Stop, think, buy: An online randomised controlled experiment comparing the effects of traffic light nutritional labelling and price promotion on steering consumer food choice.

Diet-related diseases are a global health concern, prompting governments to implement population-wide dietary improvements. In the UK, the traffic light system (TLS) of nutritional labelling aims to guide healthier food choices. However, concerns have arisen about whether retailer price promotions may counteract positive effects of the TLS on diet. To address these concerns, in the present research we investigated the effects of the TLS and price promotions on the healthiness of food choice, both individually and in combination. A pre-registered online randomised controlled trial (RCT) was conducted using a 2x3 factorial between-subjects design with TLS (control vs. TLS) and price promotion (no promotion vs. healthiest product promotion vs. unhealthiest product promotion) as interventions. A total of 1582 UK participants were randomised across the experimental conditions and asked to make a hypothetical purchase choice amongst four unbranded snack bars of varying healthiness. Price promotions were found to effectively increase the likelihood of choosing a promoted product, whether healthy or unhealthy. Price promotions on the unhealthiest food item were found to decrease the likelihood of the healthiest product being chosen. TLS labelling did not significantly impact food choice relative to the control. However, there was a tendency for the labelling to amplify the effect of price promotions on healthy products and dampen the effect on unhealthy products. Overall, our research offers new insights into how different forces may interact when multiple policy interventions are implemented in the retail environment and highlights the need to examine them in combination.