There are a number of possible causes of weight loss or gain in cats, including medical conditions and overfeeding/underfeeding.
As the cause can be caused by a disease or dietary, it is important that you seek the advice of your veterinarian to determine the cause. The vet will do a complete physical examination, obtain a medical history from you, ask questions about diet, what food, how much, how often, and possibly take blood and urine samples for testing.
If the cause is dietary, your veterinarian can advise on the best type and brands of food for your cat. There are so many varieties for different stages in your cat’s life, or which cover medical conditions (diet for kidney disease etc.
Weight gain can have long-lasting health implications on your cat and it is important that if overfeeding is the cause, that this is addressed. Cats should not be suddenly put on a severe calorie restricted diet as it can lead to hepatic lipodisos, which is a life-threatening disease in which the body uses fat stores as fuel. These are sent to the liver, which breaks them down. The liver can become overwhelmed and unable to process the fat as quickly as necessary, resulting in a build-up of fat in the liver, resulting in impeded liver function.
A common mistake pet owners make is feeding table scraps to pets. This is unnecessary and harmful. There are a number of human foods which are unsuitable to cats, especially in large quantities. They are nutritionally inadequate and can lead to deficiencies, in addition to weight gain. Cats should stick to cat food.
Stress – Some possible causes of stress include; moving house, loss of companion, new pet/person in the house, hospitalisation, being boarded
How do I know if my cat is underweight or overweight?
The best way to determine if your cat is overweight or underweight by feeling the body. The chart below clearly explains this. Do bear in mind, however, the body shape differences from cat to cat. For example, a Siamese or Oriental cat is long and slender with fine bones, a British Shorthair is cobby. They are on different ends of the normal spectrum as you can see in the image below, the Oriental has finer bones and smaller muscles compared to the British Shorthair, but both cats are a good weight.
I like to go by body tone, a cat should have a small amount of fat under the skin on the body, but it should not be so much that you can’t feel the underlying skeleton. The shoulders and legs should be nicely muscled.
The underweight cat will have easily palpable ribs, spine, and hips. There will be an obvious abdominal tuck. The hind legs look bony.
The cat within the healthy weight range will have ribs which can be felt, but with a slight fat covering.
The overweight cat will have ribs which are not palpable, large stores of sub-cutaneous fat, no waist.