Health killer or exaggerated risk: Do you know “ultra-processed food”?

In the mid-1990s, Brazilian nutritional epidemiologist Carlos Monteiro noticed a worrying problem: obesity rates among Brazilian children were rising rapidly.

To find out why, he and colleagues at the University of São Paulo pored through data on Brazilian household food purchasing patterns to see if they had changed in recent years. The researchers found that people were buying less sugar, salt, cooking oil and staples like rice and beans, and more processed foods like soda, sausages, instant noodles, packaged bread and cookies.

To describe the second category of foods, the team introduced a new term into the scientific literature, ultra-processed foods (UPF), and defined it, Monteiro said. They then linked ultra-processed foods to weight gain in Brazilian children and adults .

Since then, scientists have found links between ultra-processed foods and a host of health problems , including heart disease, type 2 diabetes, obesity, gastrointestinal disorders and depression, as well as premature death.

Experts say this is concerning because ultra-processed foods have become a large part of diets around the world . For example, they make up 

67% of the calories consumed by children and teenagers in the United States .But many questions remain. What exactly are ultra-processed foods? And how strong is the evidence that they’re harmful? We asked the experts to answer these and other questions.

 What are ultra-processed foods?To study foods based on how they are processed, Monteiro and his colleagues developed a food classification system called NOVA, which means “new” in Portuguese and Latin, and has since been adopted by researchers around the world.The NOVA 

system divides foods into four categories :Unprocessed  

or minimally processed foods , such as fresh or frozen fruits and vegetables, beans, lentils, meat, poultry, fish, eggs, milk, plain yogurt, rice, pasta, cornmeal, flour, coffee, tea, spices.

cooking ingredients such as cooking oil, butter, sugar, honey, vinegar and salt.

Processed  foods are a combination of the previous two categories of food that have been preserved or modified using relatively simple methods, such as canning, bottling, fermenting, and baking. This category includes freshly baked bread, most cheeses, and canned vegetables, beans, and fish. These foods have a very long shelf life.

Ultra –  processed foods are made using industrial methods and ingredients you don’t usually find in grocery stores, such as high-fructose corn syrup, hydrogenated oils, and protein concentrates like soy protein isolate. They often include additives like flavorings, colors, or emulsifiers to make them look and taste more appealing. Examples include soda 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, vegetarian meats, and breakfast cereals.“If you look at the ingredient list and see something you wouldn’t use in a home-cooked meal, that’s probably an ultra-processed food,” said Brenda Dawe, a nutrition professor at Virginia Tech.

Notably, the NOVA system doesn’t classify foods by nutrient content, such as fat, fiber, vitamins or minerals. It’s “nutrient-agnostic,” says Maya Vadivelu, an associate professor of nutrition at the University of Rhode Island.

Nutrition experts have therefore debated whether the system can be used to describe a food’s healthfulness , Wadiwelu said, in part because many ultra-processed foods — such as whole-wheat bread, flavored yogurt and infant formula — can provide valuable nutrients.

Are ultra-processed foods harmful?

Most of the studies linking ultra-processed foods to poor health have been observational, with researchers asking people about their diets over several years and then tracking their health. In a large review of studies published in 2024 , scientists said ultra-processed food intake was associated with 32 health problems, with the strongest evidence for heart disease-related deaths, type 2 diabetes and common mental health problems such as anxiety and depression .Such studies are valuable because they cover large populations — the 2024 review includes results from nearly 10 million people — and over many years, allowing the development of chronic health problems to be observed, said Yossimel Mattei, an associate professor of nutrition at the Harvard T.H. Chan School of Public Health. She also said the consistency of the association between ultra-processed foods and health problems reinforces her belief that they are problematic.But Lauren O’Connor, a nutrition scientist and epidemiologist who previously worked at the Department of Agriculture and the National Institutes of Health, said observational studies have limitations. She said there is a link between these foods and chronic diseases, but that doesn’t mean ultra-processed foods directly cause health problems.

O’Connor believes that lumping such “distinct” foods like Twinkies and breakfast cereals together may not be beneficial. Some ultra-processed foods, such as soda and processed meat , are more harmful than others. However, ultra-processed foods such as flavored yogurt and whole-wheat bread are associated with a lower risk of type 2 diabetes.O’Connor said that to definitively determine whether ultra-processed foods directly cause health problems, clinical trials are needed. She said there is only one such study, and it was small and had some flaws.

In the study, published in 2019, 20 adults of various sizes spent four weeks at a National Institutes of Health research hospital. For two weeks, they ate mostly unprocessed or minimally processed foods, and for the other two weeks, they ate mostly ultra-processed foods. The two diets were similar in calories and nutrition, and the participants could eat as much or as little of the food as they wanted.During the two weeks on the ultra-processed diet, the participants gained an average of nearly a kilogram (1.25 lb) in weight and consumed about 500 more calories per day than during the two weeks on the unprocessed diet, during which they lost about a kilogram (1.25 lb).The findings may help explain the link between ultra-processed foods and obesity and other metabolic problems, said Kevin Hall, a nutrition and metabolism researcher at the National Institutes of Health who led the trial. But the findings need to be replicated, which Hall is doing.

Why Ultra-Processed Foods Might Be HarmfulHall said there are a lot of “violent arguments” about why ultra-processed foods are unhealthy. But “there’s not really a lot of rigorous scientific basis for the exact mechanism,” he said.

Because ultra-processed foods tend to be cheap, convenient and readily available, they may be replacing relatively healthful foods in our diets , Hall said.

But he and other scientists think such foods may have a more direct impact on our health. They are easy to overeat — perhaps because they contain an irresistible combination of carbohydrates, sugar, fat and salt , are high in calories and easy to chew. The resulting spike in blood sugar may damage arteries or increase inflammation , or certain food additives or chemicals may interfere with hormone levels, make the gut “leaky” or disrupt the gut flora. Researchers including Hall and Dawe are now conducting small clinical trials to test these hypotheses. Such studies could help identify the most harmful ultra-processed foods and even provide insights into how they might be made healthier, Hall says. Still, most researchers agree that foods cause harm in a variety of ways. “In nutrition, the relationship between food and certain health outcomes can rarely be explained by just one single factor,” Wadivelu says.

How should we treat ultra-processed foods?

In 2024, new Brazilian dietary guidelines co-authored by Monteiro recommended avoiding ultra-processed foods.

Other countries, such as Mexico , Israel and Canada , have also explicitly recommended avoiding or limiting the intake of ultra-processed or “very processed” foods. The U.S. dietary guidelines do not make similar recommendations, but an advisory committee is currently reviewing the evidence that ultra-processed foods cause weight gain , which may affect the 2025 version of the guidelines. Ultra-processed foods are a thorny issue in the United States because so many foods are already ultra-processed, and low-income people may be particularly dependent on such foods, Hall said.”At the end of the day these are important sources of food, and food is food,” Mathai agreed. “We can’t devalue them.”While the research is ongoing, and experts disagree on how to treat ultra-processed foods, Monteiro said the safest approach is to avoid them altogether — like replacing flavored yogurt with plain and fruit, or buying fresh bread from a local bakery instead of packaged bread, if your finances allow. Vadivelu offers a more moderate strategy, focusing on limiting ultra-processed foods that don’t provide valuable nutrients, such as soda and cookies. She also recommends eating more fruits, vegetables, whole grains (whether ultra-processed or not), legumes, nuts and seeds. Cook at home as much as possible and use as little processed food as possible, Dawe said. “Other than that, there’s not much else to say.”