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The global obesity epidemic has been on the rise for four decades, yet sustained prevention efforts have barely begun. An emerging science using quantitative models has provided key insights into the dynamics of this epidemic, and made it possible to combine different pieces of evidence and calculate the impact of behaviors, interventions and policies at multiple levels – from person to population. Forecasts indicate large effects of high levels of obesity on future population health and economic outcomes. Energy gap models have quantified the relationships of changes in energy intake and expenditure to weight change, and documented the dominant role of increasing intake on obesity prevalence. The empirical evidence base for effective interventions is limited but growing. Several cost-effective policies are identified that governments should prioritize for implementation.
Systems science provides a framework for organizing the complexity of forces driving the obesity epidemic and has important implications for policy-makers. Multiple players (including governments, international organizations, the private sector, and civil society) need to contribute complementary actions in a coordinated approach. Priority actions include policies to improve the food and built environments, cross-cutting actions (such as leadership, health-in-all policies, and monitoring), and much greater funding for prevention programs. Increased investment in population obesity monitoring would improve the accuracy of forecasts and evaluations. Embedding actions within existing systems in both health and non-health sectors (trade, agriculture, transport, urban planning, development) can greatly increase impact and sustainability. We call for a sustained worldwide effort to monitor, prevent and control obesity.
The obesity1–4 epidemic has grown worldwide, in countries both rich and poor, and among all segments of society. Action by government and other relevant institutions is clearly needed to halt the obesity problem, but what action is justified? In tobacco control, the adverse behavior is more readily identified, but even in this case major successes of the past have been linked to the application and implementation of a broad range of policies.5,6 Obesity control policy is in many ways more complex.
Obesity is caused by a chronic energy imbalance involving both dietary intake and physical activity patterns. While these behavioral patterns and their environmental determinants are complex, important drivers of the obesity epidemic have been identified.7 Evidence indicates that increases in energy intake are driving recent obesity increases.7–12 Key drivers include changes in the global food system that moved from individual to mass preparation, “lowered the time price of food consumption,”8 produced more highly processed food (adding sugar, fats, salt and flavour enhancers), and marketed them with increasingly effective techniques. Marketing foods and beverages is especially effective among children,13,14 is associated with obesity prevalence,15 and has been a focus of policy strategies.16
Other moderators amplify or attenuate the impact of these drivers and produce observed disparities in obesity prevalence across and within populations: these include national wealth, government policy, cultural norms, the built environment,7 genetic17 and epigenetic mechanisms,18 biological bases for food preferences19 and biological mechanisms that regulate motivation for locomotion and contribute to the decline in physical activity from childhood into adulthood.20
The changes needed to reverse the epidemic will likely require many interventions that span multiple levels and are sustained for many years. These include individual behavior change, setting change in schools, homes and workplaces, and sector change within agriculture, food services, education, transportation and urban planning.21 While there is overwhelming evidence on the need to reduce obesity, there is less clear consensus on effective policy or programmatic strategies. Most countries lack sufficient population monitoring data on physical activity, dietary intake and obesity prevalence for meaningful goal setting and assessment of progress.
These characteristics plus the contested nature of potential solutions can create a “policy cacophony,”22 making the task of obesity prevention appear hopelessly difficult.23 However, recent applications of quantitative modeling have helped develop an emerging new science base that provides key insights into the dynamics of this epidemic, and brings together different pieces of evidence and approaches.7,24–26 In this paper we review key insights from these quantitative models, including trends in obesity, health and economic outcomes, the dynamics of weight gain and loss, and cost-effectiveness of different interventions. We outline a strategy for the population prevention of obesity that builds on this growing science, and specifically links evidence for effectiveness and cost with implementation feasibility and other policymaker concerns. We outline a call to action utilizing a systems perspective with a focus on cost-effective and sustainable strategies.
