The one anastomosis gastric bypass (OAGB) is also variably referred to as Mini Gastric Bypass (MGB)  or omega loop gastric bypass. The procedure modifies the usual Roux-En-Y gastric bypass to be a simpler procedure. In the classical operation known as Roux-en-Y we create two anastomoses (joins). We join the stomach pouch to the small intestine and also small intestine to small intestine (this forms the ‘Y’ configuration). The one anastomosis gastric bypass is as the name suggests, a single reconnection (or anastomosis).

Surgeons usually perform the mini gastric bypass laparoscopically under general anaesthetic. In some cases we will perform it as an open procedure.

The procedure has in fact been performed for over 20 years but has gained popularity in recent years as emerging results from clinical studies shows very good performance of this procedure. This is both in terms of weight loss and importantly weight maintenance. It has a very robust metabolic performance which is thought to be responsible for its very good outcomes. The simplification of the technique also means a reduced risk of some of the complications associated with bypass surgery.

Here’s how surgeons perform the mini gastric bypass

  1. Your surgeon will create 5 incisions in your abdomen. Then pass a camera and small instruments through.
  2. Next, they will use an endoscopic stapler to divide the stomach into a small pouch and large remnant stomach.
  3. Your surgeon will create this long narrow pouch from the portion connected to your oesophagus. This will be your new smaller stomach (gastric pouch).
  4. Then they reconnect (anastomose) your newly created pouch to a loop of your small intestine. The connection bypasses up to 200 cm of the upper part of your intestine.
  5. This means the remaining larger portion of stomach (remnant) and the top part of the small intestine (duodenum and jejunum) are bypassed. Your stomach will still produce digestive juices from this portion, but will no longer store food. The juices will pass down the upper part of the small intestine and then beyond the gastric pouch where they will come into contact with food from the pouch. Then digestion and absorption will take place. 
  6. This has been depicted in the diagram. 

How does the procedure work for weight loss?

Like gastric sleeve, the new smaller stomach limits the volume of food intake. It also has a larger anastomosis (join) between the pouch and the loop of small intestine. This is because the procedure relies more on its “metabolic kick” than in restrictive eating. Signal changes from the gut to the brain and vice versa are altered by the new gut configuration- the net effect of this new “plumbing” is suppression (reduction) of appetite and early satiety (feeling full after eating only a very small volume). The single anastomosis gastric bypass is very effective for weight loss. Much the like the Roux-en-Y gastric bypass, the OAGB is a reversible procedure, though this is rarely necessary.

Average weight loss is between 30% to 40% body weight from baseline. This usually occurs rapidly over the first 6 months and then more slowly for a further 18 months.

It is very important to emphasise that, just like any other weight loss procedure, surgery is only part of the equation. Successful and safe weight loss requires lifestyle changes and other important factors. This includes:

  • dietary modification
  • multivitamins (especially important in the OAGB where malabsorption can contribute to vitamin, mineral and protein deficiencies)
  • adequate fluid intake
  • fibre
  • regular load bearing exercise and
  • paying attention to your mental health and wellbeing.

This is where the team approach works so well. Your surgeon works with dietitians, psychologists, and other specialists to ensure you get the best opportunity to achieve your goals safely.

How does this procedure compare with others?

Unlike gastric sleeve, a gastric bypass is a reversible procedure. As the one anastomosis gastric bypass is a simpler procedure than Roux-en-Y gastric bypass, it reduces operating time. There are also fewer potential complications with the procedure. The International Federation for the Surgery of Obesity explains further:

“The advantage of the OAGB is its relative simplicity, compared to the RY gastric bypass.The single anastomosis results in a shorter operating time and less operative complications. Long term, the OAGB, results in fewer intestinal obstruction problems and less risk for internal herniation. As stated above, over the long-term, a OAGB usually brings about better weight loss and a higher diabetes resolution rate than a RYGB.” IFSO One Anastomosis Gastric Bypass.

What are the risks of OAGB?

As with all surgeries there are risks involved. There can be risks associated with the surgery, or with the anaesthetic during your operation. Other complications may arise after surgery. This might include reflux, ulcers, or nutritional deficiencies (rectified through careful monitoring of vitamin and mineral intake and supplementation). Your surgeon will explain these in detail when you see them to discuss weight loss surgery.

What is the criteria for this surgery?

Your unique situation will determine whether surgery is right for you, and which surgery is best. The general criteria for most weight loss surgeries is a BMI of 35 or over with associated complications of obesity. Or, BMI over 40 on its own. But, there are instances where a lower BMI would indicate candidacy. For instance, where a patient has comorbidities such as uncontrolled Type 2 diabetes, hypertension, fatty liver, sleep apnoea or joint problems. A patient with Type 2 Diabetes and other indicators may be a good candidate for the single anastomosis bypass surgery. Research generally shows good results for these patients with this surgery.

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