Unexplained, Sudden Weight Loss in Cats

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Veterinarian examining cat in vet's surgery
Veterinarian Examining Cat In Vet's Surgery

Is your cat is losing weight? Unintended weight loss is usually a sign of an underlying health problem. Many owners think that weight loss is normal for senior cats, but this is not the case. It's important to take action if you notice unexplained weight loss in your cat.

How to Tell if Your Cat is Losing Weight

It is hard to tell if your cat is really losing weight if it happens gradually. If your cat has a lot of hair or used to be slightly overweight, then it can be harder to tell when weight loss has occurred.

To assess your cat's body condition, start by looking at your cat's body from above. At an ideal weight, there should be a tuck at the waist that is noticeable but not extreme. Next, run your hands along your cat's sides. The ribs should be palpable with a thin covering of fat. If the ribs feel very prominent and are visible, your cat is likely underweight.

grey cat
grey cat

What Causes Cats to Lose Weight?

In many cases, cats lose weight when they are not eating enough. However, some diseases cause weight loss despite adequate food intake. Depending on the cause, weight loss may or may not accompany other signs of illness. Many health problems can cause weight loss in cats, some more serious than others.


Hyperthyroidism is a relatively common illness that most often affects older cats. Cats with hyperthyroidism produce too much thyroid hormone due to an enlargement of the thyroid gland. This enlargement is usually caused by a benign tumor that grows on the thyroid.

Common signs of hyperthyroidism include weight loss, increased appetite, and increased thirst and urination. Some cats also experience vomiting, diarrhea, and hyperactivity. Some will vocalize and act restless. Cats with hyperthyroidism may have coats that appear unkempt and greasy. Hyperthyroidism is treated with radioactive iodine or oral medications.

macro photography of brown tabby cat
macro photography of brown tabby cat

Chronic Kidney Disease

Chronic kidney disease is one of the most common illnesses seen in senior cats. The kidneys produce important hormones, filter out wastes from the blood, help regulate blood pressure, and facilitate the production of new red blood cells. When a cat's kidneys stop functioning properly, it leads to a variety of other issues.

Increased thirst and urination are among the first signs noticed when a cat has kidney issues, followed by loss of appetite, weight loss, and lethargy. Chronic kidney disease cannot be cured, often be medically managed with medication, diet change, and fluid supplementation.


Diabetes mellitus is another common ailment that can affect cats. This endocrine disorder affects the ability of the pancreas to produce insulin, a hormone needed to regulate blood glucose.

brown and white cat on brown wooden table
brown and white cat on brown wooden table

Signs of diabetes include weight loss, increased appetite, thirst, and urination, and lethargy. Diabetes is typically managed with insulin and a diet change. Other medications may be used. Some cats will even revert back to normal after several months of treatment.

Gastrointestinal Problems

Any issue in the GI tract can affect a cat's weight. First, GI problems can reduce appetite. Second, some issues prevent the GI tract from properly digesting food and absorbing nutrients, leading to weight loss. Some GI problems seen in cats include intestinal parasites, inflammatory bowel disease, pancreatitis, and other pancreatic issues, and even cancers of the GI tract.

GI issues may cause loss of appetite, weight loss, vomiting, diarrhea, lethargy, and more. Treatment of GI parasites may be as simple as deworming the cat. Other GI issues typically require medications and supportive care.

selective focus photography of cat walking on floor
selective focus photography of cat walking on floor

Dental Problems

Oral and dental issues can cause extreme pain, decreasing appetite and leading to weight loss. Common dental problems in cats include periodontal disease, resorptive lesions, and tooth fractures. Some cats develop stomatitis, a painful inflammation of a cat's mouth and gums that may be immune-mediated.

Signs of dental issues include bad breath, drooling, pawing at the mouth, or even oral bleeding. The first step to treatment is for the vet to put your cat under anesthesia and do a professional dental cleaning, exam, and treatment as necessary. Some cats will need oral surgery and/or tooth extractions.


Like people, cats can get cancer just about anywhere in their body. Cancer may or may not be seen in the form of a tumor. Lymphoma is one of the common cancers seen in cats and it can live in the GI tract, mouth, lymphatic system, and more. Most forms of cancer will eventually cause general malaise, lethargy, pain, muscle wasting, appetite loss, and overall weight loss.

selective focus photography of brown cat
selective focus photography of brown cat


Cats can be very sensitive to changes in their home. Because they are often excellent at hiding outward signs of stress, they can experience bigger symptoms later on. Any environmental stressors can lead to anxiety and stress in your cat. Reduced appetite is a common sign of stress and will eventually lead to weight loss.

There are a number of other health issues that can lead to weight loss. If your cat has an underlying health issue, you may or may not notice other signs of illness. In addition, many diseases have similar symptoms, so diagnosis requires a veterinarian.

Treatment for Weight Loss in Cats

The treatment for weight loss in cats depends on the cause. If you notice your cat is losing weight, your first step should be to schedule a vet appointment. Your vet will do a physical exam first. Next, lab tests and/or x-rays may be needed to determine the problem. Based on the findings, your vet may recommend medication, diet change, surgery, or other treatment.

white and black cat on white surface
white and black cat on white surface
brown tabby cat in close up photography
brown tabby cat in close up photography

If your vet gives your cat a clean bill of health, then the weight loss may be caused by inadequate food intake or some unknown or undetectable condition. Ask your vet for advice about feeding and environmental enrichment. If you can determine a source of stress for your cat, start by working to reduce that stress. Your vet can also recommend a diet that is right in nutrients and calories, potentially helping your cat gain weight.

If your cat's weight loss continues despite changes you make, then make sure to follow up with your vet about it. Your vet may refer you to a veterinary specialist for advanced diagnostics.

How to Prevent Weight Loss in Cats

You can prevent weight loss in your cat by regularly monitoring body condition and visiting the vet regularly for wellness examinations. Cats are experts at hiding illness and injuries, but your vet may be able to detect a problem before it gets out of hand. Be sure to report any changes in your cat's behavior to your vet right away. It is much easier to treat a health problem in the early stages than to wait until your cat becomes very ill.

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