They sell chew toys for children. Generally children with autism use them, but I don't see why your little guy wouldn't benefit from it. He may have a sensory need that he is trying to satisfy through chewing. I wouldn't discourage it, but redirect it towards something else. Many children will chew on their clothes and other things until they fall apart. It happens.
You could give him something just a bit safer to chew, such as those wax things they make for kids at the penny-candy store (if they still make them) or a hard biscuit like a teething cracker, or simply gum. But I would first wonder if he might be craving some trace mineral and go with that angle and get him on a kids' multi and make sure it has minerals in it.
No he isn't on any vitamins hes a great food eater i never thought about multi-vitamins. Little bits every now and then, yea i think he does it cause he likes to chew. But i'm not sure if he also like to eat it too.