This behavior of the dog is rooted in its nature. Guarding food
from other animals is normal behavior. It is a struggle for survival. A dog should not defend food at mealtimes from its owners. Each one act must be stop on time. If it is not in yours ability is necessary to seek for professional help.
The dog has got need to learn sharing its food. For the best result this must be done when is puppy. There are proven working rules that must be follow when dog will eat for achieve that.
To have happy lives with your dog not neglect this behavior.