Sudden Change

My cat is nineteen years old and has been very thin and bony for quite a while. However very recently she has got a very podgy stomach, as if maybe obese. However she does not eat as much as my other nine year old cat. Why is this? Is she in any pain?
   
Please Help :(

She is an older girl so there could be many things going on, Kidney disease, Hyperthyroidism,Diabetes, cancer or some other type of tumor just to name a few things. I would take her to the vet and have them check her out they may be able to feel if something is going on in there and i think bloodwork would be a good idea, at least then you will know were you stand.

If the abdomen is very hard & firm, it could be abdominal cancer. Take her to the vet to find out.