Effects of probiotic Bifidobacterium bifidum G9-1 on the gastrointestinal symptoms of patients with type 2 diabetes mellitus treated with metformin: an open-label, single-arm, exploratory research trial

AIMS/INTRODUCTION Metformin is associated with the risk of gastrointestinal complications, and probiotic Bifidobacterium bifidum G9-1 (BBG9-1) can improve the symptoms of diarrhea. This study aimed to clarify the effects of probiotic BBG9-1 on the gastrointestinal symptoms of type 2 diabetes mellitus patients using metformin. MATERIALS AND METHODS In this open-label single-arm exploratory study, 40 patients (mean age 64.0 ± 9.4 years) were given probiotic BBG9-1 for 10 weeks. Changes in the gastrointestinal symptom rating scale total score, which was the primary end-point, gastrointestinal symptom rating scale subscale scores, glycated hemoglobin levels and gut microbiota after the administration of probiotic BBG9-1 were evaluated by the Student's t-test. RESULTS The gastrointestinal symptom rating scale total score significantly improved (from 2.02 ± 0.51 to 1.59 ± 0.43, change, -0.43 ± 0.49, P < 0.001). Furthermore, all gastrointestinal symptom rating scale subscale scores, including diarrhea (from 2.32 ± 1.14 to 1.89 ± 0.99, change, -0.42 ± 0.95, P = 0.007) and constipation (from 3.00 ± 1.16 to 2.20 ± 1.07, change, -0.80 ± 1.19, P < 0.001), scores also significantly improved. However, the glycated hemoglobin levels did not change (from 7.0 ± 0.7 to 7.0 ± 0.6%, change, 0.0 ± 0.4, P = 0.91). The relative abundance of the genus Sutterella decreased by the use of probiotic BBG9-1 (from 0.011 ± 0.009 to 0.008 ± 0.006, change, -0.003 ± 0.006, P = 0.002). CONCLUSIONS Type 2 diabetes mellitus patients treated with metformin showed significant improvement in all gastrointestinal symptom rating scores after using probiotic BBG9-1 without changing the glucose control. This study showed the potential usefulness of probiotic BBG9-1 for improving gastrointestinal symptoms, including constipation and diarrhea, in type 2 diabetes mellitus patients treated with metformin.