Systematic Review of Natural Experiments for Childhood Obesity Prevention and Control

Adult obesity treatment and prevention: A trans-agency commentary on the research landscape, gaps, and future opportunities

Given the high and growing prevalence of obesity among adults in the United States, obesity treatment and prevention are important topics in biomedical and public health research. Although researchers recognize the significance of this problem, much remains unknown about safe and effective prevention and treatment of obesity in adults. In response to the worsening obesity epidemic and the many unknowns regarding the disease, a group of key scientific and program staff members of the National Institutes of Health (NIH) and other federal and non-government agencies gathered virtually in September 2021 to discuss the current state of obesity research, research gaps, and opportunities for future research in adult obesity prevention and treatment. The current article synthesizes presentations given by attendees and shares their organizations' current initiatives and identified gaps and opportunities. By integrating the information discussed in the meeting and current initiatives, we identify potential targets and overlapping priorities for future research, including health equity and disparities in obesity, the heterogeneity of obesity, and the use of technological and innovative approaches in interventions.

Effects of policies or interventions that influence the school food environment on children's health and nonhealth outcomes: a systematic review

CONTEXT

Globally, 1 in 3 children under 5 years is undernourished or overweight, and 1 in 2 suffers from hidden hunger due to nutrient deficiencies. As children spend a considerable time at school, school-based policies that aim to improve children's dietary intake may help address this double burden of malnutrition.

OBJECTIVE

This systematic review aimed to assess the effects of implementing policies or interventions that influence the school food environment on children's health and nonhealth outcomes.

DATA SOURCES, EXTRACTION, AND ANALYSIS

Eleven databases were searched up to April 2020 and the World Health Organization (WHO) released a call for data due in June 2020. Records were screened against the eligibility criteria, and data extraction and risk-of-bias assessment were conducted by 1 reviewer and checked by another. The synthesis was based on effect direction, and certainty of evidence was assessed using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach.

CONCLUSIONS

Seventy-four studies reporting 10 different comparisons were included. The body of evidence indicates that interventions addressing the school food environment may have modest beneficial effects on certain key outcomes. Nutrition standards for healthy foods and beverages at schools, interventions that change how food is presented and positioned, and fruit and vegetable provision may have a beneficial effect on the consumption of healthy foods and beverages. Regarding effects on the consumption of discretionary foods and beverages, nutrition standards may have beneficial effects. Nutrition standards for foods and beverages, changes to portion size served, and the implementation of multiple nudging strategies may have beneficial effects on energy intake. Regarding effects of purchasing or selecting healthier foods, changes to how food is presented and positioned may be beneficial. This review was commissioned and supported by the WHO (registration 2020/1001698-0). WHO reviewed and approved the protocol for the systematic review and reviewed the initial report of the completed systematic review.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no: CRD42020186265.

Heterogeneity in place effects on health: The case of time preferences and adolescent obesity

We leverage a natural experiment in combination with data on adolescents' time preferences to assess whether there is heterogeneity in place effects on adolescent obesity. We exploit the plausibly exogenous assignment of military servicemembers, and consequently their children, to different installations to identify place effects. Adolescents' time preferences are measured by a validated survey scale. Using the obesity rate in the assigned installation county as a summary measure of its obesity-related environments, we show that exposure to counties with higher obesity rates increases the likelihood of obesity among less patient adolescents but not among their more patient counterparts.

Our Healthy Community Conceptual Framework and Intervention Model for Health Promotion and Disease Prevention in Municipalities

This paper introduces the conceptual framework and intervention model of Our Healthy Community (OHC), a new, coordinated, and integrated approach towards health promotion and disease prevention in municipalities. The model is inspired by systems-based approaches and employs a supersetting approach for engaging stakeholders across sectors in the development and implementation of interventions to increase health and well-being among citizens. The conceptual model includes a combination of a bottom-up approach emphasizing involvement of citizens and other community-based stakeholders combined with a top-down approach emphasizing political, legal, administrative, and technical support from a variety of councils and departments in local municipality government. The model operates bidirectionally: (1) by pushing political and administrative processes to promote the establishment of conducive structural environments for making healthy choices, and (2) by involving citizens and professional stakeholders at all levels in co-creating processes of shaping their own community and municipality. An operational intervention model was further developed by the OHC project while working with the OHC in two Danish municipalities. The operational intervention model of OHC comprises three main phases and key actions to be implemented at the levels of local government and community: (1) Local government: Situational analysis, dialogue, and political priorities; (2) Community: Thematic co-creation among professional stakeholders; and (3) Target area: Intervention development and implementation. The OHC model will provide municipalities with new tools to improve the citizens' health and well-being with available resources. Health promotion and disease prevention interventions are developed, implemented, and anchored in the local community by citizens and local stakeholders at municipal and local community levels using collaboration and partnerships as leverage points.

