Ginger cat

Cats often put on weight in the winter, when they're less active.

© Shutterstock

Why is my cat losing weight but still eating?

By Dr. Liz Barton MA, VetMB, MRCVS Veterinarian

Updated on the

Is your cat losing weight but still eating as much as ever? It could be due to an underlying health condition or even the season.

There are plenty of reasons why, despite still eating normally, your cat might be losing weight. It could be due to their age, a disease or even the time of year. The important thing is to know when to see a vet and how to change their diet – if needed.

What are the reasons for sudden weight loss in cats?

Weight loss is a case of calorie balance – either reduced intake, reduced absorption or increased use or loss. Reduced intake can include reduced appetite, pain eating (such as dental disease), or a lower calorie diet. Reduced absorption can be due to diarrhoea and diseases affecting the gut or liver, which processes food. Increased use can be increase in growth, healing, exercise or metabolism. Increased metabolism can be due to endocrine diseases, and there are also other calorie-consuming conditions, such as heart disease and cancer. Increased loss can be due to renal disease (loss of protein in the urine), vomiting and diarrhoea.

What are the causes of cat weight loss?

Weight loss will occur in cats when the balance between calories in versus calories out swings to the negative.

What treatment is there for underweight cats?

A first step should always be to check a cat is getting a high-quality, digestible diet in the right quantity for their stage of life and size. If they are, then swapping to a higher-calorie diet or increasing the amount fed gradually (by 10 per cent each week) is the next step. All cats' metabolisms will alter slightly and the feeding guidelines may not be enough for some active cats. If this doesn’t cause weight gain to a healthy weight, it is important to have your cat checked by a vet to rule out disease-related causes of low body weight.

Why is my cat getting so skinny?

If your cat is getting very skinny, they may have more severe forms of calorie-consuming problems – or more than one. It is not uncommon for older cats to have increased calorie use through hyperthyroidisim and heart disease, and increased loss through the kidneys.

Is it normal for cats to lose weight as they age?

It is common for older cats to lose muscle mass as they age. A vet will be able to check if this is due to painful arthritis, which may be helped by medication. If older cats are less active, they may actually gain weight. Kidney disease and metabolic conditions are common in older cats, so if weight loss occurs it is best to have your cat checked by a vet, as many of these conditions do not make your cat ‘sick’ until they are quite advanced.

What should I do if my cat is losing weight?

Try increasing their calorie intake and, if this does not help, then it is best to seek veterinary advice. If your cat is so skinny that you can feel their bones, it is best to see a vet straight away before changing their diet.

Why is my cat losing weight yet eating constantly?

Cat who are getting skinny but still eating – especially ravenously and in old age – are likely to be losing calories (for example in liver or kidney disease), or using them up (for example in hyperthyroid disease, diabetes and some cancers). Often in older cats there can be more than one condition occurring at the same time.

When should I see a vet?

If your cat is older, it is best to see a vet if they are losing weight, because there are many underlying conditions that can become suddenly worse in older cats. If your cat is younger, then checking and adjusting their diet first is a sensible step, provided they are still eating. A cat of any age who is not eating but is losing weight should be checked by a vet before the cat becomes underweight.

How should I talk to a vet about the best diet for my cat?

It is a good idea to take the packaging of what you feed your cat when you go to see a vet, so they can check that the diet is suitable. If you weigh out how much you’re feeding your cat, that helps to ensure you are giving a consistent amount (especially if more than one person shares responsibility for feeding). Together, you and the vet can then safely adjust what your cat is eating to the best diet for maintaining a healthy body weight. Remember, there will be fluctuations, such as when a young cat is growing or when an older cat becomes less active. Many cats tend to put on weight in the winter, as they are less active, and lose it again in the spring and summer, as activity levels increase again.

More advice on...

What did you think of this advice article?

Thanks for your feedback !

Thanks for your feedback !

2 people found this advice article helpful.

Leave a comment
Connect to comment
Want to share this article?