In the last 50 years, there has been a dramatic rise in obesity and type-2 diabetes, while sperm quality in men has significantly declined.
Scientists have long suspected that one of the key reasons behind these troubling trends is the growing popularity of ultra-processed foods.
These are foods made with industrial ingredients that are often found in packaged snacks, fast food, ready meals, and sugary drinks.
Although previous research has linked these foods to poor health, it was unclear whether the danger came from the ingredients themselves, the way they are processed, or simply because they make people eat more.
But now, a new international study has provided clearer answers. Published in the journal Cell Metabolism, the study shows that ultra-processed foods harm health even when people eat the same number of calories as they do with healthier, less processed foods.
The findings also reveal that eating ultra-processed foods can introduce dangerous pollutants into the body, which affect hormone levels and sperm quality.
The study was led by Jessica Preston, who conducted the research during her PhD at the University of Copenhagen’s Center for Basic Metabolic Research.
According to her, the results prove that ultra-processed foods damage both reproductive and metabolic health—even when not eaten in large amounts. This means the problem lies in how the foods are made, not just how much people eat.
To test this, researchers studied 43 healthy men between the ages of 20 and 35. Each man followed two different diets for three weeks each, with a break of three months between them. One diet was based on unprocessed foods, while the other included mostly ultra-processed items.
The participants were not told which diet they were on. Some received the exact number of calories they needed, while others received 500 extra calories per day. Both diets had the same amount of protein, fat, and carbohydrates.
The results were striking. On the ultra-processed diet, the men gained an average of one kilogram (about 2.2 pounds) of body fat—regardless of how many calories they were given. Their markers for heart health also worsened during this period.
Even more alarming was what the researchers found in their blood. Men who ate the ultra-processed foods had much higher levels of a chemical called cxMINP.
This is a type of phthalate, a hormone-disrupting chemical commonly used in plastics. At the same time, these men showed lower levels of testosterone and follicle-stimulating hormone—both of which are crucial for producing healthy sperm.
Professor Romain Barrès, senior author of the study, said they were shocked by how many parts of the body were affected in just a few weeks, even in young, healthy men. He warned that the long-term impact of regularly eating ultra-processed foods could be very serious, especially as these foods are so common in many people’s daily diets.
This study is one of the clearest signs yet that ultra-processed foods are not just unhealthy because they make us eat more, but because their very makeup can harm our bodies in multiple ways. It calls for a serious rethink of food guidelines and public health policies to better protect people—especially young adults—from chronic illnesses linked to diet.
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The study is published in Cell Metabolism.
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