The Washington PostDemocracy Dies in Darkness

Traffic light diets label foods ‘red,’ ‘yellow’ and ‘green.’ That’s too black and white.


Traffic lights are useful for managing intersections — less so for making food choices. The traffic light diet and related food-labeling systems have gradually become more popular over the past several years, used in dieting apps, on food labels and in cafeterias. Even Google and the Army are on board. But the danger is that labeling foods as “green,” “yellow” or “red” won’t really help us become healthier eaters — just guiltier ones.

The original traffic light diet was developed in the 1970s for use in pediatric weight-loss research. It’s largely based on calories: Green foods are low in calories, yellow foods are moderate and red foods are high. The system has been copied and adopted by weight-loss diet programs or apps for both adults and children, and it is widely used by pediatricians when advising patients and families.

California pediatrician Miriam Rhew learned the traffic light system during her residency in the 1990s; the rationale was that it was a simple model to use for kids. However, she stopped short of fully implementing it because “something bothered me about giving them a ‘go’ to eat certain foods and a ‘stop’ for other foods.” ­Instead, she spoke with families in more general terms about which foods to limit, which to eat freely and which to eat in moderation. Sort of a traffic light system, but without the lights.

One concern about calorie-based traffic light labels is that they label all calorie-dense foods — foods that have a lot of calories in a small volume, often because of fat or sugar content — as “red,” ignoring that some calorie-dense foods are more nutritious than others. For example, orange juice and orange soda may both be “red,” even though, unlike soda, orange juice contains natural sugar, not added sugar, and is also rich in antioxidants and other nutrients. Similarly, nuts and pepperoni may both be “red,” but unlike pepperoni, nuts contain healthy fats and fiber, along with many nutrients. Avoiding all “red” foods could limit users’ options for getting the nutrients people need.

“Lots of calorie-dense nutritious foods have nutrients that many people don’t eat at recommended levels,” said Michele Redmond, an Arizona-based registered dietitian and chef. For example, she said, nuts, seeds, tofu, avocados, eggs, cheese and fatty fish such as salmon, herring and mackerel — foods found often on “red” lists, sometimes on “yellow” lists and rarely on “green” lists — contribute under-consumed nutrients such as vitamins A, C, D and E, calcium, potassium, fiber, magnesium and choline. “A low-sugar, high-fiber granola bar with chia seeds and nuts may end up with a red flag.”

Even worse, the “rules” about what makes a food green, yellow or red — or to what degree red foods should be limited — are not consistent. For example, on one family-oriented website, one blog post encourages parents to remove red foods from their homes, while another recommends including some red foods each week and explains the difference between “healthy” and “unhealthy” red foods. Nuts are tagged as one of the “healthy” red choices, which contradicts a downloadable traffic light work sheet that lists nuts as a yellow food.

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A version of traffic light labeling used in the United Kingdom and Australia has more of a public health bent because it was designed to help steer people away from foods high in saturated fat and added sugar. Traffic light lists published by the Australian Department of Health and Human Services put plain nuts and seeds and all fish in the green category, with fruit juice and regular dairy foods in the yellow category. But some experts think even this form of traffic light labeling has a downside. “You can tell consumers a ‘red-light’ food isn’t forbidden, but they still may feel self-conscious about adding ‘red-light’ foods to their grocery cart,” Redmond said, adding that even if someone typically eats well, seeing “red” labels on food may create guilt and anxiety. “Our food culture is already vulnerable to dieting, and these overly simplified messages are diet-promoting.”

No matter what version of the “traffic light” you’re looking at, the larger question is: Does it help change behavior? While studies have generally found that traffic light labeling helps people identify healthier foods, what’s unclear is whether this labeling nudges people to make healthier choices. A 2016 systematic review highlighted the lack of high-quality randomized controlled trials ­using real-world settings.

The research that has been done has had mixed results. A study published in July found that traffic light labeling in a Boston hospital cafeteria was ­associated with fewer “red” food purchases and an overall reduction in calories, yet a 2011 study found that most people ate the same number of or more calories from a buffet that used traffic light food labeling, despite choosing more “green” foods and fewer “red” foods. In either case, here’s some food for thought: There’s no way to know how people who choose green and yellow food in cafeterias or buffets that use the traffic light system eat the rest of the day.

During the 2014-2015 school year, Harvard University implemented traffic light labeling in two student cafeterias, placed healthier foods and beverages in more visible and accessible locations in two others, and changed nothing in two cafeterias that served as a control group. Research showed that traffic light labeling helped students identify healthier choices and that most wanted it to continue; however, it did not lead to significant changes in choices. In another study, the labeling raised concerns among some students that traffic light labeling might contribute to eating disorders in susceptible people. This is no small issue, because rates of eating disorders worldwide doubled between 2000 and 2018. Traffic light systems pose a real risk of harm, with potentially little gain.

Rhew, the California pediatrician, said her thinking has evolved in her two decades of working in public health and pediatrics. She now realizes that restricting certain foods actually makes them more desirable to some people. “I also see that labeling foods as ‘red’ makes them ‘bad,’ which in turn makes the parents and child feel that they are ‘bad’ if they eat those things.”

Another shortcoming of traffic light labeling for children is that it makes choosing what to eat an external process that doesn’t help kids develop and trust their ability to choose healthy foods for themselves. “Rather than give them external mandates about what to eat and not eat, we need to provide them skills from the very beginning to learn when they are truly hungry, to choose foods that will nourish their bodies, and to enjoy eating.”

Dennett is a registered dietitian nutritionist and owner of Nutrition by Carrie.

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