Overview

• Researchers tested 43 men in a within-person 2×2 crossover, feeding each participant three weeks of unprocessed and ultra-processed diets with a 12-week washout, while matching calories and macronutrients.
• Participants accrued about 1 kg more fat mass on the ultra-processed plan, with weight gain seen in both adequate- and excess-calorie arms.
• Reproductive markers shifted, with follicle-stimulating hormone decreasing in the excess-calorie arm and testosterone trending lower in the adequate-calorie arm.
• The phthalate metabolite cxMINP rose during the ultra-processed phase, and cardiometabolic changes included a higher LDL:HDL ratio in the adequate-calorie arm and higher diastolic blood pressure in the excess-calorie arm.
• Study authors argued processing itself likely drives harm and urged updates to nutrition guidance, while noting limits from the short, male-only trial.