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Why Is My Older Cat Losing Weight? 11 Likely Reasons

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By Nicole Cosgrove

old sick gray tabby cat

If your cat is losing weight, it’s critical to find out why. While weight loss in older cats may be due to a simple cause such as stress, weight loss can also be a sign of serious health problems and so it should never be ignored. There are many potential causes of weight loss in cats, including diabetes, cancer, intestinal parasites, kidney disease, and an overactive thyroid gland.

If your older cat is losing weight, read on to find out why as well as the signs to look out for.

The 11 Reasons Why Your Older Cat Is Losing Weight

1. Anxiety, Stress, or Depression

Cats of any age when under psychological stress may stop eating, causing them to lose weight. Situations that may upset a cat include interference from other animals either when they eat or in their feeding area, disturbing noises, and issues with their food bowl—including small issues such as placing it too close to the litter box. A change in their routine such as when a person leaves the home or when another pet is introduced can also be stressful for cats.

angry cat hissing
Image Credit: Fang_Y_M, Pixabay

2. Arthritis

Arthritis by itself does not cause cats to lose weight directly, but as the disease progresses and movement gets harder, your cat may find that the effort to get food—even just walking to the food bowl—is very painful. This can cause your cat to cut back on their nutrition which eventually leads to weight loss. Also, as your cat is moving less they will most likely lose muscle mass, further exacerbating the weight loss.

3. Cancer

Most cancers in cats, wherever they are in the body, are hard to detect until at an advanced stage. As cancer develops your cat will probably experience pain and as a result, become lethargic and less active and they may also lose their appetite. All these factors mean that cancer is a common cause of weight loss in older cats. It’s important to talk with your veterinarian about how to support your cat and what to feed them.

vet doctor examining cat in x-ray room
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4. Dental and Mouth Problems

If your cat suddenly stops eating and begins to lose weight, but seems otherwise healthy, it could be a dental or oral problem.  Toothache, gum disease, sore throat, mouth infection, mouth ulcers, and severe gingivitis are all potential causes of your cat’s loss of appetite as they may make eating quite painful and cause your cat to eat less. Drooling and pawing at the mouth may be other signs of a dental issue. If you suspect that your cat’s loss of appetite is due to a dental or oral problem, take them to the vet for an examination. The vet will be able to determine the cause of the problem and recommend the best course of treatment.

5. Diabetes

Diabetes, usually caused by either the body’s ability to produce the hormone insulin or a reduced ability to respond to it, regularly causes cats to lose weight. Without insulin or the correct response to insulin, the body can’t use all the calories in the diet for daily energy needs and as a result, a cat may lose body mass. You might also notice your cat drinking more water than usual, urinating more, generally acting sluggish, and maybe having a short temper.  Diabetes in cats can be treated with daily insulin injections, and then they can regain weight.

veterinarian giving injection to a cat
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6. Feline Immunodeficiency Virus (FIV)

FIV is the feline equivalent of the human immunodeficiency virus (HIV) and causes a disease similar to acquired immune deficiency syndrome (AIDS) in humans. It is a highly species-specific virus that only infects felines. The disease has three phases. In the first phase, the acute phase, an infected cat may lose their appetite which will cause the cat to lose weight. The second phase is asymptomatic and may last from months to years, with some cats never progressing beyond it and during which time the cat will not have any outward signs of infection. During the final phase, the cat’s immune system will be compromised, and they will develop secondary infections or diseases, usually leading to death.

There was an FIV vaccine available at one stage but it has been taken off the market in North America 1.

7. Feline Infectious Peritonitis

Feline infectious peritonitis 2 (FIP) is caused by strains of a virus commonly called the feline coronavirus. Feline coronaviruses are usually found in the gastrointestinal tract and do not cause significant disease. FIP is often found in catteries where many cats are kept and raised together. Cats that go on to develop the disease get a fever as their bodies battle inflammation which often leads to loss of appetite and weight loss.

a thin cat
Image Credit: Cédric VT, Unsplash

8. Gastrointestinal Problems and Inflammatory Bowel Disease

The gastrointestinal tract can cause cats to lose weight either through poor absorption of nutrition or through loss of appetite. Symptoms that may accompany weight loss and could indicate a GI problem include diarrhea, vomiting, and a lack of appetite. Diseases that commonly cause GI problems in cats resulting in weight loss include inflammatory bowel disease, food allergies, and certain infections. Parasitic infections and worms are a particularly common cause of GI problems leading to weight loss.

9. Hyperthyroidism

If your cat is eating normally or eating more than usual and is still losing weight, then they may be suffering from hyperthyroidism 3. Hyperthyroidism is caused by an otherwise benign tumor on the thyroid gland that increases levels of the thyroid hormone. Imbalances in the thyroid hormone, as well as causing weight loss, can drive your cat to drink more water than usual and cause excessive urination.

old calico cat lying down on wooden deck
Image Credit: Kristi Blokhin, Shutterstock

10. Normal Aging

Weight loss in cats is a natural part of aging and happens through normal changes in the metabolic process which cause loss of both muscle and general body weight. This happens slowly over time and in small incremental amounts. Weight loss through aging never happens suddenly. Nevertheless, as a cat owner if you notice weight loss you should not assume that it is normal, even for an older cat, until you have had your cat checked out by a veterinarian.

11. Organ Failure

As cats age and as their bodies wear out it is common for organ functions to degrade, causing the cat to change and get sick, although organ disease can happen to young cats as well. Chronic kidney disease 4 is one such illness that is quite common in cats. The accumulation of damage to the kidneys over a lifetime from infections, toxins, and illnesses results in the slow degradation of the function of the kidneys. An early sign that your cat’s kidneys are not functioning well is an increase in drinking. However, this is easy to miss as it is a sign of many other diseases as well. As the disease progresses your cat may experience weight loss, poor appetite, smelly breath, a sore mouth, vomiting, and weakness.

person petting a sick cat
Image Credit: Alexander Andrews, Unsplash

What’s the Average Lifespan of a House Cat?

The average lifespan of a cat is 12–18 years. House cats typically live longer than outdoor cats and have a life expectancy of about 10 to 15 years, although a few long-lived feline friends can live up to the grand old age of 20. House cats tend to live longer as they have few if any predators to worry about, generally have a good and consistent diet, and are looked after in their old age.  Taking your cat to the vet for regular checkups will also help your cat to live a nice long life.


In conclusion, old age can take a toll on your cat’s body and one thing to always look out for is weight loss. If you notice that your cat is losing weight, it may be a sign that your cat either has or is developing a serious illness. The reason behind the weight loss can vary from external stresses to infections or parasites to old age itself. Unfortunately, the symptoms for all of these are very similar and may include loss of appetite, lethargy, vomiting, or diarrhea. Check your cat’s intake of food and water, and their energy levels to see whether they are eating normally then go and visit your veterinarian and have your cat checked out.

Featured Image Credit: Mahlebashieva, Shutterstock

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