Causes Of IBS: 9 Interesting Theories.

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The causes of IBS are not yet fully understood.

No single cause of IBS could apply to every patient.


Understanding the specific cause of YOUR IBS may be the first real step to overcome It.

Based on what specifically caused you IBS, you and your doctor can define the best treatment strategy.

I gathered here all the research about IBS causes, in a simplified form.

Read thoroughly, and try to figure out what caused you IBS.

The 9 Causes Of IBS:

1- Abnormal Motility Of Your Intestine.

This is one of the oldest theories about the causes of IBS, it was suggested that abnormal patterns of movement of your colon and small intestine is the cause of your IBS.

causes of IBS: abnormal gut motility


Your intestine and colon contracts and relaxes in “waves”. These waves are synchronized. We normally don’t feel them.

A wave of contraction in your colon moves slowly downwards followed by a wave of relaxation. Then a wave of contraction starts again and travels slowly, this helps:

  • Moving the food you eat down through your intestine and colon.
  • Mixing food with digestive fluids & enzymes.
  • Absorption of nutrients and water.
  • Defecation.

With IBS: [REF] [REF] [REF]

It was suggested that IBS occurs due to:

    • Bowel contractions occur more frequently: For example, an IBS patient may experience about 20 contraction waves (peristalsis) instead of a normal of less than 10 waves per minute. More frequent bowel movements mainly cause IBS- diarrhea.
  • Contractions occur less frequently: this can increase the time food resides inside your intestine. The more time food stays in your gut the more water is absorbed into your blood making your stool become hard. Also, the more gas is produced resulting in IBS-constipation, IBS bloating, and IBS gas distension.
  • Irregular bowel contractions: the abnormal direction of the wave of contraction or irregular time intervals may lead to the gut pain you feel with IBS.

Evidence and how this can be applied:

The link between abnormal motility of your intestine and your IBS exists. But research is still defective as:

  • These patterns of abnormal motility don’t present in all IBS patients.
  • Its relation to your symptoms is unclear. I.e. some patients may have an abnormal bowel movement but no corresponding symptoms and others may have typical IBS symptoms and no abnormal motility couldn’t be detected.

The abnormal bowel contractions are the basis of different antispasmodic treatments whether prescription or over the counter antispasmodics like Buscopan or Peppermint oil capsules.

Also, some other drugs may modify this abnormal colon motility, for example, Immodium (Loperamide) slows down the motility of your colon and consequently relieves diarrhea


The response to these “motility drug” is variable. So, it may be the cause in some IBS patients but not all of them.

2- Your Colon Is Over-sensitive.


Pain is perceived from your intestine by stretch receptors and other chemical mediators. This occurs when there are an extra-amounts of gas or food (distension and bloating).

Extra gas in your colon -> more stretch of colon walls -> stimulation of stretch receptors inside your colon wall -> sends a signal to your spinal cord and brain to feel pain.

With IBS [REF1] [REF2]

You as IBS patient may feel gut pain, bloating, and distension even with normal amounts of gas inside your intestine.

Normal amounts of gas in your colon -> abnormally stimulate the stretch receptor in your colon wall -> sends a false signal of distension -> you feel pain (colics, distension, or bloating).

ibs causes: over-sensitiive colon

Source: This study.

Evidence & how this can be applied.

It is unclear whether the hypersensitivity of the colon is due to abnormal receptors inside your intestine or due to abnormal perception of pain by your brain.

But the point is that colon hypersensitivity is a frequent finding in many IBS patients.

Drugs modulating pain sensations (like Tricyclic Antidepressants)  may play a role in IBS relief.

3- Actual Inflammation Inside Your Colon Wall!

The widely accepted theory about irritable bowel syndrome is that it is a “functional disease”.

But there is scientific evidence that an actual inflammation could happen.

This is more common with IBS-diarrhea and Post-infectious IBS.

In 2002, Dr. Törnblom and his team found a low-grade inflammation and inflammatory cells inside the colon wall of 10 patients with severe IBS.

Researchers not only found inflammatory cells (like lymphocytes and mast cells) but also found pro-inflammatory mediator proteins (cytokines.)

This may suggest that IBS is caused by an organic cause and it is an actual disease.

4- a previous attack of gastroenteritis (post-infectious IBS)

Having an attack of enteritis raises your odds of getting IBS Up to 6 folds [REF]. This is more common with:

  • Younger age.
  • If you had a prolonged fever with the enteritis attack.
  • Anxiety and depression.

post infectious ibs cause

Source: This Review study

It can occur following any type of gut infection (Bacterial, protozoal, viral. Or helminthic).

Researchers still don’t have a clear explanation of why this occurs, but causes may be [REF] [REF] [REF]:

  • Impaired fluid and nutrient absorption following infection.
  • Antibiotic use during the attack of enteritis.
  • Changes in the colon wall cells (increased inflammatory cells).

If your IBS has started after a severe attack of gastroenteritis you have to consider post-infectious IBS.

Discuss the issue with your Doctor.

5- changes in the types of colon bacteria may be the real cause of IBS.

Your colon is an entire world of bacteria and micro-organisms. Micro-organisms present in your colon don’t harm your colon.

causes of IBS

These organisms are vital for your colon health as they:

  • Help digestion of certain substances.
  • Help normal motility of your colon.
  • Help the absorption of certain vitamins and nutrients.

An interesting study about the role of fecal micro-organisms (Microbiota) in IBS found that:

  • Transferring fecal microbiota from IBS patients to rats led to the development of IBS like symptoms in these rats.
  • On the other hand, transmitting fecal microbiota of normal human (not having IBS) did not evoke IBS symptoms in rats.

These eye-opening observations may lead us to a better understanding of the causes of IBS.

