Mechanism of bariatric and metabolic surgery: beyond surgeons, gastroenterologists and endocrinologists

Bariatric-metabolic surgery is the safest, most effective and long-lasting treatment for obesity and its associated co-morbidities, whether they be metabolic (type 2 diabetes, hyperlipidemia non-alcoholic fatty liver disease) or cardiovascular (myocardial infarction, stroke). Due to the obesity pandemic, bariatric-metabolic surgery is the second most frequent intra-abdominal procedure and the gastroenterologist and the surgeon must be aware of the physiologic changes caused by the anatomic reconfiguration following surgery. Among the mechanisms of action, independent of the loss of weight and fat tissue, surgery leads to the release of gut hormones related to carbohydrate metabolism (the rapid and continuous release of insulin), appetite and degree of satiety (glucagon-like peptide 1, peptide Y-Y, grhelin). As a result, indications for surgery have been extended to earlier disease stages. Apart from the neurohormonal effects, changes in the metabolism of biliary acids and the microbiota have also been reported. The aim of this review is to describe the physiologic changes caused by bariatric-metabolic surgery.