiency: BOND-KIDS” Project series builds the evidence for why and how an ecological approach is needed to assess and interpret the impact of interventions to improve the nutritional status and functional development of children and adolescents during these 3 developmental periods. This paper synthesizes the environmental evidence underlying children’s nutrition and responses to interventions, with specific attention to how distal and proximal environments impact nutrition and school-age children’s and adolescents’ functioning, including growth, physical and mental health, cognition, socio-emotional development, physical activity, and school attendance and behavior.

Introduction

Nutrition plays a critical role in human capital development, including the skills, knowledge, cognition, and abilities that enable individuals to contribute to economic productivity. Building support for human capital depends on conceptualizing a continuum of health and development from preconception through age 19 years [1–3]. To fully interpret the critical role of nutrition in the health, development, and well-being of children, including the impact of nutrients and dietary behavior, requires attention to interactions with nutrition ecology.

Human growth and development depend on complex biological systems that interact with the nutrition ecology, which is the focus of this paper. Nutrition ecology includes both internal systems (biological, developmental, genetic, health, and nutritional) and external environments (home, community, social/behavioral/cultural, and physical) [1]. Childhood and adolescence, defined as ages 5–19 years for this manuscript, are critical developmental periods with differential nutritional requirements, increasing autonomy, and susceptibility to marketing and other influences on dietary choices [4]. Interdependencies between the nutrition ecology and children’s health and development have been examined during the “first 1000 days,” the formative period of human development from conception through the first 2 years of life [5]. However, there has been limited attention to the nutrition ecology and the growth and development of children from 5 to 19 years of age [3]. This age grouping represents 3 unique developmental phases: primary school-age (pre-puberty, approximately 5–10 years of age), early adolescence (puberty/peri-pubescent, approximately 11–14 years of age), and late adolescence (post-puberty, approximately 15–19 years of age).

Health services for school-age children and adolescents focus primarily on annual preventive services and treatment for acute illnesses. School-age children are primarily with their families or in schools (or childcare settings), under the auspices of educational services. To ensure that nutrition interventions have a broad reach, they are often delivered through families, schools, and childcare settings. However, the lack of attention to the nutrition ecology to determine the impact of nutrition interventions is a significant gap that threatens both the impact and sustainability of nutrition interventions on the functional outcomes of children (e.g., growth, physical and mental health, cognition, socio-emotional, physical activity, and school attendance and behavior). The “Biomarkers of Nutrition for Development: Knowledge Indicating Dietary Sufficiency: BOND-KIDS” Project fills that gap by building the evidence for why and how an ecological approach is needed to understand and assess the impact and sustainability of interventions to improve nutritional status and the functional development of school-age children and adolescents, thereby contributing to their human capital development.

The BOND-KIDS Project includes 4 working groups charged with addressing the biological and environmental components, measurement, and translation/implementation of new knowledge to support the evaluation of relevant systems and efforts to assess program efficacy [1]. The first paper describes critical factors in children’s internal environment with specific reference to the intersection of nutrition, biological, and health outcomes (i.e., linear growth/body composition, metabolic systems, neurodevelopment, physical activity, and immune function) [6]. The second paper (this paper) focuses on children’s external environment and their bi-directional relations to the functional outcomes of programs that address the nutritional status of school-aged children and adolescents. The third paper uses a set of core principles for nutritional assessment to integrate elements defined by the first two papers into an approach to assess the impact of interventions to improve the nutritional status of school-aged children and adolescents [7]. The fourth paper covers factors engaged in implementing and evaluating programs to support children’s and adolescents’ health, development, and well-being [8].

Nutrition Ecology Framework

The Nutrition Ecology Framework (Figure 1) offers a comprehensive, systems-based perspective, considering the dynamic interplay among distal environment factors: climate, geopolitical, and food systems and proximal factors: community food options, services (health, social, and food), and school policies and programs. Families play central roles by mediating and integrating distal and proximal influences with their own interpretation, values, and beliefs related to food and nutrition.

Figure 1.

The Nutrition Ecology Framework.

While children’s internal environment dictates basic nutrient requirements and metabolic functions [6], children’s external environment influences food choices, nutrients needed (e.g., energy requirements change in response to physical activity), and whether nutrient intakes are sufficient for optimal functional outcomes. The external environment can moderate the impacts of nutrition interventions, leading to differential effects on children. Thus, the concept of nutrition ecology has significant implications for the design and interpretation of context-specific and equitable approaches to improve the nutrition, health, and development of children and adolescents.

The Nutrition Ecology Framework uses a life-course perspective to illustrate how distal and proximal factors interact and impact the functional outcomes of children and adolescents. Incorporating the nutrition ecology into program design facilitates the interpretation of nutrition interventions and informs the development of future policies, programs, and research related to child and adolescent functioning. The Nutrition Ecology Framework is based on a robust empirical foundation, drawing from reviews, series, commissions, and authoritative sources, such as the Disease Control Priorities [3]. The concepts driving Nutrition Ecology apply to children and adolescents globally; however, most of the evidence is from the United States (US). Therefore, this review relies primarily on examples from the US, with inclusion of highly relevant global policies from reviews and international agencies. To illustrate that the Nutrition Ecology Framework applies globally, we include a case example from Haiti. This review includes eight sections:

1. Cross-cutting themes, including child and adolescent development, nutrition equity, and food, nutrition, and water security

2. Distal environmental components including climate, geopolitical, and food systems

3. Proximal environmental components, including community food options; healthcare, social, and food assistance services; and school policies and programs.

