I don't doubt there are some people who likely have issues which require medicated shampoos but the human body should be able to regulate oil production and a healthy scalp etc on its own. This guy you're replying to says he uses shampoo once a week and though that might scare you off, take into account that at such an increment his scalp is probably being confused. If you're going to try no shampoo, you've gotta go all the way. When the grease stops, that's the worst part gone (as it's visual). There's a little smell for a time but eventually it goes away.

I do suggest you try and see if you have any food allergies just in case before trying it as I'd hate for you to have rashes and itching on top of it all.