What this means
A long or thick coat can hide weight loss, so the first changes are noticed not with the eyes but with the hands: gently feel the back and the ribs. If the bones have become easier to feel or the muscle along the back is thinning, show it to a vet. Even a small loss matters in a cat, because a cat weighs so little. If you can, weigh your cat every few weeks and write the result down.
Weight loss has many causes, and when a cat eats well or even more than before, that is an important sign too. Sometimes it loses weight because it eats less from mouth pain or nausea; sometimes, although it eats, the body does not get or cannot use what it needs. Diabetes, kidney disease, gut disease, anaemia or cancer can show up exactly like this.
The loss often comes slowly and is easy to put down to age, but an old cat should not be losing weight either. Do not try to change or give anything at home instead of an examination. Note since when it has been losing weight, how much it drinks, how it eats and how it passes stools, and show this to your vet.
Possible causes
These are things that can cause this sign. It is not a diagnosis, and they are not equally likely for your cat.
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Diabetes
When insulin falls short, the body uses its own fat and muscle, so a cat loses weight even while eating well. It also drinks and urinates more.
About the condition: Diabetes mellitus -
Kidney disease
When the kidneys start to work less well, a cat drinks and urinates more, eats less and slowly loses weight.
About the condition: Chronic kidney disease -
Gut disease
When the gut digests or absorbs poorly, a cat loses weight although it eats. Sometimes vomiting or diarrhoea come with it.
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Anaemia
When there are too few healthy red blood cells, a cat becomes listless, eats less, its gums look pale and its weight falls.
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Cancer
Lymphoma and other tumours can gradually cause weight loss, a poorer appetite, vomiting or listlessness.
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An abnormal protein building up in the organs
In some diseases an abnormal protein collects in the organs and slowly disturbs how they work. A cat drinks more, eats less and loses weight.
About the condition: Amyloidosis
What else to watch for
These observations help your vet build the picture faster. Note down what you saw and when.
- Since when, and how much, your cat has lost weight, if you have weighing records
- Whether it eats as before, more or less
- Whether it drinks and urinates more, or the clumps in the litter box are bigger
- Whether it vomits or has diarrhoea
- Whether its coat has turned unkempt or dull
- Whether it has become less lively, sleeps more or breathes harder
When to book a routine visit
Book an examination if your cat is losing weight for no clear reason, even if it eats well and looks bright. If it is also not eating for a day or more, has turned very weak or is vomiting, contact a vet the same day.
Related conditions
Conditions whose entries mention this sign. The list is somewhere to read on, not a way to reach a diagnosis.
- Amyloidosis General health A condition in which an abnormal protein, called amyloid, builds up in the organs and slowly disturbs how they work. In cats it can settle in the kidneys, the liver or other organs, so over time these organs can start to work less well.
- Chronic kidney disease Kidneys and urinary tract A disease in which the kidneys slowly, over months or years, lose their ability to clean the blood and concentrate urine. It develops quietly, so its first signs are easy to put down to old age.
- Diabetes mellitus Hormones and metabolism A condition in which the body can no longer keep the level of sugar in the blood under control, because it makes too little insulin or stops responding to it. Without insulin the cells go hungry while sugar piles up in the blood and spills into the urine.
- Feline immunodeficiency virus (FIV) Infections A virus that slowly weakens a cat's immune system, so the body finds it harder and harder to fight off other infections. An infected cat can look perfectly healthy for a long time, even for years.
- Feline infectious peritonitis (FIP) Infections A severe disease that develops when the coronavirus living in cats' guts changes inside a cat's body and starts spreading throughout it. It inflames blood vessels and organs, and fluid can collect in the belly or chest.
- Feline leukaemia virus (FeLV) Infections A virus that spreads between cats through saliva and can cause anaemia and lymphoma and weaken the immune system. Not every infected cat falls ill, but a cat in which the virus takes hold faces serious disease.
- Hyperthyroidism (overactive thyroid) Hormones and metabolism A disease in which the thyroid, a small gland at the front of the neck, makes too much hormone. The whole metabolism speeds up, so the cat loses weight even though it eats more than ever.
- Intestinal worms Parasites Parasites that live in a cat's gut: roundworms, tapeworms and others. They take nutrients, irritate the gut and can slow a kitten's growth.
- Lymphoma Cancer A cancer that arises from lymphocytes, the white blood cells that defend the body against disease. Because these cells are found throughout the body, lymphoma can affect the gut, the lymph nodes, the chest, the kidneys or other organs.
- Pancreatitis Digestion and liver Inflammation of the pancreas, a gland beside the stomach and gut. In cats it can show only as a few vague signs, such as listlessness and a lost appetite, so it is easy to miss.
- Polycystic kidney disease Kidneys and urinary tract An inherited kidney disease in which fluid-filled sacs, called cysts, form in the kidneys. They slowly grow, press on healthy tissue and make it harder for the kidneys to work.
- Pyruvate kinase deficiency Blood and immunity An inherited disease in which the red blood cells lack an enzyme they need to make energy. These cells break down sooner than they should, so the cat can develop anaemia.
Body systems: General health Kidneys and urinary tract Hormones and metabolism Infections Parasites Cancer Digestion and liver Blood and immunity