People choose healthy and sustainable lunches if given the green light

The study, published in the journal Appetite, also shows that in some cases people were even inclined to choose 'greener' meals over 'healthier' meals.

The researchers looked at the use of traffic lights in a simulated lunchtime canteen set up, for which the colours (red, amber, green) were designed to indicate how environmentally friendly and how healthy the meal options were.

The idea being that, when people see the traffic lights associated with different meals, they will opt for the more environmentally friendly options and the healthy options.

Previous studies have examined the impact of traffic light systems on consumer choices for individual food products, but this study considered their use in an everyday simulated lunch time set up much like the kinds of situation where people make actual meal choices.

This kind of behavioural intervention designed to improve decisions in our day-to-day lives is commonly known as a 'nudge'.

What is novel about this study is that it is able to compare the relative impact of traffic lights, as nudges, to support positive changes in behaviour when the traffic lights indicate healthy eating, and when they indicate environmental friendliness.

The findings also show that when accompanied with more information about what the traffic lights refer to, such as the actual values of daily calorie intake and acceptable levels of carbon emissions, this then boosted the positive changes towards healthier and more environmentally friendly meals.

Dr Magda Osman, lead author of the study from Queen Mary University of London, said: "We show that using traffic light labels on menus influences the meals people choose, and so this simple technique could easily be implemented on menus in bars, cafes, restaurants as well as canteens, to indicate to people the greenness as well as the healthiness of food items.

"In addition, and more importantly, the findings show that the persuasive effects are boosted by general information about daily calorie intakes and acceptable levels of carbon emissions associated with meals. This means, that while traffic light nudges are intuitive to understand, people need additional information to interpret more precisely what the different colours of traffic lights actually refer to."

The study involved seeing pictures of meals available during lunch that participants could choose from where the range of meals were more or less healthy, and more or less environmentally friendly. The experiment compared meal choices when no traffic lights were present, and then when they were present, and looked at the changes in meal choices based on the presence of the traffic lights.

Although presenting two traffic lights, one indicating 'greener' meals and the other indicating 'healthier' meals, at the same time might overload the consumer, the researchers found that presenting both compared to just one actually boosted the positive effect on consumer meal choices.

Dr Osman added: "Given the current social policy interests in persuading people to make choices that mean we eat more sustainably, which means eating less red meat, less of depleted fish stocks, and less dairy, and move towards eating more vegetables, then studies like the one we conducted help to show what methods could be used to inform people about sustainable meal options in a clear and intuitive manner."