Comparison of front-of-package nutrition labelling schemes in Costa Rica: a multi-arm parallel-group randomised controlled trial assessing objective understanding and purchase intention.

Different front-of-package labelling (FOPL) schemes have been developed worldwide to encourage informed and healthier food purchase decisions. However, few studies have formally compared different schemes, particularly in the Latin American context. This study aimed to assess the effects of four different FOPL schemes on the objective understanding of the nutritional content and intention to purchase products. This single-blinded multi-arm randomised controlled trial was conducted using a face-to-face survey with adult shoppers, recruited at supermarkets in Costa Rica (n=1350). Participants randomly assigned to intervention groups saw 12 mock-up products presented at random and balanced orders featuring one FOPL scheme or none: black octagonal warning labels (OWL), Nutri-Score (NUS), traffic-light labelling (TFL), guideline daily amounts (GDA), or no FOPL scheme (control group). Similar number of participants were analysed in each group: OWL (n=264), NUS (n=279), TFL (n=263), GDA (n=273), and control (n=271). Compared to the control group, the odds for correctly identifying the least harmful option more often were three times higher in the OWL group (OR 3.08; 95% CI, 2.26-4.20), and 89%, 57% and 19% higher in the TFL (1.89; 95% CI, 1.40-2.56), the GDA (1.57; 95% CI, 1.16-2.21) and the NUS (1.19; 95% CI 0.89-1.60), respectively. OWL also was more efficacious in helping participants to correctly identify a product with excessive amounts of sugars, sodium, and/or saturated fats, as well as in encouraging the intention to purchase the least harmful or the intention to choose none of the options in the choice task. OWL performed best in helping shoppers to correctly identify when a product contained excessive amounts of nutrients to limit, to correctly identify the least harmful option, and to intend to purchase the least harmful option, more often.