Thyroid Diet Guide: What to Eat (and Avoid) for Hypothyroidism

Iodine is the essential mineral most closely associated with thyroid health — it is literally incorporated into thyroid hormone molecules (T4 contains four iodine atoms, T3 contains three). Iodine deficiency is the most common preventable cause of hypothyroidism and intellectual disability worldwide. In developed countries, iodine deficiency has been largely eliminated through iodised salt, but it has made a partial return in some populations — particularly those using non-iodised artisan salts, following strict vegan diets (which may be low in dairy and seafood, the primary dietary sources), or living in iodine-poor regions.

The recommended daily intake for adults is 150 mcg/day (250 mcg for pregnant women). Food sources: seaweed (nori, kelp — though concentrations vary enormously and excessive kelp consumption can paradoxically suppress thyroid function through iodine excess), cod and other white fish (99 mcg per 85 g), shrimp, cow's milk (approximately 100 mcg per cup in iodine-sufficient regions), plain yoghurt, eggs, and iodised table salt (approximately 71 mcg per ¼ teaspoon).

Critical point: more iodine is not better, especially for those with Hashimoto's. The Wolff-Chaikoff effect means that excess iodine can paradoxically suppress thyroid hormone production. People with Hashimoto's autoimmune thyroiditis may be particularly sensitive to iodine excess, and high-dose iodine supplementation can trigger flares. Aim for the RDA from food sources rather than megadose supplementation.

Selenium is the second critical thyroid-specific micronutrient. The thyroid gland has the highest selenium concentration per gram of any organ in the body, for good reason: selenoproteins including glutathione peroxidase and thioredoxin reductase protect the gland from oxidative damage during thyroid hormone synthesis (a process that generates significant hydrogen peroxide). Selenium is also required for the deiodinase enzymes that convert inactive T4 to active T3 in peripheral tissues.

For people with Hashimoto's thyroiditis, selenium has particularly compelling evidence. Multiple randomised controlled trials have shown that selenium supplementation (200 mcg/day as selenomethionine) significantly reduces thyroid peroxidase antibodies (TPO-Ab) — the immune markers of Hashimoto's — compared to placebo, and improves quality of life and mood. The most recent meta-analyses support a meaningful role for selenium supplementation specifically in Hashimoto's management.

Food sources: Brazil nuts are by far the richest source (one nut typically provides 70–90 mcg, so two to three per day meets the RDA of 55–70 mcg). Other sources: tuna, halibut, sardines, pork, beef, eggs, brown rice, and sunflower seeds. Note that selenium toxicity (selenosis) can occur at regular intakes above 400 mcg/day — symptoms include hair loss, nail brittleness, and neurological symptoms. Stick to two to three Brazil nuts daily and avoid megadose supplementation without medical guidance.

Goitrogens are naturally occurring compounds in certain foods that can interfere with thyroid hormone synthesis or iodine uptake. They have generated enormous amounts of anxiety among thyroid patients — much of it disproportionate to the actual risk in people who are iodine-sufficient.

The primary goitrogenic foods are cruciferous vegetables (broccoli, cauliflower, kale, Brussels sprouts, cabbage), soy products, millet, sweet potatoes, cassava, and peanuts. These contain glucosinolates (cruciferous vegetables) or isoflavones (soy) that, at very high doses in iodine-deficient conditions, can suppress thyroid function.

For people eating iodine-sufficient diets (the vast majority of adults in developed countries), moderate consumption of cruciferous vegetables and soy is unlikely to cause meaningful thyroid suppression, particularly when these foods are cooked — cooking deactivates a significant proportion of the goitrogenic compounds. The health benefits of cruciferous vegetables (cancer-protective, anti-inflammatory, high fibre) far outweigh their very modest goitrogenic potential in well-nourished individuals.

The key practical rules: avoid eating very large quantities of raw cruciferous vegetables daily; cook them rather than eating exclusively raw; moderate rather than eliminate soy; and ensure adequate iodine intake to counterbalance any goitrogenic effect. If you have severe hypothyroidism or are on borderline adequate iodine intake, discuss your specific situation with your doctor.

Hashimoto's is an autoimmune condition in which the immune system attacks thyroid tissue. Beyond the selenium evidence discussed above, several dietary considerations are specific to the autoimmune context:

Gluten and Hashimoto's: the relationship is complex and often overstated. Coeliac disease — an autoimmune reaction to gluten — is significantly more common in people with Hashimoto's than in the general population, and undiagnosed or untreated coeliac disease can worsen thyroid autoimmunity. All Hashimoto's patients should be tested for coeliac disease. However, for those without coeliac or diagnosed non-coeliac gluten sensitivity, a strict gluten-free diet has not been consistently shown to reduce TPO antibodies or improve thyroid function in randomised trials. That said, some patients report symptom improvement on a gluten-reduced diet — and given that both share inflammatory and autoimmune pathways, trying a gluten-free diet for 3–6 months is a reasonable experiment when done under dietary guidance.