Application1: probiotics

Based on this speculation, probiotics emerged as an effective treatment modality for IBS.

Probiotic is a “living microorganisms” that can revert or decrease the change of your colon microbiota, thus improving your IBS symptoms.

Probiotics can be formed from a single strain or multiple strains of bacteria. They are found in many forms (capsules, sachets, probiotic yogurts, and others).

Although some studies couldn’t detect significant changes in fecal microbiota following the administration of probiotics, the improvement of the IBS symptoms with probiotics is evident.

Application2: Fecal transplantation!!

Another Super-interesting application of this theory is FMT. FMT or fecal Microbiota Transplantation is a trial of transfusing the fecal matter of a healthy person to another IBS patient.

Some studies showed that FMT can be an effective permanent treatment for IBS, But results still conflicting and still under trials.

The FMT is an established treatment in certain medical conditions like “Clostridium difficile infections”.

But it still under trial in IBS.

6- Bacterial Overgrowth (Is SIBO The Cause Of Your IBS?)

[SIBO= Small Intestinal Bacterial Over Growth].

In the previous section, I explained to you How the changing the type of your Microorganisms can be the cause of your IBS.

But what about the Micro-organisms that already present inside your gut.

What if they decided to behave differently?

Bacterial overgrowth means that the naturally occurring Microorganisms inside your intestine increase in number.

This overgrowth may have drawbacks on your intestine. The “too much” microorganisms may produce too much waste like gases or toxins. And the unwanted gas and waste may cause your symptoms like distension, colics.

Small Intestinal Bacterial Overgrowth (SIBO) is linked to IBS. but the research is conflicting:[REF | REF |REF]

  • Some evidence exists that eradication of this bacterial overgrowth with antibiotics is associated with improvement in IBS symptoms.
  • However, another study found that SIBO is not a consistent finding in All IBS Patients. In this study, SIBO was found in only 4% of IBS patients (they exactly the same percentage of SIBO found in the healthy persons included in the study).

What does this mean?

The Link between SIBO and IBS is still weak. But eradicating Bacterial overgrowth is evidenced to improve Many IBS symptoms

For Example, a gut antibiotic called Rifaximin (Xifaxan) is approved for the treatment of IBS-diarrhea with good results.

7- Food Allergy:

Can food be the cause of your IBS?

Several studies have investigated the role of food in IBS. and as always, there is some evidence.but also conflicting results present.

For example, A study showed that the number of people with food allergies (detected by skin tests) is greater in those who have IBS than non-IBS patients.

However, another study concluded that foods that tested positive by skin test didn’t necessarily cause IBS attacks.

Here are the 2 most suggested food causes of IBS:

A- Carbohydrates:

The most common carbohydrates that cause IBS symptoms are FODMAPs. FODMAPS are a special type of carbohydrates (short-chain sugars).

When they enter your gut they become readily fermented and produce too much gas and cause IBS symptoms.

Restricting FODMAPs is one of the best strategies that can help your IBS symptoms.

FODMAP= “Fermentable Oligo, Di, Monosaccharides, And Polyols.”

Fermentable: means that gut bacteria break them down producing lots of gas.

Oligosaccharides: Refers to compounds called fructans and galacto-saccharides present in wheat, barley,  rye, onion, garlic, and legumes.

Disaccharides: Refuse to fructose sugar present in milk ice cream custard and yogurt.

Monosaccharides: Refers to free fructose present in Apples, pears, mangoes, cherries, watermelon, asparagus, sugar snap peas, honey, high-fructose corn syrup.


Polyols: They are substances called sorbitol mannitol xylitol and maltitol present in certain types of fruits like apples and watermelon and in artificial sweeteners like artificially sweetened gum and alcohols.

B- Gluten: 

Gluten is a protein present in wheat and barley. Some people have extreme gluten intolerance; a condition called celiac disease.

People with celiac disease usually experience chronic diarrhea, weight loss, and anemia.

Some studies suggested the presence of Mild or Hidden gluten sensitivity in IBS patients. [REF | REF]

Also, you may experience symptom relief after cutting gluten from your diet. Also, we (doctors) may need to test for celiac disease if you have IBS (specially IBS-diarrhea).

8- Brain-gut Dysfunction (stress):

Stress is the enemy of IBS.

One of the most commonly suggested causes of IBS is Psychological dysfunction or (brain-gut axis dysfunction.)


Your colon has local nerve plexuses called the “myenteric plexus”.

the Myentereic plexus acts as a local gut-brain. Also, it is connected to our main brain.

Psychological stress lets the brain send abnormal orders to your gut, causing the pain and stool changes (diarrhea or constipation).

The most common psychological conditions that may cause you to have IBS:

  • Daily stressful events like work, exams, … etc.
  • Major stressful events like the death of the beloved one.
  • Depression.
  • Phobias like fear from getting a dangerous disease (this is a frequent finding I always experience with my patients).

9- Genetic Causes Of IBS!

If one of your family members has IBS you may have increased risk of you getting IBS.

Although the association is not strong. Some studies suggest that genetic causes of IBS may exist.

For example:

This interesting study evaluating the occurrence of IBS in identical twins versus non-identical twins.

causes of ibs: genetic

Source: This study

They found that identical twins (who have the exact same genes) are more liable to concurrently have IBS than non-identical twins.

My conclusion about IBS causes:

An endless amount of research about the causes of IBS is present. but no suggested cause of IBS can be applied to all patients

My personal opinion; Every IBS patient has its own circumstances. your Unique IBS cause may influence your Unique plan of treatment

Understanding the specific cause of your IBS may help you to make the right decisions about your condition.

always discuss the real cause of IBS with your doctor.

yellow stool with IBS
Dr. I. Farahat

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