Irritable Bowel Syndrome (IBS) -The Microbiome and FODMAPS

Sep 03, 2012
Irritable bowel syndrome (IBS), The Microbiome and FODMAPS

IBS Microbiome and FODMAPS Research

The following is a summary with some editorial comments of an important, recently published paper:

The Rome Foundation is an international group that meets regularly to review the literature and recommend changes to the guidelines for diagnosis and management of gastrointestinal disorders is called the Rome Foundation. This group has over the years published three diagnostic criteria for Irritable Bowel Syndrome (IBS). We currently use the “Rome 3 Criteria” to diagnose IBS. A subgroup of this Foundation including two Canadians recently published a paper on the connection between intestinal microbiota (gut bugs) and functional bowel disorders (mostly referring to Irritable Bowel Syndrome). I am hopeful that this paper may signal a sea change in the management of IBS. This considered expert paper validates a wide array of correlates of IBS namely: gut motility, visceral hypersensitivity, altered brain-gut function, low-grade inflammation, psychosocial disturbance and intestinal microbes.

The 2012 Rome Report sheds light on the role of the microbiome in IBS

  • Bacteria living in the human gastrointestinal tract outnumber human cells (in the whole body) by a factor of 10:1.
  • Most bacterial species live in the colon. There are some bacteria living in the terminal end of the small intestine. These are very quickly responsive to ingested sugars.
  • Gut bugs have a symbiotic relationship with their human hosts. We need them just as much as they need us. They produce things we need (eg vitamin K and the amino acid serine). They make short-chain fatty acids and natural antibiotics which prevent pathogenic bugs from moving in. They affect bowel motility, interact with the immune system and produce metabolites that can affect our brains (affecting pain, behaviour or mood).
  • It is difficult to accurately identify the microbes that live in the bowel. 90% of them are anaerobic and difficult to grow in the lab. It is estimated that 80% of colonic bacteria have never been cultured.
  • Babies are born with sterile guts (no bugs present). They are colonized immediately by the mother’s vagina and gut.
  • The types of bugs that grow in the colon change over the lifespan.
  • Human genetics determine our immune responses to gut bugs thus affecting which ones grow more in certain individuals.
  • Diet has a major impact on what grows in the bowel and samples in different countries with different diets vary considerably.
  • The bacteria that are found in fecal samples are not the same as those that live in the mucosal layer coating the bowel. The mucosal layer is very hard to study.
  • There is much left to learn.

How do You Study Gut Microbiota?

The great leap forward in the study of intestinal microbiota has occurred with the ability to detect them through their DNA fingerprint rather than the laborious process of culturing each bug. All this being said, it is increasingly clear that both the bugs that live in the lumen and those that live in the mucosa have the ability to interact with the “host” (ie us) for better and worse.

Is IBS Caused by Gut Bacteria?

Gastroenteritis is a known trigger for IBS. The severe diarrhea of stomach flu cleans out the colon and it tends to be recolonized by more bad guys than good guys. Bacterial gastroenteritis is more likely to precipitate IBS than viral gastroenteritis.

A recent study showed that the species and numbers of bacteria in the colons of patients with IBS differ significantly from those of healthy controls.

The role of Small Bowel Bacterial Overgrowth (SIBO) continues to be debated. Bacteria live predominantly in the colon (large bowel). But when they are fed their favourite foods like poorly absorbed carbohydrates they tend to overgrow and move into the small bowel. Dr. Kenny De Meirleir talks about a classical pain just to the right of the belly button which he believes is a signal of this problem. You may recall from his Calgary presentation in 2006 that he recommends the use of a glucose and lactose breath test to measure overgrowth, a test also described in the Rome Foundation paper. The rationale for this test is that if there are more bugs than usual, ingesting a yummy sugar like glucose or lactose will cause them to metabolize and replicate producing hydrogen gas which can be measured in the breath. Because of debate about the accuracy and correct interpretation of test results, this test is not easily available in Calgary.

Although contested for the past few decades several studies report that more people with IBS have SIBO than healthy controls; another piece of evidence (though still debated) that gut bugs play a role in IBS. The use of PPIs, the common anti-acid drugs like Pantoloc® and Nexium® may increase the risk of developing SIBO.

