How Does Your Thyroid Impact Your Metabolism

Your thyroid is a small gland at the base of your neck that produces hormones that directly influence the rate your body uses energy. When your thyroid levels are low, energy uptake and metabolism slow down. If your levels are too high, your metabolism kicks into overtime, potentially hindering your metabolic performance. Keep reading to learn about the link between the thyroid and metabolism.

By Julia Zakrzewski, RD 

Understanding the Thyroid

Your thyroid is an endocrine gland that sits at the base of your neck. It produces three main hormones: thyroxine (T4), triiodothyronine (T3), and calcitonin. Only T4 and T3 are proper thyroid hormones. They work by increasing metabolic rate and signaling energy uptake. Calcitonin is a hormone that regulates the amount of calcium in your blood and bone metabolism.¹ 

To make the right amount of hormones, your thyroid gland needs some help from your pituitary gland. This gland sits at the base of your brain and produces another thyroid hormone, thyroid stimulating hormone (TSH). TSH tells your thyroid how much T4 and T3 to release into your bloodstream.² 

Iodine is the main building block for thyroid hormones. Your body can’t produce this mineral, so you must get it through your diet. People with limited access to iodine-rich foods are at risk of a deficiency and can develop thyroid diseases, such as goiter and hypothyroidism. Because foods like table salt are fortified with iodine, it’s very rare you would be at risk for low iodine. 

How Do Thyroid Hormones Influence Metabolism?

Your thyroid levels help control energy expenditure in the body.¹ Specifically, T3 and T4 hormones affect your basal metabolic rate (resting metabolic rate) through changes in your internal temperature, the pace of your heartbeat, and how quickly food is broken down into energy.¹ 

How to Test Thyroid Levels

You need to complete a blood test to measure your thyroid levels and TSH. Blood tests can determine if your thyroid levels are within a normal range.

When there are low levels of T3 and T4 in the blood, your anterior pituitary releases TSH to prompt the thyroid gland to produce more hormones. 

In some people, the thyroid doesn’t get the message, so TSH continues to get pumped into the bloodstream, but T3 and T4 levels remain low.

The reverse can also be true. Sometimes, the thyroid produces too much T3 and T4 and suppresses the secretion of TSH.

Here is a simple way to understand your test results: 

• If your TSH levels are high, it is a sign your thyroid is underactive. 
• If your TSH levels are low, which is rare, your thyroid is overactive. 

In both scenarios, medication and lifestyle changes can help normalize your thyroid levels and improve associated symptoms. 

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Understanding Metabolism

Your metabolism is a system in your body that converts food into usable energy for your organs, muscles, and tissues. Ideally, a healthy and robust metabolism will burn food quickly to prevent energy storage that can lead to unwanted weight gain.  

• To maintain a healthy weight, it is generally accepted that your body needs to burn similar amounts of energy as you are consuming. 
• To lose weight, it is recommended to burn more energy than what you are consuming. 

Why is Metabolism an Important Bodily Function for Weight Loss?

Your metabolism is directly linked to how efficiently your body burns energy. If you have a slow metabolism you might be more susceptible to gaining weight. 

Weight gain, especially around the midsection, has been linked to increasing your risk of diabetes, heart disease, and metabolic syndrome. 

Losing 5-10% of your weight can help improve your health. It has been shown to reduce blood pressure, lower cholesterol, and reduce blood glucose levels. Having an active (fast) metabolism will help you achieve these outcomes. 

How Hypothyroidism Affects Metabolic Rate

Hypothyroidism is the clinical diagnosis of an underactive thyroid, which is a thyroid that is not producing enough thyroid hormone.³

As of 2019, it is estimated that 5% of the general population is affected by hypothyroidism.³

There are two classes for a diagnosis:

• Primary hypothyroidism: the thyroid produces insufficient T3 and T4, which leads to the over secretion of TSH.  
• Secondary hypothyroidism: the anterior pituitary gland is not releasing enough TSH which leads to inadequate T3 and T4. 

There is a third scenario that can lead to thyroid disease. This is called Hashimoto’s disease, which is an autoimmune condition that targets the thyroid and decreases hormone production and secretion.³

How Do You Know If You Have Hypothyroidism? 

Hypothyroidism can have non-specific symptoms, including:³  

• Weight gain 
• General fatigue 
• Poor concentration 
• Low mood 
• Menstrual irregularities 
• Decreased tolerance for cold 

These symptoms can be similar to other conditions, like an iron deficiency, which is why a blood test needs to be done to confirm the diagnosis. 

What Causes it? 

Current literature suggests there is a 65% chance that hypothyroidism will be genetically passed down from a blood relative.⁴ There are no ways to prevent a thyroid condition, you can only manage the symptoms.³,⁴ 

Fortunately, the current treatment options to manage hypothyroidism are simple. Your doctor (either a primary care provider or endocrinologist) will prescribe medication to help bring your thyroid normals back up to normal. The root cause of your underactive thyroid will determine how long you will need to take your medication.

