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


  • Happens when food (especially sugar) moves too quickly from the stomach into the small intestines
  • Includes symptoms like nausea, diarrhea, bloating, fainting, anxiety, and weakness
  • Treated through diet changes

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.


  • Depletion of bodily fluids
  • Caused by not drinking enough fluids
  • Treated by increasing fluid intake

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.


  • Unhealthy teeth and gums
  • Caused by vitamin and mineral deficiency and/or pH changes in the saliva
  • Treated by closely monitoring vitamin levels and adjusting supplements accordingly

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.


  • Caused by eating too quickly, too much, or not chewing enough
  • Treated by avoiding these causes

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


  • Small cholesterol stones formed in the gall bladder
  • Treated with prescription bile salt supplements or gallbladder removal

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.


  • Small stones in the kidney related to decreased urine volume or increased excretion of stone-forming elements
  • Avoided through drinking enough liquids

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. Drinking lots of water, which gastric bypass patients should do anyway, will help to dilute the urine and may help prevent kidney stones.

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