Intestinal Microbiota in Diabetes—Does the Pathomechanism and Diversity Depend on the Type of Diabetes and Coexisting Metabolic Disorders?

Emerging evidence strongly suggests that gut microbiota dysbiosis plays a significant role in the development and progression of both type 1 and type 2 diabetes mellitus. Quantitative and qualitative changes in the intestinal microbiota's composition are linked to these distinct pathomechanisms. In type 1 diabetes mellitus, dysbiosis is thought to initiate or accelerate the autoimmune destruction of pancreatic beta cells. This may occur through increased intestinal permeability, which allows microbial components and endotoxins to enter the systemic circulation. This exposure triggers inflammatory and autoimmune responses in individuals who are genetically predisposed. Conversely, in type 2 diabetes mellitus, gut dysbiosis contributes significantly to the characteristic metabolic derangements. Specific microbial shifts can lead to impaired energy metabolism, contributing to insulin resistance in peripheral tissues. Furthermore, dysbiosis is associated with the altered production of microbial metabolites, such as short-chain fatty acids, and the induction of low-grade chronic inflammation, which contribute to the pathogenesis of type 2 diabetes mellitus. Hyperglycemia, dyslipidemia and other metabolic changes also influence the gut microbiota. Understanding these type-specific microbial roles offers potential for novel diagnostic and therapeutic strategies.