Why Is My Cat Losing Weight? Causes, Tests and When to Worry

By Tailwisp Editorial TeamUpdated October 20, 20265 min read

Cats are fluffy, and weight loss often sneaks up. By the time an owner notices bones under the coat, a cat may have lost a lot. Because many serious illnesses begin with a slow slide on the scale, tracking weight is one of the simplest and most useful things you can do for your cat.

How to tell if your cat is losing weight

Run your hands along the ribs and spine. A healthy cat has ribs you can feel under a thin layer of fat, and a waist when viewed from above. Prominent ribs, hip bones and a spine you can feel easily, or a thin look in the face and over the hind legs, suggest a problem. Weigh your cat every month, using a baby or kitchen scale, or by weighing yourself with and without the cat. Write the numbers down. A drop of a few ounces in a small cat matters. See how to check your cat's vital signs.

Weight loss with a big appetite

When a cat eats well, or even ravenously, and still loses weight, think of:

• Hyperthyroidism, an overactive thyroid. Other signs include restlessness, vomiting, a rough coat and increased thirst. See hyperthyroidism in cats.
• Diabetes, where the body cannot use glucose. See diabetes in cats.
• Intestinal disease or malabsorption, such as inflammatory bowel disease or intestinal lymphoma. See inflammatory bowel disease in cats and lymphoma in cats.
• Pancreatic insufficiency, a rare condition.
• Intestinal parasites. See worms in cats.

Weight loss with reduced appetite

When a cat eats less, the cause may be:

• Dental pain. See cat dental disease.
• Kidney disease. See chronic kidney disease in cats.
• Nausea, pancreatitis or gut problems. See pancreatitis in cats.
• Liver disease.
• Cancer. See cancer in cats.
• Infections, such as respiratory disease that blocks smell. See feline calicivirus and herpesvirus.
• Pain, for instance from arthritis. See signs of pain in cats.
• Stress, or a diet change. See cat not eating: causes.

Other causes

• Heart disease, with muscle loss.
• Competition for food in multi-cat homes. See feeding cats in a multi-cat home.
• Poor-quality or inadequate food, or an incorrect portion. See how much should I feed my cat.
• Age-related muscle loss, called sarcopenia.
• Pregnancy and nursing, which increase calorie needs.

Muscle loss versus fat loss

Cats can lose muscle even when they appear to carry fat, especially seniors. Feel along the spine and over the hips for muscle. Muscle loss, called muscle wasting, is a warning sign that many owners miss. Vets use a muscle condition score, alongside body condition, to grade it.

What a vet will do

Expect a full exam, including a check of the mouth, thyroid area in the neck, heart and abdomen. Common tests include bloodwork, a urinalysis, a thyroid test, a fecal test and blood pressure. Imaging such as ultrasound or X-rays may follow. See cat blood tests explained. Bring your weight log, and notes on appetite, thirst, vomiting and stool.

Treatment

Treatment depends on the cause: medication or radioactive iodine for the thyroid, insulin for diabetes, special diets for kidney disease, dental treatment, anti-nausea medication, appetite stimulants, parasite control and others. Nutrition support is often a part, since a thin cat needs calories. Do not push your cat to eat by force. See healthy cat treats.

What you can do at home

• Weigh monthly.
• Feed measured portions of a good diet.
• Offer small, frequent meals.
• Warm food slightly, to boost its smell.
• Reduce stress.
• Watch for changes in drinking, urination and stool.

A simple monthly routine

Pick the same day each month. Weigh your cat on the same scale, and write the number in your phone with the date. Take a side photo and a top-down photo, since changes in shape can be easier to see than a number. Feel the ribs and spine, and note whether you can feel the bones easily. If your cat is losing more than a couple of percent of its weight a month, or has lost 5 to 10 percent over a few months, book a visit. Bring the log, because the trend is often more useful to your vet than a single weight.

Senior cats and muscle loss

Older cats often lose muscle, even if fat is stable. That can make a cat look thin along the back and hips, with a narrow spine. Muscle loss is linked with illness and a shorter life, so do not dismiss it as age. Good protein, regular play, regular vet checks and early treatment of kidney, thyroid and dental disease all help. See best food for senior cats.

Weight loss in a multi-cat home

If you have several cats, you may not know which one is losing weight, or which one is eating. Use separate feeding stations, closed doors or microchip feeders, to see who is eating what. Weigh each cat. A quiet cat that is bullied away from food may need to be fed alone. See feeding cats in a multi-cat home.

Do not wait

Because many causes are treatable, and some are urgent, do not wait for weeks to see if a thin cat bounces back. Early tests are simple, and finding a cause early often means a simpler treatment.

When to see a vet

See a vet if your cat loses weight over a few weeks, even if it eats well. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.