• Allison Fahrenbach

The Connection Between Gut & Thyroid Health

In many ways the gut is the center of health. It is connected to many areas of the body, and the thyroid is no exception.

The health of the gut affects thyroid health, and vice versa.

The gut can have a major impact on thyroid regulation, and the thyroid influences the gut in significant ways, such as producing the necessary hormones that regulate metabolism and protect the gut from inflammation.


These days there’s a lot of talk about the thyroid, but what exactly is it?

What does it do, and why is it so important?

The thyroid is a butterfly-shaped gland about two inches long located in the front of the throat. It’s part of the body’s endocrine system (composed of glands that release hormones into the bloodstream to support the functioning of each cell). The thyroid’s primary role is to produce hormones that regulate the body’s metabolism – in other words, how your body uses energy.

Besides helping regulate metabolism, the thyroid plays an important role in immune function, detoxification,determining weight, determining sex hormones, blood pressure regulation, body temperature, breathing, cholesterol levels, heart rate, muscle strength, sleep patterns and tissue development.

It’s small, but powerful. So when it fails to function properly many systems are affected.


There are two ways the thyroid can malfunction: hypothyroidism and hyperthyroidism.

Hypothyroidism occurs when not enough thyroid hormone is produced. The most common cause is an autoimmune condition called Hashimotos thyroidits. Common symptoms include weight gain, hair loss, brain fog, dry skin, mood swings and fatigue.

Hyperthyroidism on the other hand occurs as a result of too much thyroid hormone. The most common cause of hyperthyroidism is Graves’ disease which is another autoimmune condition. Symptoms of Graves can include weight loss, anxiety, heart palpitations, tremors, insomnia, difficulty concentrating and bulging eyes.

Goiter is another common thyroid condition often caused by hyperthyroidism or a deficiency of iodine in the diet. It is a noncancerous inflammation of the thyroid gland. Symptoms include tightness or swelling in the neck, difficulty breathing or swallowing, wheezing, coughing and hoarseness.

The common theme with these thyroid imbalances is that they typically emerge as autoimmune issues. Autoimmune conditions usually result from a combination of genetic, and environmental factors. Those environmental triggers must find their way into the body and one key entry point is the gut.

Which is why issues with the gut have been linked to thyroid dysfunction.

One example is that thyroid autoimmune conditions occur at higher rates among those with celiac disease.

Another example of how the health of the gut plays a role in the health of the thyroid is the connection between leaky gut and thyroid function. If the gut is leaky it can allow toxins and dangerous pathogens to slip through. When this happens, the immune system goes into a hyperalert state as it tries to stabilize and detoxify.

If the gut continues to leak in this way, the body will go into a state of chronic inflammation.

This vicious cycle causes cortisol levels to rise, which in turn decreases thyroid hormone production.

Another connection is that people with autoimmune disease have been found to also have dysbiosis, or altered gut bacteria.


There are two main types of hormones released by the thyroid: triiodothyronine (T3) and thyroxine (T4).

T4 is the inactive form of the thyroid hormone; the body converts it into the active form, T3. The bacteria in your gut play a role in the conversion of T4 into T3.

Stress in the GI tract, such as inflammation from dysbiosis, and leaky gut can impair this conversion process, and result in the production of an inactive form of T3 called “reverse T3” (rT3).

This “looks” like T3 but doesn’t work the same, which is problematic because too much rT3 can suppress thyroid function.

And a person with this issue can actually have normal lab results unless the test specifically looks for rT3. People with high levels of rT3 often experience symptoms of hypothyroidism, and unfortunately it often goes unaddressed.


The thyroid is part of a feedback loop called the hypothalamic-pituitary- thyroid (HPT) axis. The hypothalamus monitors the levels of thyroid hormone produced and autoimmune conditions can result when there is a communication breakdown in this system.

For example, in Hashimotos the signal from the hypothalamus makes it to the thyroid but there isn’t enough thyroid to meet the demand.

In Graves’ disease, the immune system produces what’s called TSI (thyroid stimulating immunoglobulin. This attaches to thyroid cells, mimicking TSH from the pituitary in the brain and telling the thyroid to produce too much hormone.

The hypothalamus regulates the production of thyroid hormones, ensuring that the right amount is being produced. But inflammation can interfere with this, and inflammation can come from anywhere, including the gut.

For example LPS (lipopolysaccharide) is a toxin produced by gut bacteria. If the gut is inflamed (as in leaky gut) LPS can escape. It’s thought that this causes the thyroid to become overrun with toxins, which in turn, alters thyroid production.


The gut produces hormones to directly communicate with the thyroid through the vagus nerve. This communication is what’s referred to as the gut-thyroid axis. Through this conversation gut bacteria and their hormones can affect the thyroid and thyroid hormones can affect the gut.

If the gut is unhealthy and not properly communicating, it can weaken thyroid function.

