A small but rigorous study just published in Cell Metabolism (Preston 2025) has shown that a diet of ultra-processed foods caused an increase in fat gain, along with concerning effects on reproductive hormones in men, compared to when they ate a diet of unprocessed foods. This clinical trial also compared adequate versus excessive calories provided by the diets. This effect was the same no matter how many calories the diets had, so the extra fat was due to some factor specific to the ultra-processed food. What that might be is unknown, but it is concerning.