Hypothyroidism and Intermittent Fasting: Is It a Good Idea?

Published on December 14, 2022 | Update on October 13, 2023

8 min read

Verified by Melissa Mitri

MS, Registered Dietitian, Former President of CT Academy of Nutrition & Dietetics

Table of Contents

What Is Hypothyroidism?
Can Diet and Eating Habits Influence Thyroid Function?
How Does Intermittent Fasting Affect Thyroid Function?
Is Intermittent Fasting Good for Hypothyroidism?
How to Do Intermittent Fasting If You Have Hypothyroidism?
Final Words

Intermittent fasting (IF) can help you lose weight, but what happens if you have a specific medical condition such as thyroid issues? How will IF affect your thyroid function? Will it help mediate the disorder, or will it worsen the situation? Can you lose weight with intermittent fasting even if you have hypothyroidism?

In this post, we discuss the association between hypothyroidism and intermittent fasting and aim to answer all these questions along the way. We also explore how you can safely practice intermittent fasting if you have hypothyroidism.

What Is Hypothyroidism?

Hypothyroidism, also known as underactive thyroid, arises when your thyroid gland doesn’t produce enough of the thyroid hormones that your body needs.

The thyroid gland is an endocrine gland located in your neck. It produces hormones involved in metabolism, growth, and body development.

Hypothyroidism can occur when your thyroid is damaged for some reason, such as in the case of the autoimmune condition called Hashimoto’s Disease. It can also occur when your pituitary gland fails to secrete enough thyroid-stimulating hormone (TSH).

How Does It Affect Weight Gain?

Hypothyroidism is often associated with unexpected weight gain along with other symptoms such as fatigue, low cold tolerance, and muscle weakness [1].

So how does a faulty thyroid bring about weight gain?

The thyroid gland produces two thyroid hormones named triiodothyronine (T3) and thyroxine (T4) [2]. These thyroid hormones, especially T3, play a major role in regulating your metabolism. They are specifically crucial in the metabolism of carbohydrates, lipids, and proteins [3].

Your metabolism when the body is resting is known as the Basal Metabolic Rate (BMR). This measurement tends to be low in those with hypothyroidism.

If your BMR is low, it means your body is using energy at a slower rate. This can result in a positive energy balance, usually deposited as fat, and that surplus can result in weight gain.

The situation can become more pronounced if you regularly consume high amounts of calories.

Another reason for weight gain apart from fat accumulation in those with hypothyroidism is the retention of salt and water [4].

That weight can come off when hypothyroidism is properly treated.

However, undiagnosed, low-lying hypothyroidism can even cause obesity. Therefore, it is essential to check your thyroid levels if you experience unexplained weight gain or suspect an existing thyroid disorder.

Can Diet and Eating Habits Influence Thyroid Function?

Although there are myths about specific ‘hypothyroidism diets,’ those claims are not scientifically confirmed.

According to the British Thyroid Foundation, there are no set foods or dietary supplements that can be used to treat thyroid issues [5].

General healthy eating guidelines apply if you’re suffering from hypothyroidism. That translates to eating plenty of fruits, vegetables, and dietary fiber.

However, some foods, such as calcium-rich foods and soy products, may interfere with the absorption of thyroid medication, so you need to be mindful of the timing of your meals and medications [5].

On the other hand, certain minerals—such as selenium and zinc—are known to boost thyroid function. Of them, iodine is especially important as it is essential for thyroxine production.

Related article: How to Improve Your Nutrition Today

How Does Intermittent Fasting Affect Thyroid Function?

If you’re thinking about following an IF routine and you’ve been diagnosed with hypothyroidism, there are a few facts you need to consider. The main one is that fasting can lower your thyroid hormone levels.

Research indicates that fasting reduces the level of the T3 hormone in the blood [6]. One study reported that during a fast, T3 levels can decrease up to 55% of their starting values [7].

However, this drop in blood T3 concentrations is only temporary. They will rise back to their pre-fasting values after eating.

That said, your diet during your eating window should be balanced. Ensure your diet contains enough carbs, proteins, fruits, and vegetables [8].

Intermittent Fasting and Hypothyroidism Symptoms

How intermittent fasting affects hypothyroidism symptoms has still not been investigated in depth. It doesn’t seem to directly impact thyroid function or hormone production. However, in some cases, intermittent fasting appears to help those with hypothyroidism in other ways.

