Gastric bypass surgery in detail

What is gastric bypass surgery?

In our normal bodies we have a gullet (oesophagus) which carries food and liquid from our mouth to our stomach. After our stomach has finished processing this food, it passes through various parts of our small bowel before continuing into the large bowel. During this journey through our small bowel the food mixes with digestive juices and this is when our body absorbs all the nutrients, calories and fats.

Figure 1 - Roux-en-Y gastric bypass

The  most common version of this operation is called the Roux-en-Y gastric bypass. It is named after the Swiss surgeon (Roux) who first described it and the Y shape made by the re-routed bowel. A small gastric pouch is made by stapling and dividing off a small part of the stomach just below the gullet (Figure 1). A small opening is then made in the pouch and a Y loop of the small intestine is joined to this opening. This loop is 1.5 metres long. The greater part of the stomach, duodenum (first part of the bowel beyond the stomach) and top part of the small intestine is joined to the bottom of the Roux loop (Figure 1). It is at this point that the food eaten mixes with the digestive juices allowing digestion to begin. The gastric bypass is usually performed laparoscopically (by keyhole surgery) and takes 1-2 hours to perform. This typically involves making five small cuts on your tummy, to enable the camera and instruments necessary to perform the operation to be inserted. Post-operative stay is usually 2 days.

How does the gastric bypass work?

The gastric bypass works in two ways:

  • The small gastric pouch restricts the amount of food you can eat at one sitting, helping you stick to a controlled diet. There is no escaping from this. You need to stay on a healthy, restricted diet to lose weight

  • In addition, the gastric bypass takes part of the small bowel out of the digestive loop (the small bowel is the part that absorbs or takes in digested food and nutrients). The Roux loop in a sense is acting purely as a pipe without significant digestion or absorption taking place, leading to a degree of malabsorption. Thus a gastric bypass works by reducing the amount of calories or energy that the body can take in from food eaten in small meals. If you take a lot of people who have had a gastric bypass, the average weight loss is 60 % of their excess body weight at five years. Much of this weight will be lost in the first year

Alternatives to gastric bypass

It would be best to avoid surgery altogether. Making major lifestyle changes to include dieting, healthy food choices and regular movement and exercise will be required after surgery anyway, and many people find that these things alone help them to lose weight without the need to undergo an operation. Others find that the addition of prescribed weight loss drugs such as Orlistat provides all the help they need to get their weight down.

If these things don't help, or the effects don't last, it is reasonable to consider weight loss surgery, at which point the major consideration becomes which operation is best for you. Apart from the gastric bypass, current surgical options include the gastric sleeve, gastric band, duodenal switch and the gastric balloon (see other sections).

Benefits of gastric bypass

Gastric bypass surgery is a relatively safe operation. However, it involves more major surgery than the gastric band, with a greater risk of complications and a longer length of hospital stay by several days.  The gastric bypass however is a more reliable weight loss operation. Furthermore, while attention to your diet is important, if you do occasionally eat more than you should, much of what you excessively eat will be passed out of your body as diarrhoea, and will not be absorbed. Persistent overeating though will enlarge the gastric pouch, allowing you to store larger meals, and this can result in subsequent weight gain.

For most patients who have gastric bypass surgery, the benefits in terms of losing weight are much greater than the risks. In particular, most patients with recently-diagnosed diabetes mellitus (less than 5 years) can be cured of their diabetes with a gastric bypass, and this may all happen within a few days of surgery, well before any significant weight loss has occurred.

Risks of gastric bypass

Performing a gastric bypass involves an operation. There are thus the risks of the general anaesthetic, and there are the risks of the operation itself.

Modern anaesthetics are very safe, but being overweight does add a slight risk when having a general anaesthetic, and if, for example, you have other illnesses such as diabetes or heart disease then the anaesthetic risk is a little higher again.

A gastric bypass is like a plumbing job. The pipework of your intestines is cut and rejoined in several places. Like any plumbing job, these joins can leak. This is a serious complication and often requires urgent, further surgery to correct. Damage to your stomach, intestines or liver is possible during the operation and bleeding or perforation of the stomach or bowels may be the result. Bleeding is not usually too much of a problem as long as it is recognised and fixed promptly. The need for a blood transfusion as a result of a gastric bypass is highly unlikely. Similarly, perforation of the stomach or bowels is not usually of major concern if the perforation is recognised and fixed.

The other main risk of surgery is blood clots. This can happen to anyone having any operation, not just a weight loss surgery operation. Every attempt is made by the Weight Loss Surgery Scotland team to minimise this risk around the time of your operation. We do this by using injections to thin the blood, as well as special stockings and calf pumps during the procedure. Getting you up out of bed moving as quickly as possible after the operation is also important to keep the blood circulating in your legs.

Long term complications of the gastric bypass operation

Pouch dilation
If you regularly overeat into the small gastric pouch, it will stretch and get bigger. This will mean you can eat bigger meals and thus lose less weight, or indeed put weight on. Sometimes, if picked up early, more careful eating behaviour can reverse this dilation.

Internal herniation
The operation rearranges your bowel anatomy and this can cause potential sites for abnormal rotation and internal herniation of the bowel. If you develop severe crampy abdominal pain, or the feeling of abdominal distension (the feeling of being blown up like a balloon), and feel unwell with it, you should seek urgent medical attention. A CT scan is often required to help with this diagnosis.

Vitamin and other nutrient deficiencies
Because of the malabsorption component of this operation, you may not absorb sufficient minerals and nutrients from your food for your body's needs. Deficiencies can generally be prevented by keeping your protein intake up, and taking a daily multivitamin supplement for life.

Is my gastric bypass for life?

You should consider the gastric bypass as an operation for life. However, occasionally the operation is required to be reversed; although the need for this is very rare. This is a difficult operation and often requires open surgery through a large incision to reverse. The main reason for reversal is vitamin or other nutrient deficiencies that cannot be corrected by medication and nutrient supplements in diet and tablet form.

Will you keep me under review?

Once you have recovered from your surgery, an annual check up including blood tests to look for early signs of nutrient deficiencies is often all that is necessary. You will be able to eat most foods with time. Some foods will pass through the bowel very quickly, and trial and error will help you avoid these. However, we recommend that you do take multivitamin tablets (which often contain other important things like iron and calcium) to minimise the risk of deficiencies. Such follow up can often be arranged with your GP and does not require you to return to see your hospital specialist.

Gallstones are common in the UK. Patients who lose weight are more likely to develop gallstones. You may require an operation to remove your gallbladder along with the stones at some point after your gastric bypass, if they cause symptoms.