Nutritional warnings have been recently proposed as an interpretative front-of-package nutrition labelling scheme to highlight unhealthful products. This scheme is particularly relevant in food markets characterized by a high availability of processed products with unfavourable nutrient profile. However, it remains unclear to what extent, how and under which circumstances warnings on food packages can change consumers’ food choices. The present study aimed at evaluating the influence of nutritional warnings on consumers’ purchase decisions by exploring within-category product substitution or abandonment of the category, as well as to identify consumer groups that differ in reaction to the warnings. A repeated purchase simulation was conducted with 395 Uruguayan consumers. Participants were asked to complete two successive choice-tasks with eight product-categories. Results showed that warnings modified the choices of approximately half of the participants. Within-category product substitution was the most common change in participants’ choices. However, abandonment was the dominant effect in categories for which all products included at least one warning. Consumers reacting more strongly to the warnings were characterized by greater health motivation. These results confirm the potential of nutritional warnings to encourage consumers to make more healthful choices, point to the market potential of reformulated products, and stress the need for policy makers to increase consumer’s health motivation.