Why Is My Cat Losing Weight? Getting to the Bottom of It

In this guide

Steady, unexplained weight loss in a cat that is eating normally, or even eating more than usual, is one of those signs that owners sometimes brush off for weeks before booking a vet visit. It should not be brushed off. Weight loss in cats is rarely just about diet or age, and the sooner the underlying cause is found, the easier most of them are to manage.

How to actually notice it

Cats are experts at hiding decline, and a thick or long coat can disguise weight loss for a surprisingly long time. Running your hands along the ribs and spine every few weeks is more reliable than eyeballing your cat, and keeping a simple monthly weight log, even on a basic kitchen scale by weighing yourself holding the cat and then without, catches a slow decline long before it becomes visually obvious.

Common underlying causes

• Hyperthyroidism, an overactive thyroid gland, mostly seen in cats over ten years old, typically alongside a ravenous appetite and restlessness
• Kidney disease, especially in senior cats, often with increased thirst and urination
• Diabetes mellitus, usually with increased appetite, thirst, and urination together
• Intestinal parasites, particularly relevant for cats with any outdoor access or a street cat background
• Dental disease, which makes eating painful even when the cat still shows interest in food
• Inflammatory bowel disease or intestinal cancer, more likely if weight loss comes with vomiting or diarrhoea
• Stress, particularly relevant in multi-cat homes, or after a house move, new pet, or change in routine

What your vet will want to check

Expect a thorough physical exam, a full blood panel including thyroid hormone levels, kidney and liver values, blood sugar, and a urine test. Depending on findings, this may extend to a faecal test for parasites, X-rays or an ultrasound of the abdomen, and sometimes a referral for further imaging if nothing obvious turns up on the first round of tests. Bring a note of exactly how much and how often your cat is eating, since this detail genuinely shapes which conditions your vet prioritises.

Managing weight loss once a cause is found

• Hyperthyroidism: managed with daily medication, a prescription iodine-restricted diet used as the sole food source, or in some cases a permanent procedure to remove the overactive thyroid tissue
• Kidney disease: managed with a renal-support diet, hydration support, and regular monitoring rather than a cure
• Diabetes: managed with insulin injections and a consistent feeding schedule
• Dental disease: often needs a professional cleaning and extractions under anaesthesia before appetite genuinely improves

Do not try to fatten up a thin cat with extra food before a cause is identified. In several of these conditions, more food does not translate into weight gain, and it can delay you noticing that something is genuinely wrong.

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