Impact of environmental interventions based on social programs on physical activity levels: A systematic review

Background

The design of social programs at the environmental level such as in schools, parks, bicycle paths, or workspaces generates changes in the behavior of individuals and modifies lifestyles by increasing physical activity (PA) levels.

Objective

To determine the effectiveness of environmental interventions based on social programs by changing the population's level of PA.

Methodology

Natural experiment studies that involved environmental intervention programs at a social level were included. The primary outcome was PA levels with consideration of both objective and subjective measurements. An electronic search was carried out in Medline/Pubmed, SCIENCE DIRECT, WEB OF SCIENCE, and CINAHL databases up to January 2022 with two reviewers screening titles and abstracts and selecting studies for full-text reading. Two reviewers also acquired relevant data and evaluated study quality using the ROBINS I tool. A qualitative analysis was performed.

Results

Three thousand eight hundred and sixty-five articles were found in the 4 consulted databases. After eliminating duplication (200), two reviewers screened 3,665 titles and abstracts and excluded 3,566 that did not meet the inclusion criteria, leaving 99 articles to be read in full text. The 99 full texts were reviewed of which 24 papers met the eligibility criteria. All were natural experiments published between 2011 and 2020 and all evaluated environmental social programs revealing that social programs at the environmental level promoted PA in various populations at the community level worldwide.

Conclusion

The 24 reviewed studies suggest innovative proposals for social programs that seek to increase PA and promote healthy lifestyles related to public activity policies developed in the countries in which they were generated. Environmental social programs can positively impact PA levels among children and adults.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=229718, identifier: CRD42021229718.

Policies to prevent zoonotic spillover: protocol for a systematic scoping review of evaluative evidence

INTRODUCTION

The increasing incidence of pathogen transmission from animals to humans (zoonotic spillover events) has been attributed to behavioural practices and ecological and socioeconomic change. As these events sometimes involve pathogens with epidemic or pandemic potential, they pose a serious threat to population health. Public policies may play a key role in preventing these events. The aim of this review is to identify evaluations of public policies that target the determinants of zoonotic spillover, examining approaches taken to evaluation, choice of outcomes measures and evidence of effectiveness. Our approach to identifying and analysing this literature will be informed by a One Health lens, acknowledging the interconnectedness of human, animal and environmental health.

METHODS AND ANALYSIS

A systematic scoping review methodology will be used. To identify articles, we will search Medline, SCOPUS, Web of Science and Global Health in May 2021 using search terms combining animal health and the animal-human interface, public policy, prevention and zoonoses. We will screen titles and abstracts and extract data according to published guidelines for scoping reviews. All evaluations of public policies aiming to prevent zoonotic spillover events will be eligible for inclusion. We will summarise key data from each study, mapping policies along the spillover pathway and outlining the range of policies, approaches to evaluation and outcome measures. Review findings will provide a useful reference for researchers and practitioners, outlining the state of the evaluative evidence around policies to prevent zoonotic spillover.

ETHICS AND DISSEMINATION

Formal ethical approval is not required, because the study does not involve primary data collection. The findings of this study will be disseminated through a peer-reviewed publication, presentations and summaries for key stakeholders.

Does an active play standard change childcare physical activity and healthy eating policies? A natural policy experiment

Background

In 2017, the provincial government of British Columbia (BC) implemented a mandatory policy outlining Active Play Standards (AP Standards) to increase physical activity (PA) levels, sedentary and motor skills among children attending licensed childcare centers. Concurrently, a capacity-building initiative was launched to help implement policies and practices supporting both PA and healthy eating (HE) in the early years. This study evaluated differences in center-level PA and HE policies and practices before and after the enforcement of the new provincial AP Standards.

