Single Anastamosis Gastric Bypass

The Procedure

The Single Anastamosis gastric bypass has been around since in late 1960s and, because it is slightly easier to perform laparoscopically than the standard Roux-en-Y gastric bypass, has started to come back into fashion.

It is slightly more effective than sleeve gastrectomy, but easier and not quite as effective as Roux-en-Y gastric bypass. The BMI recommendations for the Single Anastamosis Gastric Bypass are that you have a BMI at least 35, or a BMI of at least 30 with one or more weight-related medical complications.

The main difference between the standard Roux-en-Y gastric bypass procedure and the Single anastomosis gastric bypass can be seen by comparing the two diagrams below. In the case of the Single anastomosis gastric bypass there is only one bowel join (anastomosis) whereas in the Roux-en-Y gastric bypass there are two joins– an upper and a lower. Because of this the Single anastomosis gastric bypass can be done more quickly than the standard gastric bypass, and theoretically with fewer early complications.

In both operations there stomach is divided into a small upper portion, leaving the larger lower portion of the stomach with its storage capacity, untouched. This enables only a small amount of food to be taken at any one time. A loop of bowel is joined to the small upper part of the stomach allowing food to pass from the small stomach straight into the bowel, bypassing the storage capacity of the main stomach. Fats and sugars therefore bypass the stomach, duodenum and upper part of the small bowel where they are normally absorbed, instead passing downstream as waste. Fewer calories absorbed results in weight loss.


  • Very similar to operation to standard Roux-en-Y gastric bypass
  • Weight loss and health benefits resulting are essentially the same as for standard Roux-en-Y gastric bypass.
  • A more advanced procedure than sleeve gastrectomy
  • Quicker to perform laparoscopically than standard gastric bypass.


  • May result in more reflux than standard gastric bypass
  • If reflux is problematic, may need to be converted to standard gastric bypass
  • The long term results of allowing bile into the stomach are unknown
  • Not as much data on the long term outcomes as for standard gastric bypass, sleeve gastrectomy and adjustable gastric banding.


Lee w-J et al. Laparoscopic Roux-en-Y vs mini-gastric bypass for the treatment of Morbid Obesity: a 10 Year Experience. Obes Surg 2012; 22: 1827-1834.

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