The impact of warning labels versus traffic light labels on food choice and negative emotional responses: two randomised controlled trials among UK adult populations with and without an eating disorder

Background In the UK, front-of-pack traffic light labels (TLL) are implemented voluntarily. The UK Government are considering alternative FOP approaches, such as nutrient warning labels (WL). However, the effects and potential harm of TLL versus WL in UK consumers are unclear. We compared the effects of WL, TLL, and no label on unhealthy food item selection and negative affect among UK adults with and without an eating disorder (ED). Methods We conducted two online randomised controlled trials. In Study 1, 924 UK adults without an ED diagnosis were randomly assigned (1:1:1) to a WL, TLL, or no labels condition and completed a food-choice task. In Study 2, 240 UK adults with an ED diagnosis completed a baseline no-label food choice task and were subsequently randomly assigned (1:1:1) to WL, TLL, or no labels for a follow-up food choice task. The primary outcome was the number of task-specific unhealthy food items selected. Negative affect before and after food choice tasks was measured as a secondary outcome. Findings In Study 1 (data collected 02/25 - 04/25), unhealthy food selection differed by condition (p = .013). Of five products selected, WL participants selected 0.20 fewer unhealthy items than TLL participants (8.0%; p = .038) and 0.28 fewer than controls (10.7%; p = .004). In Study 2 (data collected 11/25 - 02/26), unhealthy selection decreased by 0.39 items with WL (17.7%; p = .015), 0.13 with TLL (5.3%, p = .286), and 0.00 with no labels. The reduction was greater with WL than with no labels (p = .029). Label condition did not differentially affect task-related negative affect in either study (Study 1, p = .757; Study 2, p = .448). Interpretation WL tended to be associated with lower unhealthy food selection compared to TLL in UK adults. There was minimal evidence that WL or TLL caused negative emotional responses. Funding This research was funded by the National Institute for Health and Care Research (NIHR) Oxford Health BRC. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care. Registration ClinicalTrials.gov NCT07339969