4. The home and family provide linkages between the proximal and distal components and children’s and adolescents’ functional outcomes

5. Functional outcomes in children and adolescents including growth, physical and mental health, cognition, social-emotional development, physical activity, and school attendance link with the biological outcomes [6]

6. Case study from Haiti that illustrates how distal and proximal aspects of nutrition ecology relate to children’s functional outcomes, highlighting the necessity of considering environmental conditions in interpreting the effects of nutrition interventions

7. Research gaps and future opportunities to deepen understanding of the linkages between nutrition ecology and functional outcomes in children and adolescents

8. Summary and conclusions

Section 1: Cross-cutting themes

Child and adolescent development

The BOND-KIDS Project [1] focuses on 3 distinct developmental phases during childhood and adolescence. For primary school children and early adolescents (ages 5–9 and 10–14 years, respectively), most food is purchased, prepared, served, and consumed at home or in school. For many children, schools are the primary source of nutrition interventions.

Early adolescence is marked by puberty, increased growth and hormonal processes, expanded neuro-processing and cognitive capacities, increasing independence, and transitions from primary to secondary or middle school [9]. In many countries, secondary school is neither free nor compulsory [10]. Thus, globally millions of children leave school during adolescence, often due to school unavailability or unaffordability, family issues, or personal choice. When adolescents lose educational resources, they also lose access to school-provided meals.

Adolescents increasingly consume meals away from home and make independent choices on what, when, and how much to eat, particularly as they transition to the labor market [11]. In the US, diet quality tends to worsen as children become adolescents and are increasingly influenced by proximal and distal environments. For example, based on the National Health and Nutrition Examination Survey, in 2015–2016, 52% of children (aged 6–11 years) and 66% of adolescents (aged 12–19 years) had poor quality diets [12]. The increased availability and promotion of unhealthy foods and beverages that are particularly attractive to children and adolescents contribute to poor diet quality [13].

Nutrition equity and social determinants of health

Nutrition equity refers to universal access to optimal nutrition and a healthy diet. Inequities refer to unfairness and injustice [14] and disparities refer to differences in access that are not necessarily unjust, but are often associated with social, economic, and environmental disadvantages. Both inequities and disparities can occur at all levels of the nutrition ecology, can impact children’s and adolescents’ ability to consume a healthy diet, and often disproportionately affect low-income communities and communities of color [15, 16]. Evaluating nutrition interventions by monitoring health disparities can measure progress towards health equity [17]. The fourth BOND paper [8] addresses equity during implementation of nutrition interventions.

Here we emphasize the need to integrate the impact of ecological factors, such as the social determinants of health into the design and evaluation of nutrition interventions. The social determinants of health refer to non-medical factors that can influence children’s health, considering places that children were born, live, play, and attend school [15, 16]. Examples of social determinants of health related to children’s and adolescents’ health and nutrition include parental leave policies, household food and nutrition insecurity, school-level policies to provide foods to children, zoning for growing and selling food, availability of and access to healthy and cultural foods, marketing of foods to children and families, food pricing and price incentives, food and nutrition assistance programs, and water security [18].

Addressing the social determinants of health is critical to promote nutrition equity for populations most in need of nutrition interventions, particularly in understanding why interventions may not benefit all children. Addressing nutrition equity highlights how the nutrition ecology can increase healthy options, reduce barriers to health-promoting behaviors, improve social and economic resources, and empower communities to address social and structural determinants of health that may impact children and adolescents [19–21].

Socioeconomic disparities.

Family socioeconomic status (SES) impacts the resources available for purchasing and preparing healthy foods. The socioeconomic composition of the community determines the quality of resources available to families [22]. Consequently, socioeconomic disparities often coincide with structural inequities (e.g., disinvestment and lack of health resources in low-income communities and schools), unfavorable psychosocial conditions (e.g., lack of nutritional knowledge, low social support) and sociocultural factors [23, 24]. Children and adolescents in low-income families experience higher rates of poor dietary quality and related morbidity than children from middle- and high-income families [25–28].

Race and ethnicity.

Children of color experience higher rates of food insecurity than white children in the US, leading to increased health issues and morbidity. Food insecurity is attributed to multiple factors, including reduced access to healthy foods [29], weathering (i.e., constant stress related to social, economic, and political marginalization) [30], and structural racism [31, 32].

Food and nutrition security.

As detailed in the BOND-KIDS Project overview [1], food and nutrition insecurity are important social determinants of health and essential drivers of efforts of community- and school-based interventions aimed at addressing child nutrition. Household food security refers to consistent, dependable access to enough food for active, healthy living [33], while nutrition security goes further, emphasizing equitable access to nutrition-rich food that supports optimal health and well-being [34, 35].

Food and nutrition insecurity negatively impact the quantity and quality of nutritious foods consumed, such as fruits and vegetables [36], and adversely affect children’s and adolescents’ behavior, academic performance, and emotional development [37]. In response to a lack of adequate food, families may rely on less expensive, energy-dense, low-nutrient foods, increasing the risk for deficiencies of micronutrients associated with poor cognitive development [38, 39]. Food and nutrition insecurity have been associated with both underweight and overweight [40]. Weight loss can occur when there is inadequate food and weight gain may occur with the consumption of energy-dense, low-nutrient food.

