08 January 2021

Section 2a: How the gastric bypass works

Section 2a: How the gastric bypass works 


The gastric bypass operation assists in weight loss when combined with a healthy, balanced diet and exercise in two main ways: 


  1. A small stomach “pouch”, about 30ml in size, is separated from the main stomach by a line of staples. This decreases the amount that can be eaten at meals before feeling satisfied. None of the stomach or bowel is actually removed. 


3. Figure 1: the gastric bypass 

4. Food leaves the small pouch via a newly fashioned opening called the gastro-jejunal anastomosis and passes directly into the jejunum (second part of the small intestine), bypassing around 150cm of the bowelEnzymes produced in the main body of the original stomach join the food in the jejunum through a second anastomosis (the jejuno-jejunal anastomosis). 

This change in the digestive structure means that food is delivered to the small intestine almost immediately after eating, as opposed to 2-3 hours after eating.  This results in changes in gut hormones – those that help you to feel satisfied increase, and those that cause you to feel hungry decrease. This changes the signalling to the part of the brain that controls appetite, helping you to feel more satisfied on smaller portions of food and overall, less hungry. 

The alterations in your digestive tract also result in fewer vitamins and minerals being absorbed from food. You will therefore be required to take lifelong vitamin and mineral supplementation and undergo regular blood tests to help prevent nutritional deficiencies. 

Follow-up with specialist dietitians is crucial for long-term success. 



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