What the heck is SIBO?

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What is SIBO?

Small intestinal bacterial overgrowth (SIBO) occurs when gut bacteria become too plentiful in the small intestine. The most common symptom is diarrhea.

In a healthy gut there are huge numbers of bacteria in the large intestine (which is also called the colon) and relatively small numbers of bacteria in the small intestine. The bacteria present in the colon feed on the indigestible components of our food, like fibre, fermenting it to produce compounds that are beneficial to our health and digestion (like the anti-inflammatory short chain fatty acid called butyrate).

The small intestine is a 20 foot long tube between your stomach and colon. This is where food is broken down so that you can absorb nutrients through the wall of the small intestine. If bacteria become too plentiful in the small intestine, they are given access to an all you can eat buffet! The result is a large amount of fermentation in the wrong segment of the gut. This misplaced fermentation contributes to symptoms, most notably diarrhea.

SIBO typically occurs due to an underlying dysfunction of intestinal motility which results in stasis. Under normal circumstances, the small intestine contracts and relaxes in an organized manner, constantly moving undigested food particles and gut bacteria downstream to the colon (this is called peristalsis, in case anyone quizzes you). When normal intestinal motility becomes compromised, bacteria is permitted to grow to excessive numbers in the wrong segment of the gut.

In a person with SIBO, the resulting build up of gas and bacterial toxins causes digestive symptoms while also perpetuating the condition by causing ongoing damage to intestinal motility. It’s a vicious cycle! Normal digestion and nutrient absorption can become severely compromised and body systems outside the gut may be affected (i.e. brain, skin, thyroid, joints)

Signs and Symptoms of SIBO:

  • Diarrhea is the most common symptom
  • Bloating and flatulence, but not in isolation
  • Weight loss
  • Iron and vitamin B12 deficiency otherwise unexplained
  • Peripheral neuropathy due to vitamin B12 deficiency

Risk Factors for SIBO:

  • anatomical changes due to intestinal surgery or Crohn’s disease strictures
  • long term use of proton pump inhibitors for GERD treatment
  • medications that alter motility i.e. opioids, anticholinergics
  • conditions that alter gastrointestinal motility i.e. diabetes
  • impaired secretion i.e. low stomach acid, gall bladder removal, pancreatic insufficiency
  • inflammatory bowel disease (Crohn’s disease, ulcerative colitis)
  • conditions of malabsorption such as celiac disease, alcoholism
  • an episode of gastroenteritis or food poisoning
  • irritable bowel syndrome, diarrhea type

How is SIBO diagnosed?

The best lab test for diagnosing SIBO is a non-invasive breath test that measures abnormal gasses in the breath following the ingestion of glucose sugar. Although a similar test using lactulose sugar has been the test of choice in recent years and is still in use by many practitioners treating SIBO, the use of lactulose for breath testing is no longer recommended due to the high incidence of false positives.

Translation: If you’ve had SIBO diagnosed based on a lactulose breath test, it’s time to get another opinion!

The glucose breath test is not perfect but it is far more sensitive and specific to SIBO, meaning you are less likely to be misdiagnosed and given the wrong treatment (or misdiagnosed and given no treatment). Performed at home, the 3 hour glucose breath test requires that you follow a special diet for 1 day prior to testing and then fast overnight before performing the test the following morning. On the morning of the test you collect a baseline breath sample, then you drink a glucose sugar solution and proceed to collect a series of 9 additional breath samples every 20 minutes. The process takes 3 hours. These samples are analyzed by a lab to detect unusual elevations in hydrogen gas which will be present in high levels if you have SIBO.

Treating people with SIBO has become a special interest in my integrative medicine practice where I focus on the connection between gut health and chronic disease. Here are some frequently asked questions about small intestinal bacterial overgrowth:

Q: My physician or gastroenterologist has run imaging and other tests and said there is nothing wrong but I still have symptoms. Is it possible that I have SIBO?

