The Lindo Wing, St Mary’s Hospital,
Praed Street, London W2 1NY

More information on Mini Gastric Bypass

What is Mini gastric bypass?

This is an operation where some of the stomach and part of the small intestines are bypassed. The stomach is stapled to leave a smaller pouch and then a section of the small intestine is attached (usually by staples) to the stomach pouch that has been created (see picture below). The operation is done as ‘keyhole’ surgery while you are under a general anaesthetic.



Having this procedure will be a tool to help you change how and what you eat. You will not be able to eat as much as before because after this type of surgery patients generally feel fuller much sooner and less hungry.

This method of surgery is recommended for patients with a BMI (body mass index) of 35 and over. On average, patients tend to lose 30% of their total body weight in the first year after their surgery.

Are there any risks associated with this operation?

Most people will not experience any serious risks from their surgery.

However, as with any operation, there are risks associated with having a general anaesthetic. Specific to this operation, there is a 2 per cent risk of:

  • Leakage from the joint to the bowel, narrowing of the join or ulceration of the gastric pouch
    A second operation may be required to correct these.

  • Bowel obstruction
    This may happen if the small bowel becomes blocked which prevents food, fluids, and gas from moving through the bowel in the normal way.

  • Chest infection
    You can help by practising deep breathing exercises with your inspirometer and following the instructions of the physiotherapist. If you smoke, we strongly advise you to stop.

  • Wound infection
    You may be prescribed antibiotics to treat this if it occurs.

  • Wound hernias
    Even though the scars are very small, you may develop a small lump in the wound which may need further treatment.

  • Deep vein thrombosis (blood clot in the leg), also known as DVT
    Major surgery carries a risk of clot formation in the leg. A small dose of heparin (blood thinning medication) will be injected once or twice daily until you go home. You can help by moving around as much as you are able and in particular regularly exercising your legs. You may also be fitted with some support stockings for the duration of your stay in hospital. If you smoke, we strongly advise you to stop.

  • Pulmonary embolism (blood clot in the lungs)
    Rarely, a blood clot from the leg can break off and become lodged in the lungs. This is treated with anticoagulant (blood thinning or clot dissolving) medication. Your surgeon will explain more if this rare event occurs.

  • Bleeding
    A blood transfusion may be needed, or, very rarely, further surgery may be required. If you are unable to receive blood products, please discuss this with your surgeon.

  • Heartburn
    There is a risk for bile reflux and heartburn, and medication may be needed to control it. Rarely, further surgery may be required.

  • Loose stool and diarrhoea
    There is a risk for loose stool and sometimes diarrhoea. Dietary changes and medication may be needed to control it. Rarely, further surgery may be required.

Please note that there is a 1 in 300 risk of death caused by having this surgery.

There are certain foods that you may not tolerate very well after your surgery. These tend to be foods that are high in sugar and fat. Please refer to the diet sheet ‘Diet for Gastric, Bypass and Sleeve’ for advice.

What are the benefits of having this operation?

You will lose weight and this will improve your health.

Are there any alternatives to this operation?

  • Lifestyle management

  • Drug treatment

  • Gastric band surgery

  • Sleeve gastrectomy surgery

Your surgeon will discuss other options with you if appropriate.

What happens before the operation?

A few weeks before your operation, we will ask you to attend the pre-admission assessment clinic. This appointment is to check your current health and the factors that may affect your surgery, and make sure that you are fully informed about for your admission, treatment and discharge home. You may also have investigations such as blood tests, ECG (recording of your heart) or a chest x-ray if they have not been done already. You will be assessed by a surgeon and an anaesthetist.

Anaesthesia means ‘loss of sensation’. Medications that cause anaesthesia are called anaesthetics. Anaesthetics are used for pain relief during tests or surgical operations so that you do not feel pain or touch.


You will be asked for your consent before the hospital staff begin your treatment. Your doctor and/or clinical nurse specialist/key worker will carefully explain the procedure. Details will vary according to each individual case. No medical treatment can be given without your written consent.

If you do not understand what you have been told, let your surgeon know straight away, so they can explain again. You may also find it useful to write a list of questions before your appointment and to have a relative or friend with you to help you remember the discussion when the treatment is explained.

You will receive a copy of all communications sent to your GP, but please let us know if you prefer not to receive this.

Is there anything I should do to prepare for my operation?

  • Please follow the pre-operative diet sheet for bariatric surgery before your operation - your surgeon will advise the duration for this. This is primarily to shrink the size of your liver. It is important you follow this diet carefully as if your liver has not reduced in size enough, your operation may have to be cancelled.

  • Make sure you go for a 30-minute walk every day, as this is good cardiovascular exercise. This will reduce the risk of complications after surgery, as well as help you lose some weight prior to surgery.

  • If you take blood-thinning medications (such as warfarin, aspirin or clopidogrel) and/or you are allergic to any medications, please contact the ward or the bariatric team for advice before you come in to hospital. Generally, these will have to be stopped for seven to 10 days before your surgery.

  • If you are a smoker, you must stop smoking at least six weeks before your operation. Stopping smoking will improve your chances of a good recovery. It will also improve wound healing and reduce the likelihood of you getting complications after surgery.

  • Please do not eat anything (not even sweets or chewing gum) six hours before surgery. You may sip only water until two hours before your surgery.

  • If you regularly take medicines in the morning, you should take them before 7:00am, with a small sip of water if necessary.

  • If you have diabetes, you must not take your insulin or diabetic tablets on the morning of your operation unless you have been advised otherwise.

What happens on the day of my operation?

You will be admitted to the ward on the day of your operation. Your temperature, blood pressure, breathing rate, height, weight and urine will be measured. We will measure you for special stockings (sometimes known as ‘TEDS’) to prevent blood clots (DVT) from forming in your legs following surgery. We may also start you on anti-coagulant (blood-thinning) injections to help minimise this risk.

