Gastrectomies are performed to treat stomach cancer and perforations of the stomach wall.it may be necessary to remove the lower portion of the stomach called the pylorus and the upper portion of the small intestine called the duodenum. If there is a sufficient portion of the upper duodenum remaining a Billroth I procedure is performed, where the remaining portion of the stomach is reattached to the duodenum before the bile duct and the duct of the pancreas. If the stomach cannot be reattached to the duodenum a Billroth II is performed, where the remaining portion of the duodenum is sealed off, a hole is cut into the next section of the small intestine called the jejunum and the stomach is reattached at this hole. As the pylorus is used to grind food and slowly release the food into the small intestine, removal of the pylorus can cause food to move into the small intestine faster than normal, leading to gastric dumping syndrome

Another major effect is the loss of the intrinsic-factor-secreting parietal cells in the stomach lining. Intrinsic factor is essential for the uptake of vitamin B12 in the terminal ileum and without it the patient will suffer from a vitamin B12 deficiency. This can lead to a type of anaemia known as megaloblastic anaemia (can also be caused by folate deficiency, or autoimmune disease where it is specifically known as pernicious anaemia) which severely reduces red-blood cell synthesis (known as erythropoiesis, as well as other haemotological cell lineages if severe enough but the red cell is the first to be affected). This can be treated by giving the patient direct injections of vitamin B12. Iron-deficiency anemia can occur as the stomach normally converts iron into its absorbable form