A few recent observations, some confirming earlier hypotheses/knowledge despite the no-water-trick (see below):
1. Avoiding watery meals and water/fluid 1 hour before to 5 hours after each meal made a huge difference (banana milk seems to be an exception). It seems some foods that I thought I have to avoid can in fact be eaten when water is avoided. I now do this always. It is important to mix some water into the foods, so it's wet, but not watery, because otherwise there are pretty bad digestion problems.
I suspect that what causes much of the symptoms is a water-soluble compound that gets flushed down the intestinal tract to the microbes that metabolize it when a meal is watery or when I drink water/fliud with the meal.
The compound is probably rapidly and to a large degree absorbed, deactivated or metabolized in the stomach or upper small intestine, so the mechanism by which avoiding water/fluid works is probably not to flush it down too quickly and give it time to be absorbed or otherwise removed from the meal during initial digestion.
2. Cooking all foods in copious amounts of water (if possible) and discarding the cooking water also seems to help, so cooked pasta is better than bread.
3. The problematic compound likely is not choline as hypothesized earlier. I can eat spaghetti with a few eggs with no/few symptoms as long as water is avoided 1 hour before to 5 hours after the meal. Other meals that contain larger amounts of choline like mussles or non-aged meat also do not seem to cause a lot of symptoms.
4. For some reason, green peas seem to have a bad effect long term, i.e., there are no initial symptom flares, but consuming them regularly is probably bad. My condition improved overall after I struck them from my diet.
5. High amounts of monounsaturated fats (e.g., 2-3 avocados, 100g of peanut butter, which would be about 50-80g of monounsaturated fatty acids) seem to cause immediate symptoms after absorption (3-5 hours after the meal). Polyunsaturated fats do not seem to have the same effects as it looks like I can eat 100g of walnut butter without a symptom flare. I am not sure about saturated fats.
6. All greens probably should/have to be avoided (even with the no-water-trick). Basil (eaten as pesto) appeared to be the worst (spinach, kale and wild garlic leaves also didn't work).
7. Nightshades should be limited to an occasional tomato. Especially early-harvest potatos (which contain elevated glycoalkaloid levels) cause symptom flares lasting 2-3 days. Late-harvest potatos appear to be much better tolerated, which makes me believe the glycoalkaloids are responsible.
8. High amounts of all carotenoids should probably be avoided. Sweet potato with mayonnaise or cow's milk yoghurt didn't work (beta carotine). Tomato pesto (lycopine) also didn't work, but just cooked tomatos with not fat (90% less absorption of many carotenoids) did work. Important to take Vitamin A as a supplement.
9. All legumes appear to be bad overall even with the water-trick and that's bad because there isn't an awful lot I can eat and I really needed legumes to make my diet plan more varied and palatable. But it is what it is. I limit legumes to occational
I found the following meals relatively safe if the no-water-trick is observed and foods are cooked and the water discarded where applicable (yes, I know, it's a bland list) - salt is in almost all meals, so it's not always mentioned:
*Spaghetti with 1-2 tomatos, cooked.
*Spaghetti with a few blue mussles, cooked
*Spaghetti with a bit of nutritional yeast to spice it up a little
*Spaghetti with feta cheese (thoroughly heated to kill bacteria)
*Homemade, quick fermentation white bread with homemade walnut butter and a bit of honey
*Pasta and lentils, both cooked
*Banana milk
*Bananas plain
*Hummus with homemade white bread (Tahin frozen to avoid fermentation, chickpeas cooked fresh)
I put a few meals in the B category, because I am not 100% sure what they do or they cause some symptoms, but I need them because my diet would be too bland otherwise:
*Pizza (white flour dough, freshly openend tomato passata, mozzarella cheese, a few basil leaves)
*Homemade falafel (frozen dough) with homemade white pita and home-pasteurized yoghurt, cucumber and tomato
*Several late-harvest potato dishes, including potato-leek stew (non-watery), mashed potatos, Swiss Rösti or roast potatos.
While these dietary restrictions sound pretty terrible, progress on this diet has actually been quite good. I want to continue it a bit to be sure it's not a coincidence before giving a more detailed progress update.