Food insecurity may also be accompanied by caregiver mental health problems, specifically depression and anxiety, as caregivers struggle to meet basic needs. Caregiver mental health issues are often associated with increased behavioral and developmental problems in children and adolescents, including psychopathology [41]. School-age children and adolescents are often aware of their household’s food insecurity, reporting increased food responsiveness and experiencing physical and mental health problems [42, 43].

Water security.

Although shortages of potable water are common globally [44] and a growing concern in the US [45], water insecurity has received limited attention. Measures of water security encompass water use, access, availability, safety, and stability [44], and assess household and individual water security [46]. Severe water insecurity can lead to diarrheal diseases and other mental, physical, and economic impacts [44]. Because water insecurity often coexists with food insecurity, it can significantly impact children’s nutrition ecology and response to nutrition interventions [47].

2: Distal environmental components

Climate

Human interactions drive significant global environmental changes, including climate change, land use change, alterations in the water cycle, changes in biogeochemical cycles such as phosphorus and nitrogen, and biodiversity loss. Climate change has been extensively studied for its impact on human health and well-being. The complex interlinkages among the climate system, food system, ecosystems, and socioeconomic systems highlight the 2-way interactions and implications for food security [48].

Observed climate change adversely affects food security, primarily in lower-latitude regions, by decreasing yields of stable crops [48]. Malnutrition (undernutrition, overweight, and obesity) is increasingly associated with climate change, and can increase disease susceptibility [49]. Future climate change is projected to further decrease crop yields, while rising carbon dioxide concentrations reduces the nutrient density of major cereal crops. These intersecting hazards create a vicious cycle of malnutrition, reduced food production and work performance, deteriorating health, and further reductions in food/nutrition security. Monitoring the micronutrient content of plant-based foods is essential to bridge the elemental gap between human requirements and plant offerings [50]. Additionally, changing temperatures and carbon dioxide concentrations are expected to alter the effectiveness of plant-based medicines, particularly among Indigenous and marginalized populations [51, 52], affecting the health and well-being of school-age children.

The risks of climate change are not evenly distributed geographically or across population groups, with the countries that emit the lowest greenhouse gas emissions being the most affected [49], increasing existing inequities in a warming world [53]. Children, particularly those living in poverty, are at risk today and throughout their life course as climate-related exposures evolve [54, 55]. Globally, approximately one billion children live in extremely high-risk countries [56].

Climate shocks, loss of biodiversity, and damage to water, air, and soil are worsening the nutritional prospects of millions of children, especially in the context of low resources [57]. The extent of the impact on school-aged children’s food quality and quantity will depend on proactive and timely investments in research, technology development, and implementation of effective and efficient nutrition intervention programs, alongside efforts to reduce greenhouse gas emissions.

Geopolitical

The geopolitical context has downstream effects on multiple levels of the nutrition ecology, impacting the effectiveness of nutrition interventions on school-age children and adolescents. These influences stem from international relations and conflicts, along with national, regional, and local politics, that shape allocation of resources, trade, food policies, food and economic systems, and food access for children and adolescents [58–60]. In extreme cases, armed conflict and other humanitarian emergencies may significantly disrupt community food availability and quality, both directly and by precipitating population migration, and poverty and economic social hardship [57]. Additionally, geopolitical actions have contributed to globalization and urbanization, which have had variable effects on food availability and the prevalence of under- and over-nutrition [61, 62].

Global and US approaches to address climate change natural disasters, economic shocks, and the COVID-19 pandemic have resulted in inequities in food security, disproportionately affecting vulnerable populations and increasing migration [58, 63–68]. Child migrants are at elevated risk for the double burden of obesity and stunting, as well as deficiencies in iron and vitamin D associated with low quality, energy-dense food [69]. Politics at global, national, regional, and local levels also affect availability of important assets that can help mitigate the impact of destabilizing forces on child health. These assets include robust nutrition monitoring systems, effective emergency feeding programs, social capital (e.g., community advocacy, social mobilization), gender equity efforts, and community level services that provide regular access to nutritious food, clean air and water, and stable housing [58, 70–73].

Food systems

Food systems represent a complex and dynamic set of interacting components, including agriculture, water sources, and forests and rangelands, together with production, processing, storage, distribution, retail, pricing, marketing, and consumer behavior [74, 75]. Food systems are influenced by geopolitical and climate forces and policies [76, 77], and in turn can influence the nutrition ecology of school-age children and adolescents through multiple pathways [18, 75, 78].

The shift in global food systems, characterized by the consumption of processed foods high in fat, sugar, and salt, has led to a global rise in childhood overweight [57]. Based on the United Nations Sustainable Development Goals [79] and the United Nations Decade of Action on Nutrition 2016–2025 [80], strengthening food systems is recommended to address child hunger and malnutrition, while ensuring availability of sufficient quality and quantity, affordable, safe, and culturally acceptable foods for children.

Food processing.

Food processing, including heating, drying, fermenting, adding salt and other preservatives, and fortification or enrichment with nutrients, transforms foraged and cultivated products into safe, palatable, convenient, non-perishable, and affordable foods and beverages. The industrialization of food systems has yielded numerous benefits, including reductions in chronic undernutrition and consequent child wasting, stunting, and micronutrient deficiencies [81]. However, globalization of the food supply is also negatively shaping food options and choices. For example, the proliferation of ultra-processed foods (UPF) – foods that have been altered through industrial processes, and have added ingredients, such as sugars, sodium, or unhealthy fats [82]. UPF can increase the risk for nutrition-related deficiencies, including obesity and chronic diseases [13, 83].

Food prices and marketing.

