Hypothyroidism (underactive thyroid)

Written by Bonnie Gifford
Bonnie Gifford
Nutritionist Resource Content Team

Last updated 22nd July 2022 | Next update due 21st July 2025

Hypothyroidism is a medical condition where the thyroid isn't producing enough hormones. Also known as an underactive thyroid, symptoms typically include weight gain, feeling low, and tiredness.  Here, we will look at how nutrition and diet affect thyroid function, and how a balanced diet can help to manage conditions linked to hypothyroidism.

What is hypothyroidism?

Having an underactive thyroid (hypothyroidism) means your thyroid gland doesn't produce enough hormones. This can leave you feeling tired, depressed, and can cause weight gain. Anyone can develop the condition at any age, although it is more commonly seen in women. Around 5-10% of those who give birth will experience hypothyroidism in the following months. For many, this will fade over time, while others will experience it permanently.  Babies born in the UK are screened for congenital hypothyroidism at five days old.

In the UK, hypothyroidism affects around 2% of the overall population, and 5% of those aged 60 and over. Some studies now think that around 2.2 million in the UK may have hypothyroidism, with an estimated one in 20 having some kind of thyroid issue. 

When should I speak to my GP?

If you suspect you have an underactive thyroid problem, be sure to visit your GP for a diagnosis. Hypothyroidism can be treated by taking tablets prescribed by your GP to replace the hormones that your thyroid is struggling to produce.

Signs and symptoms of an underactive thyroid

Symptoms of hypothyroidism can be similar to many other conditions. Often developing slowly over time, it can take years for you to take note that something may be wrong. For example, some people may confuse symptoms of menopause with symptoms of an underactive thyroid. 

If you experience a combination of any of the following symptoms, it could be worth asking your GP to be tested. The only accurate way to find out if you have a thyroid problem is to have a blood test (a thyroid function test) to measure your hormone levels. 

Symptoms to look out for can include:

  • being sensitive to the cold (particularly hands and feet)
  • constipation 
  • dry skin 
  • dry and thinning hair
  • depression
  • decreased sweating
  • tiredness
  • muscle aches, weakness, stiffness or tenderness
  • slower heart rate
  • weight gain 
  • joint pain or stiffness

Without treatment, an underactive thyroid could lead to a number of complications. These can include:

  • heart disease
  • goitre (a swelling of your thyroid which results in a lump at the front of your neck)
  • problems during pregnancy (anemia)
  • fertility difficulties
  • heavier or irregular periods (menstrual changes)
  • a puffy, sensitive face
  • hoarseness
  • myxoedema coma (an extreme and rare complication which can result in fatigue, hynothermia, low blood pressure, low heart rate, and in rare cases, death)

Amongst children and teens, hypothyroidism can also lead to slower development. 

Nutrition professionals who can help with thyroid problems

What causes an underactive thyroid?

There are a number of different common causes for hypothyroidism, including iodine deficiency, medication, radiation therapy, thyroid surgery, radioactive iodine treatment, or Hashimoto's thyroiditis. Less common causes can include pregnancy, congenitial disease, pituitary disorders, and de Quervain thyroiditis. 

How can you treat an underactive thyroid?

If you receive an official diagnosis of hypothyroidism, you will be prescribed a daily hormone replacement tablet to raise your thyroxine levels. Initially, you will need regular blood tests while your GP helps you find the right dose that works for you. Once this has been achieved, you will need a single blood test each year to monitor your hormone levels. 

Treatment typically lasts for the rest of your life. However, with proper treatment and support, you can live a normal, healthy life.  

Developing coping strategies to help you manage feelings of fatigue can be helpful. Ensuring you eat enough fruit and vegetables, get good quality sleep each night, and have a healthy self-care routine can all help. 

Research has suggested that eating a balanced diet can help to counter some of the symptoms of an underactive thyroid. Ensuring you have enough iodine-rich foods (seaweed, seafood, eggs, dairy, and iodized salt) can be a big help. 

What is a hypothyroidism diet?

There is lots of conflicting information regarding nutrition and thyroid problems, however, it is widely believed that the best hypothyroidism diet is one that is varied and balanced.

Eating a well-balanced diet rich in nutrients will improve your overall health, including your thyroid health. If you choose to take supplements, be sure to get advice from your doctor or suitably qualified nutrition professional. They will be able to advise you on whether or not you need supplements and how much so as to not interfere with your thyroid medication.

