A new study suggests that diets high in ultraprocessed foods may negatively affect not just overall metabolic health, but also male reproductive health. In their research published Thursday in the journal Cell Metabolism, scientists from the University of Copenhagen enrolled 43 healthy men, ages 20 to 35, and assigned them to alternating three-week diets: one rich in ultraprocessed foods and another featuring mostly unprocessed ingredients, with a three-month break between phases. All meals were provided to control calorie, protein, carb, and fat intake.
Despite matching calories across the two diets, men gained roughly 3 pounds and increased body fat when eating ultraprocessed foods, while also showing declines in sex hormones linked to fertility—specifically, lower levels of a follicle-stimulating hormone. They also showed trends toward reduced testosterone and sperm motility. The ultraprocessed diet also led to higher levels of the chemical cxMINP, a phthalate often found in plastics, which the authors suggest could contribute to the observed hormonal changes. "Calories from minimally processed foods and calories from ultra-processed foods are not equal, so to speak," study co-author Romain Barres tells the Washington Post. "They don't have the same consequences on our bodies."
The study also noted that men eating unprocessed diets had higher levels of lithium, seen as a positive (it helps regulate mood), but also slightly elevated mercury and PFAS chemicals, likely from seafood and cookware, respectively. Ultraprocessed foods—think chips and other packaged snacks, sugary cereals, and soft drinks—now make up more than half of Americans' daily calories. These foods are engineered with additives, refined grains, and little fiber, making them shelf stable and not as expensive, but also less nutritious.
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Marion Nestle, a nutrition expert not involved in the study, called the fertility findings "a big shocker," though she also pointed out the study's short duration and variability in individual responses. Study co-author Jessica Preston notes that their findings show "ultraprocessed foods harm our reproductive and metabolic health, even if they're not eaten in excess," per a release. "This indicates that it is the processed nature of these foods that makes them harmful."