Small intestinal physiology relevant to bariatric and metabolic endoscopic therapies: Incretins, bile acid signaling, and gut microbiome

Incretins, bile acids and the gut microbiome are involved in the pathophysiology of obesity and type 2 diabetes. The incretins glucagon-like peptide-1 and glucose-dependent-insulinetrophic polypeptide, both influence beta-cell function, insulin and glucose sensitivity, and food intake. Studies have shown that concentrations of both incretins change after bariatric surgery and nowadays glucagon-like peptide-1 agonists are administered as glucose and body weight regulating agents. Bile acids also play an important role in glycemic and metabolic regulation via multiple signaling pathways. After bariatric surgical interventions increase in bile acid concentrations have been observed combined with improvement of metabolic health. It is not clear though, whether this is a direct effect of the altered concentration of bile acids or an epiphenomenon. In addition, alterations in the microbiome are seen in patients with type 2 diabetes and people with obesity. The gut microbiome, probably together with incretins and bile acids, is essential in digestion and nutrient metabolism. After bariatric procedures several alterations in bacterial abundance have been demonstrated with specific bacterial species having different effects on glycemic and metabolic conditions