What is SIBO?

diagram of sibo

SIBO stands for small intestine bacterial overgrowth which is when there is an overgrowth of bacteria or dysbiosis in the small intestine which causes uncomfortable digestive symptoms. 

SIBO is often a chronic dysbiosis that is difficult to treat. The small intestine is where humans digest and absorb food. It is not normal to have excessive amounts of bacteria there. The bacteria inhibit normal digestion of food and are linked to damage of the small intestine lining. There are a few ways patients can test: breath testing, culture, and empirical trial of antibiotics.

SIBO is also found to be one of the main causes of Irritable Bowel Syndrome. The most frustrating part for patients with the condition is that doctors and researchers still don’t understand everything about SIBO and Irritable Bowel Syndrome (IBS). The good news is that the research is growing and researchers are learning more and more each day. Our understanding of SIBO, IBS, and how the microbiome interacts with other bodily functions is bound to evolve as we learn more.

SIBO around worldHow Many People Have SIBO?

SIBO and IBS effect a ton of people around the globe which is why good information and continued research is important. Here are the numbers:

  • Around 10% of people in the world have IBS which = 700 million (1)
  • Around 60% of people with IBS have been found to have SIBO
  • Therefore, around 420 million people have SIBO in the world

Other Facts

  • Patient symptoms and quality of life varies. Some people may have a mild condition, some moderately debilitating, and some who have severe cases. The disease really exists on a spectrum and is different for each individual.
  • About 1 in 3 sufferers are male and 2 in 3 sufferers are female (1)
  • The condition is not fatal but can be very severe and make life really challenging due to various debilitating symptoms
  • It is a chronic condition for a majority of patients but not for everyone
  • Sufferers can get to a point where they live a normal quality of life through diet and treatment

What Causes SIBO?

Anything that decreases the flow of the small bowel and causes it to be over colonized by bacteria can cause SIBO.

Underlying Causes:

  • Deficient cleansing waves of the small intestine also called the migrating motor complexes which occur when fasting
  • Structural issues in the small intestine that impede the flow
    • Obstructions or adhesions
  • Failed natural protections against bacterial accumulation in small intestine
    • Hydrochloric acid of stomach
    • Enzymes or pancreatic insufficiency
    • Bile, comes out of gall bladder
    • Immune system
    • Ileocecal valve, prevents bacterial backflow

Other Factors That Can Create Underlying Causes:

  • Diseases that can create deficient MMC or structural problems
  • Drugs that slow motility
  • Cut nerves which we need for motility
  • Lifestyle factors like severe stress
  • Surgeries which cause damage
  • Many other factors that can lead to bacterial buildup

What Causes the Symptoms:

  • Bacterial gas from the microbes in small intestine
    • Main bacterial gases are hydrogen, methane, and hydrogen sulfide
  • Methane has been linked to constipation
  • Hydrogen has been linked to diarrhea
  • Pain comes from gas pressure

*Research has also shown that a percentage of sufferers develop nerve damage in their small intestine from an episode of food poisoning. This weakens their cleansing waves allowing SIBO to occur.

A normal small intestine should absorb food and powerfully clean up afterwards by sweeping the bacteria and undigested materials down your gastrointestinal tract. The intestines should work like a smooth flowing river, not a backlogged one.

Cause of SIBO

Healthy Intestines Work Like a Flowing River

One thing to remember is that SIBO is not a diagnosis and it is always caused by something else, so when talking to your doctor you need to try and examine other issues that could be causing SIBO.

Working to treat the underlying cause and taking a holistic approach which includes a change in lifestyle, diet, and working with an expert practitioner is important. 

For a more in-depth scientific overview of small intestine bacterial overgrowth check out this article.


IBS- Irritable Bowel Syndrome

SIBO- Small Intestine Bacterial Overgrowth

The terminology is confusing. IBS and SIBO are interlinked but people can also have one or the other on its own. You can see from the diagram below that up to 60% of IBS is caused by SIBO. It’s important to remember that they can occur without each other as well.

SIBO can also be caused by other medical issues such as adhesions, pseudo obstruction, narcotics, diabetes, and anything that slows down the flow of the small bowel. Researchers have found that in the 60% of IBS that contains SIBO the main cause is often an issue with the cleansing waves of the small bowel.


Here is a simple progression of the terminology of IBS so you can see how SIBO and IBS connect together.

Progression of IBS and SIBO

Photo from 2017 SIBO Symposium

You can see that the SIBO connection was brought about around 2000 when researchers discovered that 60% of patients with IBS had small intestine bacterial overgrowth and that the condition was not mainly a problem of the large intestine like they originally thought. This does not mean that all IBS is SIBO or all SIBO is IBS. There are a certain subset of people who have SIBO. The symptoms of SIBO-IBS are often more severe than IBS and usually include more gas and bloating.

IBS has always been a diagnosis of exclusion meaning if you were tested for other gastrointestinal diseases and did not match they labeled you with IBS. So, people with food intolerances and other intestinal issues can be labeled with IBS. Unfortunately, people labeled with IBS often go through various tests that don’t show anything significant and cost a lot of money.

Thankfully, research is improving and we are realizing specific connections like SIBO now. This enables patients and doctors to find better strategies for treating the disease. To learn more about what SIBO sufferers experience check out the symptoms page. If you find through testing and evidence that you are dealing with SIBO I have broken everything down for you on this site so that you can manage the condition as best as possible!