Reduced insulin resistance. A study that explored the effect of alternate-day fasting (ADF) on weight loss in patients with hypothyroidism revealed that ADF reduced insulin resistance in those individuals [9].
Improved overall well-being. Another study done on Ramadan fasting, which is somewhat comparable to IF, found that fasting increased the overall quality of life of hypothyroidism patients with respect to physical and psychological health [10].
Increased medication absorption. Fasting also increases the absorption of thyroid medication in some cases, which can be an added benefit but needs to be accounted for in your thyroid medication dosing [8].
Weight loss. In terms of weight loss, intermittent fasting does seem to promote it in those who have hypothyroidism. The previous study we mentioned also reported that alternate-day fasting brought about significant weight loss in individuals suffering from hypothyroidism when followed for more than 6 months [9].

Having said that, you need to keep in mind that every person is different, and so is their metabolic response to diet regimens. This means that your body can respond in a totally different way to any changes you make to your lifestyle. That is especially true if you suffer from a specific medical condition such as hypothyroidism.

Intermittent Fasting and Hashimoto’s Disease

As we briefly mentioned at the beginning of this post, Hashimoto’s Disease is one of the common causes of hypothyroidism. It is an autoimmune disease, meaning your immune system doesn’t recognize the thyroid as part of the body and attacks it [11]. This damages the thyroid gland and hinders its ability to produce thyroid hormones.

At the moment, there are no scientific studies that directly link intermittent fasting and Hashimoto’s disease.

However, IF has been found to better regulate other autoimmune disorders like multiple sclerosis [12]. Thus, we can assume that intermittent fasting could have some effect on this specific autoimmune disorder. Yet, further studies are needed to prove the association.

Moreover, research indicates that inflammation is closely connected to autoimmune diseases [13]. Fasting has been found to stimulate anti-inflammatory responses [14], and thus we can theorize that it could have a potential benefit on Hashimoto’s disease as well. As we said earlier, these speculations need further scientific proof.

Is Intermittent Fasting Good for Hypothyroidism?

Based on scientific evidence, an intermittent fasting routine can do you good if you are diagnosed with hypothyroidism and want to lose weight.

Apart from weight loss, you can enjoy some other benefits, such as reduced insulin resistance and improved overall health.

Nevertheless, if this is your first time trying intermittent fasting, you must be cautious. If you don’t attempt it the correct way, fasting can alter your metabolism as well as hormone levels and may aggravate your condition.

How to Do Intermittent Fasting If You Have Hypothyroidism?

If you’re new to intermittent fasting, starting slow would be a good idea.

Start with a not-too-strict fasting schedule that allows you to consume 2-3 meals per day.
A safer approach would be to extend your night-time fast and eat a delayed breakfast.
Make sure you don’t cut out too many calories from your diet. Eat balanced meals with plenty of micronutrients.
Slowly increase your fasting period over time, but keep an eye on your thyroid hormone levels along the way.

If you’re concerned about whether intermittent fasting can mess up your thyroid function, consult with a thyroid nutritionist to get an expert opinion.

Make sure you discuss your fasting plan with a medical doctor before changing your eating habits. Keep them informed about any adjustments throughout the IF process.

Final Words

Before wrapping up, let us emphasize a few key points as a take-away message for you.

An underactive thyroid can lower your metabolism and make you gain weight unintentionally.
There are no special diets that can alleviate hypothyroidism. An overall balanced diet with healthy amounts of carbs, proteins, fiber, fruits, and vegetables can help your condition.
There is no direct relationship between hypothyroidism and intermittent fasting. Yet IF can offer many benefits for those who have hypothyroidism.
They include promoting weight loss, reducing insulin resistance, and modulating immune responses.
You need to schedule your fasting in a manner that doesn’t make your hypothyroidism worse.
The best way to proceed is to start slow and adjust your fasting periods accordingly while keeping an eye on your thyroid hormone levels.
It’s best to talk with a medical doctor about your IF regimen and formulate a plan that will provide the maximum benefits.
You need to stick to your diet routine, as well as your medication timing, to get the best results. You can use a weight-loss app to help you keep track of your calories, nutrients, and fasting windows.