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Especially for any hypothyroid folks on here: Are Your Digestive Issues Related To Your Thyroid? — SIBO and Hypothyroidism


Are Your Digestive Issues Related To Your Thyroid? — SIBO and Hypothyroidism

It’s no coincidence so many individuals with hypothyroidism also have digestive disorders. While treatment typically focuses on hormone therapy, the close link between the thyroid and digestive tract often doesn’t get the attention it deserves.

The digestive tract’s connection to the thyroid is so significant that many experts consider digestive issues as a red flag for thyroid dysfunction, and vice versa. The condition known as SIBO (pronounced SEE-bow) exemplifies how poor gut health can be an obstacle to recovery. Though often overlooked, it’s estimated more than half of those with hypothyroid have SIBO to some degree!

Fortunately, new technologies and recognition of SIBO have led to improvements in understanding, diagnosis, and treatment. There are also many things you can do on your own.

SIBO: an acronym for small intestinal bacteria overgrowth and defined as the presence of excessive bacteria in the small intestine.

The gut microbiome is one of the fastest growing areas of research today and its significance cannot be overstated. The GI tract which extends from the mouth to the anus, houses ten times the number of bacterial cells than exist in the human body. Ideally, the majority of bacteria live in the large intestine, but with SIBO some colonies are displaced in the small intestine or the stomach where they don’t belong. When an imbalance in microbes occurs, a range of issues can ensue.

Sectors of the population most susceptible to SIBO can be identified by the risk factors below.

Risk factors for SIBO:

Abnormalities in the GI tract such as from disease or surgery.




Food poisoning

Heartburn medications



Leaky gut

Metabolic disorders, i.e. diabetes.

A combination of diagnostic testing along with symptom recognition is considered the best way for identifying whether SIBO exists. Upon review of the symptoms below, one can see they may or may not be attributed to SIBO. It is important to keep the big picture in mind.

Symptoms of SIBO:



Constipation or diarrhea


Abdominal pain



In order to interpret symptoms for what they are, it’s important to think in terms of bacteria.

There are trillions of bacteria in the digestive tract and their overgrowth can lead to disturbances ranging from mild to severe, i.e. IBS. Consequences of imbalanced microbia go beyond digestion extending to immune function, digestion, skin, metabolism, cardiovascular system, as well as the brain. SIBO is also known to cause menstrual disturbances in women.

Why Hypothyroid Patients Are Susceptible

Individuals with hypothyroidism are susceptible to SIBO because of the impact low thyroid hormone levels have on digestion. For instance, two processes that predispose a person to SIBO are also common characteristics of hypothyroid patients, i.e. reduced motility and low stomach acid. Note that SIBO can also be the cause of these issues. It’s a two way street.


Low levels of thyroid hormone, which are the basis of hypothyroidism, prominently cause a reduced rate of digestion. Ultimately, food moves through the digestive tract too slowly causing bacteria to grow in types and quantities where they don’t belong, i.e. in the small intestine. Constipation is one of the many digestive discomforts that can occur as a result, further perpetuating bacterial overgrowth.

Stomach acid

In hypothyroidism production of stomach acid is often reduced, fostering an environment conducive to digestive disorders, i.e. GERD and gastritis. Proper acidity is necessary for signaling the body to pass food from the stomach to the small intestine. Stomach acid also protects against bacterial overgrowth and facilitates nutrient absorption.

Heartburn medications are commonly prescribed to hypothyroid patients due to the discomforts of having low stomach acid (though it feels like there is too much). However, long-term use of the medications (PPI’s) adds to the problem by further reducing stomach acid.

SIBO Leads to Nutrient Deficiencies

Considering SIBO and the effects of hypothyroidism just described, it is no surprise nutrient deficiencies are common.

Nutrient absorption is dependent on a properly functioning digestive tract. As a result of factors such as low stomach acid and bacterial overgrowth, imbalances in the small intestine can damage the intestinal lining where nutrients are absorbed.

Deficiencies may also occur as a consequence of bacteria feeding on nutrients meant for absorption. Common depletions include:

Vitamin B12 and iron (are the most common)



Fat soluble vitamins A, D, E, and K

Ironically, several depleted nutrients are ones needed to support healthy thyroid function, i.e. zinc, tyrosine, selenium, vitamins A and D. The fact that approximately 20% of the thyroid hormone relies on healthy gut flora for production further adds to the equation.

It quickly becomes clear how gut health affects the thyroid, just as the reverse is true. For this reason, digestive issues such as GERD can be a red flag for thyroid disorders.

How Is SIBO Diagnosed?

SIBO is a complex disorder to diagnose as it shares symptoms with other digestive disorders and test methods are controversial. However, with such strong evidence of SIBO’s association with hypothyroidism, it is recommended that those who also suffer chronic digestive issues be evaluated. On the flip side, it would be prudent for those with chronic digestive issues to be evaluated for thyroid disease.

Generally speaking, SIBO is underdiagnosed. There is also controversy as to the best test method. Currently, hydrogen breath tests are considered the best tests available. Breath tests are easy, patient friendly, non-invasive tests. The basis of hydrogen breath tests is that they measure the type of gas the bacteria produce, methane or hydrogen. Keeping mind the tests aren’t full proof, it is always important to consider symptoms along with the test results.

How To Eliminate SIBO

Eliminating SIBO takes some time and effort, but it can be done. The following is a general guide:

Eliminate or modify the underlying cause.

Induce remission via antibiotics (i.e. Rifaximin*), Elemental Diet, or combination.

Promotility or prokinetic supplements (to keep things moving)

Dietary modifications, i.e. low FODMAP, Fast Tract or SCD diets

Compensate for nutrient deficiencies via supplementation.

Eat smaller meals.

Probiotics (supplements, fermented foods)

*Research shows that Rifaximin coupled with fiber, and quality probiotics have a better outcome than Rifaximin alone. Note that one does NOT want to overkill bacteria, but rather eradicate some and then focus on rebalancing.

All in all this is a general overview. Implementing an individual treatment plan is best done with guidance from a knowledgeable and qualified health practitioner.


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