Promoting environmentally sustainable food purchases in online grocery shopping: insights from a pilot randomised controlled field trial

Objective: It remains unclear which interventions are effective in promoting more environmentally sustainable food choices within online grocery shopping environments. We set out to (1) use a plug-in (browser extension) to implement a pilot randomised controlled trial of eco-labels providing information on the environmental impact of specific food products, and (2) collect data to inform a larger trial investigating the effectiveness of eco-labels and other interventions promoting environmentally sustainable online food purchases. The plug-in was custom-built and active on a large UK supermarket website, accessed using the Google Chrome browser on a desktop or laptop. Results: Of the 504 participants screened, 161 met eligibility criteria and were invited to participate in the study. 57 of these downloaded the plug-in (23 in the control group, 34 in the intervention group), of which 22 shopped at least once over the 1-month trial. There was no significant difference in average eco-score of purchases between the control and intervention groups (mean ± SD: 32 ± 13 vs. 41 ± 14; p = 0.22). 69/161 eligible participants responded to a follow-up survey and suggested technical support, reminders, greater incentives, and more information about eco-labels were needed for the full trial. We showed that it is feasible to evaluate online grocery shopping interventions without the collaboration of a supermarket using a web browser extension. Trial registration: This pilot trial was not registered, as its main purpose was to test the implementation of the plugin and gather data useful for planning the main trial, which is registered under ISRCTN18800054 as of 27/03/2024.