Methods

Using a repeat cross-sectional design, surveys were distributed to managers and staff of licensed childcare facilities serving children aged 2–5 years before (2016–2017 or ‘time 1’) and after (2018–2019 or ‘time 2’) implementation of the AP Standards across BC. The total sample included 1,459 respondents (910 and 549 respondents at time 1 and time 2, respectively). Hierarchical mixed effects models were used to examine differences in 9 and 7 PA/sedentary policies and practices, respectively, as well as 11 HE policies between time 1 and time 2. Models controlled for childcare size and area-level population size, education, and income.

Results

Compared to centers surveyed at time 1, centers at time 2 were more likely to report written policies related to: fundamental movement skills, total amount of Active Play (AP) time, staff-led AP, unfacilitated play/free play, total amount of outdoor AP time, limiting screen time, breaking up prolonged sitting, staff role modeling of PA, and training staff about PA (P < 0.01 for all 9 policies examined). Compared to time 1, centers at time 2 reported more frequent practices related to ensuring children engaged in at least 120 min of AP, 60 min of outdoor AP daily, and limiting screen time (P < 0.01 for 3 out of 7 practices examined). Despite no additional policy intervention related to HE, centers were more likely to report having written policies related to: HE education for children, encouraging new foods, having family-style meals, offering only milk or water, limiting the amount of juice served, staff role modeling of HE, limiting the types of foods at parties/celebrations and foods brought from home (P < 0.05 for 9 out of 11 HE policies).

Conclusion

Approximately a year after the implementation of a governmental policy targeting PA supported by a capacity-building initiative, childcare centers reported positive changes in all 9 PA/sedentary policies examined, all 3 out of 7 PA/sedentary practices and 9 out of 11 HE policies evaluated at the center-level.

A rapid review of the evidence for children’s TV and online advertisement restrictions to fight obesity

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The relationship between obesity and exposure to food advertising meets all criteria commonly used to demonstrate the presence of a causal relationship in epidemiology.

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Younger children (≤8 years of age) are more susceptible to the impacts of food marketing, in terms of quantity and quality of calories consumed, than older children and adults, although emerging evidence suggests that adolescents (10–19 years) may be most susceptible to the impacts of online advertisements.

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Children from socio-economically disadvantaged and ethnic minority backgrounds are disproportionately exposed to unhealthy food advertisements.

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Statutory regulation is a potentially cost-effective policy option, in terms of healthcare savings outweighing the costs of implementing the policy. However, advertising restrictions must be accompanied by community-based interventions that address other causes of poor diet and sedentary behaviour; this is because online and TV advertisements represent one small dimension in the wider obesogenic environment.

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Voluntary bans are ineffective. Exposure to unhealthy food advertising is similar before and after the introduction of voluntary food advertisements.

The World Health Organisation has urged all governments to address rising rates of obesity by implementing population-based interventions, such as restrictions on the marketing to children of unhealthy food and beverage items. However, the relationship between unhealthy food advertisements and childhood obesity is disputed by industry-sponsored reports, which recommend promoting physical activity and weight loss campaigns rather than policies to limit exposure to advertisements. We aimed to elucidate this debate by providing a narrative review of the evidence on the relationship between unhealthy TV and online food advertisements, short-term food consumption and childhood obesity. We also examined the impact of unhealthy food advertisements on vulnerable groups and identified which policy interventions are supported by current evidence.

We conducted a rapid overview of reviews published since 2006. From a synthesis of 18 reviews meeting the inclusion criteria, we conclude that exposure to unhealthy TV and online food advertising is a contributing factor to childhood obesity. Evidence of a relationship between exposure to unhealthy food advertisements and childhood obesity was evident at all stages of the causal pathway, including a clear dose-response relationship. The evidence base was particularly strong for children aged 3–12 years of age and for children from socio-economically disadvantaged and minority ethnic backgrounds.

The introduction of statutory regulation is a potentially cost-effective policy option, in terms of healthcare savings outweighing the costs of implementing the policy, although voluntary codes were shown to be ineffective, with exposure to unhealthy food advertisements similar in countries before and after their introduction. Food advertising, however, is just one factor in the wider obesogenic environment and further advertising restrictions must be implemented alongside population-based interventions that aim to address systemic causes of poor diet.

Ripple effects mapping: capturing the wider impacts of systems change efforts in public health

BACKGROUND

Systems approaches are currently being advocated and implemented to address complex challenges in Public Health. These approaches work by bringing multi-sectoral stakeholders together to develop a collective understanding of the system, and then to identify places where they can leverage change across the system. Systems approaches are unpredictable, where cause-and-effect cannot always be disentangled, and unintended consequences - positive and negative - frequently arise. Evaluating such approaches is difficult and new methods are warranted.

