Small Intestinal Bacterial Overgrowth (SIBO)
Small Intestinal Bacterial Overgrowth (SIBO) has entered the gut health chat.
As awareness of digestive health grows, so too has interest in SIBO as a possible explanation for persistent gastrointestinal symptoms. However, increased attention also raises important questions about diagnosis, evidence, and whether SIBO is over- and misdiagnosed in some cases.
Let’s take a closer look at what the research suggests.
What is Small Intestinal Bacterial Overgrowth (SIBO)?
Let’s get sciency! The actual definition of SIBO is “an increase of bacteria equal to or greater than 105 colony-forming units per mL of upper gut aspirate, causing symptoms.” (1) Okkkkk. What that actually means is that your gut has found its philanthropist streak and is trying to house more bacteria than it can handle. This includes offering shelter to microorganisms in your small intestine, which should be more or less off-limits.
For the most part, the body is pretty good at herding bacteria and other organisms to where they belong, but if one of these defensive mechanisms fails, SIBO can occur. The causes are complex and can include:
Gastric acid and bile failing to act as bouncers: adequate levels of these substances can prevent microorganisms from entering and remaining in the small intestine. Any alterations or insufficiencies can cause this mechanism to fail. Long-term use of proton pump inhibitors may increase this risk. (2)
Insufficient enzymes: the pancreas releases specific enzymes that act antibacterially, if produced in sufficient amounts. (2)
Reduced motility: slowed gastric emptying, leading to organisms and food lingering in the upper gastrointestinal tract, which increases the risk of colonisation and overgrowth in the small intestine. (3)
Anatomical abnormalities: structural differences you may have been born with or have acquired. For example, chronic disease or surgery can lead to pockets or blockages in your small intestine, promoting the growth of organisms. (4)
Impaired Immune function: the intestinal immune system plays a crucial part in your body’s defence mechanism, which includes secreting substances that act antimicrobially or blocking organisms from attaching. Disruptions of these mechanisms increase the risk of overgrowth. (4)
What are the symptoms of SIBO?
Common symptoms that may be caused by unwanted bacteria occupying your small intestine include (2):
Persistent bloating
Gas
Abdominal pain or discomfort
Loose stools
Vitamin deficiencies (particularly Vitamin B12).
These symptoms could be used to describe numerous gut disorders, and are not particularly specific. It’s also important to mention that SIBO does not manifest the same in everyone, with the types of microorganisms deciding to set up camp in your small intestine varying greatly and likely causing different symptoms. (8)
The SIBO type is determined by the primary gas that these unwelcome guests produce:
hydrogen,
methane or
hydrogen sulfide
Hydrogen-SIBO is more associated with diarrhea, while Methane-SIBO manifests more commonly as constipation. However, neither is opposed to cohabiting, so mixed symptoms are also possible. (9)
Why do I have SIBO?
The majority of SIBO cases are linked to chronic inflammation of the pancreas, irritable bowel syndrome or intestinal motility disorders. (2) Also, if you are a woman, congratulations, as once again we are coming on top, though sadly under rather unfortunate circumstances. (2) Some early research has also identified a higher incidence among females suffering from endometriosis (10) or following an influenza infection (11) (give me a break!). I should say that these claims require a lot more in-depth and higher-quality studies, but they give you a flavour of how little is actually known at this point.
How is SIBO diagnosed?
If you have been struggling with gut issues, you may have had the pleasure of the ‘truly moving’ experience of a colonoscopy or gastroscopy. Unfortunately, sneaky SIBO pulls a Houdini during the internal sightseeing tour and simply does not show up. SIBO requires specific sampling during an endoscopy using a catheter (I’ll spare you the details) and cultivating the bacteria in the laboratory. This approach is not only uncomfortable for the patient (did I mention the catheter), but it is also riddled with other issues, such as risk of cross-contamination with other microorganisms during sampling, insufficient numbers of organisms, or the collected bacteria simply not wanting to grow in the lab, on top of being a time-consuming and expensive procedure. (4, 12) However, this small intestine aspirate is the gold standard of testing.
Considering the above, most opt for non-invasive breath tests instead. (13) However, a major downfall of these is the lack of sensitivity and specificity (meaning a higher risk of false positive or false negative test results), making it crucial to meticulously follow procedures before and during the testing. (14) This, for example, includes up to 4 weeks of a washout period before the test, where you need to stay off antibiotics, probiotics, motility regulators and more (basically, likely all the things that you are taking to manage the symptoms in the first place…). (8, 15)
How it all works is you’ll sip on a sweet, carby drink and then breathe into a tube every 15-30 minutes, for up to 3 hours. (8) This will measure the concentration of hydrogen, methane or (less commonly) hydrogen sulfide being produced by the microorganisms potentially occupying your small intestine, after fermenting either lactulose or glucose, consumed in the drink of choice at the beginning of the testing. (8)
How is SIBO treated?
The obvious goal in treating SIBO is to evict the uninvited bacteria and ensure they never return. Additionally, underlying deficiencies or disorders need to be managed. There is no single treatment in isolation to manage SIBO, rather a combination of strategies to reduce the overgrowth and the risk of the bacteria returning. Some ways SIBO may be treated include:
Antibiotics: Usually considered the first-line treatment of SIBO. Oral broad-spectrum antibiotics have been shown to play a key role in reducing the overgrowth in your small intestine.
Diet: Some elimination diets, such as the low-FODMAP diet, have been shown to reduce common bowel symptoms including bloating, gas, diarrhea and more. While diet changes can’t “cure” the SIBO, they can help you manage your symptoms or any side effects of the antibiotic therapy.
Probiotics: It may seem counterintuitive to add more bacteria to your gut. However, by consuming and supporting the growth of beneficial bacteria via probiotics, the risk of bad guys making themselves at home again is reduced. There are specific and well-studied strains to consider here, so always consult with the appropriate health professional first.
Herbal extracts: Some emerging research suggests positive effects of a mixture of plant extracts (such as oregano, berberine, thyme, and ginger). I should point out that the effectiveness of the different treatments can differ widely among individuals, because of SIBO’s complexities and individual characteristics. This area of research is still evolving, and there is a lot more to learn.
Is SIBO a legitimate diagnosis?
In short, yes! However, due to inaccurate breath tests, results need to be considered together with any symptoms you may experience, as well as your medical history.
While several theories are proposed to explain the development of SIBO, the underlying root causes, such as why contributing factors occur in the first place, must also be considered to successfully treat SIBO and prevent recurrence.
There is yet to be a one-size-fits-all treatment approach, but the good news is that the research in this field is ongoing, and scientists are working hard to better understand SIBO and to develop better diagnostic tools as well as treatments. (8, 16)
I just wanted to add something- since we explained the ‘whys’ further above- the causes for even getting to the ‘whys’, such as low motility, etc., would also need to be considered
This article was written by Melanie Bruckberger.
BSc (Biomedical Science)
Master of Human Nutrition
Currently undergoing Certificate III & IV in Fitness
TDC Intern
Whether it’s cellular processes, microorganisms, nutrition or the environment, Mel loves sharing scientific insights in a digestible way (pun intended!) and empowering people to make dietary and lifestyle-informed choices.
References
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