The aim of the present work was to evaluate the influence of two front-of-pack nutrition information schemes (traffic-light system and Chilean warning system) on consumer purchase of ultra-processed foods in a simulated online grocery store.

Following a between-subjects design, participants completed a simulated weekly food purchase in an online grocery store under one of three experimental conditions: (i) a control condition with no nutrition information, (ii) a traffic-light system and (iii) the Chilean warning system. Information about energy (calories), sugar, saturated fats and salt content was included in the nutrition information schemes.

Participants were recruited from a consumer database and a Facebook advertisement.

People from Montevideo (Uruguay), aged 18–77 years (n 437; 75 % female), participated in the study. All participants were in charge of food purchase in the household, at least occasionally.

No significant differences between experimental conditions were found in the mean share of ultra-processed foods purchased by participants, both in terms of number of products and expenditure, or in the mean energy, sugar, saturated fat and salt content of the purchased items. However, the Chilean warning system decreased intended purchase of sweets and desserts.

Results from this online simulation provided little evidence to suggest that the traffic-light system or the Chilean warning system in isolation could be effective in reducing purchase of ultra-processed foods or improving the nutritional composition of the purchased products.

Warnings have recently been proposed as a new type of directive front-of-pack (FOP) nutrition labelling scheme to flag products with high content of key nutrients. In the present work, this system was compared with the two most common FOP nutrition labelling schemes (Guideline Daily Amounts (GDA) and traffic-light system) in terms of goal-directed attention, influence on perceived healthfulness and ability to differentiate between products.

Goal-directed attention to FOP labels was evaluated using a visual search task in which participants were presented with labels on a computer screen and were asked to indicate whether labels with high sodium content were present or absent. A survey with 387 participants was also carried out, in which the influence of FOP labels on perceived healthfulness and ability to identify the healthful alternative were evaluated.

Warnings improved consumers’ ability to correctly identify a product with high content of a key nutrient within a set of labels compared with GDA and received the highest goal-directed attention. In addition, products with high energy, saturated fat, sugar and/or sodium content that featured warnings on the label were perceived as less healthful than those featuring the GDA or traffic-light system. Warnings and the traffic-light system performed equally well in the identification of the most healthful product.

Results from the present work suggest that warnings have potential as directive FOP nutrition labels to improve consumer ability to identify unhealthful products and highlight advantages compared with the traffic-light system.