Elsevier

The Lancet

Volume 378, Issue 9793, 27 August–2 September 2011, Pages 838-847
The Lancet

Series
Changing the future of obesity: science, policy, and action

https://doi.org/10.1016/S0140-6736(11)60815-5Get rights and content

Summary

The global obesity epidemic has been escalating for four decades, yet sustained prevention efforts have barely begun. An emerging science that uses quantitative models has provided key insights into the dynamics of this epidemic, and enabled researchers to combine evidence and to calculate the effect of behaviours, interventions, and policies at several levels—from individual to population. Forecasts suggest that high rates of obesity will affect future population health and economics. Energy gap models have quantified the association of changes in energy intake and expenditure with weight change, and have documented the effect of higher intake on obesity prevalence. Empirical evidence that shows interventions are effective is limited but expanding. We identify several cost-effective policies that governments should prioritise for implementation. Systems science provides a framework for organising the complexity of forces driving the obesity epidemic and has important implications for policy makers. Many parties (such as governments, international organisations, 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, healthy public policies, and monitoring), and much greater funding for prevention programmes. Increased investment in population obesity monitoring would improve the accuracy of forecasts and evaluations. The integration of actions within existing systems into both health and non-health sectors (trade, agriculture, transport, urban planning, and development) can greatly increase the influence and sustainability of policies. We call for a sustained worldwide effort to monitor, prevent, and control obesity.

Introduction

The prevalence of obesity—defined as a body-mass index of more than 30 kg/m2 in adults1 and according to standards for children specific to age and gender2, 3, 4—has been increasing worldwide over the past 30 years in both rich and poor countries, and in all segments of society.5 Clearly, action by governments and other relevant institutions is needed to halt the obesity epidemic, but what measures are justified? Although the associated adverse behaviour is more readily identified than for obesity, the major successes of tobacco control have been linked to the application and implementation of a broad range of policies.6, 7 Obesity control policy is in many ways more complex.

Key messages

  • Childhood and adult obesity is increasing in countries of high, middle and low income. A growing body of evidence links obesity to short-term and long-term health, social, and economic consequences.

  • Empirical evidence of how to prevent obesity is limited but growing. The evidence base needs to be broadened beyond randomised controlled trials to include evaluation of natural experiments, policy changes, and costs.

  • Mathematical modelling provides important insights into the causes and dynamics of weight gain and loss. The energy gap framework provides a common metric for translating changes in dietary intake and physical activity into weight change.

  • Comparative effectiveness and cost-effectiveness policy and programme analyses indicate that several are both effective and cost saving.

  • The application of a systems approach to obesity prevention is novel but already has policy implications including: the need for multiple actions especially in non-health sectors, investments in cross-cutting support systems, policies that target the food and built environments, and additional data for forecasts and evaluation.

  • Governments need to lead obesity prevention, but so far few have shown leadership. The food industry has been very active through various pledges, self-regulatory codes, and product reformulation, although the effect of these changes should be independently assessed.

  • The UN High-Level Meeting on non-communicable diseases in September, 2011 is an important opportunity for the international community to provide the leadership, global standards, and cross-agency structures needed to create a global food system that offers a healthy and a secure food supply for all.

Obesity is caused by a chronic energy imbalance involving both dietary intake and physical activity patterns. Although the behavioural patterns and their environmental determinants are complex, important causes of the obesity epidemic have been identified.8 Evidence shows that increased energy intake is causing the rise in obesity,8, 9, 10, 11, 12, 13 which is a result of changes in the global food system: the movement from individual to mass preparation “lowered the time price of food consumption”,9 and produced more highly processed food (with added sugar, fats, salt, and flavour enhancers), and marketed them with increasingly effective techniques. Additionally, marketing of food and beverages is associated with increasing obesity rates14 and is especially effective among children,15, 16 and therefore is a focus of policy strategies.17 Other factors amplify or attenuate the effect of these causes and produce observed disparities in obesity prevalence across and within populations. National wealth, government policy, cultural norms, the built environment,8 genetic18 and epigenetic mechanisms,19 biological bases for food preferences,20 and biological mechanisms that regulate motivation for physical activity21 all influence growth of the epidemic.

The changes needed to reverse the epidemic are likely to require many sustained interventions at several levels. Necessary alterations include: individual behaviour change; interventions in schools, homes, and workplaces; and sector change within agriculture, food services, education, transportation, and urban planning.22 Despite the overwhelming evidence showing the need to reduce obesity, no clear consensus on effective policy or programmatic strategies has been reached. Most countries do not have sufficient population monitoring data on physical activity, dietary intake, and obesity prevalence to set meaningful goals and assess progress.

