This study examined how a beneficial bacteria called Escherichia coli Nissle 1917 combined with different types of sugar affects gut bacteria. Researchers found that the effectiveness of these treatments depends heavily on each person’s unique starting microbiota composition, which is shaped by their diet, lifestyle, and health status. The results show that one-size-fits-all probiotic treatments don’t work equally for everyone, and doctors should personalize treatments based on an individual’s existing gut bacteria profile.