A question recently was asked of me as to what kind of food cats should be fed. The person said "some people say that it is really bad to feed a cat dry food and you should only ever feed them wet food, is this true?" I thought that was a great question and worthy of more than just a quick email.
For those who just want the quick bullet point, here is the summarized answer: canned/wet food is better but dry food isn't bad.
Why is that? Several reasons, actually.
Cats are obligate carnivores. In the wild they eat small, frequent meals of small prey such as mice, voles, birds, and lizards. Yes, you may see cats occasionally nibbling on grass but that is not a good source of nutrition for them. They need the high protein, low carbohydrate diet comparable to the prey they would eat if they weren't our pets. Studies have shown that this protein/carb balance (sometimes referred to tongue-in-cheek as the "Catkins" diet) manages weight and blood sugar much better than a dry food that has a higher comparative carbohydrate percentage. Underweight cats tend to gain weight and overweight cats more easily lose weight. I've personally had borderline diabetic cats with blood glucose successfully managed with only this kind of diet.
Our domesticated cats originated from small desert cats in the Middle East, particularly Egypt. Their physiology is still very much like a desert animal, as they have very efficient kidneys that resorb water well, and they tend not to drink a lot of water. The downside to such a system is that their urine concentrates so well that they can be prone to kidney disease, urinary tract infections, and urinary blockages. The best way to prevent these problems is to ensure a high level of fluid intake, thus keeping a constant flow of fluid through the kidneys and promoting more frequent urination. Since cats don't drink much we can aid good renal and urinary health with canned/wet foods. By their very nature these foods contain 3-4 times the amount of water per volume as dry foods. There are a few urinary disorders in cats that can only be consistently treated by using specialized canned foods.
All of this sounds pretty compelling, right? And indeed it is. Growing evidence shows that wet foods really are better for a cat's overall health. So why feed dry food?
Convenience and cost. That's really what it comes down to. It is far less expensive to feed dry food than to feed canned food, and that can add up over time. Dry food also stores well and doesn't start to dry out and look nasty if it sits in the bowl. Really we feed dry food for our sake, not our cats'.
But that doesn't mean that dry food is automatically bad and that you should never feed it. The average cat does perfectly fine on dry food and can live their entire lives without any weight problems or issues with their urinary system. Modern commercial cat foods have been carefully formulated over several decades of use and research to be the best they possibly can for our feline friends.
Several years ago after reading the recent research I started switching my cats over to an exclusively canned diet. I quickly discovered the difference in cost, and that was the number one reason I switched back to dry food. The cats I currently have only eat dry kibble and have done so all of their lives. As I mentioned above, cost and convenience were the reasons I chose to feed dry.
So what should you do for your cat? If you can afford it and don't mind the smell or mess, I do recommend using canned/wet foods. If that isn't really feasible for you I wouldn't lose sleep over feeding a dry food or worry that you're automatically killing your cat. In the end it comes down to a personal choice and a necessary balance between your cat's health and the practical realities of life.