A sensitivity to grains can also be a sensitivity to oligosaccharides... especially if you present with digestive issues. Bread can cause multiple problems.
I also don't think people are quite aware that part of the reason gluten-free foods are so popular is they can help with conditions that are not caused by gluten sensitivities as they omit ingredients which cause multiple health problems. Multiple of which were poorly understood at the time gluten free foods exploded, which drove scepticism because people could not understand why so many people were buying these foods if they did not have celiac disease and often seemed to be often be able to tolerate some amount of gluten.
If you have food sensitivities I'd visit a doctor & do deep research and do trial/error.
I wish there was a website where you could input your food sensitivities and it would tell you what digestive dysfunction you have. Personally I am sensitive to restaurant pad thai and also tonkotsu ramen. Eating either of those will guarantee prompt digestive problems for me. But I'm at a loss to explain why those two things are bad. Especially the pad thai when it's seemingly just another noodle dish.
My wife has a bunch of yet unconfirmed food intolerances, but her journey to work out what it is exactly has really opened my eyes to how complicated this is. To the point that I struggle to think a system as simple as you point out is feasible. Things like the ripeness of an avocado or banana can be trigger, or if a protein is seared vs boiled/braised. It's also not binary, a trigger won't always immediately cause a reaction. It's like the body has a threshold of a given thing it can process, and a half-life on how quickly it metabolises and can take on more. But that half-life itself is variable based on other things you're ingesting. So are you intolerant of bananas? Or is it actually amines and the reason you had a reaction is because you also had dark chocolate 4 days ago, and a charred T-bone the day before that? Or maybe it actually is the banana, or more specifically the chitinase in it. Let's test it by seeing if you react to a higher intake of green beans too.
Each time there's a reaction if you want to try an actually isolate the cause it's back to nothing but plain rice and boiled chicken breast for literally weeks. Then from a neutral state you can introduce the new hypothesis, but given the whole half-life aspect you need to work out whether it's a certain amount of that food over a certain amount of time. If you get a reaction, there's still probably two or more reasons why (e.g., amines vs chitinase vs potassium vs whatever) so now you start again to isolate that. And/or you still need to work out the interaction with other foods. Over and over it repeats. It sucks.
At some point you also want to actually enjoy your life and not spend years being a walking diet experiment.
How can you tell any of these conclusions are valid and it’s not just pattern-matching on random events? Especially if you keep finding that whatever you theorized from some experience is disproven by what happens next.
That exists, it's called social media. Just publicly post "I suffer from x" and you'll summon a baker's dozen experts to tell you "it's not x, it's y" in no time.
I hope you don't mind my joke. I meant no disrespect towards you and would never wish to minimize any suffering you experience.
I was poking fun at self-appointed experts who are more concerned with "um actually-ing" than rendering any help, and I now realize my comment doesn't help either.
I hope you find the answers and relief you deserve.
For anybody wanting to initiate research on this topic, a recommended keyword to start with is "FODMAP diet". A lot of people exhibit food intolerances to the types of fermentable carbohydrates covered by this acronym that fall short of an allergy but can nonetheless be quite unpleasant (IBS, etc.)
I also don't think people are quite aware that part of the reason gluten-free foods are so popular is they can help with conditions that are not caused by gluten sensitivities as they omit ingredients which cause multiple health problems. Multiple of which were poorly understood at the time gluten free foods exploded, which drove scepticism because people could not understand why so many people were buying these foods if they did not have celiac disease and often seemed to be often be able to tolerate some amount of gluten.
If you have food sensitivities I'd visit a doctor & do deep research and do trial/error.