Is there a link between thyroid function and diet? There certainly is. The best-known fact, also acknowledged by conventional medicine, is that iodine deficiency can cause hypothyroidism. Yet, the thyroid gland also needs other nutrients. Moreover, not every kind of hypothyroidism benefits from iodine.
Iodine deficiency as a trigger for hypothyroidism
The thyroid gland produces two hormones: thyroxine (T4) and triiodothyronine (T3). These messenger substances control our energy metabolism, including temperature balance, weight gain or loss and heart rate, bone metabolism and growth in children.
To make T3 and T4, the thyroid needs the trace element iodine. We only need trace elements in tiny amounts – hence the term –, but we do need them, and they have to come from the diet.
Iodine deficiency goitre
If the thyroid gland lacks iodine, it cannot produce sufficient amounts of hormones, causing hypothyroidism in the long term. To compensate for this, thyroid tissue multiplies and a goitre – or iodine-deficiency goitre – develops.
In this day and age, however, the condition has become very rare. Much more common causes of hypothyroidism are inflammation and autoimmune disease, as well as hypothyroidism after thyroid surgery or radiation. If the autoimmune condition Hashimoto’s disease is the underlying reason for an underperforming thyroid, iodine is not the answer and can even make the symptoms worse. For that reason, it is crucial to get the correct diagnosis.
In conventional medicine, the treatment of choice for an underperforming thyroid is medication with l-thyroxine, regardless of the underlying reason. Doctors, therefore, often see no reason to investigate the exact cause of hypothyroid conditions. If you are keen to support your thyroid function with diet alongside your medication, you need to know more.
Thyroid Labs
In routine blood tests, thyroid function is most commonly checked by measuring thyroid-stimulating hormone (TSH) and free T4. If, based on your symptoms, you or your doctor suspect hypothyroidism, the doctor may also tick the box for free T3, but that is often where it ends. Another value of interest is reverse T3 (rT3), which can act as a brake on thyroid function. So, you may end up with ‘adequate’ thyroid values and are told that there is nothing wrong … but you still feel awful. An rT3 reading provides further information and may explain why this is.
A value doctors rarely take because it is unlikely to affect their treatment of your condition are anti-thyroid antibodies, which would indicate the autoimmune condition Hashimoto’s thyroiditis or Hashimoto’s disease.
If you are keen to follow a thyroid-friendly diet after diagnosis, you really need to know.
Unfortunately, Hashimoto’s is incurable. However, with a low-sugar, possibly gluten-free diet, as well as intermittent fasting, you may be able to reduce the symptoms. The underlying strategy is to eat an anti-inflammatory diet that strengthens the immune system.
Gluten tolerance should always be tested in Hashimoto’s patients – intolerance is common. If you are intolerant to gluten or casein, your body produces antibodies against those substances. To those antibodies, your thyroid cells look very much like casein[i]/gluten[ii], and – in a case of mistaken identity called ‘molecular mimicry’ – they start attacking your thyroid. This in itself can trigger and fuel an autoimmune condition.
In this case, avoid cereals containing gluten (wheat, spelt, rye, barley) and instead use gluten-free grains such as buckwheat, quinoa and amaranth. Quinoa or buckwheat in muesli, bread or as a side dish also provide essential minerals and protein.
Foods your thyroid will love
Iodine is not the only nutrient the thyroid needs to make thyroid hormones. Selenium and zinc are also required. Both activate thyroid hormones, and zinc is also necessary to produce TSH. In developed countries, zinc is abundant in food, but selenium deficiency is common as our soils are depleted of this trace element. If selenium is missing, the thyroid hormone triiodothyronine (T3) cannot be activated. The trace element also has an anti-inflammatory effect on Hashimoto’s disease.
Needless to say, I recommend a real food diet to start with – as always. This will give your body what it needs and avoid what it doesn’t. It is always advisable to go for minimally-processed foods.
Protein – at every meal – helps to keep you fuller for longer. Good protein sources are dairy products (if tolerated), fish, meat, pulses and mushrooms.
Vegetables – prepared with high-quality oils, supplemented by low-sugar fruit (such as berries).
Fish – Sea fish such as haddock, plaice, pollock and cod are excellent sources of iodine and omega-3s. Seafood and seaweed also contain the trace element. Doesn’t that sound like sushi makes excellent thyroid food?
