While it is not necessarily harmful for a dog to eat cat food, it can be dangerous for a cat to eat dog food, which lacks nutrients essential to feline health, according to a recent story from the  Blanco County News .

The story lists the following five nutrients as essential for cats:

1. "First, cats require a higher protein to calorie ratio than dogs," said John Bauer, a professor of animal nutrition at Texas A&M.
2. Cats are not able to make their own vitamin A, which has to be added to their food and is essential to their health, whereas dogs produce this vitamin.
3. Bauer said cats also are not able to make the amino acid taurine, which helps to maintain feline heart function, vision and reproduction.
4. Felines also need arachidonic acid, a fatty acid dog food doesn't have. The compound is necessary to produce an inflammatory response that helps the body protect itself.
5. Bauer said the fifth nutrient cats need is niacin, a B vitamin. According to www.peteducation.com , niacin deficiencies can cause loss of appetite, inflamed gums, weight loss and hemorrhagic diarrhea.

"If your cat sneaks dog food once in a while, it is not going to compromise its health," said Bauer, "but if they are only eating dog food then they are not going to be getting nutrients needed to maintain their health."