Impact of Gut Microbiota Transplant Capsules versus Metformin on HbA1c Reduction in Newly Diagnosed Type 2 Diabetics: A Narrative Review

Type 2 diabetes mellitus (T2DM) is a growing global health burden characterised by insulin resistance and progressive beta-cell dysfunction. Metformin remained the first-line pharmacotherapy due to its robust efficacy in lowering glycated haemoglobin (HbA1c) levels and its favourable safety profile. Emerging evidence suggests that gut microbiota dysbiosis contributes to T2DM pathogenesis, and gut microbiota transplant capsules offer a novel approach to restoring metabolic health through microbial reconstitution. This narrative review compared the impact of gut microbiota transplant capsules versus metformin therapy on HbA1c reduction in newly diagnosed type 2 diabetics. A narrative synthesis of published literature was conducted, evaluating mechanisms of action, efficacy in HbA1c reduction, safety profiles, practical considerations, and future directions of both interventions. Metformin lowers HbA1c by an average of 1–1.5% through reduced hepatic gluconeogenesis and enhanced insulin sensitivity, with additional benefits on weight and cardiovascular risk. Gut microbiota transplant capsules have shown promising HbA1c reductions of 0.4–0.8% in early trials by restoring microbial diversity, enhancing short-chain fatty acid production, and improving insulin sensitivity. While metformin’s efficacy is well established, FMT capsule evidence remained preliminary, with questions surrounding durability, optimal dosing, and long-term safety. Both interventions are generally well tolerated, though metformin carries gastrointestinal side effects, and FMT capsules require rigorous donor screening and standardisation. Gut microbiota transplant capsules present a promising complementary approach to metformin for HbA1c reduction in T2DM. Larger, longer-term trials are warranted to define their role in routine diabetes management.