Genetics play a big role too.
I am allergic to almost everything and can only eat a few things without feeling like shit after a while.
Discussion
thats a gut issue and a lot it could probably be fixed. There are some things you are born with and are allergic to genetically.
But a lot of problems start with leaky gut, food getting places it shouldn't and your immune system seeing it and tagging it. Now when ever it sees it again you have a reaction.
Fix your gut, let your immune system reset and a lot them will probably go away.
That’s what I have been doing for the past year. Still a way to go but getting healthier and healthier.