Remove the dog food bowl after your dog finishes eating. Allowing a dog access to eat anytime he chooses is unhealthy and fosters a sense of possessiveness in some dogs. Optimally, the dog should eat to his fill 3 times a day and his bowl picked up after each feeding.
Hand feed your dog. Instead of putting his bowl down and letting him eat quickly, make your dog eat his food a couple of pieces at a time, from your hand. Make him sit down and hold out your hand, backside first to keep him from snapping. If he attempts to take the food too quickly, tell him "No" and only open your hand when he is waiting calmly. Hold the food in the flat of your hand, not your fingertips.
Put extra bits of food in his bowl as he eats, to tame his food aggression. After feeding him by hand for a week or so, it's time to return to bowl feeding. Place only a small amount in his bowl and add a few bits every minute or so. Your dog will get the idea that when you come near his bowl, it's a good thing. Continue this training for a couple of weeks until the dog welcomes you near the bowl.
Remove children from the dog's feeding area. Most bites happen when adults are not paying attention to what is going on. Young children should not be in charge of the dog's feeding if there are food aggression problems. Even a tame dog may nip at a small child.
Feed your dog enough. A hungry dog is more likely to be protective of his food than a dog that is well fed. This is just common sense, but hunger in a dog is one of the main causes of food aggression.
Visit a veterinarian to rule out medical causes. If your dog's teeth hurt, he may not be able to chew adequately and he won't be getting enough food. Other mouth and throat problems could figure in. Eliminate any medical causes and then work on re-training.