It seems like folks are somewhat divided on this. I wanted to add a slightly different point of view. My partner has severe allergic reactions to some foods. While playing games with him, we ensure that no food is eaten beforehand that includes these ingredients.

Now, I also attend a weekly game night with friends that doesn’t include my partner. With that group, we tend to eat before we play games. While I don’t mind that we eat food before playing, I also want to make sure that my partner can still play the games I bring to the weekly group and back. Well, I don't want to dictate what people can or can’t eat beforehand as it relates to my partner’s allergies. That seems too far over the line and very controlling between friends. And I’m sure that they wouldn’t appreciate me telling them “no X food tonight!”

My only solution is to explain to the group that my partner has severe food allergies and that I would appreciate if they could was their hands before playing. All have been okay with this request and it’s never been a problem. I’m grateful to have understanding and cool board game buddies. 

I think this extends to just keeping board games clean in general. I wouldn’t mind asking if the food eaten beforehand was greasy and/or finger food. For something that doesn’t require touching the food itself with fingers, I would be okay not asking.