Bariatric & Metabolic Surgery

Gastric Bypass

Gastric Bypass

The first gastric bypass procedure was performed 50-years ago in 1967 and for many experts remains the “gold standard” surgical weight loss procedure.  There is no doubt that in expert hands and with careful long-term support, the gastric bypass is a safe and extremely effective procedure.

The Procedure

There are very many versions of the gastric bypass – also known as ‘Roux-en-Y gastric bypass’ – but in principle they all do much the same thing.

There are two parts to the procedure. First, a small stomach pouch – about the size of a walnut – is created by dividing the top of the stomach from the remaining body of the stomach.  This is achieved using a special instrument that cuts and staples at the same time.

Next, the first portion of the small intestine (bowel) is divided, and the bottom end of the divided small intestine is brought up and connected to the newly created small stomach pouch. The procedure is completed by connecting the top portion of the divided small intestine to the small intestine further down so that the stomach acids and digestive juices from the bypassed stomach and first portion of small intestine will eventually mix with the food.

Gastric Bypass Information

How does it work?

It was originally thought that the gastric bypass procedure produced weight loss mainly through malabsorption – i.e. calories from food and drink could not be absorbed across the bypassed section of small bowel.  This is not the case.

The gastric bypass does not result in significant calorie malabsorption but works by three other mechanisms.

First the very small pouch restricts the amount of food that can be eaten at any one time, which means fewer calories consumed.

Secondly – and most importantly – re-routing of the food stream and bypassing a segment of small bowel, results in major changes in a variety of appetite hormones, including ghrelin.  The net effect of these changes is a dramatic suppression of appetite.

Finally, patients undergoing gastric bypass report significant changes in food preferences, with a reduced interest in sweets, high fat foods and alcoholic drinks.

How much weight will I lose?

The average excess weight loss after a gastric bypass is around 70%.  In other words, if you were 100lbs overweight before surgery you can expect to lose around 70lbs.  As with the sleeve gastrectomy there is a tendency towards weight re-gain over time, but even at 10-years most patients will keep at least 50% of their excess weight off.  Furthermore, weight loss with the gastric bypass seems to be greater and more durable than with either the gastric band or the sleeve gastrectomy.

What are the health benefits?

Gastric bypass has the strongest effect on high blood pressure, high cholesterol levels and other obesity-associated health problems.

It’s especially important to note the impact of the gastric bypass on Type 2 diabetes.  A recent study of 20,000 patients showed that showed that 84% of patients experienced complete reversal of their diabetes. Rapid improvement in blood sugar levels and reduction or elimination of diabetes medication is often seen in the immediate post-operative period – well before any significant weight loss has occurred.  This is due to the profound effects the bypass has on gut hormones, especially those involved in blood sugar regulation.  In fact, in those undergoing bypass, the need for diabetes medication declines to about 8% over time.  And – assuming weight loss in maintained – these benefits persist for life.

What are the risks of the surgery?

Although a gastric bypass is an invasive operation requiring quite significant changes to the anatomy of the bowel and stomach, in experienced hands it is a remarkably safe procedure; studies shows that 99.8% of patients survive the procedure.  In fact the risk of a gastric bypass (0.2%) is about the same as having your gallbladder removed (0.15%) and safer than a hip-replacement (0.29%) or a C-Section (0.4%).

The general risks of gastric bypass are the same as those with any major surgical procedure and include

  • Excessive bleeding
  • Infection
  • Adverse reactions to anesthesia
  • Blood clots
  • Lung or breathing problems
  • Leaks in your bowel/stomach
  • Death (rare)

Longer term risks and complications of bypass surgery include:

  • Dumping syndrome, causing diarrhea, nausea or vomiting
  • Gallstones
  • Hernias
  • Low blood sugar (hypoglycemia)
  • Vitamin and mineral deficiencies
  • Bowel obstruction
What is Dumping Syndrome?

Dumping syndrome is a condition that can develop after gastric bypass and also after sleeve gastrectomy.  It occurs when sugars move from the stomach into the bowel too quickly.

Most people with dumping syndrome develop signs and symptoms, such as abdominal cramps and diarrhea, 10 to 30 minutes after eating. Other people have symptoms one to three hours after eating, and still others have both early and late symptoms.  These include:

  • Nausea
  • Vomiting
  • Abdominal cramps
  • Diarrhea
  • Flushing
  • Dizziness, lightheadedness
  • Rapid heart rate

Generally, you can help prevent dumping syndrome by changing your diet after surgery. Changes might include eating smaller meals and limiting high-sugar foods.

Although around 60-70% of gastric bypass patients develop some degree of dumping, in only around 5% does to become chronic and require specific treatment in the form of medication or (rarely) surgery.

Some patients even claim to like dumping because they regard it as a form of aversion therapy – to stay away from sweet things!

Vitamin and Mineral deficiencies

Although calories are generally absorbed as normal after a gastric bypass, vitamins and minerals are most certainly not.   So, it is absolutely essential for you to take regular (daily) vitamins and minerals after bypass surgery.  If you fail to do this, you are almost certain to run into serious health problems, such as anaemia, nerve damage and bone disease.

Key micronutrients include Vitamin B12, B1 (thiamine) and D, calcium, iron and zinc.

You will be given detailed information regarding vitamin and mineral supplements after surgery.


Advantages and disadvantages of the gastric bypass
Advantages Disadvantages
Excellent initial weight which is well maintained over many years Difficult to reverse – essentially permanent alteration in stomach and bowel.
No requirement for adjustments (unlike the band), though regular clinic follow-up is essential to ensure nutritional adequacy. Lifelong daily vitamin and mineral supplementation essential to avoid deficiency diseases
Reduces hunger hormones (unlike the gastric band) Risk of dumping-syndrome
Has major beneficial impact on Type 2 diabetes and other obesity-related health problems
Especially appropriate for patients with a higher BMI
The procedure has been in use for more than 50-years