Modelled trends from more than 200 countries (1980–2008) indicate steadily increasing obesity prevalence in every region of the world, including most low and middle income countries, with steepest increases in higher income countries.27 There are persistent socioeconomic and racial/ethnic disparities.21,28–31 Despite some evidence for a flattening of upward obesity trends in some high income nations,32 these countries are still at historically high levels.
Worldwide increases in obesity prevalence along with the excess mortality attributed to obesity 33 have led to forecasts of lowered future life expectancy.21,34,35 Studies have projected large increases in short and long term health care expenditures and other economic outcomes as a consequence of obesity. 21,26,36–39
One hopeful characteristic is that children are rarely born obese. Although there are developmental risks factors for later obesity,40,41 infant risks explain little of adult obesity, and early childhood obesity often changes.42 Hence policymakers begin each year with a new birth cohort and a low rate of obesity, and the opportunity to maintain this level in the future. Tempering this optimism, however, quantitative models find that, in the absence of other measures to control obesity, changing rates of early childhood obesity will, in the short run, have a relatively small influence on overall population prevalence.21,43 Hence, successful strategies to rapidly lower population obesity need to change risks among all age groups, employing a life course approach.44
Commentators worldwide have called for action at many levels to address the growing obesity epidemic7,21,45–47 But what action is justified? Recent studies have cited clear cost effective evidence for action to reduce noncommunicable disease (NCD)’s.48 The evidence base for obesity research has been growing, with the development of databases and reviews of studies, generally randomized controlled trials (RCTs) of preventive and treatment interventions. A 2005 Cochrane review indicated limited evidence for effective preventive interventions for children.49 More recently the Guide to Community Preventive Services reported that behavioral interventions to reduce screen time are effective in preventing obesity in children, and that some counseling interventions (e.g. with pedometers) and worksite programs are effective in preventing obesity in adults.50 For obese adults, Cochrane reviews indicate small effects for a low glycaemic load diet,51 exercise,52 or pharmacotherapy,53 and larger effects for bariatric surgery.54 For adults with prediabetes55 and obese children, small effects are observed for dietary and physical activity interventions.56 There is limited evidence for interventions in low and middle income countries.57,58
These and others reviews of interventions59–62 are limited in both what is studied as well as the criteria used to evaluate evidence. Rather than following the path of clinical decision-making where the evidence base is dominated by RCTs with high internal validity, there is value in considering different types of evidence, for example evaluating natural experiments and policy changes.63–65 The consideration of broader types of evidence was important in tobacco control. Evaluations indicated the clear effectiveness of cigarette taxes in reducing smoking, a policy change where RCT’s are not possible.5,6 The need for broader forms of evidence may be particularly important in low and middle income countries where efficacy studies may not be feasible: flexible methodologies are needed so large-scale interventions can be evaluated as they are implemented.58
Policymakers are increasingly asking not only whether an intervention works, but whether it offers value-for-money. Few obesity interventions or policy changes have been subjected to rigorous economic evaluation.66,67 Implementation issues are also critical for decision makers, including feasibility, sustainability and effects on equity.68 Policy-makers may need to weigh the relative benefits of effective interventions reaching a modest number of people with less effective interventions reaching wider populations. Including effectiveness, cost, and outcomes (e.g. Disability Adjusted Life Years (DALY)) as well as implementation issues demands a systems perspective and integrative models.6 The recent Strategic Plan for NIH Obesity Research recognizes the importance of comparative and cost effectiveness research, and highlights emerging methodologies that enable researchers to model the dynamic complexity of obesity and test effects of intervention strategies on individual and societal outcomes.69
