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  • Writer's pictureNicola Hodges Nutrition

Your thyroid and your gut, What you need to know.

Updated: Aug 20, 2021


Firstly- any concerns with bowel habit or symptoms needs to be investigated by your doctor first and foremost. Nutritional therapy is not a substitute for medical advice.




Okay, so this is long one, however, the gut is fascinating- so make a cuppa and settle in. You may not see your guts in the same light afterwards.


There is a link between your thyroid health and your gut health. We call it the 'The gut thyroid axis'.


Let's start right at the beginning to get a full picture. Living in your gut is a wealth of bacteria, we evolved this way and live in a symbiotic relationship with these little critters. In fact, there are more bacteria in our guts than there are cells in our bodies- trillions upon trillions of them and they add up to about 2kg in weight! Gross! I hear you whisper.....


Why do we have a symbiotic relationship with these bacteria that have set up home in our guts? We call the mix of these bacteria the gut 'microbiome'. When the gut microbiome is in balance it manufctures vitamins that promote our health such as B vitamins and vitamin K. The microbiome also contributes to making feel-good neurotransmitters, such as serotonin, dopamine and more! Studies show that Bifidobacterium supports the production of GABA (the brain calming neurotransmitter) and Lactobacillus supports serotonin production- pretty amazing!


A healthy gut works with our immune system from birth to educate and support its maturation in order to avoid allergies and becoming oversensitive to the wrong things. It has to learn what to tolerate and when to fire up- think about all of the things from the outside world we eat or put in our mouths from childhood and throughout life! We want our immune system to only react to things that could endanger our health and not get activated over the everyday foods we eat. About 80% of our immune system is in our gut!


When we're born our gut is not totally sterile as first thought, scientists have found that the placenta even has a microbiome! Natural vaginal births and breastfeeding are a natural and fast way to introduce friendly bacteria into the system from day one. A baby will spend the first two years of life building their gut microbiome diversity, the species or 'families' of bacteria are set and done by 2/3 years of age- but that's by far not the full picture! There are two categories of gut bacteria diversity, alpha diversity and beta diversity. Think of alpha diversity as a colony of different families or species- they're the ones that set up shop and colonise the gut by age of 2/3.


The beta microbial diversity lives a fast-paced life which changes daily, a good way to view them is as the children and cousins of the alpha diversity family/species of bacteria. In reality, they're the different strains or subtypes of the main bacterial species. The beta diversity is the aspect that we can influence with good nutrition and lifestyle. Lots of things can positively affect the beta bacteria. Things such as gardening and being in close contact with the microbes in the soil, living with pets, children playing in the mud and even exercise has a positive influence! Equally, stress, trauma and fear can negatively affect the good bacteria in our guts- potentially allowing an imbalance to take hold.


I like to think of the microbiome as a well-populated garden full of nature's diverse plant flora. Imagine a flourishing garden that is full of a huge variety of flowers and plants that all work together to help each other stay healthy and help each other grow- effectively it's an ecosystem!


When our guts become out of balance due to a standard western diet of high carbohydrates, sugar, processed foods, alcohol, stress and poor nutrient density the effect can spread far and wide outside of our gut. Diseases such as cardiovascular disease, obesity, type two diabetes, infertility, autoimmune diseases including thyroid autoimmune diseases, anxiety, depression and fatty liver to name a few- all of these can be linked to our microbiome in some cases! Gut dysbiosis (that means unbalanced gut bacteria) may be a driver behind the symptoms of IBS, both the constipation type and the diarrhoea type- sometimes people suffer both interchangeably. P.s (There can be a myriad of other reasons for gut symptoms- some serious, don't self diagnose, always talk to your doctor first before seeking to implement complementary therapies).


So what does this have to do with thyroid problems? Well, sadly autoimmune thyroid diseases such as Hashimoto's and Graves disease often coexist with intestinal issues ranging from IBS to Coeliac disease.


The lining of the gut should be made up of tight junctions that only allow the right amount of nutrients from digested food through in order to nourish us. A healthy microbiome (ecosystem) is needed to maintain these tight junctions- (how they do this is another blog for another day). When these junctions become loose we call this increased 'gut permeability' or 'leaky gut' (leaky gut being a term I'm told conventional medicine does not like, which is fair enough- so let's just call it 'increased gut permeability').


