For decades, the rising tide of obesity, diabetes, and declining sperm counts has puzzled doctors. Something in our modern world, it seemed, was fundamentally messing with our health. A new study offers a striking answer—and it may be hiding in your pantry.
In a meticulously controlled trial, scientists from the University of Copenhagen and international partners found that ultra-processed foods—regardless of calorie content—disrupted hormone levels, increased body fat, and introduced pollutants linked to poor sperm quality.
The findings, published last week in Cell Metabolism, deliver some of the most direct evidence yet that it’s not just how much we eat that matters—but what our food is made of, and how it’s made.
“Our results prove that ultra-processed foods harm our reproductive and metabolic health, even if they’re not eaten in excess,” said Jessica Preston, lead author of the study. “This indicates that it is the processed nature of these foods that makes them harmful.”
Same Calories, Different Outcomes
The researchers recruited 43 healthy men between the ages of 20 and 35. Each participant followed two tightly controlled diets—one rich in ultra-processed foods and one based on unprocessed ingredients—for three weeks each, with a 12-week washout period in between.
Crucially, both diets were matched for calories, macronutrients, and even protein, fat, and carbohydrate composition. Some participants received a normal caloric load; others received 500 extra calories per day to simulate overconsumption.
But even under these tightly matched conditions, the ultra-processed diet stood out for all the wrong reasons.
Men gained significantly more fat mass (about 1 kg) on the ultra-processed diet, whether or not they were overeating. Markers of metabolic health also worsened. Participants had increased cholesterol levels, higher LDL:HDL ratios, and a spike in diastolic blood pressure.
Senior author Romain Barrès suggests these weren’t just random fluctuations. “We were shocked by how many body functions were disrupted by ultra-processed foods, even in healthy young men. The long-term implications are alarming and highlight the need to revise nutritional guidelines to better protect against chronic disease.”
Hormonal Earthquake Served on a Plate
Beyond weight gain and cholesterol, the ultra-processed diet altered several hormones involved in metabolism and reproduction.
Follicle-stimulating hormone (FSH), essential for sperm production, dropped in participants on the ultra-processed diet. Testosterone levels trended lower. And total sperm motility—a key metric for male fertility—declined.
At the same time, blood samples revealed a disturbing rise in phthalates, specifically a compound called cxMINP, a metabolite of the plasticizer diisononyl phthalate (DINP). Manufacturers often use these chemicals in packaging, and scientists classify them as endocrine disruptors.
“The presence of cxMINP in higher levels after ultra-processed food consumption suggests that contaminants from packaging or processing may be leaching into the food supply,” the researchers wrote.
Lithium and mercury—elements that play roles in brain and reproductive function—also declined in the blood and semen of participants on the ultra-processed diet. Though the long-term consequences of such changes remain unclear, the authors note that trace elements and hormone-disrupting pollutants are likely underestimated in these kinds of studies, due to the relatively clean nature of the experimental diets compared to participants’ usual eating habits.
What Makes a Food “Ultra-Processed”?
The study used the NOVA classification, a widely accepted system that ranks foods by their degree of processing. Ultra-processed foods (NOVA Group 4) include items made primarily from industrial formulations—think extruded snacks, frozen meals, soft drinks, and shelf-stable baked goods.
These foods often include ingredients rarely found in home kitchens, like hydrolyzed proteins, maltodextrins, artificial flavorings, and stabilizers. They are engineered for convenience, long shelf life, and irresistible flavor.
But at what cost?
In the ultra-processed diet used in this study, over 77% of calories came from NOVA 4 foods. In contrast, the unprocessed diet drew 66% of calories from whole foods, including fresh fruits, vegetables, meats, and legumes.
Both diets were delivered to participants’ homes, pre-portioned and ready to eat. The scientists monitored compliance with daily food diaries and questionnaires, ensuring the only variable was the nature of the food itself.
Why Does This Matter?
Ultra-processed foods have long been associated with poor health outcomes, such as higher risks of obesity, heart disease, cancer, and depression. But critics have often argued that these effects could be the result of overeating, not the food itself.
This study, however, eliminates that excuse.
By controlling for calories and macronutrients, the researchers isolated the effect of food processing. What they found is that even when people eat the same number of calories, the body responds very differently depending on how those calories are delivered.
Ultra-processed diets led to greater fat gain, altered hormone levels, and changes in markers of inflammation and pollutant accumulation—even without excess calories.
A Call for Change?
Sperm counts have dropped by more than 50% since the 1970s, a trend documented across continents. At the same time, diets in countries like the U.S., U.K., and Australia have shifted dramatically: over half of daily calories now come from ultra-processed foods.
The new study does not prove that processed foods alone are to blame for global fertility declines. But it strengthens a growing body of evidence that they may play a key role.
The authors note that they limited their trial to three-week interventions. They have yet to determine whether the damage accumulates or normalizes over time.
Still, the study provides a rare and controlled glimpse into the physiological cost of modern eating habits. And for many researchers, it tips the scales.
The implications are wide-ranging. If the structure of our food—not just the nutrients—alters how we store fat, regulate hormones, and reproduce, then public health strategies may need a dramatic overhaul.
Nutrition labels focusing solely on calories and fat content may be missing the bigger picture. And for consumers trying to navigate the supermarket aisle, it raises a thorny question: How much of what we’re eating is food—and how much is product?