All make-up, nail varnish, jewellery (except wedding rings, which can be taped into place), body piercings and dentures must be removed. One of the nurses will then come and prepare you for the operating theatre.

What happens after the operation?

You will wake up in the recovery room before you are taken back to the ward.
Please tell us if you are in pain or feel sick. We have tablets/injections that we can give you as and when required, so that you remain comfortable and pain free.  

You may feel light-headed or sleepy after the operation. This is due to the anaesthetic and may continue until the next morning. You may have a sore throat for two or three days after having a general anaesthetic. This sometimes happens because the anaesthetist has to pass a tube down your windpipe to give you the anaesthetic gases that keep you asleep during the operation.We will ask you to stand up and start moving around four hours after your operation. It is important that you move/walk about as much as possible, as this will reduce the risk of any complications and speed up your recovery.

Please make sure that you do your breathing exercises using the inspirometer 10 times every hour (between 8:00am and 10:00pm) and walk around for 10 minutes every hour and every day that you are in hospital.

Your wound will have been closed with surgical clips, which we will remove when you return for your first follow-up clinic appointment, seven to10 days after surgery. You can remove the dressing covering your wound 24 hours after your operation and also have a shower at this stage, using a clean towel to pat your wounds dry.

For the remainder of your stay, the nurses will take your temperature, pulse and blood pressure at regular intervals to check your recovery and it will sometimes be necessary to wake you up to do this. It is very important that we monitor your progress after your operation, so please be patient with the nursing staff during this time. The bariatric team will also visit you every day to check on your recovery.

You may have a drain (tube) inside your wound. This is so that any blood or fluid that collects in the area can drain away safely and will help prevent swelling. The tube will be removed when it is no longer collecting fluid, usually one to two days after surgery. In some cases, the drain may be left in and removed at your first follow-up appointment seven to 10 days after surgery.

A ‘drip’ will also be attached to a needle in your arm or neck to provide you with fluids and prevent dehydration.

If you are diabetic, your blood sugars will be monitored four hourly and if required you will be given an injection of insulin to help reduce your blood sugar levels

Dietary advice after surgery

You will be allowed to start slowly sipping liquids such as water, tea, coffee, milk or squash the day after surgery.

  • From day two after surgery until day 10 you will be on a liquid diet

  • From day 11 to five weeks after surgery, you will be on a puréed diet

  • Weeks six to 12 after surgery, you will be on a soft diet

  • Week 12 onwards, you can start a regular textured, healthy diet

For further details, please see the diet plan given to you before surgery by the dietitian.
Dumping syndrome is a common side effect after bariatric surgery. This happens when the small bowel fills too quickly with undigested food from the stomach. ‘Early’ dumping begins during or right after a meal. Symptoms of early dumping include nausea, vomiting, bloating, cramping, diarrhoea, dizziness and fatigue. ‘Late’ dumping happens 1 to 3 hours after eating. Symptoms of late dumping include weakness, sweating and dizziness.

Please refer to your diet sheet for more advice.

If you can no longer tolerate dairy products such as milk (if this makes you feel nauseous), please contact your dietitian.

When can I go home?

Provided you are well enough, you should be able to go home on the morning of the first or second day after your operation. We will give you a one-week supply of medication to take home with you. Any further medication will need to be prescribed by your GP. Please make sure that you arrange this before the one-week supply runs out.

Please arrange for someone to come and collect you by car on the day of your discharge home, as you will not be able to drive yourself or travel on public transport. It is important that you make the necessary plans as you will be expected to make your own arrangements for going home.

After returning home

You will start you on an acid reducing tablet (PPI) to protect your stomach pouch, which you will need to continue to take for life. You will also need you to take multivitamin and mineral supplements (for life) and possibly another medicine to reduce gallstone formation after surgery (six months) unless you have had your gallbladder removed.

You may feel different sensations in your wound such as tingling, itching or numbness. This is normal and is part of the healing process.

However, if you experience a high temperature or fever, new or worsening stomach pains, constant vomiting or feel unwell in any way, please contact the bariatric team immediately. We will give you a list of emergency contact numbers before you go home.

If you have any swelling, pain, discharge or excessive redness around the wound site, please contact your GP as you may have a wound infection.

You should continue to walk for 30 minutes every day for the next eight weeks, as this is good cardiovascular exercise. It will reduce the risk of complications after your operation.

You should also do your breathing exercises three times each day for the next eight weeks, using your inspirometer as instructed by your clinical nurse specialist. p.7

First week after surgery

  • You may still have some abdominal discomfort, which can be caused by excess wind, your wound or the reduced size of your stomach. You can take painkillers for this if necessary

  • You should be able to return to work. However, you should avoid doing any heavy lifting for the next six weeks

  • We will ask you to return to the outpatient clinic to see us 7 to 10 days after surgery. We will remove your skin clips and check that you are taking your medications correctly. If you have diabetes, please bring your glucose monitoring diary with you

Three months to two years after surgery

We will send you appointments three, six, twelve months and two years after surgery to see us so that we can check your progress and that you are taking your medications correctly. We will also ask you to have some blood tests.

One year after surgery

Following your one year review you will be discharged back to the care of your GP and should continue to see your GP yearly thereafter so that he/she can check your progress to ensure that you are eating correctly, that you are taking your medications and have all the vitamins and minerals that you need. Your GP will also ask you to have some blood tests. If you want a longer follow up package please speak to our team.

Get in touch with us if you have any questions by
Calling Us on 0203 312 6130

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Please note, most insurance policies in the UK do not cover weight-loss surgery. However, we will do our utmost to provide the best package for you should you choose to have your surgery with us.