Purpose: Front-of-package labelling (FOPL) schemes have been developed to provide more useful information to consumers and facilitate more critical and healthier food choices. This single-blinded multi-arm parallel-group randomised controlled trial aimed at assessing the effect of different FOPL schemes on the objective understanding of the nutritional content and intention to purchase products, in El Salvador.
Methods: Participants (n = 1204) were exposed to two-dimensional images of 15 mock-up products presented at random and balanced orders. Participants were exposed to mock-ups featuring no FOPL scheme (control group, n = 305) or one of the following schemes: black octagonal warning labels (OWL) (n = 302), traffic-light labelling (TFL) (n = 297), or guideline daily amounts (GDA) (n = 300).
Results: The odds for choosing to purchase the least harmful of the options more often was the highest in the OWL group compared to the control group: two times higher in the OWL group (OR 2·21, 95% confidence interval 1·58 - 3·11), and 49% higher in the TFL (1·49, 95%CI 1·06 - 2·11), with no changes in the GDA (1·06, 95%CI 0·75 - 1·50). OWL also resulted in the highest odds for correctly identifying the least harmful option (OR 3·77, 95%CI 2·79 to 5·09), and for correctly identifying a product with higher amounts of sugars, sodium, total fat, and/or saturated fats (3·26, 95%CI 2·40 to 4·43).
Conclusion: OWL outperformed GDA and TFL in its ability to improve objective understanding of nutritional information and purchase intention. Results support the adoption of OWL in El Salvador.
Trial registration number: ISRCTN 12,389,597.
Date of registration: 17 July 2023 (retrospectively registered).
Keywords: Decision making; Food choice; Food labelling; Front-of-package labelling; Health policy; Nutrition & dietetics; Public health.
© 2025. Pan American Health Organization (PAHO).