Why a cat may be losing weight

Unexplained weight loss in a cat is never something to wait out. Many causes are treatable, and early care helps. Weigh your cat, note its appetite and thirst, and book a vet visit. Do not change the diet or start any treatment yourself. A cat that is losing weight and also not eating, vomiting or very thirsty needs to be seen soon.

Why it matters

Cats are small, so a loss that looks minor on the scale can be large in proportion. A loss of half a pound in a ten-pound cat is five percent. Many vets treat steady loss of ten percent of body weight as significant. Cats also lose muscle, especially along the spine, with age or illness, and the loss can hide under fat or a thick coat.

Weight loss is a sign, not a diagnosis. It can come from eating too little, from illness that burns or wastes energy, or from stress. Only an exam and tests can tell which.

Is the cat really losing weight

Check before you worry. Some changes look like loss.

• Planned loss. A cat on a vet-approved diet to lose weight should lose slowly. Fast loss is dangerous.
• Grooming and coat. A summer clip, a shed or a thinner coat can change the look of a cat.
• Kittens becoming adults. A growing kitten may look leaner as it stretches.
• Measurement error. Home scales vary. Weigh the same way each time, with a baby scale or by weighing yourself with and without the cat.

Use the weight and body condition tracker to record weight, and the body condition score to judge shape. Feel the ribs, spine and hips with flat fingers. You should feel them under a thin layer of fat, not sharp and bony. From above, look for a waist, and from the side, a slight belly tuck. Bony hips and a prominent spine suggest your cat is too thin.

Common reasons

Weight loss has many possible causes. Your vet will look for them. Here are some of the more common.

Not eating enough

• Dental pain or mouth disease, such as periodontal disease, makes eating painful.
• Nausea from gut, kidney, liver or pancreas problems.
• Stress or changes at home, a new pet, a move or a different food.
• A food the cat dislikes, a bowl it avoids, or competition at feeding time.
• Poor sense of smell during a respiratory infection.
• Pain from arthritis or other disease, which makes reaching the bowl hard.

Eating but still losing

• hyperthyroidism: an overactive thyroid, common in older cats. Typical signs include weight loss with a big appetite, restlessness, and sometimes thirst and vomiting.
• diabetes mellitus: the body cannot use sugar well. Signs include thirst, urinating more, a big appetite and weight loss.
• Intestinal parasites, especially in kittens.
• Poor absorption from gut disease.
• Cancer, including lymphoma.
• Heart disease and other conditions that waste muscle.

Kidney and other organ disease

• chronic kidney disease is common in older cats. Signs include thirst, urinating more, poor appetite, nausea and weight loss.
• Liver disease and pancreatitis.
• Infection, such as feline leukemia virus or feline immunodeficiency virus.

Older age

Older cats can lose muscle as they age. Do not accept it as normal. Many age-related problems can be managed, and early care helps.

Hepatic lipidosis

A cat that stops eating can develop a serious liver problem called hepatic lipidosis, especially an overweight cat. This is why a cat that has not eaten for a day or more needs a vet.

What to do, step by step

1. Weigh your cat. Use a scale you can repeat. Record the date and weight.
2. Check the body. Feel the ribs, spine and hips. Look for lumps, bad breath, drooling or a poor coat.
3. Note the details. Write down: - Appetite: more, less or the same. - Thirst: how often the bowl is refilled. - Litter box: the amount of urine and stool, diarrhea or straining. - Vomiting: how often, and what it looks like. - Behavior: hiding, restlessness, night crying or lethargy. - Any change at home.
4. Watch the food. See if your cat eats its food, and how much. If you have several cats, work out who is eating what.
5. Call your vet. Describe the loss and the signs. Ask how soon to book. Do not wait for more loss.
6. Prepare for the visit. Bring your records, the food and a list of treats and medicines. A short video of unusual behavior helps.
7. Expect tests. The vet will examine your cat and may suggest blood tests, a urine test, a stool test, a thyroid check, imaging or other tests. Ask what each is for.
8. Follow the plan. Many causes can be managed with diet, medicine or care. Take your vet's advice about food and treatment, and ask about follow-up weighing.

Common mistakes

• Waiting weeks to see whether weight returns.
• Adding calories or supplements without a diagnosis. This can hide the problem or cause harm.
• Giving human medicines or appetite aids.
• Blaming old age or fussiness.
• Forgetting that a cat that eats well can still be sick.
• Overlooking dental pain.
• Putting a heavy cat on a rapid diet.
• Leaving a weight record until the vet visit. Keep it monthly.

When to call a vet or get help

Book a vet visit soon for any unexplained weight loss, even if your cat seems well. Go to a vet within a day if your cat has weight loss together with any of these:

• Not eating, or eating much less.
• Drinking and urinating much more.
• Vomiting or diarrhea.
• Weakness, hiding or lethargy.
• Bad breath, drooling or trouble chewing.
• A big appetite, restlessness or a racing heart.
• A swollen belly.
• Yellow gums or eyes.

Go to an emergency clinic at once if your cat is not eating and is lethargic, is breathing with effort, or is collapsed.

Summary

• Weigh your cat regularly and use a body condition score.
• Unexplained loss is a reason to see a vet, not a reason to wait.
• Causes include dental pain, thyroid disease, diabetes, kidney disease, gut disease, parasites and cancer.
• Do not change the diet or give supplements before a diagnosis.
• A cat that has not eaten for a day or more needs help now.