The retail food sector is an important determinant of child and adolescent nutrition. For example, price increases on sugar-sweetened beverages and promotion of healthy beverages in grocery stores result in reductions in sugar-sweetened beverage sales and consumption [84–87]. In the US, food companies and restaurants spend approximately $14B annually in product promotion [88]. Over 80% of total marketing promotes foods and beverages that should be limited for optimal health [89–91] and few countries regulate food marketing to children and adolescents [92]. Children in racial and ethnic minority families have greater exposure to advertisements for energy-dense, nutrient-poor foods than children in majority families [93–95]. The frequent exposure to the marketing of unhealthy foods can undermine interventions to improve child nutrition and health.

Section 3: Proximal environmental components of nutrition ecology

Community food options

Where children live impacts their nutrition ecology and health. Families may live in food “deserts” (i.e., locations with lack of easy access to affordable or high-quality food) or food “swamps” (i.e., locations with excess access to high-calorie, low-nutrient, processed foods). Food deserts and food swamps, combined with poverty, have negative effects on children’s nutrition [96]. In high-income countries, including the US, lower-income, ethnic/racial minority, and rural neighborhoods are most often affected by poor access to supermarkets and healthful food and greater presence of fast-food restaurants and energy-dense foods [95]. In low- and middle-income countries, high SES neighborhoods and urban areas tend to have overall healthier dietary patterns – but also higher energy, cholesterol, and saturated fat intakes [97].

Designing community-level nutrition interventions requires a comprehensive understanding of how the community food environment impacts children’s and adolescents’ diets; recognizing the relative influences of socioeconomic, social, and built environment factors [22]; and how children and adolescents navigate this environment [98]. Community interventions have addressed these barriers by improving access to low-cost, high energy, and nutrient-dense foods; decreasing access to cheap, unhealthy foods; or leveraging local resources to promote healthy eating [99], with some improvements in children’s dietary behaviors [100, 101]. In response to the obesity epidemic, there has been a global increase in policies supporting healthy lifestyles through environmental change, such as taxes on sugar-sweetened beverages and limitations on unhealthy dietary ingredients, with some positive impacts on consumption [86, 102]. However, relatively few obesity prevention policies have been enacted into law [103], illustrating that policy makers have yet to fully address how the nutrition ecology relates to children’s and adolescents’ dietary choices.

Healthcare, social services, and food assistance

Access to comprehensive primary healthcare, social services, and food assistance programs can significantly influence children’s health and nutrition outcomes by potentially mitigating negative impacts of the distal environment factors and the social determinants of health at the family level [104–106]. For example, healthcare and social service programs can screen families and children for food insecurity and health, growth, and developmental problems and link them to specialized services and resources, such as food pantries and government food, economic, and housing assistance programs (e.g., US programs such as the Supplemental Nutrition Assistance Program (SNAP) [107], Temporary Assistance for Needy Families [108], and childcare assistance [109]).

However, the eligibility criteria and infrastructure to facilitate referrals across systems and to decrease administrative burdens for families can vary substantially across states and communities [105, 110, 111]. Some populations (e.g., immigrants) may be leery of government assistance. Additionally, the quality of available resources may vary based on government allocation of resources. For example, efforts have been made to increase access to nutrient dense foods and nutrition education in the US emergency food system (i.e., community-based food banks, and food pantries) [112, 113]. Understanding the extent to which families can access healthcare, social services, and food assistance, and the quality and functioning of these systems is important when interpreting results of child nutrition interventions.

School policies and food environments

Nutrition-related school policies and food environments can have a substantial impact on children’s and adolescents’ dietary intake and functional outcomes [114–119].

The World Food Program reports that globally approximately 50% of school children (388 million children), receive school meals daily in at least 161 countries [120]. The National Center for Educational Statistics reports that in 2024–2025, 91% of public schools in the US participated in the United States Department of Agriculture (USDA) meal programs [121]. A Cochrane systematic review of school feeding studies reported positive impacts on growth, educational outcomes (e.g., attendance), and cognitive development, with some variability across age groups and socioeconomic contexts [122]. Access to school meals should be considered when evaluating their impact; access is not universal in some countries (including the US). However, emerging evidence suggests that providing free universal school meals is not only cost-effective [123], but also reduces stigma, increases participation, and improves students’ diet quality, food security, and academic performance [124, 125].

School food environments.

Individual school, school district, regional, or national policies regulate and influence foods provided in schools [126]. In the US, school district wellness policies are federally mandated, but are developed, implemented, and evaluated locally [127]; variability in the policies enacted and enforced can influence the food environment and child and adolescent nutrition-related outcomes [118, 128]. Globally, 91% of 198 countries have policies, standards, or guidelines related to school nutrition [126]. Mandated meal pattern requirements, designed to ensure that nutritious foods (e.g., fruits and vegetables) are routinely offered, have demonstrated positive impacts on meal quality, student dietary intake, and weight status [128–130]. However, evaluation of the impact of mandated standards must account for the variability of implementation practices related to local cost and availability of policy-compliant foods, access to non-compliant foods, and cultural and social acceptability [131].

Nutrition education.

Nutrition education through schools for students, families, and the community may influence the impact of nutrition interventions, such as school meals, by encouraging healthy food choices and behaviors, while modifying social attitudes towards healthy options. However, competing academic priorities, lack of resources, and limited integration of nutrition education into school wellness policies or curriculum standards can affect the delivery of nutrition education [132, 133]. Successful nutrition education interventions for students involve parent engagement, trained facilitators, age-appropriate activities, and a duration of at least 6 months [132, 134, 135]. When evaluating school meals, the intensity, quality, and uptake of the nutrition education provided should be included, along with factors such as food quality, freshness, and time spent waiting in line to best understand education’s role in the observed outcomes.

