Why is My Cat Losing Weight?

Dr. Jason Gagné, DVM, DACVIM
By Dr. Jason Gagné, DVM, DACVIM
Updated: 5/20/20242-4 minutes
Cat with a child

Many cat owners are concerned about keeping their feline at a healthy weight. Most commonly concerns are centered around cat obesity, but your cat losing weight unintentionally could also be a sign that something’s wrong.

Your feline may be eating well and still losing weight, they may have a reduced appetite, or they may just be avoiding food entirely. Weight loss can be a sign of several different health problems so, if your cat is losing weight, it’s best to contact your vet as soon as possible.

In this guide we look at the most common reasons why your cat may be losing weight as well as the other symptoms you should be on the lookout for.

Causes of Weight Loss in Cats

There may be many reasons why your cat might be losing weight unintentionally, ranging from psychological issues and changes at home, to underlying health conditions. Here are some of the most common causes of weight loss in cats:

1. Feline Hyperthyroidism

More common in cats that are over seven years old, hyperthyroidism is a condition where the thyroid gland becomes enlarged and starts to produce too much thyroid hormone. Weight loss is a very common sign of hyperthyroidism in cats, alongside an increased appetite, as well as increased thirst and urination.

Your cat’s coat may also start to appear greasy and unkempt. Generally, this condition is treated with radioactive iodine, oral medications, diet, or surgery.

2. Cat Cancers

Diabetes in cats is a disease that is caused by the failure to produce insulin or the lack of ability to respond to it.

Signs of cat diabetes include weight loss (as well as weight gain) and a change in appetite, which may also be paired with signs such as excessive drinking and urination, lethargy, urinary tract infections, and sweet-smelling breath – so if your cat starts showing any of these symptoms, be sure to get in contact with your vet straight away. If your cat has this disease, feline diabetes is usually managed with insulin and a change in diet.

4. Gastrointestinal Problems in Cats

Problems that affect your cat’s gastrointestinal (GI) tract may cause weight loss, as they can result in a reduction in appetite, or they can prevent your cat from digesting food properly to absorb the nutrients they need. The more typical forms of gastrointestinal issues include inflammatory bowel disease, pancreatitis, and cancers of the GI tract.

5. Cat Dental Issues

Dental issues and problems that affect your cat’s mouth could result in a lot of pain, which may mean your cat is not able to eat very much or this may stop them eating altogether. Both situations will often result in weight loss.

Some of the dental issues frequently seen in cats include gum disease, “resorptive” lesions on the teeth, and even tooth fractures. Your cat may display other symptoms such as bad breath, drooling, bleeding from the mouth, trembling of the jaw, food dropping from their mouth, starting to favor soft food over hard, or pawing at their mouth. If you suspect dental problems are the cause of your cat’s weight loss, get in contact with your vet, who will advise you on whether your cat needs to be seen.

6. Cat Kidney Disease

The kidneys are responsible for a great number of jobs within the body, including producing hormones, filtering waste products from the blood, helping to regulate blood pressure, and assisting with the production of new blood cells. So, as you can imagine, when things go wrong within the kidneys, it can cause a great number of problems, including your cat losing weight.

Other signs of kidney disease in cats include increased thirst and urination, lack of appetite, and lethargy. Unfortunately, kidney failure is quite common in older cats, so if you suspect your cat may have kidney disease, it’s best to book an appointment with your vet ASAP as prompt intervention often results in better outcomes.

7. Cat Intestinal Parasites

Cat worms can lead to your cat losing weight unintentionally, and these parasites can also result in diarrhea, bloating, and vomiting. It’s extremely important that you keep up to date with regular parasite control to help prevent issues caused by worms, especially in cats that like to hunt. Even indoor cats should still be wormed regularly, as fleas can carry and transmit worm larvae if they are accidentally carried into the house. If you’re unsure about how often you should worm your cat, it’s best to consult your vet.

When to See a Vet About Your Cat Losing Weight

As the causes of weight loss in cats vary so greatly, it’s important that you take your cat to the vet as soon as possible so that, if necessary, your vet can check your cat’s weight, take a history, and complete a full physical examination to identify why your cat is losing weight. Your vet will then discuss an appropriate treatment plan with you. It’s important to bear in mind that, in lots of cases, early intervention can improve your cat’s prognosis.

If you're concerned about your cat's health, tracking your cat's weight at home can be done through a smart litter box monitor. A smart litter box monitor can alert you to fluctuations in your cat's weight that may indicate you need to take your cat to the vet. It will also provide your vet with more information that, along with a full physical examination, could help identify why your cat is losing weight.

Want more cat health tips? Get advice from our experts with our other cat health articles.

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