I am now working towards balancing my diet. I still prefer to eat non animal-based foods in the evening incase I do get symptoms, but since my recent addition of Shilajit (and when I went a few days without it), it is clear to me that my body is deficienct in certain key minerals that is bottlenecking the methylation and immune functions which keep my POIS condition at bay. I feel much better and can tolerate non animal based foods far better with Shilajit!
Fixing nutrient deficiencies (methyl nutrients like B vitamins, choline, SAM-e, or immune nutrients like D3, magnesium, zinc, or general nutrients like minerals, etc) have been #1 for giving my life back. It's taken me a few years to realise this, but everything that I've had long-term sustained success with has been with replenishing nutrient deficiencies: red meat, eggs, SAM-e, B complex, magnesium, D3, etc...
I'm still on this immune stack but tbh I don't know if it's going to work. I am going to stay on it for a while just to give it the best shot I can, but ultimately replenishing nutrients has been by far been the biggest bang for my buck. I share this to help others. I really think your POIS will improve by taking on that mindset of exploring what nutrients your body is missing that is making the POIS inflammation far worse than it would be if it had everything it needs. And not just having a nutrient in "range", but at an optimal level. For example, on my bloods, my magnesium was technically in range, but on the low end. When I take magnesium, I feel better! A sign that my body probably needs much more.
I also think a great long-term strategy that's worked for my food sensitivities is focusing on the foods that 1) are the most nutrient dense but also 2) you have the last reaction to... for me this is red meat, eggs, greek yoghurt, mussels, sardines, and Shilajit. Now my health has improved so much, I am getting to the level where I can more comfortably eat non animal based foods that I would typically react to. I'm now trying to eat much more vegetables, plants, dark leafy greens, nuts, etc in the evening to make up for any nutrient deficiencies on my animal-based diet. So it's been a step by step process.
I think everyone here would benefit tremendously from getting the most comprehensive nutritional testing possible. From there you can then supplement any nutrients you are deficient in or at the low end, accordingly. That way you won't be buying a bunch of useless supplements. I also think each one of us will have unique deficiencies, that create unique bottlenecks. Thus for one person, zinc might be paramount in their "POIS stack" but for another, completely pointless: purely because that first person has a zinc deficiency, of course, that will improve their immune function in response to POIS and subsequently improve symptoms... The ultimate solution (at least when it comes to minerals, vitamins, methyl nutrients, etc for POIS) is to get ALL of them in optimal range.