Supermarket voluntary price promotion ban: a public health study

ISRCTN	ISRCTN23476580
DOI	https://doi.org/10.1186/ISRCTN23476580
Secondary identifying numbers	NIHR167794

Submission date: 01/07/2025
Registration date: 22/10/2025
Last edited: 22/10/2025

Recruitment status: Recruiting
Overall study status: Ongoing
Condition category: Other

Prospectively registered

Protocol

Statistical analysis plan

Results

Individual participant data

Record updated in last year

Plain English summary of protocol

Background and study aims
In the UK, many people eat too much unhealthy food. There are many reasons for this. One important reason is that it can be cheaper than healthier foods. A lot of unhealthy food in the UK is sold using special offers, like ‘buy one get one free’ deals. Special offers may make some people eat more unhealthy food, harming their health. Stopping special offers on unhealthy products could improve people’s health. However, some people may use special offers to save money, making their weekly shop affordable. Stopping special offers may leave some people with less money. Governments in the UK are interested in stopping the use of special offers, but have not done so yet. There may be other unintended effects of stopping special offers. For example, supermarkets might start doing other things to increase sales of unhealthy foods. Changes in what people buy may affect other important things, like jobs and taxes paid. Two UK supermarkets have chosen to voluntarily stop using special offers. This provides a valuable opportunity to understand the real-world impacts of stopping the use of special offers. This study aims to understand the health and economic impacts of supermarkets choosing to stop using special offers on unhealthy foods.

Who can participate?
Healthy volunteers who shop at one or more supermarkets in the UK and can participate in an interview.

The study will also recruit 10 diverse individuals from different parts of the UK to join a public or PPI panel. They will meet four times. They will help with the study design and the sharing of findings. A member of the public with experience in doing these things will join the research team and lead this work.

What does the study involve?
The study will examine the impact of two supermarkets discontinuing the use of special offers. First, the researchers will use data collected by market research companies on consumers’ food shopping habits. They will compare the quantity and types of food purchased before and after the special offers were discontinued. They will also analyse changes in consumer spending on food and compare these trends with those observed in other supermarkets that continued offering promotions. Second, the researchers will use this data to estimate the potential effects of changes in food purchasing on public health. They will also assess the implications for NHS costs. Third, the study will explore the impact of ending special offers on the two supermarkets and the food manufacturers that supply them. This will involve analysing company accounts and employment data to compare business performance before and after the change. Fourth, the researchers will engage with customers to understand their views and usage of special offers. They will also examine food industry documents, trade publications, and press statements to gain insight into corporate strategies and perspectives. Finally, all findings will be synthesised to provide a summary of the overall impacts.

The researchers have consulted with 11 people from the NIHR North Thames ARC PPI group. They support the work and reviewed this summary. In response to their feedback, customer interviews were added, and the language used was changed.

What are the possible benefits and risks of participating?
Possible benefits: Participants can express and share their views about changes that affect the food purchased in UK supermarkets, and contribute to research that may inform the development of food and health policy.
Possible Risks: Participants will be asked to share their views and experiences of shopping, either in small groups or in an interview. Some people may find this uncomfortable.

Where is the study run from?
UCL Great Ormond Street Institute of Child Health, UK

When is the study starting and how long is it expected to run for?
June 2025 to May 2027

Who is funding the study?
National Institute for Health and Care Research (NIHR), UK

Who is the main contact?
Dr Oliver Mytton, o.mytton@ucl.ac.uk

Contact information

Dr Oliver Mytton
Public, Scientific, Principal Investigator

UCL Great Ormond Street Institute of Child Health, 30 Guilford St
London
WC1N 1EH
United Kingdom

