The thyroid diet

Thyroid Health

In the third part of our autoimmune disease series, we look closely at autoimmune thyroid disease and explain more about the 'thyroid diet' in order to help optimise and maintain a healthy and functional thyroid.

21/02/2019


Emily Condon
BSc (Hons) Biological Sciences

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Autoimmune thyroid disease

According to the British Thyroid Foundation, 1 in 20 people is affected by a thyroid disorder in the UK [1]. There are a number of different thyroid conditions that can influence the normal functioning of the thyroid. Although not always, commonly the cause is due to an autoimmune thyroid disease which occurs when the body’s immune system attacks the thyroid cells as though they were foreign cells. In response, the thyroid gland either becomes underactive (hypothyroidism) or overactive (hyperthyroidism). 

Although autoimmune disease is often to blame for thyroid disease, diet also plays a significant role in thyroid health. Scientific research is ongoing in order to better understand the exact impact of foods and nutrients on thyroid health, but there is some evidence for how a few specific food types affect thyroid function.

Gluten free diet 

Having one autoimmune disorder also puts you at higher risk of developing other autoimmune disorders, because of this, the risk of developing coeliac disease is higher in those with an autoimmune thyroid disease. In those with coeliac disease, the immune system mistakes gliadin, one of the substances that make up gluten, as a threat to the body. Tiny tube-shaped growths called villi which cover the intestines surface, are damaged reducing their ability to absorb key nutrients from food. Gluten is the protein found in wheat and some other grains, the molecular structure of gliadin is similar to the molecular structure of the thyroid gland [2].

In those with a gluten sensitivity or coeliac disease, when gliadin passes the protective barrier of the gut and enters the bloodstream, the immune system tags it with antibodies for destruction. Because of the similar structures, immune system can mistake the thyroid for gluten, causing it to also come under attack. It is important to note that not everyone with a thyroid condition is sensitive to gluten. While research on the relationship between gluten and the thyroid is still ongoing, gluten may act as a trigger for the immune response against the thyroid in those who are already sensitive to gluten. Speak to your doctor before making any major dietary changes.

The thyroid diet

We spoke to nutritionist Effie Parnell-Hopkinson and asked her if there are any particular foods that can aid thyroid function and keep it healthy:

“There are no specific diets or food groups that are proven to eliminate thyroid disease or hypothyroidism, but by following a thyroid-friendly diet you can help minimise your symptoms and help you maintain a healthy weight as it encourages eating whole, unprocessed foods and lean protein. There are several nutrients that are important to optimise and maintain a healthy and functional thyroid. The top three nutrients include iodine, selenium and zinc, and these can all be obtained through consuming a varied and balanced diet.

Iodine

Iodine is an essential nutrient needed to make thyroid hormones and consequently, iodine deficiency leads increases the risk of developing hypothyroidism [3]. Iodine supplements are not necessary as it is possible to get enough iodine from your diet alone, however, if you are you do not consume many iodine-rich foods it is a convenient method to top your levels up [4]. By eating seaweed, white fish, dairy and eggs you can provide your body with enough iodine for normal thyroid function [5]. Adding iodised table salt to your food will also help to meet your iodine requirements, however, as government recommendations are to reduce salt intake for health reasons, you should not rely on iodised table salt as a means of increasing your iodine intake. 

If you have thyroid disease, are taking other medication, or have experienced iodine deficiency over many years, you should speak to your GP before taking additional iodine. The recommended daily amounts of iodine are 150 mcg/d for adults and 200 mcg/d for pregnant and breastfeeding women (based on the European Food Safety Authority (EFSA) recommendations).

Too little iodine can have negative effects on thyroid health and function and in particular lead to thyroid swelling (a goitre). There have been foods identified as goitrogenic, meaning they can interfere with iodine uptake in the thyroid gland and interfere with the synthesis of thyroid hormones. These include cruciferous vegetables such as bok choy, broccoli, brussels sprouts, cabbage, cauliflower, chinese cabbage, collard greens, kale and turnips. The rosaceae family of fruits, which includes almonds, apricots, cherries, peaches, pears, plums, raspberries, and strawberries, are also goitrogenic. The goitrogen content of foods can be reduced through steaming or boiling.

