Can a New Thyroid Health Food Live Up to the Hype?


For months, every veterinary publication I receive has been plastered with full-page advertisements for a new prescription cat food. The ad is even featured on the second page of the most recent Journal of the American Veterinary Medical Association. That’s some pricey real estate.

The new cat food is called Hill’s y/d –or, more formally, Hill’s┬« Prescription Diet┬« y/dÔäó Feline Thyroid Health on the company’s website. Call me old-fashioned, but I am naturally suspicious of any food that has two ┬«s and a Ôäó. Might the diet be more marketing ploy than medical breakthrough?

y/d is purported to treat feline hyperthyroidism, a common problem in older cats — though “epidemic” might be a better description. It occurs when usually noncancerous tumors develop in the thyroid gland and secrete thyroid hormone, which, in excess, wreaks havoc on the body. Consequences include weight loss, increased thirst and appetite, nighttime vocalization and agitation, heart damage, and potential kidney damage.

The cause is unknown. Hereditary and dietary links are suspected but remain unproven. Cats with the condition unequivocally need treatment.

There are three conventional forms of treatment for hyperthyroidism. Methimazole (also known as tapazole) can be administered orally or rubbed inside the ear to suppress the production of thyroid hormone. It is effective, but some cats develop side effects such as gastrointestinal or skin problems.

In my opinion, radioiodine therapy is the best option. It is simple, involving a single injection of a special type of iodine, and usually permanent. However, it must be performed in a special facility and it is relatively expensive.

Surgical removal of the thyroid gland is a crude but effective therapy preferred by many old-school types, especially those who practice where radioiodine is not available. However, surgical complications are possible.

y/d is supposed to offer a fourth form of treatment by providing a diet that is very limited in iodine. Thyroid hormone contains large quantities of iodine, so the diet, in theory, will reduce output of the hormone.

Any time I hear about something that sounds good in theory, I like to paraphrase that guy from Jerry Maguire: Show me the study! So far, I have tracked down only two studies on y/d. Both consisted of small samples run over relatively short time periods, and both were run by Hill’s. Both showed that the diet is effective, but anyone with a shred of scientific background should be able to tell that the studies aren’t very strong, and that more research is indicated.

Larger, long-term studies are needed to determine what happens when cats without thyroid disease eat y/d. Plenty of people have more than one cat, and cats eat from one another’s bowls. Also, a very significant number of cats with hyperthyroidism also have kidney disease. How will this diet affect kidney function? Finally, most people like to plan on their cats living for several more years (I would hope that a 7-year-old cat diagnosed with hyperthyroidism might make it to 15 or even 20). I believe the longest study on record so far lasted two years. What will happen to cats that eat y/d for 10 years?

In short, I believe that Hill’s has unleashed y/d with too little research and too much hype. The food may turn out to be a veritable godsend, or it could be a disaster. Only time, and more studies, will tell. And there will be plenty of studies. The diet has caused huge interest and controversy in the veterinary community, and it’s a safe bet that many legitimate researchers will take a hard look at y/d.

For now, no matter how many fancy ads I see, I am hesitant to recommend the food unless a cat absolutely is not a candidate for any of the other three hyperthyroidism treatments.

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