Weight loss and diabetes remission after BPD DS is mainly due to hormonal and genetic changes. Role of food restriction or malabsorption is secondary. After this operation Ghrelin hormone levels come down as fundus of the stomach is removed. GLP 1, Peptide YY hormone levels increase as food directly enters from 1st part of duodenum into distalileum (last part of small intestine). Food doesn’t enter the remaining duodenum, jejunum and proximal ileum. So levels of anti incretin hormones come down. There will be more than 200 hormonal changes after surgery. Removal of body of stomach alters several genes involved in energy balance. These hormonal and genetic changes reduce appetite, increase energy expenditure and reset the ‘fat mass’ to a lower level, resulting in long lasting, effective weight loss. Same hormonal changes are responsible for long lasting type 2 diabetes remission. Ghrelin and anti incretins act against insulin. As levels of these hormones come down, insulin resistance comes down. Since GLP 1 hormone is increased, insulin production increases and insulin resistance comes down. Significant diversion of biliopancreatic juices also contributes to the metabolic effects of this surgery.