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All the T's and your Metabolism

The thyroid is a small, butterfly-shaped gland located in the front of your neck. It is made up of two lobes, that lie along the larynx and are joined together by a narrow band of thyroid tissue, known as the isthmus (1)

This small but important gland helps to control the body’s metabolism.

Metabolism is the sum-total chemical processes that occur within the body to maintain life – and importantly determines how fast or slow we burn the calories from food and how efficiently we produce energy (1)

Every cell in the body depends on thyroid hormones for metabolic regulation

Much like cortisol, the production of your thyroid hormones begins in your brain — your hypothalamus, to be exact.

T3 & T4 are regulated by “Thyroid Stimulating Hormone” (TSH) which is produced in the pituitary gland, which in turn is regulated by “Thyrotropin-Releasing Hormone” (TRH) produced by the hypothalamus.

The thyroid gland produces two types of thyroid hormone –Triiodothyronine (T3) and Thyroxine (T4).

Each molecule of T4 and T3 is made of the amino acid tyrosine and iodine.

T4 contains 4 molecules of iodide and T3 contains 3 molecules of iodide – hence the names T4 & T3. T4 is produced by the thyroid gland in much greater amounts than T3, around 90% more. When T4 reaches organs and tissues, it’s converted into T3 which is the active form of thyroid hormone that exerts a metabolic effect inside your cells (2)

Your thyroid hormones help your mitochondria to function properly. Your mitochondria are the energy powerhouse in your cells. Since the thyroid has this critical role in energy production, its dysregulation has major downstream ramifications that can affect everything else in your body.


In addition to mitochondrial function, a few of the thyroid functions include:

  • Tissue repair and healing

  •  Controlling blood flow

  •  Managing protein, fat, and carbohydrate metabolism

  •  Regulating nutrition and vitamin consumption

  •  Managing digestion

  •  Controlling other hormones


As you can see, the thyroid plays a major role in blood flow, metabolism, digestion, and hormone balance. High levels of thyroid can feedback and affect insulin and cortisol secretion.

Interestingly, low levels can also do the exact same thing.

The levels of thyroid hormone in your body are regulated by a complex feedback loop involving the hypothalamus and pituitary glands which detect the levels of thyroid and related stimulating hormones in the body and adjust accordingly. A simple analogy to help understand how this works is that the thyroid hormone is like heat – the pituitary is the thermostat that switches off when the heat gets too high – and the hypothalamus is like the person who controls the heater itself. Of course, thyroid physiology is far more complicated than this, but for our purpose it is enough to understand that there are numerous steps involved.

There are several problems that can occur with the thyroid gland

Autoimmune disease is an immune system issue where body interprets the thyroid gland as a threat and produces antibodies that target thyroid cells and destroy it. The prevalence of thyroid autoimmune disease is increasing western countries.

These disorders include Graves’ Disease which results in an over-active or hyperthyroid gland, and Hashimoto’s Disease which causes an underactive or hypothyroid gland.

Underactive thyroid affects more women, and is the most common type of thyroid disorder.

A third possible situation is known as sub-clinical hypothyroid. This is when blood tests appear normal, but symptoms of underactive thyroid are present, and this may be attributed to the thyroid hormone not being active enough at the tissue level (2)

Signs your thyroid gland may be unhappy include:

Underactive Thyroid Symptoms

Persistent fatigue

Weight gain (even when eating the healthy options)

Prone to constipation

Low mood or depression

Menstrual abnormalities

Brain fog/ Trouble concentrating

Dry skin

Dry hair

Hair loss (outer 3rd of eyebrow is disappearing)

Brittle nails

Cold hands and feet

Overactive Thyroid Symptoms

Prone to nervousness/anxiety


Rapid heartbeat

High blood pressure

Prone to diarrhea

Eyes that appear large and sometimes bulge

Weight loss (with no change in diet)

Difficulties sleeping (Insomnia)

High blood pressure

Note: Just because you identify with one or two of the above does not mean you should diagnose yourself with a thyroid issue. There are a number of symptoms above that also correlate with other hormonal imbalances or health issues. Please raise the question with your health professional and request testing.

Thyroid Testing

Comprehensive assessment for thyroid issues may include some or all the following. Typically only TSH is tested but in my opinion it is important to see the results of a full thyroid panel, particularly if you have many of the symptoms in one of the categories above.

For your knowledge:

TSH or Thyroid Stimulating Hormone fluctuates in line with the level of thyroid hormone in your system. If thyroid hormone levels are low, then TSH secretion is increased. If thyroid hormone levels are high, TSH is reduced. (2)

Free T3 measures the free active thyroid hormone in your blood, however rarely used to diagnose hypothyroidism. Free T3 levels will usually only be low if hypothyroidism is severe. (2)

Free T4 (Thyroxine) is the main thyroid hormone in your blood. Free T4 refers to the amount of total inactive form T4 available to your tissues. (2)

rT3 or Reverse T3 is an inactive form of T3. Normally a large T4 % is converted to T3, with a smaller % becoming rT3. Under stress however, 50% or more T4 may convert to rT3. This is a problem because rT3 competes with T3, and ends up inhibiting T3 production. (2)

Thyroid Peroxidase or Thyroglobulin Antibodies detects an autoimmune response to elements essential for thyroid hormone production. (2)

Elements for Healthy Thyroid Function

Healthy thyroid function requires the amino acid tyrosine, iodine, iron, copper, zinc, vanadium, selenium, Vitamins A, B2, B3, B6, D & E, and antioxidants (2)