Meat – selenium is found in reasonable amounts in pork and offal (liver and kidney).
Eggs – a great source of protein that comes with selenium and iodine, especially in the yolk.
Gluten-free grains and seeds – rice, buckwheat, quinoa – but not millet (see below), chia and flaxseed
Nuts – are good sources of all trace elements. Brazil nuts supply the most selenium; cashews contain iodine.
Other selenium-rich foods are salmon, mushrooms, and wheatgrass powder.
Omega-3 fatty acids – apart from fish, you can get some from high-quality linseed or hemp oil. Note, however, that omega-3s from plant sources alone are not enough. If you do not eat fish, consider supplementing with algae oil, which contains the long-chain omega-3s that you need.
Phytonutrients from colourful vegetables and spices such as dark cocoa, cinnamon, ginger, pepper, turmeric have an anti-inflammatory effect.
Prebiotics (dietary fibre) and probiotics strengthen the intestinal flora. Think sauerkraut, yoghurt, miso, tempeh. An intact intestinal flora may also make losing weight easier.
Drinks: preferably water, coffee (max. 3 cups), herbal tea (fennel, chamomile, dandelion, yarrow, sage) and vegetable juices.
Foods the thyroid is not keen on
Sugar and refined starches – have a pro-inflammatory effect and only serve to fuel the fire. Starch turns into sugar in the digestive process, so its impact is the same. Avoid sugar, sweets, cakes, biscuits, chocolate, ice cream and the like.
Some foods can promote the formation of a goitre. These “goitrogenic” foods interfere with iodine metabolism and thus thyroid hormone production. They include uncooked cabbage and other cruciferous vegetables like broccoli and cauliflower, mustard, radishes, and horseradish as well as soya foods[iii], millet[iv]. To render the goitrogens in the veg harmless, you can cook them. Limit your intake of raw cabbage (think coleslaw), but don’t worry about sauerkraut and kimchi. Here, the fermentation has made the cabbage safe. It’s the same with soya: fermented soya products such as fermented tofu, tempeh, natto or tamari no longer exert a goitrogenic effect.
What about dairy?
Milk and yoghurt are decent sources of selenium and iodine. Cheese provides iodine, too. However, dairy also contains a protein called casein that causes problems in many people. I recommend getting tested. If casein affects your thyroid health, you may feel much better without dairy. Note that sensitivity to dairy is not the same as lactose intolerance. Lactose is a sugar contained in milk. Antibodies are formed only as a reaction to proteins – in this case, casein. So, purchasing lactose-free milk is not going to help!
Strategies for a healthy weight
Body fat and abdominal fat, in particular, contribute to inflammation. A healthy body weight may therefore help reduce the symptoms of impaired thyroid function. Alas, it’s a viscious circle as an underperforming thyroid makes it even harder to lose weight! Intermittent fasting and a low-carbohydrate diet may help.
In intermittent fasting, you could leave 16 hours overnight between dinner and the first meal of the day. If your thyroid is compromised, you may want to be cautious, though. Start very slowly by pushing your breakfast back further and further and fast for 12 hours at first, then 14 hours. Sugar-free drinks such as water, tea and black coffee in moderation are allowed during the fasting phase, as well as two meals a day – but no snacks in between.
This takes a little getting used to, so take your time, all the while monitoring your symptoms. Unfortunately, there is very little research about intermittent fasting for people with an underperforming thyroid. For many, it works a treat, for some, it makes symptoms worse.
- Leech S (1998): Molecular mimicry in autoimmune disease. Arch Dis Child. 1998 Nov; 79(5): 448–451.
- Krysiak R, Szkróbka W, Okopień B (2018): The Effect of Gluten-Free Diet on Thyroid Autoimmunity in Drug-Naïve Women with Hashimoto’s Thyroiditis: A Pilot Study. Exp Clin Endocrinol Diabetes. 2019 Jul;127(7):417-422.
- Doerge DR, Sheehan DM (2002): Goitrogenic and estrogenic activity of soy isoflavones. Environ Health Perspect. 2002 Jun;110 Suppl 3(Suppl 3):349-53.
- Gaitan E, Lindsay RH, Reichert RD, Iet al (1989): Antithyroid and goitrogenic effects of millet: role of C-glycosylflavones. J Clin Endocrinol Metab. 1989 Apr;68(4):707-14.
