The Processed Food Fight
Some researchers are targeting artificial foods as a leading public health problem. As with so many dietary issues, though, the evidence tells a more nuanced tale.
After decades of searching, many scientists believe they have finally pinned down the main problem with our modern diets—the factor driving ever-escalating rates of obesity, diabetes, heart disease and any number of other serious chronic conditions. The culprit isn’t saturated fats, trans fats or some new killer fat you haven’t of. It’s not cholesterol, carbs or sugars; dairy, gluten or meat. It isn’t a specific thing at all.
The problem, according to this increasingly popular argument, is that we’re eating lots of ultra-processed food or UPF. Traditionally, people used limited processing techniques such as cooking and pickling to preserve food or to make it more pleasant to eat. Modern food companies transform food much more extensively through techniques such as extrusion and molding, adding lab-derived components including flavorings, emulsifiers and preservatives. They use this additional processing to make foods that are cheaper, longer-lasting and more convenient.
“There’s a long, formal scientific definition, but it can be boiled down to this: If it’s wrapped in plastic and has at least one ingredient that you wouldn’t find in your kitchen, it’s UPF,” writes author and infectious disease doctor Chris van Tulleken in his recent, widely praised book, Ultra-Processed People: The Science Behind Food That Isn’t Food. These ultra-processed foods have come to represent a major part of people’s diets—a large majority in countries such as the United States, the United Kingdom and Canada. “We’ve started eating substances constructed from novel molecules and using processes never previously encountered in our evolutionary history, substances that can’t really even be called ‘food.’”
Many researchers and nutritionists say this shift has been a costly one. They point to a series of studies suggesting that ultra-processed food is a major driver of obesity, heart disease, cancer and even neurodegenerative conditions like Alzheimer’s. As the scientific evidence accumulates, some countries have responded by adopting public health policies to try to decrease the amount of ultra-processed food that people eat. The message has entered the popular media in increasingly alarming reports. “Ultra-processed food isn’t just bad for your health—it messes with your mind,” reported National Geographic in November. “What makes ultra-processed foods so bad for your health?” probed The Economist in August.
Although there is good research raising concerns about ultra-processed food, we should be hesitant to declare it the primary scourge of the modern diet. The case against ultra-processed food isn’t as solid as the headlines and public outcry would lead us to believe. The research connecting these processed foods to health problems has limitations, and there is contradictory evidence as well. This is a classic example of how research doesn’t speak for itself: It must always be interpreted, by people, in the context of other, often conflicting evidence. “Are there really studies that show that ultra-processed foods are unhealthy? It’s pushing very weak data to make a case,” says Gunter Kuhnle, a nutrition researcher at the University of Reading.
The field of nutrition has a long history of overreacting to contemporary research trends, and we risk making the same mistake now with processing. “We’ve had that issue in the past, as with low-fat recommendations” that later turned out to be counterproductive, says Duane Mellor, a dietitian at Aston University in England. “We’ve messed up too many times. We need to make smarter changes more carefully.” The evidence on ultra-processed food, as is often the case in science, refuses to yield simple, black-or-white answers.
The idea that distinctive modern foods cause distinctive modern health problems started gaining traction in the popular press and popular imagination.
The term “ultra-processed food” was introduced 15 years ago, when University of São Paulo physician, epidemiologist and nutritionist Carlos Monteiro published a short commentary in the journal Public Health Nutrition arguing that industrial foods were “hardly compatible with survival,” and that “diets that include a lot of ultra-processed foods are intrinsically nutritionally unbalanced and intrinsically harmful to health.”
Monteiro concluded by recommending the adoption of policies like those used to make alcohol and tobacco more expensive and less accessible. He and several colleagues soon created a food-categorization system called NOVA, with unprocessed or minimally processed food in group 1 and ultra-processed foods in group 3. (The system was later expanded to four groups.) UPFs were said to include a wide range of sweet, salty and fast foods such as soft drinks, chicken nuggets, ice cream, chips and cookies. It also encompassed products not usually thought of as junk food but made for convenience or with ingredients that are not used in home cooking, such as fruit yogurt, sliced bread, infant formula and breakfast cereal with low levels of added sugar.
Other researchers began using the NOVA categorization system to examine the potential health effects of ultra-processed food, comparing people who ate lots of ultra-processed food with those who ate more natural fare. A series of these studies found that UPFs were consistently associated with worse health outcomes.
A 2011 study in Guatemala found higher body-mass index and rates of obesity among people who ate more highly processed foods—a 10 percentage point increase in consumption of processed food translated to a 4.3% increase in BMI. A 2019 study of a group in the U.S. found a connection between eating ultra-processed food and experiencing metabolic disturbances such as high blood sugar and high blood pressure, conditions that increase the risk of obesity, diabetes and heart disease.
As more studies emerged, the idea that distinctive modern foods cause distinctive modern health problems started gaining traction in the popular press and popular imagination—and among many physicians as well. “Ultra-processed food feeds into this idea that everything was better in the past,” Kuhnle states. “On one side, you have the farmer going in the field. On the other side, you have smoking factories. And you can add that there is sort of this general distrust in people of science, of industry, of government.”
But there is one key, well-known limitation of this kind of retrospective research: Correlation does not prove causation. In these studies, people who ate lots of ultra-processed food were usually in worse health—not much worse, as in the case of smoking, but somewhat worse. That could be interpreted to mean that ultra-processed foods cause health problems, but there are other factors, or confounders, that could also explain the correlation. People who eat lots of processed food might have unhealthier lifestyles overall, which could explain why they have worse outcomes. People who listen to public health advice about eating fresh foods might also choose to walk up stairs rather than use the elevator, an increase in physical activity that might well not show up in research surveys. Researchers try to correct for these confounders, but different categories of people are too complicated to be perfectly statistically measured and compared.
A study of Spanish university students found that people who ate the most ultra-processed food were one-third more likely to develop depression over 10 years than people who ate the least.
Observational studies are also prone to an issue called reverse causality: Did diet soda make people gain weight, or did overweight people who wanted to shed some pounds start drinking diet soda? What’s more, there are major questions about how well people remember what they eat and therefore how accurately they can report it in observational studies. Some researchers say this kind of evidence doesn’t merit the boldface attention it often gets. “How this stuff gets published in The New England Journal of Medicine,” says
