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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Sales of unhealthy food and drinks were lower than expected after Transport for London (TfL) restricted advertising of these products. Average weekly household purchases of energy were 7% lower than predicted without the ban. Reductions were seen in fat, saturated fat, and sugar content. The largest reductions were seen for energy content from chocolate and sweets.

Obesity levels are rising, and many governments are considering advertising bans as part of strategies to prevent obesity. In February 2019, the transport network TfL introduced a policy to ban the advertising of foods high in fat, salt, and sugar (HFSS) on its space. This included underground tubes, bus stops, and railway stations.

Modelling work by the research team predicts that this policy could lead to 5% fewer individuals living with obesity, reduce the incidence of diabetes and heart disease, and save £218 million for the NHS and social services. The largest benefits would be expected in the least well-off groups, suggesting that the policy could help tackle health inequalities.

Further work is needed to track the impact of the policy over the long-term. However, these findings could encourage other governments and local authorities to consider similar policies.

What’s the issue?

Obesity is a health crisis in the UK, and more than 1 in 4 adults are living with the condition. Consuming too many calories is a key driver of obesity.

Advertising for unhealthy foods is known to be linked to poor diet and obesity. Billboards, buses and other outdoor public spaces are thought to be seen by 98% of the UK population at least once a week. People in more disadvantaged groups and in areas of deprivation are most exposed to advertising for unhealthy food and drink. 

Many governments and local authorities are considering restrictions on the advertising of unhealthy products. However, there is little evidence on whether advertising bans lead to people buying or consuming less of these foods.

In 2019, the Mayor of London, Sadiq Khan, introduced restrictions on advertising of unhealthy food and drinks across the TfL network. TfL has some of the most prominent outdoor advertising space in the UK, including on tubes, buses and bus stops, taxis, trains, and land outside railway stations. The transport network received £152 million revenue from its outdoor advertising space in 2017/18. This is 40% of spending on outdoor advertising in London and 20% of the total across the UK.

Researchers wanted to see whether the advertising ban was followed by changes in household take-home purchases of unhealthy food and drink.

What’s new?

The researchers estimated what household food purchases would have been without the ban. They used data from London before the ban, and took into account trends (such general changes over time, seasonal changes) seen in a separate area without such a ban (North of England). They compared these estimates with actual purchases after the ban.

The study included all products classified as HFSS such as chocolate and sweets, puddings and biscuits, sugary drinks, sugary cereals, and savoury snacks. More than 5 million household food and drink purchases were recorded by 1,970 households (977 households in London, and 993 households in the North of England).

10 months after the introduction of the advertising ban:

  • the average weekly household purchase of energy from unhealthy products was 7% or 1,000 kcal lower than predicted; this corresponds to a reduction of 385 kcal (roughly 1.5 bars, or 72g of milk chocolate) per person per week
  • reductions were seen in weekly household purchases of fat (57.9 g), saturated fat (26.4 g) and sugar (80.7 g)
  • the largest reductions were seen for energy from chocolate and sweets (19.4%, 317.9 kcal)
  • there were no changes in purchases of other (non-HFSS) products.

Over the 10 months of the study, there was a general trend towards increased purchases of unhealthy food. The advertising ban was therefore associated with a smaller increase in purchases (relative reduction), rather than a drop in purchases (absolute reduction).

The results suggested that bigger reductions in purchasing occurred in less well-off households, households where the main food shopper was living with overweight or obesity, and in shoppers who used public transport more frequently. However, these analyses were on a small number of people, and the researchers say the observations should be considered with caution.

Why is this important?

This is the first study to look at the implementation of the TfL advertising ban. It found that advertising restrictions are feasible, and could have a meaningful impact on population health.

The findings could encourage governments and local authorities to consider similar policies to prevent obesity. The TfL restrictions were part of a childhood obesity strategy, but they could influence the whole population. Previous research suggests that ‘low agency’ interventions (such as policy to restrict advertising) that do not rely on individual decision-making, are more likely to be effective than interventions that require individuals to understand and act on information.

After this study, the researchers went on to predict the effect of the policy on health benefits, cost savings, and inequalities, from the perspective of the NHS and social services. They adapted an existing health economic model and estimated that in 1 year, the TfL ban would result in almost 95,000 (5%) fewer individuals living with obesity in Greater London. After 3 years, it would mean 3000 fewer people with diabetes, and 2,000 fewer with heart disease.  

According to this model, the policy would save the NHS and social services £218 million over the lifetime of the current population. The largest benefits (greatest reductions in obesity, and highest increases in years of good health) would be seen in the least well-off groups compared to the most well-off, suggesting that the policy would reduce health inequalities.

What’s next?

Transport use and food purchasing were so disrupted during the pandemic, that it will not be possible to track the effect of the TfL ban in the longer term. The researchers say evaluations of similar bans are needed. This study looked at household purchase; further work could explore whether such ban also reduce purchases made outside of the house.

The researchers will monitor the wider effects of the policy. The ban could help change attitudes towards healthy eating. It may encourage brands to create healthier recipes (so that they can advertise their products), to advertise on other platforms (such as online) or to focus on promoting their brand.

Outside of London, routine use of public transport is lower, and outdoor advertising reaches fewer people. Further research is needed to see whether advertising bans would be effective in other locations. Future modelling studies could take into account government and local authority costs (such as loss of advertising profit), to help tailor interventions to local areas. Further work is also needed to explore whether advertising restrictions can reduce drinking, gambling or impact on other public health policy areas.

Obesity levels are increasing. Advertising restrictions could play a role in slowing the trend, but multiple strategies are needed to actively reduce levels of obesity. The researchers have shared their results with the Department of Health and Social Care (DHSC), local authorities, and at international policy events. They say that other local authorities, including Bristol City Council, are implementing similar policies.

You may be interested to read

This summary is based on: Yau A, and others. 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 2022;19:e1003915.

NIHR School for Public Health Research (SPHR) research briefing on this study

Other papers by the same research group:

On modelling the effects of the TfL ban: Thomas C, and others. The health, cost and equity impacts of restrictions on the advertisement of high fat, salt and sugar products across the transport for London network: a health economic modelling study. International Journal of Behavioral Nutrition and Physical Activity 2022;19:93

On implementing the advertising ban: Meiksin R, and others. Restricting the advertising of high fat, salt and sugar foods on the Transport for London estate: process and implementation study, Social Science & Medicine 2022;292:114548

On news and trade press reactions to the advertising ban: Thompson C, and others. Media representations of opposition to the ‘junk food advertising ban’ on the Transport for London (TfL) network: A thematic content analysis of UK news and trade press, SSM – Population Health 2021;5:100828

On sociodemographic differences in exposure to unhealthy food advertising: Yau A, and others. Sociodemographic differences in self-reported exposure to high fat, salt and sugar food and drink advertising: a cross-sectional analysis of 2019 UK panel data. BMJ Open 2021;11:e048139

Funding: This study is funded by the NIHR School for Public Health Research.

Conflicts of Interest: The study authors declare no conflicts of interest.

Disclaimer: Summaries on NIHR Evidence are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that the views expressed are those of the author(s) and reviewer(s) at the time of publication. They do not necessarily reflect the views of the NHS, the NIHR or the Department of Health and Social Care.

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