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Bariatric surgical procedures cause weight loss by restricting the amount of food the stomach can hold, causing malabsorption of nutrients, or by a combination of both gastric restriction and malabsorption. Most weight loss surgeries today are performed using minimally invasive techniques (laparoscopic surgery).


The most common bariatric surgery procedures are gastric bypass, sleeve gastrectomy and adjustable gastric band. Each surgery has its own advantages and disadvantages.

Gastric Bypass

Gastric Bypass

The Roux-en-Y Gastric Bypass – often called gastric bypass – is considered the ‘gold standard’ of weight loss surgery.

If you're interested in being a candidate for a gastric bypass, you can watch this video about how the procedure works. 

The Procedure

There are two components to the procedure.

  • First, a small stomach pouch, approximately one ounce or 30 milliliters in volume, is created by dividing the top of the stomach from the rest of the stomach.

  • Next, the first portion of the small intestine 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 enzymes from the bypassed stomach and first portion of small intestine will eventually mix with the food.


The gastric bypass works by several mechanisms.

  • First, similar to most bariatric procedures, the newly created stomach pouch is considerably smaller and facilitates significantly smaller meals, which translates into less calories consumed.

  • Additionally, because there is less digestion of food by the smaller stomach pouch, and there is a segment of small intestine that would normally absorb calories as well as nutrients that no longer has food going through it, there is probably to some degree less absorption of calories and nutrients.


Most importantly, the rerouting of the food stream produces changes in gut hormones that promote satiety, suppress hunger, and reverse one of the primary mechanisms by which obesity induces type 2 diabetes.

Before surgery



  • Getting informed.

    • It is beneficial to equip yourself with some knowledge of obesity and obesity surgeries. Hopefully this website would provide you with some useful information. 

    • You are welcome to attend one of our free information seminars or simply ask your questions here 

    • It is important to know your options and discuss this thoroughly with your surgeon. Sometimes a second opinion may not be a bad idea. Different surgeons may have different preferences towards a particular procedure based on their training and experience. It is important that you are comfortable and understand your decision before you sign the operation consent.


  • Consultations

    • Meetings with your surgeon and dieticians are important. Use the opportunity to ask questions. Prepare a list if it helps. Consider the option of bringing a family member or close friend along.

    • More than one consultation may be required before a decision is made on the best procedure for you.

    • Sometimes you may be referred to see other specialists when you have other medical conditions, such as obstructive sleep apnoea, diabetes, ischaemic heart disease. This is to ensure your medical condition is optimized before the surgery and thus minimizing all relevant perioperative risks.


  • Pre-operative investigations

    • Base-line blood tests will be requested. This is important especially if you have any risks of developing anaemia or vitamin deficiencies or previous liver or kidney diseases. Please bring along any recent pathology results you might have within the last 6 months, as this could save on unnecessary duplications.

    • Please advise your surgeon if you have any rare blood type or issues with previous blood transfusion or if you are a Jehovah’s Witness. Blood transfusion is rarely required for any type of weight loss surgery. However special and early arrangement may be required under these circumstances.

    • Gastroscopy may be required, especially if you have gastric reflux symptoms or previous history of stomach inflammation or ulcer. The findings of the gastroscopy may potentially influence the decision on the best procedure for your weight-loss surgery. For example, if you have severe reflux disease or severe hiatus hernia detected from gastroscopy, gastric bypass may be a much better option than sleeve or gastric band.

    • Other investigations such as CT scans or gastrograffin swallow/meal studies are not required routinely. However they may be useful or even crucial in pre-operative planning for some patients.


  • Meal replacement program

    • Most patients would need to undertake two weeks of intensive meal replacement before the operation in the form of very low calorie liquid diet. This is designed to boost your weight loss and reduce the fatty contents and size of your liver, so the operation would be easier and safer.

    • Optifast® is commonly used in Australia for such purpose. You will meet with our dietician to formulate a plan for your individual needs.

    • Our dietician will guide you through this process. You are encouraged to keep a regular contact during this period especially when you have trouble following your plan for whatever reason or developed symptoms such as light headedness, fatigue or food intolerance.


  • Quit smoking

    • Smoking is not only ‘bad’ in general. It poses increased risks for your operation, including deep vein thrombosis, pneumonia, wound infection and delayed wound healing.

    • In the medium and long-term, smoking also increases the risk of developing “marginal ulcers” (ulcer at the joint between the smaller stomach pouch and small bowel), which can lead to abdominal pain, bleeding or if severe even perforation.

