A system for inducing weight loss ina patient includes (a) an elongated element extending from a proximal end to a distal end, the elongated element separating a duodenum into first and second channels, wherein the elongated element is expandable and (b) a retainer connected to the elongated element and securing the elongated element in a desired orientation within the duodenum. In the desired orientation, all chyme flowing through the duodenum enters the first channel and the second channel is open to a papilla of vater so that digestive fluids from the papilla of vater enter the second channel.
