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Restricting HFSS Price Promotions Shows No Effect on Energy Purchased in Simulated Supermarket
A large three-arm randomised controlled trial of 9,004 UK adults found no significant differences in total energy, basket cost, energy density, or proportion of high fat, sugar, and salt (HFSS) items purchased when price promotions on HFSS foods were either removed or silently applied without promotional labelling. The only statistically significant difference was a marginally higher item count in the usual-practice group compared to the no-promotion group (11.4 vs. 11.1 items), a difference of limited practical magnitude.
What Was Studied
This trial examined whether restricting price promotions on HFSS foods — or allowing discounts to remain in place while removing any promotional communication about them — could reduce unhealthy food purchasing. The primary outcome was total energy (kilocalories) in participants’ shopping baskets, with secondary outcomes including total spend, energy density, total items selected, and the proportion of the basket comprising HFSS products.
How It Was Studied
This was a between-subjects randomised controlled trial with three experimental arms: a “Usual Practice” condition in which HFSS items were sold at a reduced price and clearly labelled as promotions; a “No Communication” condition in which HFSS items were similarly discounted but not identified as promotional; and a “No Promotion” condition in which HFSS items were sold at their standard price. Participants were 9,004 adults drawn to be representative of the UK population. Each participant completed a single shopping session in a purpose-built simulated online supermarket, selecting food and drink for two days with no restrictions on the number of items chosen or the budget available. Outcomes were compared across arms after adjustment for age, gender, household income, ethnicity, and area-level deprivation.
What Was Observed
- No significant differences in total energy purchased were detected across any of the three conditions after covariate adjustment. This null result for the primary outcome indicates that neither removing promotional pricing nor removing promotional labelling reduced the caloric content of shoppers’ baskets.
- Secondary basket metrics were also unchanged. Total basket cost, overall energy density (kcal per 100g), and the proportion of items classified as HFSS did not differ significantly between the Usual Practice, No Communication, and No Promotion groups, suggesting that pricing changes alone had no broad impact on nutritional quality of purchases.
- A small but statistically significant difference in item count was observed: participants in the Usual Practice group selected slightly more items on average than those in the No Promotion group (11.4 vs. 11.1 items). The authors do not characterise this as a meaningful dietary difference, and no equivalent difference in energy or HFSS proportion accompanied it.
Why This Matters
Price promotions are disproportionately applied to HFSS foods, and the assumption that restricting them would steer consumers toward healthier choices has informed proposed retail policy in the UK. These findings challenge that assumption, at least within an online retail environment, suggesting that promotional pricing restrictions alone may not be sufficient to meaningfully alter purchasing behaviour. The authors conclude that further price-based interventions, particularly those tested in real-world settings, are required before confident policy recommendations can be made.
How to Read This Result
Although this was a well-powered, large-scale RCT with a population-representative sample, all findings come from a controlled simulation rather than genuine supermarket behaviour, and the absence of any budget constraint may have reduced the sensitivity of the design to detect price-driven effects that would emerge under real spending pressures.
Limitations
The study was conducted entirely within a simulated online supermarket environment, which may not capture the full range of cognitive, social, and financial pressures that shape real purchasing decisions. Participants shopped in a single session with no budget limit, reducing the ecological validity of the price manipulation — an intervention that would only be consequential to shoppers who are genuinely constrained by cost. The authors themselves acknowledge these constraints and call for real-world trials to generate the evidence base needed for robust policy guidance.