Is your cat losing weight? 40 reasons why and how to tell

Signs That Your Cat is Losing Weight

The first question then is: is your cat losing weight? I’ll tell you how I know if my cat is losing weight. If my cat has lost weight I can feel his vertebrae more distinctly. I know how distinct they are.

Also I know him so well that if he is losing weight I can tell the difference visually. Another good check, perhaps even better is to get to know how your cat feels. We all stroke are cats. We can feel the bones on his shoulders and perhaps his rib cage. You can feel how much muscle mass and how much fat there is under the coat.

It is more difficult to tell visually whether a long-haired cat has lost weight or not. I am minded to think of the well-known Main Coon cat. They have shaggy medium-long fur and when you feel these cats they can be quite slender underneath their beautiful coats. To have to get know how your cat feels by gently palpitating (the veterinary word for feeling a cat) your cat.

I’m sure that 99% of observant cat owners can tell if there cat is losing weight. I would have thought to that if your cat is losing weight he is also losing his appetite. He’ll be eating less. She will show less interest in her food. Food will be left in the bowl. These are all observable signs of loss of appetite and therefore loss of weight.

So, you have decided that your cat is losing weight. What to do next? Well the obvious answer is take your cat to veterinarian but there is no harm in doing some research beforehand.

Therefore, I list below about 40 reasons why a domestic cat is losing weight.

Is your cat losing weight? 40 reasons why and how to tell
Underweight cat. Photo in public domain
Two useful tags. Click either to see the articles:- Toxic to cats | Dangers to cats

Gastrointestinal Parasites

I won’t go over these in detail because I have already done so on other pages. However gastrointestinal parasites cause a general decline in a cat’s health. You will note decreased appetite, loss of weight, possible protrusion of the third eyelid, anaemia and diarrhoea.

Giardiasis – A Protozoal Parasite

These are single celled animals invisible to the naked eye. Cats acquire the infection by drinking water from streams and other sources infected with cysts. Diarrhoea may develop and it may be acute or chronic and accompanied by weight loss.


This is a rare bacterial infection. Cats acquired it from the bite of a bloodsucking tick or flea. Or the cat might come into direct contact with an infected wild animal or carcass. The cat will show weight loss, fever apathy and depression.

Acute Viral Respiratory Infection

We all know about this one. Symptoms will vary in their severity. Cats may lose their taste food and refused to eat. This is caused by stomatitis. There may be a secondary bacterial infection leading to rapid weight loss.

Feline Infectious Peritonitis

This is a complicated and devastating disease. The wet form as it is called produces symptoms of loss of appetite, weight loss, listlessness and depression.

Feline Leukaemia Virus Disease Complex

This is another serious disease. Signs of illness can be non-specific but include fever, apathy, weight loss due to loss of appetite.

Feline Immunodeficiency Virus

This is another top level, serious disease in cats. Cats suffer from a variety of unexplained signs of ill-health including weight loss with emaciation, fever and recurring upper respiratory infections et cetera.


This disease is caused by a fungus found in central United States near the great Lakes, the Appellation mountains, Texas and the valleys of Mississippi, Ohio and the St Lawrence Rivers. It causes fever, loss of appetite, weakness, weight loss and debilitation.

Bulging or Sunken Eye

This occurs with glaucoma, tumours and abscesses. The sunken eye occurs with weight loss, eye pain, gentleness and dehydration.

Film over the Eye

This is not a disease in itself but a sign that the cat is ill. It is associated with sunken eye, dehydration or chronic weight loss which reduces the size of the fat pad behind the eye.

Nasal Infections

This concerns bacterial infections causing sneezing nasal discharge et cetera. There may be secondary bacterial infections in the sinuses. The cat will feel ill with a diminished appetite that can lead to rapid weight loss.

Gum Disease

This is periodontitis, an infection of the teeth and gums. There will be an offensive mouth odour. The cat will find it painful to chew and decline to eat leading to weight loss.

