A new study involving University of Liverpool researchers, published in PLOS Medicine, shows the restriction of outdoor advertising of high fat, salt and sugar (HFSS) foods and drinks across the Transport for London (TfL) network significantly decreased the average amount of calories purchased by households every week from these products.
Led by the London School of Hygiene & Tropical Medicine (LSHTM) in collaboration with the Universities of Liverpool, Cambridge, Bristol, Hertfordshire and Fuse, the Centre for Translational Research in Public Health, the study used data on nearly two-million grocery purchases of HFSS foods and drinks to estimate the effect of the policy, which saw restrictions on advertising across the TfL estate. This includes the London Underground, the TfL Rail network, and at bus stops.
Background
Policies that restrict the advertising of HFSS products have been promoted as potentially effective tools to reduce the purchase and consumption of HFSS products, with the aim of improving diet, reducing obesity and diet-related diseases and tackling health inequalities.
In November 2018, restrictions on the outdoor advertising of HFSS foods and drinks across the Transport for London (TfL) network were announced by the Mayor of London and were fully implemented on 25 February 2019.
In order to find out if this policy could contribute to improvements in diet the research team used household food and drink purchase data collected by Kantar, a commercial consumer data company, to evaluate the impact of the intervention.
Study
The study ran from 18 June 2018 to 29 December 2019, and compared average weekly purchases of HFSS products in 977 London households to an estimate of what would have happened without the policy. This estimate was based on the trend in purchasing in London before the policy and changes seen in households in a control area (North of England) after the policy was implemented, which accounts for secular trends and seasonal variation in HFSS purchasing.
After controlling for key factors including sex, age, socioeconomic position, number of adults and children in the household, and festivals such as Christmas, they estimated the changes in household purchases of energy and nutrients from HFSS products associated with the TfL advertising policy.
Assuming an average household size of 2.6 people in the sample, and an even energy distribution, the team estimated that the intervention reduced energy purchases by 385 calories per person per week – equivalent to every Londoner in the study purchasing about 1.5 fewer standard size bars of milk chocolate per week.
Findings
The researchers found that the policy was associated with an estimated 6.7 per cent decrease in average weekly household purchases of HFSS products compared with what would have happened without the policy.
Average weekly household purchases of fat, saturated fat and sugar from HFSS products were similarly lower in intervention households in London compared to expected levels in households not exposed to the intervention.
Dr Amy Yau, from LSHTM and study first author, said: "Many governments and local authorities are considering advertising restrictions to reduce consumption of high fat, salt and sugar (HFSS) products as part of obesity prevention strategies. However, evidence of the effectiveness of such policies, especially away from broadcast media, is scarce.
"Our study helps to plug that knowledge gap, showing Transport for London's policy is a potential destination for decision-makers aiming to reduce diet-related disease more widely."
Professor Steven Cummins, from LSHTM and Chief Investigator of the study, said: "The impacts we observed are larger than those reported for the UK Soft Drinks Industry Levy, those predicted for a 9PM advertising watershed on HFSS foods or a 20 per cent tax on sugary snacks.
"The findings are particularly significant in light of the Health Bill currently going through Parliament, as they provide further evidence for the effectiveness of advertising restrictions and help support the case for the Government's proposed ban on the online advertising of high fat, salt and sugar foods and drinks."
'Effective restrictions'
Dr Emma Boyland, one of the co-authors of the study is a Professor in Food Marketing and Child Health at the University of Liverpool and advises the World Health Organization on food marketing policy in the European region and beyond: "Studies conducted here at the University of Liverpool have shown that exposure to advertising for unhealthy foods and drinks can alter alters food preferences in favour of unhealthy choices and leads to greater food intake. It is reassuring to see that these types of policies can result in reduced consumption of HFSS products by making a simple change to the current advertising environment.
"Supporting more effective restrictions around food advertising is not about pandering to a nanny state agenda, far from it, rather it is acknowledging that what we think of currently as free choice is in fact anything but. Our every food-related decision is influenced by a myriad of factors beyond our control - the availability, accessibility, affordability, marketing and promotion of processed items all seeking to grab our attention and be the one we purchase to the detriment of competitor brands' bottom lines. Take away the advertising and manipulation, and we can begin to tip the balance in favour of being able to make our own minds up about what we eat and drink."
'Ground-breaking measures'
The Mayor of London, Sadiq Khan, said: "It is a scandal that London has such high levels of child obesity and, that in a city as prosperous as ours, where you live and the amount you earn can have such a huge bearing on whether you have access to healthy and nutritious food.
"There is no denying that advertising plays an enormous role in putting less healthy food and drink in the spotlight, and I am pleased to see the positive impact these ground-breaking measures have had, leading to a real reduction in the amount of junk food being purchased."
The authors acknowledge limitations of the study, including that it was focused on products to take home (grocery purchase) and did not include takeaway purchases from fast-food outlets, restaurants, cafes etc. Effects may well be larger if takeaway purchases had been included.
The research was an independent evaluation funded by NIHR School for Public Health Research.
The full paper, entitled 'Changes in household food and drink purchases following restrictions on the advertisement of high fat, salt, and sugar products across the Transport for London network: A controlled interrupted time series analysis', can be found here.