METHODS

Ripple Effects Mapping (REM) is a qualitative method which can capture the wider impacts, and adaptive nature, of a systems approach. Using a case study example from the evaluation of a physical activity-orientated systems approach in Gloucestershire, we: a) introduce the adapted REM method; b) describe how REM was applied in the example; c) explain how REM outputs were analysed; d) provide examples of how REM outputs were used; and e) describe the strengths, limitations, and future uses of REM based on our reflections.

RESULTS

Ripple Effects Mapping is a participatory method that requires the active input of programme stakeholders in data gathering workshops. It produces visual outputs (i.e., maps) of the programme activities and impacts, which are mapped along a timeline to understand the temporal dimension of systems change efforts. The REM outputs from our example were created over several iterations, with data collected every 3-4 months, to build a picture of activities and impacts that have continued or ceased. Workshops took place both in person and online. An inductive content analysis was undertaken to describe and quantify the patterns within the REM outputs. Detailed guidance related to the preparation, delivery, and analysis of REM are included in this paper.

CONCLUSION

REM may help to advance our understanding and evaluation of complex systems approaches, especially within the field of Public Health. We therefore invite other researchers, practitioners and policymakers to use REM and continuously evolve the method to enhance its application and practical utility.

A nationwide school fruit and vegetable policy and childhood and adolescent overweight: A quasi-natural experimental study

BACKGROUND

School free fruit and vegetable (FFV) policies are used to promote healthy dietary habits and tackle obesity; however, our understanding of their effects on weight outcomes is limited. We assess the effect of a nationwide FFV policy on childhood and adolescent weight status and explore heterogeneity by sex and socioeconomic position.

METHODS AND FINDINGS

This study used a quasi-natural experimental design. Between 2007 and 2014, Norwegian combined schools (grades 1-10, age 6 to 16 years) were obligated to provide FFVs while elementary schools (grades 1-7) were not. We used 4 nationwide studies (n = 11,215 children) from the Norwegian Growth Cohort with longitudinal or cross-sectional anthropometric data up to age 8.5 and 13 years to capture variation in FFV exposure. Outcomes were body mass index standard deviation score (BMISDS), overweight and obesity (OW/OB), waist circumference (WC), and weight to height ratio (WtHR) at age 8.5 years, and BMISDS and OW/OB at age 13 years. Analyses included longitudinal models of the pre- and post-exposure trajectories to estimate the policy effect. The participation rate in each cohort was >80%, and in most analyses <4% were excluded due to missing data. Estimates were adjusted for region, population density, and parental education. In pooled models additionally adjusted for pre-exposure BMISDS, there was little evidence of any benefit or unintended consequence from 1-2.5 years of exposure to the FFV policy on BMISDS, OW/OB, WC, or WtHR in either sex. For example, boys exposed to the FFV policy had a 0.05 higher BMISDS (95% CI: -0.04, 0.14), a 1.20-fold higher odds of OW/OB (95% CI: 0.86, 1.66) and a 0.3 cm bigger WC (95% CI: -0.3, 0.8); while exposed girls had a 0.04 higher BMISDS (95% CI: -0.04, 0.13), a 1.03 fold higher odds of OW/OB (95% CI: 0.75, 1.39), and a 0-cm difference in WC (95% CI: -0.6, 0.6). There was evidence of heterogeneity in the policy effect estimates at 8.5 years across cohorts and socioeconomic position; however, these results were inconsistent with other comparisons. Analysis at age 13 years, after 4 years of policy exposure, also showed little evidence of an effect on BMISDS or OW/OB. The main limitations of this study are the potential for residual confounding and exposure misclassification, despite efforts to minimize their impact on conclusions.

CONCLUSIONS

In this study we observed little evidence that the Norwegian nationwide FFV policy had any notable beneficial effect or unintended consequence on weight status among Norwegian children and adolescents.

