Underweight Cat - What Causes It? Cat Weight Loss 101

When it comes to animals, most pet owners are more worried about their pets gaining weight and all the trouble it brings. Did you know that the opposite of overweight cats also come with a whole host of problems? That’s right! If your cat is underweight, it is also dangerous for your cat! 

Unexplained weight loss in your cat may be a sign of an underlying medical problem. If your cat is eating well, it should not be losing weight so there must be a reason. There is a whole host of reasons and medical situations that may cause your cat to lose weight so it is important to consult with your local weight. 

underweight cat
Photo by Lisa Algra on Unsplash

How to tell if your cat is underweight? 

The weight of your cat is dependent on many factors such as its age, breed, activity level and overall health. Generally, a housecat will weigh about 10 pounds but some breeds can go up to twice that weight and be fully healthy. 

To determine if your cat is at a healthy weight or not, you should be able to feel its ribs and backbone but not see them. If you can see their ribs and backbone, your cat is underweight! 

The average cat weight varies greatly so it is best to talk to your vet to make sure your cat’s weight is not too low and is at a healthy level. 

There are two ways to determine if your cat is underweight at home before you head to the vet. You can use the body condition score way or the hand test

Cat Body Condition Score

This is usually used at the vets. It is like the body mass index for humans. A body condition score chart can help you determine if your cat is too skinny or too fat. 

Hand Test

You can also use your hand to determine your cat’s body condition and feel if it is too thin to be at a healthy level. To do so, you will need to feel the ribs and backbone. Be gentle when you do so as your cat may not be used to you touching them this way. 

Causes of Cat Weight Loss

This article should give you an idea about what you should be prepared to hear about your cat. There can be several causes such as:

1. Diabetes

Diabetes is a disease that commonly causes weight loss in cats. Usually your cat’s appetite will drop and drink excessive amounts of water, therefore urinating more than usual. 

This is because the cat’s body has failed to produce a hormone called insulin or your cat’s body has an impaired ability to respond to it. 

Other symptoms to look out for if your cat has diabetes include urinary tract infections and having a sweetly scented breath.

2. Not enough food

This may be an obvious factor but you would be surprised how often it is overlooked. When your cat does not consume enough calories, it will lose weight. Some cats are rather picky when it comes to food and can lose interest in food quickly, going days without taking a bite. 

There may also be competition from other cats or dogs for the food available so be sure to ensure the food bowls are filled constantly!

3. Cancer

Cancer is a relatively common cause for your cat being underweight. It will cause your cat to lose appetite, thus explaining the loss in weight. 

Your cat will also be rather lethargic. You should definitely visit your vet if you suspect it has cancer!

4. Feline infectious peritonitis

Feline infectious peritoniti is a virus and is most commonly found in cats that are raised in catteries. This virus is known to cause wasting. 

Cats with this virus will often seem sick with a fever.

5. Age

Older cats usually have some sort of weight loss as they age. Their metabolism changes and sometimes drops so it can be rather difficult to determine other health issues other than age. 

However, as your cat grows older, there are certain diseases your cats will be more prone to such as kidney disease.

6. Kidney disease

Weight loss is an indicator of kidney disease in cats. Kidney disease can actually manifest in your cat’s body three years before other signs through weight loss!

7. Hyperthyroidism

If you observe your cat eating more than usual but is still losing weight, it may be hyperthyroidism. 

A benign hormone-producing tumor on the thyroid gland which will elevate levels of the thyroid hormone will result in hyperthyroidism. 

Older cats are more prone to developing hyperthyroidism. As a human or as a cat,  growing old in age physically comes with a host of problems!

Other symptoms of hyperthyroidism are:

    • Increased drinking of water
    • Increased urination
    • Increase activity
    • Vomiting
    • Diarrhea
    • Muscle wasting

    8. Intestinal parasites

    These are also known as worms. Gross? Yes but your cat needs you! Take it to the vet! 

    It causes your cat to lose weight and other symptoms, though not always present, include diarrhea, bloating, vomiting and trouble breathing.

    9. Mental health

    Yes, some cats, like some humans, also suffer from mental health issues such as anxiety, stress or depression. If your cat is under psychological stress, it may stop eating, which results in an underweight cat. 

    There can be many situations that cause your cat to face stress and anxiety including but not limited to excessive noise, dirty food dishes, the closeness of its food dish to its litter box and other factors like a change of routine.

    10. Gastrointestinal problems (GI)

    There are different varieties and ranges of gastrointestinal problems that may cause your cat to lose weight. Other symptoms may also include diarrhea, lack of appetite and vomiting. 

    Your cats may also be underweight because of other common GI problems such as inflammatory bowel disease, food allergies and infections.

    11. Toothache

    If your teeth are painful, it can be rather hard to eat. The same goes with your cat. If it stops eating due to toothache, it can start to lose weight. 

    Other signs of a toothache in your cat are drooling and pawing at the mouth. 

    Your cat may also have mouth ulcers or severe gingivitis which will contribute to pain in its mouth.

    12. Arthritis

    If your cat is rather old, it may experience difficulty in actually getting to its food bowl, especially if it has arthritis. It can be painful to walk to the food bowl so it just stops eating.

    13. Medication

    Certain medications prescribed for your cat can change its appetite. Due to the loss in appetite, your cat will stop eating or eat a lot less and lose weight.

    14. Failing sense of smell

    The aroma of food has to be very appealing to your cat for it to eat. This is why raw food is recommended for cats such as Petcubes’ Cat Variety Pack. Although the smell of raw food to us humans is absolutely pungent, it is very delicious for your cat and entices it to eat. 

    If your cat’s sense of smell is failing, its food may be just not very appetizing.

    15. Skinny old cat syndrome (SOCS)

    The skinny old cat syndrome (SOCS) is a common cause for cat weight loss. This condition is most often seen in cats which are consuming high carbohydrates and lower protein. 

    As your cat is an obligate carnivore, it actually needs a high protein and low carb diet to thrive. As it ages, the need for more protein in its diet increases so that it will gain a healthy muscle weight. Sometimes you have an underweight cat simply because of its diet not being very balanced. 

    Treatment for Underweight Cats

    First of all, you have to take your cat to the veterinarian so that a complete physical exam, blood work and urinalysis can be done. This is the best way to determine what is causing your cat’s weight loss and design the best treatment plan for it. As the owner, you will also be reassured and have peace of mind once you find out exactly what is wrong with your cat and have a plan in place. 

    Of course, depending on the reason, there will be a treatment for an underweight cat or a way for you to treat its underlying medical condition. Do not worry too much. Weight loss can often be treated as long as the conditions are addressed. 

    You can do more research on what to feed an underweight cat. Your cat might need high calorie cat food, but be sure not to overfeed it and make it an overweight cat instead


    If you find that you have an underweight cat, it is almost certainly a sign that it has an underlying medical condition. Most adult cats maintain their weight unless it falls sick. The many causes of your cat losing weight is a cause for concern and should not be taken lightly. If your cat totally stops eating, take it to the vet right away but you should also take it for regular checkups so that your veterinarian can catch any signs of sicknesses right away. Implementing the right treatment plan for your cat can be life-changing and soon enough, you will have a cat that is at a healthy weight.