Ultra-Processed Foods Harm Metabolism and Hormones

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A controlled dietary intervention has shown that ultra-processed foods may harm cardiometabolic and reproductive health, even when consumed in quantities matched to unprocessed diets. The human study found participants gained fat mass and showed altered hormone levels after just three weeks of eating ultra-processed foods, pointing to the processing methods themselves as a key factor in driving these changes.

Ultra-processed foods

These are products made using industrial processes and ingredients not typically found in home kitchens. 

Industrial processing and health outcomes

Ultra-processed foods are defined by the Nova classification system as products that contain synthetic or industrial ingredients not typically used in home cooking. These include artificial flavorings, stabilizers and colorings, as well as ingredients derived through high-level industrial processing. Common examples include packaged snacks, soft drinks and ready-to-eat meals.

While the link between these foods and health conditions like obesity and type 2 diabetes is well established, it has remained unclear whether the health effects stem from the nature of the ingredients, the food processing methods or increased energy intake. In this new study, researchers aimed to isolate the role of processing.

Same calories, more fat mass

The study involved 43 healthy men aged 20–35 years, who consumed both ultra-processed and unprocessed diets in a randomized crossover design. Each diet period lasted three weeks and was separated by a three-month washout phase. Participants received meals with identical macronutrient content – equal amounts of protein, fat and carbohydrates – and the same number of calories. Half the group consumed a calorie-balanced diet, while the other half received an additional 500 calories per day.

Regardless of energy intake, participants gained approximately one kilogram more fat mass on the ultra-processed diet compared to the unprocessed diet. Several cardiovascular health markers were also negatively affected during the ultra-processed food phase.

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

Dr. Jessica Preston.

Hormone changes linked to food packaging contaminants

In addition to weight changes, the researchers found that the ultra-processed diet introduced elevated levels of a phthalate compound called cxMINP. This substance, commonly found in plastic food packaging, is known to act as an endocrine disruptor. Participants on the ultra-processed diet showed increased levels of cxMINP in their blood and a corresponding decrease in hormones critical for sperm production, including testosterone and follicle-stimulating hormone.

Phthalates

A group of chemical compounds used to make plastics more flexible.

Follicle-stimulating hormone (FSH)

A hormone involved in reproductive processes. In men, FSH supports sperm production by stimulating the testes.

“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.”

Dr. Romain Barrès.

The study, conducted by a team at the University of Copenhagen’s NNF Center for Basic Metabolic Research and the Université Côte d’Azur, indicates that even without excessive caloric intake, ultra-processed foods may pose metabolic and reproductive risks.

Reference: Preston JM, Iversen J, Hufnagel A, et al. Effect of ultra-processed food consumption on male reproductive and metabolic health. Cell Metab. 2025:S1550413125003602. doi: 10.1016/j.cmet.2025.08.004

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