Effects of probiotics on glycemic control and intestinal dominant flora in patients with type 2 diabetes mellitus A protocol for systematic review and meta-analysis

Background: With the rapid development of modern society, people's dietary structure has been changing accordingly. Diets high in salt, fat, and sugar have led to an increase in the incidence of diabetes year by year, posing a great threat to human health. More than 90% of diabetic patients have type 2 diabetes mellitus (T2DM). It is currently believed that the onset of T2DM is mainly related to factors such as genetics, insulin resistance, impaired insulin cell function, and obesity. The main mechanisms are as follows: 1. It affects the intestinal intake of single-chain fatty acid (SCFAs). The decrease of SCFAs leads to the decrease of the number of islet cells and the decrease of insulin sensitivity, which in turn leads to insulin resistance (IR). 2. Intestinal barrier function is inhibited, which leads to intestinal nonspecific inflammation. Then, it leads to changes in the structure and function of intestinal endothelial cells and affects the transport of insulin, which leads to IR. 3. Intestinal flora participates in bile acid metabolism and liver circulation, and affects the metabolism of carbohydrates and lipids. Imbalance of intestinal flora leads to disorders of carbohydrate and lipid metabolism. 4. Intestinal flora can reduce oxidative stress and improve islet cell function and insulin metabolism. Imbalance of intestinal flora can lead to impaired islet cell function and insulin resistance. 5. Normal intestinal flora can increase the content of YY peptide and correct the abnormal nerve conduction in hypothalamic feeding center. The dominant flora of normal intestinal tract is mainly anaerobic bacteria which are beneficial to the human body. Under certain conditions, when intestinal flora is maladjusted, harmful bacteria and opportunistic bacteria become the dominant intestinal bacteria, resulting in metabolic disorders. Ingestion of probiotics can correct the imbalance of intestinal flora, and then, have a therapeutic effect on T2DM. Therefore, we designed this study to evaluate the effects of probiotics on blood glucose control and intestinal dominant flora in patients with T2DM. Methods: The retrieval period of meta-analysis literature is set from January 1, 1990 to September 2020. We will mainly search five English electronic databases, including Cochrane Library, Pubmed, Excerpt Medical Database (EMBASE), Science Direct and Web of Science, and search the following four Chinese databases: China Biomedical Literature Database (CBM), China National Knowledge Infrastructure (CNKI), China Science Journal Database (VIP), Wanfang Database, and so on. At the same time, the two reviewers will independently conduct research selection, data extraction and deviation risk assessment, and use Review Manager 5. 3 software provided by the Cochrane Collaboration for meta-analysis and heterogeneity assessment. Results: This study will demonstrate an evidence-based review of probiotics on glycemic control and intestinal dominant flora in patients with type 2 diabetes mellitus. Conclusion: This study can be used to evaluate the efficacy and safety of probiotics on glycemic control and intestinal dominant flora in patients with T2DM. Registration number: is INPLASY20209010 4.