Preventing Childhood Obesity in Primary Schools: A Realist Review from UK Perspective

Childhood obesity is a global public health concern. While evidence from a recent comprehensive Cochrane review indicates school-based interventions can prevent obesity, we still do not know how or for whom these work best. We aimed to identify the contextual and mechanistic factors associated with obesity prevention interventions implementable in primary schools. A realist synthesis following the Realist And Meta-narrative Evidence Syntheses-Evolving Standards (RAMESES) guidance was with eligible studies from the 2019 Cochrane review on interventions in primary schools. The initial programme theory was developed through expert consensus and stakeholder input and refined with data from included studies to produce a final programme theory including all of the context-mechanism-outcome configurations. We included 24 studies (71 documents) in our synthesis. We found that baseline standardised body mass index (BMIz) affects intervention mechanisms variably as a contextual factor. Girls, older children and those with higher parental education consistently benefitted more from school-based interventions. The key mechanisms associated with beneficial effect were sufficient intervention dose, environmental modification and the intervention components working together as a whole. Education alone was not associated with favourable outcomes. Future interventions should go beyond education and incorporate a sufficient dose to trigger change in BMIz. Contextual factors deserve consideration when commissioning interventions to avoid widening health inequalities.

Effects of programs and interventions related to the social environment on childhood and adolescent obesity: A systematic search for and scoping review of natural experiments

Given the potential importance of social environment on obesity and to better understand their causal relationship amongst children and adolescents, this scoping review systematically searches for and evaluates programs and interventions using natural experiment designs. A majority of the studies assessing peer and social norm effects reported significant findings. Peer effects with nontrivial effect sizes likely have practical implications for interventions, while a strong conclusion cannot be drawn for social norm and neighborhood safety effects. Leveraging naturally occurring data might provide future research with a promising way of establishing a more robust causal inference for the topic of interest.

Nutritional Strategies for Childhood Obesity Prevention

BACKGROUND

Reducing the spread of obesity represents a challenge for clinicians in which obesity prevention plays a key role in achieving this purpose. The aim of this review is to analyze the nutritional interventions that can be implemented to prevent childhood obesity.

METHODS

Searching PubMed and Cochrane Library between 2019 and 2021. Further searching with no date range for articles selected for their specific relevance in the pediatric area or for their scientific relevance. A total of 871 articles were identified and 90 were included.

RESULTS

We organized the results of the selected articles into age groups, and according to the subjects targeted for interventions or to the site of interventions, reserving an in-depth analysis on specific nutritional aspects. Promotion of breastfeeding, reduction of protein content of formulated milks, and diet of the first 12-24 months, involving family and schools in interventions that promote physical activity and healthy diet, are promising strategies for reduction of the risk of obesity. To increase the efficacy of interventions, a multidimensional approach is crucial.

CONCLUSIONS

A multidimensional approach, which takes into consideration different areas of intervention, is pivotal for childhood obesity prevention. Integrated programs involving several components (nutrition and physical activity at first) at different levels (individual, family, school, and institutional) are crucial.

A secondary analysis of the childhood obesity prevention Cochrane Review through a wider determinants of health lens: implications for research funders, researchers, policymakers and practitioners

BACKGROUND

Randomised controlled trials (RCTs) are often regarded as the gold standard of evidence, and subsequently go on to inform policymaking. Cochrane Reviews synthesise this type of evidence to create recommendations for practice, policy, and future research. Here, we critically appraise the RCTs included in the childhood obesity prevention Cochrane Review to understand the focus of these interventions when examined through a wider determinants of health (WDoH) lens.

METHODS

We conducted a secondary analysis of the interventions included in the Cochrane Review on "Interventions for Preventing Obesity in Children", published since 1993. All 153 RCTs were independently coded by two authors against the WDoH model using an adaptive framework synthesis approach. We used aspects of the Action Mapping Tool from Public Health England to facilitate our coding and to visualise our findings against the 226 perceived causes of obesity.

RESULTS

The proportion of interventions which targeted downstream (e.g. individual and family behaviours) as opposed to upstream (e.g. infrastructure, environmental, policy) determinants has not changed over time (from 1993 to 2015), with most intervention efforts (57.9%) aiming to change individual lifestyle factors via education-based approaches. Almost half of the interventions (45%) targeted two or more levels of the WDoH. Where interventions targeted some of the wider determinants, this was often achieved via upskilling teachers to deliver educational content to children. No notable difference in design or implementation was observed between interventions targeting children of varying ages (0-5 years, 6-12 years, 13-18 years).

CONCLUSIONS

This study highlights that interventions, evaluated via RCTs, have persisted to focus on downstream, individualistic determinants of obesity over the last 25 years, despite the step change in our understanding of its complex aetiology. We hope that the findings from our analysis will challenge research funders, researchers, policymakers and practitioners to reflect upon, and critique, the evidence-based paradigm in which we operate, and call for a shift in focus of new evidence which better accounts for the complexity of obesity.

