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The Link Between SIBO and Your Thyroid

Learn how SIBO may affect your thyroid.
The Link Between SIBO and Your Thyroid
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The thyroid and the gut are intricately connected. Thus, when one system is not working correctly, the other will often suffer. This relationship is especially true for people with thyroid disorders, especially autoimmune Hashimoto’s thyroiditis, which is the leading cause of hypothyroidism in the United States. Because inflammation, bacterial imbalance, and thyroid dysfunction often go hand-in-hand, it is no surprise that small intestinal bacterial overgrowth – also known as SIBO – is common in people with thyroid disease. Ahead, let’s explore the link between SIBO and thyroid health.  

What is SIBO?

In SIBO, there is an abnormal increase in your overall gut bacteria in the small intestine. The small intestine is where digestive juices break down food and nutrients absorb into the bloodstream. The bacteria that cause SIBO are not commonly found in the digestive tract.

There are several risk factors for SIBO. SIBO can occur when a health condition or surgical procedure alters GI motility, causing the passage of food and waste products to slow in your digestive tract. Essentially, people develop SIBO because a slower digestive system is a breeding ground for bacteria to proliferate. When bacteria become overgrown, they can release toxins and affect your ability to absorb nutrients.

What are the symptoms of SIBO?

Bacterial imbalance in the small intestine can lead to the following common symptoms:

  • Loss of appetite
  • Nausea
  • Bloating
  • Abdominal pain
  • Diarrhea
  • Unintentional weight loss
  • Malnutrition
  • Feeling uncomfortably full after eating

You should see your doctor for a diagnosis and treatment if you have any of these gastrointestinal symptoms.

Does SIBO affect your thyroid health?

Gut health can affect the whole body, including the thyroid gland. When the gut microbiota is unbalanced, it can lead to systemic inflammation, which can exacerbate autoimmune diseases. Thus, SIBO can be especially harmful to people with Hashimoto’s and Graves’ disease.  

One study found that over 50% of people with hypothyroidism have SIBO. Several factors play a role, but one of the most likely causes is constipation, a common symptom in hypothyroidism. Because people with hypothyroidism often struggle with slowed gastric motility, digestive contents can stay in the GI tract for too long, making it easier for bacteria to become overgrown.

Intriguingly, some studies correlate SIBO with levothyroxine. However, it is hard to discern if the medication itself increases your risk or if it is the underlying hypothyroidism.

If SIBO goes untreated, it can cause several complications that are worsened by thyroid dysfunction. For example, SIBO in the presence of thyroid disease can lead to:

  • Vitamin deficiency, because your body cannot fully absorb fat-soluble vitamins
  • Poor absorption of fats, protein, and carbohydrates, which can cause diarrhea
  • Osteoporosis, which is worsened by thyroid disease, specifically hyperthyroidism
  • Inflammation of the gut mucosa, leading to autoimmune flares

How can you test for SIBO?

While most gastrointestinal infections are diagnosed with a stool test, SIBO testing involves either a breath test or a fluid culture from an endoscopy procedure.

Most people opt for the breath test because it is more convenient and less invasive. However, fluid aspiration during an endoscopy procedure remains the gold standard for a definitive diagnosis.

To conduct the breath test, you drink a mixture of glucose and water. Then, you blow into a device that detects gases emitted by bacteria in your small intestine. Fermentation in your small intestine makes these gases detectable via a breath test. If you have a rapid rise in exhaled hydrogen or methane, it can indicate you have bacterial overgrowth. 

Along with either form of SIBO testing, your doctor may also do a blood test to check your vitamin levels and a stool test to see if you have fat malabsorption or other intestinal infections.  

How is SIBO treated?

Treatment for bacterial overgrowth primarily focuses on correcting the underlying problem. For example, additional surgery may be necessary if a person has SIBO due to delayed gastric emptying after gastric surgery. Similarly, people with SIBO and hypothyroidism need to treat their underlying thyroid disease and implement a bowel regimen to keep their intestines moving.


Most people diagnosed with SIBO will take a course of antibiotics to reduce the overgrowth of bacteria. When taken in the short term, antibiotics can decrease the number of abnormal bacteria in the gut. However, antibiotics can also wipe out the healthy bacteria in your gut, causing some of the same symptoms as SIBO, including diarrhea and bloating.


Probiotic supplements – which feed the good bacteria in the gut – can be helpful in people with SIBO and bacterial overgrowth, especially if they are taking antibiotics for treatment.


Foods that have sugars in them can cause bacterial proliferation. Therefore, eliminating these foods from your diet can help reduce the presence and symptoms of abnormal bacteria. Diets that can help people manage SIBO include the low FODMAPS diet, the GAPS diet, and the elemental diet.


Taking nutritional supplements can help prevent vitamin deficiencies. For example, you may want to supplement with iron and calcium. Additionally, some people may need vitamin B12 injections, as people with SIBO often cannot absorb this nutrient.

A note from Paloma

If you have both SIBO and a thyroid condition, you should regularly test your thyroid levels. You can get your thyroid tested with the convenient Paloma Complete Thyroid Blood Test. The affordable Paloma at-home thyroid test kit measures Thyroid Stimulating Hormone (TSH), Free Thyroxine (Free T4), Free Triiodothyronine (Free T3), and Thyroid Peroxidase Antibodies (TPO), with an option to add on tests for Reverse T3 (RT3) and vitamin D. 

Treating hypothyroidism along with SIBO is not a one-size-fits-all process. During a virtual consultation with one of our trusted Paloma endocrinologists, you can work together to create a tailored treatment plan unique to your needs.

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Julia Walker, RN, BSN

Clinical Nurse

Julia Walker, RN, BSN, is a clinical nurse specializing in helping patients with thyroid disorders. She holds a Bachelor of Science in Nursing from Regis University in Denver and a Bachelor of Arts in the History of Medicine from the University of Colorado-Boulder. She believes managing chronic illnesses requires a balance of medical interventions and lifestyle adjustments. Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.

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