Doctor checking woman's thyroid

How Does Your Thyroid Impact Your Metabolism?

In theory, maintaining a healthy weight should be a simple math equation of "calories in, calories out," but it doesn't always work out that way. For some of us, weight loss can be a struggle. If that's been the case for you, perhaps you've worried if your thyroid gland health has anything to do with it.

Does your thyroid impact your metabolism—and therefore, make it harder to lose weight? To get the answer to this question, we interviewed Life Extension's Director of Scientific Affairs, Dr. Carrie Decker, who talked us through the intricacies of the relationship between thyroid health, metabolism, and weight.

The basics: How your thyroid works

Doctor examining woman's thyroid

You might not have thought very much about your thyroid before—but as Dr. Decker explained, this gland plays a role in many bodily functions, and whether your thyroid is healthy can impact everything from your weight to your fingernails.

What is the thyroid?

The thyroid is a butterfly-shaped gland in the front of your neck. Much like other glands in the body (examples being the pituitary gland, adrenal glands, and ovaries), the thyroid gland produces hormones, which are signaling factors that broadly impact the body.

What does the thyroid do?

The question actually should be what do thyroid gland hormones not do! As the primary regulator of metabolism, the thyroid plays an important role in how all systems of the body function. The thyroid gland produces thyroid hormones that affect your basal metabolic rate (resting energy expenditure), weight, skin, fingernails (including whether you have fingernail ridges) and bone density, heart rate, brain function and development, body temperature, reproductive health (for both men and women), and much more.

Thyroid health, metabolism, weight and body fat

Woman with thyroid issues standing on a scale

Next it was time for Dr. Decker to answer some "weighty" questions. Since, as she mentioned the thyroid gland produces hormones that maintain metabolism and weight, does that mean that thyroid hormones are the reason your metabolism isn't fast or you're having trouble losing weight? Not necessarily...

Does your thyroid affect your metabolism?

The relationship between thyroid and metabolism is fairly simple: when thyroid hormones increase, metabolism revs up; when they decrease, things slow down.

On a more complex level, thyroid hormone interacts with nuclear receptors to tell your body which genes to turn on and turn off. These genes play a major role in supporting growth and already-healthy cholesterol, as well as glucose metabolism. This is why we see numerous downstream metabolic effects when the thyroid is not functioning optimally.

What would make thyroid hormones increase vs. decrease?

Countless things! Stress can play a role, what you eat (or don't eat) – these are just some of the many things that can cause thyroid hormones to go up or down.

How do I know if my thyroid is affecting my weight?

By taking lab tests. Because thyroid function can change over time, thyroid tests should be done routinely, particularly with increasing age and after a woman goes through menopause. These tests look at your thyroid hormones--including TSH, thyroxine or T4, and T3 (see sidebar below).

If my thyroid lab tests are normal, does that mean hormones aren’t to blame for my difficulty maintaining a healthy weight?

No! Thyroid hormone is not the only hormone that influences body weight and composition – estrogen and testosterone do as well. Levels of these sex hormones also change with age and can be a factor that contributes to the difficulty some people have with losing weight and maintaining muscle mass as they get older.
Another key hormone that can shift the needle on the scale higher is cortisol, the stress hormone. As each of these hormones can also influence metabolic maintenance of glucose and already-healthy cholesterol in addition to body weight, it is important to consider doing comprehensive hormone test panels when one wants to be proactive about their health.

Does your thyroid have anything to do with how much body fat you have?

Yes! An interesting fact that most people don't realize is that adipose tissue (commonly known as body fat) is actually a gland. Adipose tissue produces hormones, known as adipokines, which impact metabolism as well.

Here's where it gets tricky: there are different types of adipose tissue, generally known as brown and white adipose. Brown adipose has positive metabolic effects and generally is associated with a healthy body weight and metabolic function. Recent research suggests that thyroid hormone not only increases the metabolic rate of adipose tissue, it also plays a role in the "browning" of white adipose tissue.

So brown adipose tissue is the “good” kind. Is there anything else you can do to turn your body fat brown?

Some common dietary supplements like curcumin, resveratrol, and quercetin promote adipose browning. Given their favorable safety profile and positive findings in animals, one might want to consider including them in their wellness regime for the broad health benefits they provide.

