Like several others here I'm having good success treating POIS using leaky gut healing diets and supplementation. I'm leaving this post open as a placeholder to add more information as I learn more and post results of this 'treatment'.
In November 2018 I spent over $3,000 in lab tests to try to identify root causes of my food issues. With only receiving partial test results back what I've learned is that I have leaky gut. Basically the intestinal permeability (how our food is absorbed) in my body is so liberal that most food molecules enter my blood stream, whether they should be there or not. This has happened for 30 years of my life. In a nutshell my body has been attacking these unwanted food particles, which has increased my white blood cell count and created significant inflammation that crosses the blood brain barrier and effects my concentration, memory, motor skills, emotions - i.e. brain fog.
Strangely enough, leak gut is the leading cause of autoimmune diseases in front of genetics. Type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, grave's, Hashimoto's, etc. Succinctly, the person's immune system that has leaky gut is constantly attacking unwanted food particles and overtime turns on itself. I'm moderately confident that POIS is an automimmune disease in my case and that leaky gut is the cause (and it's treatment is the maintained cure of leaky gut).
I've been on the leaky gut diet and supplement stack for 2 weeks now, the beginning of 90 days of strict diet, and already I'm seeing positive results and perhaps a reversal of POIS (reduction of symptom intensity and duration).
Important side note - leaky gut was once a fallacy to chiropractic medicine BUT over the past two decades of immense scientific research and studies is now proven and more understood/documented than most modern day diseases. The link between leaky gut and POIS is real.