The impact of warning labels versus traffic light labels on food choice and negative emotional responses: two randomised controlled trials among UK adult populations with and without an eating disorder

In the aisles of a modern supermarket, the packaging of food has become a silent language of health. For years, governments have tried to teach consumers to read this language, hoping that clearer information would lead to better choices. In the United Kingdom, the most common system in use is the traffic light label. This approach uses a simple color code—green, amber, and red—to show how much fat, sugar, salt, and saturated fat is in a product, much like a traffic signal indicates whether it is safe to proceed or if one should stop. While this system has been in place for over a decade, it remains voluntary, meaning not all manufacturers use it. As obesity rates continue to rise, policymakers are looking for more forceful ways to guide the public. One alternative gaining attention is the nutrient warning label, a stark, black-and-white notice that explicitly states a product is high in a specific unhealthy nutrient. The question facing scientists and officials is whether these bold warnings work better than the familiar color codes, and more importantly, whether they cause unintended harm to the mental well-being of shoppers, particularly those who already struggle with their relationship to food.

Two recent studies conducted by researchers at the University of Liverpool set out to answer these questions with a direct comparison. The team recruited two distinct groups of adults: one group of 924 people without a history of eating disorders, and a second group of 240 people who had been diagnosed with an eating disorder. The researchers wanted to see if the type of label on a package changed what people chose to buy, and if it made them feel anxious or upset. To do this, they created an online shopping simulation. Participants were asked to imagine they were in a supermarket and had to pick one item from a selection of six similar products in five different categories, such as breakfast cereals, potato chips, or ready-made pasta meals. The products were identical in every way except for the label they displayed. Some participants saw the standard traffic light colors, others saw the stark warning labels, and a control group saw no labels at all. The goal was to measure how many unhealthy items each person selected and to track their emotional state before and after the task.

The results revealed a clear difference in how the labels influenced behavior. Among the participants without an eating disorder, those who saw the warning labels chose significantly fewer unhealthy items than those who saw the traffic light labels or no labels at all. Specifically, the warning label group selected about 0.2 fewer unhealthy items on average compared to the traffic light group, a difference that translated to roughly an 8 percent reduction in unhealthy choices. When compared to the group with no labels, the reduction was even more pronounced, at nearly 11 percent. In the second study involving people with eating disorders, the trend was similar. Those exposed to warning labels reduced their selection of unhealthy foods by nearly 18 percent from their baseline choices, whereas the traffic light group showed only a small, statistically insignificant drop. The warning labels appeared to be more effective at discouraging the purchase of foods high in saturated fat and salt for this group as well.

Despite the warning labels being more effective at changing choices, the study found no evidence that they caused emotional distress. A common concern with food labeling is that seeing warnings about calories or nutrients might trigger anxiety or negative feelings, especially in people with eating disorders. However, the researchers measured the participants' feelings of fear, worry, and distress before and after the shopping task. They found that neither the warning labels nor the traffic light labels increased these negative emotions. In fact, for the group without eating disorders, the traffic light labels actually caused slightly more negative arousal than the warning labels, though the difference was small. The study also looked at how much people disliked or wanted to avoid the labels. While people with eating disorders reported feeling more annoyed by the warning labels than the traffic light ones, the overall emotional impact of seeing either label was minimal.

The findings suggest a complex picture for public health policy. The warning labels were objectively better at helping people choose healthier options, yet they were less popular with the public. Participants in both studies expressed stronger support for the familiar traffic light system, and those without eating disorders rated it as more effective at discouraging unhealthy choices, even though the data showed the warnings worked better. This gap between what people prefer and what actually changes behavior highlights a challenge for policymakers. The researchers noted that the traffic light system has been in the UK for over a decade, so consumers are likely more comfortable with it. The warning labels, by contrast, are new and direct, which may explain why they were more effective but also why they felt more intrusive to some.

The study also addressed the specific vulnerability of people with eating disorders. There has been a fear that any form of nutritional labeling could be harmful to this group, potentially triggering distress or unhealthy behaviors. The results of these trials offered reassurance. Even among the 240 participants with diagnosed eating disorders, the warning labels did not lead to an increase in negative emotional responses. This suggests that while the labels successfully shifted food choices, they did not cross a line into psychological harm. The researchers did note that their study used hypothetical choices without real money involved, and the labels did not include calorie counts in most scenarios, which limits how perfectly the results predict real-world shopping. However, the consistency of the findings across two large groups suggests that warning labels could be a powerful tool for improving public health without the feared psychological cost.

Ultimately, the research points toward a potential shift in how food is labeled in the UK. The evidence indicates that mandatory warning labels could reduce the selection of unhealthy foods more effectively than the current voluntary traffic light system. While the public may currently prefer the familiar color codes, the data suggests that the simpler, more direct warnings are better at achieving the goal of healthier eating. The study concludes that the government should consider moving toward a mandatory warning label strategy, or at least significantly improving the current system, to better support the population in making healthier choices without causing emotional harm.