Underactive thyroid - how much does diet matter?

Emma Brown - Nutritionist | 14 Jun, 2017

Our thyroid gland is important for secreting hormones involved in maintaining a healthy metabolism.

Thyroxine is a hormone which is produced naturally in the body by the thyroid gland. Having too little thyroxine or too much thyroxine can cause health problems.

  • Hyperthyroidism means your thyroid gland is overactive – this can lead to a faster metabolism and weight loss.
  • Hypothyroidism means your thyroid gland is underactive – this can lead to a slower metabolism and weight gain.

If you've been diagnosed with an underactive thyroid...

....you will usually be prescribed with medication (such as Levothyroxine) which is a synthetic version of thyroxine to boost your natural hormone to the right level. The correct dosage will be determined by your GP on the basis of your blood test results. Having an underactive thyroid is sometimes blamed for having difficulty in losing weight, but once your condition is being treated with medication, there is no reason why you shouldn't be able to manage – or lose – weight as normal. The medication effectively replaces the deficiency in your body and restores your hormone levels back to what they should be.

There isn't a particular diet you can follow to help manage hypothyroidism as such – but certain foods can affect how your medication is absorbed, so it's worth being aware of these.


1. Broccoli

Vegetables such as broccoli and cabbage contain chemicals which can affect thyroid hormone synthesis. So eating very large amounts of these vegetables could potentially affect your thyroid function and reduce absorption. But it's unlikely that many people in the UK with hypothyroidism would actually be eating large enough amounts to do this, and these are an important vegetable group for other nutrients in the diet.


2. Milk

The calcium in foods such as cow's milk and yogurt can impact the absorption of thyroxine medication. For this reason it's recommended to separate the consumption of calcium-rich foods and your medication by around 4 hours.


3. Seaweed

This is naturally high in iodine – and although we need enough iodine to ensure our thyroid gland functions as it should, too much iodine can have the opposite effect.


4. Soya

It is possible the plant hormones found in soya could impact on the absorption of thyroxine – so people taking this mediation are advised to avoid soya products if possible, or leave a long time between taking medication and eating soya.

Nutritionist Emma Brown (ANutr), MSc Human Nutrition is passionate about how food science applies to the human body, and how the nutrients in what we eat affect us and ultimately have an impact on our health.