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Medical Causes for Weight Gain in Cats

Though overfeeding and subsequent overeating causes more overweight cats than all other reasons combined, they aren’t the only reasons for weight gain in cats. If your cat has a healthy diet and gets proper exercise but still seems to be packing on the pounds, it’s possible that they have underlying medical condition. In many cases, treatment of the underlying cause can help your cat get back to their ideal weight. Your veterinarian can help determine if your cat’s weight gain may be caused by other medical conditions, including:

Spaying and neutering. These procedures, in themselves, don’t make your cat fat. But spayed and neutered cats typically require fewer calories than intact felines. If you notice your cat putting on a few pounds after spaying or neutering, consult your veterinarian. He or she can recommend the right amount of food that still meets the needs of your growing cat.

Pregnancy. On the other side of the coin, if your cat isn’t spayed and has access to other cats, there could be a very logical reason for that expanding waistline.

Arthritis. Osteoarthritis is a common condition where the joints become inflamed or degenerative, making movement painful. This joint pain leads to inactivity and is one of the primary reasons, after overeating, for weight gain in a cat.

Fluid retention. A number of medical conditions can lead to ascites, or fluid in the abdomen, which can lead to a pot-bellied appearance. With right-sided congestive heart failure, the organ has trouble pumping blood effectively, so fluid backs up into the belly. Feline infectious peritonitis (FIP), a viral disease, may also result in the accumulation of fluid in the abdomen and possibly the lungs. Additionally, fluid-producing tumors can cause ascites.

Acromegaly. In most cases, this disease is caused by a benign pituitary tumor that causes excessive secretion of growth hormone. This can interfere with how the cat uses insulin, often leading to insulin-resistant diabetes mellitus. Cats with diabetes often eat more, because insulin resistance prevents cells from getting the glucose they need. The first sign that a cat may have acromegaly may be when diabetes is difficult to control with injectable insulin.

Medications. Some medications can lead to weight gain. Chronic use of steroids, for example, may cause cats to eat more, but this effect is typically more common in dogs. Long-term steroid use may also lead to Cushing syndrome, or hyperadrenocorticism. While this condition is more common in dogs, it can lead to weight gain in cats.

Hypothyroidism. This disease is caused by a deficiency of thyroid hormone. While hypothyroidism is more common in dogs, cats are more likely to have hyperthyroidism, or an overabundance of thyroid hormone. In rare cases, cats can become hypothyroid, such as when treated for hyperthyroidism with surgical removal of the thyroid glands or radioactive iodine treatment.

In the vast majority of cases, proper diet and exercise (not to mention fewer treats) will help your cat reach an ideal body condition score. But if your cat still isn’t losing weight, despite your best efforts, consult your veterinarian.


The information in this blog has been developed with our veterinarian and is designed to help educate pet parents. If you have questions or concerns about your pet's health or nutrition, please talk with your veterinarian.


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