A: You cannot see SIBO with diagnostic imaging like an ultrasound, x-ray, CT scan, MRI, endoscopy or colonoscopy. Current small intestinal culture techniques are invasive, expensive and not satisfactory for the diagnosis of SIBO. Physicians in Ontario rarely perform glucose breath tests and this means that a typical workup by a family doctor or gastroenterologist does not rule out SIBO. If your main symptom is diarrhea and you’re not responding to standard treatment, ask your doctor about SIBO testing (but make sure it it is the glucose test).

Q: My physician or gastroenterologist told me I have IBS. Could I have SIBO?

A: Although one study found that people with IBS were allegedly way more likely to have SIBO, this study used the wrong test to come to a diagnosis of SIBO (lactulose, not glucose). As a result, this study grossly overestimated the prevalence of SIBO in people with IBS such that we were led to believe that SIBO was really common in those with IBS! This has now been debunked. IBS is very common. Most people with IBS do not have SIBO.

Q: Is there a cure for SIBO?

A: It depends on the underlying cause of the case of SIBO in question. Remember, the bacterial overgrowth is a side effect of an underlying condition affecting gut motility. If that underlying condition or root cause can be successfully treated, it may be possible to put SIBO into remission by simply killing off the bacterial overgrowth. When the underlying cause of SIBO does not go away, SIBO is likely to relapse after a period of time even if the bacterial overgrowth is successfully eradicated by antibiotics. This doesn’t mean treatment is useless, it just means that treatment needs to be repeated periodically to keep your symptoms under control in the context of your underlying health condition.

Q: What does SIBO treatment look like?

A: The successful treatment of SIBO typically requires a course of the antibiotic rifaximin, in addition to addressing the underlying condition or risk factors that allowed bacterial overgrowth to occur in the first place. Herbal antimicrobials are sometimes used although these are not considered to be evidence based at this time. Herbal medicines and nutraceuticals are often used to address gut motility and assist with symptom management.

Q: Can you treat me for SIBO without performing the breath test?

A: No. A correct diagnosis is required in order for SIBO treatment to be responsibly recommended. This is essential to avoid treating you for the wrong thing, which can cause a whole hose of problems. Other conditions requiring different treatments can mimic SIBO, such as IBS. Jumping into SIBO treatment based on symptoms alone could be ineffective, a waste of your resources, and potentially dangerous if something even more serious has been missed.

Q: I can’t tolerate FODMAPs. Could I have SIBO?

A: Foods containing high levels of fermentable carbohydrates (FODMAPs) tend to exacerbate symptoms of SIBO but these foods also trigger symptoms in people with other conditions, like IBS, which is far more common than SIBO.

Q: Will a special diet cure SIBO? Did my food choices cause my SIBO?

A: No! Despite what you may read about online, there is no special diet that will reliably cure SIBO. In some cases, the dietary restrictions suggested for SIBO treatment could cause more harm than good – further harming digestive health and even affecting mental health since food fear can fuel disordered eating. Nutrition is super important and there are some special considerations when treating SIBO, but it is important to work with a medical professional who understands what food can do – and also what it can’t do. And no, you did NOT cause SIBO by eating a certain way 🙂

The Low FODMAP Diet, Specific Carbohydrate Diet and Elemental Diet are often recommended to treat SIBO. These diets reduce or completely eliminate fermentable carbohydrates for a period of time in order to starve gut bacteria. While the Low FODMAP Diet may reduce symptoms, research has not found it to be curative for SIBO. There is some research to support the efficacy of the elemental diet in inducing remission although this approach is incredibly restrictive and needs to be supervised by a qualified practitioner (it’s not really a diet but a medical food/formula).

SIBO diets may help with symptom management in the short term but but they do not address the underlying motility dysfunction and patient risk factors that led to SIBO in the first place. Many foods restricted by these diets are healthy foods that are needed in the diet to feed gut bacteria; restricting these foods for too long can cause more harm than good to the microbiome, not to mention your stress level and social life!

This post was updated on 2022 06 27 and contradicts information that was previously shared, because science says so! When we know better, we can do better.