Cat losing weight: common causes and when to see a vet

A cat losing weight without being on a diet is telling you something is wrong, even if it still seems happy. Weight loss is often the first sign owners notice, and sometimes the only one. If you’re unsure how quickly to act, our should I go to the vet check can help you decide.

Why is my cat losing weight?

A cat loses weight when it takes in fewer calories than its body uses. VCA Animal Hospitals groups the reasons into a few types:

• Eating less, because of a poor appetite, mouth pain, trouble swallowing or loss of smell
• Burning energy faster, as happens with an overactive thyroid
• Not absorbing food properly, because of gut disease or pancreas problems
• Losing nutrients, through vomiting, diarrhea or passing a lot of urine
• Needing more energy, during growth, pregnancy or cold weather

VCA considers weight loss clinically significant once a cat has lost more than 10% of its normal body weight. For a 10-pound cat, that’s just over 1 pound. The faster the loss, the more concerning it is. Because cats are small, a loss that looks minor on the scale can be a big share of their body weight.

What does weight loss with a good appetite mean?

Weight loss with a good appetite, or even a bigger one, narrows the list. VCA describes it as a characteristic sign of some feline diseases, where the body burns energy too fast or can’t use the food it’s given.

Hyperthyroidism is the classic example. Cornell Feline Health Center lists weight loss, increased appetite and increased thirst and urination as its most common signs. The 2021 AAFP Feline Senior Care Guidelines report that it affects about 10% of cats over 10 years old, and that it’s treatable if found early. See our guide to hyperthyroidism in cats.

In diabetes, Cornell explains, the body’s cells can’t take in sugar from the blood. The body breaks down fat and muscle for energy instead, so the cat loses weight despite eating more. Excessive thirst and urination often come with it. Read more about diabetes in cats.

What does weight loss with a poor appetite mean?

When a cat eats less and loses weight, the cause can be almost anything that makes it feel unwell. VCA notes that most long-term diseases cause weight loss at some point.

Mouth pain is easy to miss. A cat may go to the bowl hungry and walk away, which VCA lists as a feeding problem vets look for. Our guide to cat dental disease covers the signs.

The AAFP senior care guidelines list weight loss and muscle wasting among the signs of chronic kidney disease that owners can overlook, along with drinking and peeing more, nausea and a poor coat. See our guide to cat kidney disease.

A cat that has stopped eating completely is a more urgent problem. Cornell Feline Health Center explains that a near-total refusal of food almost always comes before or with hepatic lipidosis, a liver condition that is likely to be fatal if not treated promptly. Read cat not eating and call your vet.

Why does senior cat weight loss need a vet?

Senior cat weight loss can look slow and harmless. It still needs checking. The AAFP senior care guidelines say that unexplained changes in weight, body condition or muscle condition are problems to investigate and manage as diseases. They also point out that:

• With age, weight loss becomes more common than weight gain.
• A body condition score below 5 out of 9 is linked with shorter survival.
• Weight loss may be the only sign of digestive disease in older cats.
• Gut disease, cancer, pancreatitis, pancreas insufficiency and parasites are common causes of weight loss when there are no other signs.

Some muscle loss is part of normal aging. The guidelines call it sarcopenia, and older cats can show it as weaker jumping. But muscle loss from illness looks similar, and only an exam and tests can tell them apart. That’s why “he’s just getting old” isn’t a safe explanation for a thinner cat.

How can I monitor my cat’s weight at home?

The AAFP senior care guidelines recommend teaching owners to track body weight, body condition and muscle condition at home, because it helps catch problems early. Here’s how:

1. Weigh regularly. Use the same scale at the same time of day. A baby or pet scale shows small changes better than a bathroom scale. With a bathroom scale, weigh yourself, then weigh yourself holding your cat, and subtract.
2. Write it down. Keep a simple log with the date and weight. A trend over weeks is more useful to your vet than a single number.
3. Check body condition. Vets use a 9-point body condition score. Run your hands along your cat’s ribs, spine and hips. Ribs you can see, or bones that feel sharp, suggest your cat is too thin. Our cat body condition score tool walks you through it.
4. Feel for muscle loss. The AAFP guidelines note that body composition can change even when weight stays the same. Check the muscle over the spine, shoulders and back legs. Bones that feel more prominent than before can mean muscle loss.
5. Track food intake. Note what and how much your cat eats each day. Our cat calorie calculator gives a rough idea of how much a cat of that size needs, which helps you and your vet judge whether your cat is eating enough.

Bring your notes and weights to the appointment. Also mention changes in thirst, urination, stools, vomiting, energy and chewing.

What will the vet do for a cat losing weight?

Your vet will ask about diet, appetite and other signs, then examine your cat from nose to tail. They’ll check the mouth, feel the belly and the neck, where an enlarged thyroid can sometimes be felt, and listen to the heart.

VCA lists the most common screening tests for weight loss as:

• Complete blood count and blood chemistry panel
• Urine test
• Stool test for parasites
• Thyroid hormone (T4) level

Depending on the results, your vet may also suggest blood pressure, x-rays, an ultrasound or more specific blood tests. Treatment depends on the cause. Many causes of weight loss, including hyperthyroidism and diabetes, can be treated well, especially when they’re caught early.

Can I help my cat gain weight at home?

Don’t try to fix unexplained weight loss with food alone before a vet visit. Extra food can hide the problem while an illness gets worse, and a cat with hyperthyroidism or diabetes may keep losing weight however much it eats.

While you wait for an appointment, and after your vet has a diagnosis:

• Offer a food your cat already likes, and don’t switch diets suddenly.
• Warm wet food slightly so it smells stronger.
• Feed in a quiet place away from other pets.
• Keep weighing and keep notes.
• Never give human appetite stimulants or supplements. Your vet can prescribe a cat-safe appetite stimulant if it’s needed and will set the dose for your cat.

For other signs worth checking, browse our cat symptoms guides, or see when to see a vet.

Written by the CatsMed Team from the sources above. This guide isn’t reviewed by a veterinarian and isn’t a substitute for one. See how we research.