Ultra-processed foods harm reproductive and metabolic health in men, study shows

A tightly controlled human trial has found that ultra-processed foods can increase body fat and disrupt hormone levels even when calorie intake is identical to that of unprocessed meals.

The research, conducted at the University of Copenhagen’s NNF Centre for Basic Metabolic Research, revealed that young men consuming ultra-processed diets gained around one kilogram more fat mass than when eating minimally processed foods. The findings suggest that it is not only the calorie content but the processed nature of these foods that may contribute to long-term health risks.

The study, published in Cell Metabolism, also identified elevated levels of phthalates, plastic-derived chemicals known to interfere with hormone function, in participants on the ultra-processed diet. At the same time, levels of testosterone and follicle-stimulating hormone, both crucial for sperm production and fertility, declined.

Rates of obesity and type 2 diabetes have risen sharply over the past half century, while average sperm quality has fallen. Scientists have long suspected that the growing prevalence of ultra-processed foods plays a role, but debate has continued over whether the harm arises from additives, industrial processing methods, or simply the tendency of such foods to encourage overeating.

The trial involved 43 healthy men aged 20 to 35. Each participant spent three weeks on a diet of ultra-processed foods and three weeks on a diet of unprocessed meals, separated by a three-month break. The two diets were matched for calories, protein, carbohydrate and fat content.

Despite these controls, participants gained significantly more fat mass while consuming ultra-processed foods, regardless of whether they were eating a maintenance diet or one with an additional 500 daily calories. Several cardiovascular risk markers were also affected.

The researchers reported a marked rise in the phthalate cxMINP among participants on the ultra-processed diet. Declines in key reproductive hormones raised further concern about possible links between dietary processing, fertility and wider metabolic health.

Jessica Preston, lead author of the study, said: “Our results demonstrate that ultra-processed foods harm reproductive and metabolic health, even when consumed in moderation. This indicates that the processing itself is what makes these foods harmful.”

Senior author Professor Romain Barrès added: “We were struck by how many body functions were affected in otherwise healthy young men. The long-term implications are deeply concerning and highlight the need to revise nutritional guidelines to protect against chronic disease.”

The findings come at a time of mounting concern over rising obesity rates and associated health conditions, as well as ongoing evidence of a global decline in male fertility.