I have been hosting a few friends for a weekly girls night in my home for about the last year and a half. Once in awhile another friend will host but about 95% of the time it's me hosting. Once in awhile other people will bring food, but it's pretty rare, so I'd say I'm also doing about 95% of the cooking for these gatherings.
One friend, Emily, was diagnosed with diabetes last fall. Since then, she has gone on an extreme low carb diet, and often rants to me online about carbs in foods, and even about her roommate's eating habits. I know you need to take my word for it but she is generally a very nice person other than her issues with food.
Before her diagnosis, girls night used to be very enjoyable. We would often experiment with different recipes together out of my different middle eastern and medieval cookbooks as both of us share an interest in cooking and medieval reenactment. Now I walk on eggshells about cooking, as sometimes even mostly healthy foods will have her standing over the stove muttering to herself "too many carbs, too many carbs".
At one point last winter, I had a box of chocolate truffles sitting on the counter that I'd purchased for my family. I hadn't even served them they were just sitting there, but she knows that all the food I put out on the counter is fair game for whoever when people come over. So she decided to eat one. Then gave herself a panic attack about eating it and I had to deal with tears and freaking out for the next half hour. (She has undiagnosed, untreated anxiety issues too and refuses to get counseling).
Since then I have completely stopped serving desserts at girls nights to try to accommodate her (she will only make sugar free desserts for herself, and will only make those in her home when she's hosting me even though artificial sweeteners aggravate my ulcer and I can't eat them)
Her diet is confusing to follow and accommodate. Sometimes I will make what I assume is a fairly healthy meal (scrambled eggs with veggies, serving naan bread on the side so she can choose to eat it or not), only to have her bring a bag of potato chips. Several times I've gotten both regular pizza and thin crust to accommodate her needs, and she's eaten the thick crust. So I assumed she was not doing the low carb thing so much anymore, and the last time she came over I made a very healthy, low fat, low calorie dish of fresh vegetables and some rice noodles. Only to have her tell me "This is really carby Dragonflymom." It almost made me cry.
Even before the diagnosis there was a long list from her of what she would and wouldn't eat, that I have been continuing to accommodate.
No mushrooms - her husband (who usually joins us for girls night) doesn't like them.
No fish - she doesn't like it.
No shrimp - her husband doesn't like them
No onions - she doesn't like them and I have to substitute more expensive leeks if the recipe calls for them
No walnuts or pecans - she doesn't like them, so again I have to substitute much more expensive pine nuts if the recipe calls for them
No sun dried tomatoes, dried fruits except dates and figs, or other foods with sulfates - she thinks they give her migraines but it's undiagnosed
I should probably include in here that my husband and I have our own medical/food issues too. He's also diabetic, and his doctor recommended a low fat, high fiber diet for him. I have an ulcer and high blood pressure, and my doctor recommended the same low fat, high fiber diet for me, and in addition I need to avoid acidic foods. She seems to expect us to disregard our medical needs in order to accommodate the extreme diet that she's chose in order to cope with her medical issues.
I don't know how to handle hosting her going forward. For now I'm stalling and told her that I'm having a hard time cooking a big dinner for everyone once a week in the few hours I've got between work and people coming over, and having a hard time working around food issues, so I'm only going to be able to host once a month. She said this was fine, so I'm clear for awhile.
But I don't know how to handle this issue about the rude and negative comments about the food I serve in my home. I keep waffling between hashing it out with her pre-emptively and telling her she hurt my feelings and her commentary was inappropriate and the polite way to handle food issues is to eat what you can and don't eat what you can't, or waiting til she does it again and having something prepared to say with her to shut this down.