How Does Intermittent Fasting Affect Thyroid Function? – Technology Org

Have you heard of Intermittent Fasting? It’s actually been around for hundreds of years and has many great health benefits. But what if you have certain medical conditions such as thyroid disease? How will intermittent fasting affect the function of your thyroid?

Image credit: Engin Akyurt via Pixabay, free license

Image credit: Engin Akyurt via Pixabay, free license

Could it help with any of your symptoms or possibly make them worse? Can those with hypothyroidism still lose weight with this method? These are all valid concerns. In this article, we are going to discuss the function of the thyroid, the diseases associated with it, and whether or not intermittent fasting is a safe and effective method for weight loss for those with a thyroid condition.

What is the thyroid?

The thyroid is an extremely important endocrine gland that is located just under the larynx at the base of the neck. The gland has two connecting lobes on either side and resembles the shape of a butterfly. It has the essential task of producing the hormones triiodothyronine (T3), thyroxine (T4), reverse triiodothyronine (RT3), and calcitonin.

All of these vital hormones make up what we refer to as thyroid hormone and have an effect on several critical functions throughout the body. Though T4 is not the main hormone that controls metabolism, it is the primary hormone the thyroid produces. As the thyroid produces T4 it is then converted into T3 which is the biologically active hormone that directly controls the metabolism process and the speed at which it operates.

As for RT3, this hormone is also converted from T4 though not much of it is produced. Its primary function is to reverse the effects of T3 in the event that too much is produced. Calcitonin’s primary function is to control the amount of calcium in the bloodstream.

Additional functions of the thyroid include:

  • Metabolism regulation
  • Growth and development
  • Brain Development
  • Maintenance of the Skin and Bone
  • heart rate
  • Digestion
  • breathing
  • Body Temperature
  • Fertility

It is important to note that for any of these bodily functions to occur there must be enough iodine in the system for the appropriate hormone levels to be achieved and to function appropriately. Iodine is typically ingested through a food source such as fish, iodized salt, certain dairy products, and chicken among others.

When there is not enough iodine or too much, thyroid diseases may develop and lead to chronic illness as the thyroid will be unable to produce the proper amount of thyroid hormone.


Hypothyroidism is a medical condition in which the thyroid gland is not producing enough thyroid hormone therefore too little thyroid hormone is being distributed into the bloodstream. Also known as an underactive thyroid, the symptoms associated with this condition include:

  • weight gain
  • Exhaustion
  • Feeling cold
  • Poor Concentration
  • Brain Fog
  • Depression

This condition is treatable and often managed with regular checkups and medication prescribed by your Primary Care Provider (PCP). It is also important to be mindful of what you are consuming on a daily basis as diet has a huge effect on your hormone levels and overall well-being.


Hyperthyroidism is essentially the opposite of hypothyroidism. Also known as overactive thyroid, this medical condition is when there is too much thyroid hormone being produced and dumped into the bloodstream.

Because there are so many varying symptoms that are also associated with other common diseases, it can be difficult to obtain a diagnosis of hyperthyroidism. Additionally, in cases of individuals with hyperthyroidism, they may not experience many symptoms, but a blood test ordered by your physician will indicate whether or not you have a thyroid disorder.

The symptoms associated with this condition include:

  • Weight Loss
  • Heat Intolerance
  • Anxiety
  • Sore or scratchy eyes
  • Hand tremors
  • Rapid Heartrate
  • Irregular heart rate
  • Thinning skin
  • Sleep Disorders
  • Muscle Weakness
  • Brittle, thinning hair

Fortunately, just as with hypothyroidism, this condition can also be treated with medications that decrease the number of hormones the thyroid can produce. In more extreme cases, surgery to remove either part or all of the thyroid may be recommended by your physician.

If this is the case, the patient will have to take hormone replacement medications for the rest of their life. It is very important to look into all of the available options and possibly get a second opinion before making that decision.

Intermittent fasting and thyroid function

Now the big question. How does intermittent fasting affect the thyroid and is it a good method for losing weight if you have a thyroid condition?

Intermittent fasting - artistic impression.

Intermittent fasting – artistic impression. Image credit: Kirill Tonkikh via Unsplash, free license

Studies have shown that intermittent fasting actually does have a profound effect on thyroid function as the levels of T3 can decrease by over 50% in the bloodstream while in a fasted state. This can be a problem if you have been diagnosed with hypothyroidism as your thyroid is already deficient in this hormone. This article on Fasting and Hypothyroidism gives a more detailed explanation of the benefits and drawbacks of intermittent fasting with this thyroid condition.

The good news is that these effects are only temporary. Once you consume your next meal the thyroid hormones should go back up to their previous levels before the fast state. If you decide that you wish to try intermittent fasting, it is important that you consume balanced meals with adequate amounts of carbs, protein, and healthy fats.

Another thing to note is that there are different methods of intermittent fasting. One method that has been shown to be helpful to those with hypothyroidism is the alternate-day fasting method. This method of fasting has been used to reduce insulin resistance, increase medication absorption, and assist in weight loss, especially when followed over a long period.

To recap

The thyroid is a gland located at the base of the neck and it plays a vital role in the production of metabolic hormones. In order for these hormones to be produced and regulated appropriately the body needs iodine. If it is insufficient or perhaps excess amounts of iodine, thyroid diseases such as hypothyroidism or hyperthyroidism can develop.

Intermittent fasting does affect thyroid function as it has been shown to lower T3 levels but can be effective for weight loss in those with hypothyroidism if the appropriate intermittent fasting method such as the alternate-day fasting method is adopted.

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