Gastric Bypass Side Effects - The 9 Most Common

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Gastric bypass side effects are largely avoidable with the right diet and lifestyle habits, but they can lead to more serious complications if not addressed. The most common include:

  • Dumping syndrome
  • Dehydration
  • Dental problems
  • Difficulty swallowing
  • Gallstones
  • Kidney stones
  • Hair loss
  • Indigestion (dyspepsia)
  • Intolerance to certain foods

Read and click the sections below for details about each of the possible side effects of gastric bypass.

We have an entire page dedicated to this topic because it is a possible side effect of other bariatric procedures like gastric sleeve surgery and duodenal switch.

The side effects that result from gastric bypass dumping syndrome include weakness, dizziness, flushing and warmth, nausea and palpitation immediately or shortly after eating and produced by abnormally rapid emptying of the stomach especially in individuals who have had part of the stomach removed.

While this sounds like a bad thing, many patients view it as a “blessing in disguise.” The symptoms of dumping syndrome are completely avoidable by eating a proper bariatric diet… can you think of a more convincing way to keep you on track? In fact, some patients who do not suffer from dumping syndrome will comment that they wish they did, as “dumping” removes some of the choice involved in food selections.

See our Dumping Syndrome page for more details.

An abnormal depletion of body fluids. You will need to drink a lot of water in the months following surgery – as much as 2 liters per day. Not doing so can lead to nausea and vomiting which can lead to even worse dehydration and other problems. In severe cases of dehydration patients may need to return to the hospital for IV fluids and vitamins.


Due to malabsorption, not taking proper vitamins in the right amounts, potential pH changes in the saliva after surgery, poor dental hygiene and not addressing significant reflux or vomiting issues (stomach acid in the mouth is bad for the teeth), some patients experience problems with their teeth after surgery.

See our Dental Problems After Gastric Bypass Surgery page for a dialoge between several patients, dentists and bariatric surgeons about the issue.

Can be caused by eating too quickly, too much or not chewing food enough and can usually be fixed by avoiding these issues.

Are small stones of cholesterol formed in the gall bladder or bile passages. They can be created following rapid weight loss which leads to their development in as many as 1/3 of bariatric surgery patients. As a result, your surgeon may remove your gallbladder during surgery or prescribe bile salt supplements after surgery.

  • Kidney stones are stones in the kidney related to decreased urine volume or increased excretion of stone-forming components such as calcium, oxalate, urate, cystine, xanthine and phosphate. The stones form in the urine collecting area (the pelvis) of the kidney and may range in size from tiny to staghorn stones the size of the renal pelvis itself (1).Although additional research is needed, one study suggests that the risk of developing kidney stones increases after bariatric surgery due to changes in digestion and the resulting changes in the chemical makeup of patients’ urine. Click here to learn more.Drinking lots of water, which gastric bypass patients should do anyway, will help to dilute the urine and may help prevent kidney stones.

Occurs to some degree for most patients and can be caused by nutritional deficiencies or as your body’s response to major surgery or extreme weight loss. Most patients stop losing and start regrowing hair within 3 to 6 months following surgery. Supplementing your diet with protein, vitamin B, magnesium, calcium and zinc, among other bariatric vitamins, will help prevent hair loss and improve hair growth.

The inability to digest or difficulty in digesting food, the incomplete or imperfect digestion of food or a case or attack of indigestion marked especially by a burning sensation or discomfort in the upper abdomen.

Treatment is usually as simple as changing your diet, such as avoiding greasy foods or limiting liquid intake to certain times of day. Alcohol, aspirin and other drugs are also causes. If diet changes don’t work, antacids and H2 blockers are sometimes prescribed.

  • Intolerance to certain foods, beverages and drugs – With a changed stomach size and digestive system, there will be certain foods, beverages and drugs that you’ll need to avoid and certain diet habits you’ll need to maintain (2).It is important to talk with your doctor before taking ANY drugs, as they can damage your stomach pouch after gastric bypass surgery and cause ulcers (including over the counter pain relievers – Motrin, Advil, aspirin, Aleve).
    Regarding alcohol, a little may still be okay, but it will have a profoundly different effect on your body than it used to. First, it’s bad for your diet due to the large amounts of calories found in many alcoholic beverages. Second, you will become intoxicated more quickly following surgery which could lead to a number of problems. Finally, following surgery the effects of alcohol on your system could make liver disease more likely.As for smokers, you must stop now. If you smoke after gastric bypass surgery, there is a good chance that you will get an ulcer in your pouch.Following are additional potential gastric bypass side effects of the above intolerances to certain foods, beverages, and drugs:
    • Nausea and vomiting is one of the most common gastric bypass side effects and is experienced in up to 70% of patients. In one study, patients on average reported feeling nauseous 2.6 times per week and reported vomiting 0.2 times per week on average after gastric bypass (3).Following your doctor’s bariatric diet recommendations exactly will typically fix or improve the problem. While in the hospital, receiving a larger amount of IV fluids at a faster rate may make you less likely to feel nauseous or vomit (4). Keeping a food journal for a couple of days may help you to pinpoint the foods which seem to cause nausea and vomiting.
    • Change in bowel habits – bowel function after bariatric surgery may change in a number of ways, including (5):
      • Diarrhea or loose stools – usually completely dependent on diet – you will need to figure out and avoid foods that “trigger” diarrhea. It could also be the result of lactose intolerance (not a side effect of surgery, but surgery can make you more sensitive to a problem that you didn’t know you had) which would require dairy products to be removed from the diet.
      • Constipation – usually fixed by increasing the amount of water you are drinking and by taking fiber supplements.

Alcoholism & Gastric Bypass Surgery

There seems to be an increased risk of alcohol abuse among some gastric bypass patients. Advance awareness of this potential problem should help to mitigate this effect. See this story for more information.

The right diet and eating habits after gastric bypass surgery can improve or eliminate all of the above gastric bypass side effects.  See the following 2 pages for more information…

Worried About potential Side Effects? Ask A Top Gastric Bypass Surgeon About The Possible Risks


References for Gastric Bypass Side Effects

  1. Definition of risk from The Free Dictionary at:
  2. Niccole Siegel, MS, RD, Barrie Wolfe, MS, RD, Giovanni Dugay, NP, Christine J. Ren, MD.  REPORTED INCIDENCE OF VARIOUS POST OPERATIVE EXPERIENCES ASSOCIATED WITH THE LRYGB, LAGB AND LBPD/DS.  New York University Program for Surgical Weight Loss, New York, NY, USA.  June 2004. Abstracts of the 21st Annual Meeting – American Society for Bariatric Surgery.
  3. Schuster R, et al. Intra-operative Fluid Volume Influences Postoperative Nausea and Vomiting after Laparoscopic Gastric Bypass Surgery. Journal Obesity Surgery Volume 16, Number 7 / July, 2006 Pages 848-851.
  4. American Society of Metabolic and Bariatric Surgery. Bariatric Surgery: Postoperative Concerns. ASBS Public/Professional Education Committee – May 23, 2007 Revised February 7, 2008. Available at: Accessed: September 20,2009.
  5. Definition of a Kidney Stone.  Available at: Accessed: September 19, 2009.