Weight loss surgery (Bariatric surgery)


Weight loss surgery (Bariatric surgery)
Weight loss surgery (Bariatric surgery)

What is weight loss surgery?

  • Weight loss surgery, sometimes called bariatric surgery, is a treatment for people who are severely obese. It makes the stomach smaller so it feels fuller sooner and less food is eaten.
  • The main types of weight loss surgery are gastric bypass, gastric band, gastric balloon and sleeve gastrectomy.
  • To be considered for NHS weight loss surgery you'll usually need a body mass index (BMI) of 40 or more and have tried to lose weight through a healthy diet, exercise and medicine.
  • You'll also need to agree to lifestyle and diet changes and regular check-ups after surgery.
  • You'll have the operation in hospital and usually go home 1 to 3 days after surgery. Recovery time is usually 4 to 6 weeks.

Find out more about losing weight through a healthy diet and exercise.

Who can use it?

In Wales the Welsh Health Specialised Services Committee has produced a policy document which sets out the criteria that need to be fulfilled for an individual to qualify for consederation for Bariatric Surgery. This policy applies to all seven Health Boards in Wales.

The policy says that individuals must satisfy all elements of the access criteria for assessment and treatment to proceed.

The access criteria for specialised bariatric services are set out below:

  • The individual is aged 18 years or over;
  • The individual has a BMI of 40 or greater;
  • Morbid/severe obesity has been present for at least five years;
  • The individual has received, and complied with, an intensive weight management programme at a multi-disciplinary weight management clinic (level 2/3 of the All Wales Obesity Pathway) for at least 24 months duration, but has been unable to achieve and maintain a healthy weight; and
  • The individual is approved for surgery by the bariatric MDT at the Welsh Institute of Metabolic and Obesity Surgery, Abertawe Bro Morgannwg University Health Board.

When weight loss surgery isn't suitable 

Weight loss surgery may not be recommended if you have a serious illness that would not be improved after the operation, such as:

Weight loss surgery is also unlikely to be recommended if a mental health condition or other underlying factor means you'd be unable to commit to long-term follow-up and lifestyle changes.

Examples of these conditions and factors include:

  • schizophrenia for which you are refusing to seek treatment
  • actively abusing alcohol or drugs
  • a previous history of not complying with medical recommendations about your care
  • patients who are unable or unwilling to participate in prolonged medical follow-up.
  • active/Unstable mental health illness
  • severe depression, personality and eating disorders.
  • active alcohol abuse and/or drug dependencies.
  • a previous history of not complying with medical recommendations about your care


Weight loss surgery would only be considered to treat obese children in exceptional circumstances, and only if the child is physically mature (around the age of 13 for girls and 15 for boys).

Most experts in obesity would only recommend surgery as a last resort treatment for children who are severely morbidly obese (a BMI of 50 of above), or who are morbidly obese (a BMI of 40 or above) and also have a serious health condition that would improve if they lost weight.

Read the NICE guidelines on managing overweight and obesity among children and young people.

How is it performed?

The three most widely used types of weight loss surgery are gastric banding and sleeve gastrectomy. These procedures moderate patients’ appetite and stimulate metabolism to cause substantial and sustained weight loss.

These operations are usually performed as a type of laparoscopic (keyhole) surgery, where a series of small incisions are made in the abdomen, rather than one large incision. The advantage of this type of surgery is it causes less pain afterwards and has a faster recovery time.

However, laparoscopic surgery may not always be possible in severely morbidly obese people, or those who have had other abdominal operations.

They are carried out under general anaesthetic, which means you'll be asleep during surgery and won't feel any pain.

The surgeon makes the incisions in your abdomen, then inserts an instrument known as a laparoscope through one of the cuts. A laparoscope is a thin, rigid tube containing a light source and a camera. The camera relays images of the inside of your abdomen to a television monitor.

Each type of surgery is discussed in more detail below.

Gastric banding

Other small instruments are placed through the cuts to place a gastric band around the top of your stomach, effectively dividing your stomach into two, leaving a small pouch at the top.

As it takes less food to fill the pouch, it takes less food to make you feel full.

The band is connected to an access port, which is placed under the skin. Saline (sterile salt water) can be injected into this port to inflate the band. This allows the band to be adjusted as required after surgery.

The surgery usually takes around an hour to complete.

