Abstract. When analyzing this literature, the causes and prevention of diabetes mellitus and its complications are analyzed. The significant role of environmental factors, such as intestinal colonizing bacteria in diabetes mellitus, its role and significance in the development and progression of this disease, as well as its role in the regulation of metabolism, systemic and local immunity. Intestinal microflora plays an important role in food absorption and regulation of the immune system. Disturbances in the microbiome can lead to inflammation and related diseases, including diabetes. Patients with diabetes may have an imbalance in their gut microflora, as well as low bacterial diversity. This can lead to higher levels of inflammation, which in turn increases insulin resistance and contributes to the development of diabetes.