As outlined in the second paper in this series, validated mathematical models have clarified the dynamic relationships of changes in dietary intake and physical activity to weight change. The energy gap framework provides a common metric (kj/day (kcal/day)) to use in describing these changes, and models indicate that the body weight response to a change of dietary energy intake is slow, with half-times of about one year.25 A small but chronic “Daily Energy Imbalance” gap has driven the continuing weight gain seen in most countries. Prevention of further excess weight gain can thus be accomplished with relatively small changes, on the order of 10’s of kcals/day.25 However, population weight has been accumulating in most countries for decades, 27 and higher weights require greater energy intake to maintain. Thus a much larger “Maintenance Energy Gap” needs to be overcome,25 which can be viewed as the energy needed to both stop gaining additional weight and that needed to lose a specified level of excess weight. For example, the Healthy People 2010 goal in the United States was to reduce excess weight levels to those found in 1970.70 With this goal, the “Maintenance Energy Gap” for an average adult in the US currently amounts to about 1 MJ/d (240 kcal/d). For adults with a BMI of 35 or more (currently 14% of adults71), more than double this change is required.25
Thus it is important for countries to focus on prevention, as it becomes increasingly more difficult to reverse obesity trends as excess weight accumulates. Children are a particularly important focus for action because they have accumulated little excess weight, and thus small changes are an effective strategy.72 Large energy balance changes also require a longer time to accomplish if sequential smaller changes are involved. Since political timetables often demand quick results, support may be difficult to generate if interventions take years to show effect. The energy gap framework can also assist by quantifying the impact of different preventive actions: e.g. calculations indicate a typical 9-year-old boy weighing 30 kg burns an extra 630 kj (150 kcal) by replacing 1.9 hours of sitting with 1.9 hours of walking; this is equivalent to replacing one can of sugar sweetened beverage with water.72
The Australian Assessing Cost-Effectiveness (ACE) in Obesity73 and ACE Prevention studies74 are examples of integrative modeling strategies that bring together a broad range of evidence for informing resource allocation decisions. Details of intervention selection, modeling of intervention implementation, costing of intervention and associated cost-offsets, and the simulation models used are published elsewhere.75,76 These studies evaluated preventive and treatment interventions for obesity: 11 among children and youth and 9 among adults. Interventions were modeled using local data and consistent methodology to facilitate cost-effectiveness ranking.73 Interventions were reviewed by a stakeholder group to assess strength of evidence, effects on equity, acceptability to stakeholders, feasibility of implementation, affordability and sustainability, each which can impact policy decisions.73,74
The results – expressed as a cost per DALY averted – are presented in Table 1. Strength of evidence for effectiveness is ranked from 1 to 5, following the classification used in ACE74 and building on other research.68,77–80 Levels 1 and 2 indicate evidence is sufficient for decision making, and is generally based on interventions including RCTs and robust evaluations of policies. Those rated 3 or 4 do not provide such clear evidence, and 5 indicates inadequate or inconclusive evidence. Studies assumed a decision threshold of AUD 50,000 (US 49,500) per DALY prevented to determine whether an intervention was cost-effective or not, reflecting empirical evidence on what constitutes acceptable value-for money in Australia.81, 82 Use of standardized methods enhances comparability of results, although lower strength of evidence for many interventions limits the generalizability of findings, and costs can vary.
Eight of the twenty interventions were found to be both health improving and cost saving (“dominant”). Three were very cost-effective in that they improved health at a cost of less than AUD10, 000 per DALY prevented; three improved health at a cost of between AUD10,000-AUD50,000 per DALY prevented. The first 11 interventions in Table 1 (8 dominant and 3 highly cost-effective) should only be ignored if decision-makers have serious reservations about the evidence base, or are faced with insurmountable problems in relation to other considerations such as their implementation feasibility, equity impacts or acceptability to stakeholders.
