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A Complete Guide to Intermittent Fasting and Hypothyroidism

Hypothyroidism is a condition in which your thyroid is underactive and does not produce sufficient levels of thyroid hormone. The result is that you cannot control your metabolism, heart rate, or body temperature adequately.

Common symptoms of the illness may include lethargy, depression, difficulty losing weight or sudden weight gain, sensitivity to cold, and constipation. Usually, older women get it.

It may be caused by Hashimoto’s disease, which is an autoimmune disorder that causes your immune cells to attack your healthy tissues.

Concerning the thyroid, this condition causes your immune cells to attack throat tissue, thus leading to thyroid inflammation.

Hashimoto’s disease often causes thyroid damage and a reduction in thyroid hormone levels.


A Complete Guide to Intermittent Fasting and Hypothyroidism

This is not entirely true as the association between intermittent fasting and hypothyroidism is complex.

Intermittent fasting works by minimizing the number of calories that you consume. Your body then responds by using up its internal reserves; this translates to weight loss.

As the above changes occur, they also profoundly affect your metabolism as there is an adjustment made when you are fasting versus when you are fed.

Such metabolic changes also have implications on your thyroid functioning as the thyroid is primarily responsible for this biological role.

Intermittent fasting and hypothyroidism may not always go together because of the former’s effect on your inactive and active thyroid hormones.

The active thyroid hormone called T3 often binds to your receptors and is essential in normal thyroid functions. However, intermittent fasting causes a substantial decrease in the level of T3.

Conversely, it also leads to an increase in the levels of reverse T3, which is your inactive thyroid rT3 hormone. This often leads to competition between the T3 and rT3 for protein receptors.

The result is a decline in thyroid functioning. However, that is only if one fast for prolonged periods of time.

According to this study, it was shown that thyroid-stimulating hormones significantly declined after fasting than before fasting. It was thus stated that caution should be taken for people with hypothyroidism.

On the flip side, another research showed that there were no alterations in the level of thyroid-stimulating hormone following intermittent fasting. However, this study dealt with subclinical hypothyroidism, not those who already had the condition.

Therefore, intermittent fasting is not necessarily good for hypothyroidism, but it may also not be detrimental within certain limits.


The simple answer is yes.

Fasting has an effect on your thyroid hormone levels. This means that if you are on medication, the kind of changes the medication has on your thyroid hormones will change slightly.

Therefore, you may have to make some minor adjustments to the dosages, but you do not have to stop fasting altogether.

This was proven through two studies that were done in patients with hypothyroidism who were fasting during Ramadan. In Ramadan, individuals only eat from dusk to dawn and stay hungry all day.

In this experiment, patients with hypothyroidism than were on levothyroxine medications had their thyroid-stimulating hormones (TSH) checked before the fast and after the fast.

It was found there were minor changes in their TSH levels, which meant that dosage levels of their medication needed to be increased.

You can thus take your medication, but you need to alter the dosage and also the time that you take it.

This research showed that hypothyroid patients who were fasting needed to adjust their medication to 2 hours before their last meal. This implies that intermittent fasting and hypothyroidism work only if you are careful about meal and medication timing.


Intermittent fasting and hypothyroidism have a profound effect on another critical hormone in your body known as cortisol. This hormone is responsible for the regulation of blood sugar in your body.

If you have low blood sugar, your brain gets stimulated and releases cortisol to return your blood sugar to normal levels. However, when you are fasting intermittently, you always have low blood sugar.

This means that your body constantly has to release cortisol.

When you restrict your food intake as is the norm during fasting, you may chronically have low blood sugar and continuous cortisol levels. This means that you will experience a condition known as hypocortisolism.

According to this journal article, hypocortisolism is associated with autoimmune diseases and thyroid dysfunction. If you are predisposed to hypothyroidism or already have it, cortisol problems could exacerbate it.

Therefore, intermittent fasting may not be a good idea for hypothyroidism.

Nonetheless, if you don’t have hypothyroidism and are looking to simply rest your thyroid, intermittent fasting could be beneficial.

It achieves this through its effect on inflammation. When a person has Hashimoto’s disease, they are susceptible to excess inflammation.

Consequently, if you can find a way of minimizing that inflammation, you will be well on your way to becoming healthy. Intermittent fasting is one of the ways to achieve this.

According to this study, inflammation biomarkers were reduced substantially after intermittent fasting. You may thus say that fasting only resets your thyroid when you don’t have full-blown hypothyroidism.


You should be aware that hypothyroidism is a condition that requires medical attention. Taking vitamin supplements could interfere with the treatment of your diseases.

It is thus best to work with a medical practitioner before taking any supplements, as these have the potential to counteract your thyroid medication.

You don’t always have to get your vitamins from supplements. You may opt for dietary sources as these have no synthetic compounds.

Vitamin B12 is quite helpful in treating hypothyroidism, especially if Hashimoto’s disease caused it. You may get it from supplements or fish, milk, eggs, and cheese.

You also need vitamin C in plenty to minimize the level of thyroid antibodies in your body. Supplements may suffice, or you could eat citrus fruits like oranges, grapefruit, and vegetables like Brussels sprouts, peppers, and broccoli.

A vitamin D deficiency may also lead to thyroid dysfunction. Some common vitamin D sources include oily fish, red meat, liver, and sun exposure.

For intermittent fasting and hypothyroidism, always ensure that you include the above vitamin sources whenever you break your fast.


Intermittent fasting and hypothyroidism is a complex situation. If you have the condition and wish to fast, then proceed with caution.

Realize that fasting has an effect on your thyroid hormones as it causes their elevation. Therefore, you may worsen hypothyroidism if you fast continuously.

On the other hand, if you have hypothyroidism and treat it with medication, consider adjusting the dosage and timing as advised by your doctor.

That way, you are likely to compensate for thyroid functioning changes that happen when food is restricted during fasting.

You may also want to increase certain nutrients such as vitamin B12, C, and D because they improve your thyroid or minimize other conditions like Hashimoto’s disease that may lead to hypothyroidism.

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