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Therapeutic hyperthyroid diet safe for cats

Q: One of my cats is hyperthyroid, and I’m thinking of treating her disease without medication, by feeding Hill’s y/d, a prescription low-iodine diet. It would be easiest for me to feed all my cats the same food. Is y/d safe for cats that are not hyperthyroid?

A: Yes. Hill’s y/d contains a reduced but adequate amount of iodine, an important component of thyroid hormone, so even healthy cats that eat y/d produce normal levels of the hormone.

When cats with hyperthyroidism eat a conventional diet, one with abundant iodine, they produce too much thyroid hormone. Treatment options include y/d, a single dose of radioactive iodine, surgery, or a daily medication called methimazole, which can be given orally or applied to the skin.

A recent study evaluated thyroid function over a two-year period in 14 healthy cats fed the limited-iodine diet and 12 healthy cats fed a conventional diet. The cats were young and had normal thyroid function at the start of the study.

Every six months, researchers performed a full panel of blood work, urinalysis, thyroid hormone levels and thyroid ultrasound. They found that all the cats–including those eating the limited-iodine diet–maintained normal thyroid size and function. So, you can feel confident feeding y/d to your entire cat family.


Lee Pickett, V.M.D. practices companion animal medicine in Pennsylvania. Contact her at askdrlee@insurefigo.com.

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