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Does Fish-Flavored Cat Food Cause Hypothyroidism? Vet-Approved Facts

Written by: Genevieve Dugal

Last Updated on June 3, 2024 by Catster Editorial Team

cat eating food in the bowl

Does Fish-Flavored Cat Food Cause Hypothyroidism? Vet-Approved Facts


Dr. Amanda Charles Photo


Dr. Amanda Charles

BVSc GPCert (Derm) MRCVS (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

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Just like humans and dogs, cats can suffer from hypothyroidism, though it is quite rare. This endocrine disease is mainly due to the decrease in the secretion of thyroid hormones, which when in short supply, cause an imbalance in the various functions of the cat’s body.

Although some cat owners may be concerned about the potential link between fish-flavored cat foods and hypothyroidism, there is no scientific evidence to suggest that it is a causative factor. That said, there are a few studies that suggest a link between fish-flavored cat foods and hyperthyroidism in cats1.

So, let’s review the role of the thyroid gland in cats, hypothyroidism vs. hyperthyroidism, and whether fish-flavored cat food plays a factor.

Note: If you have any concerns about your cat’s health, it’s always best to consult your veterinarian, who can provide a proper diagnosis and recommend appropriate treatment options.

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What Does the Thyroid Gland Do in Cats?

The thyroid gland produces a hormone essential for regulating the metabolism of your cat’s body. To make this hormone, it needs iodine, which is provided to your feline through their diet.

If this hormone is produced in too low quantities, the body begins to suffer the consequences. This endocrine disease is called hypothyroidism.

American shorthair male cat tabby
Image Credit: Apisit Hrpp, Shutterstock

What Is Hypothyroidism in Cats?

Hypothyroidism is a condition in which the thyroid glands, located in the neck, do not produce enough thyroid hormones. These play a crucial role in regulating metabolism and growth. Therefore, when they are lacking, the overall health of the cat can be negatively affected. Hypothyroidism can be present at birth (congenital) or acquired. The most common acquired cause is when a cat has hyperthyroidism and has a treatment that “overcorrects” the issue, causing them to have hypothyroidism.

However, this type of endocrine disease is rather rare in cats.

How to Recognize Hypothyroidism in Cats

Cats with congenital or acquired hypothyroidism may exhibit the following signs:
  • Weight gain
  • Lethargy
  • Dry skin
  • Hair loss
  • Lack of appetite
  • Dull coat
  • Scaly skin

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Hyperthyroidism Complications

At the other extreme, when the glands produce too much thyroid hormone, the cat’s whole body goes into overdrive and may struggle to keep up. This can lead to complications in various systems:

This can lead to complications in various systems:
  • Kidneys
  • Cardiac
  • Muscular
  • Neurological
  • Dermatological
  • Digestive

This is called hyperthyroidism, and it is the most common endocrine disease in cats. It is characterized by an excess of thyroid hormones in the blood and by an abnormal enlargement of the thyroid gland.

vet holding burma cat
Image Credit: Elpisterra, Shutterstock

What the Research Says About the Causes of Hyperthyroidism in Cats

According to the American Animal Hospital Association, it’s hard to know for sure what causes hyperthyroidism in cats, but a 2016 study published in the American Chemistry Society’s Environmental Science & Technology journal suggested a link between this endocrine disease and fish-flavored cat food.

The researchers evaluated samples of feline blood and fish-flavored cat food and identified derivatives of polychlorinated biphenyls and polybrominated diphenyl ethers that may be linked to hyperthyroidism in cats. They concluded that “the by-products that were detected at high levels in the cats’ blood samples likely came from fish-flavored [cat] food.”

Moreover, researchers in another study looked at the medical records of about 100 cats with hyperthyroidism and compared them to 163 control cats (ones without hyperthyroidism). The study aimed to determine if environmental or dietary factors played a role in the development of hyperthyroidism in cats. The researchers found that “cats that prefer to eat certain flavors of canned cat food [fish or liver and giblets flavors] may have a significantly increased risk of hyperthyroidism.”

Therefore, while these studies aren’t definitive proof that fish-flavored foods can contribute to the development of hyperthyroidism in cats, it’s probably best to buy other food options for your beloved kitties if you are concerned about their thyroid function.

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Tips for Caring for a Hypothyroid Cat

cat jumps and plays with a rope and an elastic band
Image Credit: ketlit, Shutterstock

If your feline companion has hypothyroidism, you can help improve their quality of life with the following tips. That said, be sure to get an accurate diagnosis from your veterinarian first, as this type of endocrine disorder is rare in cats:

  • Follow your veterinarian’s treatment plan: This type of treatment aims to restore normal blood levels of thyroid hormones. This is usually done by giving an oral thyroid medication supplement, either in liquid or tablet form.
  • Monitor your cat’s weight: Hypothyroidism can lead to excessive weight gain, so it’s essential to monitor your cat’s weight and adjust their diet as needed. Your veterinarian can help you determine the appropriate amount and type of food for your pet.
  • Play with your cat: Exercise can help your pet maintain a healthy weight and improve their overall health. Encourage your cat to play, and do regular activities with them, like using interactive toys or chasing a laser pointer.

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Bottom Line

Although there is some scientific evidence to suggest that fish-flavored cat food may increase the risk of hyperthyroidism in cats, there is currently no link between this food flavor and hypothyroidism. Indeed, the causes of hypothyroidism in cats are mainly related to a congenital anomaly or an acquired form, which is usually iatrogenic and related to treatment for hyperthyroidism.

Fortunately, this rare endocrine disorder in felines can usually be treated with appropriate oral thyroid medication. Cats with hypothyroidism should be fed a high-quality diet as recommended by their veterinarian, but whether it is fish flavored or not doesn’t seem to matter.

Featured Image Credit: Okssi, Shutterstock

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