Discharge information for GP: post gastric bypass

Information sheet to patients and general practitioners after laparoscopic gastric bypass

Please forward this to your GP as well.


The proposed mechanism:

Similar to the sleeve gastrectomy, the gastric bypass works in three ways by reducing the size of the stomach (volume restriction to prevent over eating), reduce hunger stimulus by reducing the hormone ghrelin (reduces craving for food and the constant need to snack) and help maintain post-prandial satiation longer (gives patient better satisfaction after meals and decrease the need to eat repetitively), which is known as the neuro-endocrine brake effect (action on the central brain via the entero-insular axis).

This is the hindgut theory with the secretion of distal gut hormone GLP-1, which is considered important feedback to the brain to stop the hunger stimulus and induce fullness sensation. This same hormone may also has an incretin effect on the pancreas, important for the secretion of insulin, which helps with glycemic control, reduction of medications (oral hypoglycemic tablets or insulin), may halt the progression of diabetes or remission of type 2 diabetes mellitus for some patients.

The reduction in food consumption and achieving negative energy balance, patients will gradually lose excess body weight over the 6-12 months after surgery.

The long limb gastric bypass may also have a malabsorption component. Some people experience diarrhoea and offensive stools as a result of rapid food passage through the GI system. This is one mechanism where fatty meals are more likely to be passed out and less absorption into the blood stream or stored in the body.

Equally as important are the less tangible benefits, which includes better education/understanding of nutrition (allowing patients to make good food choices in controlled portions) and improved long-term post-operative eating habits (minimize compulsive or binge eating behaviour and snacking). Greatest success after the gastric bypass is achieved amongst the group of patients who eats large portion of food and snacks frequently, less success with emotional eating.

The key points are that surgery is a tool to assist patients to lose excess body weight, visceral fat, reduce chronic inflammation, cardio-vascular risk and the risk for metabolic syndrome and causing a complete behavior, eating habits and lifestyle change.

  • Bariatric surgery results in appetite suppression (satiety) as well as helping people feel full with small meals (satiation).
  • Emphasis on controlled or good food portions
  • Good food choices
  • Good eating habits
  • Eating healthy (metabolically active) foods
  • Plenty of aerobic exercises are encouraged
  • Escape from food addictions (especially sweets, soft drinks, alcohols) and correct eating disorders




Diet advice after surgery

For the first 2 weeks patients are advised to continue with oral fluids (such as vegetable soup, fruit juice, Gatorade or Powerade drinks) as well as the protein supplemental drinks (VLCD shakes) or Nutribullet drinks.

  • The very low calorie diet (VLCD) is usually commenced 2 weeks before bariatric surgery and is continued for a month after surgery (during the transition period). These shakes provide the protein that is required as well as the necessary vitamins and minerals.

For the second 2 weeks, commence on soft puree foods (puree vegetables, yoghurts, custards).

Then 2 weeks after that (or a month after the initial surgery), solid meals are introduced if there are no nausea or vomiting. Most patients will start with soft-boiled eggs, steam fish, boiled chicken without the skin or minced meat.

Ultimately the aim is to have a regular meal schedule and 3 small meals a day. Remember to eat slowly (over 30 minutes), stop eating when feeling full and drink fluids at least 30 minutes after meals. This will reduce the discomfort sensation, reduce regurgitation or vomiting and in the long term prevent stretching of the proximal gastric pouch, which may result in loss of restriction.

The daily protein intake should be 1g/kg ideal body weight per day, hence for most people it is 60-70g protein a day.

The non-calorie fluid (water or non caffeinated beverages) intake should be at least 1.5 to 2 litres a day.

In the long term patients are encouraged to have “healthy” fresh fruits and vegetables, beans, nuts, steamed fish, lean meat. The thermogenic effect of these healthy foods will help to maintain an active metabolic rate.  Patients are encouraged to avoid the “lazy” foods, especially carbs, sweets, fatty/oily foods and the processed/refined food.

Also having a consistent level of low impact aerobic physical activity and exercise regularly is important to preserve lean body muscle mass, uphold a consistent basal metabolic rate, which in turn will assist in further weight loss, truncal fat loss and body contour. This may help reduce the excess skin folds after massive weight loss.


Early and late post op problems

The most serious complications of a gastric bypass are anastomotic leaks and strictures. This usually occurs within the first week of surgery and whilst you are an in-patient. Corrective procedures with endoscopy or more surgery might be needed.

