Hyperthyroidism in cats - Diet for cats with hyperthyroidism (2023)

Hyperthyroidism is a surprisingly common condition in cats, and you’re sure to have some questions about how to manage it. Here we look at the different options and speak to clinical animal nutritionist Marge Chandler for her advice on dietary changes.

How will I know if my cat has an overactive thyroid?

The thyroid glands in your cat’s neck produce a hormone called thyroxine, which helps the kidneys, liver, brain and digestive system to function well. If your pet’s thyroid glands produce too much thyroxine, her metabolism will speed up, which can make her either hyperactive or sluggish. This is called hyperthyroidism. Although this condition can affect cats of any age, it’s more common in older pets.

If your cat has an overactive thyroid she could appear anxious and agitated, and may spend a lot of time dashing around in an unexpected way. Your cat may also want to eat and drink more, however, as the condition can make it harder for her body to absorb nutrients, her coat might look dull and unkempt. (A small number of cats with hyperthyroidism appear tired and lethargic instead, so make sure to look out for any unusual changes in your pet’s usual behaviour.) You might also notice your cat being more vocal than usual, and possibly panting. Diarrhoea, vomiting and weight loss can also be signs.

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What causes the thyroid gland to change?

In most cases hyperthyroidism is caused by a non-cancerous tumour somewhere on the thyroid gland. However, in very rare cases the tumour can develop into thyroid cancer.

What are the most common kinds of treatment?

As your vet may have mentioned, there are a number of treatment options for hyperthyroidism. Different treatments suit different pets, and while surgery and radioactive-iodine therapy can provide a permanent cure, they are not always the best way for older cats. Although it isn’t covered under your Petplan insurance, another option is to give your cat a low-iodine diet to stop the thyroid glands producing thyroxine, alongside her daily medication.

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Can dietary changes help?

Yes. Giving your cat a low-iodine diet can help ease the symptoms of hyperthyroidism, as iodine controls how active the thyroid glands are.

However, low-iodine diets have to be followed to the letter to be successful. That means making sure your cat doesn’t eat any special treats, and prey such as birds or mice. This can be tricky because your cat may not enjoy eating a low-iodine diet, and it can be challenging to stick to. If you try to mix a low-iodine food plan with your cat’s regular food, the uncomfortable signs of hyperthyroidism are likely to continue. To help lower the amount of iodine your cat takes in, try to avoid products such as supplements, some flavoured medications, and human food.

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Does my cat need to eat more?

Cats with hyperthyroidism can lose a noticeable amount of weight, especially older cats who may already find it more difficult to absorb essential nutrients. Generally, cats with overactive thyroid glands need a high-calorie diet with enough fat, and plenty of high quality, animal-based protein. Speak to your vet or an animal nutritionist about the best sources of these nutrients. But there are no other specific vitamins or minerals that a cat with hyperthyroidism needs.

What else should I know about hyperthyroidism?

Treating hyperthyroidism in older cats can sometimes reveal other conditions, such as kidney disease, which is why vets often use a reversible treatment like medication or a special diet first.

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If your cat has been diagnosed with hyperthyroidism, have a chat with your vet about general health at the same time. Arrange regular weigh-ins and, when making changes to your cat’s diet, always do them gradually.


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