Growing evidence of the links between overweight and severity of covid-19 outcomes has added even greater urgency to the imperative to act on the large and increasing epidemic of obesity. 
Since the Government Office for Science Foresight report on “Tackling Obesities” was published in 2007 there has been no excuse for failing to appreciate the nature or magnitude of the challenge we face: “People in the UK today don’t have less willpower and are not more gluttonous than previous generations. Nor is their biology significantly different to that of their forefathers. Society, however, has radically altered over the past five decades, with major changes in work patterns, transport, food production and food sales.” 
Obesity is a problem driven by our circumstances, by obesogenic environments with ever-increasing barriers to physical activity and healthy eating. The most disadvantaged people face the greatest obstacles, and inequalities in the numbers of people living with obesity have widened over the years since the Foresight report drew attention to the obesogenic environment. However, despite this we remain assailed by the rhetoric of “choice” and “lifestyle”, and campaigns exhorting us to change our behaviour as if obesity were a knowledge deficit disorder. It is not. 
Many drivers of behaviour are out of people’s control, ranging from cheap junk food on every high street to a lack of safe walking or cycling routes. But policy responses to obesity are skewed towards interventions that rely on personal agency to act on information or advice, despite the low effectiveness of such policies and their propensity to widen inequalities.  There are many reasons for this skew, including an evidence base driven by research systems that prioritise studies on short term outcomes of individual level interventions, and public discourse that promulgates a stigmatising and erroneous construction of obesity as a “failure” of willpower. 
Foresight showed clearly that “the causes of obesity are embedded in an extremely complex biological system, set within an equally complex societal framework.”  But despite lip service to notions of “complexity” and “whole systems,” policy responses remain constrained by narrow, linear models of cause and effect, failing adequately to consider interactions, synergies, or unintended consequences.
Discourse around obesity is all too often split into false dichotomies such as diet/activity, treatment/prevention, or adults/children, but as a complex systems problem it requires action across the piece, taking account of interactions, time scales, multiple levers at multiple levels, feedback, adaptations, and more. That’s not straightforward, but it’s not impossible either, and we’ve had well over a decade since Foresight to work on it.
Both Public Health England and the Department for Health and Social Care have generated strong proposals for tackling obesity in the population in recent years. Some of them—such as the sugar drinks industry levy—have seen the light of day, but many remain in consultation limbo. As Sally Davies’ made clear in her parting report as Chief Medical Officer, much stronger and more extensive action is required. 
This is the space into which the government’s latest obesity strategy has been launched.  Many of the proposals are reliant on personal agency for their effects, such as a new information campaign and plans to increase referrals to weight management services. But there are also policies aimed at addressing the obesogenic environment, including a ban on advertising unhealthy food on TV and online before 9pm, and ending price promotions of these products in supermarkets. The proposals are welcome, if long overdue, but they remain inadequate to meet the government’s own target of halving childhood obesity by 2030, let alone narrowing the stark and growing inequalities in prevalence. 
While we understand the drivers of obesity across food, transport, economic, political, and health systems, all too often we ignore the causes of the causes, such as entrenched inequalities, across as well as within generations; persistent failure to internalise the health and environmental externalities of the food, car and other industries; and those same industries relentlessly pushing a focus on personal responsibility while abrogating their own. 
This isn’t only about junk food: think how different our eating habits might be if we’d dealt with the scourge of plastic waste properly from the start, instead of being persuaded by the people selling litter that it was unavoidable, and our job to pick it up.  Or how easy it could be to walk and cycle if we rejected the fiction that we only need to switch fuel from petrol or diesel to electricity for our cars to be “green” and got properly to grips with creating healthy, safe, equitable habitations with clean air and truly sustainable mobility.
As Public Health England say in their recent report “Drivers of excess calorie intakes and low levels of physical activity, within the environments people live, will need to change at a national and local level to support population-level weight change.”  The time for relying on nudges and campaigns is long since past. Policy now needs robustly to tackle the root causes of obesity, and the social factors that underpin those causes. 
Obesity is an unintended consequence of the ways in which our societies have been set up, the commercial activities that have been prioritised, the vested interests that exert power, and the ways in which these structural drivers have become embedded. Changing all that will take time, but the longer we postpone meaningful action the harder it becomes, and the more deeply the inequalities become entrenched. We urgently need robust action across the life course, and across all aspects of society and the obesogenic environment. The latest policy announcements make a number of significant advances, but we should not delude ourselves that they represent a remotely adequate response.
Harry Rutter, Professor of Global Public Health, University of Bath
Louise Marshall, Senior Public Health Fellow, The Health Foundation
Adam Briggs, Senior Policy Fellow, The Health Foundation; Associate Clinical Professor, University of Warwick
Declaration of Interests: ADMB reports grants from National Institute for Health Research Applied Research Collaboration West Midlands. HR and LM have no conflicts of interest to declare.
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