YT's are very possessive of their humans. My Teddy does the exact same thing with our cat i.e. chases him off when he is on my lap or in the living room at the same time as we all are..
I correct Teddy when he does this by using the command 'LEAVE IT' so he doesn't chase the cat away who was here first! Also, hubby holds Teddy while I pet the cat and we give Teddy and the cat treats during this time so they both know that one is not over the other and both are given equal attention. It has helped a lot. Teddy still has outbursts of possessiveness, as does the cat now, but the instances have been reduced and they like to chase each other around the house now (in play) more than anything else.
Since your puppy is being possessive over food, I would try to feed him from your hand while petting him and also teaching him to wait for his food before allowing him to eat it. I have taught Teddy the command LAY DOWN and I put the bowl of food down, walk off and come back and command OK as permission for him to eat his food. This has stopped him from being extremely possessive of the food and slows down his eating. He kinda knows that he's eating because I have allowed him to and not cuz he's entitled to eat and be a jerk at the same time..lol
I have read a lot of things which say that you should either put your hand in their food bowl while they eat, and pet them etc. to show them that you're not taking their food OR to just leave them alone while they eat since doing anything else is threatening to them and provokes a possessive response. I'm not sure which is right, to be honest. I have always put my hand in Teddy's bowl while he ate and the most he has ever done is gobble as much as he could before backing off and waiting for me to remove my hand. However, I cannot take treats from him without him snarling, snapping and biting so I can't tell you for sure which approach I think is best.
I hope some of this has helped, even a little, and maybe someone else can come along to add some extra advice!
