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My active outdoor cat is thin but eats a lot. How can he gain weight?

Updated on September 23rd, 2025

Pet's info: Cat | Mixed Breed | Male | neutered

My cat is very thin. He almost always eats all of his food. He is an outdoor cat and moves around a lot, but how can I get him to gain weight?

3 Answers

Most Helpful Answer

Answered By Andrea M. Brodie, DVM

Veterinarian

Published on May 7th, 2016

He may just be one of those cats that metabolise their food very quickly and never will gain weight. He may also have tape worm. You should worm him every three months with a wormer containing praziquantel which hits tapeworm. Food: Feed him good quality canned food, pate style, 3.5 oz twice daily. This would be double the regular amount of food and if he does not gain weight with that over the next 4-6 weeks, then you should take him to the vet for some blood tests including thyroid test.

27Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Dr. Strydom, DVM
Veterinarian
Published on December 16th, 2019
It doesn't sound like worms but anything is possible. If he is eating and drinking and not gaining weight my best guess would be hyperthyroidism. This can be easily diagnosed with simple blood testing. I suggest you get him to a vet for an exam.
1Pet Parents found this answer helpful
Answered By Jessica Desrosiers
Veterinary Technician
Published on April 23rd, 2016
Failure to gain weight can be due to problems such as internal parasites, or even a result of metabolic or other illness. Checking for parasites in the stool is one way to tell, however some types of parasites may not be grossly visible. Bringing in a stool sample to your vet is the best way to have this tested. If there are no parasites present in the stool, your vet may want to examine your cat for any issues and may recommend blood work to check for any underlying problems. Feeding a complete and balanced diet appropriate for your cat's age and size can also help ensure he is getting enough nutrition.
32Pet Parents found this answer helpful

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Why is my active 10-month-old cat underweight despite eating a lot?

Poor Canelo. I am sorry that it has been difficult to get him to gain weight. With him being young and petite and intact then I would not be too concerned. Of course, without doing an exam I cannot say this for sure. If he is really skinny and all of his bones are showing then yes, I would be more concerned. If his bones are not showing and you cannot see his ribs then I would be less concerned. Some cats are more petit and slender especially if they are very active and outdoors. I would also recommend to have him neutered as that may also help him gain weight. Finally, if he is really skinny and you are able to see his bones, I would recommend to ensure your vet tested his thyroid (high thyroid isn't common is young cats but possible). Then I would recommend to increase the amount of food you are feeding and if he is still not gaining weigh then the next step would be abdominal x-rays or ultrasound. I hope this helps some. I would love to talk to you more on the forum or if you would like to set up a consult.

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Cats can be thin for a variety of reasons. Make sure he has been checked for parasites or dewormed recently. Some cats will also become thin due to kidney disease or hyperthyroidism. Sometimes this can happen even before kidney disease begins. Any GI disease will also cause a thin body. Lastly, some cats have a fast metabolism. Make sure Choo Choo's bloodwork is all normal and that parasites are not a concern. Then you may try focusing on nutrition. I recommend the brand Royal Canin. It's diets are all tested and formulated to contain appropriate protein levels that are high quality and easy to digest. Feed one of the higher calorie diets available. This may help to put weight on him. You can also supplement with a high calorie canned like A/D or R/S.

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Why is my cat so skinny and not gaining weight even though he eats?

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