I’m not sure why you are dismissing the result of probably the widest study and stating that autism is the result of not eating the right food.
In the real world, autism develops. If the medical profession treated the diagnosis as something other than a chronic condition that a person is going to have for the rest of their life, they might figure out how to treat it.
While Genetics are good explanations for some things, using 'bad genes' as an explanation is frequently a distraction from a person's actual problems. See my reply to your other comment about the streetlight effect.