When left to their own devices, cats are carnivores, so grain and corn free cat food makes sense if you are trying to feed your cat a natural diet. Cats don't need grains to survive, but commercial cat foods use them because they are cheaper than protein sources.
Corn in Cat Food
Corn is used in several commercial cat and dog foods because it is a cheap filler, but it has very little nutritional value for your pet. However, it has more value for cats than dogs as cats seems to prefer corn and do better with corn than most other grains. In fact, some veterinarians that provide healthy homemade recipes recommend using cornmeal or polenta as filler in some foods.
However, most high quality commercial foods don't use it, and low quality foods, especially kibble, that rely on it are not providing your cat with enough nutrients. While most foods have a maximum of 30 percent protein, cats eat 47 percent protein in the wild. The only grains or plant matter they receive are in the gut of their prey.
High Quality Foods
There are many varieties of food that don't rely on corn as a primary ingredient. Wellness offers several different canned and dry foods that are corn-free, including chicken, beef and chicken, beef and salmon, turkey and salmon, turkey, chicken and herring, chicken and lobster, sardine, shrimp and crab, and salmon and trout. Your cat may not like all brands as some cats don't like beef since it isn't a natural prey, and these brands have fruits and vegetables, which cats also don't consume naturally.
Natural Balance Ultra formula contains chicken broth, chicken liver, duck and salmon, acquiring grain through brown rice. However, it has a lower percentage of protein than Wellness. Natural Balance has several other varieties, all of which are also corn free.
As a cheaper option, Fancy Feast flaked fish and shrimp formula is also grain-free. However, it also has a low protein content and some varieties have lower quality ingredients than others. Read labels before purchasing and compare those to other brands.
Newman's Own Organics brands don't use corn or wheat, but they have been criticized for utilizing too many grains, such as brown rice and oat bran. While many people find these preferable to corn, your cat still doesn't require these grains and would benefit from a higher level of protein.
Feline's Pride is a raw diet, which doesn't use grains or fruits and vegetables for additional filler. It consists primarily of chicken, bones, liver and egg yolks, but it is much more expensive than other brands and must be stored in the freezer.
There are many other varieties of food that don't rely on corn, most of which can be found at local pet stores if not at chain pet stores. It's important to remember that not all cats will do well on the same diet so experiment with your cat. If he likes his diet, it's a good diet. Read food labels and find one with high quality ingredients that your cat likes.