The association between sugar-sweetened beverage availability in school vending machines and school staff sugar-sweetened beverage consumption

Reducing sugar-sweetened beverage (SSB) consumption is a leading strategy to help combat high rates of adult obesity and overweight. Regulating SSB sales in schools has reduced access among youth. However, current federal school nutrition standards are focused on student rather than staff environments (i.e. school staff lounges). This study examines the association between the availability of SSBs in school vending machines and school staff SSB consumption.

The study sample included 51 public schools in California, Oregon, Washington, Maryland, and Washington DC participating in an evaluation of Kaiser Permanente’s Thriving Schools initiative in school year 2017–18. Data collection included: 1) observations of school cafeterias, staff lounges, stores and outdoor snack areas for the presence of, and content in, vending machines, and 2) an online survey of school staff about their SSB consumption.

Fifty-nine percent (n = 1586) of staff responded to the survey; 1229 (77% of respondents) reported on SSB consumption. Thirty percent of schools had staff lounges with SSB vending machines and 34% of staff reported drinking ≥1 SSBs/day. On average, the probability of consuming ≥1 SSBs/day was 6.6% greater in staff in schools with SSBs available in staff lounge vending machines (95% CI: 0.11%, 13.12%).

Staff in schools with SSB vending machines in staff lounges were more likely to report consuming ≥1 SSBs per day compared to staff without SSB vending in staff lounges. Examining the impact of extending SSB regulations to the entire school environment on school staff SSB consumption is an important next step.

Methods and Risks of Bias in Natural Experiments in Obesity: Opportunities for the Future Informed by a Systematic Review

OBJECTIVE

This paper promotes rigorous methods and designs currently underutilized in obesity research, informed by a recent systematic review of the methods and risks of bias in studies of policies, programs, and built environment changes for obesity prevention and control.

METHODS

To determine the current state of the field, relevant databases from 2000 to 2017 were searched to identify studies that fit the inclusion criteria. Study design, analytic approach, and other details of study methods were abstracted. These findings inform recommendations for obesity researchers and the field as a whole.

RESULTS

Previously identified were 156 natural experiment studies. Most were cross-sectional (35%), pre-post single group comparison (31%), or difference-in-differences designs (29%). Few used rigorous causal designs such as interrupted time series with more than two time points, propensity score methods, or instrumental variables. The potential relevance for obesity research is discussed, and recommendations for obesity researchers are provided.

CONCLUSIONS

To strengthen natural experiment study designs and enhance the validity of results, researchers should carefully consider and control for confounding and selection of comparison groups and consider study designs that address these biases.

Socioeconomic Inequalities in the Retail Food Environment around Schools in a Southern European Context

Across Europe, excess body weight rates are particularly high among children and adolescents living in Southern European contexts. In Spain, current food policies appeal to voluntary self-regulation of the food industry and parents’ responsibility. However, there is no research (within Spain) assessing the food environment surrounding schools. We examined the association between neighborhood-level socioeconomic status (NSES) and the spatial access to an unhealthy food environment around schools using both counts and distance measures, across the city of Madrid. We conducted a cross-sectional study citywide (n = 2443 census tracts). In 2017, we identified all schools (n = 1321) and all food retailers offering unhealthy food and beverages surrounding them (n = 6530) using publicly available data. We examined both the counts of retailers (within 400 m) and the distance (in meters) from the schools to the closest retailer. We used multilevel regressions to model the association of neighborhood-level socioeconomic status (NSES) with both measures, adjusting both models for population density. Almost all schools (95%) were surrounded by unhealthy retailers within 400 m (median = 17 retailers; interquartile range = 8–34). After adjusting for population density, NSES remained inversely associated with unhealthy food availability. Schools located in low-NSES areas (two lowest quintiles) showed, on average, 29% (IRR (Incidence Rate Ratio) = 1.29; 95% CI (Confidence Interval) = 1.12, 1.50) and 62% (IRR = 1.62; 95% CI = 1.35, 1.95) more counts of unhealthy retailers compared with schools in middle-NSES areas (ref.). Schools in high-NSES areas were farther from unhealthy food sources than those schools located in middle-NSES areas (β = 0.35; 95% CI = 0.14, 0.47). Regulating the school food environment (within and beyond school boundaries) may be a promising direction to prevent and reduce childhood obesity.