Sudden weight loss in a cat can be a sign of a serious medical issue.

By Brendan Howard
November 11, 2020
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As a cat owner, you're worried. Your cat's chubby tummy is gone now, and there's suddenly a very visible waist behind the ribs. You can see and feel your cat's ribs (you couldn't before!), and your cat's back is bony now, where before it was smooth petting.

If you're not actively trying to help your cat lose weight, sudden weight loss or signs or undernourishment can be serious, says Renee Rucinsky, DVM, Dipl., ABVP at Mid Atlantic Cat Hospital in Queenstown, Md.

"It may be as simple as the cat not taking in enough calories for its lifestyle, or there could be an underlying medical issue," says Rucinsky.

8 Reasons Your Cat May Be Losing Weight

No matter where on your cat's body you notice weight loss, your cat's loss of fat or muscle could be caused by "just about anything," Rucinsky says. 

Here are a few medical issues that can contribute to rapid weight loss in cats:

  1. Intestinal disease or parasites can cause nausea or make it difficult for your cat to absorb nutrients from food. Gas or inflammation in the digestive tract can cause problems and may be connected to other medical conditions.
  2. Dental disease can cause your cat to avoid food, because it hurts to eat.
  3. Cancer
  4. Chronic kidney disease
  5. Diabetes mellitus
  6. Heart disease
  7. Hyperthyroidism
  8. Pancreatitis

My Cat Is Eating...So Why Is He Still Losing Weight?

Cats who are seeing weight loss but still eating are at risk, says Kelly St. Denis, DVM and current president of the American Association of Feline Practitioners.

"Cats eating less than normal, normal, or more than normal amounts are all potentially experiencing health issues if they have weight loss," says St. Denis.

Senior cats in particular may still be eating their food, but their nutritional needs change as they age. A cat who ate voraciously at a younger age might not be eating as much or as often. The change can be so gradual that you don't notice, but your cat's eating habits may not be keeping up with nutritional needs.

"A cat who's losing weight but still eating is extremely common in older cats, and is a primary sign of hyperthyroidism," Rucinsky says. "This disease is super-common and one of the most treatable problems we see. Weight loss but still eating can also be caused by inflammatory bowel disease, which commonly alters the way that nutrients in the food are absorbed."

Your cat may also be drinking a lot and losing weight, which can be a sign of chronic kidney disease or diabetes mellitus.

Visit your veterinarian to make sure that there aren't any underlying medical issues and to get some solid nutrition recommendations. (St. Denis recommends a Cat Friendly Practice.)

What To Do If Your Cat Starts Losing Weight Fast

If your cat's not eating, St. Denis says to see a veterinarian immediately. "A loss of appetite in a cat often occurs when the cat has even low-grade nausea and develops an aversion to food as a result," she says.

The same goes for weight loss, she says, which can be an early sign of diseases two or three years before signs show up. "If you notice your cat losing weight, schedule a veterinary visit as soon as possible," St. Denis advises.