Gastric bypass

Gastric bypass uses special surgical staplers to create a small pouch at the top of your stomach. This pouch is then connected directly to a section of your small intestine, bypassing the rest of the stomach and bowel.

This means it takes less food to make you feel full and you'll also absorb fewer calories from the food you eat.

Sleeve gastrectomy

During a sleeve gastrectomy, part of the stomach is removed. This restricts the amount of food that can be eaten and results in you feeling full sooner than normal when eating.

It can also moderate the appetite and stimulate metabolism to cause substantial and sustained weight loss.

Bypass, banding or sleeve?

All three types of surgery have advantages and disadvantages.

There's usually more weight loss after a gastric bypass and sleeve gastrectomy than after a gastric band.

Most people with a gastric band lose around half their excess body weight, whereas most people with a gastric bypass or sleeve gastrectomy lose around two-thirds of their excess body weight.

However, because it's more technically demanding, a gastric bypass carries a higher risk of complications, including death. Read about the risks of weight loss surgery.

A gastric band is reversible, so if you find it difficult to cope with the restrictions associated with life after surgery, you can have the band removed.

Although if the band is removed any restriction to your appetite is reduced and weight regain may occur.

A gastric bypass or a sleeve gastrectomy, on the other hand, can't be reversed. You'll also be required to take nutritional supplements for the rest of your life if you have a gastric bypass or a sleeve gastrectomy.

A gastric bypass often has a much greater impact on type 2 diabetes, in a shorter time, than either a gastric band or sleeve gastrectomy.

Discuss the advantages and disadvantages of both types of surgery with your surgical team.

Other types of bariatric surgery

Other types of weight loss surgery, which are less commonly used, are outlined below.

Bilo-pancreatic diversion

A bilo-pancreatic diversion is similar to a gastric bypass, except a much larger section of the small intestine is bypassed, meaning you'll absorb even fewer calories from the food you eat.

A bilo-pancreatic diversion can achieve a good level of weight loss (up to 80% of excess body weight) but it carries a high risk of complications and can cause unpleasant side effects, such as unpleasant-smelling diarrhoea.

Because of this, a bilo-pancreatic diversion is usually only recommended when it's felt that rapid weight loss is required to prevent a serious health condition, such as heart disease, from getting worse.

Intra-gastric balloon

An intra-gastric balloon is a soft silicone balloon that's surgically implanted into your stomach. The balloon is filled with air or saline solution (sterile salt water), and so takes up some of the space in your stomach. This means you don't need to eat as much before you feel full.

This procedure is only temporary, and the balloon is usually removed after six months. The procedure is useful if you don't meet the criteria for the other types of surgery – for example, because you're too obese.

An intra-gastric balloon procedure can usually be done without making an incision in your abdomen. Instead, the balloon can be passed through your mouth and down into your stomach using an endoscope (a thin, flexible tube that has a light and a camera on one end).

Read more information about a gastroscopy.


After weight loss surgery, you will need a few days to recover. It may also be several weeks or months before you can resume normal activities, depending on the type of surgery you have.

Recovering from a gastric band operation

When you wake after surgery, you will probably have some pain at the site of the surgery. This is normal and should pass within a few days.

Blood clots are an uncommon but serious complication that can occur after banding, including:

To reduce the risk of blood clots, you may be given a blood-thinning medication, such as heparin, and compression stockings to wear.

Once you feel well enough, move around as much you can as this will further reduce your risk of blood clots.

For the first 24 hours, you will only be allowed to drink a small amount of liquid to prevent vomiting.

Gradually, small amounts of solid food will be introduced into your diet. For more information, see Weight loss surgery - recommendations.

Gastric band surgery may be carried out as a day case and most people are well enough to leave hospital within 24 hours of surgery. You can resume normal activities within two to three weeks.

Four to six weeks after surgery, your stomach should have healed enough that your band can be adjusted by inflating it with saline (sterile salt water).

This is done by inserting a needle via the access point through which the saline is pumped. The band will then inflate and constrict the upper pouch of your stomach. The whole process takes around 15 minutes. This is sometimes done after numbing your abdomen with a local anaesthetic, using an X-ray to locate the band.

Often, this process of adjustment is a fine balancing act. For example, if the band is too loose you may not lose weight, but if the band is too tight, you may vomit after eating.

Therefore, it can take a number of sessions before the ideal adjustment for your band is reached.

