If you place your dog's food down and he growls or snaps at you, this is called food aggression or food guarding. This can have severe effects on your relationship with the dog as well as his relationship towards you and your family.
Oftentimes, this can behavior must be trained out of the animal, or it will continue indefinitely. Dogs have an instinctive need to guard there food. Most times, this doesn't present itself because the dog trusts his master above all else. Sometimes, though, this instinct surfaces in dogs and can be a hazard to you and your family if left alone. What the dog must learn is that he should not be threatened by you when it is feeding time.
If you are angry or violent in your training habits when teaching your dog about food aggression, then he may have a tendency to become aggressive back, hindering the training process. Hitting or using a leash to pull the dog away from his food during these periods of aggression can make him even more agitated and can become dangerous for both of you.
Food aggression will not go away overnight, but with continued patience and working with the animal, the problem can be resolved. A routine is the best solution to this problem. Using certain stimuli that tell the dog it is time to eat and there is no need to be anxious or nervous is the key. During this routine, ensure that there are not distractions such as kids or other animals in the room. Another animal walking by or a child passing can become an immediate step back while training for food aggression.
As you prepare to feed the dog, tell him to sit. Make him wait for you to place the food down. He must learn that you are the master and he must wait on you. If you can get him to start eating only after a voice command, then that is a great step, although for some it may be asking too much at first. If you are training a puppy, it will be a little easier because as he eats, walk around, pet, and praise him. If he growls, pet him and let him know you are not going to take his food. For a week or two, only work on these steps. For older dogs, try dropping a treat or tidbit for him as a reward – treats that are tastier than his dog food. By doing this, he will learn that people passing him is a good thing.
This is a good starting place. Other steps can be implemented down the road, but this foundation is what you want to build on. By progressing slowly, it will not be long before food aggression is no longer an issue.