Thyroid and Diet: What Actually Matters

By Puja Matharu, Australian Certified Nutritionist Published 2026-08-02 Medically reviewed by Puja Matharu, Australian Certified Nutritionist, on 2026-08-02.

Thyroid conditions attract more bad nutrition advice than almost any other health topic. Search for a thyroid diet and you'll be told to eliminate gluten, avoid all cruciferous vegetables, take iodine supplements and buy a protocol.

Most of that is wrong, and some of it is actively harmful. What follows is what the evidence actually supports — which is narrower and more boring than the internet suggests, and starts with an important framing: diet does not treat thyroid disease. Medication does. Nutrition supports the gland and avoids interfering with treatment.

What the thyroid does

The thyroid produces hormones (T4 and T3) that set your metabolic rate, influencing energy, body temperature, heart rate, digestion, mood and menstrual cycles. Two directions of dysfunction:

Hypothyroidism — underactive. Fatigue, weight gain, cold intolerance, constipation, dry skin, hair thinning, low mood. The most common cause in Australia is Hashimoto's thyroiditis, an autoimmune condition.
Hyperthyroidism — overactive. Weight loss, heat intolerance, palpitations, anxiety, tremor. Usually Graves' disease.

Both are diagnosed by blood test (TSH, free T4, sometimes antibodies) and both are medically managed. If you have the symptoms above and no diagnosis, get the blood test rather than the diet.

The nutrients that genuinely matter

Nutrient	Role	Australian sources
Iodine	The raw material for thyroid hormone	Iodised salt, bread (fortified since 2009), dairy, seafood, eggs
Selenium	Converts T4 to active T3; antioxidant in thyroid tissue	Brazil nuts, seafood, eggs, wholegrains
Iron	Required for thyroid peroxidase; deficiency is common and worsens fatigue	Red meat, legumes, tofu — see iron-rich foods
Zinc	Involved in hormone production and conversion	Oysters, meat, legumes, seeds
Vitamin D	Commonly low in autoimmune thyroid disease	Sunlight, oily fish, eggs, fortified foods
Vitamin B12	Deficiency is more common in Hashimoto's	Animal foods; supplement if plant-based

Iodine is the one to be careful with, in both directions. Too little impairs hormone production; too much can trigger or worsen thyroid dysfunction, particularly in autoimmune disease. Australia fortifies bread with iodised salt precisely because population intake had fallen, so most people eating a normal diet get enough. Do not take high-dose iodine or kelp supplements to "support" your thyroid — kelp in particular can contain wildly variable and sometimes enormous iodine doses. This is one of the few places where a well-intentioned supplement causes real harm.

Similarly with Brazil nuts: two or three a day covers selenium comfortably. A handful daily can push you toward selenium toxicity. More is not better.

If you take thyroid medication, timing matters

This is the most practically useful thing on this page. Levothyroxine absorption is affected by food and by several common supplements:

Take it on an empty stomach, typically 30–60 minutes before breakfast, or at bedtime well after eating — follow your prescriber's instruction.
Separate it by at least four hours from calcium and iron supplements, which bind it and substantially reduce absorption.
Be consistent. Taking it the same way every day matters more than which way you choose, because your dose was titrated against your habit.
Coffee reduces absorption — leave a gap.

People sometimes spend months adjusting their diet when the actual problem was taking their tablet with a calcium supplement. Check this first.

The myths worth dismantling

"Avoid all cruciferous vegetables"

Broccoli, cabbage, kale and cauliflower contain goitrogens, which can interfere with iodine uptake — at intakes far beyond anything achievable by eating vegetables, and largely deactivated by cooking. Unless you're eating raw cruciferous vegetables in genuinely extreme quantities with inadequate iodine, this is a non-issue. These are nutrient-dense foods; keep eating them.

"Everyone with Hashimoto's must go gluten-free"

Coeliac disease is more common in autoimmune thyroid disease, so it's reasonable to be tested — while still eating gluten, or the test is unreliable. But blanket gluten elimination without coeliac disease isn't supported for thyroid outcomes, and it removes a fortified iodine source in Australia, where bread is a major iodine contributor.

"Soy destroys thyroid function"

In people with adequate iodine and normal thyroid function, soy foods don't cause thyroid problems. If you take levothyroxine, separate it from soy as you would from other foods.

"A thyroid diet will fix your weight"

Once thyroid hormones are adequately replaced, metabolic rate largely normalises, and weight then responds to the same things it does in anyone else. If weight isn't shifting despite well-controlled thyroid levels, the answer is in why weight loss stalls, not in a thyroid protocol.

This page is general nutrition education. Thyroid disease is diagnosed and treated medically — nothing here replaces your GP or endocrinologist, and nothing here should prompt you to change or stop medication. If you're pregnant or planning pregnancy, iodine requirements rise and supplementation is routinely recommended in Australia; that's a conversation for your GP.

Where to start

Check your medication timing against the list above — it's free and it's the most common fixable problem. Use iodised salt at home and don't take iodine supplements without being told to. Ask your GP about iron, vitamin D and B12, which are commonly low and commonly explain residual fatigue after thyroid levels are corrected.

Then eat like everyone else should: the pattern in the Australian Dietary Guidelines, with enough protein and fibre. There is no special thyroid diet beyond that.

Frequently asked questions

What foods are good for thyroid health?

The nutrients that matter are iodine (iodised salt, bread fortified since 2009, dairy, seafood, eggs), selenium (Brazil nuts, seafood, eggs), iron, zinc, vitamin D and B12. Beyond adequate intake of these, there is no special thyroid diet — the standard Australian Dietary Guidelines pattern is the right target.

Should I take an iodine supplement for my thyroid?

Not without medical advice. Too little iodine impairs hormone production, but too much can trigger or worsen thyroid dysfunction, particularly in autoimmune disease. Australia fortifies bread with iodised salt, so most people eating a normal diet get enough. Kelp supplements in particular can contain very large and variable iodine doses.

Do I need to avoid broccoli and cabbage with a thyroid condition?

No. Cruciferous vegetables contain goitrogens that can interfere with iodine uptake, but only at intakes far beyond anything achievable by eating vegetables, and cooking largely deactivates them. These are nutrient-dense foods and there is no reason to avoid them.

When should I take levothyroxine relative to food?

On an empty stomach, typically 30 to 60 minutes before breakfast or at bedtime well after eating, following your prescriber's instruction. Separate it by at least four hours from calcium and iron supplements, which bind it and substantially reduce absorption. Coffee also reduces absorption. Consistency matters more than which option you choose.

References

Get this applied to your body, not the average one

Everything above is general guidance. Our AI nutritionist turns it into a plan built around your goals, your preferences and your history — and a certified nutritionist is there when you need a human.

Try it free Book a consultation

General nutrition information only — not medical advice, diagnosis or treatment. See our health disclaimer.