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Dr Linia Patel provides an overview of thyroid disease and the role nutrition plays in maintaining a healthy thyroid.

“I have a tough time losing weight because of my thyroid.” You’ve probably heard this complaint time and time again from clients who have thyroid disease – and with good reason too. The thyroid is a small, butterfly-shaped gland that regulates metabolism, but it does more than that. Every cell in the body has receptors for thyroid hormones. So, although tiny, it is a mighty gland.

Thyroid physiology

The thyroid is one of the master controllers that regulates nearly every major metabolic function in the body. It regulates fat and carbohydrate metabolism, respiration, body temperature, cholesterol levels, menstrual cycles, skin integrity, blood calcium levels, functioning of the heart and nervous system and more1.

The thyroid gland secretes a number of hormones. The hormone that is secreted the most (90%) is called thyroxine or T4. T4 has minimal metabolic effects on the body and is therefore considered a prohormone. Triiodothyronine (T3) is the active thyroid hormone but only 7% is produced by the thyroid gland. The rest has to be converted from T4. When produced, T4 is bound to a protein (thyroid-binding hormone) allowing it to be transported around the body. When the T4 reaches the kidney and liver, it is converted to T3. Free T3 then gets into the cells to exert its metabolic effect1. It’s also important to note that about 20% of the thyroid hormone must be converted to active T3 in the gut using an enzyme called intestinal sulfatase, which comes from your beneficial microbes! This means that, if your gut health is out of whack (clinically known as dysbiosis), this may reduce the conversion of the inactive T4 to the active T32.

What happens when the thyroid doesn’t work so well?

Occasionally, the thyroid gland doesn’t release thyroid hormones. This is called primary hypothyroidism or underactive thyroid and is the most common type of hypothyroidism. Approximately 90% of primary hypothyroidism is caused by Hashimoto’s disease, which is an autoimmune disease. An underactive thyroid can slow down metabolism, causing weight gain as well as any of the symptoms in the box below1, 3.

On the other end of the spectrum, hyperthyroidism or an overactive thyroid gland is another common thyroid condition. The most prevalent form is Grave’s disease, in which the body’s autoimmune response causes the thyroid gland to produce too much T4 and T3. Symptoms of an overactive thyroid can include weight loss and high blood pressure, as well as the symptoms in the box below1, 3.

Hypothyroidism Hyperthyroidism
Weight gain Weight loss
Fatigue Fatigue
Feeling cold constantly Sweating and trouble tolerating the heat


Constipation An overactive digestive system – diarrhoea


Joint pain Muscle weakness
Depression, ‘brain fog’, memory loss Anxiety, difficulty concentrating
Coarse, dry hair and skin Hair loss
Puffy face Bulging eyes (exophthalmos)


Infertility, irregular periods Infertility, irregular periods

Women are five to eight times more likely to be diagnosed with hypothyroidism than men, possibly because oral contraceptives, hormone replacement therapy and the hormonal shifts that take place during and after pregnancy, as well as during perimenopause, can all boost risk1. All thyroid issues also have a strong genetic link with other autoimmune disorders such as type 1 diabetes, rheumatoid arthritis, lupus and celiac disease1, 2, 3.

Diagnosis of thyroid issues

As well as taking into consideration the symptoms in the above box, there are various tests that can be done to screen for different thyroid conditions, including blood tests, scans and fine needle aspirations. Once a diagnosis is made, the treatment plan is a spectrum, as not all people need treatment1, 3. Depending on the type of thyroid issue and severity, treatments can include medication, surgery or oral radioactive iodine1. While medical input may be necessary to manage healthy thyroid levels, there are also some lifestyle changes and things you can do to support healthy thyroid function and to reduce the intensity of your symptoms.

Thyroid diet – things to consider

Many nutritional factors play a role in optimising thyroid function. Micronutrient deficiencies and excesses can trigger or exacerbate symptoms6. Food alone won’t cure thyroid issues; however, a combination of the right medication and right nutrients can help restore thyroid function and minimise your symptoms if diagnosed1.


