Mini gastric bypass

The mini bypass has many other names:

One anastomosis gastric bypass
Omega loop bypass
Single anastomosis gastric bypass

They are all the same procedure

The one anastomosis gastric bypass is proving to be an effective weight loss operation whilst avoiding some problems of the more involved Roux en Y gastric bypass. More restriction is achieved through a different type gastric pouch along with a better metabolic effect through slightly longer length of bypassed bowel length

No matter what name you call it, the “mini” bypass is making a “maxi” difference. It is proving a good option for those with significant weight to lose (BMI > 40) and particularly those with diabetes and/ or other metabolic disorders. Remarkably, 3 year data demonstrates that both weight loss and diabetic control are greater than sleeve and even the roux en Y bypass.

Having said that, it is not a good option for all. The “mini” still involves alteration of the normal GI configuration, with around 2 metres of small bowel bypassed. A small number of people suffer from bile reflux that needs conversion to a roux en Y bypass (another operation) and an even smaller number of people have problems with the join (bleeding and/or stricture). We do not offer it for people who smoke or use corticosteroids and it can aggravate bowel frequency in people who are susceptible.

Dr Leigh Archer has refined his technique for this procedure through experience at Concord, Sydney. There he was mentored by two surgeons who have pioneered this procedure in Australia, having completed over a thousand bypass procedures with remarkable results. He believes, these results should also be offered to the Rockingham and Mandurah community.

The procedure is done through keyhole with five small cuts. A long but thin pouch is fashioned, very similar to the tube of a sleeve gastrectomy, running about 2/3 the length of stomach. A new opening is made in that pouch and then joined to a piece of small bowel. Only one join is made and then a couple of sutures used to get everything sitting in gentle curves to direct the flow of food.

This new arrangement stops food from entering the larger piece of stomach and around 1 to 2 metres of small bowel. Because of this, less calories are absorbed and some hormonal effects are achieved. Patients must commit to taking multivitamins for life and having a few particular vitamins checked regularly with blood tests.

Because the stomach pouch is long and thin, people are offered restriction sensations similar to a sleeve gastrectomy that gives them feelings of fullness after a small meal. This shape of stomach pouch also avoids bile reflux for the majority of people. There are less spaces for other pieces of bowel to get caught (internal hernias; a problem for the roux en Y gastric bypass) and the time it takes in surgery is also quicker.

Residual stomach capacity: 30-50mls
Estimated weight loss: 60-80% EWL over 2 years.


  • Outstanding results in both weight loss and control of diabetes

  • A long thin pouch offers restriction and avoids bile reflux for most

  • Less internal hernia than roux en Y bypass

  • Excellent long term weight control


  • Nutritional/ mineral supplementsdefinitely required

  • “Dumping syndrome” is somewhat common (though encourages avoidance of sweets and chocolates)

  • Diarrhoea and or protein malnutrition can occur

  • A few people suffer stricture or bleeding at the join

  • Minor late weight regain 10-20% after 2-5 years

Risks from the procedure

Every medical procedure brings some risks. The vast majority of people get through surgery and recovery without problems but its important to know what is a known risk.

  • Clots in legs or lungs (many will use a blood thinner to help with this risk)
  • Leak from the staple line 0.5%
  • Bile reflux needing surgery to fix 2%
  • Problems with key vitamins (B12, viron and protein particularly)
  • Dumping syndrome
  • Stricture (narrowing) at the join 1%
  • Ulcer at the join 5%
  • Gallstones