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