The Kibble
Hills released their new hyperthyroid diet, Y/D on September first. According to research provided by Hills, the diet which has strictly controlled iodine levels will bring thyroid numbers to within normal range within three weeks, with many cats becoming euthyroid (having thyroid numbers within normal range) prior to that time.
What this means is that hyperthyroidism, a very common illness in senior cats can be treated with diet alone instead of the commonly prescribed medication, methiamazole (Tapazole). For cats that do not respond to medication, and therefore need either surgical correction or radioiodine treatment, this diet has no effect, according to Hills Research.
The diet, which must be fed exclusively (no treats, no ‘snacks’) to be effective, contains iodine levels below .32 ppm. According to Hills other cats in the household will suffer no ill effects from eating this food. Iodine levels are not usually provided on pet food bags, but Hills states that the cats in their control group were fed a regular commercial cat food, and it contained an iodine level of 1.9 ppm.
Cats transitioning from medication to the new food will require frequent blood tests to establish thyroid (T4) levels, and will likely discontinue taking methiamazole within two weeks of starting the new food, per Hills.
The Science
Hyperthyroidism is caused by a functional tumor, this tumor is benign, but it secretes thyroid hormones, causing raised metabolism, elevated heart rate, ravenous appetite, and weight loss, it is a common disease affecting senior cats.
The disease is readily diagnosed through testing for the primary thyroid hormone T-4 (there are others, but this is the one that is of primary concern). The treatment in most cats is medication, called methiamazole (brand name Tapazole) a medication that is not expensive and can be formulated for cats in a variety of flavors.
For the rare cats unresponsive to the medication, or who are impossible to medicate there is a radiation therapy available called radioiodine. Oncologists at specialty centers can perform this treatment, which destroys the tumor and restores normal thyroid function. The procedure is not inexpensive.
There is also a surgical option that cuts away the tumor, I personally am unfamiliar with this option other than to know of its existence. It too provides a long term, permanent solution.
Hills Research
According to materials distributed to the veterinary community, Hills’ research of this product was published in the Journal of Veterinary Internal Medicine. The three abstracts (J Vet Intern Med 2011; 25 683-684) illustrate efficacy of the product on up to 41 naturally hyperthyroid cats over a period up to 3 years.
Over the course of all three studies most of the cats fed a diet containing less than .32 ppm of iodine became euthyroid, and remained so without medications for the duration of the study. The cats showed no ill effects of eating the diet. No cats in the study had T4 concentrations below the normal range.
What the Veterinary community is saying
When I first learned of this diet, I called a veterinary hospital where I used to work and asked them for information on the product. They had none, as they were waiting to see if the diet proves safe in the long run.
As I looked for other sources within the veterinary community, the consensus seemed to be wait and see.
When asked why they were hanging back, they cited a lack of long term testing and questions about a largely untried diet that will replace a medication that has a long history of efficacy, low incidence of side effects, and is inexpensive.
The concerns of the veterinary community are the small numbers of cats tested, the lack of real independent research on other household cats eating this diet, and lack of independent research on safety and efficacy of the diet.
First the subject numbers should be addressed. Hills does research for Hills, it is not a drug manufacturer, and therefore does not need to comply with FDA regulations regarding drug trials. Some in the veterinary community feel that in the case of this new food, since it is professing to treat a disease, the rule should change. Tens of thousands of cats of every breed and description suffer from hyperthyroidism, yes research is expensive, but so is the food, to base a low iodine diet on 41 cats seems insufficient.
Second, Hills states that it has had normal (euthyroid) cats on this diet for a year, with no ill effects (nothing in the literature I received confirms this). The veterinary community knows that if one cat in a household eats a food exclusively, then everybody else does too. Their concerns are the long term effects of what they see as an iodine deficient diet on young and healthy cats. They realize that Hills has no vested interest in paying for this type of research, and therefore would feel happier if others picked up the tab and found out, in the interim, many do not feel comfortable using their own clients’ euthyroid cats as test subjects.
There is also concern about the diet for hyperthyroid cats in the long run. Hills settled on the iodine amount in the food based on what would effectively lower T4 levels, not what may be necessary over the long haul. Again, Hills has very little incentive to fund long term of studies, and therefore it is likely that they will fall to universities.
Until these questions are fully answered, all of the veterinarians I have consulted for this article are taking a wait and see attitude, and will continue to use protocols that have proven effective in the past. They did concede that they may find themselves turning to Y/D if a cat absolutely will not tolerate methiamazole, and the owners do not wish to pursue the other options available.