Actually it all depends on what type of food you are feeding. Most commercial dog foods are not even very healthy for dogs. They contain ingredients such as corn, animal by products, soy, sweeteners. If you are feeding a high quality dog food, such as Diamond, Chicken Soup for the Dog Lover's Soul, Innova, Blue Buffalo, Billjac, Wellness. Then it shouldn't be a problem. I used to feed my cat my dog's food when I first got her. She was a stray so I didn't bother with buying cat food, I just fed her my dog's food for a while. Then, once she was more tamed around me I bought her a bag of high quality cat food. A tip, a good quality dog food will not contain any of the following:
Animal By-products or Meat By-products, Animal Digest, Sweeteners, Corn, Soy, Cellulose, Artificial Colors, Ethoxyquin, BHA and BHT (evidence has been found that these cause cancer). A good quality food will have an ingredient list that has things you would find in your own kitchen. Like chicken, lamb, beef or some other form of meat as the first ingredient. The best foods have real meat, not meat by products or corn as the first ingredient. You may have to go to a pet store like Petsmart, Petco, or feed store to find a good food. Or, if you have a Costco where you live their brand, Kirkland Signature, is very good and also affordable. What I've listed goes for cat food too 