Recovering from a gastric bypass & Sleeve Gastrectomy

Once you wake after surgery, you will probably have a drip in your arm, to provide your body with liquids.

This will be removed when you are able to drink sufficient fluids by mouth.

Again, you may be given blood-thinning medication and compression stockings to wear to help prevent blood clots.

You will only be allowed a liquid diet immediately after surgery, and solids will be slowly introduced into your diet.

Most people are well enough to leave hospital one to four days after surgery and resume normal activities within four to six weeks.

Recovering from other types of weight loss surgery

The recovery time for other types of weight loss surgery are:

  • sleeve gastrectomy - one to four days to leave hospital and two to three weeks to resume normal activities
  • bilo-pancreatic diversion - one to four days to leave hospital and four to six weeks to resume normal activities
  • gastric balloon - fitting a gastric balloon is a non-invasive procedure (does not involve making incisions in your body), so you should be able to leave hospital on the same day and resume normal activities almost immediately

You'll also only be allowed a liquid diet immediately after these types of surgery, and solids will be slowly introduced into your diet.


The rapid weight loss associated with weight loss surgery can cause a number of side effects and has a number of risks. These are outlined below.

Complications immediately after surgery

Complications that can occur during or immediately after surgery include:

  • infection - this affects around 1 in 20 people
  • blood clots in the legs (deep vein thrombosis) or lungs (pulmonary embolism) - this affects around 1 in 100 people
  • internal bleeding - this affects around 1 in 100 people

Excess skin

While weight loss surgery can successfully remove the fat in the body, it cannot cause skin to revert to its pre-obesity tightness and firmness.

Therefore, if you were obese, especially for many years, you may be left with excess folds and rolls of skin, particularly around the breasts, tummy, hips and limbs.

These folds and rolls normally become most apparent 12-18 months after surgery. Many people who have lost a significant amount of weight feel that the excess skin is unsightly and can be difficult to keep clean.

Cosmetic surgery can be used to remove the excess skin. However, as this treatment is for cosmetic and not clinical reasons, it is not available on the NHS.

Abdominoplasty and apronectomy may be offered to the following groups of patients who should have achieved a stable BMI between 18 and 25 Kg/m2 and be suffering from severe functional problems:

Previously obese patients who have achieved significant weight loss and have maintained their weight loss for at least two years.

Severe functional problems include:

  • Recurrent intertrigo beneath the skin fold.
  • Experiencing severe difficulties with daily living i.e. ambulatory restrictions.
  • Where previous trauma or surgical scarring (usually midline vertical, or multiple) leads to very poor appearance and results in disabling psychological distress or risk of infection.
  • Problems associated with poorly fitting stoma bags.

The price for a course of skin-removal treatment can range from £1,500 to £6,000 depending on the amount of skin that needs to be removed.

For more information, see the topic on Cosmetic surgery.


Around 1 in 12 people will develop gallstones after weight loss surgery, typically 10 months after surgery.

Gallstones are small stones, usually made of cholesterol, that form in the gallbladder.

In most cases, gallstones do not cause any symptoms. However, if they become trapped in a duct (an opening or channel), they can irritate and inflame the gallbladder and cause symptoms, such as:

  • a sudden intense pain in your abdomen (tummy)
  • nausea and vomiting
  • jaundice (yellowing of the skin and the whites of the eyes)

Psychosocial effects of surgery

While most people who undergo weight loss surgery report an improvement in their quality of life, several psychosocial effects may be related to rapid weight loss.

Some people have reported relationship problems with their partner as their partner begins to feel nervous, anxious or possibly jealous about their weight loss.

Social occasions that revolve around food, such as family meals, can become awkward, as it's common to feel self-conscious about your reduced capacity to eat.

It's also common for a person to experience a worsening of mood when their weight stabilises, typically two years after surgery. This is often because many people realise that problems that existed before surgery, such as money worries or difficulties at work, are still there.

You may find it useful to discuss these issues with people who have also had weight loss surgery. The British Obesity Surgery Patient Association’s website contains a service directory of support groups in the UK.

Read more information and tips for dealing with psychosocial effects of surgery, such as stress, anxiety or depression..

Stomal stenosis

A common complication in people with a gastric bypass is that the hole (stoma) connecting their stomach pouch to their small intestine becomes narrowed and may get blocked by a piece of food. This is known as stomal stenosis and is thought to occur in one-fifth of people with a gastric bypass.

