Ultra-processed foods disrupt a shocking number of body functions

In the last 50 years, our eating habits have dramatically shifted. More people are living with excess weight and type 2 diabetes, men’s sperm quality has declined, and ultra-processed foods have come to dominate supermarket shelves.

The big question is whether the danger comes from the calories, the strange industrial ingredients, or the way processing itself changes food. A new study points straight at processing as the real problem.

Same calories, worse results

The researchers ran a strict experiment with 43 young men. The participants followed two diets – ultra-processed and unprocessed – for three weeks each, with a break in between.

Meals were matched for calories, protein, fat, and carbs. Some men ate just enough for their bodies, while others got 500 extra calories.

The results were striking. Men eating ultra-processed foods gained about a kilogram (2.2 pounds) more fat than when they ate unprocessed meals. This occurred whether they ate normal or excess calories. Their cholesterol and blood pressure also shifted in unhealthy directions.

Jessica Preston conducted the study while pursuing a PhD at the University of Copenhagen’s NNF Center for Basic Metabolic Research (CBMR).

“Our results prove that ultra-processed foods harm our reproductive and metabolic health, even if they’re not eaten in excess,” said Preston. “This indicates that it is the processed nature of these foods that makes them harmful.”

Processed foods and health effects

The ultra-processed diet didn’t just add fat. It threw hormones off balance. Testosterone dipped, follicle-stimulating hormone fell, and sperm motility showed signs of decline. These changes hit key systems that regulate fertility.

Other hormones shifted too. Growth/differentiation factor 15, linked to metabolism, went down. Leptin, which signals satiety, went up. These shifts hint that processed diets alter how the body regulates weight, even when people don’t overeat.

Over time, such disruptions can weaken reproductive capacity, confuse hunger cues, and increase fat storage. Together, these hormonal changes paint a picture of how processed diets slowly rewire core biological systems, raising the risk of long-term metabolic and reproductive health problems.

Hidden pollutants in foods

The men’s blood also carried more pollutants after the processed diet. Levels of phthalates, chemicals from plastic packaging, went up. These are known to interfere with hormones. At the same time, lithium, a trace element that influences mood, dropped.

Researchers also saw changes in other industrial compounds, including perfluorinated chemicals. Some of these were connected to altered thyroid hormones and cholesterol. The food wasn’t just calories – it was a chemical delivery system.

With every bite, participants ingested substances their bodies never needed, silently building up in blood and tissues. Such exposures may explain why processed diets link not only to obesity, but also to fertility problems, mood changes, and chronic disease risk over time.

Unexpected rise of inflammation

Switching to an unprocessed diet improved many health markers, but it also caused a brief rise in inflammation. Scientists think this may have occurred because participants were used to eating large amounts of processed food, and the sudden switch shocked their systems.

Mental health effects also appeared. Depression scores edged upward for some men on the ultra-processed diet, though anxiety and stress stayed about the same.

Romain Barrès is a professor at the University of Copenhagen’s NNF Center for Basic Metabolic Research and the Université Côte d’Azur.

“We were shocked by how many body functions were disrupted by ultra-processed foods, even in healthy young men,” he said. “The long-term implications are alarming and highlight the need to revise nutritional guidelines to better protect against chronic disease.”

Processed food harms health

The study makes it clear that the problem with ultra-processed foods isn’t just overeating. Even when people consume the same number of calories as an unprocessed diet, their bodies respond differently.

Hormones that regulate fertility and metabolism become unbalanced, pollutants from packaging and additives accumulate, sperm quality declines, and fat mass increases. These changes happen regardless of whether someone is eating in moderation or in excess, showing that processing itself drives the harm.

Ultra-processed foods are hard to avoid. They show up as packaged snacks, instant noodles, sweetened breakfast cereals, frozen meals, and processed meats.

They dominate many diets because they are cheap, tasty, and convenient. But the evidence now reveals that their risks go far beyond the idea of “junk calories.”

Ultra-processed foods alter body chemistry, weaken reproductive health, and quietly push the body toward chronic disease. This makes the shift to less-processed foods more than just a lifestyle choice – it is a step toward long-term health protection.

The study is published in the journal Cell Metabolism.

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