How The Gut Is Connected to Other Systems
The digestive system is involved in so many other body systems such as the nervous system, hormones, immune system, and skin. It pretty much plays a role in everything else so it's important to make sure it's functioning well. When the the gut is working well, the rest of the body will too. There's a saying in naturopathic medicine that you always "heal the gut!" and it's often one of the best places to start when addressing any issue.
There's literally a nerve connection from our brain to our digestive system. This connection is through the vagus nerve that originates in our brain and runs the length of our head, neck and chest and into our abdomen. It also connects the brain with the heart, lungs, throat and face and is involved in sleep, mood, social connectedness and digestive function. When stimulated, the vagus nerve can calm us and reduce the effects of our stress response. An important neurotransmitter called serotonin is also produced in the gut and regulates bowel function and mood.
Optimal digestive function is important for so many aspects of our wellbeing especially estrogen and progesterone balance. The liver, gallbladder and intestines play an important role in managing the circulation and excretion of these hormones and if metabolism isn't working well you can experience PMS, irregular periods, acne, thyroid disease and autoimmune disease.
The microbiome is the collection of beneficial bacteria in our digestive systems that are involved in gut health, mood, weight management, nutrient production and immune health, but there's a part of the gut microbiome that is specific to estrogen metabolism called the estrobolome. The bacteria that make up the estrobolome can convert estrogen into an active hormone using an enzyme that makes it able to bind to estrogen receptors.
After estrogen is produced, it cycles through the digestive system. Some of it is eliminated in the stool after being attached to bile from the liver. However, if bacteria in the gut activate it with enzymes, it can be reabsorbed by the body and lead to excess estrogen circulation. This effect is more likely to happen if there is low bacterial diversity in the gut or dysbiosis.
You can't have good gut health without good thyroid health and vice versa. Because most of our immune system is in our digestive tract it also plays a role in the thyroid-gut connection. Thyroid and reproductive hormones are activated, regulated, eliminated, and metabolized through processes that occur in the gut. Autoimmunity, which can affect more than just the thyroid, can be initiated by poor digestive health and leaky gut.
Thyroid hormone activation - The thyroid secretes inactive thyroxine (T4) that needs to be converted into active triiodothyronine (T3). This conversion happens in the gut with the help of an enzyme made by our gut bacteria. This is yet another reason to have a healthy microbiome populated with beneficial bacteria!
Inflammation decreases thyroid hormones - The gut is home to about 70% of our immune system as part of the gut-associated lymphoid tissue or GALT. When there is inflammation from conditions like food allergies or Celiac disease this increases the stress hormone cortisol. Cortisol can weaken the gut wall leading to leaky gut and autoimmunity. It can also increase the amount of T3 that's bound to carrier proteins, making it unusable by the body. The T3 that is available is more likely to be pushed into inactive reverse T3. This is one way the adrenals are involved in thyroid health, making stress reduction an important factor in treating thyroid conditions, too.
Metabolism and elimination of hormones - Digestive function can affect the thyroid, but thyroid function can also influence gut function. In hypothyroidism, the whole digestive system slows down leading to constipation and bloating. One way the body gets rid of hormones is by attaching them to bile and excreting them through bowel movements. Low levels of T4, seen in hypothyroidism, may reduce bile flow. If hormones aren't being eliminated they can be reabsorbed and recirculate in the body. Constipation can increase the circulation of proteins that bind thyroid hormones, making them less available.
Absorption, conversion and production of thyroid hormones - The thyroid secretes T4 but most of our body's T3 is produced elsewhere in other organs such as the liver and intestinal tract. The liver is an important organ when it comes to regulating thyroid hormones. T4 is stored and converted to T3 here. Both T3 and T4 are absorbed well in the gut, but less so if there are digestive issues that interfere with absorption. If you're taking thyroid hormone supplementation you want to make sure that you have a healthy gut to improve absorption of your medication.
The autoimmune response - If you have an autoimmune disease like Hashimoto's thyroiditis, a healthy gut is a way to decrease the inflammatory response. In this situation, inflammation caused by chronic digestive diseases or food allergies lead to a breakdown of the cells that line the digestive tract. They are usually good at controlling what substances are allowed through, but in the case of leaky gut, toxins, bacteria, and undigested food are able to pass through into the rest of our body. The immune system mounts an attack to protect us, but that can also initiate body-wide inflammation and autoimmune disease. T4 from the thyroid can act like an anti-inflammatory in the gut by influencing the activity of a group of immune cells called T-cells. When there are low levels of T4, as seen in hypothyroidism, inflammation can remain elevated.
The gut is home to about 70% of our immune system as part of the gut-associated lymphoid tissue or GALT. The gut keeps our immune system under control and defends against harmful pathogens.
When we're young our immune system has to be trained to attack harmful microbes and leave our own cells alone. Helpful bacteria assist in this training and in controlling our immune T-cells that regulate inflammation levels. This is why when our microbial balance is thrown off, immune issues like autoimmunity, allergies and asthma tend to develop. The microbiome also helps to reduce circulation of older immune cells that tend to cause damage and inflammation.
Beneficial bacteria protect us by crowding out harmful microbes and making antimicrobial compounds. They also help to maintain the protective gut barrier so pathogens can't get through and into our bloodstream. A strong intestinal barrier is important because it prevents a leaky gut from letting proteins through, which can trigger immune reactions.
The brain is connected to the gut through the vagus nerve that originates in our brain and runs the length of our head, neck and chest and into our abdomen. It connects the brain with the heart, lungs, throat and face and is involved in sleep, mood, social connectedness and digestive function. The bacteria that make up the estrobolome can convert estrogen into an active hormone and after estrogen is produced, it cycles through the digestive system. Some of it is eliminated in the stool, however, if bacteria in the gut activate it with enzymes, it can be reabsorbed by the body and lead to excess estrogen circulation. Thyroid and reproductive hormones are activated, regulated, eliminated, and metabolized through processes that occur in the gut. The gut is home to about 70% of our immune system and is involved in defending against harmful pathogens, training the immune cells, and reducing circulation of older immune cells. A strong intestinal barrier is important because it prevents a leaky gut from letting proteins through, which can trigger autoimmune reactions.
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