Gastrointestinal and thyroid activities are interrelated bodily functions. Their interactions are complex, and the medical community refers to them as the gut-thyroid axis. A damaged thyroid can cause various digestive concerns, and gut problems can trigger endocrine disorders.

This article explains how thyroid and gut health are connected, how to recognize the primary health concern, and recommends effective treatments.

Can the Thyroid Affect Gut Health?

The thyroid gland is a vital endocrine organ that regulates essential bodily functions, including metabolism, reproduction, growth, development, and the immune system. It also affects nutrient digestion and absorption via thyroid hormones thyroxine (T4) and triiodothyronine (T3), which regulate the conversion of food into energy and indirectly impact motility or how fast food moves through the GI tract.

An overactive thyroid gland (hyperthyroidism) produces too many thyroid hormones, increasing gut motility while an underactive thyroid gland (hypothyroidism) reduces motility. These changes disrupt gut microbiota composition, potentially leading to dysbiosis, increased intestinal permeability (leaky gut), and digestive problems.

How Do I Know My Gut Health Is Affected by My Thyroid?

Gastrointestinal conditions often coexist with a dysfunctional thyroid gland. The following symptoms may indicate your gut health is affected by a thyroid disorder.

Hyperthyroidism

An overactive thyroid can cause diarrhea, malabsorption, weight loss, bacterial infections, liver problems, anxiety, irritability, etc.  

Hypothyroidism

An underactive thyroid can lead to delayed gastric emptying, constipation, poor nutrient absorption, lactose intolerance, small intestine bacterial overgrowth (SIBO), low stomach acid, etc. Hypothyroid patients can also experience dry mouth, difficulty swallowing, and heartburn.

Autoimmune Diseases

Autoimmune diseases associated with thyroid dysfunction, such as Hashimoto’s and Graves’, often occur with celiac disease and non-celiac wheat sensitivity. They increase the risk of gut inflammation and leaky gut syndrome.

How Do I Know If My Thyroid Is Affected by the Gut?

Our gut health and the balance of intestinal flora directly impact thyroid function. Hypothyroidism, hyperthyroidism, and autoimmune diseases can stem from the following gastrointestinal problems.

Leaky Gut

Increased intestinal permeability allows undigested food, toxins, pathogens, and other harmful substances to enter the bloodstream, trigger inflammation, activate the immune system, and disrupt thyroid hormones.

Note: Learn more about leaky gut and how to treat it.

Poor Nutrient Absorption

Poor nutrient absorption, especially that of minerals essential for thyroid function (selenium, zinc, iron, and iodine), can disrupt thyroid metabolism and the secretion of thyroid hormones.

Gut Dysbiosis

The gut microbiome impacts thyroid health in several ways:

• It helps break down dietary fibers and create short-chain fatty acids, which aid in immune regulation.
• It impacts the activity of specific enzymes in the intestinal wall that help convert thyroid hormones T4 into their active form, T3.
• It regulates dopamine levels, which can modulate the levels of the thyroid hormone TSH.

Disturbing gut microbiota homeostasis can lead to chronic inflammation, impaired nutrient absorption, altered thyroid hormone levels, and autoimmune diseases (Hashimoto’s and Graves’).

Who Is Most Likely to Have Thyroid-Gut Health Issues?

Millions of people suffer from conditions related to thyroid and gut health. The underlying causes include genetic predisposition, impaired immune system, environmental factors, and lifestyle habits. Anyone can develop associated health problems, but some factors increase the risk of specific diseases.

• Gut dysbiosis, leaky gut syndrome, and celiac disease increase the risk of Hashimoto’s thyroiditis and Graves’ disease.
• Small intestinal bacterial overgrowth, irritable bowel syndrome, leaky gut, and bacterial infections (e.g., H. pylori) increase the risk of hypothyroidism and autoimmune reactions.
• Nutrient deficiencies and malabsorption increase the risk of impaired thyroid function.
• Chronic stress and stress-induced gut dysbiosis can suppress thyroid function.
• Antibiotics, birth control pills, and other medications can disrupt gut flora, digestion, and nutrient absorption, and lead to thyroid dysfunction.
• Women are more likely than men to experience impaired gut health and thyroid imbalances.

How Are Thyroid-Gut Issues Diagnosed?

Patients with thyroid and gut problems may have symptoms that overlap with those of other conditions. When examining a patient, doctors rely on tests for thyroid and gut-related disorders. Proper treatment depends on accurate and timely diagnosis.