For people with a properly functioning thyroid, iodine is essential as it is required for the production of thyroxine (T4)6, 7. It is a particularly important nutrient in pregnancy, helping with brain development. While in western societies autoimmune disease is the primary cause of thyroid dysfunction, iodine deficiency is the main cause worldwide. The recommended daily intake for iodine in the UK is 150mg per day. Diets that do not include fish, seaweed or iodised salt very often are found to be deficient in iodine.

In the UK, iodine deficiency is considered rare, largely due to the widespread use of iodised salt in the food system. However, the latest National and Dietary Nutrition Survey in the UK shows that iodine intake in women of childbearing age (16 to 49 years) falls short when compared against the World Health Organization criteria8. Both iodine deficiency and excess have consequences and, therefore, supplementation should be approached with caution. Extra iodine, for example, can counteract the benefits of thyroid drugs1, 6. In the UK, eating a balanced diet usually makes taking supplemental iodine unnecessary. Speaking to a medical professional is recommended before supplementation.

Vitamin D

Some studies have shown that people with low levels of vitamin D may have thyroid disorders, but the link is yet to be truly established7. However, that said, the suggested correlation and the vast role of vitamin D in general health is a reminder to ensure that vitamin D levels are kept optimal. Since most people in the UK are deficient, the guidelines advise that adults and children over the age of five take a supplement of 10mcg each day. If you have dark skin or are house bound, then you should consider supplementing with vitamin D throughout the year9.


The highest concentration of selenium in the body is found in the thyroid gland. It’s also been shown to be an essential component of the enzymes that are integral to thyroid function. A number of high-quality studies (i.e., randomised controlled studies) have shown benefits of selenium supplementation in patients with underactive thyroids; however, this effect seems to be more impactful in people with selenium deficiency from the outset10, 11. Incorporating selenium-rich foods such as brazil nuts, seafood and dairy products in your daily diet is key. Before supplementation, have blood levels assessed.

Vitamin B12

Studies have shown that about 30% of people taking thyroid medications experience a vitamin B12 deficiency. This suggests that it is important for people on medication to include foods rich in vitamin B12 such as seafood, dairy, nutritional yeast and fortified cereals in their diets1, 13.


If you have hypothyroidism and have been prescribed thyroid medication (i.e., levothyroxine) to treat hypothyroidism, it is worth noting that some calcium-rich foods (such as dairy) and supplements can interfere with absorption of the drug. Ensure that you leave a gap of four hours between taking the medication and having a calcium-rich meal to ensure there is no significant impact on the thyroid hormone levels1, 13.


Iron supplements can also interfere with the absorption of medication (i.e., thyroxine). If you are taking this medication, it is advised to leave a two-hour gap between taking thyroxine and the iron supplements. Ensure that you check your multivitamin too, as these very often contain some iron1, 13.


Known as goitrogens, there are some foods that block the uptake of iodine from the blood into the thyroid. These foods include cruciferous veggies like broccoli, cauliflower and kale, as well as sweetcorn, peanuts, turnips and cassava. It’s important to note that people with hypothyroidism don’t need to avoid goitrogenic foods. They’re not a problem for everyone. And when they are a problem, the fix is pretty simple. All they need to do is cook these foods, as heating and cooking deactivates most of the goitrogens. In addition, generally, they are not of clinical importance unless they are consumed in large amounts1, 13.

There is still a debate over whether soya is a goitrogen or not. Some evidence shows no effect and some shows that it interferes with the absorption of the thyroid medications. Current recommendation if you do eat soya is to ensure there is a gap of at least four hours between taking thyroxine and when you eat your soy-based food1, 12, 13. Kelp (seaweed), which is naturally high in iodine, is another food that needs to be limited. Although iodine is needed to make thyroxine (T4), if you take more than you need it can cause the thyroid to be overactive. Coffee and high-fibre foods can also affect the absorption of thyroid medications, so it is important to have these foods away from the time of taking thyroid medications1, 13. It is important to speak to your doctor or dietitian to get more tailored advice.

