The Gut-Thyroid Connection

If you guys haven’t already got this, I’m pretty passionate about gut and microbiome (gut bacteria) health. The gut and microbiome are crucial for optimal body function and when these two are damaged or malfunction you can see some pretty negative shifts in body composition, mental state and health. In this article I’m going to take a closer look at how the dysbiosis in the microbiome can lead to issues with thyroid hormone production.


Selenium, Iodine and the Thyroid

A health balance of selenium and iodine is crucial for optimal thyroid hormone output. There are 3 main thyroid hormones, two of which will be discussed in detail today; TSH, T4 and T3. TSH is released by the anterior pituitary gland in the brain, travels down to the thyroid gland and binds to its receptor. TSH then stimulated the thyroid to produce tetraiodothyronine (T4). T4 itself is relatively inert and needs to have an iodine molecule removed by an enzyme called a deiodinase. This then creates triiodothyronine (T3). T3 is far more potent than T4 and actively binds to many cells throughout the body to increase protein synthesis, regulate body heat and thus control metabolic rate.


The gut biome and iodine uptake

As the names suggest, T4 and T3 both require iodine. If we don’t have enough iodine in our diet we won’t be able to produce these hormones! This is where our gut microbiome is crucial. Our gut microbes actually control how much iodine we absorb. In a really cool study published in the Journal of Hormone and Metabolic Research it was shown that by killing off bacteria with an antibiotic name Kanamycin, iodine uptake was drastically reduced. This in turn results in hypothyroidism (low thyroid function). What we can take out of this is that overuse of antibiotics, not consuming enough resistant starch, or consuming foods which promote the growth of bad bacteria which outcompete good bacteria we are seriously harming our health and weight loss goals.



Selenium is crucial in the process of converting T4 to T3 as it is what makes the enzyme deiodinase. When selenium levels are too low, this conversion cannot take place leading to low T3 levels, slowed metabolic rate, weight gain and potential muscle loss. Our gut microbiome also plays a crucial role in the maintenance of selenium levels as some of the bacteria in you gut actually absorb it for themselves, as shown in this study! This means that overgrowth of these bacteria will result in you having less selenium, thus lower T3 levels.


Conclusion: How do we prevent our gut from affecting our thyroid?

As this is such a new area of research, we don’t quite have conclusive treatment or prevention methods just yet! With that being said, there are a few principles which will drastically reduce the likelihood of your microbiome playing up. Firstly, use a probiotic supplement with a high lactic acid bacteria composition (these are the italicised names on the back of your probiotic with the prefix of lacto). Secondly, avoid antibiotics unless they are completely necessary. Thirdly, eat plenty of resistance starch and fibre. Finally, DON’T EAT FOODS WHICH HARM YOUR GUT!!!!

Now I want to hear from you! Have any of your guys experienced hypothyroidism or are worried your gut health may be affecting your weight loss progress? Comment below or email me so I can help you!

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