
Unfortunately all the things you've been told to do have only reinforced his fear of going without food - which is, of course, a basic instinct. When you think about it, if a dog feels he needs to protect his means of survival (his dinner), taking it away - even if you give it back straight away - has proved to him that he was right. His life is threatened.
There are several strategies you can try to overcome this and regain his trust. He needs to be convinced that you're the
giver of food and all good things, not the one who removes it.
Put down four empty food bowls, one in each corner of the room. Put a very small amount of food in one then
immediately go to the next bowl and do the same. Keep going round and round the bowls, putting a tiny amount of the dog's meal in a bowl each time. This way he won't have time to guard the food because you've already moved on to the next.
After a few days, maybe a week or two, you'll be able to cut down the number of bowls, but still only be seen to be putting food
into his bowl - he eats the small amount, then you add a bit more and stand back while he eats it. The you put a little more in and stand back.
At no time should he be scolded for growling - just ignore it, and when his bowl's empty put in another tiny bit of food.