Selenium

Selenium is another essential nutrient that is used by the body to regulate the thyroid hormones and can be found in foods such as brazil nuts, fish, eggs and meat. The DRV for selenium is set at 60 mcg/d for women and 70 mcg/d for men, aged 19-64 respectively [6]. Similar to iodine, the amount of selenium available through a varied and balanced diet is sufficient to negate the necessity of supplementation. Low levels of selenium have been linked with an increased risk of hypothyroidism, goitre and Hashimoto's thyroiditis [7]. 

Experts recommend no more than 400 mcg/d of selenium from all sources, including food, vitamins, and supplements, in order to avoid toxicity, however, you should speak to your GP before taking any additional selenium.

Zinc

Zinc is an essential nutrient meaning that the body cannot produce or store zinc alone and needs to consumed through the diet on a daily basis. Zinc is required for metabolic function, the production of thyroid hormone, the regulation of TSH (the hormone that signals the thyroid gland to release thyroid hormones) [8] and has also been shown to increase the levels of thyroid hormone in people with goiters [9].

The recommended daily values for zinc are 9.5 mg and 7.0 mg for men and women, respectively. Zinc is widely available through a varied diet and again, negates the need for a supplement to aid in achieving the recommended values. Good sources of zinc include meat such as chicken and beef, shellfish, bread, dairy and cereal products.

Thyroid diet

The best way to optimise your diet for healthy thyroid function is to eat a varied and balanced diet rich in meat, seafood, dairy, eggs, vegetables, fruits and gluten-free grains. Foods that should be eaten in moderation include foods that contain gluten, soy products, cruciferous vegetables (cooking further lowers the risk) and caffeinated beverages. If you are taking thyroid medication please always speak to your doctor before supplementing iodine, selenium or zinc."


[1] Foundation, B. (2019). Thyroid disorders affect one in twenty people in the UK. Could you be one of them? - British Thyroid Foundation. [online] Btf-thyroid.org. Available at: http://www.btf-thyroid.org/8-general/2-thyroid-disorders-affect-one-in-twenty-people-in-the-uk-could-you-be-one-of-them [Accessed 19 Feb. 2019].

[2] Vojdani, A., O'Bryan, T. and Kellermann, G. (2008). The Immunology of Gluten Sensitivity beyond the Intestinal Tract. European Journal of Inflammation, 6(2), pp.49-57.

[3] Zimmermann, M. B. & Boelaert, K. (2015). Iodine deficiency and thyroid disorders. Lancet Diabetes Endocrinology, 3(4): 286-95.

[4] National Health Service (2016). Vitamins and Minerals: Iodine. https://www.nhs.uk/conditions/vitamins-and-minerals/iodine/

[5] The British Dietetics Association (2015). Food Fact Sheet: Iodine. https://www.bda.uk.com/foodfacts/Iodine.pdf

[6] Public Health England (2016). Government Dietary Recommendations Government: recommendations for energy and nutrients for males and females aged 1-18 years and 19+ years. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/618167/government_dietary_recommendations.pdf

[7] Ventura, M., Melo, M., & Carrilho, F. (2017). Selenium and Thyroid Disease: From Pathophysiology to Treatment. International Journal of Endocrinology, 1297658.

[8] Maxwell, C & Volpe, S. L. (2007). Effect of zinc supplementation on thyroid hormone function. A case study of two college females. Annals of Nutrition and Metabolism, 51(2), 188-94.

[9] Kandhro, G. A. et al. (2009) Effect of zinc supplementation on the zinc level in serum and urine and their relation to thyroid hormone profile in male and female goitrous patients. Clinical Nutrition, 28(2), 162-168.

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