*This article is for informational purposes only. It’s not intended to be a substitute for professional veterinary advice, diagnosis, or treatment.
The best cat food for hyperthyroidism is rich in species-appropriate protein, low-carbohydrate, and is free from ingredients that contribute to thyroid disease. Iodine management can also help.
Because it’s the only food on the market that’s formulated to reduce hyperthyroidism symptoms, we’ve chosen Hill’s Prescription Diet y/d Thyroid Care as the best cat food for hyperthyroidism.
Our list also includes non-prescription foods that may help your cat feel better before and after medical treatment.
Quick Look at Our Top 5 Picks:
Hill’s Prescription Diet Thyroid Care y/d
Unless treated with a thyroidectomy, radioiodine treatment, or lifelong drug therapy, hyperthyroidism is usually progressive and may be fatal. Click here to learn more about your treatment options.
Overproduction of thyroid hormones affects the central nervous system, gastrointestinal system, heart, liver, and kidneys. The overactive metabolism burns up fuel faster than your cat can eat it, resulting in muscle wasting and an emaciated cat.
Food is not a cure for hyperthyroidism, but the right diet can help your cat maintain or regain muscle mass and may ensure good health after treatment.
What to Look for in the Best Cat Food?
Hyperthyroid cats need highly-digestible protein.
Hyperthyroid cats have two things working against them when it comes to maintaining muscle mass. First, they have an overactive metabolism, and secondly, most of them are seniors.
New research suggests that seniors have high protein and energy needs—similar to the needs of kittens. When these needs aren’t met, they lose muscle.
Choose foods composed of over 50% calories from protein. The best protein sources are species-appropriate and highly digestible. Your cat requires meat-based food with no high-protein fillers like pea protein, potato protein, wheat gluten, and corn gluten meal.
Choose a diet that’s less than 10% carbohydrate on a dry matter basis.
Hyperthyroidism raises your cat’s blood glucose levels and often leads to insulin resistance and an impaired glucose tolerance. This is a prediabetic state. Even if this doesn’t advance to full diabetes mellitus, hyperthyroid cats are sensitive to sugar and require controlled levels of dietary carbohydrate.
What to Avoid When Feeding a Hyperthyroid Cat
Avoid fish-based foods.
A study in 2000 found that cats who preferred canned cat food in fish or liver and giblets flavors had an increased risk of hyperthyroidism. Fish and other ocean creatures have higher levels of iodine than do other foods. Since iodine is central to thyroid function, this may be part of the connection, but it’s not clear that iodine content is the only problem.
Most fish is contaminated with toxins, including PBDEs.
These fire retardant chemicals were extremely popular in the late 1970s and were used to treat everything from pajamas to curtains. Because they’re known endocrine disruptors, PBDEs were essentially phased out in the United States and European Union during the early 2000’s. That doesn’t mean they’re not still everywhere. These toxins linger in soil, dust, waterways, human bodies, and the ocean — they’re present in cans of fish-based food.
Hyperthyroid cats have higher levels of PBDEs in their bloodstream than do healthy ones.
If feeding canned food, ensure that the can is BPA-free.
Cats who eat canned foods, particularly cans with pop-top lids, have an increased risk thyroid problems. Cat food cans are often coated with an epoxy lining containing BPA. BPA acts as a thyroid receptor antagonist and alters thyroid function.
Don’t feed your cat soy.
When researchers gave 18 healthy adult cats either a soy or soy-free diet for three months, they found that the cats who ate a soy diet ended the study with “significantly higher total thyroxine (T4) and free T4 (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations.”
The soy-based diet had a small, but significant effect on the amount of thyroid hormone produced by the body.
Should you feed your cat a prescription diet for hyperthyroidism?
Hill’s Prescription Diet y/d is the leading prescription cat food for hyperthyroidism. This food is extremely low in iodine, containing less than 0.32 ppm iodine on a dry matter basis.
In the paper linked above, the writer notes that as of 2011—when the article was written—“all hyperthyroid cats managed with Hill’s Prescription Diet® y/d® Feline as the sole source of nutrition have become and remained euthyroid (having normal thyroid function) as long as the cat had no access to other sources of iodine.”
A low-iodine diet cuts off the supply of iodine, slowing thyroid hormone synthesis. It does not fix an enlarged gland. It does not prevent an adenoma from changing into a carcinoma. It only reduces the symptoms.
How much iodine does a normal cat require?
Given the diversity of iodine concentration in homemade, commercially-available, and wild-caught food, it’s difficult to identify how much iodine cats require.
In 2006, the National Research Council suggested that the dietary iodine requirement for cats was 1.3 ppm. Newer research conducted by Hill’s Pet Nutrition suggests that the requirement may actually be closer to 0.46 ppm.
The 0.32 ppm iodine in the Hill’s diet is low. While it’s currently thought that iodine is only used for thyroid hormone synthesis, we ultimately don’t know how an iodine-restricted diet will affect long-term health.
Because it’s restrictive, not species-appropriate, and isn’t a real cure, think of this diet as a temporary measure or as a last resort for cats who can’t undergo surgery or receive radioiodine.
Top 5 Best Cat Foods for Hyperthyroidism
Because they’re typically lower in carbohydrates, usually contain higher-quality protein, and are more hydrating than dry foods, all of the products on the following list are wet cat foods.
