What is SIBO

In the last post, I talked about how IBS is a collection of symptoms for which there are usually underlying causes and treatments. While there are several possible reasons for having IBS symptoms, one of the most common causes is SIBO, or small intestinal bacterial overgrowth. In fact, up to 84% of IBS sufferers’ symptoms are caused by SIBO infection (1).

So what is SIBO, and why does it to occur in the first place?

Normally, bacteria reside mainly in the colon, and in smaller amounts in the small intestine. SIBO occurs when there is an increased number of a bacterium in the small intestine, or when bacterium that normally inhabit the colon suddenly migrate to the small intestine. Normally, the acidic contents leaving the stomach prevent the growth of bacterial species in the small intestine. Lack or suppression of normal stomach acid can allow for a less acidic environment where bacterial growth can occur, thus leading to SIBO. The presence of SIBO can then damage the tight junctions sealing off the cells of the intestines, contributing to leaky gut. They also produce gases which contribute to bloating, abdominal distention, and malabsorption.

What conditions in the body allow for such an overgrowth to occur?

As mentioned before, low stomach acid due to medications that suppress its production can allow for overgrowth to occur. Antibiotic use can contribute by killing off the beneficial bacteria, allowing the pathogenic ones to take over. More often than not however, it is a past infection (either food poisoning or traveler’s diarrhea) that contributed to the favorable conditions necessary for bacterial overgrowth to occur. These infections cause damage to certain cells in the intestines, called interstitial cells of Cajal, responsible for maintaining the migrating motor complex (MMC), and regulating movement of food in the small intestines. In fact, your chances of developing irritable bowel syndrome increase six-fold after an acute gastrointestinal infection (2).The small bowel is also essential for the digestion and absorption of foods, as well as immune system function. Any damage to this portion of the digestive tract leaves one vulnerable to infection, indigestion and malabsorption.

I remember my GI problems worsened when I was put on acid-suppressing PPIs, but got completely out of control after an acute episode of gastroenteritis in college. The PPI made me more susceptible to infections because it decreased my first line of defense against pathogens—stomach acid. After living abroad for years and experiencing multiple bouts of food poisoning and traveler’s diarrhea, paired with several intense rounds of antibiotics, one can clearly see where my GI problems came from!

What is the migrating motor complex?

The MMC is a gentle sweeping motion that happens every 90 minutes when you are in a fasted state, and pushes bacteria and food material down and out of the intestinal tract. If the cells responsible for this mechanism are damaged by past infection, motility is slowed down, allowing for stagnant material to facilitate the growth of bacterial organisms in a place they normally wouldn’t. For this reason intermittent fasting (or fasting for 4-5 hours in between meals) is an important part of restoring motility if a SIBO diagnosis is made.

How do I know if I have SIBO?

If you commonly experience gas, bloating, diarrhea, constipation, abdominal pain or cramping, or have been told by a doctor that you have IBS, these are all common signs of SIBO infection. There are also tests available to determine if you have bacterial overgrowth. The most commonly and well-studied test is the lactulose hydrogen methane breath test. Lactulose is a specific type of un-absorbable carbohydrate that reacts with bacteria to create gasses. It is important to make sure you get tested for both hydrogen and methane gases, since you may have bacteria that produce one but not the other type. Testing for only one type puts you at risk for a false negative diagnosis.

It is important that if you do have SIBO, you take steps to identify and eradicate the infection.

SIBO not only affects your ability to absorb and utilize the nutrients in the foods you are eating, but also influences your susceptibility to developing food allergies and intolerances by modulating the integrity of the gut lining and contributing to leaky gut. We are not what we eat, but rather what we absorb, and eradicating SIBO infection is essential to getting the most out of a healthy diet.

Heather_Carrera_NutritionGuest Post: Heather Carrera, MS, Dr. James’ Functional Nutritionist with a passion to utilize nutrition to prevent and heal disease, and promote a healthy, active lifestyle. Contact Heather today for your first consult.



  1. http://www.ncbi.nlm.nih.gov/pubmed/20467896
  2. http://www.ncbi.nlm.nih.gov/pubmed/17661757

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