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Sudden Weight Loss in Cats: When Should I Worry?

maine coon cat lying on the floor

Cats can lose weight for all sorts of reasons. Many cats are overweight or obese. In these circumstances, it may be healthy for your cat to lose a bit of weight. However, even if your cat is already overweight, it isn’t healthy for them to lose weight suddenly. Usually, there is a reason for this—and that reason is rarely good.

Therefore, if your cat has suddenly lost weight, you likely need to take them to the vet. Once weight loss is noticed by the cat’s caregiver, it is likely already extreme and needs to be considered by a vet (who will likely order tests to ensure there isn’t an underlying issue).

However, there are some cases where weight loss can be normal to some extent. For instance, after pregnancy, cats will likely lose weight substantially. This is normal and shouldn’t be worried about. Many cats will continue to lose weight as they nurse the kittens. However, this isn’t anything you should be worried too much about.


What Causes Sudden Weight Loss in Cats

There are many different reasons for sudden weight loss in cats. Some of these are more serious illnesses that need to be attended to by a vet. Others may be able to be waited out. Usually, it is a good option to have your cat looked at by a vet if they lose tons of weight—even if you think it may be caused by something benign.

One of the top causes of weight loss is diabetes. A cat with diabetes cannot utilize the sugars in their food. Therefore, they will slowly “starve” even when eating. Specifically, this is called “cellular starvation,” as the cat will still feel full and like they are eating the proper amount of food.

Diabetes requires veterinary treatment to some extent. Some cats can be taken off medications once they are switched to an appropriate food. However, this also requires working with a vet.

cat and vet
Image Credit: Stock-Asso, Shutterstock

Stress and anxiety can affect eating. Some cats may spend more time hiding and less eating when they are stressed out. If their food bowl is out in the open, they may not feel like approaching it. If their litter box is somewhere “scary,” they may avoid it as well. In the end, this can cause UTIs and similar issues, which may also make them not eat and lose weight.

However, if your cat isn’t eating, you should be able to tell by the amount of food in its bowl. If they are eating normally and still losing weight, it is usually time to take them to the vet. After all, this is likely a sign that there is an underlying issue that needs to be resolved.

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How Much Weight Loss in a Cat Is Concerning?

It depends on the weight of the cat. Usually, by the time the owner notices the lost weight, the cat has already lost a substantial portion of their body weight and needs to be checked out by a vet. Preferably, a cat should only lose about 1% of its body weight a week. In a smaller cat, this means a very small portion of weight needs to be lost per week. In a larger cat, this allows for a bit more.

The only way to pick up on smaller weight loss is usually to weigh your feline. If you weigh your cat regularly and notice that it has lost a little bit of weight, then it is probably nothing for you to worry about. Of course, your cat shouldn’t become underweight—even if it are only losing a small amount of weight each week.

If your cat is on a diet, some amount of weight loss is to be expected. However, it does depend on the exact cat and how big it is. Some very overweight cats may lose a bunch of weight at the beginning of its diet and then slow down.

Russian Blue Cat Eating
Image Credit: slawomir.gawryluk, Shutterstock

Which Diseases Cause Weight Loss in Cats?

There are many diseases that cause weight loss in felines. Technically, any illness can lead to some degree of weight loss. In many cases, the cat simply won’t feel very good, which can decrease their appetite. Therefore, a disease doesn’t have to directly affect a cat’s digestive tract or metabolism to cause weight loss.

Intestinal parasites are a common reason for weight loss. These parasites consume your cat’s food after they eat, which reduces the calories they get. Therefore, in extreme cases, the parasite may make your cat lose weight. However, this isn’t always the case. A vet can examine your cat’s feces to determine if they have parasites.

Diabetes can also cause weight loss, as we have explained previously. Usually, this also causes cats to drink large amounts and urinate in large amounts, too. Diabetes is a fatal disease if left untreated, as cats will slowly starve. Therefore, it’s important to take your cat to the vet for dietary recommendations and insulin for treatment.

Hyperthyroidism can also cause weight loss in felines. Usually, this condition affects older cats, such as those that are over the age of 8. The thyroid produces hormones that regulate a cat’s metabolism. Obviously, if the thyroid stops performing its job correctly, it can cause all sorts of problems for a cat’s digestion. For one, it can make a cat not absorb the appropriate number of calories or burn them too quickly. In this way, a cat may lose weight even when eating regularly.

brown tabby maine coon
Image Credit: Rosa Jay, shutterstock

FIP and FeLV are two diseases that are caused by viruses in felines. They have different causes and different treatments, but weight loss is common in both. Therefore, if your cat loses weight, you may need to take them to the vet to test for these diseases. Both of them are serious and can be deadly in many instances.

Kidney disease of any sort can also lead to weight loss. It isn’t odd for your cat’s kidneys to become affected by some sort of issue as they age. Kidney disease isn’t always reversible. However, it can be helped via prescription pet food and sometimes medication.

Some types of cancer can also cause issues. However, digestive cancer isn’t the only one on this list. Anything that affects a major organ can cause appetite issues, especially if the cat is in pain.



We highly recommend getting your cat checked by a vet if you have noticed weight loss. By the time you can see weight loss on a cat, the weight loss is often quite serious. Cats are very good at hiding the symptoms of their illnesses, as any sort of weakness would have been taken advantage of by predators in the wild. However, they cannot hide symptoms like weight loss.

It is possible for your cat to have a disease, act completely fine, and lose significant amounts of weight. Often, cats’ illnesses aren’t noticed until they have progressed a bit. Therefore, we highly recommend taking your cat to the vet even if you aren’t completely sure if they’re sick.

Featured Image Credit: Remark_Anna, Shutterstock

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