Can a New Thyroid Health Food (Hill's y/d) Live Up to the Hype?

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

A new prescription cat food promises to treat hyperthyroidism in cats. 
Maybe so, if the studies pan out. Where are those studies, anyway?


Dr. Eric Barchas
www.catster.com
May 3, 2012

In the blog post entitled, Can a New Thyroid Health Food (Hill's y/d) Live Up to the Hype?, Dr. Eric Barchas provides us with a good overview of what's wrong with all the hype associated with Hill's y/d diet.

As Dr. Barchas states in the beginning of his post (1): "For months, every veterinary publication I receive has been plastered with full-page advertisements for a new prescription cat food...... The new cat food is called Hill's y/d —or, more formally, Hill's® Prescription Diet® y/d™ 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 ™. Might the diet be more marketing ploy than medical breakthrough?"

For those of you who have followed my rants about what's wrong with Hill's y/d diet (2,3), you would be able to predict that this post made me smile.

So what's this diet all about and what's the problem with it? 

First of all, Hill's y/d diet certainly does offers another treatment option for hyperthyroid cats. The basis for how the diet works to control the hyperthyroid state is by severely limiting the amount of iodine in the y/d (the diet is actually iodine deficient).

Because thyroid hormone contains large quantities of iodine, the diet should reduce secretion of the hormone. Indeed, the clinical experience of practicing veterinarians to date indicate the this diet is effective in lowering serum T4 values in many hyperthyroid cats, although not always to levels that we would consider "low enough."

The biggest concerns are in regard to the long-term side effects of feeding an low iodine or iodine deficient diet to cats. For y/d to work, no other food can be fed for the rest of the cat's life — so the y/d diet, if successful, would potentially be fed for years to a cat suffering from hyperthyroidism.

As Dr. Barchas points out in his post, large, long-term safety studies are needed to determine what happens when cats with or without thyroid disease eat y/d months to years. Now I know it seems difficult to believe, but adequate long-term safety studies of cats fed this diet have yet to be done.

Because Hill's y/d is not a drug (although it's certainly being marketed as a replacement for methimazole), the company is not required to do long-term safety studies. And it's fairly clear that they have no intention of paying to have them done.

The bottom line: 

Again, Dr. Barchas says it better than I could do so let me quote the summary for his post (1): "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.... 


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."

Related links: 

1. To read the complete post by Dr. Barchas, click this link. 
2. To read my posts on y/d on the Animal Endocrine Clinic blog, click this link.
3. To read my posts on y/d on the Insights into Veterinary Endocrinology blog, click this link.

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