A new PHI|Lab study published in PLOS Medicine found that the Transport for London restrictions on advertising of high fat, salt and sugar products was associated with a 1001 calorie reduction in weekly household energy purchased compared to the expected level.

Restrictions on the advertisement of products with a high fat, salt and sugar (HFSS) content are being considered by many local and national governments as part of obesity prevention strategies. However, there is limited evidence of their effectiveness, with only a few studies that have evaluated the impact of restricting advertisements on exposure to HFSS advertising and HFSS purchasing or consumption, most of which have been focused on television advertising.

In February 2019, the Mayor of London introduced restrictions on advertisement of HFSS products across the Transport for London (TfL) network, one of the largest transport networks in the world and an advertising estate that is worth £152.1 million. Products were no longer allowed to be directly advertised, or inadvertently mentioned, if they were considered HFSS by the UK’s Nutrient Profiling Model. This policy removed HFSS advertising across ~40% of London’s outdoor advertising space, and therefore, had great potential to reduce Londoners’ exposure to HFSS advertising, providing an excellent opportunity to evaluate a natural experiment.

Using household food and drink purchase data, we aimed to examine changes in household food and drink purchases associated with the introduction of the TfL advertising policy. This study was led by PHI|Lab members Amy Yau, Nicolas Berger, Cherry Law, Laura Cornelsen and Steven Cummins alongside Robert Greener, Vanessa Er and researchers from the University of Cambridge, University of Liverpool, University of Bristol, Teesside University and University of Hertfordshire.

We used a controlled interrupted time series design, comparing average weekly household purchases among London households following the introduction of the policy to a counterfactual scenario where the policy was not implemented. We estimated the counterfactual by extrapolating the pre-policy trend in London and incorporating the changes seen in a control area (North of England) following the introduction of the policy to account for secular and seasonal changes in HFSS purchases that were common to both areas.

We found that average weekly household purchase of energy from HFSS products was 1001 kcal, or 6.7%, lower than expected. The largest relative reduction was for chocolate and confectionery at 317.9 kcals (19.4%) lower than the counterfactual estimate. We also saw reductions in purchased fat (57.9 g), saturated fat (26.4 g) and sugar (80.7 g) from HFSS products. However, these were not absolute reductions. The policy was associated with reduced rate in growth of HFSS purchases, as HFSS purchasing increased in both London and the North of England over the study period. 

The study’s findings were welcomed by many to support further action, including the Mayor of London, Sadiq Khan. The Grocer reported that at least 70 local authorities are considering similar advertising policies in their jurisdictions. 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 HFSS foods and drinks. Food campaigner Jamie Oliver said:

This brilliant policy is popular with the public, and businesses were quick to adapt and simply promoted healthier products from their ranges. Now it’s time for Boris Johnson to put child health above short term political manoeuvring. He must deliver on his obesity strategy in full, including his own promise to restrict junk food ads on TV and online, so the whole country can benefit.”

Our study suggests these types of policies could also offer a potentially effective intervention in other important public health policy areas such as the regulation of alcohol and gambling advertising.

The research was an independent evaluation funded by NIHR School for Public Health Research (SPHR) Grant Reference Number PD-SPH-2015.

Reference:

Yau A, Berger N, Law C, et al. (2022) 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. PLoS Medicine DOI: 10.1371/journal.pmed.1003915