Gut-Thyroid Connection: Is Your Gut Causing Your Thyroid Symptoms?

If you’ve been diagnosed with a thyroid condition like Hashimoto’s, you’ve probably been told your symptoms, such as fatigue, brain fog, and low mood, are due to your thyroid’s poor function.

But what if they’re not?

Many patients continue to struggle with these symptoms even when their thyroid labs are “normal” on medication. In these cases, the real issue may not be the thyroid at all. It may be the gut.

Emerging research shows a strong gut-thyroid connection, with gut imbalances playing a key role in symptoms often blamed on the thyroid. In fact, addressing gut health can improve symptoms, reduce inflammation, and support better thyroid function.

How are Gut and Thyroid Conditions Linked?

Even if you don’t have obvious gut symptoms, it’s important to know that gut conditions and thyroid conditions are very often found in the same patients. This is called the “gut-thyroid axis” 1. 

The gut and thyroid are closely connected. The gut plays a key role in immune function, nutrient absorption, and hormone regulation, all of which directly impact thyroid health. This is especially relevant for autoimmune conditions like Hashimoto’s thyroiditis and Graves’ disease, which account for the majority of thyroid disorders. Because a large portion of the immune system is located in the gut, imbalances in gut health can trigger immune dysfunction, increasing the risk of the body attacking thyroid tissue 1.

The gut also directly affects how well the thyroid functions. It is responsible for absorbing essential nutrients like iodine, selenium, iron, and zinc, which are needed to produce and regulate thyroid hormones. In addition, gut bacteria help convert inactive thyroid hormone (T4) into its active form (T3) 2. When gut function is compromised, which can be due to inflammation, infections, or issues like leaky gut, these processes can be disrupted. This can lead to poor nutrient absorption, impaired hormone conversion, and increased inflammation, all of which may contribute to thyroid dysfunction.

Here are some examples of the gut-thyroid connection from the research:

Celiac Disease and Non-Celiac Gluten Sensitivity

• Multiple studies have found that autoimmune thyroid disease is more common in patients with celiac disease 3 4 and non-celiac gluten sensitivity 5 6

Leaky Gut

• Children with Hashimoto’s disease were found to have more markers of leaky gut when compared to controls 7 

Low Stomach Acid

• Up to 40% of Hashimoto’s patients were found to have atrophic gastritis, which may cause low stomach acid 8 
• Thyroid patients with low stomach acid require higher doses of Levothyroxine (Synthroid) 9 10

Small Intestinal Bacterial Overgrowth (SIBO)

• SIBO patients were more likely to have impaired thyroid function than healthy controls 11
• In a study of SIBO patients, the two most common co-existing health conditions were hypothyroidism and taking thyroid hormone medication 12

H. pylori Infection

• Thyroid peroxidase antibodies (TPO) were found more often in patients with H. pylori infection than in patients without H.pylori infection 13
• People with Graves’ disease were over four times more likely to have H. pylori infection than those with normal thyroid function 14

While these studies only show association and not cause, collectively, they suggest an overall pattern of gut disturbances in thyroid patients.

These “Thyroid” Symptoms May Actually Be Gut-Related

Symptoms like fatigue, brain fog, depression, anxiety, and headaches aren’t unique to hypothyroidism. In fact, they are also symptoms of gut health conditions. 

Fatigue

• A meta-analysis of 17 studies found that more than 50% of irritable bowel syndrome (IBS) patients have symptoms of fatigue 15
• 68% of patients with suspected non-celiac gluten sensitivity reported tiredness and lack of well-being 5 
• Treating leaky gut reduces fatigue and other symptoms in patients with chronic fatigue syndrome 16

Brain Fog

• Subjects with brain fog are more likely to have SIBO when compared to those without brain fog 17
• 38% of patients with suspected non-celiac gluten sensitivity reported brain fog 5 
• Patients with Crohn’s disease frequently complain of cognitive difficulties 18

Depression and Anxiety 

• A systematic review involving 22,842 subjects found IBS patients were three times as likely as healthy subjects to have either anxiety or depression 19
• 39% of patients with suspected non-celiac gluten sensitivity reported anxiety 5 

Headache

• Migraine patients are more likely to have IBS 20
• 54% of patients with suspected non-celiac gluten sensitivity reported headaches 5 

This overlap between gut symptoms and thyroid symptoms leads to a common problem for thyroid patients. Once you get a thyroid diagnosis, healthcare practitioners tend to focus exclusively on thyroid treatments and stop considering other options. The result is that you end up chasing various thyroid solutions, without ever resolving your symptoms.

