I have 3 cats (and yes, I know Unca Cecil’s feelings for felines) and have fed them the same ‘premium’ cat food since they were kittens, starting in 1991. One day, through poor planning, I ran out and it was too late in the evening to find a pet store open that carried Iams brand. Since you can’t get it at the local grocery, I figured what the hey, and bought a small box of Purina Cat Chow. All 3 of them wolfed it down in no time.
The next day, I went and bought the regular stuff (Iams) and mixed it in thier food dish with the remaining Purina.
The little buggers took out every piece of the Iams in the dish and left it on the floor and finished off the Purina stuff.
Since then, they won’t eat anything else, to the point of losing weight if the only food is the ‘good’ stuff. Granted, Purina is cheaper and easier to get, but I wonder:
Is there something in Purina that cats find more addicting than catnip?
I have talked to a few people who have done something similar, and they had basically the same experience
Dear Ghostie:
It has been my experience that cats love Purina Cat Chow, though I have no idea what they put in it. I know my cats gulp it down like they are starved wolves, but then they are at least half-feral.
I suspect certain companies are overhyping the merits of their “special formula” pet foods. My female cat had kittens last spring, and I eventually gave one to my sister. She bought some of that fancy food for kittens only and got a surprise when the little varmint wouldn’t eat it.
When she asked me what I did to the kitten, I told her I fed it regular Purina cat food and chicken bones as soon as it was weaned.
IMO, if cats have been weaned and don’t have any medical conditions, feed 'em Purina, and let them supplement it with fresh mice.
Let’s face it. Stuff that’s good for you usually doesn’t taste as good as stuff that is less nurishing. If I were not a higher thinking organism, I’d have ice cream for dinner every night. I would only eat broccoli (and other healthful but less tasty foods) when my body craved it from lack of vitamins. I think that Purina Cat Chow must taste better than Iams, but it contains enough nutrients to keep the cat healthy. You probably don’t need to worry about feeding the little fella the cheap stuff, but maybe ask your vet.
Don’t be alarmed that “Kitty” won’t go back to eating Iams. Let “Kitty” do without for a few days and he’ll eat whatever you put in front of him.
nasargent is probably correct (as far as anyone can tell, since cats can’t talk). Premium quality foods generally have less fat content than store brands, so of course the store brand is a little tastier.
Your cats should do fine on Purina - its a good food. But, there are certain advantages to the premium foods:
More consistent quality of ingredients.
Better nutritional balance overall (see above).
Concentrated (less filler) so it is digested more completely.
If you switch to Purina after feeding Iams, you will probably see a large increase in the amount the cats eat (they generally eat about half as much Iams as they do Purina). You should also notice an increase in the amount of poop in the litter box and in the smell. More filler = more undigestable ingredients = more stuff coming out the other end plus more smell. The poop will also probably be much softer than what you see on the premium food.
I have two cats here that eat only raw meat - an African Serval and an F2 Chausie (25% Jungle Cat, 75% domestic cat). They only poop once a day, a very small amount, light colored, very firm, and almost no odor 
That’s because they digest about 90% of what they eat. Raw meat is the best diet, but its also difficult and expensive. There are companies that make specially formulated raw meat diets for both dogs and cats, with the proper nutritional balance, etc. But you can’t just pour it in a bowl and let it sit all day, so its not nearly as convenient as dry food.
Too many freaks, not enough circuses.