Glossary

Obesity

Excess body fat that harms a cat's health, raising the risk of diabetes, arthritis and urinary disease.

Also called: overweight cat, fat cat, feline obesity, cat weight gain

A cat is considered overweight when it carries more body fat than is healthy, and obese when the excess is well beyond that. A large share of pet cats in many countries are overweight. Risk factors include neutering, an indoor life, free-feeding, rich food and less play, along with age and genetics. Some medical conditions, such as an underactive thyroid, are rare in cats, though a vet may still check for them.

The extra weight matters because it makes some diseases more likely. These include diabetes mellitus, osteoarthritis, urinary problems, skin problems and more risk during anesthesia. Obese cats often cannot groom their backs, may become less active and live shorter lives. Judge weight with a body condition score, not the numbers on the scale alone.

Fast weight loss is dangerous. A cat that stops eating or loses weight too quickly can develop hepatic lipidosis, a serious liver disease. A vet should set the target weight, choose the diet and portions and plan check-ups, and a slow, steady loss is the goal. Do not cut a cat's food sharply or put it on a crash diet. Ask your vet how to measure meals, add play, and make the home more active.

Last reviewed November 7, 2026

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Related terms

Body condition score A hands-on rating of how lean or fat a cat is, on a scale such as 1 to 9, used by vets because weight alone can mislead. Diabetes mellitus A disease in which a cat's body cannot make or use insulin properly, so blood sugar stays too high. Osteoarthritis Wear and inflammation of the joints that is very common in older cats and often shows up as subtle changes in behavior. Hepatic lipidosis A serious liver disease in which fat builds up in liver cells after a cat stops eating, most often in overweight cats. Spay The surgery that removes a female cat's ovaries, and usually the uterus, so she can no longer become pregnant or go into heat. Neuter The surgery that removes a male cat's testicles so he cannot father kittens, with fewer urges to roam, fight and spray.

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