    • If you are a smoker, you would be expected to have quit smoking for at least 3 months before the surgery is performed. Please seek help from you GP, Quit or Quitline (137848) to quit and stay quit.


  • Medication

    • Please bring your current medications or a list of them to your initial consultation.

    • Important medications for your surgeon to know include those that can thin your blood, such as aspirin, warfarin, Plavix, CoPlavix, Dabigatran (Pradaxa).

    • Also please advise your surgeon if you are taking any herbal medicine or fish oils, as they could potentially thin your blood and increases the risk of bleeding during or after operation as well

The procedure
Before Surgery

During your hospital stay


  • Fasting instruction

    • You will be given instructions regarding fasting before the procedure. Please adhere to these instructions strictly.

    • In general, for morning procedures, you will need to fast from the midnight before; for afternoon procedures, fasting starts from 7am.

    • If you take regular medications, instructions will be given regarding if to continue or withhold them as well.


  • Surgery is expected to take around 60-90 minutes

    • The time taken to complete each surgery varies from patient to patient. In general, gastroc bypass is expected to take around 1 to 1.5 hour for most patients.

    • After the surgery, you will spend some time in recovery for continuous and close monitoring. Then you will be taken to the ward where your family or friends can visit you.

    • Unless instructed otherwise, I would usually like to call your contact person soon after surgery to inform him or her of your progress.


  • 2-3 day hospital stay

    • In general, after gastric bypass, most patients will stay 2-3 nights in the hospital.

    • You will be encouraged to start mobilization as soon as possible. Initially you would need assistance from nursing staff, as you may be unsteady on your feet from the effects of anaethestics and surgery.

    • Also regular deep breathing is important to prevent hospital-acquired pneumonia. You shouldn’t experience severe pain. If you couldn’t breath deeply due to pain, you need to ask for pain relief from the nursing staff.


  • Dietary modifications

    • You will be allowed to drink water and thin fluid few hours after the surgery when you become fully awake.

    • The amount of liquid you can consume will be significantly reduced after the surgery. In the first few days, I would advise you not to drink more than half of a cup each time.

    • It is very important to avoid dehydration after surgery. As you wouldn’t be able to drink a large amount of fluid each time, you need to drink more often. So regular small sips is the key.

    • From Day 2 after surgery, you can start having soup and minced food. You may not have much appetite or you might feel full quickly after only a few tea spoons of food. This is all expected from the restrictive and homonal effects of the surgery. Your appetite and food portion will increase over time but remains much less than prior to your surgery. 

    • You will be expected to be able to tolerate small amount of minced soft food without stomach pain or vomiting before discharge from the hospital. 


  • Investigations in the hospital

    • Blood test. This will be done on the 1st day after your surgery.

    • Gastrograffin swallow, a special x-ray test,  is not routinely done after gastric bypass. I will advise you if this is required. 

    • Both the blood and occasionally, x-ray tests are used to help detect any potential early problems after the surgery. They are useful to safeguard your initial recovery.


  • DVT prophylaxis

    • Deep vein thrombosis (DVT) can be debilitating or potentially lethal.

    • To prevent or reduce the risk of DVT, early mobilization and adequate hydration are important

    • You will also be given Clexane injections. Clexane will be given at a prophylaxis dose (40mg) once a day for the first 10 days after surgery. It is delivered via a small syringe needle. You will be shown how to administer the injection. If you have trouble administering the injection yourself, the nursing staff can also train your family or anyone you nominate. Some GPs can also provide such service.


  • Potential ICU stay

    • Most gastric bypass patients do not require intensive care unit (ICU) after the surgery.

    • However you will be advised on such need well before the surgery during the initial consultation phase. Patients who might require ICU usually include those with significant obstructive sleep apnoea or respiratory or cardiac diseases.


  • Potential early complications

    • Most of the time gastric bypass is safe. Patients are expected to have a smooth recovery and be discharged home 2-3 days after the surgery.

    • Early bleeding can occur in about 2% of the patients. Most of the time it can be managed by observation alone and the bleeding will stop by itself. Occasionally blood transfusion may be required. Patients will be taken back to theatre if the bleeding is significant or fails to stop by itself.

