How Does Bariatric Surgery Improve Type II Diabetes? The Neglected Importance of the Liver in Clearing Glucose and Insulin from the Portal Blood

The pandemic of obesity due to food “addiction” has led to a dramatic increase in rates of Type II Diabetes \nMellitus (T2DM). T2DM is characterized by increased glucose and insulin (but not of the C-peptide) serum levels. \nIncrease of insulin serum level without increase of insulin synthesis is supposed to be due to insulin resistance. \nReduction of body weight (BW) through reduction of calories uptake is the most effective measure to treat T2DM \nand metabolic syndrome in obese patients. \nAppetite suppressant drugs which potentially reduce BW have several side effects, and as "lifestyle modifiers" are \nnot approved as potential antidiabetic drugs. In addition to the treatment of extreme (BMI ≥ 40) obesity, surgeons \nhave expanded the offer of bariatric surgery as therapeutic option for diabetic, "non-morbid" (BMI ≤ 35) obesity. As a \n"collateral effect" of this surgical intervention, acute and long-term improvement of T2DM has been observed. \nAlthough several hypotheses to explain this improvement have been reported, the exact mechanism underlying the \nreduced hyperglycemia and hyperinsulinemia immediately after surgery is unclear. Though long-term effects of the \ndifferent operations have not yet been studied thoroughly. \nBesides weight-loss, bariatric surgery may also reduce lipid accumulation in the liver. Reverse of the hepatic lipid \ndeposition may improve clearance of glucose and insulin from the liver and consequently lead to reducing their \nconcentrations in the peripheral blood. This mechanism has not, however, been considered when effects of bariatric \nsurgery on glucose metabolism have been reported. In fact, a few reports on a limited number of patients already \npublished have given data about changes of liver size and/or liver lipid content at different time points postoperation. \nFuture prospective studies should focus on the changes in glucose and lipid metabolism induced in the \nliver by the various types of surgical interventions.