Gastric Bypass

What is gastric bypass surgery?

The gastric Roux-en-Y bypass is a bariatric surgery procedure which is performed laparoscopically (keyhole surgery) under a general anaesthetic.

It has historically been the most commonly performed bariatric procedure worldwide.  During gastric bypass surgery, a smaller stomach pouch is formed from your stomach which is then attached to the second part of your small intestine, known as the jejunum (long Roux limb in above diagram).  The remaining larger portion of your stomach and first part of your small intestine known as the duodenum, is then sealed completely and left within your abdomen.  The gastric bypass surgery therefore effectively bypasses about 95% of your stomach and approximately the first 50cm of the 5-7m of bowel each person has in their body.  The unused portion of your stomach will produce less acid and fluid secretions and will not receive food.  The acid and secretions produced from this part of the stomach re-enter your gastrointestinal system via the small bowel lower down.  The new path for your food after your bypass will now be through a much smaller stomach and then into the jejunum ready for the majority of your nutrient absorption. After this surgery you should be able to comfortably eat between ½ and 1 cup of normal food per meal.

Studies show that after the gastric bypass people lose between 60-80% of their excess body weight over the first 12-24months. Longer term studies show that up to 15 years post surgery most people will regain some weight which will mean that they will have lost 50-70% of their excess body weight.

It must be noted that this surgery, along with any other bariatric procedure, is only ever a ‘tool’ to help you control your weight.  Weight loss success relies upon you optimising the use of your ‘tool’ and varies due to a number of factors such as age, starting weight, concurrent medical or psychiatric illnesses, ability to exercise, meal planning/routine as well as perseverance. It is virtually impossible to lose too much weight after a gastric bypass.  Most people get to the point where further weight loss comes at the cost of excessive effort and they therefore settle at the weight that suits them.

How does the gastric bypass work?

There are many aspects of the gastric bypass resulting in weight loss that are still not fully understood.  We do know that the creation of a smaller stomach means that people feel full on less food and that taste changes are reported which decrease the appeal of fat and sugar rich foods. We also know that there is a reduction of hunger promoting hormones produced, which assists in reducing food intake. There is an additional intolerance of high sugar/fat foods which leads to something known as ‘dumping syndrome’.  This occurs when people eat these types of foods, particularly on an empty stomach. The fast movement of sugar and fat from the stomach into the bowel causes fluid shifts, hormonal changes and results in sweating, cramping, loose stools etc. The possibility of dumping syndrome deters people from eating these high calorie foods. All of the above factors result in a reduction in calorie intake which therefore facilitates weight loss.


  • This operation has withstood the test of time having been performed for over 30 years. It has undergone a variety of modifications to be considered by many surgeons, particularly in the US, as the gold standard operation.
  • No foreign body (like the lap band) is used which decreases the chance of complications such as infection, migration or erosion.
  • The gastric bypass has been shown to reduce the incidence of diabetes, high cholesterol, joint pain and hypertension and also lowers the dosage, or negates the use altogether, of medications used to treat lifestyle diseases.
  • It may be offered as a revision or conversion surgery if needed post sleeve or band surgery.


  • As the stomach and duodenum are largely bypassed, poor absorption of nutrients such as Vitamin B12, iron and calcium can result and a predisposition to iron deficiency anaemia, B12 deficiency and osteoporosis. Multivitamins are therefore required to be taken for life.  If not taken as directed, long term and sometimes irreversible complications, such as neurological injury and permanent dementia can occur.
  • Dumping syndrome can occur in a small population of people. It is not very common and managed by the dietary restriction of trigger foods.
  • It is possible to stretch your stomach by overeating repetitively. This will not be a comfortable process.  If your stomach becomes stretched to allow for the consumption of more food, the result will be weight gain.  Keep in mind that most weight gain years after surgery is likely to be due to poor food and lifestyle choices rather than increased stomach volume capacity.


  • Early major complications can occur and can lead to life threatening situations. Breakdown of one of the joins in the bowel is well recognised as a major cause of serious complications but is not common (about 1%). The risk of death from this procedure is less than 0.1%.
  • The bypassed portion of the stomach, duodenum and segments of the small intestine cannot be easily visualised using X-ray or endoscopy if problems such as ulcers, bleeding or malignancy should occur.
  • As with many weight loss operations, rapid weight loss can lead to gallstone formation in 20-30% of patients.
  • Bowel obstruction can sometimes occur many years after the operation and can be difficult to diagnose. The risk of this occurring is thought to be at less than 3%.
  • Other complications include staple line bleeding, narrowing of the new stomach, haemorrhage, bowel injury, wound infection, hernia, post operative abscess, deep vein thrombosis, pulmonary embolism and reactions to anaesthesia/medications. This is not a complete list of all risks, please discuss any specific concerns further with your surgeon during your personal consultation.

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