Signs and Symptoms of SIBO

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Doctor with medical chart talking with patient in examination room
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Small intestinal bacterial overgrowth (SIBO) is a health condition in which an excessive amount of gut bacteria are present in the small intestine. Once thought to be a rare condition, emerging research suggests that it is under-diagnosed by physicians.

The most likely misdiagnosis is that of irritable bowel syndrome (IBS), when in fact the real problem is SIBO. Another scenario is to attribute the symptoms stemming from SIBO to a primary illness that contributes to the development or maintenance of SIBO when SIBO is in actuality present alongside that illness.

Differentiating SIBO from IBS and other health conditions is challenging. SIBO shares its symptoms with other disorders and does not present with its own unique symptoms. Although estimates vary widely across research studies, SIBO has been found to be present in a surprisingly high number of people who were diagnosed with IBS. Surprisingly high prevalence rates of SIBO have also been found in elderly people, people who have celiac disease whose symptoms are not eliminated through a gluten-free diet, and people who have cirrhosis of the liver.

Because SIBO can contribute to symptoms ranging from the mild (abdominal bloating) to the severe (nutritional deficiencies), it is important that its presence is identified. In this overview, you will learn about the primary signs and symptoms of SIBO. If you suspect that SIBO may be behind your own symptoms, you should bring your concerns to the attention of your doctor for proper evaluation and treatment.


The symptoms of SIBO can differ from one person to the next. And as you can see, many of its symptoms are very similar (if not identical) to that of IBS:

  • Abdominal bloating
  • Abdominal distension (gets worse as the day goes on)
  • Abdominal pain
  • Chronic diarrhea, sometimes with urgency
  • Excessive intestinal gas
  • Nausea
  • Soiling accidents

To further muddy the water when it comes to SIBO there is the fact that its signs and symptoms may vary according to the specific types of bacteria present in the small intestine.

How Would You Know If It Is Not IBS?

Although the symptoms of the two disorders are so similar, there are some differences. One possible sign that the problem might be SIBO as opposed to IBS is if your bloating starts within 90 minutes after you eat something. The thinking here is that it takes approximately 90 minutes for food to reach the large intestine. So if bloating is occurring prior to the 90-minute mark, it might indicate that bacteria within the small intestine are responsible.

Fatigue, weakness, and weight loss are symptoms of more severe cases of SIBO that are not typically experienced by people who have IBS.

Severe SIBO and Nutritional Deficiencies

In more rarer and more severe cases, SIBO can contribute to problems with the absorption of vitamins and other nutrients resulting in nutritional deficiencies. Malabsorption may occur when SIBO results in microscopic damage to the villi lining the walls of the small intestine. Nutritional deficiencies can lead to significant health problems, so it is important that SIBO, if present, be identified and treated. If you have experienced unexplained weight loss alongside intestinal symptoms, it is essential that you bring your symptoms to your doctor for a proper diagnosis and treatment plan.

Here are some of the nutritional deficiencies that have been associated with the presence of SIBO.

Carbohydrate malabsorption: There are several possible ways in which SIBO can cause a malabsorption of carbohydrates. The first is that SIBO may cause a premature digestion of carbohydrates by the bacteria present in the small intestine. SIBO is also thought to result in a dysfunction in the enzymes responsible for breaking down carbohydrates for absorption into the bloodstream due to damage in the villi. And lastly, people who have SIBO may also begin to restrict their carbohydrate intake in an effort to avoid bloating, diarrhea, and other symptoms.

Protein malabsorption: The damage to the villi from SIBO may result in a decreased ability for the small intestine to absorb protein into the body.

Fat malabsorption: Fat malabsorption resulting from SIBO is thought to occur because the bacteria present in the small intestine break down bile acids which are responsible for the breakdown and absorption of fat. These broken down bile acids are then thought to be absorbed in the middle part of the small intestine (the jejunum) rather than the last part of the small intestine (the ileum) which is where fat-soluble vitamins, such as vitamins A, D, E, and K, would normally be absorbed.

Fat malabsorption is thus particularly problematic as it can lead to deficiencies of these vitamins. Luckily, research has shown that only in very rare cases does severe illness develop from these deficiencies.

Fat malabsorption often has a definitive visible sign in that it can cause floating stools. Stools may also look oily and may be particularly foul-smelling.

Vitamin B-12 deficiency: The presence of SIBO raises one's risk for a B-12 deficiency because the bacteria in the small intestine utilize the vitamin themselves, and thus the vitamin is not available to your body for absorption. Such a deficiency can result in peripheral neuropathy. It can also result in megaloblastic anemia (enlarged red blood cells) or normocytic anemia (low red blood cell count).

Iron deficiency: SIBO can also cause anemia due to an iron deficiency. It is theorized that iron is not absorbed properly due to damage was done by the bacteria present to the villi within the small intestine.

Vitamin D deficiency: The presence of SIBO has been associated with a higher risk for osteoporosis. This association is thought to be the result of SIBO-caused vitamin D deficiency.

Other vitamin deficiencies: There have been case reports of people who experience vitamin E deficiency syndromes and a single case report of a person who experienced night blindness from a deficiency in vitamin A attribute to the presence of SIBO.

Health Conditions That Increase Your Risk

Emerging research has identified a wide variety of illnesses that may be present alongside SIBO. This co-existing state may be because the illness itself sets up conditions for SIBO to develop. If you have any of the following and your symptoms have been worsening in spite of medical treatment, you may want to talk to your doctor about testing you for SIBO:

What to Do If You Suspect SIBO

If the information you have read here today has made you think that perhaps SIBO is playing a role in your symptoms, you should schedule an appointment to speak to your doctor about the issue.

SIBO is diagnosed through the use of a breath test or through a biopsy taken in the course of an endoscopy. Although the breath test is less invasive, there are some concerns about its validity in terms of accurately identifying the presence or absence of SIBO.

If SIBO is found to be present, your doctor will work with you on a treatment plan. If there is an underlying illness that has set up the conditions for SIBO to develop, addressing that illness will be the primary focus. For some cases, a trial of specific antibiotics aimed at eradicating bacteria within the small intestine may be warranted. Your doctor may also assess for and recommend interventions for any existing vitamin deficiencies.

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