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Thyroid hormones: roles and function—and tests

There are three key thyroid hormones that play a role in how the thyroid gland functions:

  1. Thyroid stimulating hormone (TSH)—Secreted by the pituitary gland when stimulated by the hypothalamus, TSH signals the thyroid to commence with the thyroid hormone production of thyroxine (T4) and triiodothyronine (T3).
  2. T4—Approximately 80% of the thyroid hormone that is produced by the thyroid gland is the thyroxine or T4 form. This thyroid hormone contains four molecules of iodine (hence its name, T4!).
  3. T3—The thyroid hormone T3 is the more active thyroid hormone, produced inside the cells in nearly all the tissues of the body (e.g., liver, kidney, muscle, and brain). The body makes T3 from T4 by simply removing one atom of iodine.

Active vs. reverse T3: Reverse T3 is similar in structure to T3; however, it doesn't promote energy burning in the same way. In fact, because it binds to the same receptors, it can get in the way of T3's metabolism-promoting action.

Testing thyroid hormones: Although many healthcare providers simply assess thyroid function with a test of TSH levels, more thorough thyroid function tests will typically test for levels of TSH, free T3 and free T4 (thyroxine), and may also include other markers such as reverse T3. Ultimately, you will want to get an assessment of thyroid hormone action and thyroid hormone synthesis—not just TSH levels.

—Carrie Decker, ND

How to maintain normal thyroid hormone levels

Since having healthy thyroid hormone levels is so important—not just to your weight management goals and metabolism, but to many other health functions—is there anything you can do to be proactive? According to Dr. Decker, your diet may play a role in the health of your thyroid gland.

What nutrients encourage thyroid gland health?

Because thyroid hormones contain multiple iodine molecules, iodine is an essential nutrient for healthy thyroid gland function. Unfortunately, many people do not consume the amounts of iodine that we used to. With an interest in health, people may select a vegetarian or vegan diet, or avoid the use of table salt, which eliminates the common dietary sources of iodine and can lead to iodine deficiency.

Additionally, selenium is very important for the conversion of T4 into T3 and helps to regulate thyroid gland function. Brazil nuts are a good source of selenium, and you can also take selenium supplements.

How much iodine should adults be getting for a healthy thyroid gland?

The recommended daily allowance (RDA) of iodine for adults is 150 mcg/day while the upper limit is 1,100 mcg/day. Most healthy adults should aim for iodine intake somewhere between the RDA and upper limit, and err on the side of slightly more intake if their diet might result in iodine deficiency. (Pregnant and breastfeeding women will need more.)

Healthy ways to boost your metabolism

Man doing yoga to maintain his healthy metabolism

If you are wondering how to boost your thyroid and metabolism, Dr. Decker has these seven tips:

  1. Give your nervous system some love.

    "Stress can have adverse effects on your thyroid function, mental health, immune system, and many other facets of health," she said. Engage in healthy things that may relieve your stress like a yoga class, meditation, or just getting outside for more fresh air!
  2. Make sure you are getting enough iodine.

    Seaweed is the best food source of iodine, while seafood, dairy, and iodized salt are other dietary sources. "If you happen to avoid these foods, iodine supplements may be something you want to consider," Dr. Decker added.
  3. Exercise regularly.

    The more you move your body, the more energy you burn. Aerobic exercise and strength training both can help boost your metabolic rate. Not able to get to the gym? All types of physical activity can be helpful, even just taking the stairs or walking instead of driving!
  4. Try going gluten-free.

    Research suggest that following a gluten-free diet may support healthy thyroid function.
  5. Target your microbiome.

    "A greater diversity of bacteria in the gut is associated with having a healthy body weight and metabolic function," Dr. Decker said. "Human studies suggest that following a healthy diet like the Mediterranean diet and eating more fruits and veggies may contribute to a greater diversity of bacteria in the gut."
  6. Support your thyroid function by feeding it proper nutrition.

    Selenium and zinc are two essential minerals that are important for healthy thyroid function, while vitamins A and B12 are also important for thyroid health and function.
  7. Eat more bitter foods like artichoke and dandelion.

    "Dandelion greens and artichoke both encourage bile flow [the substance made by your liver and secreted by your gallbladder]," Dr. Decker explained. "Bile acids play a role in activating thyroid hormone inside the cell and increasing adipose tissue energy expenditure." And guess what – they just might support your digestive health as well!

Talk with your healthcare provider if you plan to incorporate thyroid supplements into your wellness routine, because some supplements may interact with other medications you may be taking or be contraindicated for other reasons.

About the Author: Jorie Mark earned an English degree from University of Pennsylvania before getting a master's degree in creative writing from American University. She is a content and social media expert with 20 years of experience in social media, editorial content, digital marketing, events, public relations and food and lifestyle writing. She is also a published author.