We know that gut permeability is often present in autoimmune conditions such as Hashimoto's and is a contributing factor to the development of the disease. Non-coeliac gluten sensitivity and other unchecked food sensitivities can promote gut permeability and set us up for autoimmunity in the genetically susceptible. A permeable gut may allow undesirable undigested food proteins into the bloodstream which activate the immune system- and so the autoimmune vicious cycle begins. So, it comes back to the gut and this is why nutritional therapists like to look at gut health first especially when it comes to autoimmunity as it often plays a part in the health puzzle.


What about the every day unpleasant symptoms of poor gut health and Hashimoto's? Well, firstly gut motility (the speed at which our guts work from digestion all the way through to passing a stool) can be slowed down with Hashimoto's, resulting in chronic constipation and an overgrowth of unfriendly bacteria as things hang around for too long. A good test to assess gut transit time is to eat sweetcorn- a decent amount, not just a few kernels and see how quickly it comes out the other end in your stool! A healthy transit time is 16- 24 hours with all of the sweetcorn completely gone by 36 hours max. Some strains of probiotics can support healthy gut motility- this is something that is strain specific and should be discussed with a qualified functional medicine/naturopathic practitioner. Obviously staying adequately hydrated is also key as is moderate exercise- it's surprising how many of us don't drink enough filtered water or get up from our desks for hours on end. I often recommend eating a gluten-free diet for life if you have Hashimoto's- this can help with constipation as well as autoimmunity.


The gallbladder is the next part to consider, the rate at which it contracts can become affected by Hashimoto's, this may result in gallstone formation and sludge in the gallbladder. Just a quick overview on what the gallbladder does- it's a little pouch that stores bile (bile is produced in the liver), this pouch lives just under the liver in the upper right part of the abdomen. Bile is needed to breakdown fatty foods. When the gallbladder starts to malfunction it may cause pain, diarrhoea and greasy fatty stools (that may float). These symptoms need to be discussed with your doctor.


Digestive enzymes are another aspect of gut health that needs covering when it comes to Hashimoto's. A hypothyroid state can impair the production and the release of digestive enzymes from the pancreas that is needed to breakdown and digest our food. It's possible to get a picture of digestive enzyme activity with a functional stool test called a 'comprehensive digestive stool analysis', within it, there's a marker called 'pancreatic elastase' which will show how well this side of things is working. This test is available from functional medicine/ naturopathic practitioners. I frequently run this test to get a full picture of gut health for my Hashimoto's clients.


So what can you do about it if you have any of these symptoms? Well, I'll say it for the final time (I promise), see your GP first if you're concerned about any symptoms you may have.

Once any other potentially serious causes have been ruled out by your GP and you're ready to work on the daily habits needed to promote good gut health, then the first place to look is the food that you eat.


Those with Hashimoto's have been shown to have a lack of gut bacteria diversity. A diet rich in diverse fibres from plant foods will promote a healthy and diverse gut microbiome. If it does not exacerbate symptoms then a diet rich in prebiotic foods like artichokes, apple pectin, onions, garlic, leeks, flax seeds and resistant starch will be beneficial. What's resistant starch? This type of starch doesn't get digested (hence the name resistant starch) and passes into the colon where it feeds the friendly bacteria. There are different types of resistant starch. One type can be found in cooked and cooled starchy foods such as rice and potatoes- they have to be really cold to fridge temperature for several hours, not room temperature to get the benefits. The action of cooling affects the chemical composition of the starch content rendering it unable to be digested- win-win! Unripe bananas also contain good amounts of resistant starch, the riper they become the less they have.


If an unbalanced gut bacteria is found to be causing IBS symptoms then working with a registered nutritional therapist can be a great place to unravel the tangled ball of gut health and food sensitivities. Working together I support you to find the right food choices for you personally (something like a low FODMAP diet might be necessary for a short time- this should be done under supervision as it's quite restrictive and not great for long term gut health), couple this with the intelligent use of supportive supplements, probiotics, prebiotics and lifestyle interventions can also be of great help.


Want to find out more about working with a nutritional therapist? Have a browse of my website or book a free 30-minute discovery call with me to find out more- follow the link below where you can also sign up to my newsletter.


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