After noticing that eating more refined carbs (pasta, rice, flour) one day made my head feel much worse, I cut them out of my diet completely. I went full ketogenic (low carb/high fat), and have been for 7 months or so. That point was when I really started making progress with my recovery from PCS. I still have symptoms if I jostle my head around too much, but it no longer rules my life.

I surmise it is the anti-inflammatory properties of the diet, so I would second looking into that type of lifestyle. Whole food, no sugar/flour, no processed food. Something of that nature. Doesn't have to be as extreme as going very low carb, but cutting out the worst offenders will do wonders.