The Best Foods to Eat for Thyroid Health (And What to Cut Back On)
What you eat has a profound effect on how well your thyroid functions — yet diet is one of the most overlooked aspects of thyroid health in conventional care. As a naturopath, I work with a lot of women who have been diagnosed with hypothyroidism or Hashimoto's and haven't been given any dietary guidance at all beyond "take your medication." That's a missed opportunity, because the right nutrition can meaningfully support thyroid hormone production, conversion, and immune regulation — and it can make a significant difference to how you feel on a day-to-day basis. In this article I want to give you a practical, evidence-informed guide to eating for thyroid health: what to include, what to limit, and why it matters.
Why Diet Matters for Thyroid Health
The thyroid gland relies on specific nutrients to produce its hormones. Without them, hormone production is compromised regardless of how well your thyroid gland itself is functioning. Additionally, the most common cause of hypothyroidism in Australia is Hashimoto's thyroiditis — an autoimmune condition — and diet has a significant influence on immune function, gut health, and systemic inflammation, all of which drive autoimmune activity. The gut also plays a surprisingly important role in thyroid health. Approximately 20% of the conversion of T4 (the inactive thyroid hormone) to T3 (the active form) happens in the gut via bacteria and enzymes. Poor gut health — including dysbiosis, leaky gut, or chronic inflammation — can impair this conversion and worsen hypothyroid symptoms even when thyroid test results appear acceptable. I explore the gut-thyroid connection more deeply in my article on how to improve your gut health.
Foods That Support Thyroid Function
Brazil nuts are one of the most important foods for thyroid health because of their exceptionally high selenium content. Selenium is required for the conversion of T4 to active T3, and it helps protect the thyroid gland from oxidative damage caused by hydrogen peroxide, which is produced during hormone synthesis. Just two to three Brazil nuts per day provides an adequate selenium intake for most people — making them one of the most cost-effective nutritional interventions available. Eggs are a nutritional powerhouse for the thyroid. They contain selenium, zinc, iodine, and tyrosine — all of which are directly involved in thyroid hormone production. The yolk is particularly nutrient-dense, so I always recommend eating the whole egg rather than egg whites only. Women who avoid egg yolks to reduce fat intake may be inadvertently limiting some of their best thyroid-supportive nutrients. Seafood and fish provide iodine (essential for thyroid hormone synthesis) as well as selenium and omega-3 fatty acids. Sardines, mackerel, salmon, oysters, and prawns are particularly rich sources. If you're vegetarian or vegan, iodine is harder to source from food, and supplementation may be warranted — but always under guidance, as too much iodine can worsen Hashimoto's in susceptible individuals. Dark leafy greens like spinach, silverbeet, and lightly cooked kale provide iron, which is required for thyroid hormone synthesis, as well as magnesium and folate. Fermented foods like yoghurt, kefir, kimchi, sauerkraut, and miso feed beneficial gut bacteria and support the gut health that is essential for T4 to T3 conversion.
Key Nutrients and Where to Find Them
Iodine is essential for thyroid hormone production — the hormones T3 and T4 contain three and four iodine molecules respectively. Good Australian dietary sources include seafood, eggs, and dairy products. Kelp and seaweed are extremely concentrated sources and should be used cautiously, particularly in Hashimoto's. Selenium is critical for thyroid hormone conversion and for reducing thyroid antibody levels in Hashimoto's. Beyond Brazil nuts, you'll find selenium in eggs, fish, meat, and whole grains. Blood testing can confirm whether you're adequate or deficient. Zinc supports thyroid hormone receptor function and T4 to T3 conversion. Good sources include red meat, shellfish (especially oysters), pumpkin seeds, and legumes. Zinc deficiency is surprisingly common and can worsen hypothyroid symptoms even when hormone levels appear normal on standard testing. Iron deficiency is very common in premenopausal women and significantly impairs thyroid hormone synthesis. Lean red meat, chicken liver, sardines, legumes, and dark leafy greens are excellent sources. If you're taking thyroid medication, take it well away from iron supplements as they compete for absorption.
