In many cultures, offering food is offering friendship - what does that mean for you and your students?
When I traveled overseas, I quickly learned that an offer of food at a house was more than a simple gesture of hospitality - it was an offer of friendship! Rejecting the food was incredibly rude, and sent a message that I didn't want to be there or connect with that family.
Translate this into our culture today. If a family offers to cook you food, accept it graciously! It may be their way of reaching out and connecting. If you have dietary restrictions and cannot eat it, you can still be grateful and enthusiastic while letting them know that while you aren't able to eat this food, you can share it with someone else who will enjoy it!
Also consider this from the student's point of view. If they go to the cafeteria and are served food that looks and tastes different from what they are used to, what might be running through their mind? Some of these students might need direct instruction in learning that it is okay to politely say no or make a different choice.