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The one anastomosis gastric bypass (OAGB), also known as the mini bypass or omega loop bypass, is very similar to the traditional roux-en-y gastric bypass. It is a relatively simple procedure with a shorter operating time. The key difference is that this technique involves only one join of the bowel (anastomosis), as opposed to the roux-en-y which requires two joins.


The OAGB is a minimally invasive procedure performed with laparoscopic (keyhole) technique. The size of the stomach is reduced by stapling at the top of the stomach to form a tube-like pouch the size and shape of a banana, which becomes the new stomach, completely separated from the rest of the rest of the stomach. This pouch is then connected to the middle part of the small intestine, bypassing up to 150-200cm of the upper part of the bowel. The unused part of the stomach remains in the body, but food is no longer digested through that part. Weight loss is achieved through restriction and malabsorption. The new stomach can only hold a small volume of food, therefore causing you to feel full after eating a lot less food than usual, and by bypassing a considerable amount of the small intestine, the amount of calories absorbed decreases.



  • Laparoscopic (keyhole) operations

  • Been around since the 1960s

  • Most durable/sustainable weight loss

  • Many weight related medical problems can be cured or significantly approved

  • Excess weight loss of 70-80%, total weight loss of around 30%*

  • Diabetes resolution rate of 50%-90%*

  • Improved quality of life

  • Nothing 'removed' so in theory reversible (although this is a big operation and rarely done)

  • Most patients only stay for two nights in the hospital

*results vary from person to person​


  • Complex operation requires high technical skill to perform laparoscopically

  • Internal hernias are possible because of moving bowel around

  • Dumping is possible

  • Need to take multivitamins, iron and calcium and have regular blood checks of vitamin levels

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