This procedure aims to achieve a permanent weight loss with mean final weight approaching 30% excess weight. This final weight depends largely on the initial excess weight. In extremely obese patients with
 > 120 % excess weight the final weight can be 40% excess weight. With an initial excess weight below 100 % the final weight may even be less than 20% excess weight..

The effect of this surgical procedure is due to two mechanisms: a temporary mechanism resulting in weight loss and a permanent mechanism to maintain this loss.

The mechanism of weight loss is based on the smaller gastric volume after distal gastrectomy. The contents empty rapidly into a distal intestinal segment via a broad gastroenterotstomy. The patient presents a temporary loss of appetite, occasionally in combination with a «postcibal syndrome» (epigastric cramping sensation after food intake).

The mechanism of weight control is based on the biliopancreatic diversion itself, which causes permanent and elective malabsorption of fat and carbohydrates.

Weight loss is most significant in the first 6 months. The final result is achieved after 12 to 18 months.