This study examines how environment-related food labels affect shopping behaviour. Using an experimental store consisting of nearly 300 available food items, we observe the food purchases of consumers before and after each product is tagged with one of three environmental labels: single traffic lights, multiple traffic lights and the kilometric format. The kilometric format indicates the greenhouse gas emissions for each product by indicating the equivalent number of kilometres driven by an average car. The other two formats are based on the traffic-light rating system used for nutrients by the British Food Standard Agency. Multiple traffic lights present three traffic lights simultaneously: one each for greenhouse gas emissions, water eutrophication and air acidity. The single traffic light label displays one unique traffic light for greenhouse gas emissions. All three types of environmental labels lead consumers to purchase more environmentally friendly food baskets (i.e., significant decreases in carbon dioxide, nitrogen and sulfur dioxide emissions). Labelling, however, does not affect the price of selected food baskets (in Euros per 100 g) or their nutritional content. By generating more product substitutions between unlabelled and labelled baskets, multiple traffic lights are more effective in reducing GHG emissions, eutrophication and acidification.