The effect of three front of pack (FOP) labeling schemes (Mexican Guideline Daily Amounts (GDA), Ecuador's Multiple Traffic Light (MTL) and Chilean Warning Labels (WL) in red) on purchasing intentions was evaluated using a randomized experiment of an online shopping simulation. The study employed an online grocery store developed for this purpose to simulate a shopping situation.

Nutrition labels may modify purchasing behavior. Different labels may influence consumer purchasing behaviors in different ways.

In general, for nutrition labels to have any effect on purchasing decisions, consumers must first be exposed to them and perceive the displayed information on the labels. Then, the effect will be mediated by consumer understanding. Based on this understanding, consumers may use the label to make inferences about the nutritional quality or healthiness of the product, which, together with other information (e.g. trust or liking of the label or taste of the product) may affect the evaluation of the product and eventually the purchase decision of the product.

GDA provide numeric information on the content of key nutrients in the food product without interpreting the information.

MTL and WL are nutrient-specific labels providing an interpretation of the nutritional content of specific nutrients in the product. The MTL uses traffic light colors to indicate the high (red) or low (green) content of key nutrients, whereas the WL are only included in a product when the content of each key ingredient is above specific criteria.

Trained undergraduate student research assistants from eight universities across the country recruited the study participants. Research assistants were trained on how to approach and recruit participants and obtain informed consent. They were instructed to recruit 20 or more participants each. Recruitment took place in public spaces previously selected by convenience by the research team, based on their use by low- and middle-income groups in Mexico (i.e., public schools, public squares, public health centers, as well as supermarket chains and shopping centers located in low-income neighborhoods). Potential participants were approached by research assistants, who explained study objectives and invited them to be part of the study. Then, individuals were screened for eligibility using a 3-item screener. To access this screener, research assistants used a tablet or laptop with internet-access, to access a unique web address where our web-based tool was hosted. Research assistants were automatically informed by the web-based tool about the eligibility of the participant. Informed consent was obtained from all eligible participants using an automated computer-based form. Then, the tablet or laptop was handed to participants, who completed a self-administered online demographic and health survey, and then accessed the online shopping site to simulate a shopping situation. Participants completed the shopping task on the same day at the public place where they were recruited.

After allocation, participants viewed a video explaining how to correctly interpret the assigned label. Each participant was asked to shop freely, to better mimic real-world grocery shopping conditions. Research assistants instructed participants as follows: "take into account the assigned label and choose your preferred products". Participants were assigned an initial budget to do their shopping, although they did not pay actual money for their groceries. This budget corresponded to their weekly expenditure in groceries reported in the demographic survey, from 500-5000 Mexican pesos ($28-280 USD), in multiples of 500. No specific instructions were given related to the number or total cost of food products purchased.

FOP nutrition labels were affixed on the food items of the virtual supermarket. The store displayed the name, price and the front of the pack image of 60 food products from 5 food groups (ready-made foods, dairy products, non-dairy beverages, salty snacks, and breakfast cereals). Products were shown on traditional shopping shelves. Participants could zoom in to look more closely at the products and their prices, and could click on the product to access a new pop-up window. This new window displayed product information (i.e., name and brand), a larger image of the front of the product packaging, and an area where they could select the amount or number of products they wanted to put in their shopping cart. The pop-up window was the only way in which participants could select the food products to "purchase". Participants could also zoom in further on this pop-up to look more closely at the package and the nutritional label.

After completing their shopping, participants revised their shopping cart and "purchased" their products. A brief feedback on the nutritional quality of the products in their shopping cart was provided as a retribution for their time.

Inclusion Criteria:

• Consuming at least one of the five food groups included in the shopping site (salty snacks, beverages, dairy products, breakfast cereals and ready-made foods)
• Shopping for groceries at least twice per week

Exclusion Criteria:

• Working in the food and beverage industry
• Having any of their direct family members working in the food and beverage industry

De-identified individual participant data will be made available upon request.

2 years after completion of recruitment

Data access requests will be reviewed by the principal investigator. Requestors will be required to sign a Data Acess agreement.