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SIBO and Thyroid Health

Published June 16 2014

Small intestinal bacterial overgrowth, also known as SIBO, is a condition which involves excessive bacteria in the small intestine.  Some of the common symptoms associated with this condition include bloating, diarrhea, abdominal pain, and weight loss.  SIBO is more prevalent in conditions such as fibromyalgia and Irritable bowel syndrome, but it’s also something that can affect some people with thyroid and autoimmune thyroid conditions.

Normally there should be a smaller amount of bacteria in the upper small intestine when compared to other parts of the gastrointestinal tract.  But it’s not only the increase in the number of organisms which characterize SIBO, but the type of organism as well.  For example, under normal circumstances, most of the bacteria in the upper small intestine should be gram-positive.  But with SIBO it’s common to have a greater amount of gram-negative organisms, such as E. Coli and Klebsiella pneumoniae, although gram-positive organisms such as Enterococcus can also be present in greater numbers (1) [1].  Most people are familiar with the problems E. Coli can cause, but Klebsiella can produce toxins which damage the mucosa, and thus interfere with absorption and lead to other problems (2) [2].

What Are Some Of The Causes Of SIBO?

One usually develops SIBO when they have conditions such as achloryhdria (low or absent production of hydrochloric acid), a deficiency of the pancreatic digestive enzymes, an immunodeficiency syndrome, small intestinal obstruction, diverticula, and/or motility disorders (3) [3].  Of these, the two conditions that most commonly predispose a person to bacterial overgrowth are diminished stomach acid secretion and small intestine dysmotility (4) [2].  This condition can lead to malabsorption problems (5) [4], and this should be suspected if the person is experiencing symptoms such as chronic diarrhea and/or weight loss.

How Does One Test For The Presence Of Bacterial Overgrowth?

Unfortunately there is no perfect test for determining whether someone has SIBO.  Small-bowel aspiration and culture is considered the current gold standard, but is rarely utilized due to its high cost, invasive nature, and sampling error (6) [5].  The two main tests used to diagnose SIBO are the lactulose breath test and the glucose breath test (7) [6].  The advantages of the lactulose breath test include 1) it can identify SIBO of the distal small bowel and 2) lactulose doesn’t pose problems with people who have blood sugar disorders.  However, there is evidence that the glucose breath test has greater diagnostic accuracy than the lactulose breath test.  This seems to be especially true in those people who have irritable bowel syndrome (8) [7].

What Is The Relationship Between SIBO And Thyroid Health?

I was only able to find one study which looked to assess the prevalence and clinical pattern of SIBO in patients who had a history of hypothyroidism (9) [8]. The study involved a small number of people, although the findings were determined to be statistically significant.  27 of the 50 patients with overt hypothyroidism tested positive for SIBO, compared to only two out of 40 from the control group.  So while larger trials need to be done, this study does demonstrate that people with overt hypothyroidism might warrant testing for bacterial overgrowth.

I personally haven’t seen a high correlation of people with hypothyroidism and SIBO in my practice.  However, it’s important to point out that the study I discussed evaluated those who had “overt” hypothyroidism.  Most of the patients I deal with have Hashimoto’s Thyroiditis, and while it is common to see a high TSH and elevated thyroid antibodies, the thyroid hormone levels aren’t always depressed.  Some people with Hashimoto’s Thyroiditis have depressed thyroid hormone levels, while others have thyroid hormone levels that are low, but still fall within the reference range.

And while it’s possible to have a hyperthyroid condition and SIBO, this isn’t common, and I couldn’t find any studies which showed any correlation between hyperthyroidism or Graves’ Disease and bacterial overgrowth.  With that being said, if anyone is having the symptoms associated with SIBO then this condition should be suspected, although to be fair, other problems with the gut can lead to bloating, flatulence, and other similar symptoms.

There is evidence that SIBO can cause a leaky gut (10) [9].  As a result, if someone has SIBO then they will not only want to take measures to correct this problem, but they may also need to follow a leaky gut protocol.  And let’s not forget that there’s a correlation between leaky gut and autoimmunity, which means that having SIBO might cause a leaky gut, which in turn can lead to a condition such as Graves’ Disease or Hashimoto’s Thyroiditis.

Can SIBO Be Treated Naturally?

Antibiotics are typically used to treat SIBO, with Rifaximin being the most common antibiotic used to treat patients with bacterial overgrowth. Unfortunately the relapse rate is high, as one study found recurrence of SIBO in 44% of patients nine months after successful treatment with Rifaximin (11) [3]. This doesn’t mean that Rifaximin shouldn’t be considered in some cases of SIBO, but it isn’t doing anything to address the cause of the problem.

When treating SIBO naturally there are a few things you need to do. Of course you want to try to remove those factors which might have caused the problem. For example, if someone is taking a proton pump inhibitor which caused the bacterial overgrowth due to a deficiency of gastric acid, then they need to work with their medical doctor in order to help wean them off of this drug. Although taking antibiotics might help, because they disrupt the gut flora and the relapse rate is high, then one might want to choose to take natural anti-microbials. Some examples include oregano oil, berberine, garlic, green tea, and thyme. However, one also needs to consider that not all “natural” anti-microbials are completely safe, as for example, taking higher doses of certain supplements and herbs can also affect the good bacteria.

Eating well is of course important. Although there is no diet which will cure SIBO, a low carbohydrate diet is usually best since bacteria feed off of carbohydrates. The Specific Carbohydrate Diet (SCD) is commonly recommended, although some people also can benefit from following the GAPs diet. Many will follow something called a low FODMAPs diet, especially if they also have irritable bowel syndrome, which is common in patients with SIBO. The acronym FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. I’ll be discuss this in greater detail in a future article.

Certain strains of probiotics can also be beneficial to take (or obtain through food). A small clinical trial involving Lactobacillus casei Shirota showed that 64% of subjects experienced a reversal in their positive early rise in breath hydrogen after lactulose test results (12) [10]. However, larger studies do need to be conducted to confirm these findings. If someone has a leaky gut as a result of SIBO then this of course needs to be addressed, and I have discussed this in past articles.

In SIBO it is common to have a deficiency of something called the migrating motor complex (MMC), which can also be the underlying cause of the condition. The MMC helps to clear bacteria from the small intestine. Taking prokinetics to help stimulate the MMC can help. D-Limonene is a natural prokinetic, and there is also a formulation commonly used by natural healthcare professionals called Iberogast that can be very effective.

So hopefully you have a better understanding of SIBO, including some of the causes, methods of testing, and treatment methods. There does seem to be a high correlation between overt hypothyroidism and SIBO, and because having a leaky gut is also common in people with SIBO, this in turn can make a person more susceptible to developing an autoimmune thyroid condition such as Graves’ Disease or Hashimoto’s Thyroiditis. Although antibiotics are the most common treatment used, one should also consider natural anti-microbials, probiotics, dietary changes, and if necessary, nutrients to help with gut repair. So far the best resource I’ve found on SIBO is the website www.siboinfo.com, and so for more information I would check this out.