It is expected that patients will feel very tired and dehydrated especially in the first 2 to 4 weeks after surgery. This is mainly because there is limited caloric intake and dehydration as a result of reduced oral consumption. Some patients take 2 weeks off work to recover and remember to stay away from the hot environment (long periods of sun exposure in summer).

Some patients will experience chest discomfort (oesophageal spasm), regurgitation, nausea, vomiting, abdominal and pain in the first month. After a gastric bypass there is a much smaller residual stomach size causing a reduced capacity to store food. Prophylactic medications (e.g. Nexium and Maxolon) may be taken for the reflux and nausea symptoms and to prevent stomal ulcers.

Some patients develop temporary food intolerance and early dumping syndrome after a gastric bypass, especially to sweet drinks and lactose or dairy products. Avoiding the high GI index foods or drinks may help alleviate early dumping syndrome. Carbs restriction (often to less than 30g a day) is the best prevention for dumping as well as to prevent a rapid blood glucose rise and insulin release, which may result in fainting symptoms.

Constipation is expected because there is no solid food being consumed in the first 2 weeks after surgery. Benefiber, plenty of oral fluids and stool softener (e.g. Movicol) may be taken if necessary.

Some patients may have pre-existing gallstones, kidney stones or irritable bowel syndrome and these symptoms may get worse after a period of fasting or rapid weight loss with diet restriction. Appropriate dietary advice is needed. Please ask your surgeon or general practitioner for advice.

The long-term anatomical problems include stomal ulcer, anastomotic stricture, internal hernia and bowel obstructions. Sump syndrome, gastro-gastric fistula, etc. are all very rare. All these are refractory problems and will require semi-urgent revisional/corrective surgery and will not settle with conservative management.


The long-term functional problems include the risk for early and late dumping, which is disabling and socially embarrassing. There may be long-term protein, micronutrient and vitamin deficiencies. Regular blood tests at least twice a year to monitor for this is necessary (in particular iron, folate, calcium, vitamin D and B12) and may need to take double strength micronutrient supplements plus periodic parenteral injections if necessary. During the rapid weight loss phase, some patients develop problems with gallstones and renal uric acid stones.



Post op referrals to allied health

Please get a referral from your surgeon or general practitioner to see a dietician or exercise physiologist. This may be part of your health care plan.

Due to the degree of fatigue and dehydration, exercise and physical training usually is commenced 1 month after surgery.

Nowadays with the social media, patients usually form a very cohesive and supportive network amongst themselves but be careful what you read on the web. Individual results may vary and you may not experience the same degree of weight loss success, hence please consult the relevant specialist when problems do arise.  Encouragement and support from family and your local general practitioner is vital or a referral to a psychologist can be made if necessary.

Follow up plans


A referral to a dietician and exercise physiologist is strongly recommended. The GP usually refers patients in their local area and this is part of the health care plan. Please select a dietician who is part of ANZMOSS (Australia and New Zealand Metabolic and Obesity Surgery Society) whenever possible.

Follow up with the surgeon is recommended for the first 6-12 months. However due to various limitations (geographical location and time), follow up can be done over the phone or emails. If there are any concerns or problems, follow up must be done in person.



Post op supplements and blood test

The VLCD provides most of the vitamins and trace mineral supplements in the peri-operative period.

Some patients will need to take extra multi-vitamins long term, especially if there are pre-existing micronutrient deficiencies. For examples some female patients who are already iron and vitamin D deficient before bariatric surgery will need to continue with these specific supplements after surgery.

The vitamin supplements can be purchased from the chemist or local supermarket, in the form of chewable or dissolvable vitamins. The supplements that are necessary are usually supplements of iron, folic acid, calcium, vitamin D, vitamin B1, B12, zinc, magnesium, chromium and selenium.

Blood tests are usually done twice a year as part of any routine medical check up. Especially for iron, folate, B12 levels, calcium and vitamin D, zinc.

If there are concerns regarding low serum calcium, then sometimes a bone scan can be ordered, especially for peri-menopausal women to exclude reduced bone mineral density or osteoporosis (DEXA usually every 5 years).

For severe deficiencies, iron infusions, intra muscular injections of vitamin B12 or vitamin D can be given. This is more likely to be required after a gastric bypass, less likely after a sleeve gastrectomy.

Unlike a gastric bypass, after a sleeve some patients only take the vitamin/mineral supplements for 3 to 6 months post op. After that if the blood tests are normal, sometimes the GP may discontinue the supplements.

