I don't know what Aspergers Syndrome is, but a lot of those behaviors you mentioned remind me of my ADHD son who is now 27 and living at home and on unemployment. He is not on drugs now as he stopped the ritalin himself at age 16. [I didn't know about natural health then!]
Is this Aspergers Syndrome something in your family line? I'm just curious why you think he has this as opposed to something else.
At 19, he may not be very compliant about changing his eating habits or taking supplements. I know there a many wise and educated folks here who will be able to help you, but one thing I have learned is that you cannot make someone do something they do not want to do.