Sugar, chocolate, coffee, white bread, starch (potatoe, pasta) and too much food in general (specially vegetables) make my POIS worse and can even give POIS symptomes itself. My hypothesis is that, since I have SIBO (small intestine bacterial overgrowth), theese foods do not only feed bad bacterias so they cause bloating and inflammation, but also raises blood sugar that promotes inflammation itself and hight insuline levels (bad for the blood vessel walls).
Coffee is a little special because it activates a stress reponse and weakens the adrenals. One cup of coffee (with coffeine) is also dramatically lowering the testosterone levels in the blood for up to 24 hours according to dr Thierry Hertoghe. The last thing we POISers need is to lower our testosterone and cortisol as those hormons are anti-inflammatory.
What do I eat one might ask? Well right now I'm on a FODMAP diet but trying to avoid too much vegetables. That means I eat mostly pork, beef, fish, chicken, eggs (but not the white), coconut cream, lots of ginger/turmeric, bonebroth (including walnuts), protein powder smoothies and berries. I try to eat every 2-3 hours and then just a small portion instead of 3 big servings a day.