On the flip side, the thyroid (when functioning properly) can help protect the gut. The lining of the gut contains endocrine cells to receive thyroid hormones, which in turn help the cells function properly. When these cells are healthy, they produce a mucus that protects the gut. In the stomach this mucus helps protect the gut from stomach acid. In the small intestine and the colon this mucus helps prevent a leaky gut by forming a barrier against gut bacteria.

In addition, the thyroid has the added indirect role in the maintenance of tight junctions in the intestinal lining. Tight junctions are important as they prevent unwanted substances from passing through. In the presence of an under active thyroid (hypothyroidism) these junctions can become less tight, leading to leaky gut.

Also worth mentioning is the role the thyroid plays in motility (the transit time of food through the gut). In the case of hypothyroidism motility is reduced, which can lead to constipation. Hyperthyroidism on the other hand can speed up motility and lead to diarrhea.

The bottom line in all of this is that the gut can affect the thyroid and the thyroid can affect the gut. When the health of one of these systems becomes impaired it can impact the health of the other.


Get consistent exercise.

Incorporating exercise into your routine is essential for thyroid health as it stimulates thyroid gland secretion. Studies have shown that patients experiencing a hypothyroid condition were able to improve thyroid function by engaging in low-impact movement.

Exercise also has been shown to improve the health of the gut. One of the leading ideas in the exercise-gut connection is that working out boosts the levels of gut microbes that produce butyrate—a short chain fatty acid that has a whole host of health benefits, from producing satiety hormones that curb hunger to playing a role in supporting the survival of existing neurons and promoting the growth of new ones.

TIP: Exercise doesn’t need to necessarily mean high intensity work that takes place in a gym. Incorporate movement that resonates most with your body. Restorative movement in particular, such as walking, swimming, yoga or biking have a very powerful impact on gut and thyroid health. For added benefit, get outside! Fresh air and sun have been shown to help improve mood and combat anxiety.


Managing stress levels is essential for proper thyroid health. When experiencing chronic stress, excess cortisol, a hormone produced by the adrenals can suppress thyroid function.

Stress also directly impacts gut health. In the short-term, stress can cause a number of digestive issues, including indigestion, cramping, acid reflux and heartburn. Stress also contributes to changes in the speed of digestion resulting in constipation or diarrhea. High levels of stress over time can increase intestinal permeability (leaky gut), which means that bacteria and undigested food can move more easily into the bloodstream, resulting in chronic inflammation

Tip: One of the greatest ways to reduce chronic stress is through deep belly breathing. Try sitting or lying down in a comfortable position and placing a hand over your belly. For 1 to 2 minutes, breathe naturally in and out through your nose. After a few minutes, without forcing it, see if you can gradually breathe more and more into your belly, watching as your hand rises and falls.

Prioritize sleep.

Getting adequate sleep each night can support thyroid function by giving the body time to fully rest and recover and therefore be more resilient to stress. A sleep restriction study showed that thyroid-stimulating hormone (TSH) levels rose in participants who were experiencing acute sleep loss.

Ideally, adults should be getting 7–9 hours of sleep each night.

Sleep quality has also been directly linked to gut health. Lack of sufficient sleep has been shown to decrease microbial diversity and a diverse microbiome is a healthy microbiome.

Tip: Carve out 10–15 minutes each night before bed to establish a pre bed routine. Choose something that helps your body and mind relax – such as yoga, meditation, journaling, or a warm bath. The body responds well to routine. Activities like this also help you wind down and will prepare your body and mind for sleep.

Reduce toxin exposure.

Reducing exposure to environmental toxins is a really important (yet often overlooked) step in cultivating and maintaining thyroid health.

The chemicals and toxins found in certain foods, cleaning supplies, chlorinated or unfiltered drinking water, plastics, and beauty products can impair thyroid function. It’s also important to avoid heavy metals (like mercury and lead) as well as pesticides and other industrial chemicals. These environmental toxins can have structures similar to those of iodine and selenium (chemicals used by the thyroid to make its hormones). When we are overexposed to these toxins, our body can mistake them for iodine and selenium, causing them to collect in the thyroid gland.

Reducing exposure to toxins will also help boost your gut health. Toxin exposure has been shown to suppress healthy microbial function, and pesticides, in particular can harm the good bacteria in your gut.

In one study, researchers spiked the diet of mice with the dioxin 2,3,7,8-tetrachlorodibenzofuran (TCDF), a common environmental contaminant, and examined the effects on gut microbiota. The results were that the TCDF altered the gut microbiota by shifting the ratio of dominant bacteria Firmicutes to Bacteroidetes, indicating that the total population of the gut microbiota was changed.

And these bacterial changes were correlated with increased bacterial fermentation, intestinal inflammation, impaired liver function, and metabolic changes that influence fat and glucose metabolism.

Tip: Hot saunas, steam baths, or even epsom salt soaks are great ways to flush toxins out of the system that could be exacerbating thyroid conditions. You can also incorporate more detoxifying foods into your diet, such as lemons, blueberries, medicinal mushrooms, garlic, or beetroots.