Lifestyle factors

The regulation and metabolism of several hormones, including thyroid hormones, is influenced by total energy intake, sleep cycles and levels of stress, meaning that these factors must also be regulated. Low thyroid is often a sign of the body under stress. When you are stressed, the body produces more cortisol (the stress hormone), which may also reduce the amount of T3 in the body. In addition, not sleeping enough may cause inflammation in your gut, which will affect the balance of good bacteria needed to convert the inactive T4 to active T31, 4, 5. Sleep is also vital in helping to restore many physiological processes in the body, so a lack of it causes the release of cortisol.

Summary and recommendations

Although there are claims about thyroid diets, there is no scientific evidence to back up a single eating pattern. It simply isn’t that simple, as there are so many factors that play a part. However, the following steps are a good place to begin:

  1. Stay away from fads. Don’t drastically restrict calories, especially if you are a woman. Thyroid hormones are very sensitive to your energy intake.
  2. Consume enough iodine. Iodine is fundamental for a healthy and functioning thyroid gland. Foods rich in iodine include seaweed, fish and seafood, dairy products and eggs. Speak to a health professional before supplementation.
  3. Eat a balanced diet, which includes high-fibre carbohydrates. It may not sound as sexy as the latest fad; however, it is fundamental for maintaining a healthy and balanced microbiota and a healthy thyroid. Thyroid and gut disease often co-exist.
  4. Sleep enough. Get seven to eight hours of sleep each night. Sleep is when our body is able to reset. It also helps us manage our stress much better.
  5. Get support from health professionals. If you are experiencing any of the symptoms in the box, request more tests from your GP. In addition, if you are living with a thyroid problem, being aware of what you are eating and how it affects your health is key. A dietitian can work with you to tailor a diet that supports thyroid health.

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About the author

Dr Linia Patel has a BSc degree in biochemistry and physiology and has recently achieved a PhD in public health. Linia is a leading dietitian and sports nutritionist. Her passion is translating nutritional science into easy-to-digest and practical advice.


1.    British Thyroid Association, 1.    Your thyroid gland | British Thyroid Foundation (, accessed on 2 February 2021.

2.    Hanieh-Sadat E (2019), Our Little Friends with Big Roles: Alternations of Gut Microbiota in Thyroid Disorders.

3.    Radetti G (2014), Clinical aspects of Hasimoto’s thyroiditis, Ann Agric Environ Med. 19/27(2): 184-193.

4.    Ihnatowicz P (2020), The importance of nutritional factors and dietary management of Hashimoto’s thyroiditis, Ann, Agric Environ Med. 19/27(2): 184-193.

5.    Fontenelle L (2016), Thyroid function in human obesity: underlying mechanisms, Endocr Metab Immune Disord Drug Targets, 48(12): 787-794.

6.    O Kane M (2018), Micronutrients, iodine status and concentrations of thyroid hormones: a systematic review, Nutr Rev., 76(6): 418-431.

7.    Liontiris M et al (2017), A concise review of Hashimoto thyroiditis (HT) and the importance of iodine, selenium, vitamin D and gluten on the autoimmunity and dietary management of HT patients. Points that need more investigation, Hel J Nucl Med, 20(1): 51-56.

8.    National Nutrition and Dietary Survey, available at 8.    National Diet and Nutrition Survey – GOV.UK (, accessed on 26 January 2021.

9.    Vitamin D Recommendations NHS, 9.    Vitamins and minerals – Vitamin D – NHS (, accessed on 26 January 2021.

10.    Winter et al (2020), Selenium in thyroid disorders – essential knowledge for clinicians, Nat Rev Endocrinol., 16(3): 165-174.

11.    Guatamacchia E (2020), Selenium and iodine in autoimmune thyroiditis, Endocr Metab Immune Disord Drug Targets, 20(3): 344-350.

12.    Pistollato F (2019), Effects of phytochemicals on thyroid function and their possible role in thyroid disease, Horm Metab Res, 1,443(1): 3-19.

13.    Jonklass J (2014), Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement, Thyroid, 24(12): 1,670-1,751.


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