Community care coordination.

Schools can serve as community hubs [136, 137], delivering education and resources to students’ families and the broader community, such as General Educational Development courses, mental health and parenting support, food assistance, and community health events. This model can broadly impact children’s well-being and health and education outcomes by enhancing trust and relationships between families, schools, and community service providers and building family resilience and support networks [137].

Section 4: Home and family

Families link the distal and proximal environmental components of the nutrition ecology with children’s and adolescents’ health, nutrition, dietary behavior, and food-related habits and attitudes. The family’s socioeconomic resources, the stability of the food system and neighborhood and school food environments, the availability and accessibility of nutrition education, food assistance, other health and social services, and parenting support all directly impact families. These factors influence the quantity and quality of food that families provide, and the consistency of their meal patterns [138].

Children learn values associated with their family’s beliefs, practices, and access to food, transmitted by modeling, routines, and practices associated with when, what, and how much to eat [139, 140]. Caregivers’ mental health and perceptions of their own health, body size, and behavior, along with those of their child or adolescent, and their ideal for them, influence the emotional food context of the home [141–144]. Caregivers’ expectations for consumption and the use of food-related discipline (i.e., using food as a reward or punishment) may also influence children’s dietary preferences and eating norms. Feeding styles (i.e., the emotional tone of caregiver interactions during eating) can influence children’s dietary intake and growth [145]. An authoritative feeding style represents reasonable demands in a sensitive caregiving context and is associated with optimal growth and eating behavior [146]. In contrast, authoritarian (i.e., controlling or forcing), indulgent or permissive (i.e., letting children eat when and what they choose), and uninvolved feeding styles are associated with lower dietary quality and often with higher child body mass index [147, 148]. These feeding styles can be embedded within cultures and may vary cross-culturally.

Children and adolescents benefit from parenting practices that include structure and promote autonomy in food choices and preparation [149]. Through family routines, children and adolescents learn to eat in response to hunger rather than emotions, promoting healthier eating behaviors. Encouraging children and adolescents to take on increasing responsibility for meal preparation, clean-up, food selection and purchase, and cooking for themselves and others are examples of how family food and meal organization can influence children’s eating habits and socio-emotional development [150].

Section 5: Functional outcomes in children and adolescents

Functional outcomes are influenced by complex interactions between nutrients and the nutrition ecology with manifestations that vary over childhood and adolescence. Disruptions in early developmental processes, including neurodevelopment, can impact multiple functional outcomes, including mental health, socio-emotional behavior, and cognition. For example, adolescents’ with iron deficiency in infancy have been shown to experience difficulties related to learning and behavior [151, 152]. Children’s and adolescents’ functional outcomes are inter-related, with ongoing bi-directional relationships with the nutrition ecology [153].

Growth and Health

Growth.

Dietary intake patterns with varying levels of nutrients and bioactive factors directly impact stature and somatic growth from an early age, modifying the physiological needs and dietary intake requirements as children grow. Linear growth or stature is recognized as a standard marker of healthy nutrition in young children. However, as children grow older, the rate of linear growth slows down, making it challenging to detect responses to interventions and environmental factors. Further, growth references for school-age children differ across countries, with no global growth standards [154, 155].

The lack of standardized indicators and the limited set of measures available for assessing growth outcomes in children older than 5 years pose constraints for evaluating the impact of the nutrition ecology on growth [156]. The indicators used to assess anthropometric status across age have been summarized [156], along with calls for more refined measures of growth in older children and adolescents [157–159].

Health.

Better nutrition is related to improved child health, a stronger immune system, lower risk of non-communicable diseases, such as diabetes and cardiovascular disease, and longevity. Globally, approximately 20% of children are overweight or obese [160]. The COVID-19 pandemic exacerbated this issue, causing dramatic lifestyle changes (e.g., increase high-energy food consumption, reduced physical activity) that promoted weight gain, especially for high-risk children [161, 162]. Excess weight is consequential; more than 60% of children and adolescents experiencing overweight have at least one cardiometabolic risk factor, such as increased blood pressure, hyperlipidemia, or hyperinsulinemia, and more than 20% have at least 2 risk factors [57, 58]. Overweight and obesity track over the life-course and increase the risk for adult obesity, with associated negative health consequences [163]. In addition to the global increases in overweight and obesity, undernutrition and nutritional deficiencies remain significant problems, especially in low- and middle-income countries and impair children’s growth, development, and long-term health, well-being, and productivity [6, 57].

Poverty and other environmental factors that result in poor diet quality can undermine children’s health through interactions with infection, affecting immunity and neurocognitive development [57, 164]. The complications arising from the interaction between nutrition and infection are accentuated by limited knowledge, poor hygiene, lack of clean water, poor housing, inadequate healthcare services, some cultural practices, and discriminatory social structures [165]. Overall, poor physical health can hinder children and adolescents in cognitive and socio-emotional activities, potentially impacting their mental health [153].

Mental health

Anxiety and depression are the most common mental health problems among children and adolescents [166] and may be associated with early neurodevelopmental processes [6]. Mental health problems often begin in adolescence, with nearly 1 in 5 adolescents globally experiencing symptoms [167]. Reviews of cross-sectional studies in both children and adults have found associations between unhealthy dietary patterns (especially UPF) and poor mental health [168, 169]. However, better understanding of the causal mechanisms, more longitudinal studies, less reliance on retrospective recall of food consumption, and attention to other methodological issues are needed to clarify the association between dietary patterns and mental health among children and adults [170].

