One of the most common gut health issues I see in hypothyroid and Hashimoto’s patients in my clinic is Small Intestinal Bacterial Overgrowth or SIBO. And, scientific research has shown a strong correlation between the two. In this article, I’ll explain what SIBO is, how SIBO and hypothyroidism are related, and how to test for and treat it.

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What is SIBO

Small intestinal bacterial overgrowth occurs when the bacteria in our gut get out of balance and overgrow. I often say, “Too much of a good thing can be a bad thing.” How do we get too much of some bacteria over others? This can manifest in several different ways, and often occurs in those eating a diet high in sugar, alcohol, and refined carbohydrates. Certain strains of bacteria feed off of refined carbohydrates and break them down into short-chain fatty acids, creating gas and causing bloating.

Another strain of bacteria can break down bile salts before your body has a chance to use them. Bile salts are crucial for the breakdown of fats; without them, the end result is fat malabsorption or diarrhea.

Finally, a third type of bacteria can produce toxins that damage the lining of the small intestine. This prevents your body from absorbing the nutrients you need, much like what we see with a leaky gut.

10 Signs you have SIBO:

1. Gas
2. Bloating
3. Diarrhea
4. Abdominal pain or cramping
5. Constipation (much less common than diarrhea)
6. Diagnosis of irritable bowel syndrome or inflammatory bowel disease
7. Food intolerances such as gluten, casein, lactose, fructose and more
8. Chronic illnesses such as fibromyalgia, chronic fatigue syndrome, diabetes, neuromuscular disorders and autoimmune diseases.
9. B12 deficiency as well as other vitamins and minerals
10. Fat malabsorption

How Hypothyroidism Causes SIBO

Your thyroid regulates all of your metabolic processes. So if it is under-active, as is the case with hypothyroidism, all of these processes slow down, including digestion. That’s why hypothyroidism so often causes constipation. When you are constipated and food lingers in your intestines, it becomes a breeding ground for pathogenic bacteria.

Many hypothyroid patients also have a decreased level of HCL, the primary stomach acid. If you are low in HCL then you can’t properly digest your food, which allows bad bacteria to overgrow in your gut.

How SIBO Contributes to Hypothyroidism

Twenty percent of your T4 (the storage form of thyroid hormone) is converted to T3 (the active form) in your gut. However, if your gut flora is disrupted and it’s not functioning up to par, this conversion is reduced, leading to hypothyroidism symptoms.

The good bacteria in your gut are also critical in preventing leaky gut, or intestinal permeability. Leaky gut occurs when the tight junctions of your small intestine open up, allowing toxins, microbes, and partially undigested food particles to escape via your bloodstream. These particles are tagged as foreign invaders by your immune system, which sends a wave of inflammation to fight them off. Leaky gut is one of the primary triggers of autoimmunity, including the autoimmune form of hypothyroidism, Hashimoto’s. If your gut remains leaky, your immune system continues to attack your thyroid relentlessly, worsening thyroid dysfunction symptoms.

So Which Came First?

As you can see, thyroid function and your microbiome are an interconnected ecosystem of their own. It’s kind of a chicken or the egg situation, where hypothyroidism contributes to bacterial overgrowth, and bacterial growth worsens thyroid dysfunction. In some cases, hypothyroidism comes first, and in others, thyroid dysfunction leads to SIBO. Since they go hand-in-hand so frequently, I highly recommend testing for SIBO if you have symptoms of both SIBO and hypothyroidism.

How to Test for SIBO

If you suspect you have SIBO, I have a symptoms quiz in both of my books, The Thyroid Connection, and The Autoimmune Solution, to help you determine if you are likely positive. I also cover SIBO testing in this article.

How to Treat SIBO

In my clinic, I use functional medicine’s 4R Approach to healing the gut for my patients with SIBO. This includes following a diet low in carbohydrates and free of refined flours, sugars, and alcohol. To kill off the bad bacteria, I recommend using Microb-Clear™, which is a blend of magnesium caprylate, berberine, and extracts from tribulus, sweet wormwood, grapefruit, barberry, bearberry, and black walnut. In addition, I start my SIBO patients on a soil-based probiotic called Primal Earth™ to replenish the good bacteria in your gut.