Oesophageal Disease

Signs of this disease include regurgitation, painful swallowing, drooling and weight loss.

Dilated Oesophagus

This means the oesophagus is enlarged. It is accompanied by regurgitation, loss of weight, episodes of aspiration pneumonia caused by reflux of food into the trachea.

Chronic Gastritis

This is an irritation of the lining of the stomach. The cat will vomit from time to time over weeks possibly. They are lethargic and lose weight.

Stomach Ulcer

These are not common in cats. The cat will vomit and the vomit will contain blood. There will be weight loss and anaemia.

Inflammatory Bowel Disease

This is an immune-mediated reaction of the gastrointestinal system to food, bacteria or parasite antigens. There are three bowel problems in cats. The symptoms include diarrhoea, sporadic vomiting, weight loss, anaemia and malnutrition.

Intestinal Obstruction

Needless to say a partial or intermittent obstruction cause for example by a tumour can lead to weight loss and intermittent vomiting or diarrhoea.


This is a liver disease in cats. Some cats will become acutely ill. Some cats show anorexia and possible jaundice. Some cats will have vomiting, depression, diarrhoea and weight loss.

Diabetes Mellitus

This is sugar diabetes. The early signs are frequent urination, drinking lots of water, a large appetite and unexplained weight loss.


Lung cancer will show symptoms of lethargy, weight loss and depression.


Most cats don’t show signs of clinical infection. Some cats may have a persistent dry cough caused by a secondary bacterial infection. Sometimes a cat will experience fever, weight loss, wheezing and nasal discharge.

Hypertrophic Cardiomyopathy

This is a heart disease. It is the most common cause of heart disease in cats causing spontaneous death in indoor adult cats. Early signs are vague but include a heart murmur, decreased appetite and weight loss.

Dilated Cardiomyopathy

This occurs when the heart muscle loses its tone and becomes flaccid. The pulse is often rapid and there is loss of appetite leading to rapid weight loss, weakness, fainting attacks.


Anaemia is a symptom caused by blood loss or inadequate red blood cell production. There will be an underlying illness. Anaemic cats lack appetite and lose weight.

Heartworm Disease

One or two worms may be enough to cause serious heart trouble or even death. The signs are a cough, lethargy, loss of weight and poor coat condition.


The vertebral column generates progressively with arthritis. The cat may have a fever, back pain and weight loss. He may also be inactive.

Bacterial Infection of the Kidney

When the disease is of long duration the cat owner will see signs of kidney failure and weight loss.

Kidney Failure

Kidney failure leads to uraemia which is excessive amino acid and protein metabolism and products in the blood that would normally be excreted. Signs of uraemia include apathy, sluggishness, loss of appetite and weight loss.

Excess or Deficiency of Vitamin A

This can induce sterility. Signs of deficiency are weight loss, loss of hair and night blindness.

Uterine Infection

I’m referring to a secondary bacterial infection in the uterus of a female cat. This can cause listlessness, loss of appetite, fever and a bloody or puss-like discharge from the vagina.

Kitten Septicaemia

This is a blood-borne infection in an infant kitten. It is caused by bacteria. The bacteria enters the cat through an abscessed umbilical stump. An alternative is bacteria from infected milk of the mother. As the disease progresses the abdomen becomes distended and other signs include weakness, dehydration and weight loss.

Thyroid Cancer (Hyperthyroidism)

Weight loss, vomiting and panting may be symptoms. The sedate older cat turns into a wild kitten.

Abscess of the Uterus

Signs include lethargy, depression, loss of appetite and therefore loss of weight.

Weight Loss in an Ageing Cat

This is a serious condition. It can often be caused by kidney disease, cancers, gum disease and loss of smell. The cat may appear to be fat but in reality there is a heart, liver, or kidney problem with fluid buildup in the abdomen.

P.S. An afterthought. It is obvious but if your cat is starving he’ll lose weight. This is about the provision of enough food.

Source: Cat Owner’s Home Veterinary Handbook.

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