Children and adolescents often have specific food preferences, occasional over- or under-eating, and concerns about body image. Eating patterns that become obsessive, harmful to personal health, or interfere with functioning may represent eating disorders that warrant psychiatric evaluation and intervention [171]. Common eating disorder diagnoses include anorexia nervosa, bulimia nervosa, binge-eating disorder, rumination disorder, and avoidant/restrictive food intake disorder.

Socio-emotional well-being

Neurodevelopment impacts multiple areas of children’s and adolescents’ functioning, including interpersonal relationships. To succeed in academics and social relationships, children need behavioral management skills, including attention, focus, perseverance, motivation, and responsivity [172]. The origins of socio-emotional development occur through interactions with family members, peers, and others. As children’s socio-emotional skills advance, they learn to recognize subtleties and interpretations of the behavior of others and evaluate the impacts of their own behavior [172].

Self-regulation, a component of socio-emotional development, refers to children’s ability to adapt to changing environments by gaining control over internal thoughts, feelings, and behavior [173]. Self-regulation develops during infancy and toddlerhood by adapting to household feeding and sleeping routines, forming the basis of self-regulation during childhood and adolescence. During the school-age years, self-regulation is reinforced by the nutrition ecology of the household, particularly family routines related to eating, sleeping, and other daily activities, and is tied to academic achievement, social competence, and social engagement. During adolescence, self-regulation expands to represent agency in the desire to establish goals, identity, and actions that represent independence not only for self, but for others. With greater responsibility for food and meals, adolescents’ nutrition ecology expands to include perceptions of cultural and social networks related to food and eating [172, 173].

Cognitive development

In situations of suboptimal nutrition, children’s learning capacity and working memory are constrained, limiting the ability to encode and store information in long-term memory for subsequent use. Such nutrition challenges can influence academic outcomes, executive function, and socio-emotional development throughout life [174].

Dietary factors can impact children’s learning and academic outcomes through multiple mechanisms [174]. Energy availability (i.e., glucose for brain functioning) can impact cognitive processes and learning. Nutrients, such as lutein, can affect executive function, language, learning and memory, and temporal processing [175]. Dietary patterns high in saturated fats, added sugars, and refined foods are associated with poor cognitive function, whereas dietary patterns high in fruits and vegetables are associated with positive cognitive function [176]. Although overall diet quality has been positively associated with cognitive performance and inhibitory control [174], investigations of diet quality in school-aged children and adolescents should account for physical activity and sleep, as they also contribute to learning and cognitive performance [176].

Physical activity

Physical activity, defined as any voluntary movement that expends energy, is aligned with nutritional requirements and can result in multiple health benefits for children and adolescents, including cardiorespiratory and muscular fitness, bone health, and improved weight status and mental health [177–179]. In contrast, high rates of sedentary behavior, particularly screen time, are negatively associated with health [180].

Both physical activity and nutrition positively impact children’s cognition and academic performance [181, 182]; however, their synergistic effects remain less explored. Attempts to define obesogenic cluster patterns of diet, physical activity, and sedentary behavior have only been modestly successful [183]. Sex differences in both the time and energy expenditure in physical activity have been consistently observed [184]. Although physical activity often declines in adolescence and in adulthood, physically active youth tend to continue to be physically active throughout life and many health benefits persist [179, 184].

Many factors influence children’s and adolescents’ engagement in physical activity, including climate, environmental opportunities, policies, and programs, and family and peer support and encouragement [185]. In 2020, the World Health Organization released updated global guidelines recommending at least 60 minutes of moderate-to-vigorous intensity daily physical activities for at least 3 days a week for children aged 5 to 17 years [186]. Including more physical activity programs into schools has multiple benefits, including improving on-task classroom behavior [187] and improving mental health among adolescents [177], without compromising school performance [188].

School attendance and performance

School attendance is often a positive outcome of school nutrition programs, as shown in a recent systematic evaluation of universal school meals in Organization for Economic Cooperation and Development countries [125]. Positive associations were also reported between universal school meals and diet quality, food security, and academic performance, and reduction in administrative costs and stigma, potentially mediated through increases in attendance [125].

Section 6: Case study

Text Box 1 presents a case study from Haiti as a demonstration of the application of nutrition ecology in a real-life situation [189, 190].

Text Box 1. Haiti School Feeding Program: a tale of 2 contexts.

• Two school feeding studies in north Haiti exemplify the importance of environmental considerations in the nutrition ecology of school-age children. Both studies, supported by the McGovern Dole US Department of Agriculture Micronutrient Fortified Food Aid Products program, tested the effect of the same school feeding snack, Vita Mamba, on child health [189, 190]. Environmental contexts, however, diverged in these 2 studies, yielding different outcomes for child health. The first study occurred in urban schools located in the densely populated city of Cap Haitien, while the second followed in rural villages of Terrier Rouge of North-East Department. Drawing from formative research, the Vita Mamba snack (50g, 260 kcal) was developed for school-aged children and comprised of peanut paste, milk powder, micronutrient fortificants, and a small quantity of sugar for palatability. When results from the urban trial showed only a minimal effect from Vita Mamba on the primary outcome of anemia, environmental factors from across the Nutrition Ecology Framework informed the design of the second study, ultimately yielding a greater positive effect on child health.

