Updated 21 September 2015

Gastric bypass surgery

Gastric bypass surgery allows food to bypass most of the stomach, causing weight loss.


Gastric bypass surgery is done to allow food to bypass most of the stomach, thereby causing weight loss. It drastically reduces the size of the stomach, and changes the physiological response of the body to food intake.

Obesity is associated with the development of serious co-morbidities, such as hypertension and diabetes, which have complications and mortality rates of their own. Bypass surgery has been shown to reduce the incidence of these complications, and reduce the associated mortality.

Who qualifies?
The selection of patients for bypass surgery is ideally done by a panel of physicians, including a specialist bariatric (weight loss) surgeon, and a specialised dietician.

This is major abdominal surgery with many possible complications, and is thus reserved only for patients meeting strict criteria:

  1. A body mass index (BMI) of 40kg/m² or more.
  2. Patients must be well informed and motivated.
  3. Those with an acceptable risk for surgery.
  4. Those who have failed to lose weight by non-surgical means.
  5. Adults with BMI >35kg/m² plus serious co-morbidities such as diabetes, sleep apnoea, severe joint disease, or obesity-related cardiomyopathy may also be considered.

Patients not suitable for such surgery are those with:

    • Untreated major depression or psychosis.
    • Current drug or alcohol abuse.
    • Binge-eating disorders.
    • Cardiac disease with unacceptable anaesthetic risk.
    • Severe blood clotting disorders.
    • Inability to comply with lifelong nutritional needs post-operatively.
    • Those of inappropriate age: the surgery is controversial in those under 18 or over 65.

How is it done?
There are several techniques, all done under general anaesthesia. Surgery may be done the conventional way, or via a laparascope, depending on the expertise of the surgeon.

The most often performed - and most successful - procedure is called the gastric bypass with proximal Roux-en-Y anastomosis.

The first stage of the operation is reduction of the stomach by about 90 percent, leaving behind a small pouch, or mini-stomach, to receive ingested food.

The second step involves rearranging the left-over piece of stomach, and making a connection between the stomach and the small intestine (in a Y-formation), which still allows food to mix with the secretions and hormones normally produced by the bowel during digestion.

Any abdominal surgery has complications, but the risk of these is greatly increased in obese patients. In addition, there are complications unique to this procedure.

Possible complications for abdominal surgery in general are:

  • Infection - of the incision, or of the internal surfaces and organs. Obesity may increase the rate of infection, but adequate peri-operative use of cephazolin reduces this significantly.
  • Haemorrhage - obese persons are more at risk, because of the extra tissue needing to be incised.
  • Hernia formation, internal, or external.
  • Bowel obstruction due to internal hernias or adhesions.
  • Pulmonary embolus - the risk is drastically increased in obese patients undergoing abdominal surgery.

Specific complications are:

  • Leakage - at the many sites of reconnecting the stomach and bowel.
  • Shrinkage (stricture) of openings into the bowel.
  • Dumping - food passes into the small bowel too rapidly because the normal outlet valve of the stomach is bypassed. Symptoms of dumping include:
    • Nausea and vomiting,
    • Dizziness,
    • Sweating, and
    • Diarrhoea
  • Gallstones - common with rapid weight loss.
  • Vomiting due to the small residual stomach.
  • Nutritional deficiencies - protein, vitamin and mineral deficiencies are common (re-arranging the anatomy to cause weight loss inevitably causes malabsorption).
  • Distension of the stomach remnant. This is rare, but can be fatal if not diagnosed and treated urgently.

After surgery
Most patients can be sent home within a few days, once they are able to move about free of pain, and can eat liquid or pureed food without vomiting. The patient will need to be taught a new way of eating (like limiting quantities to about a cupful per meal), and how to prevent nutritional deficiencies. Careful follow-up and constant motivation are needed to prevent problems.

Weight loss is excellent in nearly all patients, with average losses of about 4.5kg a month, stabilising after 24 months. Many will need cosmetic surgery to remove redundant skin folds.

There is vast improvement in obesity-related conditions such as diabetes and hypertension, and a significant improvement in the quality of life.

- Reviewed by Dr Anna Hall, B Soc Sci (SW), MB ChB, CDE.


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