The most common symptom of stomal stenosis is persistent vomiting.

Stomal stenosis can be treated by directing a small flexible tube, known as an endoscope, to the site of the stoma. A balloon attached to the endoscope is inflated to unblock the stoma.

The best way to prevent stomal stenosis is to always cut food into small chunks, chew the chunks thoroughly and avoid drinking during meals, see Weight loss surgery - recommendations.

Gastric band slippage or erosion

Gastric band complications have been reported to be as high at 50% in some studies.

The cause and seriousness of the complications vary;

  • Port Problems (Occurs in up to 20% of patients):
    • Port Site Infections: This is an infection of the port that is used to fill and un-fill the band. Minor infections in this area can be treated with antibiotics. Serious infections of the port can lead to band removal.
    • Port Leak: A port leak can cause the band to lose its fill. This results in the band not maintaining the proper fill level. Port leaks usually require a surgery to replace the port or the tubing but generally do not require the band to be replaced.
    • Port Flipping: The port, located just under your skin, can flip. This may require surgery to re-attach the port.
    • Port Migration/Dislodgement: Your port can move from its original location. This can make it hard to locate and harder to properly fill the band. This may require surgery to re-establish the port’s position.
  • Oesophageal (gullet) Dilation (Occurs in up to 14% of patients): This occurs when your pouch is placed incorrectly during surgery or it is filled too tightly. Food puts pressure on the walls of the oesophagus and can eventually cause a pouch to form. This can lead to vomiting, nausea, and acid reflux. If lowering the fill in the band does not help, a second surgery or even band removal may be required.
  • Pouch Dilation  (Occurs in up to 15% of patients): This is similar to oesophageal dilation except your stomach pouch (area above the band) dilates as a result of pressure from food and liquids over time. This can cause vomiting and acid reflux. If lowering the fill in the band does not help, a second surgery or even band removal may be required.
  • Band Erosion: (Occurs in as few as 2% and up to 9% of patients) This happens when, over time, the band rubs against the stomach or oesophagus and either erodes the wall of the stomach or erodes the wall of the band. The band stops working and food flows unrestricted. This requires the band to be surgically removed.
  • Band Slippage: This happens when the band ‘slips’ down the stomach. The pouch above the band becomes too large. This can cause vomiting and reduce the amount of weight loss. , a second surgery or even band removal may be required.
  • Leak: (Occurs in 1 to 4% of patients) The band is a man-made device and weaknesses in the plastic can lead to a leak. , a second surgery or even band removal may be required.

Food intolerance

Around 1 in 35 people with a gastric band develop a food intolerance, often many years after their surgery.

A food intolerance is when your body is unable to tolerate certain foods, such as red meat or green salad, resulting in a number of unpleasant symptoms such as:

The reason why a food intolerance can develop after surgery is unclear.

In most cases, avoiding foods that trigger a reaction should help improve symptoms, but if you have persistent symptoms associated with a number of different foods, it may be necessary to remove the band.  Further surgery is not guaranteed either in the NHS or private practice.


No surgery is entirely safe and all surgical procedures carry a risk of death. However, the outlook for weight loss surgery has greatly improved with modern techniques.

The risk of death in hospital after having any kind of weight loss surgery is around 1 in 1,000.

Complications of weight loss surgery that could lead to death include:

A number of risk factors have been identified that increase the risk of death during or shortly after weight loss surgery. These are:

  • being aged over 45 years old
  • high blood pressure
  • having a BMI of 50 or above
  • being male, as obese men tend to weigh more than obese women
  • having a known risk factor for a pulmonary embolism

Known risk factors for a pulmonary embolism include:

  • having a previous history of blood clots
  • pulmonary hypertension, when the blood pressure inside your lungs is particularly high
  • obesity hypoventilation syndrome, when you have persistent breathing difficulties related to your obesity

The risk factors above can have a significant impact on your individual risk of death. However, untreated obesity, especially morbid obesity, carries a significant risk of premature death itself.

In most cases, the benefits of surgery outweigh the risks in people who meet the criteria for weight loss surgery.

Bariatric surgery candidates should have a comprehensive clinical assessment by specialists within bariatric surgery.

For more information, see Weight loss surgery - who can use it?

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website nhs.uk
Last Updated: 18/04/2024 12:37:22