Bariatric surgery and the kidney-much benefit, but also potential harm.

Bariatric surgery is increasingly performed on overweight individuals. A significant benefit with respect to cardiovascular (CV) events and survival has been documented. After weight loss, reduction of albuminuria/proteinuria is almost consistently seen; small studies documented retardation of the glomerular filtration rate (GFR) loss after bariatric surgery; reduction of blood pressure (BP) is less consistent. It has been known for a long time that the frequency of oxalate stones is increased after bariatric surgery. The main renal threat of hyperoxaluria is renal oxalosis, often irreversible, causing persisting renal failure. The causes are reduced oxalate binding by calcium due to saponification of calcium causing fat malabsorption, increased permeability for oxalate because of increased permeability of colon mucosa triggered by increased bile salts and reduced colonization of the colon by oxalobacter formigenes. These mechanisms are susceptible to treatment.