Price promotions influence food choices and are disproportionately applied to foods high in fat, sugar and salt (HFSS), consumption of which is a known contributor to poor diet and diet-related non-communicable diseases. This study evaluates the effectiveness of (1) restricting price promotions of HFSS products and (2) allowing such promotions but restricting communications regarding them in changing purchasing behaviours.

Between-subjects randomised controlled trial with three arms: (1) reduced price, labelled a price promotion (‘Usual Practice’); (2) reduced price, not labelled a price promotion (‘No Communication’) and (3) standard price (‘No Promotion’). Participants selected food and drinks for 2 d in a one-off shop, without restrictions on the number of items to purchase or the budget, at a simulated online supermarket. We measured total energy (kcal) in basket, total cost, total number of items, energy density (kcal/100 g) and proportion of the basket that was HFSS.

Simulated online supermarket.

Adults representative of the UK population (n 9004).

There were no significant differences in energy in baskets between groups, after controlling for age, sex, household income, ethnicity and deprivation. No significant differences were found between groups’ baskets for total cost, energy density or proportion HFSS. Participants in the ‘Usual Practice’ group selected significantly more items than the ‘No Promotion’ group (11·4 v. 11·1; P = 0·003).

No significant effects of restricting price promotions, or communications of them, were found for purchasing behaviours in a simulated online supermarket. Further price-based interventions, especially in real-world settings, are needed to provide robust policy recommendations.

Social media offers many benefits but also carries risks, including exposure to distressing content. The UK’s Online Safety Act requires certain platforms to empower users to control the content they see. Content controls can reduce users’ exposure to sensitive content. However, there is little public data on how platform design shapes the use of these controls. In our online randomised controlled trial on a simulated social media platform, participants were given an initial choice between seeing ‘All content types’ or ‘Reduced sensitive content’. After browsing, they were given the opportunity to change their choice. In the Control arm, none of the options were pre-selected. 24% chose ‘Reduced sensitive content’. Pre-selecting ‘All content types’ reduced this proportion to 15%. Conversely, adding a description of ‘sensitive content’ on the choice page increased that figure to 29%. The initial choice proved to be ‘sticky’. When invited to review after browsing, those defaulted away from ‘Reduced sensitive content’ did not switch any more than those whose choice was not influenced by a default. Overall, user choice was susceptible to choice architecture, and users’ tendency to update their initial choice was weak. This highlights the importance of platform design to deliver genuine user empowerment.