Thyroid Foods to Avoid: What Matters With Hypothyroidism and Hashimoto’s

01Iodine

Iodine: too little and too much

The thyroid needs iodine to make hormones, and iodine deficiency is a cause of hypothyroidism worldwide. In countries where diets provide enough iodine, most people with hypothyroidism do not need supplements. Excess iodine, from kelp tablets, seaweed products or high-dose supplements, can trigger or worsen thyroid dysfunction, particularly in people with Hashimoto’s. A review of nutrition in Hashimoto’s thyroiditis highlighted the importance of avoiding both deficiency and excess. Foods with moderate iodine, such as dairy, eggs and fish, are fine as part of a balanced diet.

02Levothyroxine

Foods that affect levothyroxine absorption

• Coffee and espresso: can reduce absorption if taken at the same time.
• Soy products: may reduce absorption.
• High-fibre meals and bran.
• Milk and calcium-rich foods.
• Calcium and iron supplements: separate by at least four hours.
• Antacids and some other medicines.
• Grapefruit juice and some other foods have been reported to interfere.
• A systematic review confirmed that many foods and supplements can affect levothyroxine absorption.

03How

How to take levothyroxine

• Take it at the same time each day, usually in the morning on an empty stomach.
• Swallow with water, not coffee, tea or milk.
• Wait 30–60 minutes before breakfast or coffee, as advised by your doctor or pharmacist.
• Some people take it at bedtime, at least three hours after the last meal; ask your doctor.
• Keep your diet and timing consistent so blood tests reflect your usual routine.
• The NHS describes levothyroxine as the usual treatment for an underactive thyroid.

04Soy

Soy and the thyroid

A review of studies on soy and thyroid function found that soy foods and isoflavones do not adversely affect thyroid function in people with normal thyroid function and adequate iodine intake. However, soy may reduce absorption of levothyroxine, so people taking it may need monitoring if they eat a lot of soy. Rather than avoiding soy completely, keep intake consistent and take your medicine at a separate time.

05Goitrogens

Goitrogens: broccoli, cabbage and kale

Cruciferous vegetables such as broccoli, cabbage, cauliflower, kale and Brussels sprouts contain compounds called goitrogens that, in very large amounts and with iodine deficiency, could interfere with thyroid function. In normal amounts, especially when cooked, they are not a problem and provide fibre, vitamins and other benefits. There is no need to avoid them. Very large amounts of raw kale juice daily may be worth moderating.

06Gluten

Gluten and Hashimoto’s

Coeliac disease is more common in people with Hashimoto’s thyroiditis and other autoimmune conditions. People with coeliac disease must follow a strict gluten-free diet. For people without coeliac disease, evidence that a gluten-free diet improves Hashimoto’s is limited. If you have symptoms such as bloating, diarrhoea, anaemia or weight loss, ask to be tested for coeliac disease before stopping gluten, as removing gluten first can affect test results; see gluten intolerance tests.

07Supplements

Supplements to be careful with

• Kelp and iodine supplements: avoid unless prescribed.
• Biotin: high doses in hair and nail supplements can give misleading thyroid blood test results; stop for a few days before tests if advised.
• Selenium: some studies suggest it may lower thyroid antibodies, but routine supplementation is not recommended, and too much can be harmful.
• Calcium, iron and multivitamins: take at least four hours apart from levothyroxine.
• “Thyroid support” supplements: some contain thyroid hormone or iodine and can be unsafe.

08Limit

Foods to limit for general health

• Ultra-processed foods high in salt, sugar and unhealthy fats.
• Sugary drinks and sweets.
• Alcohol, which affects weight, sleep and liver health.
• These are not thyroid-specific, but hypothyroidism can make weight management harder.
• A balanced diet for hypothyroidism is covered in diet for hypothyroidism.

09Hyper

What about an overactive thyroid?

For hyperthyroidism, the main dietary issue is avoiding excess iodine, especially before radioactive iodine treatment, when a low-iodine diet may be recommended for a short period. Caffeine can worsen symptoms such as a racing heart and anxiety. Follow your specialist’s advice, as recommendations differ from those for an underactive thyroid.

10Cases

Three common situations

• Taking levothyroxine with morning coffee: take the tablet with water and wait before coffee.
• Hashimoto’s and taking kelp tablets for “thyroid support”: stop and talk to your doctor.
• Bloating and anaemia with Hashimoto’s: ask about a coeliac test before changing your diet.

11Summary

Key points to remember

• Avoid excess iodine, such as kelp supplements.
• Separate levothyroxine from coffee, soy, fibre, calcium and iron.
• Normal amounts of broccoli and cabbage are fine.
• Gluten-free diets are needed only for coeliac disease or on medical advice.