Ultraprocessed diets raise fat gain and alter reproductive hormones in young men

An international randomized controlled trial published in the journal Cell Metabolism found that diets high in ultraprocessed foods caused young men to gain more fat and showed short-term changes in reproductive hormones and pollutant exposure, even when calorie and macronutrient content were matched. Researchers led by the University of Copenhagen enrolled 43 men aged 20 to 35 and compared three-week periods of primarily ultraprocessed and primarily unprocessed diets, with a three-month washout between the two feeding phases.

Participants were randomly assigned to start on one of the diets and were not told which they were eating. Both diet plans were matched for calories, protein, carbohydrates and fat. Half the men also consumed an extra 500 calories per day during each feeding period to test effects at both adequate and excess energy intakes. Despite the caloric matching, men gained roughly one kilogram more fat mass on the ultraprocessed diet than on the unprocessed diet, the authors reported.

Beyond weight and fat gain, the trial found several metabolic and reproductive signals associated with the ultraprocessed diet. Men showed reductions in testosterone and...