The top three cost-saving interventions are environmental. They show modest effects at an individual level but prove highly cost-effective, because benefits accrue to the entire population and cost of implementation is relatively low.77 However, these interventions differ in terms of the sufficiency of evidence related to their effectiveness and differences in the additional filters. For example, while reduction of TV advertising of unhealthy food and beverages to children was found to be one of the most cost-effective interventions, regulation of advertising has not been on the political agenda of the Australian government, making implementation highly unlikely.83 The evidence around front-of-pack traffic light nutrition labeling was considered insufficient to warrant policymaker support at this time in Australia, despite plausible assumptions.84
An overriding conclusion of the ACE evaluations is that policy approaches generally show greater cost-effectiveness than health promotion or clinical interventions. This conclusion is borne out by other studies. For example, regulatory and fiscal interventions (e.g. regulation of food advertising to children) were the least expensive measures among those examined by OECD. They argued that fiscal measures were the only interventions likely to pay for themselves, i.e. they were likely to generate larger savings in health expenditure than costs of delivery.85
Translating ACE findings into practice in a particular country may require modifications. For example, an “unhealthy food and beverage tax (10%)” has not been a strong focus in the United States, but an excise tax on sugar sweetened beverages (SSB) has received much discussion. The evidence base for an SSB intervention in reducing excess caloric intake and weight is reasonably strong,86 intake is high,87,88 and a tax can raise billions of dollars ($US) per year for cash starved states.89 Different tax structures mean countries are more or less amenable to such changes.
Regulations to limit marketing of unhealthy foods and beverages to children vary widely across countries, with some more and others less restrictive than Australia. The US has a high level of television advertising (18 minutes per hour), but freedom of speech issues limit regulatory options. Nevertheless, limiting the corporate tax deductibility of advertising costs for unhealthy foods may be a politically feasible option.90
Some community based program interventions were found to be cost-effective in both ACE and OECD studies, but effects often depend on sustained public funding. Many programs are confined to specific target populations, limiting the beneficiaries. For example, some clinical interventions offer large benefits to individuals, but apply to relatively small populations.
Similar modeling exercises have been used by others. As policy makers wrestle with limited budgets, the ability to demonstrate cost-effectiveness is in great demand. Foresight21 conducted analyses useful to the cross government strategy Healthy Weight Healthy Lives in England. OECD models of multiple interventions have informed government planning in high85,91 and low and middle income countries.92 The National Institute for Health and Clinical Excellence (NICE) has published cost effectiveness studies of health care interventions93,94 as has the Dutch Centre for Public Health and the Environment.95
Thus, there are cost-effective interventions that can lower obesity prevalence and improve long term health and economic outcomes. However, even the most effective interventions will not be sufficient individually to reverse the obesity epidemic. Solutions need to be multi-faceted, with initiatives at different levels of government and across multiple sectors. Interventions that may be quite modest in terms of their impact when assessed in isolation may still constitute important components of an overall strategy. An additional challenge for low and middle income countries is the continuing dual-burden of both undernutrition and obesity.58
The most cost effective interventions evaluated to date largely fall within the realm of fiscal and regulatory actions. It appears that analogous strategies that worked to restrict tobacco may prove useful to reduce obesity.5,6
A recent Institute of Medicine (IOM) Panel on evidence and obesity decision-making outlined the need for consideration of a broad range of evidence and for utilizing a systems perspective.64 New thinking, new tools and the use of computational modelling methods are needed to facilitate a better understanding of the interconnectedness and synergies of the whole system, as well as of its individual components or sub-systems. What are the implications of a systems approach for decision-makers and policy development around obesity prevention? The IOM report borrowed from the Foresight strategic framework 21 to articulate major implications for policy-making.64 These are shown in Panel 2 with examples and an additional call for linking with other major societal challenges.
United Nations (UN) Member States will gather in New York in September 2011 for the first High-Level Meeting of the UN General Assembly focused on non-communicable diseases (NCDs). The global obesity epidemic, which has been described as a ‘wicked problem’ because of its inherent complex and intractable nature,96 will be the toughest challenge facing Member States since none has turned their obesity epidemic around. The UN meeting is in response to the overwhelming need for action on NCDs as a barrier to development in low and middle income countries. Obesity prevention is a major part of that effort. Important questions include: what actions are needed and what can be implemented?
