Very very few people have a food allergy - it is incredibly rare.
Some people have an intolerance to food, but it is still rare.
However, high sugar, high caffeine, and artificial colours won't do him any good and can affect his behaviour although it shouldn't make him violent.
If he has violent tantrums, wrap your arms firmly round his body from behind, trapping his arms. Sit on the floor with him still held like that and put your legs over his legs. He shouldn't be able to move, but this shouldn't hurt him in any way. When the tantrum subsides just ignore him and carry on as usual.
If he is simply hitting or biting people that is more difficult. If it is within the home tell him off and walk out of the room, again ignoring him. Don't give him too much attention when he behaves badly and don't laugh it off.