With the exception of the Hill’s prescription diet, these are not treatments for hyperthyroidism. Instead, they contain high levels of highly-digestible protein to maintain and restore lean muscle mass. These foods should accompany curative treatment.
If your cat has any concurrent diseases that demand a special diet, consider those needs first and talk to your veterinarian to find a food that encourages all-around health.
Hill’s Prescription Diet Thyroid Care y/d Feline Canned Review
First 5 Ingredients: Water, Pork Liver, Pork By-Products, Chicken, Corn Flour
While this food is pushed as an alternative to lifelong medication, radioiodine treatment, or a thyroidotomy, it’s not a cure for hyperthyroidism.
It starves the thyroid of fuel, but it doesn’t slow down the progression of a thyroid tumor. The tumor will continue to grow and potentially change into a carcinoma.
A cat on this diet will have to eat it for the rest of their life lest they relapse. They can’t eat any other foods, including therapeutic foods specific to common conditions like CKD, diabetes, or pancreatitis.
Lastly, the food is a high-carbohydrate, low-protein diet. The canned food is about 27% protein, 24% carbohydrate, and 49% fat. This isn’t an ideal calorie distribution for any cat, much less a senior with a propensity to lose muscle mass. Senior cats require high-quality protein to maintain healthy muscle mass, and this diet just doesn’t offer what they need.
- Inhibits excessive thyroid hormone production
- Cats tend to like the taste of the food
- A healthier alternative to the y/d dry food
- A good last resort for cats who can’t undergo other treatments
- Low protein content doesn’t help to maintain muscle mass
- Excessive carbohydrate content
- Only effective if the patient doesn’t eat anything else
Hound & Gatos Rabbit Canned Cat Food Review
First 5 Ingredients: Rabbit, Water, Agar-Agar, Salmon Oil, Choline Chloride
This canned food contains nothing besides meat, thickeners, and added vitamins, minerals, and amino acids. It’s composed of 98% meat, which means that it’s a great source of species-appropriate protein to support lean muscle mass.
Rabbit meat is a biologically appropriate source of protein and naturally low in phosphorus. It has very low carbohydrate content.
On their FAQ page, Hound & Gatos says their cans are BPA-free.
- Made from a biologically appropriate animal protein source
- High in protein for muscle mass
- Free from soy
- Packed in BPA-free cans
- Limited ingredient recipe
- Some cats dislike the flavor
Instinct by Nature’s Variety Original Grain-Free Real Lamb Recipe Canned Cat Food Review
First 5 Ingredients: Lamb, Lamb Broth, Turkey, Turkey Liver, Ground Flaxseed
Ninety-five percent of this recipe is composed of lamb, turkey, and turkey liver. These are all sources of species-appropriate protein, which will help to support healthy muscle mass and prevent sarcopenia of aging.
That said, this isn’t the most meat-dense food on this list. The recipe includes ground flaxseed, montmorillonite clay, peas, and carrots, none of which are ideal for cats. These inclusions bring the carbohydrate content to around 3% on a dry matter basis.
The company says that while they use a BPA lining in their large cans, their 5.5oz cans are BPA-free.
- High in moisture
- Rich in biologically appropriate animal protein
- Low in carbohydrates
- Free from chemical preservatives, artificial ingredients, and animal byproducts
- Contains some fruit and vegetable ingredients
Nutro Grain Free Soft Loaf Senior Cat Food Review
This food is primarily made from chicken, a great source of bioavailable protein to help maintain lean muscle mass.
The food is made with seniors in mind, which is a good thing for us considering that the average hyperthyroid patient is aged 13. At this age, your cat may have dental problems and this soft pate is easy for any cat to eat.
According to the guaranteed analysis, this cat food contains approximately 0.5% carbohydrate content, which is species-appropriate and beneficial for insulin-resistant cats.
Nutro doesn’t use BPA in any of their cat food cans.
- Made from high-quality meat ingredients with no fillers
- Soft texture is easy to eat
- Protein-dense for lean muscle mass
- Low carbohydrate content
- Free of soy
- Not all cats will enjoy it – some reviews say that their cats didn’t like the flavor
Best For Weight Gain: Wild Calling Cabin Fever Chicken Recipe Grain-Free Adult Canned Cat Food Review
First 5 Ingredients: Chicken, Water Sufficient For Processing, Chicken Liver, Natural Flavor, Guar Gum
This food from Wild Calling is 96% meat, making it a good source of the species-appropriate animal protein that is required to prevent muscle wasting. With 206 calories in every can, it’s one of the more high-calorie foods on the market. Whether your cat is currently experiencing muscle wasting or is recovering after treatment, this calorie-dense food can help to support lean muscle mass and a healthy weight.
The food does contain guar gum, which worries some consumers. While not a necessary part of the feline diet, this high-fiber inclusion doesn’t appear to have any negative health effects.
Wild Calling says that their 5.5 oz cans are BPA-free.
- One of the highest-calorie foods on the market
- Made with 96% meat – ideal nutrition for your cat
- Free from fish ingredients
- Made without soy
- BPA-free cans
- Some people say this food has a strange or unappetizing texture
About the author
Mallory Crusta is a writer and adventurecat enthusiast on a mission to make cats’ lives extraordinary. She’s one of the founders of Wildernesscat – a site for happy, healthy, and adventurous cats who are fueled by nature. Visit Wildernesscat for radically natural cat nutrition, home remedies, and lifestyle inspiration.