I'm with eeefarm on avoiding things I can that set2@s them off. But this is a young dog and the reality is, if he thinks he can bite he may escalate to more serious biting.
The best response is to get him evaluated by a behaviorist trainer. Aggressive behavior is really not responsible to try to diagnose over the internet. We can give general tips, but that's all. As for changing food, I rotate three brands. But switching to try to get to eat is a fast road to finicky eaters.
Sometimes it helps to start fresh...basic obedience for a few mins at least 3 times a day. Make sit for treats. Any display of aggression gets a firm NO and totally ignore.
I really hope you get a bit more health testing done. Teeth checked, thyroid full panel, etc. Because at this point, if it's medical, you're still looking at a dog who is developing behaviors that are not safe.
http://www.clickerlessons.com. solid clear training lessons.