Small intestine bacterial overgrowth (SIBO) is a condition in which there is an over-colonization of specific bacteria, typically that which is normally found within the large intestine, that is greater than 103 colonies, ultimately causing uncomfortable digestive symptoms to occur in those affected. 

Understanding the Role of the Small Intestine

After we put food in our mouths, it travels down to our esophagus and enters the stomach. From here, food enters the small intestine, large intestine and rectum to eventually excrete any food contents that are no longer useful to maintain our day to day health and activities.

During this process of digestion, the small intestine plays a critical role in performing as much as 90% of the digestion and absorption of food and its nutrients, whereas the remaining 10% is performed by the stomach and large intestine 1.

When present in normal quantities, the bacteria (flora) of the gut perform a variety of useful functions including assisting the digestion process by absorbing various vitamins, such as folic acid and vitamin K, as well as protect the small intestine from being invaded by harmful bacteria associated with diseases.

In the event that the normal function of the small intestine or any other part of the gastrointestinal (GI) tract is compromised, bacterial overgrowth can occur and cause a wide range of harmful effects such as inhibit normal digestion of food and damage the lining of the small intestine.

There are a few ways patients can test to see if they have SIBO including a SIBO breath test, intestinal sample culture, and an empirical trial of antibiotics.

What Exactly is SIBO?

small intestine bacterial overgrowth

SIBO, as previously mentioned, is an over colonization of bacteria that occurs within the small intestine. Since the small intestine is not typically designed to house this quantity of bacteria, these species end up interfering with the normal digestive and nutrient absorption processes that will take place in the small intestine.

Under normal circumstances, the small intestine has a number of protective measures it uses to prevent the overgrowth of bacteria, of which include:

  • Bile
  • Enzymes
  • Gut-associated lymphoid tissue (GALT)
  • Migrating Motor Complex (MMC) (click here to learn more about the role of the MMC)

SIBO is often associated with other types of illness that affect the small intestine, such as:

  • Irritable Bowel Syndrome (IBS, which is the majority of SIBO)
  • Crohn’s Disease
  • Celiac Disease
  • Achlorhydria (a chronic inflammation that prevents the stomach from producing acid normally)
  • Liver cirrhosis
  • Alcohol abuse
  • Non-alcoholic steatohepatitis (NASH) 2

SIBO Survivor is focused mainly on people who have been diagnosed with IBS where SIBO is present.

Despite these known associations with other illnesses, there is still a tremendous hole that needs to be filled regarding the understanding of both SIBO and IBS. While researchers are currently investigating the various mechanisms that play a role in the pathogenesis of both of these conditions, there is still an urgent need for more work to be done.

This article will help provide some insight on the state of SIBO within the medical field today, its current classifications and future directions expected for the treatment options available for SIBO and IBS.

How Many People have SIBO?

sibo and ibs around world

Both SIBO and IBS affect millions of people around the world each day. As a result, researchers have remained devoted to acquiring useful information on the mechanisms and potential treatment options for these disorders.

Here are the numbers:

  • Around 10% of people in the world have IBS which = 700 million 3
  • Around 60% of people with IBS have been found to have SIBO
  • Therefore, around 420 million people have SIBO in the world

Other Facts Which Help Explain SIBO & IBS

  • The symptoms and quality of life for each patient with either SIBO, IBS or both vary. While some people may experience mild symptoms, some may have symptoms that are moderately debilitating whereas others may have more severe cases of these disorders. Therefore, these diseases exist as a spectrum that is different for each individual.
  • About 1 in 3 sufferers are male, whereas the remaining 2 in 3 sufferers are female 4
  • These conditions are not fatal; however, their associated symptoms can be extremely severe and ultimately cause the affected individual’s life to be extremely challenging.
  • Both SIBO and IBS are chronic conditions for a majority of patients; however, this is not the case for everyone.
  • Sufferers can get to a point where they live a normal quality of life through proper diet and treatment.

SIBO and Food Poisoning – How it Starts

Meat Contamination

More than 250 different types of pathogenic bacteria and toxins are transmitted through food each day.

In fact, this number continues to increase when considering the different types of bacteria present in water, as well as direct contact with other animals and human beings.

Some of these bacterial species that are more well known for their harmful effects include:

  • Shigella
  • Salmonella
  • Campylobacter jejuni
  • C. difficile
  • E. coli
  • Norovirus 5

Although we may ingest minuscule amounts of bacteria within our food each day, most of the time we will not experience any severe side effects as a result of the protective methods that our GI tract is equipped with to handle any unwanted bugs.

However, when we consume food that has not been cleaned properly or is contaminated in some other way, which commonly occurs when traveling to third world countries outside of the U.S., these bacteria can attack our GI tracts and cause severe GI symptoms; a condition otherwise known as food poisoning.

The following figure demonstrates exactly what happens in our bodies when we experience food poisoning in terms ofDNA damage and cell death:

sibo sequence

The following figure demonstrates exactly what happens in our bodies when we experience food poisoning in terms of our autoimmune response 67:

ibs and sibo disease sequence

A lot of research has been conducted that has shown that following an infectious event, such as that which occurs when someone experiences food poisoning, an individual’s susceptibility to attain IBS significantly increases 8.

