The Transport for London’s unhealthy food advertising policy is estimated to have contributed to a 1,000 calorie decrease in energy from unhealthy food in consumers’ weekly shopping.
Restricting the outdoor advertising of unhealthy foods such as high fat, salt and sugar (HFSS) products across the Transport of London (TFL) network is estimated to have significantly decreased the average of calories purchased by households every week from these products.
The research, carried out by the London School of Hygiene & Tropical Medicine (LSHTM), used data on nearly two million grocery purchases of unhealthy food items that classify as HFSS 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 bus stops.
The findings are published in PLOS Medicine.
Restricting advertisements of unhealthy food
The researchers found that the policy was associated with an estimated 1,001 kcal (6.7%) decrease in average weekly household purchases of energy from HFSS unhealthy food products compared to what would have happened without the policy. Most surprisingly, the average weekly purchases of energy from chocolate and confectionary fell by 317.9 kcal (19.4%).
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: fat (57.9 g; 6.5%), saturated fat (26.4 g; 7.3%) and sugar (80.7g; 10.5%).
The team found some limited indication that effects were larger in households with individuals living with obesity.
Dr Amy Yau, from LSHTM and the study’s 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.”
Policies that restrict the advertising of HFSS unhealthy food products have been promoted as potentially effective tools to reduce the purchase and consumption of HFSS products, to improve diet, reduce obesity and diet-related diseases and tackle health inequalities.
Understanding the association
The team of researchers wanted to uncover whether the advertisement restriction on unhealthy foods could contribute to improvements in diet. Due to the absence of dietary data, the team utilised data from household food and drink purchases collected by Kantar, a commercial consumer data company, to evaluate the impact of the intervention.
The study ran from 18 June 2018 to 29 December 2019 and compared average weekly purchases of HFSS unhealthy food products in 977 London households to an estimate of what would have happened without the policy. The estimate was based on the trend in purchasing in London before the policy and changes seen in households in a control (North of England) after the policy was implemented, which accounts for secular trends and seasonal variation in HFSS purchasing.
Assuming an average household size of 2.6 people in the sample and 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.
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 9 PM advertising watershed on HFSS foods or a 20% 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.”
The team say that while the results are encouraging, the finding is in the context of actual increases in purchases of HFSS unhealthy food products in intervention and control areas over the study period, meaning intervention was effective in reducing the growth of HFSS purchases rather than achieving absolute reductions in HFSS purchases.
Professor Cummins said: “More work is needed, but our study suggests these types of policies could have a significant impact on reducing consumption of high fat, salt and sugar foods, and offer a potentially effective intervention in other important public health policy areas such as the regulation of alcohol and gambling advertising.”