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18 Reasons for Weight Loss in Cats

Sherry grew up watching her uncle raise turtles, fish, goats and sheep in his backyard. She lives with a tabby and her three kittens.

Various conditions can cause a cat to lose weight. Know when is the right time to reach a vet.

Various conditions can cause a cat to lose weight. Know when is the right time to reach a vet.

Reasons for Weight Loss in Cats

Cats are very good at maintaining a normal weight because of their habit of eating numerous small meals in a day. This is why any significant variation in their body weight should call for early intervention.

Cat Eats But Still Loses WeightCat Avoids Food

Inappropriate Diet

Oesophagal Disease

Diabetes Mellitus

Oral Cavity Problems


Congestion from Cat Flu

Inflammatory Bowel Disease

Chronic Kidney Disease

Exocrine Pancreatic Insufficiency

Feline Infectious Peritonitis


Cancers of Lymphoma and GastrinomaType

Worm Infestations

Liver Disease

Genetic Disorders


Medicines like

Toxic Liver Disease

Stress or Loneliness

Hormonal Influences in Female Cat

Blood Disorders

Thymine Deficiency

My Cat Is Losing Weight But Eats Constantly

If your cat is losing weight despite having a ravenous appetite, it may be due to inadequate diet or diseases that cause malabsorption, maldigestion, and excessive loss.

1. Inappropriate Diet

Cats tend to develop a liking for particular food types based on how they have been fed from a very young age. Sometimes they grow tired of the same food and prefer a new diet of a similar type.

If the diet is inappropriate for the growth phase of the cat, the body will not get the required nutrients despite eating.

Poor Quality Diet

The quality of a diet should be assessed for each type of cat food based on the packaging claims. One way to do this is by looking for an AAFCO statement on the package. Foods either undergo an AAFCO feeding trial or be chemically tested.

Inadequate Quantity Fed

The quantity of food and quantity of nutrition required with each meal is different. It depends on the cat's age, its weight, and sometimes the breed.

2. Diabetes Mellitus

Diabetes mellitus is a common hormonal disease in cats. Type 1 diabetes in cats results in an absolute insulin deficiency. This type of diabetes is called Insulin-dependent Diabetes Mellitus (IDDM).

Insulin is a hormone involved in the metabolism of energy, proteins, carbohydrates and lipids. With insulin deficiency, the body's metabolism is disturbed. The cat may experience weight loss, excessive urination, increased appetite and excessive thirst. The symptoms get severe as the disease progresses, leading to vomiting, anorexia, and seizures.

Give the cat a diet high in fibre and calories. Diets high in fibre increase insulin sensitivity and prevent peaking postprandial increase in sugars. A calorically dense diet will help you maintain the healthy body condition of your cat who has already lost a significant amount of weight.

3. Hyperthyroidism

Hyperthyroidism is the most common endocrine disorder in cats. It results in excessive levels of thyroid hormones. It is diagnosed most in cats by age 12 or 13 years with less than five per cent of cases diagnosed in cats younger than 10 years of age.

Like diabetes, hyperthyroidism also increases metabolism, energy need and heat production. This causes your cat to feel hungry often and still lose weight. In rare cases, cats may have reduced or normal appetite. There is muscle wasting, weakness, excessive urination and intolerance to heat.

Sometimes, cats also show behavioural changes, hyperactivity, nervousness, and tremors.

Most cats with hyperthyroidism are underweight. A diet dense in calories is recommended for these cats. Use a diet high in fats and proteins.

It is important to note that once the treatment for hyperthyroidism is begun, appetite decreases and so you might have to reconsider the dietary changes you made.

Also, note that hyperthyroidism in cats is often associated with kidney disease. Increase the protein content only after making sure that your cat is free from kidney disease.

4. Inflammatory Bowel Disease (IBD)

IBD as the name suggests refers to the inflammation of the small or large intestine or both. The disease is more likely to occur in cats of age five to ten years or older.

The most common sign includes weight loss with or without vomiting and diarrhoea. The appetite may be normal, increased or decreased. Weight loss despite normal eating is due to the poor absorption of food because of the small intestine disease. Conversely, the appetite may be reduced because of nausea.