T4 is converted to the active form T3 in the tissues by an enzyme called iodothyronine deiodinase. Deiodinases which are selenium-containing enzymes, thus dietary selenium is essential for T3 production. Deficiency of deiodinase activity can mimic hypothyroidism attributed to iodine deficiency. Zinc also assists in the conversion of T4 to T3, and cellular sensitivity to thyroid hormone is enhanced by vitamin E (2)

The reason many women develop hypothyroidism during the peri- and menopausal stages is because they have lower progesterone, a vital hormone that activates an important enzyme responsible for thyroid function. Maintaining healthy oestrogen/progesterone balance is also important because oestrogen dominance causes the liver to produce higher levels of a protein called thyroid binding globulin which decreases the amount of thyroid hormone that can be utilised by cells (2)

I'd like to point out here that many of the above nutrients are depleted by relying on processed foods, ongoing stress and taking hormonal birth control.

Food Sources of the Nutrients Required for Optimal Thyroid Health

Iodine: Sea vegetables, seafood, kelp salt

Selenium: Brazil nuts, eggs, legumes, beef, chicken, tuna, sardines

Tyrosine: Protein containing foods – meats, fish, eggs, cheese

Iron: Protein containing foods – meats, dark leafy greens, soaked beans and legumes

Zinc: Red and white meats, soaked chickpeas, spinach

Vanadium: Soaked buckwheat, fresh herbs, olive oil, garlic, tomatoes, onions

Vitamin A: Beef liver, orange vegetables, deep green vegetables, butter, eggs

Vitamin B2, B3, B6: Meat and organ meats, some nuts and seeds

Vitamin D: Fatty fish, eggs, butter, organ meats + the sunshine vitamin

Vitamin E: Almonds, avocado, mango, sunflower seeds, wild caught salmon

Other important factors to take into account:

The Microbiome

About 20% of our thyroid hormone T3 sulphate and T3 acetic acid, must be converted to active T3 by our gut bacteria. Consequently, if significant gut issues are present i.e. lack of the beneficial bacteria that perform this role then potentially one may be more likely to experience the hypothyroid state.


Are substances that disrupt the production of thyroid hormones, and include;

Soy bean derived foods, Cruciferous vegetables – brussel sprouts, broccoli, cabbage, kale, cauliflower, peanuts, radishes, spinach, and millet

These are all nutritious foods that will not usually affect thyroid function in healthy people. However, in some sensitive people who already have low thyroid function eating too many of these foods can potentially make things worse. The aim is to trial a reduction in these foods if suspected to be playing a role – not to eliminate them altogether. Cooking the vegetables, rather than eating them raw helps to reduce the goitrogenic effect.

Gluten Antibodies

Gluten sensitivity has been linked to Hashimoto’s thyroid disease. Gluten is the protein found in wheat, rye, oats, and barley. Research shows that about 16% of people with coeliac disease (an autoimmune reaction to gluten) have antibodies that attack the thyroid too. Some studies have found eliminating gluten reduces these anti-thyroid antibodies, and other studies have found it doesn’t make a difference. It is likely some people are more sensitive than others, however if you are newly diagnosed it may be worth considering a strict 1-month gluten free diet trial.

Note: Gluten free products are not necessary 'healthy' always read the labels. I recommend replacing gluten containing products with wholefoods like Kumara toast, Spiralized zucchini and carrot for pasta etc

Halogens & Other Chemicals

There is some evidence that excess halogens including fluorine, chlorine, or bromine can decrease iodine and inhibit thyroid function.

It is recommended to drink filtered water or mineral water over tap water as the chemicals that it is treated with can negatively impact the microbiome and your thyroid over time.

Agriculture chemicals like the organochlorine insecticides and fungicides are associated with an increased risk of hypothyroidism. Plasticisers including PCB’s & BPA which are found in most cans, food containers and water bottles have direct actions on the thyroid receptor too.

A note here: Iodine can be toxic if supplemented in large amounts – always obtain advice on dosage from a health professional and prioritise meeting your nutritional needs through food sources first (2)

Radiation Exposure

Excessive radiation exposure can affect the thyroid gland so always ask for a body or at least thyroid shield during radiology procedures (2)

Get Moving

Moderate regular exercise is shown to improve cellular sensitivity to thyroid hormone, and can also help manage some of the symptoms of hypothyroidism (2)


Stress can affect your thyroid function in two ways. Unmanaged stress can directly elevate cortisol levels, which feed back and suppress TSH in your midbrain, thereby also suppressing thyroid function. Stress can also indirectly affect thyroid function through adverse effects on sleep.

Disclaimer: Please note that as a Clinical Nutritionist I work primarily with food and lifestyle changes, and on a case by case bases with nutritional supplements as my primary strategy for improving wellness.

The balance of the information in this article is based on my own research gleaned from credible sources and is intended as general information only, NOT personalised advice.

If you would like personalized advice please book a consultation that will result in a unique Treatment plan for you.

This information provided takes a functional/integrative medicine perspective which includes a holistic (nutritional and environmental) approach to improving health and well-being.


1. Saladin, Kenneth (2017) ANATOMY & PHYSIOLOGY : the unity of form and function  [Place of publication not identified] : MCGRAW-HILL

2. Nussey S, Whitehead S. (2001). Endocrinology: An Integrated Approach. Available at  Oxford: BIOS Scientific Publishers


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