Ultra-processed foods lead to weight gain, disrupt hormone levels, and introduce harmful substances linked to declining sperm quality, according to a study published in the journal Cell Metabolism.
Rates of obesity and type 2 diabetes have increased significantly in the past 50 years, while sperm quality has plummeted. These changes may be caused by eating more ultra-processed foods, which are linked with a series of poor health outcomes.
However, researchers don’t know what triggers these changes: the industrial nature of the ingredients, the processing of the foods, or simply overeating. Now, an international team of scientists has discovered that not all calories are the same: people gain more weight on an ultra-processed diet compared to a minimally processed diet, even when they eat the same number of calories. The study also showed that a diet rich in ultra-processed foods introduces higher levels of pollutants that affect sperm quality.
“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,” said Jessica Preston, lead author of the study, who carried out the research during her PhD at the University of Copenhagen’s NNF Center for Basic Metabolic Research (CBMR).
To compare the health impact of unprocessed and ultra-processed diets on the same person, the team recruited 43 men aged 20 to 35, who spent three weeks on each diet, with a three-month ‘washout’ in between. Half of the participants started on the ultra-processed diet, and the other half started on the unprocessed diet. Half of the men also received a high-calorie diet with an extra 500 daily calories. In contrast, half received the normal amount of calories for their size, age, and physical activity levels. Participants were not told which diet they were on. Both unprocessed and ultra-processed diets were identical in terms of calories, protein, carbs, and fats.
Results showed that men on the ultra-processed diet gained about 1 kg more fat than those on the unprocessed diet, regardless of whether they were on a regular or an excess calorie diet. Several markers of cardiovascular health were also affected. The authors also found a worrying increase in the level of the hormone-disrupting phthalate cxMINP, a substance used in plastics, on the ultra-processed diet. Men on this diet saw decreases in testosterone and follicle-stimulating hormone levels, which are crucial for sperm production.
“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,” said the study’s senior author, Professor Romain Barrès from the University of Copenhagen’s NNF Center for Basic Metabolic Research, and the Université Côte d’Azur.
Preston, Jessica M. et al. Effect of ultra-processed food consumption on male reproductive and metabolic health. Cell Metabolism, Volume 37, Issue 10, 1950 – 1960.e2