Thyroid Tests

Thyroid tests establish how well the thyroid gland is functioning. The standard thyroid blood test measures the levels of TSH, T4, and sometimes T3. Doctors can also order antibody tests (Anti-TPO, Anti-Tg) to detect autoimmune diseases, and a thyroid scan to look for abnormal growth.

Tests for Gut Health

If a doctor suspects your digestive concerns are related to thyroid issues, they may order stool, blood, urine, and breath tests to detect inflammation, maldigestion, malabsorption, food intolerance, bacterial overgrowth (SIBO), H. pylori infection, and other issues that could be linked to thyroid health.

Note: Read our article on gut dysbiosis and a detailed list of tests for this condition.

How Do You Fix Thyroid-Gut Health?

Treatments for patients suffering from coexisting thyroid and gut problems vary depending on the specific diagnosis. They can include the following:

Dietary Changes

Patients with thyroid and gut problems often experience symptom relief after modifying their diet according to medical advice. Medical providers prescribe custom nutritional plans depending on their patients’ symptoms and diagnoses. These diets are based on anti-inflammatory foods and often involve eliminating triggers that cause unwanted symptoms (e.g., gluten in patients with celiac and autoimmune diseases).

Patients with digestive problems are advised to limit or eliminate foods that increase inflammation and disrupt thyroid hormones, such as:

• Refined sugars and carbs
• Processed foods
• Artificial sweeteners and additives
• Foods with high pesticide residues

Nutrient-dense foods high in vitamins, minerals (especially selenium, iron, and zinc), antioxidants, dietary fibers, and healthy fats typically make up the core of thyroid/gut patients’ diets. The foods include:

• Fresh fruits and vegetables
• Whole grains
• Walnuts, Brazil nuts, almonds
• Flax and chia seeds
• Eggs and grass-fed meat
• Fermented foods (yogurt, kefir, sauerkraut, pickles, kimchi, etc.)

Probiotics and Prebiotics

Probiotics are live microorganisms that enhance microbial diversity in the gut, helping to increase micronutrient absorption and regulate the synthesis of the hormone T3. Adding probiotics to a healthy, nutritionally rich diet can contribute to healthy thyroid function. Probiotics are present in fermented foods like yogurt, pickles, and sauerkraut, and dietary supplements. Some of the best probiotic strains for gut inflammation, immune support, and hormone regulation include Lactobacillus plantarum, Bifidobacterium bifidum, and Saccharomyces boulardii.

Prebiotics are foods and supplements that probiotics feed on. Foods rich in prebiotics include onions, garlic, oats, bananas, flax seeds, apples, berries, legumes, almonds, and more.

Medications and Supplements

Some patients with thyroid and gut health problems require medication in addition to a specific diet and supplements. Doctors typically prescribe hormone replacement tablets (e.g., levothyroxine) for hypothyroidism and Hashimoto’s. Medications like propylthiouracil and methimazole are indicated for an overactive thyroid gland and Graves’ disease. Permanent treatments for hyperthyroidism include radioiodine therapy and surgical removal of the thyroid gland.

Since many thyroid patients have nutrient deficiencies, doctors often prescribe vitamin and mineral supplements, including vitamins A, B, D, selenium, zinc, and iron. Patients with low stomach acid can benefit from betaine hydrochloride, which helps increase stomach acid and improve digestion and nutrient absorption.

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Lifestyle Changes

Poor lifestyle choices are often the leading cause of digestive and hormonal health issues. Besides adopting a healthier diet, medical professionals advise making the following lifestyle changes to improve health.

• Engage in stress-relieving activities to reduce chronically elevated cortisol, which contributes to inflammation, gut dysbiosis, and hormonal imbalance.
• Introduce daily exercise to restore energy, improve blood flow, aid in digestion, and stabilize hormones.
• Get 7-9 hours of sleep every night to balance hormones and reduce stress.
• Eliminate alcohol and cigarettes, as they increase inflammation, promote dysbiosis, and disrupt thyroid function.

What Happens if You Don’t Treat Thyroid-Gut Health Issues?

Symptoms of impaired thyroid and gut functions may not be noticeable at first. However, they tend to worsen over time. If left untreated, they may become uncomfortable and interfere with daily life. They may also lead to more severe and life-threatening diseases, including obesity and heart disease.

Conclusion

Thyroid and gut health are closely related. An impairment to one organ often causes damage to the other organ. Treatment strategies focus on reducing inflammation, promoting a healthy gut microbiome, and optimizing thyroid hormone levels to restore a functional gut-thyroid axis.