What to Limit or Avoid
Raw cruciferous vegetables in very large quantities can interfere with iodine uptake into the thyroid gland. This includes raw kale, raw cabbage, raw broccoli, and raw cauliflower. This doesn't mean avoiding them entirely — these are nutrient-dense foods — but cooking or lightly steaming them deactivates the goitrogenic compounds. Moderate amounts of raw cruciferous vegetables are generally not a problem for most people with hypothyroidism. Gluten deserves mention for anyone with Hashimoto's. There is a well-documented association between Hashimoto's and coeliac disease due to molecular mimicry — the immune system can confuse thyroid tissue with gliadin (a gluten protein) due to their similar structure. Research suggests that a strict gluten-free diet can reduce TPO antibody levels in women with Hashimoto's who don't have coeliac disease. For some women, this alone leads to significant symptom improvement. Ultra-processed foods, seed oils, and foods high in refined sugar promote systemic inflammation, which drives autoimmune activity and worsens thyroid function. They also tend to displace the nutrient-dense whole foods that the thyroid depends on. Soy in large quantities can interfere with thyroid hormone absorption and should be taken well away from thyroid medication.
Anti-Inflammatory Eating for Hashimoto's
Because Hashimoto's is an autoimmune condition, reducing systemic inflammation is a cornerstone of dietary management. An anti-inflammatory approach emphasises colourful vegetables and fruits, oily fish, olive oil, nuts and seeds, and herbs like turmeric and ginger, while minimising processed foods, sugar, and refined carbohydrates. Omega-3 fatty acids from oily fish and flaxseeds are particularly useful for modulating immune responses. Aiming for three serves of oily fish per week, or supplementing with quality fish oil, is a reasonable approach for women with Hashimoto's. Research shows that adequate omega-3 intake is associated with lower inflammatory markers and reduced autoimmune activity over time.
Iodine Supplementation: A Word of Caution
Iodine supplementation is often promoted for thyroid health, but it requires careful consideration. While iodine deficiency does impair thyroid function, excess iodine can trigger or worsen autoimmune thyroid disease in susceptible individuals. High-dose iodine supplementation has been shown to increase TPO antibody levels in women with Hashimoto's. My approach is to ensure adequate dietary iodine first, and only supplement with practitioner guidance if testing reveals deficiency.
Putting It on Your Plate
A thyroid-supportive plate looks like this: a good portion of quality protein (fish, eggs, or lean meat), a generous serve of cooked vegetables including some dark leafy greens, a source of complex carbohydrate like sweet potato or brown rice, and a small amount of healthy fat like olive oil, avocado, or a handful of nuts or seeds. One to two Brazil nuts alongside your meal provides your selenium for the day. A fermented food like yoghurt or a small serve of kimchi on the side supports your gut microbiome and hormone conversion. This kind of eating is straightforward, sustainable, and genuinely supports the nutrients your thyroid depends on every day.
Would You Like Personalised Guidance?
If you've been struggling with thyroid symptoms and want to understand how your diet, gut health, and nutrient status may be contributing, I'd love to work with you. A naturopathic approach that works alongside your medical treatment can meaningfully improve how you feel — not just on paper but in day-to-day life. If you're managing your thyroid condition and want to understand more about the bigger hormonal picture, read about hypothyroidism and what to do when results come back normal. Book a free introductory call to find out how naturopathic nutrition can support your thyroid health.The Impact of Other Hormones on Thyroid Function
Thyroid health doesn't exist in isolation. Your thyroid hormones interact with virtually every other hormone in your body, and deficiencies or imbalances elsewhere can significantly affect how well your thyroid functions — even if the thyroid gland itself is working adequately.
Oestrogen directly affects thyroid function in several ways. Elevated oestrogen increases thyroid-binding globulin (TBG), a protein that binds to thyroid hormones in the bloodstream and renders them inactive. Even if your body is producing adequate T4 and T3, elevated oestrogen means less free, active hormone is available to your cells. This is one reason why women in perimenopause — where oestrogen fluctuates unpredictably — often notice worsening thyroid symptoms even when their tests appear stable. If you're experiencing both hormonal and thyroid symptoms, reading about the symptoms of oestrogen dominance may provide useful context.
Cortisol, the primary stress hormone, suppresses the conversion of T4 to active T3 and promotes the production of reverse T3, an inactive form that competes for receptor sites. Chronic stress is therefore a direct physiological impediment to optimal thyroid function — which is why women under sustained high stress often feel increasingly hypothyroid even when their medication dose hasn't changed. Managing your stress response is not optional if you want your thyroid to function well; it's a core part of the treatment picture. I've written about this in detail in my post on how to lower cortisol levels.
Insulin resistance also impairs thyroid function by increasing inflammation and disrupting hypothalamic-pituitary signalling. Maintaining stable blood sugar through a protein-rich, fibre-adequate diet, regular meals, and appropriate exercise is therefore another lever you can pull for thyroid health.