Laparoscopic surgery

Surgery for Obesity

Surgery for Obesity



Weight loss surgery can work well to help some people to lose weight. However, it may not be suitable, or the right decision, for everyone who wants to lose weight. Weight loss surgery is also not something to be undertaken lightly. You need to be fully prepared for weight loss surgery and you need to be highly motivated. It is important that when considering surgery you have a full understanding of what it involves, including the risks and benefits. You should also be aware of any long-term changes to your lifestyle and eating habits that you may have to make after your surgery.



What is weight loss surgery and how does it work?

Weight loss surgery is any type of surgery that is carried out specifically to help you lose weight. Weight loss surgery is also called bariatric surgery.

Put simply, your weight depends on how much energy you take in (the calories in food and drink) and how much energy your body uses (burns) up.

  • If the amount of calories that you eat equals the amount of energy that your body uses up, then your weight remains stable.
  • If you eat more calories than you burn up, you put on weight. The excess energy is converted into fat and stored in your body.
  • If you eat fewer calories than you burn up, you lose weight. Your body has to tap into its fat stores to get the extra energy it needs.

The way weight loss surgery works can be:

  • Surgery which may prevent you from being able to eat so much - for example, by reducing the size of your stomach. This means that you will feel full more quickly and therefore eat less.
  • Surgery which may change the way that your body handles the food that you eat. The surgery can make the food that you eat bypass part of your intestine so that fewer calories are absorbed (taken up) by your body from food.
  • Some types of surgery which use a combination of both of these ways.

Some of the different types of weight loss surgery are explained in more detail below.

Weight loss surgery can work well to help lose weight. However, it may not be suitable, or the right decision, for everyone who wants to lose weight. Weight loss surgery is also not something to be undertaken lightly. You need to be fully prepared for weight loss surgery and you need to be highly motivated. It is important that when considering surgery you have a full understanding of what it involves, including the risks and benefits. You should also be aware of any long-term changes to your lifestyle and eating habits that you may have to make after your surgery. Some of these are explained further below.

Note: there is another leaflet in this series, called 'Obesity and Overweight in Adults', which provides more general information about overweight and obesity. It describes how to determine if you are overweight and obese and how to assess your body mass index (BMI). There are also separate leaflets called 'Obesity and Overweight in Children' and 'Weight Reduction - How to Lose Weight'. This leaflet just discusses weight loss surgery.

When is weight loss surgery considered?

In the UK, the National Institute for Health and Clinical Excellence (NICE) has produced some guidance to help doctors decide if someone may be suitable for weight loss surgery on the National Health Service (NHS). NICE provides national guidance on promoting good health and preventing and treating ill health. In the guidance that NICE has produced, the following conditions need to be met for someone to be offered weight loss surgery. You need:

  • To have a BMI of 40 or more, or have a BMI between 35-40 plus a health problem that could be improved if you lost weight. For example, high blood pressure, type 2 diabetes, severe problems with your mobility, sleep apnoea, etc.
  • Already to have been seen and treated by a specialist obesity team.
  • Already to have tried all other ways of losing weight for at least six months with no success. These include changes to your diet, an increase in your physical activity levels and drug treatment to help you lose weight.
  • To have no health problems that may make the operation dangerous for you.
  • To be able to commit to the long-term medical follow-up that is needed after weight loss surgery.
  • To have treatment and follow-up by a team of experts specialised in weight loss surgery available to you.

Also, NICE says that if you have a BMI of 50 or more, weight loss surgery may be considered as a first option. That is, before you have tried any changes to your diet, increased your physical activity levels or tried drug treatment for obesity.

However, in your local area, there may be slightly different guidelines with different criteria that could affect your access to weight loss surgery. Also, the availability of weight loss surgery may vary in different areas. Most of the time, you need to referred for surgery by a specialist obesity management team and not just your GP.

Private weight loss surgery may also be available but this does cost money. Also, even if you are paying privately for your surgery, it is likely that your surgeon will only operate if you fit certain strict criteria similar to those outlined above.

Note: most of the time, surgery for obesity is not recommended in children. It may sometimes be considered in exceptional cases in children who have been through puberty and who are seriously obese. You may choose to discuss this further with your child's doctor. The rest of this leaflet is about weight loss surgery in adults.

What are the benefits of weight loss surgery?

As mentioned above, in general, weight loss surgery has been shown to be very effective at helping to achieve long-term weight loss. When compared with diet, or with treatment with tablets to help weight loss, weight loss surgery has been shown to produce greater degrees of weight loss in obese people. In fact, for people who are very obese, weight loss surgery may be the most effective treatment.