If the large intestine is also affected, there will be difficulty when defecating. A cat will have several small episodes of diarrhoea, often with mucus and blood. If these signs occur with weight loss, there is enough reason to suspect the small and large intestinal disease. But, there is usually no sign of weight loss if the large intestine is only affected.

5. Exocrine Pancreatic Insufficiency (EPI)

The exocrine part of the pancreas synthesizes and secretes digestive enzymes. When the pancreas is unable to synthesize and secrete enough amounts of these enzymes it results in EPI.

Maldigestion from EPI results in weight loss despite normal eating in cats. This condition is rare in cats but is perhaps being recognized more often now.

It can affect cats of any age group. Increased appetite and vomiting with or without diarrhoea are the signs described for EPI. Faeces may be normal or yellow or pale with increased frequency.

Cats with EPI are usually also affected by IBD. The signs may thus sometimes reflect IBD and not EPI.

Dietary supplementation with pancreatic enzymes is effective in cats with EPI.

6. Hyperadrenocorticism

Hyperadrenocorticism or Cushing's syndrome in cats results from excess glucocorticoid hormone. This happens with the hyperfunctioning of the pituitary gland or adrenal gland or a high dose of exogenous glucocorticoids.

Unlike dogs, cats with hyperadrenocorticism show weight loss. Ninety per cent of cats with hyperadrenocorticism have diabetes mellitus. In these cats, weight loss may be often a result of poorly controlled diabetes.

In a more advanced stage, the signs in these cats are like signs of diabetes. They include excessive thirst and urination, and increased appetite. The abdomen appears pendulous and changes in the skin such as fragility are also noticeable with the disease progress.

7. Genetic Disorders

Flat chested kittens syndrome is an inherited disease in cats of some lines of Bengal, Burmese, and Munchkin. This condition is recognized by breeders and is less reported in the veterinarian literature. The kittens show poor weight gain during the initial years of their growth.

Inherited Red Cell Abnormalities Resulting in Anaemia

Pyruvate Kinase deficiency related to the Abyssinian and Somali breeds of a cat affects the survival time of the red blood cells. It is an autosomal recessive disorder identified in cats younger than 1 year of age.

Coomb's negative hemolytic anaemia

The symptoms shown by the cats are like other anaemic cats and include lethargy, weakness, paleness, loss of appetite and weight.

8. Worm Infestations


Roundworms are the most common type of worms affecting at least one-fourth of cats around the world. Roundworms are about four inches long, cream-coloured worms that live in the cat's gut surviving on the cat's ingested food. Kittens are more likely to get the infection than older cats.

Cats ingest roundworms by swallowing eggs while grooming or eating rodents that hoard the worm larvae in their tissues. Mother's milk can also infect the kittens.

The infected cats show vomiting, diarrhoea, constipation, loss of appetite and swollen belly. Although the infection from roundworms is relatively benign, it may lead to anaemia if left untreated.


Tapeworms have a long body that resembles a tape. They are usually picked by cats by ingesting infected insects such as fleas while grooming or by eating rodents.

The worms grow in the cat's intestine with its head embedded in the mucosal membrane absorbing nutrients from the food she eats.

The body of tapeworms ends in a series of segments all filled with eggs. As the segments of the worms mature, they are shed and passed in the faeces. These look like rice grains near the cat's tail and around the anus.

Signs of tapeworm infestation in a cat are weight loss, occasional diarrhoea and vomiting.


Heartworms though uncommon can infect cats. They are transmitted by mosquitoes. Signs include weight loss, vomiting, coughing, anaemia, swollen legs and abdomen. In serious cases, heart and liver damage may occur leading to death.


Hookworms are slender worms that are less than half an inch long. They live attached to the lining of the gut wall and feed on the blood of the infected cat. Because of their small size, they are not visible in the faeces.

The infection can result in diarrhoea and weight loss. Severe infection can lead to anaemia due to blood loss through faeces. If not treated, this can result in death.

My Cat Is Losing Weight and Has Low Appetite

1. Oesophagal Diseases

The oesophagal disease is quite rare in cats when compared with dogs. But, signs such as drooling, reduced appetite, pain on swallowing, and passive expulsion of food or fluid from the oesophagus should not be ignored.

Cats when experiencing pain during swallowing tend to extend the head and neck while swallowing. As the disease gets severe the cats find it difficult to eat. These signs point to inflammation in the oesophagus or strictures.

