Weight loss after SG TB surgery is mainly because of 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 rapidly enters from 1st part of duodenum into distal ileum. There will be more than 200 hormone 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 and effective weight loss. Same hormonal changes are responsible for long lasting type 2 diabetes remission. Ghrelin acts against insulin. As levels of Ghrelin hormone come down, insulin resistance comes down. GLP 1 increases insulin production and sensitivity. Since GLP 1 hormone is increased, insulin production increases and insulin resistance comes down. Partial diversion of biliopancreatic juices also contributes to the metabolic effects of this surgery.