Biliopancreatic diversion (also known as duodenal switch) is a complex bariatric surgery that includes a sleeve gastrectomy and long Roux-en-Y intestinal bypass. The entero-enteric anastomosis is very distal, resulting in bypass of two-thirds or more of the intestine. Patients lose weight not only because nutrients bypass most of the intestine, thereby reducing the absorption area, but also because nutrients join the biliopancreatic secretions and enzymes distally, leading to reduced digestion and absorption.