• Impact of the distal environment: External factors such as geopolitical conditions, climate, and policy heavily influences child nutrition in Haiti. Since its independence in 1804, the nation has had a history of authoritarian regimes and foreign occupation [191], leading to poor governance driven by limited resources and political factions and weakening education, health, and agricultural systems. The island nation is often isolated from regional and global trade agreements due to culture, language, and some degree of systemic bias. Land tenure policies that divide land plots for inheritance negatively impact agriculture productivity and soil health. While Haiti has evidence-based national nutrition policies linked to health communication strategies, limited public revenue often constrains implementation efforts. Climate events and disasters jeopardize food production and market viability and impede school access. These various distal environmental conditions over time have led to political unrest and entrenched poverty, heightening food insecurity nationally.

  Within the Nutrition Ecology Framework, food systems and community services differentially influence child nutrition. Haiti increasingly depends on food imports, often controlled by oligarchs and susceptible to global markets and food price volatility [192]. In the rural areas, subsistence agriculture with tubers, maize, and beans buffers the impacts of changing food prices but also limits diet diversity for school children. “Madan Sara”, a strong cadre of female entrepreneurs and primary food vendors in Haiti, predominantly sell fruits, vegetables, and animal source foods in urban areas, catering to middle- and upper-income households. Food safety is a pervasive concern in the food system, from post-harvest aflatoxin contamination to microbial pathogens from lack of cold storage and poor water, sanitation, and hygiene conditions. The health care system also has implications for nutrition in school-age children. “Rally posts” are temporary community-based units that offer well-child care services such as nutrition education, vaccines, and vitamin A supplements. While community health care workers (ajan sante) have been effective in nutrition behavior change, they are generally overworked and underpaid. Additionally, traditional medicine practices, including consultations with vodou priests (Haitian religious practice), are widely utilized in tandem with the formal healthcare system in Haiti [193].

• Impact of the proximal environment: From the inner ring of the Nutrition Ecology Framework, proximal factors more directly influenced the path to impact for Vita Mamba. The 8 school environments varied in terms of administration, teaching quality, and health and nutrition curriculum. Classrooms were generally crowded, and restrooms were available only in the urban schools, contributing to infectious disease risk. The study evaluated the built environment and physical activity by assessing recreation time, outdoor space area and density (m²/student), shade or green space, restrooms, water pumps, and electricity [194]. In the rural areas, children walked greater distances to school and had more space for play, while in the urban site, schools were located in highly congested areas with limited space. Gender played a role in physical activity as children aged, with girls becoming increasingly sedentary and boys maintaining physical activity. The food environment on school grounds was assessed, focusing on the presence of vendors and the availability of sugar-sweetened beverages, highly processed meats, fried foods, and salty and sweet snacks.

  Household level factors had implications for school-aged child nutrition across sites. Subsistence farming provided livelihoods for rural communities undergirding to some degree food security, while in urban areas, income from small businesses and construction jobs was more sporadic. Across both sites, livelihood hardships were greatest paradoxically when school tuition was due. Household wealth or assets varied (e.g., small livestock in rural areas, rotating saving clubs in urban areas) and was depleted when school tuition and uniforms were needed. Household water, sanitation, and hygiene and enteric infections were key drivers of nutrition in these studies. Acute diarrheal morbidities are highly prevalent in Cap Haitien, with evidence that environmental enteric dysfunction is negatively associated with linear growth [195]. Finally, dietary patterns across all school children showed low dietary diversity with rice or maize and beans serving as the primary staple foods. Fresh fruits and vegetables were limited in both environments, and animal source foods were largely absent in the diets of children from rural areas. Implementation science research recently explored the use of eggs for school feeding in Haiti, highlighting high acceptance and nutritional value, but revealing limitations in production and supply chains [196].

• Case study conclusions: Impact on child functional outcomes: The Haiti Vita Mamba case study highlights the importance of environmental factors in mitigating nutrition pathways to child health outcomes. Anemia was highly prevalent in both sites at baseline (74.5% urban; 52.3% rural). When deworming of all children was added to the follow-up trial in consideration of environmental conditions, there was a greater reduction in adjusted odds of anemia [189, 190]. Subsequent analyses showed factors across the Nutrition Ecology Framework mediated the effects of Vita Mamba [197]. This tale of 2 school feeding trials in 2 different contexts of Haiti illustrates a complex web of interacting environmental factors, from distal to proximal, ultimately driving the growth and development of the school-age child.

Section 7: Research gaps and future opportunities

Key research recommendations related to the distal and proximal environmental components of nutrition ecology and on determining functional outcomes in school-aged are summarized in Tables 1 and 2. Cross-cutting research recommendations related to the nutrition ecology include: 1) longitudinal designs to track how nutrition ecology affects the developmental aspects of functional outcomes in children and adolescents; 2) measures to track outcomes, accounting for age and developmental considerations; 3) examine how factors within the nutrition ecology moderate the relationship between nutrition interventions and functional outcomes in children and adolescents; 4) increase systematic understanding of the distal factors (i.e., climate change, geopolitical context, and food systems) that impact the nutrition ecology’s impact on children’s nutrition outcomes, including interactions with proximal systems (e.g., schools and health care); 5) greater probing and understanding the social determinants of health and interventions targeting SES; and 6) a systems approach to link the nutrition ecology with functional outcomes of children and adolescents to provide robust insights for policy development [198, 199].

Table 1.