While specific foods are not thought to be helpful for those with thyroid problems, there are considerations to make, especially if you are taking medication. Below we list some common hypothyroidism diet queries and advice outlined by the British Thyroid Foundation:

Should I avoid too much calcium?

Calcium should be included as part of a balanced diet. However, some foods that are rich in calcium (or calcium supplements) can interfere with levothyroxine absorption.

If you are eating something rich in calcium or taking a supplement, you may be advised to leave a gap of four hours between this and your medication to ensure there is no significant impact on your blood thyroxine levels. If you are unsure, ask your doctor for advice.

Should I avoid soya?

Soya can interfere with thyroxine absorption. If you are taking thyroxine, then you may be advised to avoid soya altogether. Alternatively, you may be advised to leave a long gap between eating soya and taking thyroxine.

Foods high in soy include vegan cheeses and meats, soy milk, soy sauce, tofu, and soybeans. 

Do I need iodine supplements?

The thyroid gland needs iodine to function normally, so some people believe it is necessary to take iodine supplements. Generally, it is advised that those with hypothyroidism avoid supplements high in iodine as it can make the condition worse. In some people, it may even provoke hypothyroidism/hyperthyroidism.

Adults require 150mcg of iodine per day, which can be obtained from a balanced diet. Too little iodine can result in Goitre, thyroid enlargement. In the UK, however, Goitre is not typically due to iodine deficiency.

If you are unsure about how to get the recommended amount of iodine in your diet, or about which foods contain iodine, speak to a nutrition professional.

Can I take iron tablets?

Some medications that contain iron can interfere with the absorption of thyroxine. Because of this, some doctors advise a two-hour interval between taking iron and thyroxine. Follow your doctor's advice regarding this, and remember that some multivitamin tablets contain iron.

Should I avoid brassicas?

Brassicas or cruciferous vegetables include cabbage, broccoli and swede. When eaten in very large amounts, it has been suggested that thyroid health may be affected. The risk however is low, as long as you are consuming these types of vegetables in moderation as part of a well-rounded diet.

With conditions like hypothyroidism, seeking expert advice is always recommended. Use our search tool to find a nutrition professional who can help.

Risk of heart disease and diabetes

As many of us are aware, weight gain leads to an increased risk of heart disease. Those with an underactive thyroid may be at a higher risk of heart disease due to complications from potential weight gain, but also due to other factors resulting from low levels of thyroid hormones. Low levels of thyroid hormones raise blood pressure and increase cholesterol and triglyceride levels.

Normalising thyroid hormone levels can in turn normalise cholesterol levels, so seeking treatment is key. Eating a heart-healthy diet and maintaining a healthy weight is also recommended for those at risk.

A strong relationship has been found between thyroid problems and diabetes. According to the British Thyroid Foundation, of those with type 2 diabetes, 12.5% have thyroid disease compared to a 6.6% prevalence of thyroid disease in the general public.

Hypothyroidism and hyperthyroidism (overactive thyroid) both affect carbohydrate metabolism and affect glucose control. To ensure your diet is in line with any additional risk or condition you have, you are advised to speak to a nutrition professional.

Lifestyle changes

Weight management

For many people with hypothyroidism, weight management can be difficult. A prominent symptom of an underactive thyroid is abnormal weight gain and difficulty losing weight.

Once the medication has stabilised your hormone production, you should find it easier to manage your weight. To support this, focusing on your health and eating nutritious foods is imperative.

Sticking to the principles of a balanced diet is recommended. This means eating plenty of whole fruits and vegetables, lean protein and whole-grain carbohydrates, and limiting processed foods. You can find out more on our weight management page.


When addressing thyroid health, it is important to look at lifestyle changes you can make to improve your overall health. A key factor in this is exercise. An underactive thyroid can cause weight gain, depression and fatigue. All of these symptoms can benefit from physical exercise.

As well as helping to manage symptoms, exercising is known to have a positive effect on your metabolism, which is affected by thyroid problems.

If fatigue is making it difficult to exercise, you are advised to start with gentle exercises, such as walking or yoga. As your treatment progresses, you may wish to increase your activity levels even more. This will complement your hypothyroidism diet changes to improve your overall health and well-being.


Having hypothyroidism can make you feel lethargic and easily overwhelmed. Because of this, it is helpful to manage your stress levels. Try to incorporate some form of relaxation into your daily routine.

Managing your stress levels can help to improve symptoms of depression that may be caused by your condition. You can find out more about how diet affects stress levels on our nutrition for stress page. 

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