Is It Bad for Your Health? 

Low thyroid levels can impair your quality of life. When you are constantly fatigued, it’s hard to bounce out of bed every morning. When you have brain fog, it can be difficult to focus on certain tasks. 

Leaving your thyroid condition untreated can lead to serious health complications. Untreated hypothyroidism has been proven to increase your risk of coronary heart disease, infertility, and some people can experience reversible dementia.⁴

How Hyperthyroidism Affects Metabolism

Hyperthyroidism is the opposite of an underactive thyroid.⁵ It is the overproduction of thyroid hormones that makes your metabolism work harder than normal. This leads to unintentional rapid weight loss. 

An overactive thyroid is rare; only 1-3% of the population have this condition.⁵ Genetics can play a role in your chances of developing hyperthyroidism. Otherwise, it is more commonly related to another diagnosis of a separate health issue or lifestyle factor, including:⁵ 

• Pernicious anemia (a vitamin b12 deficiency).
• Type 1 or Type 2 Diabetes. 
• A hormonal disorder called adrenal insufficiency.
• Smoking. 
• Consuming too much iodine (most commonly through medications that contain iodine). 
• Thyroiditis. 
• Thyroid nodules (solid or fluid-filled lumps that can impair hormone production). 
• Cancer. 

How Do You Know if You Have Hyperthyroidism? 

Symptoms of hyperthyroidism include:⁵ 

• Weight loss, despite having an increased appetite. 
• A fast or irregular heartbeat (tachycardia). 
• Twitching, a general sense of nervousness, and irritability. 
• Poor tolerance of heat, excess sweating. 
• Presence of a goiter. 

Is it Bad for Your Health?

High levels of thyroid hormones increase your risk of developing:⁵ 

• An irregular heart rate increases your risk of stroke. 
• An eye disease called Grave’s Ophthalmopathy. 
• Thinning bones or full-blown osteoporosis. 
• Fertility issues.
• A thyroid storm, which is life-threatening and can affect people with untreated high levels of thyroid hormone. 

Who Is More Prone to Hyperthyroidism?

Women who have recently given birth can be at higher risk of developing an overactive thyroid.⁵ This is secondary to the hormonal changes that naturally occur during pregnancy. Unfortunately, there is no way to prevent hyperthyroidism; it can only be monitored and treated by tracking blood work and symptoms. 

How to Keep Your Thyroid Healthy

There is very limited scientific evidence to show that your diet will influence how your thyroid functions, but you can make changes to manage side effects. 

If you have been diagnosed with an overactive thyroid, your goal will be to consume enough calories from healthy sources to prevent further weight loss. You can do this by targeting meals rich in healthy fats such as olive oil or avocado-based recipes. Incorporating more protein can help because they take your metabolism a bit longer to break down. 

Here are more general guidelines for people with overactive thyroid: 

• Choose low-iodine foods, including non-iodized salt. 
• Limit your intake of seafood (fish and shellfish tend to naturally be high in iodine). 
• Avoid caffeinated products as much as possible because they can exacerbate the symptoms of hyperthyroidism.
• Eat selenium-rich foods (turkey, lean beef, lean pork, chicken, 1-3 brazil nuts per day) to maintain healthy thyroid function and metabolism.    

People on the other end of the spectrum who have low thyroid activity may benefit from eating smaller meals that require less labor to digest. Some people who have been diagnosed with Hashimoto’s can feel better overall after eliminating gluten from their diet.⁶

If you have been diagnosed with low thyroid function you may follow these general dietary recommendations that support overall health:⁷

• Fiber-rich foods - nuts, legumes, vegetables, fruits, and whole grains. 
• Omega-3 fatty acids - chia seeds, walnuts, flax seeds, salmon, trout, mackerel.
• Unsaturated fats - avocado, olive oil, nuts again. 
• Antioxidant-rich fruits and vegetables - dark-colored berries, plums, pomegranates, oranges, green leafy spinach, or kale.

Some endocrinologists may suggest you reduce your intake of cruciferous vegetables (cabbage, broccoli, cauliflower, brussel sprouts). They may inhibit your body’s uptake of iodine, thus interfering with thyroid function and hormone production.⁸

Final Takeaways 

There is little to no evidence to suggest you can control your thyroid function, but you can make changes to your diet that can help manage the side effects associated with thyroid conditions. 

If you suffer from high thyroid levels, you will need to make sure you are getting enough calories and nutrients to maintain your energy levels and prevent further weight loss. Losing too much weight too quickly can result in the loss of muscle tissue, which is vital for maintaining your metabolic health. 

People with low thyroid levels are more susceptible to weight gain because their metabolism has slowed down. With the correct dosage and treatment, you can bring your thyroid levels up to normal and your metabolism will speed up again. 

To learn more about nutrition and your metabolism check out this new article on the Signos blog about sugar and metabolic health!