While some cats have weird eating habits, most are creatures of habit who stick to their food dish at feeding time. More importantly, cats are carnivores. Sure, they'll chew on grass and, yes, even eat the occasional chunk of cantaloupe... but by and large, cats eat meat. Now, to see how your cat is doing on the food front, I want you to go to your cat's bag of food and read the first ingredient on the list, then come back and continue reading.
I was listening to a Veterinarian who was being interviewed on TV about what to look for in pet foods: what makes pet foods healthy or non-healthy. He said, in essence, that the basic rule is this: "If the first ingredient listed on your pet's food is a meat, like chicken, lamb, beef or fish, it's probably okay for your pet. If it's some kind of corn product, don't give it to them."
Naturally, the next question was, "Why?"
As stated before, cats (and dogs) prefer meat. Furthermore, cornmeal is made from a plant that has a high sugar content and is also used to make sweeteners (i.e.: corn syrup). Sweet things taste good - even to our pets - but the sugar content is too high for them to process efficiently, therefore corn-laden pet food is more likely to lead to obesity. This, in turn, leads to lethargic behavior, which spirals out of control into more obesity, more lethargic behavior, possibly related disease(s), etc. Not to mention a cat's body isn't built to use a constant influx of starches and sugars. It's built to use meats.
A basic test to prove this theory would be this: get some cornmeal and put it in a bowl. Next, get some meat and put it in a bowl next to the cornmeal. Next, get your cat and set him/her down in front of the two bowls and see which one he chooses.
Good kitty. Eat the meat.