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Why is my cat underweight but eats a lot and is food aggressive?

Updated on September 23rd, 2025

Pet's info: Cat | Domestic Shorthair | Female | spayed | 5 lbs

Hi my cat was rescued about 18months ago and in that time she has gained no weight at all. She is extremely under weight but eats all of her dinner and anything she can grab of our plates. She is very aggressive about food. We have had her on a top quality vet recommended food all of this time, she has been worked, vaccinated and cleared for aids. She is an indoor cat but has an outdoor run and access to cat grass. Her age has been estimated at between 2 from her teeth and 12 by her joints.

1 Answer

Most Helpful Answer

Answered By Daniela Jessen, DVM

Veterinarian

Published on January 6th, 2018

Hi,
I can see Taco is underweight cat with very increased appetite and aggressive to food and the age can be 2-12 yrs old, one of the first differential to check would be Hyperthyroidism. Hyperthyroidism is a common disease in cats, BUT
it mostly affects cats that are middle-aged and older. Hyperthyroidism is caused by an increase in production of thyroid hormones from an enlarged thyroid gland in a cat’s neck. The most common clinical signs are weight loss (very thin cat), increased appetite, and increased thirst and urination. Hyperthyroidism may also cause vomiting, diarrhea, vocalization, ungroomed matted coat and hyperactivity. Diagnosis will require in most cases physical examination, blood chemistry panel including thyroid hormone levels and urinalysis. Since hyperthyroidism can predispose the cat to other conditions, it is important to evaluate also the heart (Heart rate and blood pressure) and the kidneys ( seen in the blood panel and urinalysis).
Differential diagnoses for cats with clinical signs similar to hyperthyroidism should also include: diabetes mellitus, gastro intestinal malabsorption/maldigestion, neoplasia (especially gastrointestinal lymphosarcoma), chronic kidney disease (CKd) and parasitism. I would recommend to take Taco to your vet for examination and investigation.

1Pet Parents found this answer helpful

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