Oesophagitis may occur in a cat with a history of

  • Irritants from foreign bodies
  • Chemicals
  • Caustics
  • Reflux disease
  • Persistent vomiting
  • Hiatal hernia
  • General anaesthesia

2. Oral Cavity Problems (Stomatitis, Gingivitis, Tooth Pain)

Inflammation of the mouth or gums and tooth pain associated with cavities or old age are some common problems in cats causing them to avoid food. Cats with these problems often have a poor appetite.

The cats affected keep pawing at the face, may drool and show poor grooming. Many cats suffering from stomatitis show the presence of feline viruses. Confirm the condition from your vet as soon as you can.

Offer small meals that are soft and tempting. Keep the mouth area clean with the help of warm salty water.

3. Congestion From Cat Flu

Cats refuse to eat when they are having congestion from cat flu.

A cat will not eat if she is suffering from any of the following problems:

4. Chronic Kidney Disease

Older cats are prone to kidney problems. Cats with chronic kidney disease show signs including weight loss, loss of muscle mass, and poor fur condition.

Some cats with CKD have reduced appetite. A diet with high-fat content is recommended for these cats. Restrict the dietary proteins to 28% to 32% on a dry matter basis.

Low potassium level is often seen in cats with CKD. Increase the dietary potassium by about 0.8% to 1.2% on a dry matter basis.

Polycystic kidney disease is a genetic disorder that can be inherited from just one parent. It is found in Persian and Exotic Shorthair cats. The disease causes increased thirst with urination, weight loss and weakness in cats.

5. Feline Infectious Peritonitis

FIP is an infectious neurological disease caused by a feline enteric coronavirus (FIPV). It majorly affects cats younger than two years of age. FIP manifests in either dry form or wet form, although the dry form is more common.

Cats with FIP will show neurological signs such as head tilt, blindness, ataxia. Other signs include involvement of eye with inflammation of the uvea (uveitis), choroid and retina (chorioretinitis), dehydration, weight loss, weakness, and fever.

6. Cancer (Lymphoma and Gastrinoma)

Lymphoma is the most common feline cancer. It is found in cats of any age and any breed. Purebred cats such as Manx, Burmese, and Siamese are at a greater risk.

Causes of lymphoma are often unknown; however, feline leukaemia virus and feline immunodeficiency virus are implicated.

Signs of lymphoma of the alimentary canal are vomiting, diarrhoea, anorexia, and weight loss.

There is another tumour of the pancreatic islets that results in the excessive secretion of gastrin. This condition is called ''Gastrinoma''. Excessive gastrin secretion results in the excessive release of hydrochloric acid in the stomach. This can cause ulcers and perforations in the stomach and duodenum. Signs of gastrinoma in cats include vomiting, weight loss, and poor body condition.

7. Liver Disease

The liver performs many important functions in the body including metabolism and detoxification of poisons and drugs. Inflammatory conditions affecting bile ducts, gall bladder and liver produce symptoms of general illness such as poor appetite, vomiting, and weight loss. Fever and jaundice may also be present.

Liver tumours are more common in cats than they are thought to be although they are more benign. There are several types of liver tumours.

Signs of liver problems are decreased appetite, weight loss, weakness, vomiting, abdominal swelling due to fluid accumulation and jaundice.

8. Pancreatitis

Pancreatitis is the inflammation of the pancreas. The organ secretes important enzymes and hormones for digestion and metabolism. The symptoms of pancreatitis include decreased appetite, weakness, vomiting, diarrhoea and weight loss. Dehydration, fever and abdominal pain may also be present.

9. Toxic Liver Disease

A cat's liver has fewer detoxifying enzymes compared to dogs which makes them more sensitive to drugs and poisons. Lawn poisons, antifreeze, and all manners of chemicals sprayed in the laws can be poisonous to cats.

The cat may have a sore tummy, stop eating and show weight loss. Other signs include weakness and excessive discoloured urination.

10. Stress and Loneliness

Stress or loneliness in cats can lead to changed behaviour and reduced appetite. This in the long term can result in a noticeable weight loss.

11. Hormonal Influences in Female Cat

Female cats may have a reduced appetite due to hormonal influences during their breeding season.

