To examine the impact of front-of-package (FOP) labels on perceived healthfulness, purchasing intentions and understanding of common FOP systems.

A parallel, open-label design randomised participants to different FOP labelling conditions: ‘high in’ warning labels (WL), multiple traffic light labelling (TLL), health star ratings (HSR) (all displayed per serving) or control with no interpretive FOP labelling. Participants completed a brief educational session via a smartphone application and two experimental tasks. In Task 1, participants viewed healthy or unhealthy versions of four products and rated healthiness and purchasing intention on a seven-point Likert-type scale. In Task 2, participants ranked three sets of five products from healthiest to least healthy.

Online commercial panel.

Canadian residents ≥ 18 years who were involved in household grocery shopping, owned a smartphone and met minimum screen requirements.

Data from 1997 participants (n 500/condition) were analysed. Task 1: across most product categories, the TLL and HSR increased perceived healthiness of healthier products. All FOP systems decreased perceived healthiness of less healthy products. Similar, albeit dampened, effects were seen regarding purchasing intentions. Task 2: participants performed best in the HSR, followed by the TLL, WL and control conditions. Lower health literacy was associated with higher perceived healthiness and purchasing intentions and poorer ranking task performance across all conditions.

All FOP labelling systems, after a brief educational session, improved task performance across a wide spectrum of foods. This effect differed depending on the nutritional quality of the products and the information communicated on labels.

Trial Registration: NCT03290118.