In the mid-1990s, Carlos Monteiro, a Brazilian nutritional public health researcher, noticed the alarming rapid rise in obesity rates among Brazilian children.
To understand why, he and colleagues at the University of São Paulo scoured data on the food purchasing patterns of Brazilian households to see if they had changed in recent years. Researchers found that people are buying less staple foods such as sugar, salt, cooking oil, and rice and beans, and more processed foods such as soda, sausages, instant noodles, and packaged bread and cookies. discovered.
To describe this second category of foods, the research team came up with a new term: ultra-processed foods (UPFs). This would later be associated with weight gain in Brazilian children and adults.
Since then, scientists have discovered links between UPF and a variety of health conditions, including heart disease, type 2 diabetes, obesity, gastrointestinal disease, depression, and even premature death.
Experts say this is concerning because ultra-processed foods make up a major part of people’s diets around the world. For example, he accounts for 67% of the calories consumed by children and teenagers in the United States.
However, many questions remain. What exactly are ultra-processed foods? And how strong is the evidence that they’re harmful? We asked experts to answer these questions and more.
What are ultra-processed foods?
To study foods based on processing methods, Monteiro and his colleagues developed a food classification system called Nova, named after the Portuguese and Latin word for “new.” It has since been adopted by researchers around the world.
The Nova system classifies foods into four categories.
— Unprocessed or minimally processed foodsFresh or frozen fruits and vegetables, beans, lentils, meat, poultry, fish, eggs, milk, plain yogurt, rice, pasta, cornmeal, flour, coffee, tea, herbs, spices, and more.
— processed ingredientscooking oil, butter, sugar, honey, vinegar, salt, etc.
— processed food Foods made by combining Category 1 foods and Category 2 ingredients and preserving or processing them using relatively simple methods such as canning, bottling, fermentation, and baking. This group includes fresh bread, most cheeses, canned vegetables, beans, and fish. These foods may contain preservatives that extend their shelf life.
— ultra-processed foods It’s made using industrial methods and ingredients you won’t find in your typical grocery store, including high fructose corn syrup, hydrogenated oils, and concentrated proteins like soy isolate. Additives such as flavorings, colorants, and emulsifiers are often included to make them more appealing and palatable. Carbonated and energy drinks, potato chips, candy, flavored yogurt, margarine, chicken nuggets, hot dogs, sausages, lunch meats, boxed macaroni and cheese, infant formula and most packaged breads, plant-based milks, meat substitutes, and breakfast foods. Think about something like cereal.
“If you look at the ingredient list and see something you wouldn’t use in a home-cooked meal, it’s probably an ultra-processed food,” said Brenda Davey, a nutrition professor at Virginia Tech.
Note that the Nova system does not classify foods based on nutrients such as fat, fiber, vitamins, and minerals. It’s “nutrition agnostic,” said Maya Badibello, an associate professor of nutrition at the University of Rhode Island.
For this reason, many UPF foods, such as whole-grain breads, flavored yogurts, and infant formulas, can provide valuable nutrients, and there is some debate among nutrition experts as to whether this helps explain the health status of foods. There is controversy, Badibello said.
Are ultra-processed foods harmful?
Most studies linking UPF to poor health are based on observational studies, in which researchers ask people about their diet and track their health over many years. In a large review of studies published in 2024, scientists found that UPF intake was associated with 32 health problems, including heart disease-related deaths, type 2 diabetes, anxiety and depression. showed the most convincing evidence for common mental health problems such as
Studies like this are valuable because they can examine large groups of people over the many years it takes for chronic health conditions to develop, said Josiemar Mattei, associate professor of nutrition. Harvard University TH Chan School of Public Health. She added that the consistent association between UPF and health problems increases confidence that there is a real problem with food.
But observational studies also have limitations, said Lauren O’Connor, a nutrition scientist and public health researcher who previously worked at the Department of Agriculture and the National Institutes of Health. While it’s true that there is a correlation between these foods and chronic disease, that doesn’t mean UPF directly causes poor health, she said.
Mr O’Connor questioned whether it would be helpful to group such “disparate” foods, such as Twinkies and breakfast cereals, into one category. Certain types of ultra-processed foods, such as soda and processed meat, are clearly more harmful than others. On the other hand, his UPF, such as flavored yogurt and whole grain bread, is associated with a lower risk of developing type 2 diabetes.
O’Connor said clinical trials are needed to test whether UPF directly causes health problems. Only one such study has been conducted to date, she said, although it was small and had some limitations.
In that study, published in 2019, 20 adults of various sizes lived for four weeks at a National Institutes of Health research hospital. For two weeks, they ate primarily unprocessed or minimally processed foods, and for an additional two weeks they ate primarily UPF. Each meal had similar calories and nutrients, and participants could eat as much as they wanted at each meal.
During the two weeks on the ultra-processed diet, participants gained an average of 2 pounds and ate about 500 more calories per day than when they ate an unprocessed diet. During the period on the unprocessed diet, they lost about 2 pounds.
Kevin Hall, a nutrition and metabolism researcher at the National Institutes of Health who led the study, said the findings may help explain the link between UPF, obesity, and other metabolic conditions. But the study needs to be replicated, and Hall is currently working on that.
Why can UPFS be harmful?
Hall said there are many “strong opinions” about why ultra-processed foods are bad for health. “But there’s actually not a lot of hard science on what those mechanisms are,” he added.
UPF is often cheap, convenient and readily available, so it’s likely replacing healthier foods in our diets, Hall said.
But he and other scientists believe that food may have a more direct effect on health. It’s easy to overeat, perhaps because they contain an irresistible combination of carbohydrates, sugar, fat, and salt, are high in calories, and are easy to chew. Also, the resulting spike in blood sugar levels can damage arteries and worsen inflammation, and certain food additives and chemicals can interfere with hormones, causing the intestines to become “leaky” or It may also destroy the internal microbiome.
Researchers including Hall and Davey have begun conducting small clinical trials to test some of these theories. Such research could help identify the most harmful UPFs and even suggest ways to make them healthier, Hall said.
Most researchers believe there are many different ways that foods can cause harm. “In nutrition, there is rarely a single factor that completely explains the relationship between food and health outcomes,” Badibello says.
What should we do about ultra-processed foods?
In 2014, Monteiro helped create new Brazilian dietary guidelines that encourage people to avoid ultra-processed foods.
Other countries, such as Mexico, Israel, and Canada, also explicitly recommend avoiding or limiting UPF or “highly processed foods.” Although the U.S. Dietary Guidelines do not include such advice, an advisory committee is currently examining the evidence on how UPF affects weight gain, which could influence the 2025 guidelines. It is possible to give
Hall said it’s difficult to know what to do about UPF because so much food in the U.S. is already ultra-processed and low-income populations in particular may be reliant on it. .
“After all, they are an important food source and food is food,” Mattei added. “We can’t really denigrate them,” she said.
Although research continues, experts are divided on how to approach UPF. Monteiro says the safest method is to avoid them altogether, which means swapping out flavored yogurt for plain yogurt with fruit, for example, or, if you can afford it, buying a local bakery instead of packaged bread. He said to buy freshly baked bread.
Vadiveloo suggested a more moderate strategy that focuses on limiting UPF, such as soda and cookies, which don’t provide valuable nutrients. She also recommended eating more fruits, vegetables, whole grains (ultra-processed or not), legumes, nuts, and seeds.
Minimize processed foods and cook at home as much as possible, says Davey. “I can’t say much more than that at this point.”
This article was originally published in The New York Times.