12. Blood Disorders

The spleen is an organ that produces red blood cells. Cats with a disorder of the spleen show loss of appetite, vomiting, weight loss, and an enlarged abdomen. The abdomen may be painful sometimes. You may also notice laboured breathing.

Feline hemoplasmosis is a blood disorder that results from Feline hemoplasmas, gram-negative organisms causing anaemia and illness in cats. Cats show signs like cats with anaemia. They often show weakness, paleness, loss of appetite, and weight loss.

13. Thiamine Deficiency

Thiamine is a water-soluble vitamin B. Cats need four times as much thiamine in their diet compared to dogs. Thiamine deficiency is usually seen in cats who are fed raw or undercooked fish diets. Certain raw fishes contain the enzyme thiaminase which breaks down thiamine.

Signs of thiamine deficiency include decreased food intake, drooling, weight loss, and depression. In some cases, this may progress to dilated pupils, weakness, uncoordinated muscle contractions, seizures, and eventually death.

Drugs That Can Cause Weight Loss in Cats

Some drugs can cause weight loss as a side effect in cats. Enilconazole and tocenarib show this side effect. Enilconazole is an antifungal drug, not licensed for use in many countries. Tocenarib is a medication used in tumours.

Antiviral drugs and some behaviour-modifying drugs may also cause weight loss rarely in cats.

Weight Loss in Old Cat

By ten to twelve years of age, cats tend to lose weight and their body condition declines. Some breeds of cat such as the colourpoint shorthair lose weight more notably and commonly than other breeds.

Feeding older cats differently from younger cats can be unhealthy. Owners tend to feed canned foods and table scraps to cats as they grow older. It is advisable to develop a feeding plan for your older cat based on her nutritional needs.

If your older one is eating regular diets that are rich in nutrition; it might simply mean that she has reached an age where her digestive efficiency has reduced significantly. Cats also refuse food if their sense of taste and smell is dulled.

Other reasons can be serious such as the presence of a disease. Reasons for weight loss mentioned above applies to old cats as well. Additionally, oral tumour, dental disease and other infectious diseases may also be responsible.

What Should I Do If My Cat Is Losing Weight?

1. Note Changes in the Weight

Write down the changes in your cat's weight every two to four weeks.
You can identify any loss in weight by evaluating muscle loss or wasting. A loss of muscle mass over the back or legs, a pendulous abdomen, a large inguinal fat pad or retraction of the globe may indicate a serious underlying health problem.

2. Diet Modifications

This is necessary when the cause of weight loss is related to loss of appetite due to either reluctance to eat or inability to eat. You may make mild changes in the diet or use ways to encourage the cat to eat.

Many times a therapeutic diet may be recommended for the cats. It is usually specific to the problem cat is suffering from. In such a case it is best to have a review with your cat's vet before making these changes.

To encourage the cat to eat you may:

  • Offer fresh favourite foods to the cat.
  • Use a clean, wide and shallow food container.
  • Moisten the food if the cat is having a problem with biting or swallowing it.
  • Feed-in a quiet and stress-free environment.

3. Check With a Vet

Unintentional weight loss suggests an underlying health issue. Although sometimes it might only indicate changes in your cat's feeding choices, other times it can be a sign of a life-threatening disease. Before you can find out what can be done, you need to know what is wrong.


1. Little, S. (2011). The Cat-E-Book: Clinical Medicine and Management. Elsevier Health Sciences.

2. Laflamme, D. P. (2005). Nutrition for aging cats and dogs and the importance of body condition. Veterinary Clinics: Small Animal Practice, 35(3), 713-742.

3. Steiner, J. M. (2012). Exocrine pancreatic insufficiency in the cat. Topics in companion animal medicine, 27(3), 113-116.

4. Caney, S. (2009). Weight Loss in the Elderly Cat: Appetite is Fine, and Everything Looks Normal….

5. Watson, A. D. J., Church, D. B., Middleton, D. J., & Rothwell, T. L. W. (1981). Weight loss in cats which eat well. Journal of Small Animal Practice, 22(7), 473-482.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2020 Sherry Haynes


Sherry Haynes (author) on May 01, 2020:

Hey, Liz. Thanks for reading.

Liz Westwood from UK on April 29, 2020:

This is a detailed and very helpful article for cat owners. We had a cat many years ago that lost weight. Sadly it was due to a tumour.