What is Small Intestinal Bacterial Overgrowth or SIBO?

This is a medical condition where the small intestine contains an abnormally large amount or number of bacteria and also the types of bacteria present in the small intestine resemble those bacteria present in the colon. Small intestine, which is the small bowel, is a part of the digestive system which connects the stomach with the colon or the large bowel. The function of the small intestine is digestion and absorption of food in the body. There are three parts of the small bowel, namely: the duodenum, the jejunum and the ileum.

Normally bacteria are present in the gastrointestinal tract, including the small intestine. Colon contains the highest number of bacteria, and the small intestine has lesser amount of bacteria. The types of bacteria present in the colon are different from the bacteria present in the small intestine. Small intestinal bacterial overgrowth or SIBO is also referred to as small bowel bacterial overgrowth syndrome (SBBOS).

Small Intestinal Bacterial Overgrowth or SIBO

Pathophysiology of Small Intestinal Bacterial Overgrowth or SIBO

When the food gets digested in the intestine, by the bacteria in the intestine, they produce gas. Accumulation of this gas in the abdomen leads to abdominal bloating or distension resulting in abdominal pain. The increased amount of gas also produces excess flatulence or wind. The bacteria are thought to convert the food into substances, which irritate or harm the cells that line the small intestine and colon. These harmful/irritating substances lead to diarrhea. In some cases, bacteria can also produce methane gas which may cause constipation. If the bacteria that are present in the small intestine increase to large numbers, then it starts to compete for the food with the human body resulting in malnutrition and mineral and vitamin deficiencies. In severe stages of Small intestinal bacterial overgrowth or SIBO, the bacteria use up a lot of food consumed, so much that there are not enough calories for the body to thrive which results in weight loss of the patient.

The Relationship between the Small Intestine and Bacteria

Before the baby is born, there are no bacteria present in the gastrointestinal tract. However, during the birth, the bacteria present in mother's colon and vagina get swallowed by the baby and multiply in the baby's gastrointestinal tract in the subsequent few weeks or months. The relationship between the human body and normal intestinal bacteria is difficult to explain. Both benefit each other. The bacteria benefit from the moist, warm, environment present in the small intestine and the continuous flow of food down the gastrointestinal tract is perfect for thriving of the bacteria. The human body benefits from normal bacteria in the following ways:

  • They prevent the disease-causing bacteria from growing inside the intestine.
  • They stimulate the immune system and the growth of the lining of the intestine.
  • They help in improving the small intestine's muscular activity.
  • They produce vitamin K that gets absorbed and is used by humans.

The immune system of the GI tract including the small intestine helps in protecting the intestine from disease-causing bacteria, viruses and parasites. The intestine tends to attack only the harmful bacteria and becomes tolerant of the normal bacteria. The intestine also protects itself from both harmful as well as normal bacteria through the following:

  • The mucus secreted into the intestine covers the lining of the intestine which will prevent the bacteria from reaching the lining.
  • The muscular activity also restricts the amount of bacteria present inside the intestine.
  • Antibodies get secreted by the intestine which can block and can also kill the bacteria along with substances, which prevent the bacterial growth.

Relationship between Small Intestinal Bacterial Overgrowths or SIBO & Irritable Bowel Syndrome (IBS)

One of the common gastrointestinal problems includes irritable bowel syndrome (IBS). Irritable bowel syndrome is a chronic condition and the typical symptoms of IBS comprise of pain in the abdomen, bloating, alterations in patient's bowel habit, such as diarrhea or constipation with flatulence. Symptoms of IBS can be continuous or can fluctuate over a period of months, years or even decades.

There are no conclusive diagnostic tests for IBS and the diagnosis is made on the basis of patient's history, symptoms and tests which rule out other diseases which have similar symptoms, such as infections, ulcers, cancers, tissue inflammation and intestinal obstruction.

