The administration of L. reuteri DSM 17938 for a duration of 12 weeks did not result in any significant changes in HbA1c levels among individuals with T2DM who were undergoing insulin treatment. Nevertheless, the impact of L. reuteri on the insulin response was observed to be significant only in a limited subset of individuals, leading us to hypothesize that this discrepancy could potentially be attributed to the diverse compositions of gut microbiota. The gene discussed is INS; the disease is type 2 diabetes mellitus.