I've had this idea that the human body is a wonderful thing that can do so very many different chemical processes to create things it needs from various other sources. I've also wondered if in cases of chronic poor nutrition early on, that some of these processes are unable to continue and can't be restarted.
Don't know what that means for you. But there is a kid in the UK that went blind because he would only eat sausage and chips during all his early years. Not that this has any bearing toward my first paragraph.
https://www.newsweek.com/teenager-bl...school-1456937
https://www.nst.com.my/world/2019/09...to-chips-years
https://www.independent.co.uk/news/u...-a9089331.html
You might just be letting your mind and anecdotal experiences control you too much. If medical people see no reason you can't eat other stuff, then maybe it's just you not liking to go through twinges and things you might have as your body adjusts to new things.