Researchers suspect that around 10% of people who get severe food poisoning will develop IBS following an episode.

This occurs as a result of the changed physiology, such as the effects that are caused to the MMC (cleaning waves of small bowel), that occurs both at the anatomical (structural) and neurological (nerves) level.

More specifically, the effects that food poisoning and other intestinal infections have on a patient’s intestinal motility, meaning the ability of the intestines to move food, is a leading factor that promotes bacterial overgrowth, IBS-D and IBS-M.

Click here to learn how you can protect yourself from food poisoning.

The Types of IBS vs. SIBO

Types of IBS and SIBO

As one of the most commonly diagnosed GI disorders in the world with over 1 billion patients, IBS is characterized by a number of symptoms including abdominal pain or discomfort, bloating and some type of altered stool form, such as diarrhea or constipation.

Patients with IBS may experience an increase in either the number of normal bacteria (SIBO) or in the diversity of bacteria throughout the bowel (dysbiosis).

Although IBS and SIBO are intertwined, it is important to realize that not all IBS is SIBO, and not all SIBO is IBS!

Below are the categories that medical science groups IBS into and their relationship to SIBO:

IBS-D (Diarrhea)

IBS Diarrhea

IBS-D is estimated to affect approximately 40% of individuals with IBS.

This type of IBS has been shown to be caused by SIBO and the autoimmune process that results from food poisoning highlighted previously.

Recent research has also suggested a link to hydrogen sulfide gas in diarrhea-predominant patients.

IBS-M (Mixed, alternating diarrhea or constipation)

IBS M or mixed

IBS-M is estimated to affect approximately 23% of individuals with IBS. This type of IBS has also been shown to be caused by SIBO and the autoimmune process that results from food poisoning.

SIBO has been shown to be present in both IBS-D and IBS-M due to the autoimmune process that results from a severe episode of food poisoning.

IBS-C (Constipation)

IBS C or Constipation

IBS-C is estimated to affect approximately 35% of individuals with IBS.

IBS-C is considered to be a separate microbial condition that is related to a bloom of methane-producing bugs called Archaebacteria in the small and large intestines. This subset of patients has not been shown in research to have an autoimmune component like IBS-D and M patients.

Methane gas, which is produced by archaea has been shown to slow down the intestinal tract leading to constipation.

IBS and SIBO: Connecting the Diagnosis and Symptoms

sibo symptoms and diagnosis

Breath Tests

The use of a breath test is commonly used to determine whether an individual appears to have some type of overgrowth present within their small intestine.

Breath testing is important for both IBS and SIBO, as this diagnostic technique has been confirmed through the use of meta-analysis. It has been determined that IBS patients have more positive breath tests by a factor of 10, thereby allowing us to confirm that yes, breath testing results will typically be abnormal for patients with IBS.

Click here for more information on the breath tests that are typically used to diagnose IBS and SIBO 9.


As of 2017, it has been determined that approximately 60%, at a minimum, of patients with IBS exhibit some type of bacterial overgrowth within their small intestine, particularly the duodenum which is the highest portion of this bowel.

When the specific bacterial species were analyzed to determine their involvement in both IBS-D and SIBO, researchers found that patients with IBS exhibit a significant increase in both E. coli and Klebsiella colonies within their duodenum as compared to healthy individuals.

Although both of these bacteria are present in small amounts within the small intestine, an overgrowth of both of these species can cause severe digestive issues.

IBS-D and SIBO patients are often treated with antibiotics in an attempt to provide relief to the bloating, abdominal pain and loose stool symptoms associated with this disease.

More specifically, rifaximin is the most commonly used antibiotic for the treatment of SIBO, as this treatment option has been found to specifically improve the aforementioned symptoms in patients as compared to when the placebo was used.


As one of the most common symptoms associated with both IBS and SIBO, bloating is often a result of an increased amount of gas present within the gut that is abnormally distributed.

Since the bacteria within the small intestine ferment carbohydrates, they subsequently increase the amount of gas production in this area that ultimately causes the bloating and flatulence symptoms associated with both SIBO and IBS patients.

Therefore, when considering patients with IBS who also exhibit the same bloating symptoms, it can be concluded that some association between IBS and SIBO also exists; however, there is limited data that connects these two diseases to this specific symptom.


Bacterial species that produce methane, otherwise referred to as methanogenic flora, are associated with causing slow transit time in both the small and large intestine; a disorder that is otherwise referred to as constipation dominant IBS (IBS-C).

Currently, researchers are working towards differentiating between how patients with SIBO that have high concentrations of hydrogen (H2) and hydrogen sulfide (H2S) in their breath, which typically indicates a diarrhea-predominant condition, compare to those who have a higher concentration of methane in their breath, which typically indicates a constipation-dominant condition.

See the methane gas in IBS article to learn more.

What to Do About SIBO & IBS?

what to do about SIBO

In conclusion, SIBO is the disease state that occurs when the small intestine is not functioning properly which causes numerous digestive symptoms.

On the other hand, IBS is still the term doctors use to diagnose patients with SIBO, but it has been shown that about 60% of IBS patients have SIBO which is caused by the autoimmune process that happens as a result of food poisoning.