But after a gastric bypass, patients need to take multivitamin and mineral supplements for life. Blood tests need to be done at least 2 to 4 times a year and iron infusion or IM injections of vitamin B12 or D can be given if necessary.



You must have a pre-op blood test, which usually include
FBE, ELFT, TFT, random blood glucose, fasting cholesterol/triglyceride, iron, folate, B1, B12, zinc, calcium and Vitamin D

Vitamin or mineral deficiencies need to be corrected before surgery

For patients low on vitamin D, some sunlight exposure is beneficial to boost up the vitamin D levels.

Post-op blood test usually include

FBE, ELFT, TFT, random blood glucose, fasting cholesterol/triglyceride, iron, folate, A, B1, B12, zinc, calcium, Vitamin D and PTH (if necessary).

For gastric bypass or SADI-S patients, you need lifelong blood test to monitor the above

·      Please make sure your GP agrees to do the blood test (at least 2 to 4 times a year for the rest of your life) and to administer the oral supplements and injections (iron infusion, vitamin B12 or D) when necessary

·      Please make sure you have a dietician who will see you for the next few years after weight loss surgery to monitor the vitamin/mineral levels and recommend that you have the adequate macro and micronutrients and anti-oxidants in your diet


Protein intake

The recommended daily protein is about 1 to 1.5g protein per kg ideal body weight

·      For a sleeve patient, the average is about 70g protein a day

·      For a gastric bypass patient, the average is about 70-100g protein per day

Vitamin and trace minerals

You are recommended to have multi-vitamin supplements, example include the BN chewable multi-vitamins.

·      Deficiencies in calcium and vitamin D needs to be corrected to prevent secondary hyperparathyroidism, reduction in bone mineral densities, osteopenia or osteoporosis in the long term.

·      Deficiencies in vitamin A, B1, B12 need to be corrected

·      Deficiencies in folate (especially for pregnant mothers) needs to be corrected

·      Deficiencies in minerals (iron, copper, magnesium, zinc, selenium, etc) need to be corrected



Duration of vitamin and mineral supplements

Unlike a gastric bypass, after a sleeve some patients only take the vitamin/mineral supplements for 3 to 6 months post op. After that if the blood tests are normal, sometimes the GP may discontinue the supplements.

Some patients may elect to remain on the supplements for longer period of time after a sleeve.

But after a gastric bypass, patients need to take multivitamin and mineral supplements for life. Blood tests need to be done at least 2 to 4 times a year and iron infusion or IM injections of vitamin B12 or D can be given if necessary.

For patients who are pregnant please seek special advice from your GP, obstetrician and dietitians.


Long-term results after bariatric surgery

Remember the aim is over 50% excess weight loss (%EWL) in the long term. Usually in the first year the %EWL may be over 70% but usually 2 or 3 years after surgery, there will be some weight regain. Hence the desired outcome should be 50% EWL in the long term.

Adherence to post op dietary guidelines and having a regular exercise program or physical training increases the successful long-term outcomes.

Unfortunately there will be some failures and some patients will have limited weight loss results. Weight loss failure are often multifactorial, the result of many causes such as age, genetics, physiology (lower basal metabolic rate), side effects of medications (diabetic, epileptic or anti-depression medications as well as prednisolone), lack of exercise or physical training. In the long-term weight loss can’t depend on restriction alone, instead the lifestyle changes and behavior modifications is the driving force behind good eating habits and weight loss maintenance. Poor results are often due to return of food addictions or if other problems are not addressed (especially with emotional eating and eating disorders) surgery have its limitations.

The key point is that emphasis should be on improving eating habits, behavior and lifestyle rather than on surgery or restriction alone. Some patients believe that the dysphagia, vomiting or bulimia symptom is a marker of success for weight loss surgery (akin to the gastric band surgery) but there is nothing further from the truth. Without a permanent change to eating habits or any behavior modification, weight re-gain and poor patient satisfaction is often the unwelcomed result.




  • The aim of bariatric surgery is to reduce excess weight, obesity related co-morbidities, reduce body fat, improving physical and psycho-social health.
  • Surgery combined with dietary changes produces better results.
  • Surgery combined with dietary changes and regular physical activities produces the best result.




Extra information

For more information please browse through the website www.drvictorliew.com (also click on the links).

Please research the “bariatric food pyramid”, images freely available from Google.

Other useful websites:

BOMSS (British Obesity and Metabolic Surgery Society)


Please email victorliew@live.com.au with any queries.