ORCID ID	0000-0003-3218-9912
Phone	+44 020 7242 9789
Email	o.mytton@ucl.ac.uk

Study information

Study design	Mixed methods public health evaluation of a natural experimental policy
Primary study design	Observational
Secondary study design	Longitudinal study
Study setting(s)	Community, Home, Retail/food outlet
Study type	Prevention
Participant information sheet	Not avaliable in web format, please use contact details to request a particpant information sheet
Scientific title	A public health evaluation of a voluntary ban on the use of price promotions to sell foods high in fat salt and sugar in two UK supermarket chains
Study objectives	Obesity and unhealthy diets are major causes of disease in the UK and globally. Marketing of foods high in fat salt and sugar (HFSS), including the use of price promotions (e.g. get two-for-the-price-of-one), are important contributory factors. Banning price promotions may help tackle these health issues. Two UK supermarket chains have already voluntarily banned their use on HFSS foods, in 2016 and 2022. The aim of this study is to evaluate the public health and related impacts of industry-led voluntary policies in two nationwide supermarket chains to ban the use of price promotions to sell HFSS foods.
Ethics approval(s)	Not yet submitted, University of Cambridge Humanities and Social Sciences Ethics Committee (Address not provided, Cambridge, Zip/postal code not provided, United Kingdom; Telephone number not provided; researchethics@admin.cam.ac.uk), ref: Reference number not provided
Health condition(s) or problem(s) studied	The main focus of this work is the prevention of obesity and risk of chronic non-communicable diseases through reduction of consumption of high fat salt sugar foods.
Intervention	The study is a mixed-methods public health evaluation of a natural experimental policy. The project is structured into five interlinked work packages (WPs). WP1 will engage the public and policy makers, integrate WPs and synthesize the findings and existing literature, and disseminate the findings. WP2 will provide quantitative estimates of the impact of the intervention (use of promotions; consumer purchases and food expenditure in aggregate and by sub-group) in comparison to controls using a longitudinal commercial dataset of household food purchases; findings will be triangulated with analysis in a second complementary commercial dataset (product sales dataset of loyalty card holders for one supermarket) that will also be used to explore industry adaptation and use of loyalty card price promotions. WP2 will use (controlled) interrupted time series analyses or other robust longitudinal comparative analyses to estimate the impact of the policy. WP3 will use public health modelling to estimate the impact on health and healthcare costs (in aggregate and by deprivation quintile, age and gender) based on the observed changes in purchasing from WP2. WP4 will provide quantitative estimates of the impact on industry economic performance. WP5 will use qualitative methods to understand industry and public knowledge, attitudes and behaviours towards the use of price promotions and restrictions in their use. The intervention to be studied is the policy of a voluntary ban on the use of certain types of price promotions in two UK supermarket chains. One supermarket introduced the policy in 2016, and the second in 2022. The ban extended to ‘volume driver’ type price promotions, i.e. price promotions that offered greater volume for the same price (e.g. 2-for-the-price-of-1 or get 50% extra free). Other price promotions, such as temporary price reductions (e.g. 20% price reduction) were not included in the policy. The study is an evaluation of a natural experiment that uses a combination of routinely collected quantitative data and primary collected qualitative data to evaluate the proximal, intermediate and distal outcomes of the policy from a public health perspective.
Intervention type	Other
Primary outcome measure	1. Change in purchase of foods (measured in Kcal per household) high in fat, salt and sugar (defined by the UK FSA-OFCOM model) amongst the Kantar World Panel at 12 and 24 months post-implementation 2. Change in total food expenditure (measured in GBP per household) amongst the Kantar World Panel at 12 and 24 months post-implementation
Secondary outcome measures	1. Modelled health, healthcare costs and socio-economic inequalities measured using the PRIMETime Model during the 30 years after implementation 2. Industry behaviour and economic performance (e.g. domestic turnover, employment, corporation tax, business rates; wages and salaries; pension contributions; and National Insurance contributions) measured using routinely available data (e.g. ONS Annual Business Survey) or published company reports in the 12 months post-implementation compared to the 12 months before implementation.
Overall study start date	01/06/2025
Completion date	31/05/2027

Eligibility

Participant type(s)	Population
Age group	Mixed
Lower age limit	18 Years
Upper age limit	99 Years
Sex	Both
Target number of participants	30-40
Key inclusion criteria	Adults who shop at one or more supermarket in the UK and able to participate in an interview
Key exclusion criteria	Not meeting the key inclusion criteria
Date of first enrolment	01/09/2025
Date of final enrolment	01/09/2026

Locations

Countries of recruitment

England
Northern Ireland
Scotland
United Kingdom
Wales

Study participating centre

MRC Epidemiology Unit, University of Cambridge

Level 3 Institute of Metabolic Science, University of Cambridge, School of Clinical Medicine
Cambridge
CB2 0SL
United Kingdom

Sponsor information

Great Ormond Street Hospital
University/education

Great Ormond Street
London
WC1N 3JH
England
United Kingdom

Phone	+44 020 7405 9200
Email	research.governance@gosh.nhs.uk
Website	https://www.gosh.nhs.uk/our-research/our-research-infrastructure/joint-research-and-development-office-rd/
"ROR"	https://ror.org/00zn2c847

Funders

Funder type

Government

National Institute for Health and Care Research
Government organisation / National government

Alternative name(s): National Institute for Health Research, NIHR Research, NIHRresearch, NIHR - National Institute for Health Research, NIHR (The National Institute for Health and Care Research), NIHR
Location: United Kingdom

Results and Publications

Intention to publish date	31/05/2028
Individual participant data (IPD) Intention to share	No
IPD sharing plan summary	Data sharing statement to be made available at a later date
Publication and dissemination plan	The researchers will share their findings with the public, the food industry, other researchers, and policymakers. They will talk and write about our work in different ways. For example, the researchers will share their findings through press releases and make a podcast. The researchers will talk to industry magazines. They will also report the findings in research journals. The researchers will produce short written summaries and meet with policymakers.
IPD sharing plan	The current data sharing plans for the current study are unknown and will be made available at a later date

Editorial Notes

03/07/2025: Study's existence confirmed by National Institute for Health and Care Research (NIHR) (UK).