WHO’s Global Strategy on Diet, Physical Activity and Health47 provides a framework for action on both child and adult obesity prevention that is linked to other WHO strategies such as prevention of NCDs.97 The Global Strategy framework has a long list of policy areas for action because it encompasses multiple levels of jurisdiction across a wide range of policies for health services, health promotion programs, and improved environments related to food, physical activity and the socio-economic determinants of health.98,99 A number of authoritative reports have developed priority actions needed for key actors at the global and national levels.47,100–105 There is strong consistency across these recommendations, although many are necessarily broad to accommodate different contexts.
Recommendations for obesity prevention tend to fall into two broad categories of actions: ‘direct’ actions to impact energy balance, and more indirect ‘structural’ actions which support direct action. Direct actions have logic pathways from intervention to energy balance. Recent research has documented cost-effectiveness for many potential direct actions (e.g. Table 1 and 85, 91–95). A systems approach, however, reminds us of the critical importance of ‘structural’ or cross-cutting interventions which provide support for direct action but for which cost-effectiveness evidence is often not available (e.g. what is the cost-effectiveness of an obesity monitoring system?) Just as a house needs plumbing and electricity structures to work, so an obesity prevention plan needs structural actions in place for direct actions to work. This is an especially important message for low and middle income countries which need to boost structures supporting workforce skills, knowledge creation and exchange for public health in general. Most countries still lack even basic data, with only one third of European Union countries having nationally representative data on children’s weight and height.106 Even fewer countries have set targets for rates of obesity or for changes in determinants such as dietary intake and physical activity. Political leadership for action on obesity is also low in many countries with the First Lady Obama in the United States showing the value of high level attention to the issue.107 In the following sections, we discuss progress and contributions of each of the main actors.
Governments are the most important actors in reversing the obesity epidemic, because protection and promotion of public goods, including public health, is a core responsibility. They operate at local, state, and national levels as well as being major stakeholders as Member States in most international agencies such as the UN. While the consequences of obesity mainly burden the health system, ministries outside health, such as finance, education, agriculture, transportation and urban planning arguably have the greatest influence in creating environments conducive to obesity prevention.
While many governments have developed guidelines and strategic plans to improve dietary and physical activity patterns, translating these plans into action has been disappointing. Almost all food policies recommended as priority actions, including regulations to restrict food and beverage marketing to children, front-of-pack traffic light labelling, and sugar-sweetened beverage taxes, have been heavily contested by the food industry making implementation politically difficult. A number of these direct actions are now well supported by cost-effectiveness evidence. Less contested areas of action, such as school and community actions, social marketing and promoting physical activity, find greater political favour even though the costs may be substantial and the benefits uncertain. For example, the single major investment in obesity prevention by the recent Howard Government in Australia was AUD214 million for an active after-school program108 which was not even recommended by the government’s own National Obesity Taskforce.109
Many international agencies affect food and public health, and national governments are usually the major stakeholders and funders of these bodies. The United Nations (UN) has several core agencies directly involved in health and development including the World Health Organisation (WHO), Food and Agriculture Organisation (FAO), UN Children’s Fund (UNICEF), UN Development Programme (UNDP) and the World Food Programme, as well as inter-agency bodies such as the Standing Committee on Nutrition and Codex Alimentarius Commission. All have critical roles to play in international leadership, standard setting, and creating collective agreements of national governments. Despite 60% of the global mortality coming from NCDs and 80% of the premature NCD mortality being from low and middle income countries,110 12% of the WHO budget is allocated to NCDs.111
Also powerful are the political, economic and trade related multi-national bodies including the World Trade Organisation (WTO), the World Bank, International Monetary Fund (IMF), European Union (EU) and the informal groups: G8, G20 and G70. While the primary concerns of these groups are not public health, their actions can have profound effects on public health, including obesity and chronic disease, and public health can have a profound effect on the economy of nations.
Key actions needed are in Panel 4. The UN High Level Meeting in September 2011 will be an important opportunity for Member States to demonstrate the international leadership needed for a global effort to reduce obesity and NCDs. The litmus test beyond that meeting will be how well Member States match their declarations with supportive funding and policies to support global actions. The UN Standing Committee on Nutrition is the coordinating body for food and nutrition activities across UN agencies, but in 2010 almost closed due to lack of funding. This coordination role is vital and needs support.
