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irritable bowel syndrome (IBS)


  • IBS is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause and is thus a diagnosis of exclusion.
  • IBS patients have a significantly higher prevalence of fibromyalgia, and similar chronic conditions, migraine, and depression
  • one theory is based on a leaky gut concept that some ingested proteins such as lectins damage the gut wall and that this can be repaired by appropriate gut bacteria processing foods which can be broken down to butyrate which is thought to have a protective effect:
    • thus high lectin foods such as whole wheat grains, brown rice, brown sugar, tomatoes, peppers, eggplant, corn, beans, cashews should be reduced
    • high butyrate fuels should be increased such as chicory roots, asparagus, onion, walnuts, pistacchios, jerusalem artichokes (ingesting butyrate itself doesn't work as it is broken down in the stomach unless it is protected by encapsulation)
    • probiotic bacteria that make it past the stomach such as spore-producing strains of Bacillus coagulans need to be optimised - avoiding taking substances which destroy these bacteria in the gut such as antibiotics, sugar alternatives
    • gut mucus production needs to be maintained
    • non-FODMAP prebiotic fibre such as guar gum (“Sun Fibre”)

red flag symptoms that are NOT typical of IBS

  • pain that awakens/interferes with sleep
  • diarrhoea that awakens/interferes with sleep
  • blood in the stool (visible or occult)
  • weight loss
  • fever
  • abnormal physical examination

in the news

  • peppermint may help ease pain of IBS by reducing pain transmitted from overly sensitive colonic nerve endings. It is postulated that peppermint stimulates an anti-pain channel called TRPM8. The pain sensing fibres apparently become sensitized after a bout of gastroenteritis, and then pain is produced in response to spicy foods, fatty foods, caffeine and alcohol. 1)
  • fructose intolerance may be the cause of bloating, flatus, belching, abdominal pains, and altered bowel habits in some patients:
    • unlike glucose, fructose (when ingested as fructose and not derived from sucrose) is absorbed in the small intestine through facilitative diffusion (via GLUT5), and its absorption capacity is limited to 5-50g - that is - have too much at once and once capacity is reached the remainder will pass down the bowel to be metabolised by bowel flora producing hydrogen and methane gases, which then can cause increased bowel distension and cramping pains, bloating, belching, etc.
    • fructose intolerant patients have positive fructose breath tests, in which patients gave breath samples for hydrogen and methane after receiving 150 mL of a 33% fructose solution.
    • it should be considered as a cause of non-specific bowel symptoms as reducing fructose in diet may reduce symptoms in those who are intolerant.2)
    • sucrose (sucrose gives equal amounts of glucose and fructose), honey, high fructose corn syrup (HFCS), pears, grapes and apples have high levels of fructose
    • this fructose intolerance should not be confused with the much more serious, and rare (1 in 20,000 people), autosomal recessive hereditary fructose intolerance which is a deficiency of hepatic fructose 1-aldolase which may cause vomiting, hypoglycemia, failure to thrive, cachexia, hepatomegaly, jaundice, coagulopathy, coma, renal Fanconi syndrome, and severe metabolic acidosis.
  • reducing salt intake may reduce bloating 3)

flatulence, abdominal cramps and bloating

  • flatulence is the expulsion through the rectum of a mixture of gases collectively termed flatus.
  • flatus is usually a mixture of odourless gases such as nitrogen (20-90%), hydrogen (0-50%), carbon dioxide (10-30%), oxygen (0-10%) and methane (0-10%) which has a mild odour.
  • flatus odour is due to small amounts of other gases such as hydrogen sulphide - particularly as a result of digestion of certain foods such as:
    • cauliflower, broccoli, cabbage, Brussels sprouts and other cruciferous vegetables increase the pungency of flatus.
  • flatus is derived from two main sources:
    • exogenous:
      • swallowed air (aerophagia) which may be increased by increased swallowing of saliva (eg. during nausea or gastro-oesophageal reflux), hasty eating, or anxiety.
    • endogenous:
      • produced as a metabolite of digestion, particularly by gut flora acting upon incompleted digested food arriving in the colon.
      • flatulence-producing foods are typically high in certain polysaccharides (especially oligosaccharides such as inulin).
        • examples include: beans, lentils, dairy products, onions, garlic, scallions, leeks, turnips, rutabagas, radishes, sweet potatoes, potatoes, cashews, Jerusalem artichokes, oats, wheat, and yeast in breads.
      • mushrooms contain a unique sugar called raffinose, which humans can't break down.
      • vegetarians produce more gas than meat-eaters because the intestinal enzymes can't digest the cellulose in vegetables' cell walls.
      • other non-digestible sugars such as sorbitol
      • some people are lactose intolerant and thus undigested dairy products cause flatus in these people if they include them in their diet.
      • likewise, some are fructose intolerant, or develop excess flatus by eating large quantities of fruit which exceed the fructose absorption capacity of the bowel.
      • some bowel infections (eg. giardia) increase flatus production
  • not all flatus is released from the body via the anus. When the partial pressure of any gas component of the intestinal lumen is higher than its partial pressure in the blood, that component enters into the bloodstream of the intestinal wall by the process of diffusion. As the blood passes through the lungs, this gas can diffuse back out of the blood and be exhaled. If a person holds in flatus during daytime, it will often be released during sleep involuntarily when the body is relaxed
  • food that minimise or reduce flatus production:
    • cumin, coriander, caraway and others such as ajwain, turmeric, asafoetida (Hing), epazote, and kombu kelp (a Japanese seaweed).
    • rice is the only starch that does not cause gas.
    • fermentative lactic acid bacteria such as Lactobacillus casei, Lactobacillus plantarum and Lactobacillus acidophilus
    • activated charcoal may reduce odor and quantity of flatus
  • flatus is likely to increase if gastric and small bowel transit times are decreased leading to increased partial digested food entering colon:
  • pain from flatus is likely to be increased if it's passage is not allowed:
    • intentionally holding in flatus to avoid embarrassment
    • wearing tight belts, trousers, etc, especially whilst sitting.

Mx of diarrhoea-dominant IBS

  • consider the low FODMAPs diet
  • mebeverine (Colofac) is an antispasmodic with only mild atropine-like actions and can be very useful in reducing cramping pains - usual dose 135mg tds prior to meals
    • may cause constipation, dizziness and indigestion
    • Colofac contains lactose which may be an issue for those who are also lactose intolerant
  • loperamide (2–4 mg, up to four times daily) can reduce loose stools, urgency, and fecal soiling.
  • cholestyramine may be considered for patients with cholecystectomy or who may have idiopathic bile acid malabsorption.
  • serotonin receptor agents such as alosetron
  • cognitive-behavioral treatment, dynamic (interpersonal) psychotherapy, hypnosis, and stress management/relaxation seem to be effective in reducing abdominal pain and diarrhea (but not constipation).
  • tricyclic antidepressants

Mx of constipation-dominant IBS

Pain. 2011
Am J Gastroenterol. 2003;98:1348-1353
American Journal of Gastroenterology June 2019 Re-analaysis of the Dietary Approaches to Stop Hypertension-Sodium trial (DASH-Sodium)
ibs.txt · Last modified: 2022/04/30 01:03 by gary1

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