    • Leakage from the staple line or anastomosis can occur in around 2% of cases. The risk is reduced if this is the first time you have surgery on the stomach (primary bypass). However it increases significantly if you had any stomach surgery before, eg. gastric band or hiatus hernia repair or previous sleeve. Leakage once detected, will require return to theatre to fix the problem. Comparing with a leak after sleeve gastrectomy, gastric bypass has the advantage of a better chance of quicker and smoother resolution of the leak. 

Hosp stay

After surgery


  • Short term


  • Follow-up appointments

    • The first review will take place 2 weeks after your discharge from the hospital. You are encouraged to make contact with the dietician or myself if you have any concerns with your recovery at any time.


  • Wound healing

    • The wounds are small, from 5mm to 10mm.

    • The sutures used to close your wounds are buried underneath the skin, so they won’t be visible. They are also self-absorbable after the wounds are healed, so they don’t need to be removed.

    • There will be a plastic drain coming out of one of the wounds. This is to help monitor bleeding or leakage. It will be removed after the first day if no complication is expected or observed. Removal of a drain is not painful and is done by your nurse on the ward. 

    • All wounds will be protected by waterproof dressings. Therefore you may shower after the surgery.

    • Try to keep the dressings on for the first week. If there is any concern with the dressings or wound, such as bleeding or discoloured fluid from the wound, please contact us as soon as possible.


  • Diet

    • For the first 2 weeks, it is important to remain on liquid diet only. Also remember to drink small amount but more frequently.

    • The “new” stomach will usually hold 80 to 120ml of fluid, no more than half of a cup. You will feel full very quickly. Avoid forceful and quick drinking.

    • Avoid drinking carbonated drinks, eg Coke, Solo etc.

    • It is also important to drink protein-rich fluid. A protein-rich diet is important to facilitate rapid wound healing and reduces risks of infection. It also prevents loss of muscle mass.

    • After 2 weeks, your diet can progress onto pureed form, then soft, light and eventually solid food. This process will take about 2 weeks and will be guided by the dietician.


  • Medications

    • New medications:

      • For pain: please take paracetamol regularly for the first 2-3 days (1-2 tablets every 6-8 hours). This will usually be enough to control the pain and reduce the need for stronger, opioid based analgesics.

      • For DVT prophylaxis: you will continue Clexane injection for 10 days to reduce the risk of deep vein thrombosis.

      • For reflux and stomach ulcer: you will continue Pantoprazole for 1 month (smokers will be 3 months or longer).

      • Multi-vitamins and Vit D supplement: it is recommended to continue vitamin supplements for long term. In the first week after surgery, please avoid large tablets. Need to break them or have water-soluble forms.

    • Previous medications:

      • For patients using medications for diabetes or hypertension, it is important to have close and regular reviews with your GP or medical specialists. After sleeve gastrectomy, your ‘sugar control’ or ‘blood pressure control’ is expected to improve, therefore the potential need to adjust your previous medications to avoid ‘hypo’s.


  • Long term


  • Regular reviews:

    • After the first 6 months, you will then have yearly review with us.

    • This is to ensure the long-term success of your surgery and to reduce the potential long-term complications as outlined below.


  • Weight change:

    • You will notice the most rapid weight loss during the first 12 months after surgery.

    • Most patients will have their weight stablised at 2-year’s mark.

    • Small number of patients will have ‘weight regain’ to various scales. Therefore it is important to keep working with dietician closely and maintain a healthy diet and lifestyle to reduce this risk.

    • Some patients will require a ‘revision surgery’ for a number of reasons, which include weight regain.


  • Reflux

    • Due to the nature of the surgery, a small number of patients will develop reflux after sleeve gastrectomy. In a majority of cases, the symptoms can be relieved by medications.  However some patients will eventually need to consider ‘revision surgery’ (eg. conversion to gastric bypass) in case of severe symptoms that fail to respond to medications and could impact on quality of life significantly.

    • Patients with existing reflux symptoms or confirmed large hiatus hernia before surgery would be strongly advised against sleeve gastrectomy. Instead, gastric bypass would be a much better option that can potentially reduce or ‘cure’ reflux.


  • Vitamin and micronutrient deficiency

    • Partly due to the sleeve gastrectomy, patients are at risk of developing vitamin and micronutrient deficiencies after surgery.

    • To reduce such risks, you will need to supplement your diet with regular multivitamins, mostly in the tablet forms.

    • We will monitor the levels of your iron, Vit B12, Vit D and calcium on a yearly basis.


  • Pregnancy

    • Patients planning on having children need to defer the pregnancy until at least 18 months after the surgery.

After surgery
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