The more general leaflet about obesity and overweight in adults discusses the health risks of being overweight or obese. So, it stands to reason that losing a lot of weight after surgery for weight loss may have a dramatic effect on improving your health. For example:

  • Type 2 diabetes may be completely reversed in many people who have had weight loss surgery, or, in others, the control of their diabetes may be greatly improved.
  • Studies have shown that, in seriously obese people, having weight loss surgery improves their life expectancy (in short, they will live longer).
  • Studies have also shown that people who have had surgery for weight loss are less likely to develop high blood pressure in the future than those having conventional treatment for their weight loss.

Some of the different types of weight loss surgery (discussed below) may enable more weight loss in the long-term than others. However, you should note that these operations may be more complex and may carry more in the way of risks than some of the more straightforward ones.

What are some of the risks of weight loss surgery?

No surgery is without risk and so having weight loss surgery does carry risks. Occasionally, some people die during surgery and, in others, complications after surgery are possible. The risks vary according to your age, sex and your BMI before surgery. Also, in some people, the operation may not always be successful in helping them lose weight.

There are some general risks involved in all types of weight loss surgery. Because you need to have a general anaesthetic, this itself can carry risks. The risks from an anaesthetic are greater if you are obese. There is also a small risk of pulmonary embolism (a blood clot on the lungs) after weight loss surgery. However, medication can be given to help prevent this and getting up and about quickly after the operation can also help. Infection may occur in some people after weight loss surgery. This can include infection in the lungs at the time of the operation, or infection in a skin wound after the surgery.

There are also other risks or complications that vary depending on the type of surgery that you have. These are discussed further below.

What are the different types of weight loss surgery?

There are various different types of weight loss surgery. The most common types are described below and some of their advantages and disadvantages, or risks, are also discussed. The type of surgery that may be best for you can depend on your weight, any health issues that you may have, the experience of your surgeon, etc. Your surgeon will be able to provide you with more details about the different types of surgery and help you decide the most appropriate type of surgery for your situation. The websites listed below may also be able to provide you with further help and information.

The diagram on the right is of the normal gut anatomy. This may help when some of the operations are described.

Gastric band surgery

This is the most common type of weight loss surgery that is carried out. A general anaesthetic (that puts you to sleep) is needed. During gastric band surgery, a special band is placed around the upper part of your stomach, essentially dividing your stomach into two. 

When you eat, food passes from your oesophagus (gullet) into the part of your stomach above the band. Because this upper section is smaller than the size that your whole stomach was previously, you will need to eat less than before to feel full. After eating, the food then gradually passes through to the section of your stomach below the band and is digested as normal.

Gastric bands are designed so that their position can be adjusted after the surgery and so the amount of food that you are able to eat can be changed. The band is connected to a special port under your skin to allow this adjustment. Adjustments may be needed in the first few months after your surgery so that the setting that is best for you can be found. These adjustments can usually be made quickly in an outpatient clinic and you do not need another general anaesthetic or operation. Another advantage of gastric band surgery is that is can usually be carried out using 'keyhole' surgery (laparoscopic surgery). This means a quicker recovery time afterwards. This surgery is also reversible. The band can be removed at a later date if required. However, this would then risk you putting the weight back on again.

Gastric band surgery is generally one of the safest types of surgery for weight loss. However, the surgery does still carry some risks and complications. Sometimes a gastric band can slip out of place or it may erode through (wear through) the wall of your stomach and become ineffective. A gastric band may also wear out and need replacing at a later date. However, these problems do not happen in everyone. If they do occur, another operation may be needed to replace the band. Also, for some people, it make take up to two years to get used to their gastric band and modify their eating habits so that they lose weight effectively.

Gastric bypass surgery

Commonly, an operation called a Roux-en-Y gastric bypass is done. During the surgery, your stomach is divided into two, creating a small upper stomach pouch. A part of your small intestine called the jejunum is then connected to this stomach pouch. This means that when you eat, food bypasses the main part of your stomach and the upper part of your small intestine. In this upper part of your small intestine, your food would normally start to be digested and absorbed (taken up) by your body. So, with this part of your intestine being bypassed, less calories are taken up from the food that you eat. Also, because the new stomach pouch that is created is smaller than the size of your whole stomach, the amount of food that you are able to eat is reduced, thereby restricting calories that you take in.

This operation is again mostly done using keyhole surgery and a general anaesthetic is needed. One of the main risks of gastric bypass surgery is that a leak may develop at the point where your small intestine is connected to your stomach. However, this is rare. If it does occur, further surgery will be needed to repair the leak. Also, because a part of your intestine is bypassed during the surgery, you may develop a deficiency (lack) of some vitamins and minerals as a result of the surgery. For this reason, blood tests will usually be suggested to look for deficiencies and you will be given supplements if needed. 

