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 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.


  • Performed laparoscopically (keyhole surgery)

  • Length of hospital stay is 2 nights, with a two to three week recovery rate

  • Excess weight loss of 60 – 80% over 12-18 months

  • Excellent diabetes remission rate, with Type II diabetics noticing improvement in diabetes control within days of the procedure

  • Improvement in associated conditions such as sleep apnoea and high blood pressure

  • Not associated with intestinal obstructions/internal hernias

  • Dumping syndrome less common than RYGB

  • It is a relatively simple and fast operation with low complication rates



  • May experience 'bile' reflux which can feel like acid reflux

  • In most cases not severe but 5% need a conversion to RYGB

  • Theoretical risk that bile can cause cell damage

  • Greater likelihood of nutritional deficiency due to reduced absorption of nutrients and vitamins. Lifelong vitamin and mineral supplements required, with long-term monitoring by surgeon or dietitian


(mini-gastric bypass)