Abstract

Diabetes mellitus, encompassing type 1 (T1D) and type 2 (T2D), has traditionally been viewed through lenses 
of genetics, autoimmunity, insulin resistance, and environmental risk factors such as diet and obesity. Recent 
advances in microbiome research have identified the gut microbiome as a potentially pivotal player in the 
pathogenesis of both forms of diabetes. In T1D, alterations in the early‐life microbiota, impaired intestinal 
barrier function, dysregulated immune development, and specific microbial taxa shifts precede or accompany 
islet autoimmunity. In T2D the gut microbiome influences metabolic regulation through modulation of energy 
harvest, short‐chain fatty acid (SCFA) production, bile acid metabolism, lipopolysaccharide (LPS)‐driven 
endotoxemia, inflammation, and insulin sensitivity. This review surveys the current evidence linking gut 
microbial composition and function to both T1D and T2D pathogenesis, explores mechanistic studies 
elucidating causal pathways, examines how modifiable factors (diet, antibiotics, mode of birth, 
probiotics/prebiotics) might influence risk, and evaluates translational prospects for microbiome‐based 
interventions. We emphasize that while cross‐sectional human studies are abundant, prospective cohort, 
mechanistic animal, and intervention studies are fewer, leaving gaps in the understanding of causality and 
heterogeneity among individuals. Ultimately, harnessing the gut microbiome may enable novel prevention or 
therapeutic strategies, but rigorous trials, better biomarkers, and understanding of host‐microbiome 
interactions remain essential.