Thyroid medication can be very helpful for improving your thyroid hormone levels, however, it doesn’t always lead to symptom resolution. As we see regularly in the clinic, healing your gut issues is the missing piece for many thyroid patients.

Research supports using a gut-focused approach to treating thyroid patients. Let’s take a closer look.

Can Gut Issues Cause Thyroid Symptoms?

Misdiagnosis of thyroid conditions is more common than many people realize. In some cases, a thyroid diagnosis can become a distraction, which leads patients to focus on hormone levels while the underlying issue remains unaddressed. Research suggests that conditions like hypothyroidism may be overdiagnosed, with some patients taking thyroid medication unnecessarily 21 22.

At the same time, gut conditions are both highly prevalent and frequently underdiagnosed. An estimated 10–15% of people in the U.S. have IBS, yet up to half of these cases go undiagnosed 23. More broadly, nearly 40% of adults worldwide may have a functional gastrointestinal disorder 24. This makes gut dysfunction far more common than hypothyroidism, which affects about 4.6% of the population 21. In other words, for many people experiencing fatigue, brain fog, or mood changes, the gut may be a more likely root cause than the thyroid itself.

This perspective is further supported by research showing that treating gut conditions can significantly improve thyroid markers and symptoms. 

For example, addressing H. pylori infections has been shown to 9 10 25 26:

• Reduce thyroid antibodies 
• Improve TSH levels

Similarly, treating gut pathogens like Blastocystis hominis has been associated with reductions in 27:

• Inflammation
• Thyroid antibodies
• Thyroid-stimulating hormone (TSH)

Dietary interventions also play a role, with lactose restriction being shown to lower TSH in lactose-intolerant patients, whereas a gluten-free diet may improve medication effectiveness in those with celiac-related conditions 28.

Beyond lab markers, gut-focused interventions have also been shown to improve symptoms commonly attributed to thyroid dysfunction, including fatigue, mood disturbances, and anxiety 16 29 30 31. Taken together, this evidence suggests that for many individuals, supporting gut health may be a key step in improving both thyroid function and overall well-being.

How to Improve Gut Health for Thyroid Symptoms

If you are taking thyroid medication and still have thyroid-like symptoms, improving your gut health may make a meaningful difference. This also applies if you have thyroid-like symptoms but test negative for a thyroid condition.

Step 1: Start with Diet

The foundation is a whole foods, anti-inflammatory diet. A structured approach can help you identify what works best for your body:

• Try first: For many people, a Paleo-style diet is a good starting point. It removes common inflammatory triggers while still allowing for a wide variety of satisfying, nutrient-dense foods.
• Next step: If your symptoms are more persistent or you need more structure, a more targeted approach can help. Elimination-style diets temporarily remove common trigger foods, then systematically reintroduce them to identify what your body tolerates best.

There isn’t one “perfect” gut diet. Options like Paleo, low FODMAP, or other elimination frameworks can all be effective depending on your symptoms and sensitivities.

If you’re unsure where to start, we walk through how to choose the right approach and reintroduce foods in our elimination diet guide.

Step 2: Add Probiotic Support

Alongside diet, probiotics can help rebalance the gut.

In the clinic, we use a multi-strain, multi-category approach rather than relying on a single strain. We call this the Triple Therapy Probiotic approach. This includes:

• Lactobacillus and Bifidobacterium species
• Saccharomyces boulardii (a beneficial yeast)
• Soil-based probiotics (Bacillus species)

Research suggests that multi-strain probiotics may be more effective than single strains, particularly for digestive conditions 32 33 34.  Clinically, we’ve also seen that combining categories tends to produce more consistent results than trying individual products one at a time.

We recommend trying probiotics for at least two months to see benefits. However, if you have a poor reaction, stop using it immediately. That particular probiotic may not be the right fit. 

Even modest improvements in energy, digestion, or brain fog are a good sign that your gut is playing a role. If you’re improving, continue with the same approach.

Step 3: Go Deeper If Needed

For some patients, diet and probiotics are enough to resolve symptoms. Others may need more targeted support, such as:

• HCL supplementation
• Digestive enzymes
• Nutrients to heal the intestinal lining 
• Supplements like vitamin D and selenium 
• Diagnosis and treatment for gut infections such as SIBO, H. pylori, and Blastocystis hominis. 