Research gaps in changing the nutrition ecology to improve functional outcomes of school-aged children

Distal Environment			Proximal Environment
Climate	Geopolitical	Food Systems	Community	Services	Schools	Family
Develop models to predict when, where, and for which crops the nutritional quality could change under climate change scenarios.	Implement global surveillance systems to rapidly identify humanitarian crises [201].	Investigate interactions within food systems components to identify leverage points for improving nutrition.	Identify key economic and cultural barriers and enablers to healthy nutrition.	Evaluate methods to integrate nutrition effectively into health systems and assess the outcomes of improved integration.	Assess how schools affect children’s nutrition while at school, and spillover to households and the larger community.	Assess family dietary patterns, including the emotional context of eating that may vary by socioeconomic status, race ethnicity, locale, and culture.
Evaluate the health effects of diminished grain quality and identify populations most at risk.	Develop effective strategies to respond to humanitarian crises that mitigate nutrition impacts [62].	Determine methods to measure and assess the impacts of the ‘commercial determinants’ of health [202, 203].	Build partnerships with community food providers to determine strategies to improve nutrition options.	Evaluate the economic impact of SNAP on communities and its impact on nutrition security [106].	Address how to improve student participation in healthy school meals.	Explore mechanisms underlying the transmission of family values, attitudes, and behaviors, considering varying family characteristics.
Develop solutions to maintain plant nutritional quality [51].	Utilize network analyses to identify the partners and actions needed to mobilize responses to humanitarian crises	Identify modifiable features of the food system that strengthen or mitigate impacts of interventions on nutrition.	Co-create culturally relevant trauma-informed intervention outcomes with community partners.	Assess the impact of various elements of nutrition assistance programs, such as amount and timing of benefits.	Use precise measurements, such as plate waste, and objective measures of attendance and academic outcomes to assess school-based interventions.	Identify effective guidance to help families provide healthy nutrition while fostering self-regulatory behaviors in their children.
Identify effective modifications to nutrition intervention programs in the context of a changing climate.		Evaluate the impacts of natural experiments that leverage federal, state, and local policy changes to food or nutrition.			Document links between specific physical activity and nutrition policies and academic performance [204, 205] including potential mediation by attendance [206].	Evaluate effective feeding styles and food parenting strategies as school-age children become increasingly independent.
		Conduct mixed method research to identify and evaluate multi-level strategies to promote healthy eating and physical activity.

SNAP, Supplemental Nutrition Assistance Program.

Table 2.

Research gaps on determining functional outcomes in school-aged children related to the nutrition ecology

Growth and Physical Health	Mental Health	Socio-emotional Health	Cognitive Development	Physical Activity	School Attendance and Performance
Establish global growth standards for school-aged children ensuring consistent anthropometric indicators and thresholds across populations.	Conduct rigorous research studies on the impact of breakfast consumption and its quality on mental health, particularly among adolescents.	Identify intervention strategies to promote self-regulation among school-age children, enabling them to navigate the obesogenic environment without overeating or overly restricting food intake.	Examine the interrelationships between cognitive development and the nutrition ecology, and the develop age-appropriate assessments that can be standardized to understand cognitive development among school-age children [198].	Determine strategies to sustain physical activity levels as children transition into adolescence and adulthood, particularly for girls and youth with overweight or obesity.	Examine the micronutrient content of school meals, the impact on anemia and learning, particularly in countries where anemia is prevalent.
Develop a global growth monitoring system that enables target setting and a deeper understanding of contextual differences in nutrition.	Conduct trials, rather than retrospective evaluations, on dietary patterns among children with mental health symptoms.	Identify strategies to help caregivers establish dietary routines and patterns that promote child self-regulation.	Examine associations between nutrition and cognition globally, particularly where children experience nutritional deficiencies, such as anemia [199].	Identify characteristics of active play that support key aspects of cognitive functioning.	Gain a deeper understanding of the relationship between school nutrition programs and school attendance and academic performance.
Refine growth indicators to include markers of adiposity and bone health, and investigate their relationship with other outcomes.	Examine the role of the gut-brain axis and its connection to mental health outcomes.		Assess associations between health and cognitive development, with a focus on research beyond chronic diseases.	Assess how physical activity and dietary behaviors together influence cognitive and other outcomes.

Section 8: Summary and conclusions

The nutrition ecology is comprised of interacting, bi-directional distal and proximal components that impact child and adolescent health, development, and long-term potential. The associations between distal, macro-level aspects of nutrition ecology and children’s and adolescents’ functioning are mediated through the community and ultimately through the family. Failure to consider variability in the availability of, and access to protective resources, inequitable distribution of barriers and challenges across households, and the distal and proximal environments can result in the misinterpretation of findings from the evaluation of child nutrition interventions and impede progress toward health equity. Systems-based approaches to intervention planning, implementation, and evaluation are necessary to integrate and address the complexity of these multilevel and diverse drivers of nutrition ecology and are discussed in more detail by the fourth BOND paper [8, 200].

Scaling up evidence-based programs can provide significant opportunities to modify children’s and adolescents’ environmental factors to improve nutrition ecology and functional outcomes, with additional benefits for families, schools, communities, and economies. The future nutrition ecology for children and adolescents will depend on evidence-based policies implemented at all scales, requiring an all-of-society and health-in-all-policies approach, with wide-spread benefits for future societies.

Abbreviations:

BOND- KIDS

Biomarkers of Nutrition for Development: Knowledge Indicating Dietary Insufficiency

SES

socioeconomic status