Effect of probiotics, Bifidobacterium bifidum G9-1, on gastrointestinal symptoms in patients with type 2 diabetes mellitus: study protocol for open-label, single-arm, exploratory research trial (Big STAR study)

Metformin is associated with risks of gastrointestinal complications in patients with type 2 diabetes. In contrast, probiotic Bifidobacterium bifidum G9-1 (BBG9-1) could improve the symptoms of diarrhea caused by metformin in animal models. Thus, the primary outcome of this study will be the effect of the probiotic BBG9-1 on gastrointestinal symptoms, including diarrhea, in patients with type 2 diabetes who use metformin. This open-label, single-arm, and exploratory study will examine 40 patients with type 2 diabetes who use metformin and have symptoms of constipation or diarrhea. After the baseline examination (objective 1), patients will be administered probiotic BBG9-1 for 10 ± 2 weeks. Then, examinations will be performed (objective 2). The primary outcome will be changes in the symptoms of constipation or diarrhea from objective 1 to objective 2. Secondary outcomes will include changes in gut microbiota, and correlations between changes in fecal properties and biomarkers, including HbA1c level and body mass index. This is the first study to investigate the effect of probiotic BBG9-1 on the change in the symptom of constipation or diarrhea in patients with type 2 diabetes who use metformin.