Gastric bypass surgery may lead to greater weight loss in some people than gastric band surgery but it is more difficult surgery that takes longer to carry out.

Sleeve gastrectomy

During a sleeve gastrectomy, most of one side of your stomach is removed so that you are left with a smaller 'sleeve' of stomach which is essentially a narrow tube. This remains connected to your oesophagus (gullet) above and the first part of your intestine below. So, again, the size of your stomach is made smaller, meaning that you can only eat a much smaller meal. You will also feel fuller for a longer period of time after you have eaten. Again, this type of surgery can usually be done using a keyhole procedure. 

A sleeve gastrectomy is relatively easier and quicker for surgeons than some other types of weight loss surgery. However, it may be slightly less effective than some other operations in terms of the amount of weight loss that someone can have afterwards. For this reason, it is sometimes done as a first operation in people who are very obese and who may have health issues making longer, more complex surgery more risky. Then a second operation may be suggested at a later date. For example, to convert a sleeve gastrectomy to a gastric bypass. However, some people may not need a second operation as they may lose enough weight with just a sleeve gastrectomy.

Bilo pancreatic diversion

During this operation, most of your stomach is removed, leaving just a small stomach pouch behind. This pouch is then connected to the last part of your small intestine so that the majority of your small intestine is bypassed. At the same time, your bile duct and your pancreatic duct (which normally drain bile and pancreatic enzymes into the upper part of your small intestine to help with the digestion of food) are rerouted into the lower part of your small intestine. 

The diagram on the right shows the normal structures before the rerouting.

Most of the fat and carbohydrate that you eat is normally absorbed (taken up) by your body in the upper part of your small intestine. So, after this surgery where this part of your intestine is bypassed, most of the fat and carbohydrate that you eat in your diet passes through your body and is not absorbed (taken up). One of the disadvantages of this type of surgery is that is can cause flatulence (wind) and loose, foul smelling stools. A bilo pancreatic diversion involves quite complex surgery and surgeons need to be experienced in the procedure. Therefore, this type of surgery is not available in all hospitals.

Duodenal switch

This operation is similar to bilo pancreatic diversion. The surgeon starts by carrying out a sleeve gastrectomy (see above). Then the upper part of your small intestine (called the duodenum) is cut and the lower half of your small intestine is connected to the remaining part of your duodenum. Your bile duct and pancreatic duct are then rerouted into the lower part of your small intestine as with a bilo pancreatic diversion. During this type of surgery, your body is less able to digest the fat that you eat and absorb calories from fat. This leads to weight loss but your diet does not have to change too dramatically.

A duodenal switch operation can be very successful in terms of the amount of weight loss that you can have afterwards. However, this is complex surgery and it needs to be carried out by an experienced surgeon. Therefore, this type of surgery is not available in all hospitals. The surgery takes longer and has an increased risk of some complications. It will usually mean that you need to stay in hospital for a longer period compared with some of the other types of surgery. As you are asleep under a general anaesthetic for longer, there is an increased risk of developing a blood clot in your leg or on your lungs. There is also a risk of leakage where the intestine is joined up, as with a gastric bypass operation.

Side-effects can include offensive smelling, loose stools and lots of flatulence if you do not stick to a low-fat diet. Also, this type of surgery can lead to some vitamin and mineral deficiencies and supplements of these may be needed. A duodenal switch operation can also interfere with the amount of protein that your body is able to absorb from food. Protein is important and is needed by our body to help form the structure of our muscles, tissues and organs. Protein is also needed to make various enzymes and hormones. Sometimes, a lack of protein absorbed by the body after a duodenal switch operation can lead to a condition called protein calorie malnutrition which can make you very unwell. For this reason, people who have had a duodenal switch operation are advised to eat a larger amount of protein in their diet.

Other procedures to help weight loss

There are some other procedures that are being carried out to help with weight loss which are not strictly surgical operations. However, not all of these may be available on the NHS. They may sometimes be discussed with you by your surgeon if they have received special funding for these procedures on the NHS as part of research project. They may also be an option if you are seeing a surgeon privately. If these are an option, you should discuss the procedures in full with your surgeon, including their risks and benefits. Briefly, such procedures include:

  • An intragastric balloon. A special telescope (called an endoscope) is passed through your mouth, down your oesophagus (gullet), and into your stomach. This allows a special silicone balloon to be inserted into your stomach. The balloon is filled with liquid so that is fills an area of your stomach. With the balloon in place, it can make you feel full more easily and so reduces the amount of food that you are able to eat. However, this is only a short-term option as the balloon needs to be removed after a maximum of six months.
  • Intragastric stimulation. Two electrodes are planted into the wall of your stomach using keyhole surgery. These are joined to a special stimulator that sits under the surface of your skin. The stimulator sends out electrical impulses to the electrodes in your stomach. It is thought that this then sends messages to your brain, telling your brain that you are full, and therefore reducing the amount of food that you eat.

