Cats Diet

Question
I have two female cats, one 12, one 13.  The elder eats a variety of treats, dry food (which is always available), and canned wet food, and seems quite healthy.  The younger cat is a bit larger, but has been thin for a year or more. Yet she shows no signs of illness whatsoever.  

The problem is that she seems to be ravenous all the time.  She's very talkative (demanding, in fact) and refuses to eat most anything except canned, wet, fishy food.  She snubs dry food unless it is something new; after day one, she won't touch it.  She does eat treats, but eats so quickly I have to give them to her one at a time, or she'll throw them up.  She eats a whole can of Fancy Feast, or the majority of a large can of tuna each night.  Her energy level seems quite normal.

She starts demanding her can of food when she wakes up in the afternoon and chases me around screaming for it (sometimes for hours) until she gets it. Is she not getting enough, or is she just spoiled?

Thanks very much,
J.

Answer
I can think of two possiblities why she's doing this:  1 she may have parasites and 2 her food isn't giving her enough nutrients to feel full.  If she has any kind of parasites in her intestines all the nutrients she's getting through food is being absorbed by the parasites thereby leaving her hungry all the time. Nutritionally, dry food is better.  Try weening her away from the canned by adding some dry to it at every feeding.  Add a little at a time until she is eatting a majority of dry.  A steady diet of cat treats and canned food isn't complete and when i give my cats treats I buy Sushi's favorite, whiskas temptations and the kind to improve general health and prevent hairballs.  If she has just started doing this take her to the vet rule out parasites.  Cats show different symptoms with different types of parasites present.
Kris