Simple adjustments like staying well hydrated with filtered water can help too. Filtered water helps eliminate heavy metals and groundwater containments and when you drink plenty of water it helps flush out toxins through urine and bowel movements.

Lastly, opting for organic produce can help reduce pesticide exposure and investing in a good glass or stainless steel water bottle will help!

Calm the vagus nerve.

The nerve supply of the thyroid gland is derived in part from the vagus nerve, so improving your vagal tone can directly support thyroid health. Studies show that vagus nerve stimulation can result in a significant increase in thyroid blood flow.

And the vagus nerve plays a pivotal role in gut health. The Gut-Brain Axis (GBA), also known as the Gut-Brain Connection, refers to the bidirectional communication between the central nervous system and the enteric nervous system. The enteric nervous system has been described as a second brain in the gastrointestinal tract, and the vagus nerve is the “superhighway” of this communication.

A healthy parasympathetic response, which is governed by the vagus nerve, is essential for gut and endocrine health. It allows you to repair, regenerate, digest and assimilate nutrients.

Tip: There are many ways to stimulate your vagus nerve, such as deep breathing, alternate nostril breathing, yoga, singing, humming, gargling, even washing your face with cold water!

As with everything, bio-individuality plays an important role in gut and thyroid health. It is essential to tune in to your unique needs when creating any action plan.



When it comes to thyroid health, moderation is often key in terms of carbohydrates as too much or too little can be problematic. Bio-individuality will determine your ideal macronutrient ratios, but regardless as to how much you eat, I don’t advocate eliminating carbs altogether. Especially if you have hypothyroidism.

T3 is very sensitive to calorie and carb intake. If calories or carbs drop too low, T3 levels drop and reverse T3 (rT3) levels increase. Some studies have shown that ketogenic diets can reduce T3 levels, as much as 47% in just two weeks of a sub 50g carb a day diet.

Carbs should predominantly be complex and come from whole foods. When eating for thyroid health, try to crowd out processed flours and sugar with vegetables, fruits, and whole food carb sources like potatoes, sweet potatoes, and squashes.


The thyroid is dependent on iodine and selenium. Deficiency in one or both can cause thyroid issues. While a doctor may recommend supplementation in the case of a deficiency, it’s generally preferable, and more nourishing and supportive to the thyroid, to eat a diet naturally rich in these minerals.

Iodine is found in sea vegetables (like kombu, dulse, nori, and wakame), eggs, and wild-caught seafood (especially cod, oysters, and shrimp).

Selenium can be obtained through something as simple as eating two Brazil nuts a day.

It can also be found in mushrooms, chia seeds, and grassfed red meat.


Vegetables are nourishing to the thyroid. Cruciferous vegetables – including bok choy, broccoli, brussels sprouts, cabbage, cauliflower, collard greens, and kale – are nutritional powerhouses. However, cruciferous veggies are also considered goitrogens, which are foods that can cause the thyroid to enlarge and sometimes malfunction when eaten in abundance.

Cooking or fermenting cruciferous vegetables can help minimize this effect, so those with thyroid issues will want to avoid raw cruciferous vegetables and opt for lightly cooked or fermented preparations, in moderation, instead.


Fermented foods support gut health, and gut health supports the thyroid. If you can tolerate fermented foods, try adding a tablespoon or two of sauerkraut or kimchi to meals each day. Kefir are is also loaded with healthy bacteria that support gut health.


It’s said that a diet rich in healthy fat is good for the thyroid. But diets very high in fat – e.g., the ketogenic diet – have been linked to thyroid dysfunction over time. So again, moderation - and type of fat-is key.

Consume a moderate amount of high-quality fats rich in omega-3 fatty acids from things like wild- caught fish, olives, olive oil, walnuts, and flaxseeds.


Gluten and dairy are very very inflammatory, and while I hate to restrict food groups, individuals with autoimmune conditions, such as Hashimoto’s thyroiditis, are advised to avoid gluten because it can initiate the production of thyroid antibodies.

These types of foods can also be thyroid disruptors. The molecular structure of the proteins found in both gluten and dairy resemble the thyroid. This is called molecular mimicry. If the immune system is reacting to either of these, it may also attack the thyroid.


What you eat from can be just as important as what you eat! Many everyday products contain chemicals that can get into the bloodstream and disrupt the thyroid. Glass rather than plastic food and drink containers is preferred. Groceries should be removed from plastic packaging before storage, and opt for food cans that have BPA-free linings whenever possible.


Heavy metals, like mercury, can contribute to the development of autoimmune conditions that affect thyroid health.

Mercury lurks in a lot of places, but one that’s easy to spot and control is seafood. Fish is very healthy, but certain species tend to be high in mercury.

Ahi and albacore tuna, king mackerel, swordfish, and Gulf tilefish are some of the top offenders.

The fish with the lowest mercury levels are are salmon, cod, tilapia, and catfish.

If you want help balancing gut and thyroid health, I'd love to help!

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