Effects of front-of-package nutrition labelling systems on objective understanding and purchase intention in Panama: results from a multi-arm parallel-group randomised controlled trial.

Objective: To assess the effect of different front-of-package (FOPL) schemes on the objective understanding of the nutritional content and intention to purchase products, in Panama.

Design: Single-blinded multi-arm parallel-group randomised controlled trial.

Setting: Supermarkets across Panama. Participants were exposed to two-dimensional images of 15 mock-up products presented at random and balanced orders. Participants assigned to the intervention groups were exposed to mock-ups featuring one FOPL scheme: black octagonal warning labels (OWL), traffic-light labelling (TFL), or guideline daily amounts (GDA). Control group was not exposed to any FOPL scheme.

Participants: Adult supermarket shoppers (n=1200). Participants were blinded to group assignment.

Results: Similar number of participants were randomised to and analysed in each group: OWL (n=300), TFL (n=300), GDA (n=300), and control (n=300). The odds for choosing to purchase the least harmful or none 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 2·13, 95% confidence interval 1·60-2·84), and 57% higher in the TFL (1·57, 1·40-2·56), with no changes in the GDA (0·97, 0·73-1·29). OWL also resulted in the highest odds for correctly identifying the least harmful option, and for correctly identifying a product with excessive amounts of sugars, sodium and/or saturated fats.

Conclusions: OWL performed best in helping shoppers to correctly identify when a product contained excessive amounts of nutrients of concern, to correctly identify the least harmful option, and to decide to purchase the least harmful or none of the options, more often.