Why Is My Cat Losing Weight?

By PetMD Editorial. Reviewed by Veronica Higgs, DVM on Feb. 18, 2024
white devon rex cat lounging on their side

iStock/Angela Kotsell

It’s not always easy to detect weight loss in your cat. The fluff of fur covering most cats can serve as camouflage for weight loss until there is a big change.

Unintentional weight loss in cats can be a cause for concern. If you weren’t trying to help your cat lose weight, and especially if your cat is a senior, there might be a health issue to blame.

The causes of unintentional weight loss in cats range from simple lifestyle changes to serious illness. Any noticeable weight loss in your cat warrants a visit to your veterinarian to rule out serious health conditions. They will be able to run the necessary tests to determine what might be at the root of the problem.

Here are some possible reasons why your cat is losing weight and what you should do about it.

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7 Reasons Your Cat Might Be Losing Weight

Here are a few common causes for weight loss in cats.

1. Not Getting Enough Food

Sometimes, your cat is eating less than you think. Ask yourself some questions:

  • Do you have another cat or dog in the house? Additional pets in your home could be eating your cat’s food or obstructing your cat’s access to their food bowl.

  • Did you recently change brands of food? The calorie content in a cup of food can vary greatly from one brand to another.

  • Is the food dish easy to access? Your cat could be experiencing pain, such as from arthritis, that’s making it difficult to jump up to a food dish kept on the counter or to go up and downstairs if it’s on a different floor.

Your veterinarian can help you determine if there are obstacles in your home that are preventing your cat from eating enough food.

2. Intestinal Parasites

Intestinal parasites are common in cats and can lead to weight loss if left untreated.

Pregnant mothers can give their kittens parasites, and they can also pass parasites through their milk when they are nursing. Cats can also get parasites from hunting and eating prey, or even by walking through contaminated grass and dirt and then grooming.

Your vet can examine your cat’s feces to determine if they’re carrying parasites that might be causing weight loss. If parasites are the cause, a simple dewormer can put your cat back on the road to a healthy weight.

3. Feline Diabetes

Diabetes in cats is very common and require immediate veterinary care and ongoing treatment. In addition to unexplained weight loss, diabetic cats typically drink an abnormally large amount of water and urinate large volumes as well.

Without treatment, diabetes can be a life-threatening condition. If your vet suspects diabetes, they will likely take blood and urine samples to confirm the diagnosis. Successful treatment involves diet changes and insulin

Any noticeable weight loss in your cat warrants a visit to your veterinarian to rule out serious health conditions.

4. Feline Hyperthyroidism

Middle-aged and senior cats can be at risk for hyperthyroidism.

The thyroid is a butterfly-shaped organ in the throat. It produces hormones that perform many functions, including regulating the body’s metabolism.

In a hyperthyroid cat, their metabolism goes into overdrive—they lose weight, are ravenously hungry all the time, have a very high heart rate, and often meow at night and have trouble sleeping. They may also drink a lot of water and urinate large amounts.

Your vet will do blood work to see if this is the cause of the weight loss. Treatment of hyperthyroidism involves controlling the thyroid gland, either with medicinespecial food, or inpatient radioactive iodine treatment. Your vet will guide you in choosing the best treatment.

5. Feline Viral Disease

FIPFeLV and FIV are viral diseases in cats. These viruses have different causes and possible therapies, but weight loss is a common symptom of all three.

If your vet suspects a virus is the cause of your cat’s weight loss, they may perform tests to determine if one of these viruses is the cause. If a diagnosis is made, management and treatment will be based on the symptoms your cat is showing.

6. Feline Kidney Disease

Feline kidney disease can also lead to weight loss in your cat. To determine if kidney disease is the cause of your cat’s weight loss, your vet will do blood work and a urinalysis. Treatment may include prescription food, medicine, and even sterile fluids your vet can teach you to administer at home.

7. Feline Cancer

Many different forms of cancer can cause weight loss.

The diagnosis and treatment plan will vary depending on the cancer’s type and stage. Your vet might do some the following to confirm a diagnosis:

  • Blood work

  • Urinalysis

  • X-rays

  • Ultrasounds

  • Fine needle aspirations (FNA) or biopsies 

Why Is My Older Cat Losing Weight?

Older cats can lose some weight as a normal part of aging as they lose muscle mass. However, as they age, cats may also develop certain medical conditions such as diabetes, kidney disease, hyperthyroidism, and cancer, which can also lead to weight loss. 

For senior pets, it’s best to be proactive about their care and to screen them for weight loss as well as illness. Often this means vet visits and blood work every 6 months to assess their blood sugar, thyroid, and kidneys.

If your pet develops acute signs such as vomiting, diarrhea, anorexia, or dramatic weight loss, it’s best to see the vet right away.

When To Go to the Vet

Unintentional weight loss in cats is a nonspecific sign that can have many causes. An examination and, often, blood work is needed to try to determine the underlying cause.

If you notice that your cat is losing weight, you need to call the vet. Make the appointment now. Your vet should have a documented weight from the last visit and can confirm the weight loss.

They will take a thorough history and do a complete physical exam. Based on those findings, your vet might recommend a fecal exam to check for intestinal parasites and blood work to check for clues to get to the bottom of what is causing the weight loss.

Treating Weight Loss in Cats

If your cat’s losing weight, treatment depends on the underlying cause. Often, medication or a diet change can treat the underlying condition and help your cat gain back some of the weight they lost. 

Once a cat reaches 11 years of age, it’s best to increase routine vet visits from once a year to twice a year. This helps your vet catch underlying conditions sooner and helps keep your pet from losing weight in the first place. This also helps you closely monitor your cat’s weight, as the vet’s office will weight them at each visit. 

Weight Loss in Cats FAQs

1. Why is my cat losing weight but acting normal?

There are many possible reasons a cat may lose weight but not have any other symptoms, including diabetes, early kidney disease, intestinal parasites, hyperthyroidism, and even some kinds of cancer.

2. Why is my cat suddenly losing weight?

Weight loss can be caused by many conditions, ranging from mild to serious.  Some possible causes include:

  • Intestinal parasites

  • Medical conditions (such as hyperthyroidism, kidney disease, diabetes, and cancer)

  • Behavioral situations (stress, new pet eating their food, etc.)

If your pet is losing weight, make an appointment with your vet to get to the bottom of what is going on.

3. How do I know if my cat is too skinny?

The ideal weight for the average healthy cat is 8–12 pounds; however, cats come in a variety of sizes and weight alone may not be enough to determine if they are too skinny. Your vet can help determine their body condition score, which takes in more factors such as body frame, muscle mass, overall size.

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