Dairy: similarly, some Hashimoto's patients report improvement when reducing dairy, possibly due to cross-reactivity between casein and thyroid antigens, or due to undiagnosed lactose intolerance worsening gut inflammation. Evidence is anecdotal rather than from controlled trials.

Anti-inflammatory diet: Hashimoto's is fundamentally an inflammatory autoimmune condition, and a broadly anti-inflammatory dietary pattern — rich in vegetables, fruits, oily fish, olive oil, and legumes; low in ultra-processed foods and added sugar — is supportive of immune regulation regardless of specific food triggers.

Prioritise: oily fish (iodine + omega-3s + selenium); eggs (iodine, selenium, and nutrient density); Brazil nuts (two to three per day for selenium); dairy (iodine, unless avoiding for personal reasons); seaweed in moderation — nori is preferable to kelp due to lower and more consistent iodine content; colourful vegetables and fruits for antioxidants and anti-inflammatory phytonutrients; legumes; whole grains; and extra-virgin olive oil.

Be mindful of: raw cruciferous vegetables in very large quantities — cook them instead; very high iodine foods (kelp supplements, kelp powder) — moderation is key particularly in Hashimoto's; soy in very large amounts (a moderate serving of tofu or edamame is fine for most people); foods containing significant gluten if you have coeliac disease; and millet as a staple grain.

Avoid: ultra-processed foods (drive systemic inflammation that can worsen autoimmunity); foods with very high iodine content if you have Hashimoto's (kelp supplements); gluten if coeliac disease is confirmed; and megadose iodine or selenium supplements without medical supervision.

Important medication interaction: levothyroxine should be taken on an empty stomach, 30–60 minutes before food or other medications. Coffee, calcium supplements, iron supplements, and calcium-rich foods taken within four hours of levothyroxine can significantly impair its absorption — this is one of the most common reasons for suboptimal thyroid hormone levels in treated patients.

Beyond iodine and selenium, several other micronutrients play supporting roles in thyroid physiology:

Zinc: required for the conversion of T4 to active T3 and for normal TSH production. Zinc deficiency is associated with hypothyroid symptoms. Sources: red meat, shellfish (oysters are extremely rich), pumpkin seeds, legumes, and fortified cereals. Vegetarians and vegans are at higher risk of zinc insufficiency.

Iron: thyroid peroxidase (TPO), the enzyme responsible for thyroid hormone synthesis, is an iron-dependent enzyme. Iron deficiency — the most common micronutrient deficiency worldwide, particularly in women of reproductive age — impairs thyroid hormone synthesis. Studies show that treating iron deficiency anaemia alongside hypothyroidism produces better outcomes than treating thyroid disease alone. Sources: red meat, liver, shellfish, legumes, tofu, and dark leafy greens (pairing with vitamin C improves non-haem iron absorption).

Vitamin D: low vitamin D is strongly associated with Hashimoto's and other autoimmune conditions. While causality is not fully established, correcting deficiency (very common in northern latitudes, in winter, and in darker-skinned individuals) is low-risk and broadly beneficial for immune regulation. Supplementation of 1,000–2,000 IU/day is commonly recommended to maintain adequate status.

Magnesium: hypothyroid symptoms include constipation and muscle cramps, and magnesium supports both bowel motility and muscle function. Adequate magnesium also supports the conversion of T4 to T3 indirectly.

Individual foods and nutrients matter, but thyroid health is best supported by overall dietary patterns rather than avoiding single foods or obsessively adding individual supplements. Two dietary patterns have the strongest evidence for supporting thyroid and immune health in the context of autoimmune conditions:

The Mediterranean diet — emphasising vegetables, fruits, whole grains, legumes, nuts, extra-virgin olive oil, and moderate fish and poultry consumption — is broadly anti-inflammatory, nutrient-dense, and provides adequate selenium, zinc, and iodine from food sources. Multiple studies associate Mediterranean diet adherence with reduced inflammatory markers and improved autoimmune condition management.

The Autoimmune Protocol (AIP) diet — a more restrictive elimination diet designed to reduce immune activation by removing grains, legumes, nightshades, dairy, eggs, nuts and seeds, and processed foods — has early but growing evidence in Hashimoto's. A 2019 pilot study published in Cureus found that AIP significantly reduced inflammatory markers and improved quality of life in Hashimoto's patients. The diet is demanding to maintain long-term and should be undertaken with dietitian support.

For most people with hypothyroidism without autoimmune disease, a Mediterranean-style pattern with attention to iodine, selenium, and iron adequacy is the most sustainable and evidence-supported approach. For those with Hashimoto's, the additional autoimmune-specific considerations (selenium supplementation, coeliac testing, possible gluten reduction, anti-inflammatory emphasis) layer on top of this foundation.