The symptoms of irritable bowel syndrome are remarkably similar to the symptoms of Small intestinal bacterial overgrowth or SIBO. It is thought that Small intestinal bacterial overgrowth or SIBO may also be causing the symptoms in some patients who have IBS. This theory is further strengthened from the fact that many patients suffering from IBS also have an abnormal hydrogen breath test. Other than this, IBS patients also find improvement in their symptoms after taking antibiotics, which is the first line of treatment for Small intestinal bacterial overgrowth or SIBO. However, research is still being carried out regarding this theory.

Causes of Small Intestinal Bacterial Overgrowth or SIBO

The gastrointestinal tract is a muscular tube in which the food which is to be digested travels along before reaching the colon. In normal conditions, the coordinated action of the stomach and small intestine muscles helps in propelling the food from the stomach, via the small intestine and into the colon. This coordinated muscular action also moves the bacteria from the small intestine along with restricting the number of bacteria present in the small intestine. However, if a disorder or any type or a problem occurs, then it interferes or hinders the normal activity of the small intestine resulting in accumulation of bacteria and increase in the number of bacteria by its staying longer and multiplying in the small intestine which results in Small intestinal bacterial overgrowth or SIBO. The absence or decrease of the normal muscular activity of the small intestine can also allow the bacteria to move backwards into the small intestine, from the colon.

There are many conditions which are associated with Small intestinal bacterial overgrowth or SIBO and some of the common ones are listed below:

  • If there is any intermittent or partial obstruction of the small intestine then it can interfere with the transportation/movement of the bacteria and food through the small intestine, leading to Small intestinal bacterial overgrowth or SIBO. Some of the causes of obstruction, which result in Small intestinal bacterial overgrowth or SIBO, are Crohn's disease, adhesions/scarring from any previous surgery.
  • Muscular and neurological diseases can also change the normal function of the intestinal muscles. Diabetes mellitus can cause damage to the nerves which control the muscles of the intestine. Scleroderma causes direct damage to the intestinal muscles. In both these cases, the small intestine's abnormal muscular activity causes development of Small intestinal bacterial overgrowth or SIBO.
  • Diverticulis are the small pouches that can be present in the small intestine and can allow multiplication of the bacteria inside the diverticuli.

Signs & Symptoms of Small Intestinal Bacteria Overgrowth or SIBO

  • Patient suffering from Small intestinal bacterial overgrowth or SIBO has symptoms of excess wind or flatulence.
  • There is abdominal distension/bloating.
  • Patients with Small intestinal bacterial overgrowth or SIBO also have diarrhea.
  • Abdominal pain is also present.
  • Constipation can also occur.
  • Vitamins and minerals deficiencies from improper digestion and absorption of food.
  • Weight loss due to the body not getting sufficient calories as the food gets consumed by the excessive bacteria is also one of the symptoms of Small intestinal bacterial overgrowth or SIBO.
  • Patient may also experience symptoms which are not related to the gastrointestinal tract, such as fatigue and body aches.
  • The symptoms of Small Intestinal Bacteria Overgrowth are often chronic in nature. Symptoms of SIBO tend to fluctuate in intensity over a period of many months, years or even decades before even a proper diagnosis is made.

Diagnosis of Small Intestinal Bacterial Overgrowth or SIBO

Bacterial culture from the small intestine: Culturing of bacteria is one of the methods for diagnosing the condition of Small Intestinal Bacterial Overgrowth (SIBO). A sample of fluid which contains bacteria is taken from the small intestine and culturing is done on it to determine the exact number of bacteria present in the sample. In this procedure, a long flexible tube is passed through the nose of the patient, into the throat and down the esophagus via the stomach to gather the fluid from the small intestine.

Problems which can be present in this method (culturing) for diagnosing SIBO are:

  • Using the tube is expensive and can be uncomfortable for the patient. The skill of doing this procedure is also not easily available.
  • Most of the times, sample can be taken only from one segment of the small intestine using this method, which means that overgrowth of bacteria in other segments of the intestine can be missed.
  • Most laboratories do not have this type of culturing as a routine procedure and the accuracy of it can also be questionable.

Hydrogen Breath Test (HBT): The bacteria which live in the colon can digest by using carbohydrates and sugars as their food. Gas is produced when the normal bacteria present in the colon digests carbohydrates and sugars. This gas is usually carbon dioxide, along with methane and hydrogen in smaller quantities. Small quantities of these gases get absorbed through the colon lining into the blood where they circulate and travel to the lungs and get eliminated through a person's breath. Special analyzers are used to measure these gases in the breath.

