Soldato
By that logic (when in Rome) no Muslims should be fasting here then
When you say they HAVE to adhere do you mean they just can't buy food at certain times or they could actually be arrested for eating a sandwich?
In one of my first jobs I worked with a few Muslims and during fasting periods I felt so uncomfortable walking into the staff room at lunch with a big bag of munchies from McDonald's whilst they were just sitting there unable to eat. We only had one staff room and I wasn't going to eat out on the street but at the same time I felt a bit guilty, whilst telling myself I shouldn't as it's their lifestyle choice.
You should not have felt guilty. If anyone has a problem with you eating, its their problem, after all you were in a canteen or staff room in this case where you are permitted to eat and drink. It's not like you were purposely following them around eating food and being disrespectful in any way. I actually feel uncomfortable when I see my work colleagues going out of their way to try not eat in front of me, I make sure I tell them to just carry on as normal as it's absolutely no issue.