I was diagnosed with celiac disease a few months ago.
I follow a low carb diet anyway so it’s not really what much of a change as I’ve not eaten pasta or bread in yonks, swapped out all the little things that contained gluten, so it’s been fine for me really.
PIL though think i’m on a fad diet. And they won’t listen to anything else dh tells them.
They are Italian and have taken it very personally that I won’t eat their food (pre covid times we didn’t live close to them and would I have a meal off low carb when we visited them and ate the food they cooked so as not to be rude).
Now we live very near them.
Dh told them that I couldn’t eat gluten anymore in preparation for when we go to their house to eat again, and they now think it’s because I don’t like their food.
It’s quite tough as well eating at other peoples houses as gluten is in a lot of things you don’t realise, like stock cubes, lots of sauces, so I would just take something of my own as I wouldn’t expect anyone else to navigate my dietary requirements for one meal.
This is further compounded by the fact that I am half Indian and like to cook a lot of Indian food, which is, apart form all the breads, fine for me to still eat (thank God!)
There was the comment of “oh so her food is fine, it’s ours that she won’t eat?”
Back story with Indian food is that they used to love it, until dh met me and then they decided they hated it and always had.
They also have an issue with the fact that we pay for private healthcare and this is how I was seen/diagnosed so fast (they only know this as dh had an issue that he had sorted out fast so told them about the healthcare cover).
So now, I also keep getting told that he probably wasn’t a real consultant and that he’s only diagnosed to make money from me 
and I can’t possibly have celiac as I don’t have symptoms. Which is true, I don’t get any physical symptoms - it’s a long story as to why he tested me and why was referred to him in the first place, but it’s all been confirmed with some horrible tests.
But obviously, gluten was causing issues inside my body and if i keep eating it, it will have long term health implications for me. I’m really quite strict so it’s not a case of just having one meal off - it’s all or nothing and it’s just become a way of life for me now.
Anyway they won’t let it go. Dh had repeated told them that this is how it is and to stop talking about it.
It’s ALL they talk about, ignoring them, changing the subject or telling them outright to stop doesn’t worked and it’s driving me nuts!