As I’ve covered many times throughout my posts and videos about the gut, there’s more to it than meets the eye. The gut has intricate ties to the rest of our body, and not just our digestive tract. Today we are going to cover one such tie that involves the thyroid. We’re going to further understand why a healthy gut means a healthy thyroid, and how the thyroid can throw even a healthy gut off center. Are you ready? Let’s get started!

An Introduction to the Thyroid

The thyroid is butterfly-shaped gland located right at the base of the neck; you could also say it rests right at the front of the throat. One of its most significant functions is controlling our metabolism. It’s also responsible for regulating our energy, weight, blood pressure, immune function, sleep, hormones, detoxification, and tissue development. Though the thyroid may be small, it’s pretty powerful all things considered! [1]
However, our thyroid is not immune to imbalances. It’s prone to becoming too slow during hypothyroidism, and too fast during hyperthyroidism. Common causes of thyroid imbalances include autoimmune disease (Hashimoto’s or Graves), goiter (an enlarged, cancerous enlargement of the thyroid), chronic crash dieting and caloric restriction, extreme weight loss or weight gain, intense prolonged periods of stress, inflammation, heavy metal toxicity (like mercury), poor immunity, a deficiency or overdose of the mineral iodine, and other nutritional deficiencies (Vitamin A, C, D, B1, B2, and B12, as well as iron, zinc, and magnesium). [2] [3]

The Gut-Thyroid Connection

As mentioned before, many times a thyroid imbalance can occur as a result of an autoimmune disease, like Hashimoto’s. What causes the autoimmune disease to happen in the first place comes from a combination of genetics and environmental triggers. The key entry point that the triggers use is our gut, which causes damage to its protective lining. And since most of our immune system is found in the gut, it only makes sense that the immune system would start attacking the thyroid as a result. Another link to a poorly functioning thyroid has to do with the bacteria in our gut. In the gut lies a protective lining that acts as a shield. It keeps bad things from entering the gut, as well as keeping potentially bad things from inside the gut from entering the bloodstream. One of those things is LPS or Lipopolysaccharide. [4]
LPS is a natural byproduct of our bacteria that normally stays inside the gut thanks to the protective lining. However, LPS can quickly become toxic to the body once it enters the bloodstream. And this usually happens when the lining becomes compromised. The “shield” starts to become permeable, or leaky, with holes that allow the LPS to exit out of the gut and into the bloodstream. Once they’ve entered the bloodstream, the body sees them as a threat and creates an immune response in an effort to get rid of them. [4] [5] [6]
In the process, cortisol, the stress hormone, starts going up, which can negatively affect the thyroid by lowering its function. Meanwhile, the thyroid is also helping the body to get rid of the LPS, and if there’s too much for it to handle, it can soon become overwhelmed. This could tip it into either extreme of hypo or hyperthyroidism, causing it to produce more or fewer hormones, which of course creates even more problems for our health. [4]

A damaged gut lining (or leaky gut) also influences thyroid disease, with more and more studies finding that people with autoimmune disease also tend to have imbalances with their gut bacteria. [5] Aside from the LPS issue, our bacteria also play a role in the conversion of thyroid hormones. [7]

Our thyroid releases two main types of hormones: T4, the inactive form of thyroid hormone, and T3, the active form that our body, along with our good bacteria, convert from T4. Whenever there is inflammation, stress, or an imbalance in good bacteria, this conversion process becomes impaired. Worse, it actually causes an opposite reaction: the production of reverse T3, which is an inactive form of T3. The tricky thing about reverse T3 is that although it looks like regular T3, it actually hinders thyroid function in excess. If a person were to get their thyroid hormones tested, they can come back with normal results if reversed T3 isn’t looked for. And those with high amounts of reverse T3 tend to suffer from symptoms of hypothyroidism!
Now let’s take things a step further- because the plot thickens! [8]

We have what’s known as the HPT axis in our hypothalamus (located at the base of our brain) that tells our pituitary gland to release TRH (thyroid releasing hormone) whenever T3 levels get too low. Normally, this is all fine and well, but if we’re already producing enough T3 in the gut and it’s becoming reverse T3, then having the pituitary sending more T3 down there is going to cause an overproduction of T3 and make things even worse! [8]
So, if leaky gut is the culprit, we’re overwhelming our body with inflammatory LPS while at the same time compromising our bacteria’s ability to properly convert T4 to active T3, resulting in too many problematic reverse T3s roaming about. [8]
The good news is that as long as our gut lining is strong, LPS stays where it’s supposed to be, and our thyroid can function normally. And part of that normal function involves producing the right type and number of hormones that help to regulate our metabolism and prevent our gut from becoming inflamed and leaky. The thyroid even helps with stomach acid production; if it’s imbalanced, heartburn and reflux are definite signs that something is off. It’s also involved in the production of the protective mucus in the gut that helps to keep it safe from damage. [8]
As you can see, both the thyroid and our hand go hand-in-hand in helping each other work to their best capacity. Thyroid disorders have been directly linked to gut issues, from intestinal permeability to heartburn, small intestinal bacterial overgrowth (SIBO), and other digestive-related conditions like Celiac Disease. [8]

Supporting the Connection

There are a number of ways in which the thyroid-gut connection can be maintained. These essentially boil down to lifestyle, and how you choose to nourish your body, which includes:

• Feeding the beneficial bacteria with fiber-rich foods
• Consuming probiotic-rich foods like sauerkraut and kefir (or taking a supplement)
• Managing stress
• Eating a whole-foods diet
• Limiting or restricting dairy and gluten (both of these foods have been linked to poor thyroid AND gut health, so if you’re noticing any adverse reactions from eating either of gluten or dairy, it may help to cut them out to see if your symptoms improve)
• Staying on top of lab tests if you suspect a potential thyroid or gut disorder (remember: test, don’t guess!)

So, there you have it- the gut thyroid connection. On one end, you have the gut keeping the thyroid from being overwhelmed by toxins like LPS, in addition to maintaining a healthy immune response. And on the other end, you have the thyroid helping the gut by regulating hormones, stomach acid and mucus production, which all protect the gut and keep it from leaking out the toxins that can inflict damage all over the body. It just goes to show that the gut is anything but a one-trick-pony, and that our hormones are equally as important!

Sources:

[1] https://www.endocrineweb.com/conditions/thyroid-nodules/thyroid-gland-controls-bodys-metabolism-how-it-works-symptoms-hyperthyroi
[2] https://www.healthline.com/health/common-thyroid-disorders
[3] https://www.holtorfmed.com/common-nutrient-deficiencies-in-thyroid-disease/
[4] https://www.nature.com/articles/s41598-017-06885-7
[5] https://www.sciencedirect.com/science/article/pii/S0005273606001970
[6] https://www.ncbi.nlm.nih.gov/pubmed/23965412
[7] https://www.todaysdietitian.com/newarchives/110211p36.shtml
[8] https://kresserinstitute.com/gut-microbes-thyroid-whats-connection/