Diarrhoea and dumping

This blog provides free general information for anyone who is seeking to understand more about post op diarrhoea and dumping syndrome, not intended as a medical consult. Please seek proper medical advice for individual assessment and management.


The crucial learning points are:

  • Loose stools after surgery may be due to many reasons, which may include infectious gastro-enteritis or colitis, inflammatory bowel disease, food poisoning, food intolerance (Coeliac’s disease or lactose intolerance), bacterial overgrowth, diabetic autonomic neuropathy and many other reasons
  • How to recognize and potentially avoid dumping and post op hypoglycaemia related to bariatric surgery
  • It is rare to need to reverse the bypass operation for severe dumping syndrome or malnutrition






After gastric bypass, it is expected that some patients will have diarrhoea.

This is not the same as dumping or hypoglycaemia.


The definition of chronic diarrhoea is more than 3 loose stools a day, >200g/day lasting for over 4 weeks.


Chronic diarrhoea after gastric bypass will negatively affect quality of life and social functions.

  • For example patients who operate heavy machineries or truck drivers may not be able to continue with their job.


Diarrhoea, dumping and pancreatic insufficiency may be reduced by avoiding an aggressive malabsorptive procedure.

  • For example a proximal gastric bypass is better than a long biliary limb or distal gastric bypass or a SADI-S type operation.


Diarrhoea can also be a result of intestinal bacteria overgrowth and pancreatic enzyme insufficiency. Obviously differential diagnosis needs to be excluded as well, such as infectious gastro-enteritis/colitis, pseudomembranous colitis (Clostridium difficile) or inflammatory bowel disease.


Investigations that is usually ordered include:

  • Breath test for lactulose (which may indicate bacterial overgrowth)
  • Breath test 13C mixed triglyceride (which may indicate pancreatic insufficiency)
  • Stool culture for an infective cause
  • 3 days stool samples can be sent for faecal fat and faecal elastase 1 level (which may indicate pancreatic exocrine insufficiency)
  • Secretin enhanced MRCP (for pancreatic insufficiency)





Steatorrhoea is loss of undigested dietary fats in the stools, with a faecal fat content >7g/day.

This is not the same as osmotic diarrhoea or early dumping.


The longer biliary limb (more than 50cm bilio-pancreatic limb) used in gastric bypass may result in:

  • A shorter the common channel, with a higher the risk for fat malabsorption or steatorrhoea
  • There is delay of delivery of pancreatic and other digestive enzymes to the alimentary limb
  • The long bilio-pancreatic limb may also result in bacteria overgrowth, which may deconjugate the bile salts and impede the digestion of dietary fats
  • Free bile salts may be toxic to enterocytes and worsen the steatorrhoea




Small intestinal bacterial overgrowth

This is caused by overgrowth of bacteria in the lumen of the small intestine after a bypass operation. A lactose breath test may help to diagnose this condition.


The symptoms include nausea, vomiting, bloating, increase flatulence, abdominal pain and diarrhoea.


Symptoms may improve with antibiotic (ciprofloxacin, doxycycline, amoxicillin or metronidazole) treatment, which is usually prescribed for 1 month.


However antibiotic use may be associated with Clostridium difficile infection (Pseudomembranous colitis) and makes the diarrhoea worse.

  • This is diagnosed with PCR test from the stool cultures.




Diabetic patients with autonomic neuropathy

 Up to 40% of diabetic patients may have autonomic neuropathy and enteropathy. This may result in worsening watery diarrhea after gastric bypass surgery.


Anti-motility drugs such as loperamide may help.




Food intolerance

Some patients may have undiagnosed food intolerance, such as gluten insensitivity (Coeliac’s disease) or lactose intolerance.


This can be diagnosed with blood test or gastroscopy with duodenal biopsies.




Vitamin B3 (Niacin) deficiency

Niacin deficiency may result in diarrhea, dermatitis and dementia, sometimes known as pellagra.


Treatment is to increase oral niacin tablets.



Overflow diarrhoea

Some patients may have chronic constipation or Irritable Bowel Syndrome. Diarrhoea may be the result of laxatives and artificial sweeteners.




Dumping and hypoglycaemia

Dumping and post prandial hypolgycaemia may affect up to 10% or more of patients after a gastric bypass operation. Some studies even report over 40% of patients developing dumping after a gastric bypass operation.


There are 2 types of dumping syndrome.


Early dumping usually occurs within minutes after eating a meal (usually within 15 minutes and may occur up to 1 hour later).

  • This is often a result of the rapid entry of hyper osmolar food into the small intestine, resulting in a fluid shift into the lumen of the small bowel (higher osmotic force in the lumen, fluid exiting the intra vascular volume, drop in intravascular volume sensed by the arterial baroreceptors, subsequent activation of sympathetic nervous system and leads to an increase in noradrenalin)
  • Gastro-intestinal hormones (VIP, GIP, insulin and glucagon) are released and also contribute to the early dumping.
  • GLP-1 may also activate the sympathetic nervous system, this hormone plays a role in causing early and late dumping (please read the paragraph below)
  • Symptoms of early dumping may include palpitations (fast heart rate), increased perspiration (increase sweatiness), feeling faint, fatigue, abdominal cramps, nausea and watery diarrhoea
  • Patients are advised to avoid foods that may cause early dumping (eg. avoiding the high osmotic foods, avoid the high GI index foods and limiting carb intake to <50g a day).


Late dumping or post prandial hypoglycaemia usually occurs 1 to 4 hours after a meal.

  • After a gastric or duodenal bypass, there is a faster glucose re-absorption and faster release of glucagon-like peptide 1 (GLP-1) from the distal ileum. This results in elevated post prandial insulin. With faster insulin release and improved insulin sensitivity, this will lead to reactive hypoglycaemia.
  • Many hypoglycaemia episodes may be asymptomatic.
  • Patients are advised to avoid foods that cause late dumping (eg. avoiding the high GI index foods, limiting carb intake to <50g a day).
  • Other treatment options include alpha glucosidase inhibitor Acarbose (which slows down carbohydrate digestion and absorption in the small intestine), calcium channel antagonist (inhibit insulin secretion from pancreatic Beta cells), GLP-1 analogs and somatostatin analogs (both helps to stabilize blood insulin levels)
  • Diazoxide may be another option




Mechanism of dumping syndrome

To re-iterate, although the early and late dumping syndrome symptoms may be very similar, the onset of action and mechanisms are different.


Early dumping may be due to a combination of:

  • Rapid transit of hyper osmolar load to the small bowel, excess fluid loss into the small bowel lumen, relative hypotension and sympathetic nervous system activation (without hypoglycaemia)


Late dumping or post bariatric hypoglycaemia may be due to a combination of:

  • Rapid transit of food to the distal small bowel, release of GLP-1, excess insulin release and subsequent hypoglycaemia
  • Attenuated glucagon response
  • Reduced insulin clearance
  • Impaired Beta cell secretory suppression even in the presence of hypolgycaemia


The specific diagnostic criteria for post bariatric hypoglycaemia include:

  • The presence of neuroglycopenic symptoms with a post prandial blood gluciose level ❤ mmol/L
  • Occurrence >6 months after bariatric surgery
  • In the absence of fasting hypoglycaemia







Certainly diarrhoea and associated gut symptoms are expected for all patients who had a sleeve gastrectomy or gastric bypass.


For mild symptoms this may be controlled with simple dietary alterations.


Severe symptoms associated with malnutrition are particularly difficult to treat and a few patients may even end up having to reverse the primary bariatric procedure.


Hence it is important to go through the list of possible causes and do adequate investigations to search for the above.