I agree. Our friends dog (rottweiler) does the same thing with food,bone,treats. He growls if you get too close. It may not be because he had no food before he came to your house as our friends dog came from a good home when he was a pup. I think it is definately a dominace thing. And teaching him to "drop it" is a very good thing especialy when he takes something he shouldn't!! I use the word "Thank You" but same thing. Also hand feed him and slowly start to put your hand in his bowl when he is eating. It sounds like he feels threatened when he has food and someone is going to take it away. He will slowly learn that he will always have food and treats.