Welcome to part 2 of my look into SIBO (small intestinal bacterial overgrowth), a recent gut imbalance that’s been making waves as a possible trigger for IBS (irritable bowel syndrome). For the full 101 on SIBO, its symptoms, and testing, please go back to part 1. Today, we’ll be checking out the causes of SIBO. And I have to put the disclaimer out there that this is all just general information. Always talk to your doctor if you suspect you have SIBO! With that out of the way, let’s get started!

What Causes SIBO?

There’s no number one cause with SIBO. Many things can either cause or lead to it. If you remember, part 1 was all about how bacteria from the large intestine (colon) travel up to the small intestine, which shouldn’t be as populated, and start to over-ferment foods containing starch, sugar, fiber, and alcohol. The key takeaway is an overgrowth of bacteria. [1] Even though the bacteria down in our gut are the good guys, they can be too much of a good thing, especially if they’re in the wrong place. So, what causes these good guys to turn bad and end up on the wrong side of the gut? Here are the top culprits:

Motility Issues

Motility is the contraction and movement of muscles in the GI tract. When experts talk about motility, they’re specifically referring to the sphincter muscles that divide the esophagus, stomach, small intestine, and intestine into four separate parts. [2] If any of the sphincters between them opens or closes at the wrong time (as well as stay either closed or opened), then several problems can happen, including SIBO. With SIBO, a motility disorder can prevent the migrating motor complex (MMC) in the gut from “sweeping” any leftover digested pieces and bacteria out of the small intestine. The result is a buildup of bacteria that are hungry and ready to over-ferment food. We also miss out on receiving enough bile and enzymes that are released by the MMC, giving the bacteria even larger bites of food to chow down on. [3]

Poor motility can be caused by blockages, adhesions or scar tissue (from surgery, inflammation, infections, or trauma), gastroparesis (due to diabetes), problems with the vagus nerve, spinal cord injuries, chronic stress, medications (opioid analgesics or anticholinergics) and thyroid disorders (either hyper or hypothyroid). [3]

Poor Bile Flow or Stomach Acid

Not only are bile and stomach acid necessary for digestion, but they’re also the body’s natural way of killing off invasive bacteria. Many experts believe that having low levels of both of these creates the perfect storm for SIBO, allowing excess bacteria to wind up in the small intestine.

The causes for low stomach acid include nutrient deficiencies (Vitamin B12, zinc), stomach surgery (i.e., gastric bypass), H. Pylori infection (making SIBO a result or co-overgrowth), chronic stress, age (especially in people over 65), and medications (PPIs). [4] As for low bile, it could be due to excess estrogens (too much of this essential hormone can block the release of bile salts from the liver), gallstones, cholangiocarcinoma (cancerous blockages), strictures (scars from surgery or inflammation), liver cirrhosis or damage, primary sclerosing cholangitis (especially in people with inflammatory bowel disease or IBD), primary biliary cirrhosis (due to Sjogren’s syndrome, scleroderma, rheumatoid arthritis, or thyroiditis), Vitamin D deficiency, obesity, or jaundice. [5] [6] [7]

Low Immunity

Our gut makes up about 70% of our immune system and comes into contact with more foreign substances (antigens) than “any other part of the body.” [8] [9] If our immune system becomes compromised, then so too does the function of our gut. Weak immunity can lead to overreactive responses to food and bacteria, contributing to inflammatory diseases and disorders like Celiac and IBD. [9] What does this have to do with SIBO? When immune function slows down, we become deficient in selective IgA, which helps to prevent overgrowths of pathogens and, yes, bacteria. [1] People with selective IgA deficiencies are also prone to frequent allergies, infections, pneumonia, asthma, and diarrhea. [10]

The underlying cause for low selective IgA is mostly unknown, although there may be a genetic element to it. [11] As for low or poor immune function, it could be due to HIV, cancer, malnutrition, viral hepatitis, poor hygiene and sanitation, medications (cortisone, cytostatic drugs), radiotherapy, bone marrow and lymph node tumors, extreme stress (especially post-surgery), and old age. [12] [13]

Stealth Infections

SIBO may be the side effect of other infections, including H. Pylori, varicella-zoster (also causes chickenpox and shingles), Epstein-Bar virus (mono or “kissing disease”), and Lyme disease. [14] [15]

Other Causes

SIBO can also be caused by other things, including excess alcohol consumption, chronic constipation, and food poisoning. [16]

A Quick Myth Buster: Probiotics and SIBO

A common myth going around online is that probiotics- whether from food or supplements- directly lead to bacterial overgrowth. While it seems to make sense at first glance, this theory has been debunked by many experts. Although one small study showed that probiotics caused patients to test positive for SIBO, it was misinterpreted by many people online. According to clinical researcher Dr. Michael Ruscio, DNM, DC, “The part we need to understand here is none of these patients saw a significant increase in their symptoms. A lab finding changed, but symptoms did not change. Very important. The other is to understand the physiology of probiotics, which are: the majority do not colonize you. While these people are taking probiotics, they’re transiently working their way through the system. Either they die off or come out the other end.” [17] 

Summary: you can’t have a build-up of bacteria from a probiotic because the bacteria in it cannot colonize (aka, stay) in the intestines. They have a temporary effect and die off as quickly as they came.

Test, Don’t Guess

If any of the causes or conditions I’ve listed today resonates with you, then please go and get tested. Don’t self-diagnose online and cause even more harm! For more on testing, go back to part 1. In the meantime, stick around for part 3, where I’ll be going over treatment!

Sources:

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3099351/
[2] https://www.iffgd.org/motility-disorders.html
[3] https://integrative.ca/gut-motility/
[4] https://www.healthline.com/health/hypochlorhydria#treatment
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4990760/
[6] https://www.drelenaklimenko.com/causes-of-constipation-part-2-low-bile-flow/
[7] https://www.health.harvard.edu/a_to_z/bile-duct-diseases-a-to-z
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2515351/
[9] https://www.immunology.org/public-information/bitesized-immunology/organs-and-tissues/immunity-in-the-gut
[10] https://www.mayoclinic.org/diseases-conditions/selective-iga-deficiency/symptoms-causes/syc-20362236
[11] https://rarediseases.info.nih.gov/diseases/10197/selective-iga-deficiency
[12] https://www.medicalnewstoday.com/articles/324930.php#tips-to-stay-healthy
[13] https://www.sciencedaily.com/releases/2009/09/090914111540.htm
[14] https://www.drkarafitzgerald.com/2017/03/01/7-underlying-causes-sibo-might-missing/
[15] https://www.publichealthalert.org/palsy-of-the-gut-and-other-gi-manifestations-of-lyme-and-associated-diseases.html
[16] https://www.health.com/digestive-health/sibo-causes-digestive-issues
[17] https://drruscio.com/do-probiotics-cause-sibo/