Mechanisms Underlying Type 2 Diabetes Remission after Metabolic Surgery

Type 2 diabetes prevalence is increasing worldwide. Metabolic surgery is the most effective treatment for selected patients with diabetes and/or obesity. There are different types of metabolic surgery which include the laparoscopic adjustable gastric band, the vertical sleeve gastrectomy (VSG), the Roux-en-Y gastric bypass (RYGB), and the biliopancreatic diversion (BPD) procedure, among other variants. When compared to intensive medical therapy and lifestyle intervention, metabolic surgery has shown superiority in achieving glycemic control, reducing number of medications and cardiovascular risk factors, which translates in long-term benefits on cardiovascular morbidity and mortality. The mechanisms underlying diabetes improvement after metabolic surgery have not yet been clearly understood but includes a complex interaction among improvements in beta cell function and insulin secretion, insulin sensitivity, intestinal gluconeogenesis, changes in glucose utilization, and absorption by the gut and changes in the secretory pattern and morphology of adipose tissue. These are achieved through different mediators which include an enhancement in gut hormones release, especially, glucagon-like peptide 1, Peptide YY and Oxyntomodulin, changes in bile acids circulation, gut microbiome, and glucose transporters expression. Therefore, I will try to do a comprehensive appraisal of what is known so far to better understand the mechanisms through which metabolic surgery improves glycemic control. In conclusion I will summarize that the early improvement seen in postoperative glycemic control is due to an increase in insulin sensitivity secondary to a reduction in hepatic endogenous glucose production and caloric restriction, and an improvement in beta-cell function secondary to an enhancement in GLP-1 release. The long-term benefits in glycemic control are in part due to changes in gut hormone secretion that promote fat mass loss which improves glucose.