The number of suggested interventions, plus the contested nature of potential solutions, can create a “policy cacophony”,23 which makes the task of obesity prevention appear hopelessly difficult.24 However, applications of quantitative modelling have helped to develop a new science base that provides insights into the dynamics of this epidemic, and brings together different evidence and approaches.8, 25, 26, 27 In this report, we review key findings from these models, including trends in obesity, health, and economic outcomes, the dynamics of weight gain and loss, and the cost-effectiveness of interventions. We outline a strategy for the prevention of obesity that builds on this growing science and specifically links evidence for effectiveness and cost with implementation feasibility and other concerns of policy makers. Finally, we present a call to action from a systems perspective, with a focus on cost-effective and sustainable strategies.

Section snippets

Modelled trends and forecasts

Data from more than 200 countries between 1980 and 2008 suggest steadily increasing obesity prevalence in every region of the world, including in most countries of low and middle incomes, with the steepest rises in higher-income countries.5 There are persistent socioeconomic and racial or ethnic disparities.22, 28, 29, 30, 31 Despite some evidence for a deceleration of increasing obesity numbers in some high-income countries,32 they still have historically high rates of obesity.

Worldwide rises

Evidence of effective interventions

Commentators worldwide have called for action at many levels to address the growing obesity epidemic,8, 22, 45, 46, 47 but what action is justified? Clear evidence supporting cost-effective actions to reduce non-communicable diseases is available.48 The evidence base for obesity research has been growing with the development of databases and reviews, generally of randomised controlled trials of preventive and treatment interventions. A 2005 Cochrane review reported some degree of evidence for

Dynamics of weight gain and loss and energy gap analyses

As outlined in the third paper in this Series,26 validated mathematical models have clarified the dynamic relations of changes in dietary intake and physical activity to weight change: the energy gap framework provides a common metric—kJ/day (kcal/day)—to describe these changes. Models suggest that the body-weight response to a change of energy balance is slow, with half-times of about a year.26 A small but chronic daily energy imbalance gap has caused the continuing weight gain seen in most

Cost-effectiveness of obesity interventions

Policy makers are increasingly asking not only whether an intervention works, but also whether it offers value for money. The Australian Assessing Cost-Effectiveness (ACE) in Obesity73 and ACE–Prevention studies74 are examples of integrative modelling strategies that assimilate a broad range of evidence to help with resource-allocation decisions. Details of intervention selection, the modelling of intervention implementation, costing of intervention and associated cost-offsets, and the

Translation of cost-effectiveness results to other settings

The translation of ACE findings into practice in other countries might require modifications. A tax of 10% on so-called unhealthy food and beverages has not been a strong focus in the USA, but an excise tax on sugar-sweetened beverages has received much discussion.90 The evidence base for an intervention on sugar-sweetened beverages reducing excess caloric intake and weight is reasonably strong,91 intake is high,92, 93 and a tax can raise billions of US dollars per year for cash-starved states.

A systems approach to obesity prevention

Even the most effective interventions will not be sufficient to reverse the obesity epidemic individually. Solutions need to be multifaceted, with initiatives throughout governments and across several sectors. Interventions that might have quite small effects when assessed in isolation may still constitute important components of an overall strategy. An additional challenge for countries of low and middle income is the continuing dual burden of both undernutrition and obesity.58

A recent

Call to action

UN Member States will gather in New York, USA, in September, 2011 for the first High-Level Meeting of the UN General Assembly focused on non-communicable diseases. The global obesity epidemic, described as a “wicked problem” because of its complex and intractable nature,99 will be a challenge for Member States because none of them have adequately dealt with the obesity epidemic. The meeting is in response to the overwhelming need for action: non-communicable diseases are a barrier to

Governments

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. The repercussions of obesity mainly burden the health system, but ministries outside health, such as finance, education, agriculture, transportation and urban planning,

Conclusion

This Series in The Lancet documents the emerging science of obesity prevention and control. The obesity epidemics in countries throughout the world are driven by complex forces that require systems thinking to conceptualise the causes and to organise evidence needed for action. Applications of quantitative modelling have made possible both planning for and evaluation of the effect of actions to prevent and control obesity. These models include energy gap models of individual and population

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