Transit time (how fast material moves through the GI tract) plays an important role in gut health.  For example in diarrhea, things move very fast and there is insufficient time for bacteria to fully ferment their favourite foods into short-chain fatty acids and natural antibiotics. In health, SCFAs and antibiotics prevent the colonization of pathogenic species of bacteria (bad guys). This may lead to a vicious circle of delayed recovery from an otherwise mild food reaction or viral gastroenteritis. Short-chain fatty acids are measurable in the “complete digestive stool analysis” test offered by a number of US labs. The short-chain fatty acid butyrate is available as a supplement which some patients with IBS find helpful.

There is a constant, measurable interaction between gut bugs and the host immune system. Excess mucous production in the stool may be a sign of immune activation to the bacteria living in the bowel. This immune activation may be related to the “visceral hypersensitivity” (pain) experienced by individuals with IBS. There are at least one species of bacteria Lactobacillus paracasei NCC2461 which is reported to decrease this pain sensitivity.

What is the Best Treatment for Irritable Bowel Syndrome? How Can I Treat IBS on My Own?

In terms of treatment, the paper mentions: non-absorbed antibiotics, the low FODMAP diet and probiotics (supplementing with good bugs) as the approaches having the most evidence to support them.

Antibiotics are Recommended with Caution for Several Reasons:

  1. Absorbable antibiotics are to be avoided since they will affect the entire body, not just the bowel.
  2. Non-absorbable antibiotics such as neomycin and rifaximin run the risk of overgrowth of bad bugs like Clostridium difficile.
  3. Most antibiotics kill many types of bacteria, good guys and bad guys alike.
  4. Antibiotic use results in the development of resistant strains which can be lethal for the individual patient and lead to public health nightmares.
  5. The benefits of antibiotics wear off by 12 weeks if used continuously.
  6. The bugs grow back after the antibiotics are stopped if the colonic environment is unchanged. More research is required.

Lower FODMAPS Treats IBS

The paper mentions the low FODMAPS (poorly absorbable fermentable sugars and phenols) diet as a potential therapeutic option for patients with IBS. I sourced the following relatively short summary put out by the sports dieticians of Australia which explains how FODMAPs may contribute to IBS. The foods to be avoided are poorly absorbed sugars and glycols which provide lots of food for colonic bugs. The list of dangerous foods includes most fruits, some grains, legumes and dairy products. (Yikes what is left I hear people asking). Eaten in large or even moderate quantities, patients with IBS will develop the cardinal symptoms of gas, bloating, abdominal pain and change in bowel habits (diarrhea or constipation) sooner than healthy people.  There are several studies showing that a low FODMAP diet reduces IBS symptoms.

Are Probiotics a treatment for IBS?

Probiotics (good bugs) are a popular approach and there is a chart in the paper summarizing many studies of the impact of probiotics on the IBS symptoms of pain, bloating and flatulence. The majority but not all the studies report improvements. Bacterial species successfully used include several Lactobacillus species, bifidobacteria species and several mixtures including Cultura® and VSL#3® (mentioned in my manual). My approach to probiotic use is to choose species/brands which have proven evidence and rotate species to see which works best for you.

A final note. The paper mentions that gluten can “generate IBS symptoms even in the absence of celiac disease” and that patients without celiac disease can respond positively to a gluten-free diet. In mouse models, gluten can induce innate immunity, increase small bowel permeability (leaky gut) cause neuro-intestinal dysfunction (pain and motility problems) and dysbiosis even in the absence of autoimmunity. I would posit that other foods may also have this capacity and that identifying food “sensitivities” therefore has some credibility in the approach to IBS. The approach I discuss in my manual to identify and manage all the food sensitivities, leaky gut and dysbiosis is strengthened by the publication of this paper.

Author: Eleanor (Ellie) Stein MD FRCP(C)

I am a psychiatrist with a small private practice in Calgary and am an assistant clinical professor in the faculty of medicine at the University of Calgary. Since 2000, I have worked with over 1000 patients, all with ME/CFS, FM and ES. My passion for this field comes from my own struggle with these diseases, my desire to improve my health and then pass on what I learn. My goal is for every patient in Canada to have access to respectful, effective health care within the publicly funded system. 


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