Researchers are getting closer to solving the riddle of how ultra-processed foods (UPFs) harm metabolic, reproductive, and immune health in ways that can’t be explained by calories or poor nutrient profile alone, according to a new scientific report.

The answer may lie not just in what these foods contain, but in how companies manufacture them to maximize profits and how they interact with the body, says the report published this month by Dr. Mathilde Touvier in Nature Reviews Endocrinology. It suggests UPFs may exert harm in multiple ways beyond their nutritional profile. 

Salty snacks and sugary foods are designed to replace lower-calorie meals that could have included fruits, vegetables, meats and other whole foods. But they also alter natural ingredients to promote addiction and overconsumption, and introduce chemical additives and contaminants that migrate from packaging into food. 

Ultra-processed breakfast cereal, for example, is typically made with refined grains along with sugar and other additives that make it higher in calories and less nutritious. A minimally processed whole-grain cereal is simply cleaned, rolled or toasted and packaged with little or no added ingredients.

“UPF consumption leads to an average caloric excess and contributes to displacing the consumption of nutritionally healthy foods,” Touvier wrote. “These factors are among the possible explanations for the effects of UPF on health, but they do not explain their whole impact….”

A large meta-analysis in Nature Food, also published this month, echoes that conclusion. It found UPF-heavy diets are displacing traditional eating patterns worldwide, eroding diet quality, and raising the risk of multiple chronic conditions through diverse biological mechanisms. 

Notably, those researchers say, the magnitude of risk is comparable—though in the opposite direction—to the protective effects associated with Mediterranean-style diets. Taken together, the findings contribute to mounting evidence that diet-related disease, driven by ultra-processed foods and profit-seeking industries, is a public health threat.

A turning point in ultra-processed food research? 

Ultra-processed foods and beverages are typically manufactured in factories, often containing artificial dyes, sweeteners, emulsifiers, preservatives and other additives to enhance flavor, texture, color, and shelf life. Common examples include packaged snacks, candy, fast food, sweetened drinks and ready-to-eat meals high in sugar, unhealthy fats, salt, and additives, and low in essential nutrients.

For years, researchers have been puzzled by studies showing that UPFs were linked to harmful biological effects such as obesity, diabetes, heart disease, infertility, and immune dysfunction and shortened lifespan, even when people consumed the same number of calories as those eating minimally processed diets. This year [2025] marked a turning point, the report shows, as multiple lines of evidence began to explain why those harms occur.

UPF manufacturing often involves breaking apart and reassembling whole foods in ways that can change how quickly they are eaten and how nutrients are absorbed. They are also typically pre-packaged and stored for weeks, months, or even years (and sometimes heated or reheated in their containers), which allows packaging chemicals to migrate into food.

Many UPFs are deliberately designed to be hyper-palatable and habit-forming, even addictive, hijacking reward pathways in the brain. They also pose health risks due to food additives and packaging chemicals that interact with the human body in ways only now being rigorously studied, Touvier says.

Another possible reason ultra-processed foods may harm health is the additives they contain. For years, these additives were not thought to significantly affect metabolism, chronic disease risk, or gut bacteria in people. But research from the past five years suggests that some additives can, in fact, influence all of these, according to the report.

Touvier draws on a range of well-conducted, large-scale studies on long-term health outcomes, short-term randomized controlled trials (RCTs), and laboratory experiments in animals, people or lab-grown cells to show how these harms may unfold. They include:

• A landmark RCT found that diets high in ultra-processed foods impaired cardiometabolic and reproductive health “regardless of excessive caloric intake.” Healthy young men assigned to a UPF-heavy diet gained weight, experienced worsening cholesterol profiles, and had lower-than-normal levels of hormones involved in energy use and sperm production. 
• Researchers also observed reduced sperm movement, hormonal disruptions, and elevated blood levels of a phthalate breakdown product, suggesting the adverse effects of packaging chemical exposure alongside diet. Participants also had lower-than-normal levels of lithium, a mineral essential for proper brain function, circulating in the bloodstream.
• Another study showed evidence of changes in the body’s microbes across generations of mice and higher type 2 diabetes risk linked to emulsifiers, which are commonly consumed substances used to keep foods blended.
• A third study showed that 18- to 21-year-olds consumed more and ate when not hungry after just two weeks of exposure to ultra-processed diets, suggesting adolescence may be a particularly sensitive period for developing addictive-like eating behaviors that raise long-term disease risk.

Regulatory blind spot: Additive mixtures, long-term effects

For decades, UPF manufacturers, including several major food brands once owned by the world’s largest tobacco companies, have fueled global consumption. They have also downplayed health concerns, using marketing, lobbying and political strategies to expand sales and resist regulation.

Meanwhile, regulators such as the European Food Safety Authority (EFSA) and the U.S. Food and Drug Administration (FDA) have relied largely on safety tests designed decades ago. These assessments, with industry-led studies and metrics, focus on short-term toxicity and typically evaluate additives one at a time, rather than evaluating their long-term effects or how they behave in real-world mixtures.

The report highlights this regulatory blind spot as increasingly incompatible with emerging science. For example, a large prospective cohort study of 108,643 adults linked two common additive combinations—not individual additives—to a higher incidence of type 2 diabetes. A 2025 laboratory study similarly found that mixtures of additives caused toxic effects in human colon, liver, kidney, and neuron cell models that were not observed when substances were tested alone.

“So far, safety assessments of food additives have been performed substance by substance, while mixtures of additives are consumed daily by billions of people worldwide,” Touvier wrote.

Stronger actions to protect public health are needed, she says. Earlier this month, San Francisco filed the first government lawsuit against major UPF producers. More than 100 state-level bills proposing restrictions or bans on certain food ingredients were introduced across the United States in 2025.

Other steps should combine education, dietary recommendations, and clearer food labeling. Also needed are tighter marketing regulations and fiscal policies designed to make minimally processed, nutritionally healthy, and sustainable foods affordable and accessible to everyone, Touvier says: “Existing evidence is sufficiently strong to warrant immediate public health actions to lower UPF exposure.”

Reference

Touvier, M. Health effects of ultra-processed food: uncovering causal mechanisms. Nat Rev Endocrinol (2025). https://doi.org/10.1038/s41574-025-01218-5