Procedure of the Hydrogen Breath Test: Patient needs to fast for a minimum of 12 hours before the hydrogen breath test. The patient is then told to inflate a small balloon using a single breath of air. A small amount of the test sugar (glucose or lactulose) is then ingested into it. The samples of the breath are then analyzed for methane and hydrogen every 15 minutes for three hours or more.

Treatment of Small Intestinal Bacterial Overgrowth or SIBO

Small Intestinal Bacterial Overgrowth or SIBO has been known for several years as a problem which occurs as a result of intestinal obstruction and disorders of intestinal muscles. Antibiotics are the first line of treatment and they are quite effective. The underlying cause of SIBO is not clear and patient has recurrence of symptoms after the antibiotics are stopped.

Small Intestinal Bacterial Overgrowth or SIBO & Irritable Bowel Syndrome (IBS)

Scientific studies are carried out regarding the treatment of IBS with the treatment modality that presumes the possibility of underlying Small Intestinal Bacterial Overgrowth or SIBO. Oral antibiotics and probiotics are the two most common treatments for Small Intestinal Bacterial Overgrowth or SIBO in patients who also suffer from irritable bowel syndrome. Probiotics are nothing, but live bacteria which when ingested produce a beneficial effect in the patient. There are many antibiotics, which can be used individually or in combination for treatment and which have been successful. Standard dosages of antibiotics are used for one to two weeks. Probiotics can be used in combination with antibiotics or may be used alone for prolonged maintenance.

Antibiotics vs. Probiotics for Treating Small Intestinal Bacterial Overgrowth or SIBO

According to some experts, short-term (7 to 14 days) treatment with antibiotics is more effective for Small Intestinal Bacterial Overgrowth or SIBO than probiotics. However, there are some disadvantages of using antibiotics; specifically the one where there are chances of recurrence of symptoms of Small Intestinal Bacterial Overgrowth or SIBO after discontinuation of treatment. In such patients, repeated or prolonged courses of antibiotics may be needed. There is, however, a concern for prescribing prolonged or repeated courses of antibiotics because of their long-term side effects.

There is less concern or risk regarding long-term side effects with probiotics; and for this reason doctors are more willing to prescribe probiotics to treat Small Intestinal Bacterial Overgrowth or SIBO for prolonged period of time or repeatedly. Another option is to start the treatment initially with a short course of antibiotics and follow it with long-term probiotics. Research is still going on regarding comparison of probiotics, antibiotics and combination of probiotics and antibiotics.

Brief Facts about Small Intestinal Bacterial Overgrowth or SIBO

  • Small Intestinal Bacterial Overgrowth or SIBO is a condition where bacteria resembling that of bacteria present in the colon start to multiply in huge amount in the small intestine.
  • Symptoms of Small Intestinal Bacterial Overgrowth or SIBO consist of bloating, abdominal pain, constipation, flatulence and diarrhea. Patients with advanced cases of Small Intestinal Bacterial Overgrowth or SIBO may have weight loss with mineral and vitamin deficiencies.
  • The cause of Small Intestinal Bacterial Overgrowth or SIBO may be intestinal obstruction or dysfunction of the muscles or nerves of the intestine.
  • The diagnosis of Small Intestinal Bacterial Overgrowth or SIBO is made by culturing the fluid taken from the small intestine or using hydrogen breath testing.
  • Small Intestinal Bacterial Overgrowth or SIBO can also cause symptoms in some patients who are suffering from irritable bowel syndrome.
  • Treatment of Small Intestinal Bacterial Overgrowth or SIBO consists of antibiotics, probiotics or a combination of both.

Written, Edited or Reviewed By:

, MD, FFARCSI

Last Modified On: October 12, 2016

Pain Assist Inc.

Pramod Kerkar
  Note: Information provided is not a substitute for physician, hospital or any form of medical care. Examination and Investigation is necessary for correct diagnosis.

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