Most of the time, my efforts to BLAME the FOOD, fall through.
I get hugely different results eating teh same EXACT THINGS.
Again, I think your case is very different than mine, so important to keep that in mind, but I personally have made the same observation. For many years, I couldn't link specific foods to symptom flares. It all seemed random and I could detect no pattern at all.
Today, I am certain this is because of the following:
*Some foods cause symptom flares that last for 2-3 days and are often intermittent, so a symptom flare could be triggered by a food I ate 3 days before, but I attributed it to a food I ate that day.
*Monodiets and strict elmination diets (i.e. only eating one or two foods for a few days or weeks and adding single new foods over time) seem to create symptoms as well. There is no one food I can eat all the time, i.e., no monodiet or very restrictive diet worked. That's makes it hard to find out which food caused the symptoms.
*Food isn't the only thing that causes symptom flares. Total calories, meal size, my thyroxine dose and physical activity levels are all confounding factors that can cause symptom flares that will then be attributed to the wrong food.
*Some effects seem to accumulate over time, i.e. for a week or so, it appears the food is perfectly find, but persistent symptoms start after a while. I suspect nightshades, lysine and oxalates cause symptoms only when a certain level has accumulated.
*Some foods/nutrients seem to cause symptoms when too much is eaten, but also when
too little is consumed. Lysine is probably one example.
*Some foods only cause problems in connection with another food, e.g., I can tolerate high amounts of blueberries, but when my diet is also too high in lysine, fruit starts to cause symptoms as well.
*The timing of meals seems to matter, i.e., falafel with white bread seems to be quite ok, but when the meal before or after was or is fruit, there is a symptom flare.
*Getting just one thing wrong precludes any sustainable progress. If only one mistake is made, e.g., just eating nightshades, it looks like all other adjustments are worthless or almost worthless. That makes it very complicated because in order to see any sustained improvement, I had to get several of the points right by chance, and even then the benefits were transient, unstable and often not very pronounced.
*The number of acceptable foods/meals (as far as my understanding goes today) is so limited and monotonous that there is always a strong urge to include and test new foods and a strong temptation to eat forbidden foods just to get some variety and pleasure from eating while tolerating the symptoms/worsening.
*People I deal with constantly tell me in a suble or less subtle way that the whole approach is weird and sounds like nonsense.
This is why I thought there is no pattern and this can't be about diet for such a so long time. I suspected the link to certain foods as early as in 2015, but always rejected the hypothesis because the symptom flares could not be tied to specific foods.
OMG, where could I be today had I followed that suspicion consistently back then. I might not have worsened from the 2015 level at all. I might never have stopped working, at least part time.
If only I had known...