Which Thyroid Hormones Increase Metabolism?

The thyroid gland plays a major role in regulating metabolism in the body. Located at the base of the neck, this small butterfly-shaped gland produces key hormones that control how efficiently our bodies convert food into energy.

When thyroid hormone levels are too low or too high, they can cause metabolism to slow down or speed up and lead to weight changes as well as other symptoms. Read on to learn more about how thyroid hormones influence metabolism.

T3 and T4 – The Metabolic Thyroid Hormones

The thyroid gland secretes three hormonestriiodothyronine (T3), thyroxine (T4), and calcitonin. Out of these, T3 and T4 are the primary hormones that control metabolic rate.

T4 is the main hormone produced by the thyroid gland. It is converted into the more biologically active T3 form in tissues around the body. T3 possesses greater potency than T4 and is approximately three to four times more effective in increasing metabolism.

Both T3 and T4 play crucial roles in:

  • Increasing the rate of metabolism in the body’s cells
  • Helping convert oxygen and calories into energy
  • Maintaining normal body temperature
  • Influencing protein production

When T3 and T4 levels are optimal, the body’s metabolic rate remains in a normal, healthy range. But when they are too high or low, metabolism can speed up or slow down significantly.


Hyperthyroidism – Increased Metabolism

Hyperthyroidism is a condition where the thyroid gland is overactive and produces excess T3 and T4 hormones. With high thyroid hormone levels, the metabolism is pushed into overdrive.

Symptoms of an overactive thyroid and increased metabolism include:

  • Unexplained weight loss despite increased appetite
  • Rapid heart rate or palpitations
  • Trembling hands
  • Sweating and heat intolerance
  • Fatigue
  • Irritability
  • Muscle weakness
  • Difficulty sleeping

The excess thyroid hormones drive almost all metabolic processes within the cells to work faster than normal. This metabolic overactivity causes weight loss, rapid heartbeat, and other tell-tale hyperthyroidism symptoms.

Hypothyroidism – Decreased Metabolism

On the flip side, hypothyroidism is characterized by underproduction of T3 and T4 hormones. With low thyroid levels, the body’s metabolism slows down significantly.

Common signs and symptoms of an underactive thyroid and decreased metabolism are:

  • Weight gain despite poor appetite
  • Feeling cold all the time
  • Fatigue and sluggishness
  • Constipation
  • Muscle cramps
  • Depression
  • Slow heart rate

With insufficient thyroid hormones, metabolic processes slow down, leading to weight gain, sensitivity to cold, tiredness, and other hypothyroid symptoms.

Thyroid-Metabolism Connection

Researchers are still working to fully understand the complex relationship between thyroid hormones, metabolic rate, and weight changes.

In healthy individuals, a minor increase or decrease within the normal range of T3 and T4 levels doesn’t make a big difference in metabolic rate or weight. But in people with thyroid disorders like Graves’ disease or Hashimoto’s thyroiditis, the metabolic changes are more apparent.

When hormone levels fall outside the normal range, the body’s metabolism responds accordingly. Low thyroid hormone levels slow metabolism down while high levels rev it up.

Testing Thyroid Hormones

Blood tests help check our T3, T4, and TSH (thyroid stimulating hormone) levels. The TSH blood test is the standard initial test for suspected thyroid disorders. High TSH indicates hypothyroidism while low TSH is seen with hyperthyroidism.

Based on TSH findings, doctors may order additional thyroid hormone tests to confirm the diagnosis. Evaluating T3 and T4 levels yields useful insights into the underlying metabolic changes.

Diet and Lifestyle Changes

Along with medical treatment, certain dietary and lifestyle measures can help support healthy thyroid function and metabolism. These include:

  • Eating more seafood, nuts, seeds, and fruits containing iodine and selenium to support thyroid hormone production.
  • Avoid processed foods high in sugar and hydrogenated oils that can negatively impact thyroid function.
  • Engaging in regular moderate exercise to give metabolism a gentle boost.
  • Managing stress levels through yoga, meditation, or other relaxing activities. Chronic stress slows metabolism.
  • Getting 7-8 hours of sleep nightly. Inadequate sleep hampers metabolic processes.
  • Staying adequately hydrated and drinking 8-10 glasses of water daily.


The thyroid gland produces two key hormones – triiodothyronine (T3) and thyroxine (T4). These hormones play an integral role in regulating the body’s metabolic rate. Sufficient levels of T3 and T4 hormones are essential for keeping our metabolism robust and body weight stable.

Blood tests assessing thyroid hormone levels provide vital clues into metabolic disturbances underlying thyroid disorders. Treatment aims to restore optimal T3 and T4 levels, which helps reverse metabolic abnormalities and symptoms associated with hyperthyroidism or hypothyroidism.

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