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.