Type of Pet: 7 yr old female long hair cat

Question:
I have a big fat cat who has recently lost some weight. She still eats but, not as much maybe 1 a day. She isn't very active although being a big cat she never was before either. She is strictly an indoor at will not go outside even if I tried to make her. I also have 1 more strictly indoor cat who is also 7 yrs. and no problem with her. What do you think the weight loss could be attributed to? They have both eaten science diet for the 7 yrs. that I have had them and now neither seem to eat the food.

ANSWER:
You did not mention the vaccination status of your cat, or whether or not it has ever been tested for Feline Leukemia Virus/FIV. The first thing I would do would be to test your cat for these common diseases. Also, on the list of problems that can cause weight loss are: parasite infestation, hormonal imbalances (ie. hyperthyroidism, diabetes mellitus/insipidus, others), tumors, polyps, masses, foreign body obstructions (string, etc), and weight loss can be a symptom of so many diseases. I suggest you take your cat to your vet and have a full-blood panel ran along with some xrays and a urinalysis. The key to prevention and treatment is early detection. Not so many owners are aware when their pet looses weight and kudos to you for noticing. Now, you just need to get to an answer so that the problem can be identified and addressed ASAP. Good luck!