As gut health improves, some patients absorb thyroid medication more efficiently 26 28 35 36. This can influence dosing, so it’s worth monitoring labs and symptoms with your healthcare provider. In many cases, optimizing gut health reduces the need to pursue more complex thyroid medication strategies.

Real Cases: When Gut Treatment Resolved “Thyroid” Symptoms

My clinical experience parallels the research results I have shared in this article. Here are a couple of patient stories that show how treating the gut can resolve stubborn thyroid symptoms.

Amy’s Story

Amy was diagnosed with a thyroid condition and spent over a year trying to fix her symptoms with thyroid treatment alone without success. Despite normal lab results, she continued to struggle with fatigue and other “thyroid” symptoms. After shifting focus to her gut health, her symptoms resolved, revealing that her condition had been misdiagnosed and driven by underlying gut issues rather than her thyroid.

Paige’s Story

Paige, a firefighter, was diagnosed with hypothyroidism and Hashimoto’s after developing fatigue and brain fog, but thyroid medication didn’t improve her symptoms. Even with a healthy diet, she continued to feel unwell. After addressing underlying gut issues with targeted diet and probiotics, her energy, mental clarity, and overall health returned, highlighting that her persistent symptoms were largely driven by gut dysfunction rather than her thyroid alone.

Amy and Paige’s stories show that persistent “thyroid” symptoms aren’t always about the thyroid and that addressing gut health can be the key to real recovery.

Gut-Thyroid FAQs

If my thyroid labs are normal, why do I still feel off?

Normal labs don’t always reflect how you feel. In some cases, standard testing may miss important markers or fail to give the full picture of thyroid function. If you’re unsure whether your testing was thorough, it can help to review what a complete thyroid panel includes and how to interpret it.

At the same time, persistent symptoms may be related to gut imbalances, inflammation, or poor nutrient absorption rather than thyroid hormone levels alone.

Should I stop my thyroid medication and focus on my gut instead?

No. Thyroid medication should only be adjusted with your healthcare provider. Supporting your gut can be done alongside medication and may help improve how well your body responds to treatment.

If you’re thinking about reducing or coming off thyroid medication, it’s important to do this safely and with a clear plan. We walk through when this may be appropriate and how to approach it in our guide on how to get off thyroid medication.

Do I need testing for SIBO or other gut issues?

Not always at the beginning. Many people can start with a foundational diet and probiotic support. If progress stalls, testing for infections like SIBO or H. pylori may be helpful.

Can improving gut health affect my thyroid medication needs?

It may. As gut function improves, some patients absorb medication more efficiently. This can sometimes change dosage needs, which should be monitored with your provider.

What if diet and probiotics don’t fully resolve my symptoms?

That’s where more targeted support comes in. This may include:

• Digestive support (HCl, enzymes)
• Gut-repair nutrients
• Treatment for infections
• Personalized guidance based on your case 

Resolve Your Gut-Thyroid Symptoms

Many thyroid patients suffer needlessly with unresolved symptoms, spending energy and money chasing thyroid treatments that don’t work. If you are struggling with stubborn “thyroid” symptoms, a change in focus can help.

Thyroid treatments will never fully work when the root cause of your symptoms is a gut imbalance. Simple interventions to improve gut health can lead to quick and effective symptom relief for thyroid patients. Start with simple, effective steps: an anti-inflammatory diet, targeted probiotics, and further support if needed. For many, this shift in focus is what finally leads to lasting relief.

By addressing underlying gut imbalances, many patients experience meaningful improvements in symptoms, inflammation, and overall well-being, and in some cases, even require less medication. Rather than continuing to chase thyroid solutions alone, a gut-focused approach can help you get closer to the root cause.

If you are looking for ways to help ease your gut-thyroid connection symptoms, you can find protocols and guidance in Healthy Gut, Healthy You, or schedule a consultation with our team at the Ruscio Institute for more personalized support.

Dr. Michael Ruscio is a DC, natural health provider, researcher, and clinician. He serves as an Adjunct Professor at the University of Bridgeport and has published numerous papers in scientific journals as well as the book Healthy Gut, Healthy You. He also founded the Ruscio Institute of Functional Health, where he helps patients with a wide range of GI conditions and serves as the Head of Research.