Newer operations for obesity are also being developed. They include a type of surgery called Primary Obesity Surgery, Endoscopic (POSE). This new type of weight loss surgery is carried out using an endoscope. An endoscope is a flexible tube with a camera attached that also has a number of channels through which surgical instruments can be passed. During the surgery, the endoscope is fed through your mouth and into your stomach and the surgeon operates through the channels to make your stomach smaller so that you will feel full more quickly. Because there are no incisions (or cuts) into your abdomen to reach your stomach, you are likely to recover much more quickly and will not need to stay in hospital for as long. The procedure is also less painful than conventional weight loss surgery. However, techniques such as POSE are very new in the UK and, at present, they are unlikely to be available on the NHS. Again, they may be an option if you were to have surgery privately in some areas.

What happens before the surgery?

Before the surgery, you will be seen by a team including a number of different healthcare professionals. For example, a surgeon, an anaesthetist, specialist nurses, dieticians, a psychiatrist, an endocrinologist, etc. It is important that you have full discussions with the team so that you can decide which is the best type of surgery for you, what the surgery will entail, the risks and benefits of the surgery in your situation and changes that you will have to make to your diet and lifestyle afterwards.

You may like to ask the surgeon about their experience. How many operations of this type have they done? What is their success rate: how much weight do people generally lose and how long do they keep the weight off for? What complications have people undergoing this type of surgery had? What support and follow-up will you have afterwards?

You may also need to have some investigations to make sure that it is safe for you to have the surgery. For example, these may include tests of your heart and lungs.

You may find it helpful to join a support group and meet up with other people who are waiting for, or who have been through, weight loss surgery. This will give you the opportunity to discuss with other people their experiences surrounding weight loss surgery. Various groups are available throughout the UK. Information can be found using the links below.

What happens after the surgery?

After weight loss surgery, you will need close follow-up. This will usually involve seeing a number of healthcare professionals (part of the same team mentioned above). 

It is essential that you follow eating and exercise guidelines that you are given. After the surgery, in order to lose weight, you will need to change you eating habits. You will need to reduce the amount of food that you eat compared with what you ate before the surgery. You will be given strict guidelines about what to eat in the first few weeks after surgery. Initially, this may be liquids such as unsweetened fruit juices, tea, coffee, smooth soups and build-up drinks. Then gradually you will be able to build up to softer foods such as scrambled eggs, pasta, yoghurts, etc, and then more textured food. It is important that you eat a healthy balanced diet. 

Some people find that the changes that they need to make to their diet and lifestyle after surgery for weight loss are difficult to come to terms with. You can receive help and guidance about what to eat from the team of specialists that will be looking after you. Depending on the operation that you had, you may also be advised to take some vitamin and mineral supplements.

Remember, the surgery won't work all by itself to help you lose weight. You need to work with it. You need to be aware that you will need lifelong medical follow-up after weight loss surgery. Again, you may find being part of a support group helpful.

Further help and information

British Obesity Surgery Patient Association (BOSPA)

PO Box 805, Taunton, Somerset TA1 9DH
Tel: 08456 02 04 46 Web:
Provides support and information to people in the UK considering obesity surgery.

Weight Concern

1-19 Torrington Place, London WC1E 6BT
Tel: 020 7679 1853 (not a helpline) Web:
Weight Concern is a registered charity, set up to tackle the rising problem of obesity. Weight Concern has shown how psychologists, dieticians and exercise specialists working together can help people make the lifestyle changes they want, to control their weight.

WLSinfo (Weight Loss Surgery Information and Support)

Wessex House, Upper Market Street, Eastleigh, Hampshire SO50 9FD
Tel: 0151 222 4737 Web:
A UK charity providing information and support to patients who are considering or have had weight loss surgery.

National Obesity Forum

First Floor, 6a Gordon Road, Nottingham NG2 5LN
Tel: 0115 846 2109 Web:
Website has a section for families and individuals, which offers advice and support about how to adopt a healthier lifestyle.


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Comprehensive patient resources are available at
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
© EMIS 2010    Reviewed: 16 Aug 2010   DocID: 13150   Version: 2

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