Intermittent Fasting and Your Thyroid

author avatar Dr. Eric Berg 08/31/2023

You’ve heard the buzz about the benefits of intermittent fasting:

Weight loss

More energy

Better mental clarity

And you’d like those results.

One thing, though, makes you hesitate:

You have hypothyroidism, which makes you concerned that fasting will slow down your thyroid even more than it already is prone to. Even though you’re being treated for it, you worry that a dip in the functioning of your thyroid will make your life miserable.

Because if you’ve ever lived with un- or under-treated hypothyroidism, you know how daunting it is.

You’re always cold. Your metabolism slows to a crawl, making it impossible to lose weight. In fact, you gain it.

You feel depressed, and often have unsettling dreams akin to nightmares. And because the thyroid also regulates heart and muscle function, their health and overall functioning are impaired.

A hypothyroidism word cloud

Plus, when you research you come across warnings that fasting is bad for you if your blood sugar and Fat Storing Hormone levels aren't optimal. Yours aren't necessarily terrible, but still, the warnings scare you.

There’s no way you’re going to try to get fasting's benefits on the one hand but risk other aspects of your health on the other hand.

I don’t blame you. So, let’s take a look at why you’re not risking your thyroid health when you fast. In fact, fasting supports your thyroid.

In this article: -


Here’s Why Intermittent Fasting Is Safe

People who have either Hashimoto’s Disease, an autoimmune condition in which your body develops antibodies that attacks itself, or who have regular hypothyroidism, regularly ask me:

Can I do intermittent fasting?

They’re concerned they’ll jeopardize their thyroid health if they try fasting.

So let’s take a look at what the data shows actually impairs your thyroid health:

Low-calorie diets

Though it sounds counter-intuitive, intermittent fasting is not a low-calorie diet. Rather, you’re eating the same amount of calories as usual. You’re just eating them in a compressed window of time such as 8 hours, followed by 16 hours of fasting.

In other words, you’re no longer grazing; you’re very deliberate about your eating window. As long as you’re consuming a nutrient-dense meal containing all the nutrients you need, you’ll be fine. You won’t be putting your thyroid at risk.

But if you’re doing a low-calorie diet for weight loss, you can cause additional stress for your thyroid, which can impair its proper functioning.

A low-calorie diet effectively puts you in starvation mode, sending signals to your brain to slow down your metabolism even more than it slows with hypothyroidism.

Not what you want! Ironic, isn’t it, that a diet meant for weight loss will slow your metabolism and make it more difficult to lose weight?

a picture of a woman with one tiny piece of food on her plate

Cruciferous vegetables

There is some research showing that cruciferous vegetables such as broccoli, cauliflower, and kale in large amounts will affect your thyroid. But one cause of thyroid issues is high levels of estrogen. Cruciferous vegetables are anti-estrogenic, meaning they can help you balance your estrogen levels. When you consume them, they help clear some of the excess estrogen from your body.

Thus, what I recommend is to have small amounts of cruciferous vegetables just to ensure you aren’t impacting your thyroid. At the same time, increase your intake of sea kelp in order to ensure you’re getting enough iodine, a key trace mineral required for thyroid health. Take one or two doses in the morning instead of the evening or it may prevent you from falling asleep.

a photo of a plate of cruciferous vegetables


Trace Minerals And Vitamins For Thyroid Health

In addition to iodine’s role in thyroid health, selenium is another key trace mineral to help your body convert the T4 thyroid hormone to T3. Not to get too geeky, but it’s important you understand why these two hormones are so important to your health.

T3 and T4 work together to help control your body’s metabolism, along with many other processes including:

  • Breathing

  • Heart function

  • Nervous system function

  • Body temperature

  • Cholesterol level

  • Metabolism that affects your weight

  • Brain development

  • Moisture in the skin

  • Menstruation

No wonder you feel awful when you’re hypothyroid.

Selenium is especially important if you have Hashimoto’s disease. You can easily increase your intake of selenium by consuming either brewer’s yeast or nutritional yeast, or take it as a supplement.

Besides these two trace minerals, the fat-soluble vitamins A and D play a crucial role in treating hypothyroid conditions, especially Hashimoto’s. Interestingly, not many people are aware of just how beneficial these vitamins are, especially Vitamin A.

Vitamin A is really a superstar. It has the ability to regulate thyroid function, as well as to penetrate deep into cells and positively affect the DNA. Here’s what that means:

Vitamin A works to erase what are called methyl tags present on genes, essentially showing promise of being able to reprogram cells from one type to another - and this vitamin has caught the attention of scientists in a field called regenerative medicine, which holds the promise of regenerating damaged tissues and organs in the body by stimulating the body's own repair mechanisms to heal tissues or organs. Like the thyroid.

Vitamin D plays an important role in preventing auto-immune diseases, and research shows that patients with Hashimoto’s have significantly lower levels of vitamin D than the general population. Thus, increasing your levels of this important vitamin is a smart addition to maintaining your thyroid health.

Virgin cod liver oil (link) is an excellent source of both Vitamin A and D. I highly recommend taking it when intermittent fasting to support your thyroid.

But wait, there's more.


The Connection Among Your Gallbladder, Thyroid, And Intermittent Fasting

Intermittent fasting, when done correctly helps your body convert T4 to T3, just as selenium does. Because T3 is the active form of thyroid hormone, having more of it will improve your thyroid function if you’re hypothyroid.

Interestingly, the T4 to T3 function improves during fasting because intermittent fasting also improves the gallbladder function. Your gallbladder is a key organ for the conversion of T4 to T3.

See how it all fits together?

A Quick Note About Those Warnings

Oh, and those warnings about the dangers of fasting unless your blood sugar and Fat Storing Hormone levels, indicating your Fat Storing Hormone sensitivity, are optimal? They're unfounded. In fact, I've got plenty of information showing that fasting can help regulate Fat Storing Hormone and blood sugar levels.

So not to worry.


Time To Take Up Intermittent Fasting

You can absolutely take up intermittent fasting. The sooner, the better for your health. You can see it's not only perfectly safe even when you're prone to hypothyroidism, but it can actually support the health of your thyroid.

Especially when you combine fasting with ensuring you get adequate amounts of selenium, iodine, and vitamins A and D, you're taking some of the most beneficial steps possible for your health.

Yes, even if you're currently experiencing hypoglycemia and less than optimal Fat Storing Hormone sensitivity. You can see how fasting improves your health by regulating your blood sugar and Fat Storing Hormone.

It's a win all the way around.

Don't delay - you deserve to experience the many benefits of fasting.

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Disclaimer: Our educational content is not meant or intended for medical advice or treatment.

Editor’s Note: This post has been updated for quality and relevancy.

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