Why Your Cat May Be Losing Weight

min read

A cat lays on a soft chair. One paw and both eyes are pointed directly up, reaching for something just out of view

Find food that fits your pet’s needs

Find a dog food that fits your pet’s needs

Find a cat food that fits your pet’s needs

These days, with a global trend for humans and animals to be overweight, it’s easy to be  focused on avoiding weight gain for your cat. However, unexplained weight loss is really important too, and can be one of the earliest signs of disease or illness. If you think your cat is losing weight, and it’s not because your vet has put them on a weight loss regime, then the sooner you act the better.

The importance of monitoring weight

This can’t be stressed enough. Weight gain and loss can both be signs of ill health and, as with all things when it comes to health, the sooner you notice when something is wrong, the sooner you can get help. Cats are good at hiding signs of illness, so sometimes by the time you see overt signs, the disease may be quite advanced. Spotting those early weight changes can make all the difference.

Even if your cat is healthy and is only losing weight because they just don’t like the new flavour of food you bought (or getting fat for the opposite reason!), being under- or overweight can still have a knock-on effect on their health.

From a young age, it’s wise to get your cat used to being weighed. Your vet will do this every time you visit the surgery but, as many cats find travel and vet visits a little stressful, if you get into the habit of weighing them at home you’ll both be used to it.

If your cat is pretty laid-back, you can simply place them on the bathroom scales if they will stay still long enough. Alternatively, weigh them in their cat basket and then subtract the weight of the basket. Remember to include any bedding in the sums as well. There is also the option to weigh yourself and then stand on the scales holding your cat, if they are relaxed enough to be picked up. Again, the more you make this a regular routine, the happier your cat will be. Every two weeks as a kitten, and monthly as an adult, are good intervals to use.

Causes of weight loss in cats

There are dozens of conditions and circumstances that can cause weight loss in cats. Here are some of the most common:

  • Kidney disease. Again, this is a common finding in middle-aged to older cats. One of the earliest signs may be weight loss. You may also notice your cat is drinking more than usual and may be off their food.

  • Parasites. Although heavy worm burdens are uncommon these days, they are still a potential cause of weight loss. Your vet will be able to advise on good preventative health measures for your cat’s age and lifestyle. If they regularly hunt, they may need treating more often.


  • Hyperthyroidism. This is a common disease in middle-aged to older cats. An overactive thyroid gland increases the metabolism. Your cat may eat well and even be ravenous but still lose weight. Cats with hyperthyroidism are often hyperactive and can become aggressive.

  • Cancer. Many types of cancer are not painful and can be difficult to spot. Weight loss is a very common first sign and may be the only thing you notice.


  • Gastrointestinal problems. Chronic enteropathies, adverse food reactions and other GI diseases can cause weight loss because your cat won’t be getting all the nutrients they need from their food.

  • Diabetes. Although we often associate diabetes with fat cats, weight loss is one of the most common signs once diabetes gets a hold.

  • Tooth or mouth pain. Dental disease is more common than you might imagine. Pain in the mouth or gums may put your cat off eating and cause weight loss.

  • Stress. Stressful things like conflict with other cats in the house may stop your cat eating enough to stay a healthy weight.

Not all of the causes of weight loss in cats are serious, but you can see that some most certainly are. The more you know what is normal for your cat, the sooner you’ll spot problems. Any unintended weight loss should prompt a visit to your vet. They may find an obvious problem or may need to dig a little deeper with blood or urine tests. Either way, you’ll get to the bottom of the issue and get any treatment that’s needed as soon as possible.  

Reviewed by Dr. Hein Meyer, DVM, PhD, Dipl-ECVIM-CA