The private sector includes industries involved in foods and beverages and their representative organisations, the media, and industries responsible for the built environment. They shape food and activity environments we live in and, through communications and marketing, also shape people’s perceptions, desires and accepted norms. Their active support is needed to reduce obesogenic environments. The food and beverage industries, in particular, have taken steps in recent years as individual companies and through representative organizations to respond to the obesity epidemic.112 While they have been criticized for their part in creating obesogenic food environments, they clearly have the collective power to make those same environments less obesogenic. Whether various actions and pledges by food and beverage industries can reduce obesity is uncertain, and rigorous independent evaluation is needed. The most powerful activities by the private sector relevant to the formulation of public policy is undoubtedly lobbying activities. These often undermine policies aimed at reducing obesity, e.g. in relation to regulations on marketing to children, traffic light labelling, and taxes on unhealthy foods.
Civil society organizations include public interest and consumer associations, charitable organizations, academic institutions, foundations, professional associations, and other community, religious, and advocacy groups. While they have limited funding and hold less power than other actors, they fill important advocacy and ‘watchdog’ roles. They tend to be in the forefront of calling for healthy, sustainable and fair environments, although in some non-democratic countries their freedom to speak out for change is significantly curtailed. In general, advocacy activity in low and middle income countries is limited and global non governmental organizations (NGO)s can play an important supporting role.
The final choices for eating and physical activity behaviours rest with individuals although available choices to them may already have been ‘edited’ depending on the settings. Parents and caregiverss have particular responsibilities and greatest opportunities to promote life-long healthy behaviours among children and adolescents. All individuals can influence their own home environment as well as other settings in which they interact on a regular basis such as schools, workplaces, sports clubs, churches and community organisations (Panel 4).
This Series of papers in the Lancet documents the growth of an emerging science of obesity prevention and control. The obesity epidemics in countries throughout the world are driven by a complex of forces that require systems thinking to conceptualize the drivers of the problem and to organize evidence needed for action. Applications of quantitative modeling have made it possible both to plan for and to evaluate the impact of actions to prevent and control obesity. These include energy gap models of individual and population weight gain and loss, forecasts of long term economic and health outcomes, and cost effectiveness analyses of programs and policies. A rapid scaling up of efforts is needed. The UN High Level Meeting on NCDs in September 2011 provides a key opportunity to strengthen international leadership from the UN and its agencies, as well as to galvanize other agencies and states to begin to seriously address the continuing global epidemic of obesity.
Underpinning ‘structural’ actions create stronger prevention systems to support specific ‘direct’ actions to reduce obesity.
We thank William Dietz and Angie Cradock for comments and suggestions
Funding. This work was done under auspices of the Collaborative Obesity Modeling Network (COMNet) as part of the Envision Project, supported by the National Collaborative on Childhood Obesity Research (NCCOR), which coordinates childhood obesity research across the National Institutes of Health (NIH), Centers for Disease Control and Prevention (CDC), Department of Agriculture, and the Robert Wood Johnson Foundation (RWJF). This work was supported in part by grants from RWJF (#260639 and #61468 and #66284), CDC (U48/DP00064-00S1 and 1U48DP001946), including the Nutrition and Obesity Policy, Research and Evaluation Network, and the Office of Behavioral and Social Sciences Research of NIH. This work is solely the responsibility of the authors and does not represent official views of the Centers for Disease Control and Prevention or any of the other funders.
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Author contributionsAll authors jointly formulated the major concepts, and read and approved the final version of the manuscript. SG provided overall leadership on development and drafted the paper. MM and RC drafted the section on ACE cost effectiveness and reviewed paper drafts. BS and MM drafted the systems thinking and call to action section and reviewed drafts. DL, DF, PM, TH and TM provided comments on successive drafts of the manuscript.
Conflict of interest statement: We declare that we have no conflict of interest.