Given growing interest in warning labels as a form of front-of-pack nutrition label, it is important to better understand the mechanisms via which these labels may exert their effects, especially among those making suboptimal food choices.The study aim was to assess the extent to which consumers with the weakest outcomes for objective understanding and choice in no-label conditions were able to improve their understanding and choices after exposure to warning labels on food product options.Post-hoc analyses of the cross-sectional FOP-ICE (Front-of-Pack International Comparative Experimental) study data generated from an online survey that included simulated food choice and nutritional quality ranking scenarios.Participants included 3,680 adults from the following 18 countries: Argentina, Australia, Belgium, Bulgaria, Canada, Denmark, France, Germany, Italy, Mexico, Netherlands, Poland, Portugal, Singapore, Spain, Switzerland, United Kingdom, and United States.Survey respondents selected their preferred product options and ranked foods according to their healthiness before and after exposure to mock breakfast cereal, cake, and pizza products displaying warning labels.Objective understanding and food choice were measured.Within each product category, analyses were conducted on respondents who initially incorrectly identified the healthiest option and/or selected the unhealthiest option as their preferred choice. Significant differences between proportions selecting each understanding and choice response option were assessed using 2-sample z tests for proportions.Salience of the warning labels was low; 46% reported noticing the labels while completing the survey. Just over one-third of those aware of the presence of warning labels were able to identify the least healthy option in the post-exposure condition. Approximately one-half reselected the least healthy option post exposure and just over one-fourth switched to the healthiest option.The results indicated that warning labels can assist some consumers to improve their food quality assessments and choices. However, design improvements could enhance the salience and interpretability of this label format.